SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA FACULTY OF CHEMICAL AND FOOD TECHNOLOGY Institute of Organic Chemistry, Catalysis and Petrochemistry

ORGANIC TECNOLOGY AND PETROCHEMISTRY

REPORT ON TRAINING VISIT

In the frame work of the project No. SAMRS 2010/12/10 “Development of human resource capacity of Kabul polytechnic university” Funded by

Bratislava 2010 Pro.Phd.hasani 1

Acknowledgement: The author would like to express his appreciation for the Scientific Training Program to Institute of Chemical and Environmental Engineering, Faculty of Chemical and Food Technology of the Slovak University of Technology and Slovak Aid program for financial support of this project. I would like to say my hearth thank to Assoc. Prof. Alexander Kaszonyi, PhD.. for his guidance and assistance during the all time of my training visit. My thank belongs also to Assoc. Prof. Ing. Juma Haydary, PhD. the coordinator of the project SMARS/2010/12/10 in the frame work of which my visit was realized.

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VISITING REPORT FROM FACULTY OF CHIMICAL TECHNOLOGY OF SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLOVA

This visit was organized for exchanging knowledgical views and advices between us (professors of Kabul Poly Technical University) and professors of this faculty. My visit was especially organized to the departments of organic chemistry and technology of organic materials. I did following activities in this period that includes in 3 parts:

1.Pedagogic area 2.Researches 3.Practical activities

Each part is described as following:

1. PEDAGOGIC AREA: - I attended to the lectures of the professors and, saw the methods of the lectures and teachings, I also visit the classes and sow the students and their activities, besides of these I also participated to the Conferences and Seminars presented by the professors and students.

2. RESEARCHES: - I researched about petroleum and its derivatives that is the most important factor and skeleton for economical development of a human being society and a country and especially in our country that it is the hot view of point now a days. During this period I prepared a knowledgical article which is included.

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3. PRACTICAL ACTIVITIES:- I did some syntheses of glycerol products under deferent conventions and deferent parameters and then these products were checked and evaluated by physical chemical methods that were satisfy able. These activities were done independently and with the aspirants of this faculty as well in the Technology of Organical materials’ department. These activities are written in an additional report which is included.

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PREFACE

This visit was organized for exchanging knowledgical views and advices between us (professor of Kabul Poly Technic University and professors of faculty of Chemical Technology specially departments of Technology of Organic Materials and Organic Chemistry). As we know that chemistry is one part of scientific Knowledge and Organic chemistry is the most important part of it, that products of it are used in all parts of life. Due to fast increasing inhabitance of humanity on the earth we feel more necessity for fast improving of this technology and its products, especially after discovering of petroleum and its derivatives that cover all fields of our life. For this reason all scientist and researchers of chemistry and Technology of Chemistry are interested to this field of science, Fortunately our country has a lot of rich natural minds, to educts and use these minds is needed modern technology, of course this might have improve the national economy stage and prepare good situation for the life of human being. To reach to this aim needs to learn and use the new and modern methods and technology. During this visiting we met new and modern methods and technology of chemistry that are very useful for our students and we will teach them too.

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Organic Technology and Petrochemistry

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Petrochemical

Petrochemicals are chemical products made from raw materials of petroleum or other hydrocarbon origin. Although some of the chemical compounds that originate from petroleum may also be derived from coal and natural gas, petroleum is the major source. The largest petrochemical industries are to be found in the USA and Western Europe, though the major growth in new production capacity is in the Middle East and Asia. There is a substantial inter- regional trade in petrochemicals of all kinds. World production of ethylene is around 110 million tons per year, of propylene 65 million tons, and of aromatic raw materials 70 million tons.

The following is a partial list of the major commercial petrochemicals and their derivatives:

• ethylene - the simplest olefin; used as a ripening hormone, a monomer and a chemical feedstock o polyethylenes - polymerized ethylene o ethanol - made by hydration (chemical reaction adding water) of ethylene o ethylene oxide - sometimes called oxirane; can be made by oxidation of ethylene . ethylene glycol - from hydration of ethylene oxide or oxidation of ethylene . engine coolant - contains ethylene glycol . polyesters - any of several polymers with ester linkages in the backbone chain . glycol ethers - from condensation of glycols . ethoxylates o vinyl acetate o 1,2-dichloroethane . trichloroethylene . tetrachloroethylene - also called perchloroethylene; used as a dry cleaning solvent and degreaser . vinyl chloride - monomer for polyvinyl chloride . polyvinyl chloride (PVC) - type of plastic used for piping, tubing, other things • propylene - used as a monomer and a chemical feedstock o isopropyl alcohol - 2-propanol; often used as a solvent or rubbing alcohol o acrylonitrile - useful as a monomer in forming Orlon, ABS o polypropylene - polymerized propylene o propylene oxide . propylene glycol - sometimes used in engine coolant . glycol ethers - from condensation of glycols o isomers of butylene - useful as monomers or co-monomers . isobutylene - feed for making methyl tert-butyl ether (MTBE) or monomer for copolymerization with a low percentage of isoprene to make butyl rubber o 1,3-butadiene - a diene often used as a monomer or co-monomer for polymerization to elastomers such as polybutadiene or a plastic such as acrylonitrile-butadiene-styrene (ABS) . synthetic rubbers - synthetic elastomers made of any one or more of several petrochemical (usually) monomers such as 1,3-butadiene, styrene, isobutylene, isoprene, chloroprene; elastomeric polymers are 13

often made with a high percentage of conjugated diene monomers such as 1,3-butadiene, isoprene, or chloroprene o higher olefins . polyolefins such poly-alpha-olefins which are used as lubricants . alpha-olefins - used as monomers, co-monomers, and other chemical precursors. For example, a small amount of 1-hexene can be copolymerized with ethylene into a more flexible form of polyethylene. . other higher olefins . detergent alcohols o acrylic acid . acrylic polymers o allyl chloride - . epichlorohydrin - chloro-oxirane; used in epoxy resin formation . epoxy resins - a type of polymerizing glue from bisphenol A, epichlorohydrin, and some amine

• benzene - the simplest aromatic hydrocarbon o ethylbenzene - made from benzene and ethylene . styrene made by dehydrogenation of ethylbenzene; used as a monomer . polystyrenes - polymers with styrene as a monomer o cumene - isopropylbenzene; a feedstock in the cumene process . phenol - hydroxybenzene; often made by the cumene process . acetone - dimethyl ketone; also often made by the cumene process . bisphenol A - a type of "double" phenol used in polymerization in epoxy resins and making a common type of polycarbonate . epoxy resins - a type of polymerizing glue from bisphenol A, epichlorohydrin, and some amine . polycarbonate - a plastic polymer made from bisphenol A and phosgene (carbonyl dichloride) . solvents - liquids used for dissolving materials; examples often made from petrochemicals include ethanol, isopropyl alcohol, acetone, benzene, toluene, xylenes o cyclohexane - a 6-carbon aliphatic cyclic hydrocarbon sometimes used as a non-polar solvent . adipic acid - a 6-carbon dicarboxylic acid which can be a precursor used as a co-monomer together with a diamine to form an alternating copolymer form of nylon. . nylons - types of polyamides, some are alternating copolymers formed from copolymerizing dicarboxylic acid or derivatives with diamines . caprolactam - a 6-carbon cyclic amide . nylons - types of polyamides, some are from polymerizing caprolactam o nitrobenzene - can be made by single nitration of benzene . aniline - aminobenzene . methylene diphenyl diisocyanate (MDI) - used as a co- monomer with diols or polyols to form polyurethanes or with di- or polyamines to form polyureas . polyurethanes o alkylbenzene - a general type of aromatic hydrocarbon which can be used as a presursor for a sulfonate surfactant (detergent)

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. detergents - often include surfactants types such as alkylbenzenesulfonates and nonylphenol ethoxylates o chlorobenzene • toluene - methylbenzene; can be a solvent or precursor for other chemicals o benzene o toluene diisocyanate (TDI) - used as co-monomers with diols or polyols to form polyurethanes or with di- or polyamines to form polyureas . polyurethanes - a polymer formed from diisocyanates and diols or polyols o benzoic acid - carboxybenzene . caprolactam . nylon • mixed xylenes - any of three dimethylbenzene isomers, could be a solvent but more often precursor chemicals o ortho-xylene - both methyl groups can be oxidized to form (ortho-)phthalic acid . phthalic anhydride o para-xylene - both methyl groups can be oxidized to form terephthalic acid . dimethyl terephthalate - can be copolymerized to form certain polyesters . polyesters - although there can be many types, polyethylene terephthalate is made from petrochemical products and is very widely used. . purified terephthalic acid - often copolymerized to form polyethylene terephthalate . polyesters Modern Refining

Petroleum refineries are marvels of modern engineering. Within them a maze of pipes, distillation columns, and chemical reactors turn crude oil into valuable products. Large refineries cost billions of dollars, employ several thousand workers, operate around the clock, and occupy the same area as several hundred football stadiums. The U.S. has about 300 refineries that can process anywhere between 40 and 400,000 barrels of oil a day. These refineries turn out the gasoline and chemical feedstocks that keep the country running.

Locating an oil field is the first obstacle to be overcome. The first explorers used Y-shaped devining rods and other supernatural, but ineffective, means of locating petroleum. Today geologists and petroleum engineers employ more tried and true methods. Instruments to aid the search include; geophones (uses sound), gravimeters (uses gravity), and magnetometers (uses the Earth's magnet field). While these methods narrow the search tremendously, a person still has to drill a exploratory well, or wildcat well, to see if the oil actually exists. Success brings visions of gushers soaring skyward, however today wells are capped before this happens.

Drilling

There are three main types of drilling operations; cable-tool, rotary, and off-shore. Cable- tool drilling involves a jack-hammer approach were a chisel dislodges earth and hauls up the loose sediment. Rotary drilling works at much greater depths, and involve sinking a drill 15 pipe with a rotating steel bit in the middle. Off-shore drilling involves huge semisubmersible platforms which lower a shaft to the ocean floor, containing any oil which is located.

All crude oil contains some amount of methane or other gases dissolved in it. Once the drilling shaft makes contact with the oil it releases the pressure in the underground reservoir. Just like opening a can of soda pop, the dissolved gases fizz out of solution pushing crude oil to the surface. The dissolved gases will allow about 20% recovery of oil. To get better recovery water is often pumped into the well, this forces the lighter oil to the surface. Water flooding allows recoveries of about 50%. The addition of surfactant allows even more oil to be recovered by preventing much of it from getting trapped in nooks and crannies. Yet, it is impossible to get all of the oil out of a well.

Transportation

Because crude oil is a liquid it is much easier to move than natural gas or coal. Coal is nice and dense, so it does not require large holding containers, but it cannot be pumped. Conveyor belts and cranes cannot compete with pipelines for economic efficiency. Natural gas can be pumped using expensive compressors, but it requires enormous holding tanks. A recent trick has been to inject huge amounts of water into salt strata. The water dissolves the salt, leaving truly enormous caverns. The natural gas is then pumped in and stored until needed. The ease in transporting oil is one of the reasons we have become so dependent upon it. Pound for pound natural gas and coal just cannot compete.

Reserves

The proven reserves of crude oil within the U.S. are about 3.9 billion cubic meters. This could cover the state of Minnesota with a layer one half inch thick. A reasonable value for the total amount of crude oil obtainable using current methods from around the world is 350 billion cubic meters. This could cover Minnesota with a layer of oil four and a half feet thick. Yet, at the rate we are consuming oil, the nation's reserves will be depleted by 2010, and the world's reserves will be depleted by the end of the 21st Century.

Chemistry

Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.

The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture.

The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern refineries into more valuable products. The shortest molecules, those with four or fewer

16 carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these gases are either flared off, sold as liquified petroleum gas under pressure, or used to power the refinery's own burners. During the winter, Butane (C4H10), is blended into the gasoline pool at high rates, because butane's high vapor pressure assists with cold starts. Liquified under pressure slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source for many developing countries. Propane can be liquified under modest pressure, and is consumed for just about every application relying on petroleum for energy, from cooking to heating to transportation.

The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. Cycloalkanes have similar properties to alkanes but have higher boiling points.

The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic.

These different molecules are separated by fractional distillation at an oil refinery to produce gasoline, jet fuel, kerosene, and other hydrocarbons. For example 2,2,4-trimethylpentane (isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with oxygen exothermically:[11]

Incomplete combustion of petroleum or gasoline results in production of toxic byproducts. Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures involved, exhaust gases from gasoline combustion in car engines usually include nitrogen oxides which are responsible for creation of photochemical smog.

Formation

Geologists view crude oil and natural gas as the product of compression and heating of ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature and/or pressure.[13] Today's oil formed from the preserved remains of prehistoric zooplankton and algae, which had settled to a sea or lake bottom in large quantities under anoxic conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form coal). Over geological time the organic matter mixed with mud, and was buried under heavy layers of sediment resulting in high levels of heat and pressure (known as diagenesis). This caused the organic matter to chemically change, first into a waxy material known as kerogen which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.

Geologists often refer to the temperature range in which oil forms as an "oil window"[14]— below the minimum temperature oil remains trapped in the form of kerogen, and above the maximum temperature the oil is converted to natural gas through the process of thermal cracking. Although this temperature range is found at different depths below the surface throughout the world, a typical depth for the oil window is 4–6 km. Sometimes, oil which is formed at extreme depths may migrate and become trapped at much shallower depths than where it was formed. The Athabasca Oil Sands is one example of this. 17

Crude oil reservoirs

Hydrocarbon trap.

Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon material buried deep enough for subterranean heat to cook it into oil; a porous and permeable reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents it from escaping to the surface. Within these reservoirs, fluids will typically organize themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas above it, although the different layers vary in size between reservoirs. Because most hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. However, the process is influenced by underground water flows, causing oil to migrate hundreds of kilometres horizontally or even short distances downward before becoming trapped in a reservoir. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping.

The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in petrochemical plants and oil refineries.

Non-conventional oil reservoirs

Oil-eating bacteria biodegrades oil that has escaped to the surface. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two countries have the world's largest deposits of oil sands.

On the other hand, oil shales are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not really shales and do not really contain oil, but are usually relatively hard rocks called marls containing a waxy substance called kerogen. The kerogen trapped in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits.[15]

Classification

The petroleum industry generally classifies crude oil by the geographic location it is produced in (e.g. West Texas, Brent, or Oman), its API gravity (an oil industry measure of density), and by its sulfur content. Crude oil may be considered light if it has low density or heavy if it has 18 high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it contains substantial amounts of sulfur.

The geographic location is important because it affects transportation costs to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries. Each crude oil has unique molecular characteristics which are understood by the use of crude oil assay analysis in petroleum laboratories.

Barrels from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing references throughout the world. Some of the common reference crudes are:

• West Texas Intermediate (WTI), a very high-quality, sweet, light oil delivered at Cushing, Oklahoma for North American oil • Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal in the Shetlands. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off this oil, which forms a benchmark • Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the Asia- Pacific region • Tapis (from Malaysia, used as a reference for light Far East oil) • Minas (from Indonesia, used as a reference for heavy Far East oil) • The OPEC Reference Basket, a weighted average of oil blends from various OPEC (The Organization of the Petroleum Exporting Countries) countries

A Few Terms

The petroleum industry, like other chemical industries, has a plethora of terms designed to scare off anyone who wants to understand exactly what is going on. Mastering this nomenclature is one of the main tasks facing chemistry and chemical engineering students. Here are a few commonly used terms, but be forewarned; because of the complexity of compounds in the petroleum industry some of these terms are very vague.

Hydrocarbons are chemical compounds made mainly of carbon and hydrogen. Both petroleum and coal contain many different hydrocarbons. Methane, ethanol, and benzene are examples of hydrocarbons, though there are many many others.

Bitumen is another term for hydrocarbons. Both petroleum and coal are sometimes referred to as Bituminous.

Organic compounds are chemicals made of carbon (although the classification is not totally consistent and some carbon compounds, like carbon dioxide, are not considered organic). Hydrocarbons are commonly referred to as organic compounds, and it is fair to think of the two as equivalent. Carbohydrates, proteins, and urea (found in urine) are examples or organic compounds. It was once thought that organic compounds could only be produced from organic sources. Because of their usefulness, a huge chemical industry developed around organic chemicals during the 19th Century. Dyes and pharmaceuticals where products of this industry. As chemists increased their skills they found that organic compounds could be synthesized from inorganic sources. However, by this time the classification had been firmly rooted in industry and universities and so it remains today. 19

Inorganic compounds include everything that is not considered organic (every compound in the world is ether organic or inorganic).

Aromatic compounds are organic compounds which always have a benzene ring in them. Because of this they can be quite reactive and have some interesting properties. The dye and pharmaceutical industries depend heavily on aromatic compounds.

Aliphatic compounds are organic compounds which are not aromatic. They include single bonded (ethane, propane, butane), double bonded (ethene or called ethylene, propene, butene), and triple bonded (ethyne or called acetylene, propyne, butyne) straight chain hydrocarbons as well as cyclic non-benzene structures (cyclopentane, cyclobutane) (every organic compound in the world is either aromatic or aliphatic).

A Barrel (bbl.) of crude contains 42 gallons or 158.8 liters. No one actually ships petroleum in barrels anymore because they are too small, but the term is still used to describe a defined volume.

Petroleum literally means "rock oil". It is a very broad word referring to all liquid hydrocarbons which can be collected from the ground. Even natural gas and solid hydrocarbons are sometimes referred to as petroleum. When petroleum first comes from the ground it is called crude oil. Later it is usually just referred to as oil. It can flow like water or be as viscous as peanut butter. It can be yellow, red, green, brown, or black.

Fractions are complex mixtures of chemical compounds that all have a similar boiling point. Light and heavy fractions refer to a compound's boiling point and not their actual density (these are two entirely different things). Light fractions can be very heavy (dense), and heavy fractions can be very light (go figure)!

Isomers are chemicals which have the same number and type of atoms but have them arranged in a different way. Methane (CH4), ethane (C2H6), and propane (C3H8) have no isomers because their is only one way the carbons can hook together. Butane (C4H10) has two isomers (n-butane and isobutane). Decane (C10H22) has seventy five isomers, and a molecule with 20 carbon atoms (C20H42) has over 100,000 isomers. Crude oil contains molecules having 1 to 100+ carbon atoms. Naming these compounds based upon normal chemical rhetoric would be hell on earth! The huge number of possible molecular arrangements is why people talk of fractions instead of using proper chemical nomenclature.

Natural Gas is a mixture of very low boiling hydrocarbons. Natural gas can only be liquefied under extremely high pressures and very low temperatures. It is called "dry" when methane (CH4) is the primary component, and "wet" if it contains higher boiling 20 hydrocarbons. If it smells bad, because of sulfur compounds, it is called "sour". Otherwise, it is called "sweet".

Liquefied Petroleum Gas (LPG) is a very light fraction of petroleum. It is also a fairly simple fraction containing mainly propane and butane. First, it should be noted that under normal pressures LPG is actually a gas, unlike gasoline (often just called "gas") which is really a liquid (ugh). However, under modestly high pressures these compounds can be converted to a liquid (hence their name). Being able to store them as a liquid reduces the container size by a factor of a hundred. This is no doubt why propane stoves are so popular. As cracking methods have evolved more and more LPG has been produced by refineries.

Gasoline is a light fraction of petroleum which is quite volatile and burns rapidly. Straight run gasoline refers to gasoline produced by distillation instead of cracking, although it really doesn't make a difference. Gasoline is often just called "gas", however it is a liquid at typical pressures. This confusing state of affairs developed because the first internal combustion engines ran on town gas (a mixture of carbon monoxide, CO, and hydrogen, H2, both actual gases). These engines were therefore called "gas engines". When gasoline replaced town gas people still called the motors "gas engines" and also started calling gasoline "gas". Today, the average American uses 450 gallons of gasoline a year.

Octane Number rates a fuel's ability to avoid premature ignition called knock. Premature ignition reduces an engine's power and quickly wares it out. The octane scale arbitrarily defines n-heptane a value of 0, and isooctane (2, 2, 4-trimethyl pentane) an octane number of 100. Isooctane is then added to heptane until the mixture has the same knock characteristics as the fuel being tested, and the percent isooctane is taken as the unknown fuels octane number. Tetraethyl lead used to be a common anti-knock additive which would raise a fuels octane number. High octane fuel can be used in engines with high compression ratios which in turn produce much more power. However, the additive is no longer used because of concerns over lead pollution.

Naphtha is a light fraction of petroleum used to make gasoline. Naphtha also produces solvents and feedstocks for the petrochemical industry.

Kerosene was the first important petroleum fraction, replacing whale oils in lamps over a hundred years ago. Some unscrupulous refiners failed to distill off all the naphtha from the kerosene fraction thereby increasing the volume of their final product. This lead to many lamp explosions and fires.

Diesel fuels find use in the fleet of trucks which transport the nations goods. Diesel engines power these larger engines, and use higher compression ratios (and temperatures) than their gasoline cousins. They are therefore more efficient. It is also interesting to note that diesel engines have no spark plugs, instead the fuel-air mixture is ignited by the rising temperatures and pressures during the compression stroke.

Gas Oil (or fuel oils) are used for domestic heating. In the winter refineries produce more gas oil, whereas during the summer driving months they produce more gasoline.

Heavy Fuel Oil is often blended with gas oils for easier use in industry. Ships burn heavy fuel oils but they call it bunker oil.

Atmospheric Residual is everything that cannot be vaporized under normal pressures. Atmospheric residual is fed into another distillation column, operating at lower pressures, 21 which can separate out some of the lighter compounds. Lubricants and waxes reside in this Paraffins 30% 15 to 60% fraction. Asphaltics 6% remainder Vacuum Residual is the bottom of the barrel. It includes asphalt and some coke.

Pitch is a thick, black, sticky material. It is left behind when the lighter components of coal tar or petroleum are distilled off. Pitch is a "natural" form of asphalt.

Asphalt is a high boiling component of crude oil. It is therefore found at the "bottom of the barrel" when petroleum is distilled.

Tars are byproducts formed when coke is made from coal or charcoal is made from wood. It is a thick, complex, oily black mixture of heavy organic compounds very similar to pitch or asphalt, though from a different source.

Composition

The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:[2]

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the

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1. desalting Why Desalt Crude?

• The salts that are most frequently present in crude oil are Calcium,Sodium and Magnesium Chlorides. If these compounds are not removed from the oil several problems arise in the refining process. The high temperatures that occur downstream in the process could cause water hydrolysis, which in turn allows the formation of hydrochloric acid. • Sand, Silts, Salt deposit and Foul Heat Exchangers • Water Heat of Vaporization reduces crude Pre-Heat capacity • Sodium, Arsenic and Other Metals can poison Catalysts • Environmental Compliance, i.e., By removing the suspended solids, which might otherwise become an issue in flue gas opacity norms, etc.,

Distillation

Which Fraction to Make?

Various fractions are more important at different times of year. During the summer driving months, the public consumes vast amounts of gasoline, whereas during the winter more fuel oil is consumed. These demands also vary depending upon whether you live in the frigid north, or the humid south. Modern refineries are able to alter the ratios of the different fractions to meet demand, and maximize profit.

Design and operation of a distillation column depends on the feed and desired products. Given a simple, binary component feed, analytical methods such as the McCabe-Thiele method[5][6][7] or the Fenske equation[5] can be used to assist in the design. For a multi- component feed, computerized simulation models are used both for design and subsequently in operation of the column as well. Modeling is also used to optimize already erected columns for the distillation of mixtures other than those the distillation equipment was originally designed for.

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When a continuous distillation column is in operation, it has to be closely monitored for changes in feed composition, operating temperature and product composition. Many of these tasks are performed using advanced computer control equipment.

Column feed

The column can be fed in different ways. If the feed is from a source at a pressure higher than the distillation column pressure, it is simply piped into the column. Otherwise, the feed is pumped or compressed into the column. The feed may be a superheated vapor, a saturated vapor, a partially vaporized liquid-vapor mixture, a saturated liquid (i.e., liquid at its boiling point at the column's pressure), or a sub-cooled liquid. If the feed is a liquid at a much higher pressure than the column pressure and flows through a pressure let-down valve just ahead of the column, it will immediately expand and undergo a partial flash vaporization resulting in a liquid-vapor mixture as it enters the distillation column.

Improving separation

Although small size units, mostly made of glass, can be used in laboratories, industrial units are large, vertical, steel vessels (see images 1 and 2) known as "distillation towers" or "distillation columns". To improve the separation, the tower is normally provided inside with horizontal plates or trays as shown in image 5, or the column is packed with a packing material. To provide the heat required for the vaporization involved in distillation and also to compensate for heat loss, heat is most often added to the bottom of the column by a reboiler, and the purity of the top product can be improved by recycling some of the externally condensed top product liquid as reflux. Depending on their purpose, distillation columns may have liquid outlets at intervals up the length of the column as shown in image 4.

Reflux

Large-scale industrial fractionation towers use reflux to achieve more efficient separation of products.[3][5] Reflux refers to the portion of the condensed overhead liquid product from a distillation tower that is returned to the upper part of the tower as shown in images 3 and 4. Inside the tower, the downflowing reflux liquid provides cooling and partial condensation of the upflowing vapors, thereby increasing the efficacy of the distillation tower. The more reflux that is provided, the better is the tower's separation of the lower boiling from the higher boiling components of the feed. A balance of heating with a reboiler at the bottom of a column and cooling by condensed reflux at the top of the column maintains a temperature gradient (or gradual temperature difference) along the height of the column to provide good conditions for fractionating the feed mixture. Reflux flows at the middle of the tower are called pumparounds.

Changing the reflux (in combination with changes in feed and product withdrawal) can also be used to improve the separation properties of a continuous distillation column while in operation (in contrast to adding plates or trays, or changing the packing, which would, at a minimum, require quite significant downtime).

Plates or trays

Image 5: Cross-sectional diagram of a binary fractional distillation tower with bubble-cap trays. (See theoretical plate for enlarged tray image.)

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Distillation towers (such as in images 3 and 4) use various vapor and liquid contacting methods to provide the required number of equilibrium stages. Such devices are commonly known as "plates" or "trays".[8] Each of these plates or trays is at a different temperature and pressure. The stage at the tower bottom has the highest pressure and temperature. Progressing upwards in the tower, the pressure and temperature decreases for each succeeding stage. The vapor-liquid equilibrium for each feed component in the tower reacts in its unique way to the different pressure and temperature conditions at each of the stages. That means that each component establishes a different concentration in the vapor and liquid phases at each of the stages, and this results in the separation of the components. Some example trays are depicted in image 5. A more detailed, expanded image of two trays can be seen in the theoretical plate article. The reboiler often acts as an additional equilibrium stage.

If each physical tray or plate were 100% efficient, than the number of physical trays needed for a given separation would equal the number of equilibrium stages or theoretical plates. However, that is very seldom the case. Hence, a distillation column needs more plates than the required number of theoretical vapor-liquid equilibrium stages.

Fractionation Research, Inc. (commonly known as FRI) has performed research on all types of trays measuring their capacity, pressure drop and efficiency in hydrocarbon systems from full vacuum to 500 psia.[9]

Packing

Another way of improving the separation in a distillation column is to use a packing material instead of trays. These offer the advantage of a lower pressure drop across the column (when compared to plates or trays), beneficial when operating under vacuum. If a distillation tower uses packing instead of trays, the number of necessary theoretical equilibrium stages is first determined and then the packing height equivalent to a theoretical equilibrium stage, known as the height equivalent to a theoretical plate (HETP), is also determined. The total packing height required is the number theoretical stages multiplied by the HETP.

This packing material can either be random dumped packing such as Raschig rings or structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer takes place. Unlike conventional tray distillation in which every tray represents a separate point of vapor-liquid equilibrium, the vapor-liquid equilibrium curve in a packed column is continuous. However, when modeling packed columns it is useful to compute a number of theoretical plates to denote the separation efficiency of the packed column with respect to more traditional trays. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing performance.

Another factor in addition to the packing shape and surface area that affects the performance of random or structured packing is liquid and vapor distribution entering the packed bed. The number of theoretical stages required to make a given separation is calculated using a specific vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the packed bed and the required separation will not be achieved. The packing will appear to not be working properly. The height equivalent to a theoretical plate (HETP) will be greater than expected. The problem is not the packing itself but the mal-distribution of the fluids entering the packed bed. Liquid mal-distribution is more frequently the problem than vapor. The design of the liquid distributors used to introduce the feed and reflux to a packed bed is critical to making the packing perform at maximum efficiency. Methods of evaluating the 25 effectiveness of a liquid distributor can be found in references..[10][11] Considerable work as been done on this topic by Fractionation Research, Inc.[12]

Overhead system arrangements

Images 4 and 5 assume an overhead stream that is totally condensed into a liquid product using water or air-cooling. However, in many cases, the tower overhead is not easily condensed totally and the reflux drum must include a vent gas outlet stream. In yet other cases, the overhead stream may also contain water vapor because either the feed stream contains some water or some steam is injected into the distillation tower (which is the case in the crude oil distillation towers in oil refineries). In those cases, if the distillate product is insoluble in water, the reflux drum may contain a condensed liquid distillate phase, a condensed water phase and a non-condensible gas phase, which makes it necessary that the reflux drum also have a water outlet stream.

Examples

Continuous distillation of crude oil

Petroleum crude oils contain hundreds of different hydrocarbon compounds: paraffins, naphthenes and aromatics as well as organic sulfur compounds, organic nitrogen compounds and some oxygen containing hydrocarbons such as phenols. Although crude oils generally do not contain olefins, they are formed in many of the processes used in a petroleum refinery.[13]

The crude oil fractionator does not produce products having a single boiling point, rather, it produces fractions having boiling ranges.[13][14] For example, the crude oil fractionator produces an overhead fraction called "naphtha" which becomes a gasoline component after it is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value.

The naphtha cut, as that fraction is called, contains many different hydrocarbon compounds. Therefore it has an initial boiling point of about 35 °C and a final boiling point of about 200 °C. Each cut produced in the fractionating columns has a different boiling range. At some distance below the overhead, the next cut is withdrawn from the side of the column and it is usually the jet fuel cut, also known as a kerosene cut. The boiling range of that cut is from an initial boiling point of about 150 °C to a final boiling point of about 270 °C, and it also contains many different hydrocarbons. The next cut further down the tower is the diesel oil cut with a boiling range from about 180 °C to about 315 °C. The boiling ranges between any cut and the next cut overlap because the distillation separations are not perfectly sharp. After these come the heavy fuel oil cuts and finally the bottoms product, with very wide boiling ranges. All these cuts are processed further in subsequent refining processes.

Additional information from internet:

For example:

Oil refinery From Wikipedia, the free encyclopedia 26

An oil refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas.[1][2] Oil refineries are typically large sprawling industrial complexes with extensive piping running throughout, carrying streams of fluids between large chemical processing units.

Operation

Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units.

Raw or unprocessed crude oil is not generally useful in its raw or unprocessed form, as it comes out of the ground. Although "light, sweet" (low viscosity, low sulfur) crude oil has been used directly as a burner fuel for steam vessel propulsion, the lighter elements form explosive vapors in the fuel tanks and so it was quite dangerous, especially in warships. Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a refinery into components that can be used as fuels, lubricants, and as feedstock in petrochemical processes that manufacture such products as plastics, detergents, solvents, elastomers and fibers such as nylon and polyesters. Petroleum fossil fuels are burned in internal combustion engines in order to provide power to operate ships, automobiles, aircraft engines, lawn-mowers, chainsaws, and other pieces of power equipment. These different hydrocarbons have different boiling points, which means they can be separated by distillation. Since the lighter liquid products are in great demand for use in internal combustion engines, a modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these higher value products.

Oil can be used in so many ways because it contains hydrocarbons of varying molecular masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes, dienes, and alkynes. While the molecules in crude oil include many different atoms such as sulfur and nitrogen, the most plentiful molecules are the hydrocarbons, which are molecules of varying length and complexity made of hydrogen and carbon atoms, and a small number of oxygen atoms. The differences in the structure of these molecules is what confers upon them their varying physical and chemical properties, and it is this variety that makes crude oil so useful in such a broad range of applications.

Once separated and purified of any contaminants and impurities, the fuel or lubricant can be sold without any further processing. Smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific octane requirements of fuels by processes such as alkylation or less commonly, dimerization. Octane grade of gasoline can also be improved by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics, which have much higher octane ratings. Intermediate products such as gasoils can even be reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various forms of cracking such as fluid catalytic cracking, thermal cracking, and hydrocracking. The final step in gasoline production is the blending of fuels with different octane ratings, vapor pressures, and other properties to meet product specifications.

Oil refineries are large scale plants, processing from about a hundred thousand to several hundred thousand barrels of crude oil per day. Because of the high capacity, many of the units 27 are operated continuously (as opposed to processing in batches) at steady state or approximately steady state for long periods of time (months to years). This high capacity also makes process optimization and advanced process control very desirable.

Major products of oil refineries

Most products of oil processing are usually grouped into three categories: light distillates (LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum (fuel oil, lubricating oils, wax, tar). This classification is based on the way crude oil is distilled and separated into fractions (called distillates and residuum) as can be seen in the above drawing.[2]

Common process units found in a refinery

The number and nature of the process units in a refinery determine its complexity index.

• Desalter unit washes out salt from the crude oil before it enters the atmospheric distillation unit. • Atmospheric Distillation unit distills crude oil into fractions. See Continuous distillation. • Vacuum Distillation unit further distills residual bottoms after atmospheric distillation. • Naphtha Hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit. • Catalytic Reformer unit is used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker. • Distillate Hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric distillation. • Fluid Catalytic Cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products. • Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable products. • Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more valuable reduced viscosity products. • Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides. • Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product. • Alkylation unit produces high-octane component for gasoline blending. • Dimerization unit converts olefins into higher-octane gasoline blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization. • Isomerization unit converts linear molecules to higher-octane branched molecules for blending into gasoline or feed to alkylation units. • Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker. • Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient to maintain in liquid form. These are usually spherical vessels or bullets (horizontal vessels with rounded ends. 28

• Storage tanks for crude oil and finished products, usually cylindrical, with some sort of vapor emission control and surrounded by an earthen berm to contain spills. • Amine gas treater, Claus unit, and tail gas treatment for converting hydrogen sulfide from hydrodesulfurization into elemental sulfur. • Utility units such as cooling towers for circulating cooling water, boiler plants for steam generation, instrument air systems for pneumatically operated control valves and an electrical substation. • Wastewater collection and treating systems consisting of API separators, dissolved air flotation (DAF) units and some type of further treatment (such as an activated sludge biotreater) to make such water suitable for reuse or for disposal.[3] • Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly asphaltenic materials from lubricating oil stock (or diesel stock). • Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum distillation products.

Flow diagram of typical refinery

The image below is a schematic flow diagram of a typical oil refinery that depicts the various unit processes and the flow of intermediate product streams that occurs between the inlet crude oil feedstock and the final end products. The diagram depicts only one of the literally hundreds of different oil refinery configurations. The diagram also does not include any of the usual refinery facilities providing utilities such as steam, cooling water, and electric power as well as storage tanks for crude oil feedstock and for intermediate products and end products.[1][4][5][6]

The Five Pillars of Refining

While distillation can separate oil into fractions, chemical reactors are required to create more of the products that are in high demand. Refineries rely on four major processing steps to alter the ratios of the different fractions. They are; Catalytic Reforming, Alkylation, Catalytic Cracking, and Hydroprocessing. Each of these methods involves feeding reactants to a reactor where they will be partly converted into products. The unreacted reactants are then separated from the products with a distillation column. The unreacted reactants are recycled for another pass, while the products are further separated and mixed with existing streams. In this way complete conversion of reactants can be obtained, even though not all of the reactants are converted on a given pass through the reactor. The four processing methods, along with distillation, are the pillars of petroleum refining.

Catalytic Reforming

Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed catalytic reactors. Because the reactions which produce higher octane compounds (aliphatic in this case) are endothermic (absorb heat) additional heaters are installed between reactors to keep the reactants at the proper temperature. The catalyst is a platinum (Pt) metal on an alumina (Al2O3) base. While catalysts are never consumed in chemical reactions, they can be fouled, making them less effective over time. The series of reactors used in Catalytic Reforming are therefore designed to be disconnected, and swiveled out of place, so the catalyst can be regenerated.

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Alkylation

Alkylation is another process for producing high octane gasoline. The reaction requires an acid catalyst (sulfuric acid, H2SO4 or hydrofluoric acid, HF) at low temperatures (1-40 degrees Celsius) and low pressures (1-10 atmospheres). The acid composition is usually kept at about 50% making the mixture very corrosive.

Fluidized Catalytic Cracking

Catalytic Cracking takes long molecules and breaks them into much smaller molecules. The cracking reaction is very endothermic, and requires a large amount of heat. Another problem is that reaction quickly fouls the Silica (SiO2) and alumina (Al2O3) catalyst by forming coke on its surface. However, by using a fluidized bed to slowly carry the catalyst upwards, and then sending it to a regenerator where the coke can be burned off, the catalyst is continuously regenerated. This system has the additional benefit of using the large amounts of heat liberated in the exothermic regeneration reaction to heat the cracking reactor. The FCC system is a brilliant reaction scheme, which turns two negatives (heating and fouling) into a positive, thereby making the process extremely economical.

Hydroprocessing

Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating involves the addition of hydrogen atoms to molecules without actually breaking the molecule into smaller pieces. Hydrotreating involves temperatures of about 325 degrees Celsius and pressures of about 50 atmospheres. Many catalysts will work, including; nickel, palladium, platinum, cobalt, and iron. Hydrocracking breaks longer molecules into smaller ones. Hydrocracking involves temperatures over 350 degrees Celsius and pressures up to 200 atmospheres. In both cases, very long residence times (about an hour) are required because of the slow nature of the reactions.

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline (also known as petrol). Basically, the process re- arranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as breaking some of the molecules into smaller molecules. The overall effect is that the product reformate contains hydrocarbons with more complex molecular shapes having higher octane values than the hydrocarbons in the naphtha feedstock. In so doing, the process separates hydrogen atoms from the hydrocarbon molecules and produces very significant amounts of byproduct hydrogen gas for use in a number of the other processes involved in a modern petroleum refinery. Other byproducts are small amounts of methane, ethane, propane and butanes.

This process is quite different from and not to be confused with the catalytic steam reforming process used industrially to produce various products such as hydrogen, ammonia and methanol from natural gas, naphtha or other petroleum-derived feedstocks. Nor is this process 30 to be confused with various other catalytic reforming processes that use methanol or biomass- derived feedstocks to produce hydrogen for fuel cells or other uses.

History

Universal Oil Products (also known as UOP) is a multi-national company developing and delivering technology to the petroleum refining, natural gas processing, petrochemical production and other manufacturing industries. In the 1940s, an eminent research chemist named Vladimir Haensel[1] working for UOP developed a catalytic reforming process using a catalyst containing platinum. Haensel's process was subsequently commercialized by UOP in 1949 for producing a high octane gasoline from low octane naphthas and the UOP process become known as the Platforming process.[2] The first Platforming unit was built in 1949 at the refinery of the Old Dutch Refining Company in Muskegon, Michigan.

In the years since then, many other versions of the process have been developed by some of the major oil companies and other organizations. Today, the large majority of gasoline produced worldwide is derived from the catalytic reforming process.

To name a few of the other catalytic reforming versions that were developed, all of which utilized a platinum and/or a rhenium catalyst:

• Rheniforming: Developed by Chevron Oil Company. • Powerforming: Developed by Esso Oil Company, now known as ExxonMobil. • Magnaforming: Developed by Englehard Catalyst Company and Atlantic Richfield Oil Company. • Ultraforming: Developed by Standard Oil of Indiana, now a part of the British Petroleum Company. • Houdriforming: Developed by the Houdry Process Corporation. • CCR Platforming: A Platforming version, designed for continuous catalyst regeneration, developed by UOP. • Octanizing: A catalytic reforming version developed by Axens, a subsidiary of Institut francais du petrole (IFP), designed for continuous catalyst regeneration.

Chemistry

Before describing the reaction chemistry of the catalytic reforming process as used in petroleum refineries, the typical naphthas used as catalytic reforming feedstocks will be discussed.

Typical naphtha feedstocks

A petroleum refinery includes many unit operations and unit processes. The first unit operation in a refinery is the continuous distillation of the petroleum crude oil being refined. The overhead liquid distillate is called naphtha and will become a major component of the refinery's gasoline (petrol) product after it is further processed through a catalytic hydrodesulfurizer to remove sulfur-containing hydrocarbons and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.

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The naphtha from the crude oil distillation is often further distilled to produce a "light" naphtha containing most (but not all) of the hydrocarbons with 6 or less carbon atoms and a "heavy" naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils are referred to as "straight-run" naphthas.

It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high- octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics (most particularly benzene) that gasoline may contain.[3][4][5]

It should be noted that there are a great many petroleum crude oil sources worldwide and each crude oil has its own unique composition or "assay". Also, not all refineries process the same crude oils and each refinery produces its own straight-run naphthas with their own unique initial and final boiling points. In other words, naphtha is a generic term rather than a specific term.

The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:

Typical Heavy Naphtha Feedstocks

Crude oil name Barrow Island Mutineer-Exeter CPC Blend Draugen Location Australia[6] Australia[7] Kazakhstan[8] North Sea[9]

Initial boiling 149 140 149 150 point, °C

Final boiling 204 190 204 180 point, °C

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Paraffins, 46 62 57 38 liquid volume %

Naphthenes, 42 32 27 45 liquid volume %

Aromatics, 12 6 16 17 liquid volume %

Some refinery naphthas include olefinic hydrocarbons, such as naphthas derived from the fluid catalytic cracking and coking processes used in many refineries. Some refineries may also desulfurize and catalytically reform those naphthas. However, for the most part, catalytic reforming is mainly used on the straight-run heavy naphthas, such as those in the above table, derived from the distillation of crude oils.

The reaction chemistry

There are a good many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of about 5 to 45 atm.[10]

The commonly used catalytic reforming catalysts contain noble metals such as platinum and/or rhenium, which are very susceptible to poisoning by sulfur and nitrogen compounds. Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a hydrodesulfurization unit which removes both the sulfur and the nitrogen compounds.

The four major catalytic reforming reactions are:[11]

1: The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the conversion methylcyclohexane (a naphthene) to toluene (an aromatic), as shown below:

2: The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of normal octane to 2,5-Dimethylhexane (an isoparaffin), as shown below:

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3: The dehydrogenation and aromatization of paraffins to aromatics (commonly called dehydrocyclization) as exemplified in the conversion of normal heptane to toluene, as shown below:

4: The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of normal heptane into isopentane and ethane, as shown below:

The hydrocracking of paraffins is the only one of the above four major reforming reactions that consumes hydrogen. The isomerization of normal paraffins does not consume or produce hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming of petroleum naphthas ranges from about 50 to 200 cubic meters of hydrogen gas (at 0 °C and 1 atm) per cubic meter of liquid naphtha feedstock. In the United States customary units, that is equivalent to 300 to 1200 cubic feet of hydrogen gas (at 60 °F and 1 atm) per barrel of liquid naphtha feedstock.[12] In many petroleum refineries, the net hydrogen produced in catalytic reforming supplies a significant part of the hydrogen used elsewhere in the refinery (for example, in hydrodesulfurization processes). The hydrogen is also necessary in order to hydrogenolyze any polymers that form on the catalyst.

Process description

The most commonly used type of catalytic reforming unit has three reactors, each with a fixed bed of catalyst, and all of the catalyst is regenerated in situ during routine catalyst regeneration shutdowns which occur approximately once each 6 to 24 months. Such a unit is referred to as a semi-regenerative catalytic reformer (SRR).

Some catalytic reforming units have an extra spare or swing reactor and each reactor can be individually isolated so that any one reactor can be undergoing in situ regeneration while the other reactors are in operation. When that reactor is regenerated, it replaces another reactor which, in turn, is isolated so that it can then be regenerated. Such units, referred to as cyclic catalytic reformers, are not very common. Cyclic catalytic reformers serve to extend the period between required shutdowns.

The latest and most modern type of catalytic reformers are called continuous catalyst regeneration reformers (CCR). Such units are characterized by continuous in-situ regeneration of part of the catalyst in a special regenerator, and by continuous addition of the regenerated catalyst to the operating reactors. As of 2006, two CCR versions available: UOP's CCR Platformer process[13] and Axen's Octanizing process.[14] The installation and use of CCR units is rapidly increasing.

Many of the earliest catalytic reforming units (in the 1950s and 1960's) were non-regenerative in that they did not perform in situ catalyst regeneration. Instead, when needed, the aged catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst manufacturer's to be either regenerated or to recover the platinum content of the aged catalyst. Very few, if any, catalytic reformers currently in operation are non-regenerative.

The process flow diagram below depicts a typical semi-regenerative catalytic reforming unit.

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Schematic diagram of a typical semi-regenerative catalytic reformer unit in a petroleum refinery

The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5 to 45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowing through a heat exchanger. The preheated feed mixture is then totally vaporized and heated to the reaction temperature (495 to 520 °C) before the vaporized reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics (as described earlier herein) which is highly endothermic and results in a large temperature decrease between the inlet and outlet of the reactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream is reheated in the second fired heater before it flows through the second reactor. The temperature again decreases across the second reactor and the vaporized stream must again be reheated in the third fired heater before it flows through the third reactor. As the vaporized stream proceeds through the three reactors, the reaction rates decrease and the reactors therefore become larger. At the same time, the amount of reheat required between the reactors becomes smaller. Usually, three reactors are all that is required to provide the desired performance of the catalytic reforming unit.

Some installations use three separate fired heaters as shown in the schematic diagram and some installations use a single fired heater with three separate heating coils.

The hot reaction products from the third reactor are partially cooled by flowing through the heat exchanger where the feed to the first reactor is preheated and then flow through a water- cooled heat exchanger before flowing through the pressure controller (PC) into the gas separator.

Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the recycle hydrogen gas compressor and the net production of hydrogen-rich gas from the reforming reactions is exported for use in other the other refinery processes that consume hydrogen (such as hydrodesulfurization units and/or a hydrocracker unit).

The liquid from the gas separator vessel is routed into a fractionating column commonly called a stabilizer. The overhead offgas product from the stabilizer contains the byproduct methane, ethane, propane and butane gases produced by the hydrocracking reactions as explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may also contain some small amount of hydrogen. That offgas is routed to the refinery's central gas processing plant for removal and recovery of propane and butane. The residual gas after such processing becomes part of the refinery's fuel gas system.

The bottoms product from the stabilizer is the high-octane liquid reformate that will become a component of the refinery's product gasoline.

Catalysts and mechanisms

Most catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina support base, and some contain both platinum and rhenium. Fresh catalyst is chlorided (chlorinated) prior to use.

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The noble metals (platinum and rhenium) are considered to be catalytic sites for the dehydrogenation reactions and the chlorinated alumina provides the acid sites needed for isomerization, cyclization and hydrocracking reactions.[11]

The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is reduced over time during operation by carbonaceous coke deposition and chloride loss. The activity of the catalyst can be periodically regenerated or restored by in situ high temperature oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative catalytic reformers are regenerated about once per 6 to 24 months.

Normally, the catalyst can be regenerated perhaps 3 or 4 times before it must be returned to the manufacturer for reclamation of the valuable platinum and/or rhenium content.[11]

Alkylation

In a standard oil refinery process, isobutane is alkylated with low-molecular-weight alkenes (primarily a mixture of propylene and butylene) in the presence of a strong acid catalyst, either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to as a sulfuric acid alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU). However, oil refinery employees may simply refer to the unit as the Alkyl or Alky unit. The catalyst is able to protonate the alkenes (propylene, butylene) to produce reactive carbocations, which alkylate isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a two-phase reaction. It is important to keep a high ratio of isobutane to alkene at the point of reaction to prevent side reactions that lead to a lower octane product, so the plants have a high recycle of isobutane back to feed. The phases separate spontaneously, so the acid phase is vigoriously mixed with the hydrocarbon phase to create sufficient contact surface.

The product is called alkylate and is composed of a mixture of high-octane, branched-chain paraffinic hydrocarbons (mostly isopentane and isooctane). Alkylate is a premium gasoline blending stock because it has exceptional antiknock properties and is clean burning. Alkylate is also a key component of avgas. The octane number of the alkylate depends mainly upon the kind of alkenes used and upon operating conditions. For example, isooctane results from combining butylene with isobutane and has an octane rating of 100 by definition. There are other products in the alkylate, so the octane rating will vary accordingly.

Most crude oils contain only 10 to 40 percent of their hydrocarbon constituents in the gasoline range, so refineries use a fluid catalytic cracking process to convert high molecular weight hydrocarbons into smaller and more volatile compounds. Polymerization converts gaseous alkenes into liquid gasoline-size hydrocarbons. Alkylation processes transform low molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with a high octane number.

Combining cracking, polymerization, and alkylation can result in a gasoline yield representing 70 percent of the starting crude oil. More advanced processes, such as cyclicization of paraffins and dehydrogenation of naphthenes to form aromatic hydrocarbons in a catalytic reformer, have also been developed to increase the octane rating of gasoline. Modern refinery operation can be shifted to produce almost any fuel type with specified performance criteria from a single crude feedstock.

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In the entire range of refinery processes, alkylation is a very important process that enhances the yield of high-octane gasoline. However, not all refineries have an alkylation plant. The oil and gas journal annual survey of worldwide refining capacities for January 2007 lists many countries with no alkylation plants at their refineries.

A primary factor in deciding to install alkylation is usually economics. Refinery alkylation units are complex and there is substantial economy of scale. In addition to a suitable quantity of feedstock, the price spread between the value of alkylate product and alternate feedstock disposition value must be large enough to justify the plant. Alternative outlets for refinery alklylation feedstocks include sales as LPG, blending of C4 streams directly into gasoline and feedstocks for chemical plants. Local market conditions vary widely between plants. Variation in the RVP specification for gasoline between countries and between seasons dramatically impacts the amount of butane streams that can be blended directly into gasoline. The transportation of specific types of LPG streams can be expensive so local disparities in economic conditions are often not fully mitigated by cross market movements of alkylation feedstocks.

Another factor in the decision to build an alkylation plant concerns the availability of a suitable catalyst. If sulfuric acid is used, significant volumes are needed. This requires access to a suitable plant for the supply of fresh acid and the disposition of spent acid. If a sulfuric acid plant must be constructed specifically to support an alkylation unit, this will have a significant impact on both the initial capital requirements and ongoing operating costs. The second main catalyst option is hydrofluoric acid. Consumption rates for HF acid in alkylation plants are much lower than for sulfuric acid. HF acid plants can process a wider range of feedstock mix with proplyenes and butylenes. HF plants also produce alklyate with better octane than sulfuric plants. However, due to the hazardous nature of the material, HF acid is produced at very few locations and transportation must be managed rigorously. Thermal cracking

William Merriam Burton developed one of the earliest thermal cracking processes in 1912 which operated at 700-750 °F (370-400 °C) and an absolute pressure of 90 psia (620 kPa) and was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the Universal Oil Products Company, developed a somewhat more advanced thermal cracking process which operated at 750-860 °F (400-460 °C) and was known as the Dubbs process.[9] The Dubbs process was used extensively by many refineries until the early 1940's when catalytic cracking came into use.

Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An overall process of disproportionation can be observed, where "light", hydrogen-rich products are formed at the expense of heavier molecules which condense and are depleted of hydrogen. The actual reaction is known as homolytic fission and produces alkenes, which are the basis for the economically important production of polymers.

A large number of chemical reactions take place during steam cracking, most of them based on free radicals. Computer simulations aimed at modeling what takes place during steam cracking have included hundreds or even thousands of reactions in their models. The main reactions that take place include:

Initiation reactions, where a single molecule breaks apart into two free radicals. Only a small fraction of the feed molecules actually undergo initiation, but these reactions are necessary to 37 produce the free radicals that drive the rest of the reactions. In steam cracking, initiation usually involves breaking a chemical bond between two carbon atoms, rather than the bond between a carbon and a hydrogen atom.

CH3CH3 → 2 CH3•

Hydrogen abstraction, where a free radical removes a hydrogen atom from another molecule, turning the second molecule into a free radical.

CH3• + CH3CH3 → CH4 + CH3CH2•

Radical decomposition, where a free radical breaks apart into two molecules, one an alkene, the other a free radical. This is the process that results in the alkene products of steam cracking.

CH3CH2• → CH2=CH2 + H•

Radical addition, the reverse of radical decomposition, in which a radical reacts with an alkene to form a single, larger free radical. These processes are involved in forming the aromatic products that result when heavier feedstocks are used.

CH3CH2• + CH2=CH2 → CH3CH2CH2CH2•

Termination reactions, which happen when two free radicals react with each other to produce products that are not free radicals. Two common forms of termination are recombination, where the two radicals combine to form one larger molecule, and disproportionation, where one radical transfers a hydrogen atom to the other, giving an alkene and an alkane.

CH3• + CH3CH2• → CH3CH2CH3

CH3CH2• + CH3CH2• → CH2=CH2 + CH3CH3

Thermal cracking is an example of a reaction whose energetics are dominated by entropy (∆S°) rather than by enthalpy (∆H°) in the Gibbs Free Energy equation ∆G°=∆H°-T∆S°. Although the bond dissociation energy D for a carbon-carbon single bond is relatively high (about 375 kJ/mol) and cracking is highly endothermic, the large positive entropy change resulting from the fragmentation of one large molecule into several smaller pieces, together with the extremely high temperature, makes T∆S° term larger than the ∆H° term, thereby favoring the cracking reaction.

Here is an example of cracking with butane CH3-CH2-CH2-CH3

• 1st possibility (48%): breaking is done on the CH3-CH2 bond.

CH3* / *CH2-CH2-CH3 after a certain number of steps, we will obtain an alkane and an alkene: CH4 + CH2=CH-CH3

• 2nd possibility (38%): breaking is done on the CH2-CH2 bond.

CH3-CH2* / *CH2-CH3

38 after a certain number of steps, we will obtain an alkane and an alkene from different types: CH3-CH3 + CH2=CH2

• 3rd possibility (14%): breaking of a C-H bond after a certain number of steps, we will obtain an alkene and hydrogen gas: CH2=CH-CH2- CH3 + H2 this is very useful since the catalyst can be recycled.

Fluid catalytic cracking

From Wikipedia, the free encyclopedia

Fluid catalytic cracking (FCC) is the most important conversion process used in petroleum refineries. It is widely used to convert the high-boiling hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases and other products.[1][2][3] Cracking of petroleum hydrocarbons was originally done by thermal cracking which has been almost completely replaced by catalytic cracking because it produces more gasoline with a higher octane rating. It also produces byproduct gases that are more olefinic, and hence more valuable, than those produced by thermal cracking.

The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. The FCC process vaporizes and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.

In effect, refineries use fluid catalytic cracking to correct the imbalance between the market demand for gasoline and the excess of heavy, high boiling range products resulting from the distillation of crude oil.

As of 2006, FCC units were in operation at 400 petroleum refineries worldwide and about one-third of the crude oil refined in those refineries is processed in an FCC to produce high- octane gasoline and fuel oils.[2][4] During 2007, the FCC units in the United States processed a total of 5,300,000 barrels (834,300,000 litres) per day of feedstock[5] and FCC units worldwide processed about twice that amount.

Flow diagram and process description

The modern FCC units are all continuous processes which operate 24 hours a day for as much as 2 to 3 years between shutdowns for routine maintenance.

There are a number of different proprietary designs that have been developed for modern FCC units. Each design is available under a license that must be purchased from the design developer by any petroleum refining company desiring to construct and operate an FCC of a given design.

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Basically, there are two different configurations for an FCC unit: the "stacked" type where the reactor and the catalyst regenerator are contained in a single vessel with the reactor above the catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are in two separate vessels. These are the major FCC designers and licensors:[1][3][4][6]

Reactor and Regenerator

The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon the "side-by-side" configuration. The preheated high-boiling petroleum feedstock (at about 315 to 430 °C) consisting of long-chain hydrocarbon molecules is combined with recycle slurry oil from the bottom of the distillation column and injected into the catalyst riser where it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the very hot powdered catalyst from the regenerator. All of the cracking reactions take place in the catalyst riser. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about 535 °C and a pressure of about 1.72 barg.

The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated from the so-called spent catalyst by flowing through a set of two-stage cyclones within the reactor and (b) the spent catalyst flows downward through a steam stripping section to remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator. The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst line.

Since the cracking reactions produce some carbonaceous material (referred to as coke) that deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is regenerated by burning off the deposited coke with air blown into the regenerator. The regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 barg. The combustion of the coke is exothermic and it produces a large amount of heat that is partially absorbed by the regenerated catalyst and provides the heat required for the vaporization of the feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that reason, FCC units are often referred to as being heat balanced.

The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot flue gas exits the regenerator after passing through multiple sets of two-stage cylones that remove entrained catalyst from the flue gas,

The amount of catalyst circulating between the regenerator and the reactor amounts to about 5 kg per kg of feedstock which is equivalent to about 4.66 kg per litre of feedstock.[1][7] Thus, an FCC unit processing 75,000 barrels/day (12,000,000 litres/day) will circulate about 55,900 metric tons per day of catalyst.

Chemistry

Before delving into the chemistry involved in catalytic cracking, it will be helpful to briefly discuss the composition of petroleum crude oil.

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Table 1 Petroleum crude oil consists primarily of a mixture of hydrocarbons with small amounts of other organic compounds containing sulfur, nitrogen and oxygen. The crude oil also contains small amounts of metals such as copper, iron, nickel and vanadium.[2]

Hydrogen 10-14% Nitroge 0.1-2% Carbon 83-87% n Sulfur 0.5-6% Metals < 0.1% Oxygen 0.1-1.5%

The elemental composition ranges of crude oil are summarized in Table 1 and the hydrocarbons in the crude oil can be classified into three types:[1][2]

• Paraffins or alkanes: saturated straight-chain or branched hydrocarbons, without any ring structures • Naphthenes or cycloalkanes: saturated hydrocarbons having one or more ring structures with one or more side-chain paraffins • Aromatics: hydrocarbons having one or more unsaturated ring structures such as benzene or unsaturated polycyclic ring structures such as naphthalene or phenanthrene, any of which may also have one or more side-chain paraffins.

Figure 2 : A schematic flow diagram of a Fluid Catalytic Cracking unit as used in petroleum refineries

Olefins or alkenes, which are unsaturated straight-chain or branched hydrocarbons, do not occur naturally in crude oil.

Figure : Diagrammatic example of the catalytic cracking of petroleum hydrocarbons

In plain language, the fluid catalytic cracking process breaks large hydrocarbon molecules into smaller molecules by contacting them with powdered catalyst at a high temperature and moderate pressure which first vaporizes the hydrocarbons and then breaks them. The cracking reactions occur in the vapor phase and start immediately when the feedstock is vaporized in the catalyst riser.

Figure 2 is a very simplified schematic diagram that exemplifies how the process breaks high boiling, straight-chain alkane (paraffin) hydrocarbons into smaller straight-chain alkanes as well as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naphthenes).[9]

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The breaking of the large hydrocarbon molecules into smaller molecules is more technically referred to by organic chemists as scission of the carbon-to-carbon bonds.

As depicted in Figure 2, some of the smaller alkanes are then broken and converted into even smaller alkenes and branched alkenes such as the gases ethylene, propylene, butylenes and isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks. The propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum refining processes that convert them into high-octane gasoline blending components.

As also depicted in Figure 2, the cycloalkanes (naphthenes) formed by the initial breakup of the large molecules are further converted to aromatics such as benzene, toluene and xylenes which boil in the gasoline boiling range and have much higher octane ratings than alkanes.

By no means does Figure 2 include all the chemistry of the primary and secondary reactions taking place in the fluid catalytic process. There are a great many other reactions involved. However, a full discussion of the highly technical details of the various catalytic cracking reactions is beyond the scope of this article and can be found in the technical literature.[1][2][3][4]

Catalysts

Modern FCC catalysts are fine powders with a bulk density of 0.80 to 0.96 g/cc and having a particle size distribution ranging from 10 to 150 μm and an average particle size of 60 to 100 μm.[10][11] The design and operation of an FCC unit is largely dependent upon the chemical and physical properties of the catalyst. The desirable properties of an FCC catalyst are:

• Good stability to high temperature and to steam • High activity • Large pore sizes • Good resistance to attrition • Low coke production

A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder and filler. Zeolite is the primary active component and can range from about 15 to 50 weight percent of the catalyst. The zeolite used in FCC catalysts is referred to as faujasite or as Type Y and is comprised of silica and alumina tetrahedra with each tetrahedron having either an aluminum or a silicon atom at the center and four oxygen atoms at the corners. It is a molecular sieve with a distinctive lattice structure that allows only a certain size range of hydrocarbon molecules to enter the lattice. In general, the zeolite does not allow molecules larger than 8 to 10 nm (i.e., 80 to 90 angstroms) to enter the lattice.[10][11]

The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and provide most of the catalytic activity. The acidic sites are provided by the alumina tetrahedra. The aluminum atom at the center of each alumina tetrahedra is at a +3 oxidation state surrounded by four oxygen atoms at the corners which are shared by the neighboring tetrahedra. Thus, the net charge of the alumina tetrahedra is -1 which is balanced by a sodium ion during the production of the catalyst. The sodium ion is later replaced by an ammonium ion which is vaporized when the catalyst is subsequently dried, resulting in the formation of Lewis and Brønsted acidic sites. In some FCC catalysts, the Brønsted sites may be later replaced by rare earth metals such as cerium and lanthanum to provide alternative activity and stability levels.[10][11]

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The matrix component of an FCC catalyst contains amorphous alumina which also provides catalytic activity sites and in larger pores that allows entry for larger molecules than does the zeolite. That enables the cracking of higher-boiling, larger feedstock molecules than are cracked by the zeolite.

The binder and filler components provide the physical strength and integrity of the catalyst. The binder is usually silica sol and the filler is usually a clay (kaolin). Hydrocracking

In 1920 a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in Germany[8].

Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial pressure of hydrogen gas. Similar to the hydrotreater, the function of hydrogen is the purification of the hydrocarbon stream from sulfur and nitrogen hetero-atoms.

The products of this process are saturated hydrocarbons; depending on the reaction conditions (temperature, pressure, catalyst activity) these products range from ethane, LPG to heavier hydrocarbons comprising mostly of isoparaffins. Hydrocracking is normally facilitated by a bi functional catalyst that is capable of rearranging and breaking hydrocarbon chains as well as adding hydrogen to aromatics and olefins to produce naphthenes and alkanes.

Major products from hydrocracking are jet fuel and diesel, while also relatively high octane rating gasoline fractions and LPG are produced. All these products have a very low content of sulfur and other contaminants.

It is very common in India, Europe and Asia because those regions have high demand for diesel and kerosene. In the US, Fluid Catalytic Cracking is more common because the demand for gasoline is higher.

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Case Study: Petroleum Origins of the Industry

The American chemical engineer and the American petroleum industry developed side by side over the past century. The petroleum industry began when Edwin L. Drake drilled a successful oil well at Titusville Pennsylvania in 1859. Others quickly followed his lead, and before long oil wells covered the countryside. Just ten years after California's Gold Rush, Pennsylvania had developed its own brand of "gold fever". Some, like John D. Rockefeller, accumulated vast fortunes from this "black gold", while others like Mr. Drake died broke. The difference between success and failure was often a fine line.

"Enough already...go to the end."

Ancient, and Less Ancient, Times

Small amounts of petroleum have been used throughout history. The Egyptians coated mummies and sealed their mighty Pyramids with pitch. The Babylonians, Assyrians, and Persians used it to pave their streets and hold their walls and buildings together. Boats along the Euphrates were constructed with woven reeds and sealed with pitch. The Chinese also came across it while digging holes for brine (salt water) and used the petroleum for heating. The Bible even claims that Noah used it to make his Ark seaworthy.

American Indians used petroleum for paint, fuel, and medicine. Desert nomads used it to treat camels for mange, and the Holy Roman Emperor, Charles V, used petroleum it to treat his gout. Ancient Persians and Sumatrans also believed petroleum had medicinal value. This seemed a popular idea, and up through the 19th Century jars of petroleum were sold as miracle tonic able to cure whatever ailed you. People who drank this "snake oil" discovered that petroleum doesn't taste very good!

The Search for Oil

Yet despite its usefulness, for thousands of years petroleum was very scarce. People collected it when it bubbled to the surface or seeped into wells. For those digging wells to get drinking water the petroleum was seen as a nuisance. However, some thought the oil might have large scale economic value. George Bissell, a lawyer, thought that petroleum might be converted into kerosene for use in lamps. An analysis by Benjamin Silliman, Jr., a Yale chemistry and geology professor, confirmed his hunch.

In 1854 Bissell and a friend formed the unsuccessful Pennsylvania Rock Oil Company. Not one to be easily dismayed, in 1858 Bissell and a group of business men formed the Seneca Oil Company. They hired an ex-railroad conductor named Edwin Drake to drill for oil along a secluded creek in Titusville Pennsylvania. They soon dubbed him "Colonel" Drake to impress the locals. But the "Colonel" needed help so he hired Uncle Billy Smith and his two sons who had experience with drilling salt wells. In 1859 this motley crew found oil at a depth of 69 ˝ feet.

Pennsylvania's "Black Gold" 44

Drake's well produced only thirty-five barrels a day, however he could sell it for $20 a barrel. News of the well quickly spread and brought droves of fortune seekers. Soon the hills were covered with prospectors trying to decide where to dig their wells. Some used Y- shaped devining rods to guide them. Others followed Drake's lead and drilled close to water, a technique that was dubbed "creekology". Many found oil, but usually at 4 or 5 hundred feet below the surface. Drake had just been lucky to find oil so high up!

To dig the wells six-inch wide cast iron pipes were sunk down to the bedrock. A screw like drill was then used to scoop out dirt and rock from the middle. Many discovered to their dismay that once they hit oil they had no way to contain all of it. Until caps were added to the wells vast quantities of oil flowed into the appropriately named Oil Creek.

The First Pipeline

Transporting the oil was also a problem. In 1865 Samuel Van Syckel, an oil buyer, began construction on a two-inch wide pipeline designed to span the distance to the railroad depot five miles away. The teamsters, who had previously transported the oil, didn't take to kindly to Syckel's plan, and they used pickaxes to break apart the line. Eventually Van Syckel brought in armed guards, finished the pipeline, and made a ton-o-money. By 1865 wooden derricks were bled 3.5 million barrels a year out of the ground. (Giddens) Such large scale production caused the price of crude oil to plummet to ten cents a barrel.

How Much Oil?

Andrew Carnegie was a large stockholder in the Columbia Oil Company. Carnegie believed that the oil fields would quickly run dry because of all the drilling. He persuaded Columbia Oil to dig a huge hole to store 100,000 barrels of oil so that they could make a killing when the country's wells went dry. Luckily there was more oil than they thought! But don't feel too sorry for Carnegie, he didn't let the setback slow him down very much, and went on to make his millions in the steel industry.

In contrast, "Colonel" Drake was committed to the oil business. He scoured the country looking for customers willing to buy his crude oil. However, the bad smell, muddy black color, and highly volatile component, called naphtha, caused few sales. It became obvious that one would have to refine the oil to find a market.

Early Refining

By 1860 there were 15 refineries in operation. Known as "tea kettle" stills, they consisted of a large iron drum and a long tube which acted as a condenser. Capacity of these stills ranged from 1 to 100 barrels a day. A coal fire heated the drum, and three fractions were obtained during the distillation process. The first component to boil off was the highly volatile naphtha. Next came the kerosene, or "lamp oil", and lastly came the heavy oils and tar which were simply left in the bottom of the drum. These early refineries produced about 75% kerosene, which could be sold for high profits. (Giddens, p.14)

Kerosene was so valuable because of a whale shortage that had began in 1845 due to heavy hunting. Sperm oil had been the main product of the whaling industry and was used in lamps. Candles were made with another whale product called "spermaceti". This shortage of natural sources meant that kerosene was in great demand. Almost all the families across the country started using kerosene to light their homes. However, the naphtha and tar

45 fractions were seen as valueless and were simply dumped into Oil Creek. (I would like to point out that these first refineries were not operated by chemical engineers!)

Later these waste streams were converted into valuable products. In 1869 Robert Chesebrough discovered how to make petroleum jelly and called his new product Vaseline. The heavy components began being used as lubricants, or as waxes in candles and chewing gum. Tar was used as a roofing material. But the more volatile components were still without much value. Limited success came in using gasoline as a local anesthetic and liquid petroleum gas (LPG) in a compression cycle to make ice. The success in refined petroleum products greatly spread the technique. By 1865 there were 194 refineries in operation.

John D. Rockefeller

In 1862 John D. Rockefeller financed his first refinery as a side investment. He soon discovered that he liked the petroleum industry, and devoted himself to it full time. As a young bookkeeper Rockefeller had come to love the order of a well organized ledger. However, he was appalled by the disorder and instability of the oil industry. Anyone could drill a well, and overproduction plagued the early industry. At times this overproduction meant that the crude oil was cheaper than water. Rockefeller saw early on, that refining and transportation, as opposed to production, were the keys to taking control of the industry. And control the industry he did!

In 1870 he established Standard Oil, which then controlled 10% of the refining capacity in the country. Transportation often encompassed 20% of the total production cost and Rockefeller made under-the-table deals with railroads to give him secret shipping rebates. This cheap transportation allowed Standard to undercut its competitors and Rockefeller expanded aggressively, buying out competitors left and right. Soon standard built a network of "iron arteries" which delivered oil across the Eastern U.S. This pipeline system relieved Standard's dependence upon the railroads and reduced its transportation costs even more. By 1880 Standard controlled 90% of the country's refining capacity. Because of its massive size, it brought security and stability to the oil business, guaranteeing continuous profits. With Standard Oil, John D. Rockefeller became the richest person in the World.

So What?

But what came out of all this activity? In short the early petroleum industry:

Brought a revolution in lighting with kerosene.

Helped keep machines in good conditions with lubricants. (it was the "Machine Age" after all)

Provided a new source of national wealth (in 1865 it was the countries 6th largest export).

Aided the Union in the Civil War by strengthening the economy (also petroleum was used to treat wounded soldiers at the battle of Gettysburg).

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Modern Refining

Petroleum refineries are marvels of modern engineering. Within them a maze of pipes, distillation columns, and chemical reactors turn crude oil into valuable products. Large refineries cost billions of dollars, employ several thousand workers, operate around the clock, and occupy the same area as several hundred football stadiums. The U.S. has about 300 refineries that can process anywhere between 40 and 400,000 barrels of oil a day. These refineries turn out the gasoline and chemical feedstocks that keep the country running.

The Search

Locating an oil field is the first obstacle to be overcome. The first explorers used Y-shaped devining rods and other supernatural, but ineffective, means of locating petroleum. Today geologists and petroleum engineers employ more tried and true methods. Instruments to aid the search include; geophones (uses sound), gravimeters (uses gravity), and magnetometers (uses the Earth's magnet field). While these methods narrow the search tremendously, a person still has to drill a exploratory well, or wildcat well, to see if the oil actually exists. Success brings visions of gushers soaring skyward, however today wells are capped before this happens.

Drilling

There are three main types of drilling operations; cable-tool, rotary, and off-shore. Cable- tool drilling involves a jack-hammer approach were a chisel dislodges earth and hauls up the loose sediment. Rotary drilling works at much greater depths, and involve sinking a drill pipe with a rotating steel bit in the middle. Off-shore drilling involves huge semisubmersible platforms which lower a shaft to the ocean floor, containing any oil which is located.

All crude oil contains some amount of methane or other gases dissolved in it. Once the drilling shaft makes contact with the oil it releases the pressure in the underground reservoir. Just like opening a can of soda pop, the dissolved gases fizz out of solution pushing crude oil to the surface. The dissolved gases will allow about 20% recovery of oil. To get better recovery water is often pumped into the well, this forces the lighter oil to the surface. Water flooding allows recoveries of about 50%. The addition of surfactant allows even more oil to be recovered by preventing much of it from getting trapped in nooks and crannies. Yet, it is impossible to get all of the oil out of a well.

Transportation

Because crude oil is a liquid it is much easier to move than natural gas or coal. Coal is nice and dense, so it does not require large holding containers, but it cannot be pumped. Conveyor belts and cranes cannot compete with pipelines for economic efficiency. Natural gas can be pumped using expensive compressors, but it requires enormous holding tanks. A recent trick has been to inject huge amounts of water into salt strata. The water dissolves the salt, leaving truly enormous caverns. The natural gas is then pumped in and stored until needed. The ease in transporting oil is one of the reasons we have become so dependent upon it. Pound for pound natural gas and coal just cannot compete.

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Reserves

The proven reserves of crude oil within the U.S. are about 3.9 billion cubic meters. This could cover the state of Minnesota with a layer one half inch thick. A reasonable value for the total amount of crude oil obtainable using current methods from around the world is 350 billion cubic meters. This could cover Minnesota with a layer of oil four and a half feet thick. Yet, at the rate we are consuming oil, the nation's reserves will be depleted by 2010, and the world's reserves will be depleted by the end of the 21st Century.

Yet, oil is not the only source of hydrocarbons. Natural gas and coal are both available in much greater amounts (see Distillation Figure). However, we may decide that it is not such a good idea to burn all of these hydrocarbons. Carbon dioxide is a strong greenhouse gas (along with water and methane), and the results to the global environment could be catastrophic to human life. Nuclear fission, solar power, hydroelectric power, and geothermal power offer immediate alternatives, however energy produced by these methods would be more expensive than burning oil, coal, or natural gas. The holy grail of power production, nuclear fusion, continues to elude scientists and engineers. In any case, refining techniques will remain vital to produce not only fuels but raw materials for petrochemical industries (plastics, pharmaceuticals, agrochemicals, etc.).

"The Kingdom of Heaven runs on righteousness, but the Kingdom of Earth runs on OIL!"

Quote by Ernest Bevin at the British Parliament during a heated discussion concerning the Middle East.

Chemistry

Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.

The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture.

The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern refineries into more valuable products. The shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these gases are either flared off, sold as liquified petroleum gas under pressure, or used to power the refinery's own burners. During the winter, Butane (C4H10), is blended into the gasoline pool at high rates, because butane's high vapor pressure assists with cold starts. Liquified under pressure slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source for many developing countries. Propane can be liquified under modest pressure, and is

48 consumed for just about every application relying on petroleum for energy, from cooking to heating to transportation.

The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. Cycloalkanes have similar properties to alkanes but have higher boiling points.

The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic.

These different molecules are separated by fractional distillation at an oil refinery to produce gasoline, jet fuel, kerosene, and other hydrocarbons. For example 2,2,4-trimethylpentane (isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with oxygen exothermically:[11]

The amount of various molecules in an oil sample can be determined in laboratory. The molecules are typically extracted in a solvent, then separated in a gas chromatograph, and finally determined with a suitable detector, such as a flame ionization detector or a mass spectrometer[12].

Incomplete combustion of petroleum or gasoline results in production of toxic byproducts. Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures involved, exhaust gases from gasoline combustion in car engines usually include nitrogen oxides which are responsible for creation of photochemical smog.

Formation

Geologists view crude oil and natural gas as the product of compression and heating of ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature and/or pressure.[13] Today's oil formed from the preserved remains of prehistoric zooplankton and algae, which had settled to a sea or lake bottom in large quantities under anoxic conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form coal). Over geological time the organic matter mixed with mud, and was buried under heavy layers of sediment resulting in high levels of heat and pressure (known as diagenesis). This caused the organic matter to chemically change, first into a waxy material known as kerogen which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.

Geologists often refer to the temperature range in which oil forms as an "oil window"[14]— below the minimum temperature oil remains trapped in the form of kerogen, and above the maximum temperature the oil is converted to natural gas through the process of thermal cracking. Although this temperature range is found at different depths below the surface throughout the world, a typical depth for the oil window is 4–6 km. Sometimes, oil which is formed at extreme depths may migrate and become trapped at much shallower depths than where it was formed. The Athabasca Oil Sands is one example of this.

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Crude Oil

Crude oil reservoirs

Hydrocarbon trap.

Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon material buried deep enough for subterranean heat to cook it into oil; a porous and permeable reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents it from escaping to the surface. Within these reservoirs, fluids will typically organize themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas above it, although the different layers vary in size between reservoirs. Because most hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. However, the process is influenced by underground water flows, causing oil to migrate hundreds of kilometres horizontally or even short distances downward before becoming trapped in a reservoir. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping.

The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in petrochemical plants and oil refineries.

[Non-conventional oil reservoirs

Oil-eating bacteria biodegrades oil that has escaped to the surface. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two countries have the world's largest deposits of oil sands.

On the other hand, oil shales are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not really shales and do not really contain oil, but are usually relatively hard rocks called marls containing a waxy substance called kerogen. The kerogen trapped in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits.[15]

Abiogenic origin

Main article: Abiogenic petroleum origin 50

A number of geologists in Russia adhere to the abiogenic petroleum origin hypothesis and maintain that hydrocarbons of purely inorganic origin exist within Earth's interior. Astronomer Thomas Gold championed the theory in the Western world by supporting the work done by Nikolai Kudryavtsev in the 1950s. It is currently supported primarily by Kenney and Krayushkin.[16]

The abiogenic origin hypothesis lacks scientific support, and all current oil reserves have biological origin. It also has not been successfully used in uncovering oil deposits by geologists.[17]

Classification

See also: Benchmark (crude oil)

A sample of medium heavy crude oil

The petroleum industry generally classifies crude oil by the geographic location it is produced in (e.g. West Texas, Brent, or Oman), its API gravity (an oil industry measure of density), and by its sulfur content. Crude oil may be considered light if it has low density or heavy if it has high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it contains substantial amounts of sulfur.

The geographic location is important because it affects transportation costs to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries. Each crude oil has unique molecular characteristics which are understood by the use of crude oil assay analysis in petroleum laboratories.

Barrels from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing references throughout the world. Some of the common reference crudes are:

• West Texas Intermediate (WTI), a very high-quality, sweet, light oil delivered at Cushing, Oklahoma for North American oil • Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal in the Shetlands. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off this oil, which forms a benchmark • Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the Asia- Pacific region • Tapis (from Malaysia, used as a reference for light Far East oil) • Minas (from Indonesia, used as a reference for heavy Far East oil) • The OPEC Reference Basket, a weighted average of oil blends from various OPEC (The Organization of the Petroleum Exporting Countries) countries

There are declining amounts of these benchmark oils being produced each year, so other oils are more commonly what is actually delivered. While the reference price may be for West Texas Intermediate delivered at Cushing, the actual oil being traded may be a discounted

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Canadian heavy oil delivered at Hardisty, Alberta, and for a Brent Blend delivered at the Shetlands, it may be a Russian Export Blend delivered at the port of Primorsk.[18]

Petroleum industry

Main article: Petroleum industry

NYMEX Light Sweet Crude prices 1994 2005 to Nov 2008

to Mar 2008

The petroleum industry is involved in the global processes of exploration, extraction, refining, transporting (often with oil tankers and pipelines), and marketing petroleum products. The largest volume products of the industry are fuel oil and gasoline (petrol). Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics. The industry is usually divided into three major components: upstream, midstream and downstream. Midstream operations are usually included in the downstream category.

Petroleum is vital to many industries, and is of importance to the maintenance of industrialized civilization itself, and thus is critical concern to many nations. Oil accounts for a large percentage of the world’s energy consumption, ranging from a low of 32% for Europe and Asia, up to a high of 53% for the Middle East. Other geographic regions’ consumption patterns are as follows: South and Central America (44%), Africa (41%), and North America (40%). The world at large consumes 30 billion barrels (4.8 km³) of oil per year, and the top oil consumers largely consist of developed nations. In fact, 24% of the oil consumed in 2004 went to the United States alone.[19] The production, distribution, refining, and retailing of petroleum taken as a whole represent the single largest industry in terms of dollar value on earth.

In the US, in the states of Arizona, California, Hawaii, Nevada, Oregon and Washington, the Western States Petroleum Association (WSPA) is responsible for producing, distributing, refining, transporting and marketing petroleum. This is non-profit trade association that was founded in 1907, and is the oldest petroleum trade association in the United States.[20]

History

Kerosene lamp

Ignacy Łukasiewicz - creator of the process of refining of kerosene from crude oil.

Oil derrick in Okemah, Oklahoma, 1922

Oil field in California, 1938.

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Petroleum, in one form or another, is not a recent discovery. More than four thousand years ago, according to Herodotus and confirmed by Diodorus Siculus, asphalt was employed in the construction of the walls and towers of Babylon; there were oil pits near Ardericca (near Babylon), and a pitch spring on Zacynthus.[21] Great quantities of it were found on the banks of the river Issus, one of the tributaries of the Euphrates. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society.

Oil was exploited in the Roman province of Dacia, now in Romania, where it was called picula.

The earliest known oil wells were drilled in China in 347 CE or earlier. They had depths of up to about 800 feet (240 m) and were drilled using bits attached to bamboo poles.[22] The oil was burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs. The ancient records of China and Japan are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum was known as burning water in Japan in the 7th century.[21] In his book Dream Pool Essays written in 1088, the polymathic scientist and statesman Shen Kuo of the Song Dynasty coined the word 石油 (Shíyóu, literally "rock oil") for petroleum, which remains the term used in contemporary Chinese.

The first streets of Baghdad were paved with tar, derived from petroleum that became accessible from natural fields in the region. In the 9th century, oil fields were exploited in the area around modern Baku, Azerbaijan, to produce naphtha. These fields were described by the Arab geographer Abu al-Hasan 'Alī al-Mas'ūdī in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. Petroleum was distilled by the Persian alchemist Muhammad ibn Zakarīya Rāzi (Rhazes) in the 9th century, producing chemicals such as kerosene in the alembic (al-ambiq),[23] and which was mainly used for kerosene lamps.[24] Arab and Persian chemists also distilled crude oil in order to produce flammable products for military purposes. Through Islamic Spain, distillation became available in Western Europe by the 12th century.[25] It has also been present in Romania since the 13th century, being recorded as păcură.[26]

The earliest mention of petroleum in the Americas occurs in Sir Walter Raleigh's account of the Trinidad Pitch Lake in 1595; whilst thirty-seven years later, the account of a visit of a Franciscan, Joseph de la Roche d'Allion, to the oil springs of New York was published in Sagard's Histoire du Canada. A Russian traveller, Peter Kalm, in his work on America published in 1748 showed on a map the oil springs of Pennsylvania.[21]

In 1710 or 1711 (sources vary) the Russian-born Swiss physician and Greek teacher Eyrini d’Eyrinis (also spelled as Eirini d'Eirinis) discovered asphaltum at Val-de-Travers, (Neuchâtel). He established a bitumen mine de la Presta there in 1719 that operated until 1986.[27][28][29][30]

Oil sands were mined from 1745 in Merkwiller-Pechelbronn, Alsace under the direction of Louis Pierre Ancillon de la Sablonnière, by special appointment of Louis XV.[31] The Pechelbronn oil field was active until 1970, and was the birth place of companies like Antar and Schlumberger. The first modern refinery was built there in 1857.[31]

The modern history of petroleum began in 1846 with the discovery of the process of refining kerosene from coal by Nova Scotian Abraham Pineo Gesner. Ignacy Łukasiewicz improved Gesner's method to develop a means of refining kerosene from the more readily available "rock oil" ("petr-oleum") seeps in 1852 and the first rock oil mine was built in Bóbrka, near 53

Krosno in Galicia(Poland/Ukraine) in the following year. In 1854, Benjamin Silliman, a science professor at Yale University in New Haven, was the first to fractionate petroleum by distillation. These discoveries rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields at Baku in 1861. At that time Baku produced about 90% of the world's oil.

The first commercial oil well in Romania was drilled in 1857, and the world's first oil refinery opened at Ploiesti, Romania being the first country in the world with a crude oil output officially recorded in international statistics, namely 275 tonnes[32][33]. The first oil well in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The US petroleum industry began with Edwin Drake's drilling of a 69-foot (21 m) oil well in 1859, on Oil Creek near Titusville, Pennsylvania, for the Seneca Oil Company (originally yielding 25 barrels per day (4.0 m³/d), by the end of the year output was at the rate of 15 barrels per day (2.4 m³/d)). The industry grew through the 1800s, driven by the demand for kerosene and oil lamps. It became a major national concern in the early part of the 20th century; the introduction of the internal combustion engine provided a demand that has largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and Ontario were quickly outpaced by demand, leading to "oil booms" in Texas, Oklahoma, and California.

Early production of crude petroleum in the United States:[21]

• 1859: 2,000 barrels (~270 t) 5 • 1869: 4,215,000 barrels (~5.750×10 t) 6 • 1879: 19,914,146 barrels (~2.717×10 t) 6 • 1889: 35,163,513 barrels (~4.797×10 t) 6 • 1899: 57,084,428 barrels (~7.788×10 t) 7 • 1906: 126,493,936 barrels (~1.726×10 t)

By 1910, significant oil fields had been discovered in Canada (specifically, in the province of Alberta), the Dutch East Indies (1885, in Sumatra), Iran (1908, in Masjed Soleiman), (1863, in Zorritos District) Peru, Venezuela, and Mexico, and were being developed at an industrial level.

During World War II, oil facilities were a major strategic asset and were extensively bombed.

Even until the mid-1950s, coal was still the world's foremost fuel, but oil quickly took over. Following the 1973 energy crisis and the 1979 energy crisis, there was significant media coverage of oil supply levels. This brought to light the concern that oil is a limited resource that will eventually run out, at least as an economically viable energy source. At the time, the most common and popular predictions were quite dire. However, a period of increased production and reduced demand caused an oil glut in the 1980s.

Today, about 90% of vehicular fuel needs are met by oil. Petroleum also makes up 40% of total energy consumption in the United States, but is responsible for only 2% of electricity generation. Petroleum's worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world's most important commodities. Access to it was a major factor in several military conflicts of the late twentieth and early twenty-first centuries, including World War II[34] and the Persian Gulf Wars (Iran–Iraq War, Operation Desert Storm, and the Iraq War)[35]. The top three oil producing countries are Saudi Arabia, Russia, and the United States.[36] About 80% of the world's readily accessible reserves are located in the Middle East, with 62.5% coming from 54 the Arab 5: Saudi Arabia (12.5%), UAE, Iraq, Qatar and Kuwait. However, with high oil prices, (above $100/barrel) Venezuela has larger reserves than Saudi Arabia due to crude reserves derived from bitumen.

Distillation

Oil contains a complex mixture of hydrocarbons. The first step in obtaining something of value from this muck is to de-salt and de-water it. Then the oil is heated and sent into a huge distillation column operating at atmospheric pressure. Heat is added at the reboiler, and removed at the condenser, thereby separating the oil into fractions based upon boiling point. A typical atmospheric column can separate about 4,000 cubic meters (25,000 barrels) of oil per day. The bottom fraction is sent to another column operating at a pressure of about 75 mm Hg (one tenth of an atmosphere). This column can separate the heaviest fraction without thermally degrading (cracking) it. Whereas atmospheric columns are thin at tall, vacuum columns are thick and short, to minimize pressure fluctuations along the column. Vacuum columns can be over 40 feet in diameter!

Which Fraction to Make? February 2009

Various fractions are more important at different times of year. During the summer driving months, the public consumes vast amounts of gasoline, whereas during the winter more fuel oil is consumed. These demands also vary depending upon whether you live in the frigid north, or the humid south. Modern refineries are able to alter the ratios of the different fractions to meet demand, and maximize profit.

Petroleum: Origins of the Industry

A Few Terms

The petroleum industry, like other chemical industries, has a plethora of terms designed to scare off anyone who wants to understand exactly what is going on. Mastering this nomenclature is one of the main tasks facing chemistry and chemical engineering students. Here are a few commonly used terms, but be forewarned; because of the complexity of compounds in the petroleum industry some of these terms are very vague.

Hydrocarbons are chemical compounds made mainly of carbon and hydrogen. Both petroleum and coal contain many different hydrocarbons. Methane, ethanol, and benzene are examples of hydrocarbons, though there are many many others.

Bitumen is a another term for hydrocarbons. Both petroleum and coal are sometimes referred to as Bituminous.

Organic compounds are chemicals made of carbon (although the classification is not totally consistent and some carbon compounds, like carbon dioxide, are not considered organic). Hydrocarbons are commonly referred to as organic compounds, and it is fair to think of the two as equivalent. Carbohydrates, proteins, and urea (found in urine) are examples or organic compounds. It was once thought that organic compounds could only be produced from organic sources. Because of their usefulness, a huge chemical industry developed around

55 organic chemicals during the 19th Century. Dyes and pharmaceuticals where products of this industry. As chemists increased their skills they found that organic compounds could be synthesized from inorganic sources. However, by this time the classification had been firmly rooted in industry and universities and so it remains today.

Inorganic compounds include everything that is not considered organic (every compound in the world is ether organic or inorganic).

Aromatic compounds are organic compounds which always have a benzene ring in them. Because of this they can be quite reactive and have some interesting properties. The dye and pharmaceutical industries depend heavily on aromatic compounds.

Aliphatic compounds are organic compounds which are not aromatic. They include single bonded (ethane, propane, butane), double bonded (ethene or called ethylene, propene, butene), and triple bonded (ethyne or called acetylene, propyne, butyne) straight chain hydrocarbons as well as cyclic non-benzene structures (cyclopentane, cyclobutane) (every organic compound in the world is either aromatic or aliphatic).

A Barrel (bbl.) of crude contains 42 gallons or 158.8 liters. No one actually ships petroleum in barrels anymore because they are too small, but the term is still used to describe a defined volume.

Petroleum literally means "rock oil". It is a very broad word referring to all liquid hydrocarbons which can be collected from the ground. Even natural gas and solid hydrocarbons are sometimes referred to as petroleum. When petroleum first comes from the ground it is called crude oil. Later it is usually just referred to as oil. It can flow like water or be as viscous as peanut butter. It can be yellow, red, green, brown, or black.

Fractions are complex mixtures of chemical compounds that all have a similar boiling point. Light and heavy fractions refer to a compound's boiling point and not their actual density (these are two entirely different things). Light fractions can be very heavy (dense), and heavy fractions can be very light (go figure)!

Isomers are chemicals which have the same number and type of atoms but have them arranged in a different way. Methane (CH4), ethane (C2H6), and propane (C3H8) have no isomers because their is only one way the carbons can hook together. Butane (C4H10) has 56 two isomers (n-butane and isobutane). Decane (C10H22) has seventy five isomers, and a molecule with 20 carbon atoms (C20H42) has over 100,000 isomers. Crude oil contains molecules having 1 to 100+ carbon atoms. Naming these compounds based upon normal chemical rhetoric would be hell on earth! The huge number of possible molecular arrangements is why people talk of fractions instead of using proper chemical nomenclature.

Natural Gas is a mixture of very low boiling hydrocarbons. Natural gas can only be liquefied under extremely high pressures and very low temperatures. It is called "dry" when methane (CH4) is the primary component, and "wet" if it contains higher boiling hydrocarbons. If it smells bad, because of sulfur compounds, it is called "sour". Otherwise, it is called "sweet".

Liquefied Petroleum Gas (LPG) is a very light fraction of petroleum. It is also a fairly simple fraction containing mainly propane and butane. First, it should be noted that under normal pressures LPG is actually a gas, unlike gasoline (often just called "gas") which is really a liquid (ugh). However, under modestly high pressures these compounds can be converted to a liquid (hence their name). Being able to store them as a liquid reduces the container size by a factor of a hundred. This is no doubt why propane stoves are so popular. As cracking methods have evolved more and more LPG has been produced by refineries.

Gasoline is a light fraction of petroleum which is quite volatile and burns rapidly. Straight run gasoline refers to gasoline produced by distillation instead of cracking, although it really doesn't make a difference. Gasoline is often just called "gas", however it is a liquid at typical pressures. This confusing state of affairs developed because the first internal combustion engines ran on town gas (a mixture of carbon monoxide, CO, and hydrogen, H2, both actual gases). These engines were therefore called "gas engines". When gasoline replaced town gas people still called the motors "gas engines" and also started calling gasoline "gas". Today, the average American uses 450 gallons of gasoline a year.

Octane Number rates a fuel's ability to avoid premature ignition called knock. Premature ignition reduces an engine's power and quickly wares it out. The octane scale arbitrarily defines n-heptane a value of 0, and isooctane (2,2,4-trimethyl pentane) an octane number of 100. Isooctane is then added to heptane until the mixture has the same knock characteristics as the fuel being tested, and the percent isooctane is taken as the unknown fuels octane number. Tetraethyl lead used to be a common anti-knock additive which would raise a fuels octane number. High octane fuel can be used in engines with high compression ratios which in turn produce much more power. However, the additive is no longer used because of concerns over lead pollution.

Naphtha is a light fraction of petroleum used to make gasoline. Naphtha also produces solvents and feedstocks for the petrochemical industry.

Kerosene was the first important petroleum fraction, replacing whale oils in lamps over a hundred years ago. Some unscrupulous refiners failed to distill off all the naphtha from the kerosene fraction thereby increasing the volume of their final product. This lead to many lamp explosions and fires.

Diesel fuels find use in the fleet of trucks which transport the nations goods. Diesel engines power these larger engines, and use higher compression ratios (and temperatures) than their gasoline cousins. They are therefore more efficient. It is also interesting to note that diesel 57 engines have no spark plugs, instead the fuel-air mixture is ignited by the rising temperatures and pressures during the compression stroke.

Gas Oil (or fuel oils) are used for domestic heating. In the winter refineries produce more gas oil, whereas during the summer driving months they produce more gasoline.

Heavy Fuel Oil is often blended with gas oils for easier use in industry. Ships burn heavy fuel oils but they call it bunker oil.

Atmospheric Residual is everything that cannot be vaporized under normal pressures. Atmospheric residual is fed into another distillation column, operating at lower pressures, which can separate out some of the lighter compounds. Lubricants and waxes reside in this fraction.

Vacuum Residual is the bottom of the barrel. It includes asphalt and some coke.

Pitch is a thick, black, sticky material. It is left behind when the lighter components of coal tar or petroleum are distilled off. Pitch is a "natural" form of asphalt.

Asphalt is a high boiling component of crude oil. It is therefore found at the "bottom of the barrel" when petroleum is distilled.

Tars are byproducts formed when coke is made from coal or charcoal is made from wood. It is a thick, complex, oily black mixture of heavy organic compounds very similar to pitch or asphalt, though from a different source.

Composition

The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:[2]

Co mp osit ion by wei ght

Element Percent range Carbon 83 to 87% 58

Hydrogen 10 to 14% Nitrogen 0.1 to 2% Oxygen 0.1 to 1.5% Sulfur 0.5 to 6% Metals less than 1000 ppm

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil.[3]

Composition by weight Hydrocarbon Average Range

Paraffins 30% 15 to 60%

Naphthenes 49% 30 to 60%

Aromatics 15% 3 to 30%

Asphaltics 6% remainder

Most of the world's oils are non-conventional.[4]

Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish or even greenish). In the reservoir it is usually found in association with natural gas, which being lighter forms a gas cap over the petroleum, and saline water which, being heavier than most forms of crude oil, generally sinks beneath it. Crude oil may also be found in semi-solid form mixed with sand and water, as in the Athabasca oil sands in Canada, where it is usually referred to as crude bitumen. In Canada, bitumen is considered a sticky, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow.[5] Venezuela also has large amounts of oil in the Orinoco oil sands, although the hydrocarbons trapped in them are more fluid than in Canada and are usually called extra heavy oil. These oil sands resources are called non-conventional oil to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570×109 m3) of bitumen and extra-heavy oil, about twice the volume of the world's reserves of conventional oil.[6]

Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both important "primary energy" sources.[7] 84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including gasoline, diesel, jet, heating, and other fuel oils, and liquefied petroleum gas.[8] The lighter grades of crude oil produce the best yields of these products, but as the world's reserves of light and medium oil are depleted, oil refineries are increasingly having to process heavy oil and bitumen, and use more complex and expensive methods to produce the products required. Because heavier crude oils have too much carbon and not enough hydrogen, these processes generally involve removing carbon from or adding hydrogen to the molecules, and using fluid catalytic cracking to convert the longer, more complex molecules in the oil to the shorter, simpler ones in the fuels.

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Due to its high energy density, easy transportability and relative abundance, oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics; the 16% not used for energy production is converted into these other materials.

Petroleum is found in porous rock formations in the upper strata of some areas of the Earth's crust. There is also petroleum in oil sands (tar sands). Known reserves of petroleum are typically estimated at around 190 km3 (1.2 trillion (short scale) barrels) without oil sands,[9] or 595 km3 (3.74 trillion barrels) with oil sands.[10] Consumption is currently around 84 million barrels (13.4×106 m3) per day, or 4.9 km3 per year. Because the energy return over energy invested (EROEI) ratio of oil is constantly falling (due to physical phenomena such as residual oil saturation, and the economic factor of rising marginal extraction costs), recoverable oil reserves are significantly less than total oil in place. At current consumption levels, and assuming that oil will be consumed only from reservoirs, known recoverable reserves would be gone around 2039, potentially leading to a global energy crisis. However, there are factors which may extend or reduce this estimate, including the rapidly increasing demand for petroleum in China, India, and other developing nations; new discoveries; energy conservation and use of alternative energy sources; and new economically viable exploitation of non-conventional oil sources.

Image 1: Typical industrial distillation towers

2. desalting Why Desalt Crude?

• The salts that are most frequently present in crude oil are Calcium,Sodium and Magnesium Chlorides. If these compounds are not removed from the oil several problems arise in the refining process. The high temperatures that occur downstream in the process could cause water hydrolysis, which in turn allows the formation of hydrochloric acid. • Sand, Silts, Salt deposit and Foul Heat Exchangers • Water Heat of Vaporization reduces crude Pre-Heat capacity • Sodium, Arsenic and Other Metals can poison Catalysts • Environmental Compliance, i.e., By removing the suspended solids, which might otherwise become an issue in flue gas opacity norms, etc.,

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Design and operation

Design and operation of a distillation column depends on the feed and desired products. Given a simple, binary component feed, analytical methods such as the McCabe-Thiele method[5][6][7] or the Fenske equation[5] can be used to assist in the design. For a multi- component feed, computerized simulation models are used both for design and subsequently in operation of the column as well. Modeling is also used to optimize already erected columns for the distillation of mixtures other than those the distillation equipment was originally designed for.

When a continuous distillation column is in operation, it has to be closely monitored for changes in feed composition, operating temperature and product composition. Many of these tasks are performed using advanced computer control equipment.

Column feed

The column can be fed in different ways. If the feed is from a source at a pressure higher than the distillation column pressure, it is simply piped into the column. Otherwise, the feed is pumped or compressed into the column. The feed may be a superheated vapor, a saturated vapor, a partially vaporized liquid-vapor mixture, a saturated liquid (i.e., liquid at its boiling point at the column's pressure), or a sub-cooled liquid. If the feed is a liquid at a much higher pressure than the column pressure and flows through a pressure let-down valve just ahead of the column, it will immediately expand and undergo a partial flash vaporization resulting in a liquid-vapor mixture as it enters the distillation column.

Improving separation

Although small size units, mostly made of glass, can be used in laboratories, industrial units are large, vertical, steel vessels (see images 1 and 2) known as "distillation towers" or "distillation columns". To improve the separation, the tower is normally provided inside with horizontal plates or trays as shown in image 5, or the column is packed with a packing material. To provide the heat required for the vaporization involved in distillation and also to compensate for heat loss, heat is most often added to the bottom of the column by a reboiler, and the purity of the top product can be improved by recycling some of the externally 61 condensed top product liquid as reflux. Depending on their purpose, distillation columns may have liquid outlets at intervals up the length of the column as shown in image 4.

Reflux

Large-scale industrial fractionation towers use reflux to achieve more efficient separation of products.[3][5] Reflux refers to the portion of the condensed overhead liquid product from a distillation tower that is returned to the upper part of the tower as shown in images 3 and 4. Inside the tower, the downflowing reflux liquid provides cooling and partial condensation of the upflowing vapors, thereby increasing the efficacy of the distillation tower. The more reflux that is provided, the better is the tower's separation of the lower boiling from the higher boiling components of the feed. A balance of heating with a reboiler at the bottom of a column and cooling by condensed reflux at the top of the column maintains a temperature gradient (or gradual temperature difference) along the height of the column to provide good conditions for fractionating the feed mixture. Reflux flows at the middle of the tower are called pumparounds.

Changing the reflux (in combination with changes in feed and product withdrawal) can also be used to improve the separation properties of a continuous distillation column while in operation (in contrast to adding plates or trays, or changing the packing, which would, at a minimum, require quite significant downtime).

Plates or trays

Image 5: Cross-sectional diagram of a binary fractional distillation tower with bubble-cap trays. (See theoretical plate for enlarged tray image.)

Distillation towers (such as in images 3 and 4) use various vapor and liquid contacting methods to provide the required number of equilibrium stages. Such devices are commonly known as "plates" or "trays".[8] Each of these plates or trays is at a different temperature and pressure. The stage at the tower bottom has the highest pressure and temperature. Progressing upwards in the tower, the pressure and temperature decreases for each succeeding stage. The vapor-liquid equilibrium for each feed component in the tower reacts in its unique way to the different pressure and temperature conditions at each of the stages. That means that each component establishes a different concentration in the vapor and liquid phases at each of the stages, and this results in the separation of the components. Some example trays are depicted in image 5. A more detailed, expanded image of two trays can be seen in the theoretical plate article. The reboiler often acts as an additional equilibrium stage.

If each physical tray or plate were 100% efficient, than the number of physical trays needed for a given separation would equal the number of equilibrium stages or theoretical plates. However, that is very seldom the case. Hence, a distillation column needs more plates than the required number of theoretical vapor-liquid equilibrium stages.

Fractionation Research, Inc. (commonly known as FRI) has performed research on all types of trays measuring their capacity, pressure drop and efficiency in hydrocarbon systems from full vacuum to 500 psia.[9]

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Packing

Another way of improving the separation in a distillation column is to use a packing material instead of trays. These offer the advantage of a lower pressure drop across the column (when compared to plates or trays), beneficial when operating under vacuum. If a distillation tower uses packing instead of trays, the number of necessary theoretical equilibrium stages is first determined and then the packing height equivalent to a theoretical equilibrium stage, known as the height equivalent to a theoretical plate (HETP), is also determined. The total packing height required is the number theoretical stages multiplied by the HETP.

This packing material can either be random dumped packing such as Raschig rings or structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer takes place. Unlike conventional tray distillation in which every tray represents a separate point of vapor-liquid equilibrium, the vapor-liquid equilibrium curve in a packed column is continuous. However, when modeling packed columns it is useful to compute a number of theoretical plates to denote the separation efficiency of the packed column with respect to more traditional trays. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing performance.

Another factor in addition to the packing shape and surface area that affects the performance of random or structured packing is liquid and vapor distribution entering the packed bed. The number of theoretical stages required to make a given separation is calculated using a specific vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the packed bed and the required separation will not be achieved. The packing will appear to not be working properly. The height equivalent to a theoretical plate (HETP) will be greater than expected. The problem is not the packing itself but the mal-distribution of the fluids entering the packed bed. Liquid mal-distribution is more frequently the problem than vapor. The design of the liquid distributors used to introduce the feed and reflux to a packed bed is critical to making the packing perform at maximum efficiency. Methods of evaluating the effectiveness of a liquid distributor can be found in references..[10][11] Considerable work as been done on this topic by Fractionation Research, Inc.[12]

Overhead system arrangements

Images 4 and 5 assume an overhead stream that is totally condensed into a liquid product using water or air-cooling. However, in many cases, the tower overhead is not easily condensed totally and the reflux drum must include a vent gas outlet stream. In yet other cases, the overhead stream may also contain water vapor because either the feed stream contains some water or some steam is injected into the distillation tower (which is the case in the crude oil distillation towers in oil refineries). In those cases, if the distillate product is insoluble in water, the reflux drum may contain a condensed liquid distillate phase, a condensed water phase and a non-condensible gas phase, which makes it necessary that the reflux drum also have a water outlet stream.

Examples

Image 2: A crude oil vacuum distillation column as used in oil refineries 63

Continuous distillation of crude oil

Petroleum crude oils contain hundreds of different hydrocarbon compounds: paraffins, naphthenes and aromatics as well as organic sulfur compounds, organic nitrogen compounds and some oxygen containing hydrocarbons such as phenols. Although crude oils generally do not contain olefins, they are formed in many of the processes used in a petroleum refinery.[13]

The crude oil fractionator does not produce products having a single boiling point, rather, it produces fractions having boiling ranges.[13][14] For example, the crude oil fractionator produces an overhead fraction called "naphtha" which becomes a gasoline component after it is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value.

The naphtha cut, as that fraction is called, contains many different hydrocarbon compounds. Therefore it has an initial boiling point of about 35 °C and a final boiling point of about 200 °C. Each cut produced in the fractionating columns has a different boiling range. At some distance below the overhead, the next cut is withdrawn from the side of the column and it is usually the jet fuel cut, also known as a kerosene cut. The boiling range of that cut is from an initial boiling point of about 150 °C to a final boiling point of about 270 °C, and it also contains many different hydrocarbons. The next cut further down the tower is the diesel oil cut with a boiling range from about 180 °C to about 315 °C. The boiling ranges between any cut and the next cut overlap because the distillation separations are not perfectly sharp. After these come the heavy fuel oil cuts and finally the bottoms product, with very wide boiling ranges. All these cuts are processed further in subsequent refining processes.

Oil refinery

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Anacortes Refinery (Tesoro), on the north end of March Point southeast of Anacortes, Washington

An oil refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas.[1][2] Oil refineries are typically large sprawling

64 industrial complexes with extensive piping running throughout, carrying streams of fluids between large chemical processing units.

Operation

Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units.

Raw or unprocessed crude oil is not generally useful in its raw or unprocessed form, as it comes out of the ground. Although "light, sweet" (low viscosity, low sulfur) crude oil has been used directly as a burner fuel for steam vessel propulsion, the lighter elements form explosive vapors in the fuel tanks and so it was quite dangerous, especially in warships. Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a refinery into components that can be used as fuels, lubricants, and as feedstock in petrochemical processes that manufacture such products as plastics, detergents, solvents, elastomers and fibers such as nylon and polyesters. Petroleum fossil fuels are burned in internal combustion engines in order to provide power to operate ships, automobiles, aircraft engines, lawn-mowers, chainsaws, and other pieces of power equipment. These different hydrocarbons have different boiling points, which means they can be separated by distillation. Since the lighter liquid products are in great demand for use in internal combustion engines, a modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these higher value products.

Oil can be used in so many ways because it contains hydrocarbons of varying molecular masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes, dienes, and alkynes. While the molecules in crude oil include many different atoms such as sulfur and nitrogen, the most plentiful molecules are the hydrocarbons, which are molecules of varying length and complexity made of hydrogen and carbon atoms, and a small number of oxygen atoms. The differences in the structure of these molecules is what confers upon them their varying physical and chemical properties, and it is this variety that makes crude oil so useful in such a broad range of applications.

Once separated and purified of any contaminants and impurities, the fuel or lubricant can be sold without any further processing. Smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific octane requirements of fuels by processes such as alkylation or less commonly, dimerization. Octane grade of gasoline can also be improved by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics, which have much higher octane ratings. Intermediate products such as gasoils can even be reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various forms of cracking such as fluid catalytic cracking, thermal cracking, and hydrocracking. The final step in gasoline production is the blending of fuels with different octane ratings, vapor pressures, and other properties to meet product specifications.

Oil refineries are large scale plants, processing from about a hundred thousand to several hundred thousand barrels of crude oil per day. Because of the high capacity, many of the units are operated continuously (as opposed to processing in batches) at steady state or approximately steady state for long periods of time (months to years). This high capacity also makes process optimization and advanced process control very desirable. 65

Major products of oil refineries

Most products of oil processing are usually grouped into three categories: light distillates (LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum (fuel oil, lubricating oils, wax, tar). This classification is based on the way crude oil is distilled and separated into fractions (called distillates and residuum) as can be seen in the above drawing.[2]

Common process units found in a refinery

The number and nature of the process units in a refinery determine its complexity index.

• Desalter unit washes out salt from the crude oil before it enters the atmospheric distillation unit. • Atmospheric Distillation unit distills crude oil into fractions. See Continuous distillation. • Vacuum Distillation unit further distills residual bottoms after atmospheric distillation. • Naphtha Hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit. • Catalytic Reformer unit is used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker. • Distillate Hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric distillation. • Fluid Catalytic Cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products. • Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable products. • Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more valuable reduced viscosity products. • Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides. • Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product. • Alkylation unit produces high-octane component for gasoline blending. • Dimerization unit converts olefins into higher-octane gasoline blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization. • Isomerization unit converts linear molecules to higher-octane branched molecules for blending into gasoline or feed to alkylation units. • Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker. • Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient to maintain in liquid form. These are usually spherical vessels or bullets (horizontal vessels with rounded ends. • Storage tanks for crude oil and finished products, usually cylindrical, with some sort of vapor emission control and surrounded by an earthen berm to contain spills. • Amine gas treater, Claus unit, and tail gas treatment for converting hydrogen sulfide from hydrodesulfurization into elemental sulfur. 66

• Utility units such as cooling towers for circulating cooling water, boiler plants for steam generation, instrument air systems for pneumatically operated control valves and an electrical substation. • Wastewater collection and treating systems consisting of API separators, dissolved air flotation (DAF) units and some type of further treatment (such as an activated sludge biotreater) to make such water suitable for reuse or for disposal.[3] • Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly asphaltenic materials from lubricating oil stock (or diesel stock). • Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum distillation products.

Flow diagram of typical refinery

The image below is a schematic flow diagram of a typical oil refinery that depicts the various unit processes and the flow of intermediate product streams that occurs between the inlet crude oil feedstock and the final end products. The diagram depicts only one of the literally hundreds of different oil refinery configurations. The diagram also does not include any of the usual refinery facilities providing utilities such as steam, cooling water, and electric power as well as storage tanks for crude oil feedstock and for intermediate products and end products.[1][4][5][6]

The Five Pillars of Refining

While distillation can separate oil into fractions, chemical reactors are required to create more of the products that are in high demand. Refineries rely on four major processing steps to alter the ratios of the different fractions. They are; Catalytic Reforming, Alkylation, Catalytic Cracking, and Hydroprocessing. Each of these methods involves feeding reactants to a reactor where they will be partly converted into products. The unreacted reactants are then separated from the products with a distillation column. The unreacted reactants are recycled for another pass, while the products are further separated and mixed with existing streams. In this way complete conversion of reactants can be obtained, even though not all of the reactants are converted on a given pass through the reactor. The four processing methods, along with distillation, are the pillars of petroleum refining.

Catalytic Reforming

Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed catalytic reactors. Because the reactions which produce higher octane compounds (aliphatic in this case) are endothermic (absorb heat) additional heaters are installed between reactors to keep the reactants at the proper temperature. The catalyst is a platinum (Pt) metal on an alumina (Al2O3) base. While catalysts are never consumed in chemical reactions, they can be fouled, making them less effective over time. The series of reactors used in Catalytic 67

Reforming are therefore designed to be disconnected, and swiveled out of place, so the catalyst can be regenerated.

Alkylation

Alkylation is another process for producing high octane gasoline. The reaction requires an acid catalyst (sulfuric acid, H2SO4 or hydrofluoric acid, HF) at low temperatures (1-40 degrees Celsius) and low pressures (1-10 atmospheres). The acid composition is usually kept at about 50% making the mixture very corrosive.

Fluidized Catalytic Cracking

Catalytic Cracking takes long molecules and breaks them into much smaller molecules. The cracking reaction is very endothermic, and requires a large amount of heat. Another problem is that reaction quickly fouls the Silica (SiO2) and alumina (Al2O3) catalyst by forming coke on its surface. However, by using a fluidized bed to slowly carry the catalyst upwards, and then sending it to a regenerator where the coke can be burned off, the catalyst is continuously regenerated. This system has the additional benefit of using the large amounts of heat liberated in the exothermic regeneration reaction to heat the cracking reactor. The FCC system is a brilliant reaction scheme, which turns two negatives (heating and fouling) into a positive, thereby making the process extremely economical.

Hydroprocessing

Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating involves the addition of hydrogen atoms to molecules without actually breaking the molecule into smaller pieces. Hydrotreating involves temperatures of about 325 degrees Celsius and pressures of about 50 atmospheres. Many catalysts will work, including; nickel, palladium, platinum, cobalt, and iron. Hydrocracking breaks longer molecules into smaller ones. Hydrocracking involves temperatures over 350 degrees Celsius and pressures up to 200 atmospheres. In both cases, very long residence times (about an hour) are required because of the slow nature of the reactions.

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline (also known as petrol). Basically, the process re- arranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as 68 breaking some of the molecules into smaller molecules. The overall effect is that the product reformate contains hydrocarbons with more complex molecular shapes having higher octane values than the hydrocarbons in the naphtha feedstock. In so doing, the process separates hydrogen atoms from the hydrocarbon molecules and produces very significant amounts of byproduct hydrogen gas for use in a number of the other processes involved in a modern petroleum refinery. Other byproducts are small amounts of methane, ethane, propane and butanes.

This process is quite different from and not to be confused with the catalytic steam reforming process used industrially to produce various products such as hydrogen, ammonia and methanol from natural gas, naphtha or other petroleum-derived feedstocks. Nor is this process to be confused with various other catalytic reforming processes that use methanol or biomass- derived feedstocks to produce hydrogen for fuel cells or other uses.

History

Universal Oil Products (also known as UOP) is a multi-national company developing and delivering technology to the petroleum refining, natural gas processing, petrochemical production and other manufacturing industries. In the 1940s, an eminent research chemist named Vladimir Haensel[1] working for UOP developed a catalytic reforming process using a catalyst containing platinum. Haensel's process was subsequently commercialized by UOP in 1949 for producing a high octane gasoline from low octane naphthas and the UOP process become known as the Platforming process.[2] The first Platforming unit was built in 1949 at the refinery of the Old Dutch Refining Company in Muskegon, Michigan.

In the years since then, many other versions of the process have been developed by some of the major oil companies and other organizations. Today, the large majority of gasoline produced worldwide is derived from the catalytic reforming process.

To name a few of the other catalytic reforming versions that were developed, all of which utilized a platinum and/or a rhenium catalyst:

• Rheniforming: Developed by Chevron Oil Company. • Powerforming: Developed by Esso Oil Company, now known as ExxonMobil. • Magnaforming: Developed by Englehard Catalyst Company and Atlantic Richfield Oil Company. • Ultraforming: Developed by Standard Oil of Indiana, now a part of the British Petroleum Company. • Houdriforming: Developed by the Houdry Process Corporation. • CCR Platforming: A Platforming version, designed for continuous catalyst regeneration, developed by UOP. • Octanizing: A catalytic reforming version developed by Axens, a subsidiary of Institut francais du petrole (IFP), designed for continuous catalyst regeneration.

Chemistry

Before describing the reaction chemistry of the catalytic reforming process as used in petroleum refineries, the typical naphthas used as catalytic reforming feedstocks will be discussed.

Typical naphtha feedstocks

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A petroleum refinery includes many unit operations and unit processes. The first unit operation in a refinery is the continuous distillation of the petroleum crude oil being refined. The overhead liquid distillate is called naphtha and will become a major component of the refinery's gasoline (petrol) product after it is further processed through a catalytic hydrodesulfurizer to remove sulfur-containing hydrocarbons and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.

The naphtha from the crude oil distillation is often further distilled to produce a "light" naphtha containing most (but not all) of the hydrocarbons with 6 or less carbon atoms and a "heavy" naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils are referred to as "straight-run" naphthas.

It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high- octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics (most particularly benzene) that gasoline may contain.[3][4][5]

It should be noted that there are a great many petroleum crude oil sources worldwide and each crude oil has its own unique composition or "assay". Also, not all refineries process the same crude oils and each refinery produces its own straight-run naphthas with their own unique initial and final boiling points. In other words, naphtha is a generic term rather than a specific term.

The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:

Some refinery naphthas include olefinic hydrocarbons, such as naphthas derived from the fluid catalytic cracking and coking processes used in many refineries. Some refineries may also desulfurize and catalytically reform those naphthas. However, for the most part, catalytic reforming is mainly used on the straight-run heavy naphthas, such as those in the above table, derived from the distillation of crude oils.

The reaction chemistry

There are a good many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of about 5 to 45 atm.[10]

The commonly used catalytic reforming catalysts contain noble metals such as platinum and/or rhenium, which are very susceptible to poisoning by sulfur and nitrogen compounds. 70

Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a hydrodesulfurization unit which removes both the sulfur and the nitrogen compounds.

The four major catalytic reforming reactions are:[11]

1: The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the conversion methylcyclohexane (a naphthene) to toluene (an aromatic), as shown below:

2: The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of normal octane to 2,5-Dimethylhexane (an isoparaffin), as shown below:

3: The dehydrogenation and aromatization of paraffins to aromatics (commonly called dehydrocyclization) as exemplified in the conversion of normal heptane to toluene, as shown below:

4: The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of normal heptane into isopentane and ethane, as shown below:

The hydrocracking of paraffins is the only one of the above four major reforming reactions that consumes hydrogen. The isomerization of normal paraffins does not consume or produce hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming of petroleum naphthas ranges from about 50 to 200 cubic meters of hydrogen gas (at 0 °C and 1 atm) per cubic meter of liquid naphtha feedstock. In the United States customary units, that is equivalent to 300 to 1200 cubic feet of hydrogen gas (at 60 °F and 1 atm) per barrel of liquid naphtha feedstock.[12] In many petroleum refineries, the net hydrogen produced in catalytic reforming supplies a significant part of the hydrogen used elsewhere in the refinery (for example, in hydrodesulfurization processes). The hydrogen is also necessary in order to hydrogenolyze any polymers that form on the catalyst.

Process description

The most commonly used type of catalytic reforming unit has three reactors, each with a fixed bed of catalyst, and all of the catalyst is regenerated in situ during routine catalyst regeneration shutdowns which occur approximately once each 6 to 24 months. Such a unit is referred to as a semi-regenerative catalytic reformer (SRR).

Some catalytic reforming units have an extra spare or swing reactor and each reactor can be individually isolated so that any one reactor can be undergoing in situ regeneration while the other reactors are in operation. When that reactor is regenerated, it replaces another reactor which, in turn, is isolated so that it can then be regenerated. Such units, referred to as cyclic catalytic reformers, are not very common. Cyclic catalytic reformers serve to extend the period between required shutdowns.

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The latest and most modern type of catalytic reformers are called continuous catalyst regeneration reformers (CCR). Such units are characterized by continuous in-situ regeneration of part of the catalyst in a special regenerator, and by continuous addition of the regenerated catalyst to the operating reactors. As of 2006, two CCR versions available: UOP's CCR Platformer process[13] and Axen's Octanizing process.[14] The installation and use of CCR units is rapidly increasing.

Many of the earliest catalytic reforming units (in the 1950s and 1960's) were non-regenerative in that they did not perform in situ catalyst regeneration. Instead, when needed, the aged catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst manufacturer's to be either regenerated or to recover the platinum content of the aged catalyst. Very few, if any, catalytic reformers currently in operation are non-regenerative.

The process flow diagram below depicts a typical semi-regenerative catalytic reforming unit.

Schematic diagram of a typical semi-regenerative catalytic reformer unit in a petroleum refinery

The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5 to 45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowing through a heat exchanger. The preheated feed mixture is then totally vaporized and heated to the reaction temperature (495 to 520 °C) before the vaporized reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics (as described earlier herein) which is highly endothermic and results in a large temperature decrease between the inlet and outlet of the reactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream is reheated in the second fired heater before it flows through the second reactor. The temperature again decreases across the second reactor and the vaporized stream must again be reheated in the third fired heater before it flows through the third reactor. As the vaporized stream proceeds through the three reactors, the reaction rates decrease and the reactors therefore become larger. At the same time, the amount of reheat required between the reactors becomes smaller. Usually, three reactors are all that is required to provide the desired performance of the catalytic reforming unit.

Some installations use three separate fired heaters as shown in the schematic diagram and some installations use a single fired heater with three separate heating coils.

The hot reaction products from the third reactor are partially cooled by flowing through the heat exchanger where the feed to the first reactor is preheated and then flow through a water- cooled heat exchanger before flowing through the pressure controller (PC) into the gas separator.

Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the recycle hydrogen gas compressor and the net production of hydrogen-rich gas from the reforming reactions is exported for use in other the other refinery processes that consume hydrogen (such as hydrodesulfurization units and/or a hydrocracker unit).

The liquid from the gas separator vessel is routed into a fractionating column commonly called a stabilizer. The overhead offgas product from the stabilizer contains the byproduct methane, ethane, propane and butane gases produced by the hydrocracking reactions as 72 explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may also contain some small amount of hydrogen. That offgas is routed to the refinery's central gas processing plant for removal and recovery of propane and butane. The residual gas after such processing becomes part of the refinery's fuel gas system.

The bottoms product from the stabilizer is the high-octane liquid reformate that will become a component of the refinery's product gasoline.

Catalysts and mechanisms

Most catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina support base, and some contain both platinum and rhenium. Fresh catalyst is chlorided (chlorinated) prior to use.

The noble metals (platinum and rhenium) are considered to be catalytic sites for the dehydrogenation reactions and the chlorinated alumina provides the acid sites needed for isomerization, cyclization and hydrocracking reactions.[11]

The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is reduced over time during operation by carbonaceous coke deposition and chloride loss. The activity of the catalyst can be periodically regenerated or restored by in situ high temperature oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative catalytic reformers are regenerated about once per 6 to 24 months.

Normally, the catalyst can be regenerated perhaps 3 or 4 times before it must be returned to the manufacturer for reclamation of the valuable platinum and/or rhenium content.[11] Alkylation

In a standard oil refinery process, isobutane is alkylated with low-molecular-weight alkenes (primarily a mixture of propylene and butylene) in the presence of a strong acid catalyst, either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to as a sulfuric acid alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU). However, oil refinery employees may simply refer to the unit as the Alkyl or Alky unit. The catalyst is able to protonate the alkenes (propylene, butylene) to produce reactive carbocations, which alkylate isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a two-phase reaction. It is important to keep a high ratio of isobutane to alkene at the point of reaction to prevent side reactions that lead to a lower octane product, so the plants have a high recycle of isobutane back to feed. The phases separate spontaneously, so the acid phase is vigoriously mixed with the hydrocarbon phase to create sufficient contact surface.

The product is called alkylate and is composed of a mixture of high-octane, branched-chain paraffinic hydrocarbons (mostly isopentane and isooctane). Alkylate is a premium gasoline blending stock because it has exceptional antiknock properties and is clean burning. Alkylate is also a key component of avgas. The octane number of the alkylate depends mainly upon the kind of alkenes used and upon operating conditions. For example, isooctane results from combining butylene with isobutane and has an octane rating of 100 by definition. There are other products in the alkylate, so the octane rating will vary accordingly.

Most crude oils contain only 10 to 40 percent of their hydrocarbon constituents in the gasoline range, so refineries use a fluid catalytic cracking process to convert high molecular weight 73 hydrocarbons into smaller and more volatile compounds. Polymerization converts gaseous alkenes into liquid gasoline-size hydrocarbons. Alkylation processes transform low molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with a high octane number.

Combining cracking, polymerization, and alkylation can result in a gasoline yield representing 70 percent of the starting crude oil. More advanced processes, such as cyclicization of paraffins and dehydrogenation of naphthenes to form aromatic hydrocarbons in a catalytic reformer, have also been developed to increase the octane rating of gasoline. Modern refinery operation can be shifted to produce almost any fuel type with specified performance criteria from a single crude feedstock.

In the entire range of refinery processes, alkylation is a very important process that enhances the yield of high-octane gasoline. However, not all refineries have an alkylation plant. The oil and gas journal annual survey of worldwide refining capacities for January 2007 lists many countries with no alkylation plants at their refineries.

A primary factor in deciding to install alkylation is usually economics. Refinery alkylation units are complex and there is substantial economy of scale. In addition to a suitable quantity of feedstock, the price spread between the value of alkylate product and alternate feedstock disposition value must be large enough to justify the plant. Alternative outlets for refinery alklylation feedstocks include sales as LPG, blending of C4 streams directly into gasoline and feedstocks for chemical plants. Local market conditions vary widely between plants. Variation in the RVP specification for gasoline between countries and between seasons dramatically impacts the amount of butane streams that can be blended directly into gasoline. The transportation of specific types of LPG streams can be expensive so local disparities in economic conditions are often not fully mitigated by cross market movements of alkylation feedstocks.

Another factor in the decision to build an alkylation plant concerns the availability of a suitable catalyst. If sulfuric acid is used, significant volumes are needed. This requires access to a suitable plant for the supply of fresh acid and the disposition of spent acid. If a sulfuric acid plant must be constructed specifically to support an alkylation unit, this will have a significant impact on both the initial capital requirements and ongoing operating costs. The second main catalyst option is hydrofluoric acid. Consumption rates for HF acid in alkylation plants are much lower than for sulfuric acid. HF acid plants can process a wider range of feedstock mix with proplyenes and butylenes. HF plants also produce alklyate with better octane than sulfuric plants. However, due to the hazardous nature of the material, HF acid is produced at very few locations and transportation must be managed rigorously. Thermal cracking

William Merriam Burton developed one of the earliest thermal cracking processes in 1912 which operated at 700-750 °F (370-400 °C) and an absolute pressure of 90 psia (620 kPa) and was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the Universal Oil Products Company, developed a somewhat more advanced thermal cracking process which operated at 750-860 °F (400-460 °C) and was known as the Dubbs process.[9] The Dubbs process was used extensively by many refineries until the early 1940's when catalytic cracking came into use.

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Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An overall process of disproportionation can be observed, where "light", hydrogen-rich products are formed at the expense of heavier molecules which condense and are depleted of hydrogen. The actual reaction is known as homolytic fission and produces alkenes, which are the basis for the economically important production of polymers.

A large number of chemical reactions take place during steam cracking, most of them based on free radicals. Computer simulations aimed at modeling what takes place during steam cracking have included hundreds or even thousands of reactions in their models. The main reactions that take place include:

Initiation reactions, where a single molecule breaks apart into two free radicals. Only a small fraction of the feed molecules actually undergo initiation, but these reactions are necessary to produce the free radicals that drive the rest of the reactions. In steam cracking, initiation usually involves breaking a chemical bond between two carbon atoms, rather than the bond between a carbon and a hydrogen atom.

CH3CH3 → 2 CH3•

Hydrogen abstraction, where a free radical removes a hydrogen atom from another molecule, turning the second molecule into a free radical.

CH3• + CH3CH3 → CH4 + CH3CH2•

Radical decomposition, where a free radical breaks apart into two molecules, one an alkene, the other a free radical. This is the process that results in the alkene products of steam cracking.

CH3CH2• → CH2=CH2 + H•

Radical addition, the reverse of radical decomposition, in which a radical reacts with an alkene to form a single, larger free radical. These processes are involved in forming the aromatic products that result when heavier feedstocks are used.

CH3CH2• + CH2=CH2 → CH3CH2CH2CH2•

Termination reactions, which happen when two free radicals react with each other to produce products that are not free radicals. Two common forms of termination are recombination, where the two radicals combine to form one larger molecule, and disproportionation, where one radical transfers a hydrogen atom to the other, giving an alkene and an alkane.

CH3• + CH3CH2• → CH3CH2CH3

CH3CH2• + CH3CH2• → CH2=CH2 + CH3CH3

Thermal cracking is an example of a reaction whose energetics are dominated by entropy (∆S°) rather than by enthalpy (∆H°) in the Gibbs Free Energy equation ∆G°=∆H°-T∆S°. Although the bond dissociation energy D for a carbon-carbon single bond is relatively high (about 375 kJ/mol) and cracking is highly endothermic, the large positive entropy change resulting from the fragmentation of one large molecule into several smaller pieces, together with the extremely high temperature, makes T∆S° term larger than the ∆H° term, thereby favoring the cracking reaction. 75

Here is an example of cracking with butane CH3-CH2-CH2-CH3

• 1st possibility (48%): breaking is done on the CH3-CH2 bond.

CH3* / *CH2-CH2-CH3 after a certain number of steps, we will obtain an alkane and an alkene: CH4 + CH2=CH-CH3

• 2nd possibility (38%): breaking is done on the CH2-CH2 bond.

CH3-CH2* / *CH2-CH3 after a certain number of steps, we will obtain an alkane and an alkene from different types: CH3-CH3 + CH2=CH2

• 3rd possibility (14%): breaking of a C-H bond after a certain number of steps, we will obtain an alkene and hydrogen gas: CH2=CH-CH2- CH3 + H2 this is very useful since the catalyst can be recycled.

Fluid catalytic cracking

From Wikipedia, the free encyclopedia

Fluid catalytic cracking (FCC) is the most important conversion process used in petroleum refineries. It is widely used to convert the high-boiling hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases and other products.[1][2][3] Cracking of petroleum hydrocarbons was originally done by thermal cracking which has been almost completely replaced by catalytic cracking because it produces more gasoline with a higher octane rating. It also produces byproduct gases that are more olefinic, and hence more valuable, than those produced by thermal cracking.

The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. The FCC process vaporizes and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.

In effect, refineries use fluid catalytic cracking to correct the imbalance between the market demand for gasoline and the excess of heavy, high boiling range products resulting from the distillation of crude oil.

As of 2006, FCC units were in operation at 400 petroleum refineries worldwide and about one-third of the crude oil refined in those refineries is processed in an FCC to produce high- octane gasoline and fuel oils.[2][4] During 2007, the FCC units in the United States processed a total of 5,300,000 barrels (834,300,000 litres) per day of feedstock[5] and FCC units worldwide processed about twice that amount.

76

Flow diagram and process description

The modern FCC units are all continuous processes which operate 24 hours a day for as much as 2 to 3 years between shutdowns for routine maintenance.

There are a number of different proprietary designs that have been developed for modern FCC units. Each design is available under a license that must be purchased from the design developer by any petroleum refining company desiring to construct and operate an FCC of a given design.

Basically, there are two different configurations for an FCC unit: the "stacked" type where the reactor and the catalyst regenerator are contained in a single vessel with the reactor above the catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are in two separate vessels. These are the major FCC designers and licensors:[1][3][4][6]

Stacked configuration:

Each of the proprietary design licensors claims to have unique features and advantages. A complete discussion of the relative advantages of each of the processes is well beyond the scope of this article. Suffice it to say that all of the licensors have designed and constructed FCC units that have operated quite satisfactorily.

Reactor and Regenerator

The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon the "side-by-side" configuration. The preheated high-boiling petroleum feedstock (at about 315 to 430 °C) consisting of long-chain hydrocarbon molecules is combined with recycle slurry oil from the bottom of the distillation column and injected into the catalyst riser where it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the very hot powdered catalyst from the regenerator. All of the cracking reactions take place in the catalyst riser. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about 535 °C and a pressure of about 1.72 barg.

The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated from the so-called spent catalyst by flowing through a set of two-stage cyclones within the reactor and (b) the spent catalyst flows downward through a steam stripping section to remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator. The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst line.

Since the cracking reactions produce some carbonaceous material (referred to as coke) that deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is regenerated by burning off the deposited coke with air blown into the regenerator. The regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 barg. The combustion of the coke is exothermic and it produces a large amount of heat that is partially absorbed by the regenerated catalyst and provides the heat required for the vaporization of the

77 feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that reason, FCC units are often referred to as being heat balanced.

The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot flue gas exits the regenerator after passing through multiple sets of two-stage cylones that remove entrained catalyst from the flue gas,

The amount of catalyst circulating between the regenerator and the reactor amounts to about 5 kg per kg of feedstock which is equivalent to about 4.66 kg per litre of feedstock.[1][7] Thus, an FCC unit processing 75,000 barrels/day (12,000,000 litres/day) will circulate about 55,900 metric tons per day of catalyst.

Figure 1: A schematic flow diagram of a Fluid Catalytic Cracking unit as used in petroleum refineries

Distillation column

The reaction product vapors (at 535 °C and a pressure of 1.72 barg) flow from the top of the reactor to the bottom section of the distillation column (commonly referred to as the main fractionator) where they are distilled into the FCC end products of cracked naphtha, fuel oil and offgas. After further processing for removal of sulfur compounds, the cracked naphtha becomes a high-octane component of the refinery's blended gasolines.

The main fractionator offgas is sent to what is called a gas recovery unit where it is separated into butanes and butylenes, propane and propylene, and lower molecular weight gases (hydrogen, methane, ethylene and ethane). Some FCC gas recovery units may also separate out some of the ethane and ethylene.

Although the schematic flow diagram above depicts the main fractionator as having only one sidecut stripper and one fuel oil product, many FCC main fractionators have two sidecut strippers and produce a light fuel oil and a heavy fuel oil. Likewise, many FCC main fractionators produce a light cracked naphtha and a heavy cracked naphtha. The terminology light and heavy in this context refers to the product boiling ranges, with light products having a lower boiling range than heavy products.

The bottom product oil from the main fractionator contains residual catalyst particles which were not completely removed by the cyclones in the top of the reactor. For that reason, the bottom product oil is referred to as a slurry oil. Part of that slurry oil is recycled back into the main fractionator above the entry point of the hot reaction product vapors so as to cool and partially condense the reaction product vapors as they enter the main fractionator. The remainder of the slurry oil is pumped through a slurry settler. The bottom oil from the slurry settler contains most of the slurry oil catalyst particles and is recycled back into the catalyst riser by combining it with the FCC feedstock oil. The so-called clarified slurry oil or decant oil, DCO is withdrawn from the top of slurry settler for use elsewhere in the refinery or as a heavy fuel oil blending component. 78

Regenerator flue gas

Depending on the choice of FCC design, the combustion in the regenerator of the coke on the spent catalyst may or may not be complete combustion to carbon dioxide (CO2). The combustion air flow is controlled so as to provide the desired ratio of carbon monoxide (CO) to carbon dioxide for each specific FCC design.[1] [4]

In the design shown in Figure 1, the coke has only been partially combusted to CO2. The combustion flue gas (containing CO and CO2) at 715 °C and at a pressure of 2.41 barg is routed through a secondary catalyst separator containing swirl tubes designed to remove 70 to 90 percent of the particulates in the flue gas leaving the regenerator.[8] This is required to prevent erosion damage to the blades in the turbo-expander that the flue gas is next routed through.

The expansion of flue gas through a turbo-expander provides sufficient power to drive the regenerator's combustion air compressor. The electrical motor-generator can consume or produce electrical power. If the expansion of the flue gas does not provide enough power to drive the air compressor, the electric motor/generator provides the needed additional power. If the flue gas expansion provides more power than needed to drive the air compressor, than the electric motor/generator converts the excess power into electric power and exports it to the refinery's electrical system.[3]

The expanded flue gas is then routed through a steam-generating boiler (referred to as a CO boiler) where the carbon monoxide in the flue gas is burned as fuel to provide steam for use in the refinery as well as to comply with any applicable environmental regulatory limits on carbon monoxide emissions.[3]

The flue gas is finally processed through an electrostatic precipitator (ESP) to remove residual particulate matter to comply with any applicable environmental regulations regarding particulate emissions. The ESP removes particulates in the size range of 2 to 20 microns from the flue gas.[3]

The steam turbine in the flue gas processing system (shown in the above diagram) is used to drive the regenerator's combustion air compressor during start-ups of the FCC unit until there is sufficient combustion flue gas to take over that task.

Chemistry

Before delving into the chemistry involved in catalytic cracking, it will be helpful to briefly discuss the composition of petroleum crude oil.

Petroleum crude oil consists primarily of a mixture of hydrocarbons with small amounts of other organic compounds containing sulfur, nitrogen and oxygen. The crude oil also contains small amounts of metals such as copper, iron, nickel and vanadium.[2]

Table 1

Carbon 83-87%

Hydrogen 10-14% Nitrogen 0.1-2% Oxygen 0.1-1.5% 79

The elemental composition ranges of crude oil are summarized in Table Sulfur 0.5-6% 1 and the hydrocarbons in the crude oil can be classified into three types:[1][2] Metals < 0.1%

• Paraffins or alkanes: saturated straight-chain or branched hydrocarbons, without any ring structures • Naphthenes or cycloalkanes: saturated hydrocarbons having one or more ring structures with one or more side-chain paraffins • Aromatics: hydrocarbons having one or more unsaturated ring structures such as benzene or unsaturated polycyclic ring structures such as naphthalene or phenanthrene, any of which may also have one or more side-chain paraffins.

Olefins or alkenes, which are unsaturated straight-chain or branched hydrocarbons, do not occur naturally in crude oil.

Figure 2: Diagrammatic example of the catalytic cracking of petroleum hydrocarbons

In plain language, the fluid catalytic cracking process breaks large hydrocarbon molecules into smaller molecules by contacting them with powdered catalyst at a high temperature and moderate pressure which first vaporizes the hydrocarbons and then breaks them. The cracking reactions occur in the vapor phase and start immediately when the feedstock is vaporized in the catalyst riser.

Figure 2 is a very simplified schematic diagram that exemplifies how the process breaks high boiling, straight-chain alkane (paraffin) hydrocarbons into smaller straight-chain alkanes as well as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naphthenes).[9] The breaking of the large hydrocarbon molecules into smaller molecules is more technically referred to by organic chemists as scission of the carbon-to-carbon bonds.

As depicted in Figure 2, some of the smaller alkanes are then broken and converted into even smaller alkenes and branched alkenes such as the gases ethylene, propylene, butylenes and isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks. The propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum refining processes that convert them into high-octane gasoline blending components.

As also depicted in Figure 2, the cycloalkanes (naphthenes) formed by the initial breakup of the large molecules are further converted to aromatics such as benzene, toluene and xylenes which boil in the gasoline boiling range and have much higher octane ratings than alkanes.

By no means does Figure 2 include all the chemistry of the primary and secondary reactions taking place in the fluid catalytic process. There are a great many other reactions involved. However, a full discussion of the highly technical details of the various catalytic cracking reactions is beyond the scope of this article and can be found in the technical literature.[1][2][3][4]

Catalysts

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Modern FCC catalysts are fine powders with a bulk density of 0.80 to 0.96 g/cc and having a particle size distribution ranging from 10 to 150 μm and an average particle size of 60 to 100 μm.[10][11] The design and operation of an FCC unit is largely dependent upon the chemical and physical properties of the catalyst. The desirable properties of an FCC catalyst are:

• Good stability to high temperature and to steam • High activity • Large pore sizes • Good resistance to attrition • Low coke production

A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder and filler. Zeolite is the primary active component and can range from about 15 to 50 weight percent of the catalyst. The zeolite used in FCC catalysts is referred to as faujasite or as Type Y and is comprised of silica and alumina tetrahedra with each tetrahedron having either an aluminum or a silicon atom at the center and four oxygen atoms at the corners. It is a molecular sieve with a distinctive lattice structure that allows only a certain size range of hydrocarbon molecules to enter the lattice. In general, the zeolite does not allow molecules larger than 8 to 10 nm (i.e., 80 to 90 angstroms) to enter the lattice.[10][11]

The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and provide most of the catalytic activity. The acidic sites are provided by the alumina tetrahedra. The aluminum atom at the center of each alumina tetrahedra is at a +3 oxidation state surrounded by four oxygen atoms at the corners which are shared by the neighboring tetrahedra. Thus, the net charge of the alumina tetrahedra is -1 which is balanced by a sodium ion during the production of the catalyst. The sodium ion is later replaced by an ammonium ion which is vaporized when the catalyst is subsequently dried, resulting in the formation of Lewis and Brønsted acidic sites. In some FCC catalysts, the Brønsted sites may be later replaced by rare earth metals such as cerium and lanthanum to provide alternative activity and stability levels.[10][11]

The matrix component of an FCC catalyst contains amorphous alumina which also provides catalytic activity sites and in larger pores that allows entry for larger molecules than does the zeolite. That enables the cracking of higher-boiling, larger feedstock molecules than are cracked by the zeolite.

The binder and filler components provide the physical strength and integrity of the catalyst. The binder is usually silica sol and the filler is usually a clay (kaolin).

Nickel, vanadium, iron, copper and other metal contaminants, present in FCC feedstocks in the parts per million range, all have detrimental effects on the catalyst activity and performance. Nickel and vanadium are particularly troublesome. There are a number of methods for mitigating the effects of the contaminant metals:[12][13]

• Avoid feedstocks with high metals content: This seriously hampers a refinery's flexibility to process various crude oils or purchased FCC feedstocks. • Feedstock feed pretreatment: Hydrodesulfurization of the FCC feedstock removes some of the metals and also reduces the sulfur content of the FCC products. However, this is quite a costly option. • Increasing fresh catalyst addition: All FCC units withdraw some of the circulating equilibrium catalyst as spent catalyst and replaces it with fresh catalyst in order to maintain a desired level of activity. Increasing the rate of such exchange lowers the 81

level of metals in the circulating equilibrium catalyst, but this is also quite a costly option. • Demetallization: The commercial proprietary Demet Process removes nickel and vanadium from the withdrawn spent catalyst. The nickel and vanadium are converted to chlorides which are then washed out of the catalyst. After drying, the demetallized catalyst is recycled into the circulating catalyst. Removals of about 95 percent nickel removal and 67 to 85 percent vanadium have been reported. Despite that, the use of the Demet process has not become widespread, perhaps because of the high capital expenditure required. • Metals passivation: Certain materials can be used as additives which can be impregnated into the catalyst or added to the FCC feedstock in the form of metal- organic compounds. Such materials react with the metal contaminants and passivate the contaminants by forming less harmful compounds that remain on the catalyst. For example, antimony and bismuth are effective in passivating nickel and tin is effective in passivating vanadium. A number of proprietary passivation processes are available and fairly widely used.

The major suppliers of FCC catalysts worldwide include Albemarle Corporation, W.R. Grace Company and BASF Catalysts (formerly Engelhard).

History

The first commercial use of catalytic cracking occurred in 1915 when Almer M. McAfee of the Gulf Refining Company developed a batch process using aluminum chloride (a Friedel Crafts catalyst known since 1877) to catalytically crack heavy petroleum oils. However, the prohibitive cost of the catalyst prevented the widespread use of McAfee's process at that time.[2][14]

In 1922, a French mechanical engineer named Eugene Jules Houdry and a French pharmacist named E.A. Prudhomme set up a laboratory near Paris to develop a catalytic process for converting lignite coal to gasoline. Supported by the French government, they built a small demonstration plant in 1929 that processed about 60 tons per day of lignite coal. The results indicated that the process was not economically viable and it was subsequently shutdown.[15][16][17]

Houdry had found that Fuller's Earth, a clay mineral containing aluminosilicate (Al2SiO6), could convert oil derived from the lignite to gasoline. He then began to study the catalysis of petroleum oils and had some success in converting vaporized petroleum oil to gasoline. In 1930, the Vacuum Oil Company invited him to come to the United States and he moved his laboratory to Paulsboro, New Jersey.

In 1931, the Vacuum Oil Company merged with Standard Oil of New York (Socony) to form the Socony-Vacuum Oil Company. In 1933, a small Houdry process unit processing 200 barrels per day (32,000 litres per day) of petroleum oil. Because of the economic depression of the early 1930's, Socony-Vacuum was no longer able to support Houdry's work and gave him permission to seek help elsewhere.

In 1933, Houdry and Socony-Vacuum joined with Sun Oil Company in developing the Houdry process. Three years later, in 1936, Socony-Vacuum converted an older thermal cracking unit in their Paulsboro refinery in New Jersey to a small demonstration unit using the Houdry process to catalytically crack 2,000 barrels per day (318,000 litres per day) of petroleum oil. 82

In 1937, Sun Oil began operation of a new Houdry unit processing 12,000 barrels per day (2,390,000 litres per day) in their Marcus Hook refinery in Pennsylvania. The Houdry process at that time used reactors with a fixed bed of catalyst and was a semi-batch operation involving multiple reactors with some of the reactors in operation while other reactors were in various stages of regenerating the catalyst. Motor-driven valves were used to switch the reactors between online operation and offline regeneration and a cycle timer managed the switching. Almost 50 percent of the cracked product was gasoline as compared with about 25 percent from the thermal cracking processes.[15][16][17]

By 1938, when the Houdry process was publicly announced, Socony-Vacuum had eight additional units under construction. Licensing the process to other companies also began and by 1940 there were 14 Houdry units in operation processing 140,000 barrels per day (22,300,000 litres per day).

The next major step was to develop a continuous process rather than the semi-batch Houdry process. That step was implemented by advent of the moving-bed process known as the Thermafor Catalytic Cracking (TCC) process which used a bucket conveyor-elevator to move the catalyst from the regeneration kiln to the separate reactor section. A small demonstration TCC unit was built in Socony-Vacuum's Paulsboro refinery in 1941 and operated successfully. Then a full-scale commercial TCC unit processing 10,000 barrels per day (1,590,000 litres per day) began operation in 1943 at the Beaumont, Texas refinery of Magnolia Oil Company, an affiliate of Socony-Vacuum. By the end of World War II in 1945, the processing capacity of the TCC units in operation was about 300,000 barrels per day (47,700,000 litres per day).

It is said that the Houdry and TCC units were a major factor in the winning of World War II by supplying the high-octane gasoline needed by the air forces of Great Britain and the United States.[15][16][17]

In the years immediately after World War II, the Houdriflow process and the air-lift TCC process were developed as improved variations on the moving-bed theme. Just like Houdry's fixed-bed reactors, the moving-bed designs were prime examples of good engineering by developing a method of continuously moving the catalyst between the reactor and regeneration sections.

This fluid catalytic cracking process had first been investigated in the 1920s by Standard Oil of New Jersey, but research on it was abandoned during the economic depression years of 1929 to 1939. In 1938, when the success of Houdry’s process had become apparent, Standard Oil of New Jersey resumed the project as part of a consortium of that include five oil companies (Standard Oil of New Jersey, Standard Oil of Indiana, Anglo-Iranian Oil, Texas Oil and Dutch Shell), two engineering-construction companies (M.W. Kellogg and Universal Oil Products) and a German chemical company (I.G. Farben). The consortium was called Catalytic Research Associates (CRA) and its purpose was to develop a catalytic cracking process which would not impinge on Houdry's patents.[15][16][18]

Chemical engineering professors Warren K. Lewis and Edwin R. Gilliland of the Massachusetts Institute of Technology (MIT) suggested to the CRA researchers that a low velocity gas flow through a powder might "lift" it enough to cause it to flow in a manner similar to a liquid. Focused on that idea of a fluidized catalyst, researchers Donald Campbell, Homer Martin, Eger Murphree and Charles Tyson of the Standard Oil of New Jersey (now Exxon-Mobil Company) developed the first fluidized catalytic cracking unit. Their U.S. Patent No. 2,451,804, A Method of and Apparatus for Contacting Solids and Gases, describes 83 their milestone invention. Based on their work, M. W. Kellogg Company constructed a large pilot plant in the Baton Rouge, Louisiana refinery of the Standard Oil of New Jersey. The pilot plant began operation in May of 1940.

Based on the success of the pilot plant, the first commercial fluid catalytic cracking plant (known as the Model I FCC) began processing 13,000 barrels per day (2,070,000 litres per day) of petroleum oil in the Baton Rouge refinery on May 25, 1942, just four years after the CRA consortium was formed and in the midst of World War II. A little more than a month later, in July 1942, it was processing 17,000 barrels per day (2,700,000 litres per day). In 1963, that first Model I FCC unit was shut down after 21 years of operation and subsequently dismantled.[15][16][18][19]

In the many decades since the Model I FCC unit began operation, the fixed bed Houdry units have all been shut down as have most of the moving bed units (such as the TCC units) while hundreds of FCC units have been built. During those decades, many improved FCC designs have evolved and cracking catalysts have been greatly improved, but the modern FCC units are essentially the same as that first Model I FCC unit. Hydrocracking

In 1920 a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in Germany[8].

Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial pressure of hydrogen gas. Similar to the hydrotreater, the function of hydrogen is the purification of the hydrocarbon stream from sulfur and nitrogen hetero-atoms.

The products of this process are saturated hydrocarbons; depending on the reaction conditions (temperature, pressure, catalyst activity) these products range from ethane, LPG to heavier hydrocarbons comprising mostly of isoparaffins. Hydrocracking is normally facilitated by a bi functional catalyst that is capable of rearranging and breaking hydrocarbon chains as well as adding hydrogen to aromatics and olefins to produce naphthenes and alkanes.

Major products from hydrocracking are jet fuel and diesel, while also relatively high octane rating gasoline fractions and LPG are produced. All these products have a very low content of sulfur and other contaminants.

It is very common in India, Europe and Asia because those regions have high demand for diesel and kerosene. In the US, Fluid Catalytic Cracking is more common because the demand for gasoline is higher.

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Mass spectrometry

From Wikipedia, the free encyclopedia Jump to: navigation, search

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of charged particles.[1] It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios.[1] In a typical MS procedure:

1. A sample is loaded onto the MS instrument, and undergoes vaporization 2. The components of the sample are ionized by one of a variety of methods (e.g., by impacting them with an electron beam), which results in the formation of charged particles (ions) 3. The ions are separated according to their mass-to-charge ratio in an analyzer by electromagnetic fields 4. The ions are detected, usually by a quantitative method 5. The ion signal is processed into mass spectra

MS instruments consist of three modules:

• An ion source, which can convert gas phase sample molecules into ions (or, in the case of electrospray ionization, move ions that exist in solution into the gas phase) • A mass analyzer, which sorts the ions by their masses by applying electromagnetic fields • A detector, which measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present

The technique has both qualitative and quantitative uses. These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry (the chemistry of ions and neutrals in a vacuum). MS is now in very common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds.

Etymology

The word spectrograph has been used since 1884 as an "International Scientific Vocabulary".[2][3] The linguistic roots are a combination and removal of bound morphemes and free morphemes which relate to the terms spectr-um and phot-ograph-ic plate.[4] Early spectrometry devices that measured the mass-to-charge ratio of ions were called mass spectrographs which consisted of instruments that recorded a spectrum of mass values on a photographic plate.[5][6] A mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen.[7] A mass spectroscope configuration was

85 used in early instruments when it was desired that the effects of adjustments be quickly observed. Once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used even though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope.[8] The use of the term mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy.[1][1][9] Mass spectrometry is often abbreviated as mass-spec or simply as MS.[1] Thomson has also noted that a mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen.[10] ] The suffix -scope here denotes the direct viewing of the spectra (range) of masses.

History For more details on this topic, see History of mass spectrometry.

Replica of an early mass spectrometer

Francis William Aston won the 1922 Nobel Prize in Chemistry for his work in mass spectrometry

In 1886, Eugen Goldstein observed rays in gas discharges under low pressure that traveled away from the anode and through channels in a perforated cathode, opposite to the direction of negatively charged cathode rays (which travel from cathode to anode). Goldstein called these positively charged anode rays "Kanalstrahlen"; the standard translation of this term into English is "canal rays". Wilhelm Wien found that strong electric or magnetic fields deflected the canal rays and, in 1899, constructed a device with parallel electric and magnetic fields that separated the positive rays according to their charge-to-mass ratio (Q/m). Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube. English scientist J.J. Thomson later improved on the work of Wien by reducing the pressure to create a mass spectrograph.

The first application of mass spectrometry to the analysis of amino acids and peptides was reported in 1958.[11] Carl-Ove Andersson highlighted the main fragment ions observed in the ionization of methyl esters.[12]

Some of the modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F.W. Aston in 1918 and 1919 respectively. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt and Wolfgang Paul for the development of the ion trap technique in the 1950s and 1960s. In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the development of electrospray ionization (ESI) and Koichi Tanaka for the development of soft laser desorption (SLD) and their application to the ionization of biological macromolecules, especially proteins.[13]

Simplified example

Schematics of a simple mass spectrometer with sector type mass analyzer. This one is for the measurement of Carbon dioxide isotope ratios (IRMS) as in the carbon-13 urea breath test

The following example describes the operation of a spectrometer mass analyzer, which is of the sector type. (Other analyzer types are treated below.) Consider a sample of sodium 86 chloride (table salt). In the ion source, the sample is vaporized (turned into gas) and ionized (transformed into electrically charged particles) into sodium (Na+) and chloride (Cl-) ions. Sodium atoms and ions are monoisotopic, with a mass of about 23 amu. Chloride atoms and ions come in two isotopes with masses of approximately 35 amu (at a natural abundance of about 75 percent) and approximately 37 amu (at a natural abundance of about 25 percent). The analyzer part of the spectrometer contains electric and magnetic fields, which exert forces on ions traveling through these fields. The speed of a charged particle may be increased or decreased while passing through the electric field, and its direction may be altered by the magnetic field. The magnitude of the deflection of the moving ion's trajectory depends on its mass-to-charge ratio. Lighter ions get deflected by the magnetic force more than heavier ions (based on Newton's second law of motion, F = ma). The streams of sorted ions pass from the analyzer to the detector, which records the relative abundance of each ion type. This information is used to determine the chemical element composition of the original sample (i.e. that both sodium and chlorine are present in the sample) and the isotopic composition of its constituents (the ratio of 35Cl to 37Cl).

Instrumentation

Ion source technologies

Main article: Ion source

The ion source is the part of the mass spectrometer that ionizes the material under analysis (the analyte). The ions are then transported by magnetic or electric fields to the mass analyzer.

Techniques for ionization have been key to determining what types of samples can be analyzed by mass spectrometry. Electron ionization and chemical ionization are used for gases and vapors. In chemical ionization sources, the analyte is ionized by chemical ion- molecule reactions during collisions in the source. Two techniques often used with liquid and solid biological samples include electrospray ionization (invented by John Fenn[14]) and matrix-assisted laser desorption/ionization (MALDI, developed by K. Tanaka[15] and separately by M. Karas and F. Hillenkamp[16]).

Inductively coupled plasma (ICP) sources are used primarily for cation analysis of a wide array of sample types. In this type of Ion Source Technology, a 'flame' of plasma that is electrically neutral overall, but that has had a substantial fraction of its atoms ionized by high temperature, is used to atomize introduced sample molecules and to further strip the outer electrons from those atoms. The plasma is usually generated from argon gas, since the first ionization energy of argon atoms is higher than the first of any other elements except He, O, F and Ne, but lower than the second ionization energy of all except the most electropositive metals. The heating is achieved by a radio-frequency current passed through a coil surrounding the plasma.

Ion Attachment Ionization is a newer soft ionization technique that allows for fragmentation free analysis.

Mass analyzer technologies

Mass analyzers separate the ions according to their mass-to-charge ratio. The following two laws govern the dynamics of charged particles in electric and magnetic fields in vacuum:

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(Lorentz force law); (Newton's second law of motion in non-relativistic case, i.e. valid only at ion velocity much lower than the speed of light).

Here F is the force applied to the ion, m is the mass of the ion, a is the acceleration, Q is the ion charge, E is the electric field, and v x B is the vector cross product of the ion velocity and the magnetic field

Equating the above expressions for the force applied to the ion yields:

This differential equation is the classic equation of motion for charged particles. Together with the particle's initial conditions, it completely determines the particle's motion in space and time in terms of m/Q. Thus mass spectrometers could be thought of as "mass-to-charge spectrometers". When presenting data, it is common to use the (officially) dimensionless m/z, where z is the number of elementary charges (e) on the ion (z=Q/e). This quantity, although it is informally called the mass-to-charge ratio, more accurately speaking represents the ratio of the mass number and the charge number, z.

There are many types of mass analyzers, using either static or dynamic fields, and magnetic or electric fields, but all operate according to the above differential equation. Each analyzer type has its strengths and weaknesses. Many mass spectrometers use two or more mass analyzers for tandem mass spectrometry (MS/MS). In addition to the more common mass analyzers listed below, there are others designed for special situations.

Sector For more details on this topic, see sector instrument.

A sector field mass analyzer uses an electric and/or magnetic field to affect the path and/or velocity of the charged particles in some way. As shown above, sector instruments bend the trajectories of the ions as they pass through the mass analyzer, according to their mass-to- charge ratios, deflecting the more charged and faster-moving, lighter ions more. The analyzer can be used to select a narrow range of m/z or to scan through a range of m/z to catalog the ions present.[18]

Time-of-flight For more details on this topic, see time-of-flight mass spectrometry.

The time-of-flight (TOF) analyzer uses an electric field to accelerate the ions through the same potential, and then measures the time they take to reach the detector. If the particles all have the same charge, the kinetic energies will be identical, and their velocities will depend only on their masses. Lighter ions will reach the detector first.[19]

Quadrupole mass filter For more details on this topic, see Quadrupole mass analyzer.

Quadrupole mass analyzers use oscillating electrical fields to selectively stabilize or destabilize the paths of ions passing through a radio frequency (RF) quadrupole field created between 4 parallel rods. Only the ions in a certain range of mass/charge ratio are passed through the system at any time, but changes to the potentials on the rods allow a wide range of 88 m/z values to be swept rapidly, either continuously or in a succession of discrete hops. A quadrupole mass analyzer acts as a mass-selective filter and is closely related to the quadrupole ion trap, particularly the linear quadrupole ion trap except that it is designed to pass the untrapped ions rather than collect the trapped ones, and is for that reason referred to as a transmission quadrupole. A common variation of the quadrupole is the triple quadrupole. Triple quadrupole mass spectrometers have three consecutive quadrupoles arranged in series to incoming ions. The first quadrupole acts as a mass filter. The second quadrupole acts as a collision cell where selected ions are broken into fragments. The resulting fragments are analyzed by the third quadrupole.

Three-dimensional quadrupole ion trap For more details on this topic, see quadrupole ion trap.

The quadrupole ion trap works on the same physical principles as the quadrupole mass analyzer, but the ions are trapped and sequentially ejected. Ions are trapped in a mainly quadrupole RF field, in a space defined by a ring electrode (usually connected to the main RF potential) between two endcap electrodes (typically connected to DC or auxiliary AC potentials). The sample is ionized either internally (e.g. with an electron or laser beam), or externally, in which case the ions are often introduced through an aperture in an endcap electrode.

There are many mass/charge separation and isolation methods but the most commonly used is the mass instability mode in which the RF potential is ramped so that the orbit of ions with a mass a > b are stable while ions with mass b become unstable and are ejected on the z-axis onto a detector. There are also non-destructive analysis methods.

Ions may also be ejected by the resonance excitation method, whereby a supplemental oscillatory excitation voltage is applied to the endcap electrodes, and the trapping voltage amplitude and/or excitation voltage frequency is varied to bring ions into a resonance condition in order of their mass/charge ratio.[20][21]

The cylindrical ion trap mass spectrometer is a derivative of the quadrupole ion trap mass spectrometer.

Linear quadrupole ion trap

A linear quadrupole ion trap is similar to a quadrupole ion trap, but it traps ions in a two dimensional quadrupole field, instead of a three-dimensional quadrupole field as in a 3D quadrupole ion trap. Thermo Fisher's LTQ ("linear trap quadrupole") is an example of the linear ion trap.[22]

Fourier transform ion cyclotron resonance

An FT-ICR mass spectrometer For more details on this topic, see Fourier transform mass spectrometry.

Fourier transform mass spectrometry (FTMS), or more precisely Fourier transform ion cyclotron resonance MS, measures mass by detecting the image current produced by ions cyclotroning in the presence of a magnetic field. Instead of measuring the deflection of ions with a detector such as an electron multiplier, the ions are injected into a Penning trap (a static 89 electric/magnetic ion trap) where they effectively form part of a circuit. Detectors at fixed positions in space measure the electrical signal of ions which pass near them over time, producing a periodic signal. Since the frequency of an ion's cycling is determined by its mass to charge ratio, this can be deconvoluted by performing a Fourier transform on the signal. FTMS has the advantage of high sensitivity (since each ion is "counted" more than once) and much higher resolution and thus precision.[23][24]

Ion cyclotron resonance (ICR) is an older mass analysis technique similar to FTMS except that ions are detected with a traditional detector. Ions trapped in a Penning trap are excited by an RF electric field until they impact the wall of the trap, where the detector is located. Ions of different mass are resolved according to impact time.

Orbitrap For more details on this topic, see Orbitrap.

Very similar nonmagnetic FTMS has been performed, where ions are electrostatically trapped in an orbit around a central, spindle shaped electrode. The electrode confines the ions so that they both orbit around the central electrode and oscillate back and forth along the central electrode's long axis. This oscillation generates an image current in the detector plates which is recorded by the instrument. The frequencies of these image currents depend on the mass to charge ratios of the ions. Mass spectra are obtained by Fourier transformation of the recorded image currents.

Similar to Fourier transform ion cyclotron resonance mass spectrometers, Orbitraps have a high mass accuracy, high sensitivity and a good dynamic range.[25]

Toroidal Ion Trap

The toroidal ion trap is visualized as a linear quadrupole curved around and connected at the ends or as a cross section of a 3D ion trap rotated on edge to form the toroid, donut shaped trap. The trap can store large volumes of ions by distributing them throughout the ring-like trap structure. This toroidal shaped trap is a configuration that allows the increased miniaturization of an ion trap mass analyzer. Additionally all ions are stored in the same trapping field and ejected together simplifying detection that can be complicated with array configurations due to variations in detector alignment and machining of the arrays.[26]

Detector

A continuous dynode particle multiplier detector.

The final element of the mass spectrometer is the detector. The detector records either the charge induced or the current produced when an ion passes by or hits a surface. In a scanning instrument, the signal produced in the detector during the course of the scan versus where the instrument is in the scan (at what m/Q) will produce a mass spectrum, a record of ions as a function of m/Q.

Typically, some type of electron multiplier is used, though other detectors including Faraday cups and ion-to-photon detectors are also used. Because the number of ions leaving the mass analyzer at a particular instant is typically quite small, considerable amplification is often 90 necessary to get a signal. Microchannel plate detectors are commonly used in modern commercial instruments.[27] In FTMS and Orbitraps, the detector consists of a pair of metal surfaces within the mass analyzer/ion trap region which the ions only pass near as they oscillate. No DC current is produced, only a weak AC image current is produced in a circuit between the electrodes. Other inductive detectors have also been used.[28]

Analysers characteristics

Mass resolving power Main article: Resolution (mass spectrometry)

The mass resolving power is the measure of the ability to distinguish two peaks of slightly different m/z.

Mass accuracy

The mass accuracy is the ratio of the m/z measurement error to the true m/z. Usually measured in ppm or milli mass units.

Mass range

The mass range is the range of m/z amenable to analysis by a given analyzer.

Linear dynamic range

The linear dynamic range is the range over which ion signal is linear with analyte concentration.

Speed

Speed refers to the time frame of the experiment and ultimately is used to determine the number of spectra per unit time that can be generated.

Tandem mass spectrometry Main article: Tandem mass spectrometry

A tandem mass spectrometer is one capable of multiple rounds of mass spectrometry, usually separated by some form of molecule fragmentation. For example, one mass analyzer can isolate one peptide from many entering a mass spectrometer. A second mass analyzer then stabilizes the peptide ions while they collide with a gas, causing them to fragment by collision-induced dissociation (CID). A third mass analyzer then sorts the fragments produced from the peptides. Tandem MS can also be done in a single mass analyzer over time, as in a quadrupole ion trap. There are various methods for fragmenting molecules for tandem MS, including collision-induced dissociation (CID), electron capture dissociation (ECD), electron transfer dissociation (ETD), infrared multiphoton dissociation (IRMPD) and blackbody infrared radiative dissociation (BIRD). An important application using tandem mass spectrometry is in protein identification.[29]

Tandem mass spectrometry enables a variety of experimental sequences. Many commercial mass spectrometers are designed to expedite the execution of such routine sequences as 91 selected reaction monitoring (SRM), multiple reaction monitoring (MRM), and precursor ion scan. In SRM, the first analyzer allows only a single mass through and the second analyzer monitors for a single user defined fragment ion. MRM allows for multiple user defined fragment ions. SRM and MRM are most often used with scanning instruments where the second mass analysis event is duty cycle limited. These experiments are used to increase specificity of detection of known molecules, notably in pharmacokinetic studies. Precursor ion scan refers to monitoring for a specific loss from the precursor ion. The first and second mass analyzers scan across the spectrum as partitioned by a user defined m/z value. This experiment is used to detect specific motifs within unknown molecules.

Another type of tandem mass spectrometry used for radiocarbon dating is Accelerator Mass Spectrometry (AMS), which uses very high voltages, usually in the mega-volt range, to accelerate negative ions into a type of tandem mass spectrometer.

Common mass spectrometer configurations and techniques

When a specific configuration of source, analyzer, and detector becomes conventional in practice, often a compound acronym arises to designate it, and the compound acronym may be better known among nonspectrometrists than the component acronyms. The epitome of this is MALDI-TOF, which simply refers to combining a matrix-assisted laser desorption/ionization source with a time-of-flight mass analyzer. The MALDI-TOF moniker is more widely recognized by the non-mass spectrometrists than MALDI or TOF individually. Other examples include inductively coupled plasma-mass spectrometry (ICP-MS), accelerator mass spectrometry (AMS), Thermal ionization-mass spectrometry (TIMS) and spark source mass spectrometry (SSMS). Sometimes the use of the generic "MS" actually connotes a very specific mass analyzer and detection system, as is the case with AMS, which is always sector based.

Certain applications of mass spectrometry have developed monikers that although strictly speaking would seem to refer to a broad application, in practice have come instead to connote a specific or a limited number of instrument configurations. An example of this is isotope ratio mass spectrometry (IRMS), which refers in practice to the use of a limited number of sector based mass analyzers; this name is used to refer to both the application and the instrument used for the application.

Chromatographic techniques combined with mass spectrometry

An important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in tandem with chromatographic separation techniques.

Gas chromatography

A gas chromatograph (right) directly coupled to a mass spectrometer (left) See also: Gas chromatography-mass spectrometry

A common combination is gas chromatography-mass spectrometry (GC/MS or GC-MS). In this technique, a gas chromatograph is used to separate different compounds. This stream of separated compounds is fed online into the ion source, a metallic filament to which voltage is applied. This filament emits electrons which ionize the compounds. The ions can then further

92 fragment, yielding predictable patterns. Intact ions and fragments pass into the mass spectrometer's analyzer and are eventually detected.[30]

Liquid chromatography

See also: Liquid chromatography-mass spectrometry

Similar to gas chromatography MS (GC/MS), liquid chromatography mass spectrometry (LC/MS or LC-MS) separates compounds chromatographically before they are introduced to the ion source and mass spectrometer. It differs from GC/MS in that the mobile phase is liquid, usually a mixture of water and organic solvents, instead of gas and the ions fragments cannot yield predictable patterns. Most commonly, an electrospray ionization source is used in LC/MS. There are also some newly developed ionization techniques like laser spray.

Ion mobility

See also: Ion mobility spectrometry-mass spectrometry

Ion mobility spectrometry/mass spectrometry (IMS/MS or IMMS) is a technique where ions are first separated by drift time through some neutral gas under an applied electrical potential gradient before being introduced into a mass spectrometer.[31] Drift time is a measure of the radius relative to the charge of the ion. The duty cycle of IMS (the time over which the experiment takes place) is longer than most mass spectrometric techniques, such that the mass spectrometer can sample along the course of the IMS separation. This produces data about the IMS separation and the mass-to-charge ratio of the ions in a manner similar to LC/MS.[32]

The duty cycle of IMS is short relative to liquid chromatography or gas chromatography separations and can thus be coupled to such techniques, producing triple modalities such as LC/IMS/MS.[33]

Data and analysis

Mass spectrum of a peptide showing the isotopic distribution

Data representations

See also: Mass spectrometry data format

Mass spectrometry produces various types of data. The most common data representation is the mass spectrum.

Certain types of mass spectrometry data are best represented as a mass chromatogram. Types of chromatograms include selected ion monitoring (SIM), total ion current (TIC), and selected reaction monitoring chromatogram (SRM), among many others.

Other types of mass spectrometry data are well represented as a three-dimensional contour map. In this form, the mass-to-charge, m/z is on the x-axis, intensity the y-axis, and an additional experimental parameter, such as time, is recorded on the z-axis.

Data analysis 93

Basics

Mass spectrometry data analysis is a complicated subject that is very specific to the type of experiment producing the data. There are general subdivisions of data that are fundamental to understanding any data.

Many mass spectrometers work in either negative ion mode or positive ion mode. It is very important to know whether the observed ions are negatively or positively charged. This is often important in determining the neutral mass but it also indicates something about the nature of the molecules.

Different types of ion source result in different arrays of fragments produced from the original molecules. An electron ionization source produces many fragments and mostly single-charged (1-) radicals (odd number of electrons), whereas an electrospray source usually produces non- radical quasimolecular ions that are frequently multiply charged. Tandem mass spectrometry purposely produces fragment ions post-source and can drastically change the sort of data achieved by an experiment.

By understanding the origin of a sample, certain expectations can be assumed as to the component molecules of the sample and their fragmentations. A sample from a synthesis/manufacturing process will probably contain impurities chemically related to the target component. A relatively crudely prepared biological sample will probably contain a certain amount of salt, which may form adducts with the analyte molecules in certain analyses.

Results can also depend heavily on how the sample was prepared and how it was run/introduced. An important example is the issue of which matrix is used for MALDI spotting, since much of the energetics of the desorption/ionization event is controlled by the matrix rather than the laser power. Sometimes samples are spiked with sodium or another ion- carrying species to produce adducts rather than a protonated species.

The greatest source of trouble when non-mass spectrometrists try to conduct mass spectrometry on their own or collaborate with a mass spectrometrist is inadequate definition of the research goal of the experiment. Adequate definition of the experimental goal is a prerequisite for collecting the proper data and successfully interpreting it. Among the determinations that can be achieved with mass spectrometry are molecular mass, molecular structure, and sample purity. Each of these questions requires a different experimental procedure. Simply asking for a "mass spec" will most likely not answer the real question at hand.

Interpretation of mass spectra

Main article: Mass spectrum analysis

Since the precise structure or peptide sequence of a molecule is deciphered through the set of fragment masses, the interpretation of mass spectra requires combined use of various techniques. Usually the first strategy for identifying an unknown compound is to compare its experimental mass spectrum against a library of mass spectra. If the search comes up empty, then manual interpretation[34] or software assisted interpretation of mass spectra are performed. Computer simulation of ionization and fragmentation processes occurring in mass spectrometer is the primary tool for assigning structure or peptide sequence to a molecule. An a priori structural information is fragmented in silico and the resulting pattern is compared 94 with observed spectrum. Such simulation is often supported by a fragmentation library[35] that contains published patterns of known decomposition reactions. Software taking advantage of this idea has been developed for both small molecules and proteins.

Another way of interpreting mass spectra involves spectra with accurate mass. A mass-to- charge ratio value (m/z) with only integer precision can represent an immense number of theoretically possible ion structures. More precise mass figures significantly reduce the number of candidate molecular formulas, albeit each can still represent large number of structurally diverse compounds. A computer algorithm called formula generator calculates all molecular formulas that theoretically fit a given mass with specified tolerance.

A recent technique for structure elucidation in mass spectrometry, called precursor ion fingerprinting identifies individual pieces of structural information by conducting a search of the tandem spectra of the molecule under investigation against a library of the product-ion spectra of structurally characterized precursor ions.

Applications

Isotope ratio MS: isotope dating and tracking

Mass spectrometer to determine the 16O/18O and 12C/13C isotope ratio on biogenous carbonate Main article: Isotope ratio mass spectrometry

Mass spectrometry is also used to determine the isotopic composition of elements within a sample. Differences in mass among isotopes of an element are very small, and the less abundant isotopes of an element are typically very rare, so a very sensitive instrument is required. These instruments, sometimes referred to as isotope ratio mass spectrometers (IR- MS), usually use a single magnet to bend a beam of ionized particles towards a series of Faraday cups which convert particle impacts to electric current. A fast on-line analysis of deuterium content of water can be done using Flowing afterglow mass spectrometry, FA-MS. Probably the most sensitive and accurate mass spectrometer for this purpose is the accelerator mass spectrometer (AMS). Isotope ratios are important markers of a variety of processes. Some isotope ratios are used to determine the age of materials for example as in carbon dating. Labeling with stable isotopes is also used for protein quantification. (see protein characterization below)

Trace gas analysis

Several techniques use ions created in a dedicated ion source injected into a flow tube or a drift tube: selected ion flow tube (SIFT-MS), and proton transfer reaction (PTR-MS), are variants of chemical ionization dedicated for trace gas analysis of air, breath or liquid headspace using well defined reaction time allowing calculations of analyte concentrations from the known reaction kinetics without the need for internal standard or calibration.

Atom probe

Main article: Atom probe

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An atom probe is an instrument that combines time-of-flight mass spectrometry and field ion microscopy (FIM) to map the location of individual atoms.

Pharmacokinetics

Main article: Pharmacokinetics

Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine) and the need for high sensitivity to observe low dose and long time point data. The most common instrumentation used in this application is LC-MS with a triple quadrupole mass spectrometer. Tandem mass spectrometry is usually employed for added specificity. Standard curves and internal standards are used for quantitation of usually a single pharmaceutical in the samples. The samples represent different time points as a pharmaceutical is administered and then metabolized or cleared from the body. Blank or t=0 samples taken before administration are important in determining background and insuring data integrity with such complex sample matrices. Much attention is paid to the linearity of the standard curve; however it is not uncommon to use curve fitting with more complex functions such as quadratics since the response of most mass spectrometers is less than linear across large concentration ranges.[36][37][38]

There is currently considerable interest in the use of very high sensitivity mass spectrometry for microdosing studies, which are seen as a promising alternative to animal experimentation.

Protein characterization

Main article: Protein mass spectrometry

Mass spectrometry is an important emerging method for the characterization of proteins. The two primary methods for ionization of whole proteins are electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). In keeping with the performance and mass range of available mass spectrometers, two approaches are used for characterizing proteins. In the first, intact proteins are ionized by either of the two techniques described above, and then introduced to a mass analyzer. This approach is referred to as "top-down" strategy of protein analysis. In the second, proteins are enzymatically digested into smaller peptides using proteases such as trypsin or pepsin, either in solution or in gel after electrophoretic separation. Other proteolytic agents are also used. The collection of peptide products are then introduced to the mass analyzer. When the characteristic pattern of peptides is used for the identification of the protein the method is called peptide mass fingerprinting (PMF), if the identification is performed using the sequence data determined in tandem MS analysis it is called de novo sequencing. These procedures of protein analysis are also referred to as the "bottom-up" approach.

Glycan Analysis

Mass spectrometry (MS), with its low sample requirement and high sensitivity, has been the predominantly used in glycobiology for characterization and elucidation of glycan structures. [39] Mass spectrometry provides a complementary method to HPLC for the analysis of glycans. Intact glycans may be detected directly as singly charged ions by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) or, following permethylation or peracetylation, by fast atom bombardment mass spectrometry (FAB-MS).[40] Electrospray ionization mass spectrometry (ESI-MS) also gives good signals for the smaller glycans.[41]

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Various free and commercial software are now available which interpret MS data and aid in Glycan structure characterization.

Space exploration

As a standard method for analysis, mass spectrometers have reached other planets and moons. Two were taken to Mars by the Viking program. In early 2005 the Cassini-Huygens mission delivered a specialized GC-MS instrument aboard the Huygens probe through the atmosphere of Titan, the largest moon of the planet Saturn. This instrument analyzed atmospheric samples along its descent trajectory and was able to vaporize and analyze samples of Titan's frozen, hydrocarbon covered surface once the probe had landed. These measurements compare the abundance of isotope(s) of each particle comparatively to earth's natural abundance.[42] Also onboard the Cassini-Huygens spacecraft is an ion and neutral mass spectrometer which has been taking measurements of Titan's atmospheric composition as well as the composition of Enceladus' plumes. A Thermal and Evolved Gas Analyzer mass spectrometer was carried by the Mars Phoenix Lander launched in 2007.[43]

Mass spectrometers are also widely used in space missions to measure the composition of plasmas. For example, the Cassini spacecraft carries the Cassini Plasma Spectrometer (CAPS),[44] which measures the mass of ions in Saturn's magnetosphere.

Respired gas monitor

Mass spectrometers were used in hospitals for respiratory gas analysis beginning around 1975 through the end of the century. Some are probably still in use but none are currently being manufactured.[45]

Found mostly in the operating room, they were a part of a complex system, in which respired gas samples from patients undergoing anesthesia were drawn into the instrument through a valve mechanism designed to sequentially connect up to 32 rooms to the mass spectrometer. A computer directed all operations of the system. The data collected from the mass spectrometer was delivered to the individual rooms for the anesthesiologist to use.

The uniqueness of this magnetic sector mass spectrometer may have been the fact that a plane of detectors, each purposely positioned to collect all of the ion species expected to be in the samples, allowed the instrument to simultaneously report all of the gases respired by the patient. Although the mass range was limited to slightly over 120 u, fragmentation of some of the heavier molecules negated the need for a higher detection limit.[46]

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23. ^ M. B. Comisarow and A. G. Marshall (1974). "Fourier transform ion cyclotron resonance spectroscopy". Chemical Physics Letters 25 (2): 282–283. doi:10.1016/0009-2614(74)89137-2. 24. ^ Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. (1998). "Fourier transform ion cyclotron resonance mass spectrometry: a primer". Mass Spectrometry Reviews 17 (1): 1–34. doi:10.1002/(SICI)1098-2787(1998)17:1<1::AID-MAS1>3.0.CO;2-K. 25. ^ Q. Hu, R. J. Noll, H. Li, A. Makarov, M. Hardman and R. G. Cooks (2005). "The Orbitrap: a new mass spectrometer". Journal of Mass Spectrometry 40 (4): 430–443. doi:10.1002/jms.856. PMID 15838939. 26. ^ Lammert SA, Rockwood AA, Wang M, and ML Lee (2006). "Miniature Toroidal Radio Frequency Ion Trap Mass Analyzer". Journal of the American Society for Mass Spectrometry 17 (7): 916–922. doi:10.1016/j.jasms.2006.02.009. PMID 16697659. 27. ^ F. Dubois, R. Knochenmuss, R. Zenobi, A. Brunelle, C. Deprun and Y. L. Beyec (1999). "A comparison between ion-to-photon and microchannel plate detectors". Rapid Communications in Mass Spectrometry 13 (9): 786–791. doi:10.1002/(SICI)1097-0231(19990515)13:9<786::AID-RCM566>3.0.CO;2-3. 28. ^ M. A. Park, J. H. Callahan and A. Vertes (1994). "An inductive detector for time-of- flight mass spectrometry". Rapid Communications in Mass Spectrometry 8 (4): 317– 322. doi:10.1002/rcm.1290080407. 29. ^ Robert K. Boyd (1994). "Linked-scan techniques for MS/MS using tandem-in-space instruments". Mass Spectrometry Reviews 13 (5-6): 359–410. doi:10.1002/mas.1280130502. 30. ^ Eiceman, G.A. (2000). Gas Chromatography. In R.A. Meyers (Ed.), Encyclopedia of Analytical Chemistry: Applications, Theory, and Instrumentation, pp. 10627. Chichester: Wiley. ISBN 0-471-97670-9 31. ^ Verbeck, GF and Ruotolo, BT and Sawyer, HA and Gillig, KJ and Russell, DH, G; Ruotolo, B; Sawyer, H; Gillig, K; Russell, D (2002). "A fundamental introduction to ion mobility mass spectrometry applied to the analysis of biomolecules". J Biomol Tech 13 (2): 56–61. PMID 19498967. PMC 2279851. http://jbt.highwire.org/cgi/content/abstract/13/2/56. 32. ^ L. M. Matz, G. R. Asbury and H. H. Hill (2002). "Two-dimensional separations with electrospray ionization ambient pressure high-resolution ion mobility spectrometry/quadrupole mass spectrometry". Rapid Communications in Mass Spectrometry 16 (7): 670–675. doi:10.1002/rcm.623. PMID 11921245. 33. ^ Rena A. Sowell, Stormy L. Koeniger, Stephen J. Valentine, Myeong Hee Moon and David E. Clemmer (2004). "Nanoflow LC/IMS-MS and LC/IMS-CID/MS of Protein Mixtures". Journal of the American Society for Mass Spectrometry 15 (9): 1341–1353. doi:10.1016/j.jasms.2004.06.014. PMID 15337515. 34. ^ Tureček, František; McLafferty, Fred W. (1993). Interpretation of mass spectra. Sausalito: University Science Books. ISBN 0-935702-25-3. http://books.google.com/?id=xQWk5WQfMQAC&printsec=frontcover. 35. ^ Mistrik, R.(2004). A New Concept for the Interpretation of Mass Spectra Based on a Combination of a Fragmentation Mechanism Database and a Computer Expert System. in Ashcroft, A.E., Brenton, G., Monaghan,J.J. (Eds.), Advances in Mass Spectrometry, Elsevier, Amsterdam, vol. 16, pp. 821. 36. ^ Hsieh, Yunsheng; Korfmacher, WA (2006). "Systems for Drug Metabolism and Pharmacokinetic Screening, Y. Hsieh and W.A. Korfmacher, Current Drug Metabolism". Current Drug Metabolism 7 (5): 479–489. doi:10.2174/138920006777697963. PMID 16787157. 37. ^ Covey, T.R.; Lee, E.D.; Henion, J.D. (1986). "Mass Spectrometry for the Determination of Drugs in Biological Samples". Anal. Chem. 58: 2453–2460. doi:10.1021/ac00125a022. 99

38. ^ Covey, Tom R.; Crowther, Jonathan B.; Dewey, Elizabeth A.; Henion, Jack D. (1985). "Mass Spectrometry Determination of Drugs and Their Metabolites in Biological Fluids". Anal. Chem. 57 (2): 474–81. doi:10.1021/ac50001a036. 39. ^ Apte, A.; Meitei, N.S. (2009). Bioinformatics in Glycomics: Glycan Characterization with Mass Spectrometric Data Using SimGlycan™. 600. pp. 269- 281. doi:10.1007/978-1-60761-454-8_19. 40. ^ Harvey, D.; Rudd, P.M. (2000). Determining the Structure of Glycan Moieties by Mass Spectrometry. pp. 12.7-12.7.15. doi:10.1002/0471140864.ps1207s43. 41. ^ Blow (2009). "Glycobiology: A spoonful of sugar". Nature: 617-620. doi:10.1038/457617a. 42. ^ S. Petrie and D. K. Bohme (2007). "Ions in space". Mass Spectrometry Reviews 26 (2): 258–280. doi:10.1002/mas.20114. PMID 17111346. 43. ^ Hoffman, J; Chaney, R; Hammack, H (2008). "Phoenix Mars Mission—The Thermal Evolved Gas Analyzer". Journal of the American Society for Mass Spectrometry 19 (10): 1377. doi:10.1016/j.jasms.2008.07.015. PMID 18715800 44. ^ "Cassini Plasma Spectrometer". Southwest Research Institute. http://caps.space.swri.edu/. Retrieved 2008-01-04. 45. ^ Riker JB, Haberman B (1976). "Expired gas monitoring by mass spectrometry in a respiratory intensive care unit". Crit. Care Med. 4 (5): 223–9. doi:10.1097/00003246- 197609000-00002. PMID 975846. 46. ^ J. W. W. Gothard, C. M. Busst, M. A. Branthwaite, N. J. H. Davies and D. M. Denison (1980). "Applications of respiratory mass spectrometry to intensive care". Anaesthesia 35 (9): 890–895. doi:10.1111/j.1365-2044.1980.tb03950.x.

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Infrared spectroscopy

From Wikipedia, the free encyclopedia Jump to: navigation, search For a table of IR spectroscopy data, see infrared spectroscopy correlation table.

Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify and study chemicals. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer.

The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5– 25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy. The names and classifications of these subregions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.

Theory

Infrared spectroscopy exploits the fact that molecules absorb specific frequencies that are characteristic of their structure. These absorptions are resonant frequencies, i.e. the frequency of the absorbed radiation matches the frequency of the bond or group that vibrates. The energies are determined by the shape of the molecular potential energy surfaces, the masses of the atoms, and the associated vibronic coupling.

In particular, in the Born–Oppenheimer and harmonic approximations, i.e. when the molecular Hamiltonian corresponding to the electronic ground state can be approximated by a harmonic oscillator in the neighborhood of the equilibrium molecular geometry, the resonant frequencies are determined by the normal modes corresponding to the molecular electronic ground state potential energy surface. Nevertheless, the resonant frequencies can be in a first approach related to the strength of the bond, and the mass of the atoms at either end of it. Thus, the frequency of the vibrations can be associated with a particular bond type.

Number of vibrational modes

In order for a vibrational mode in a molecule to be "IR active," it must be associated with changes in the permanent dipole.

A molecule can vibrate in many ways, and each way is called a vibrational mode. Linear molecules have 3N – 5 degrees of vibrational modes whereas nonlinear molecules have 3N –

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6 degrees of vibrational modes (also called vibrational degrees of freedom). As an example H2O, a non-linear molecule, will have 3 × 3 – 6 = 3 degrees of vibrational freedom, or modes.

Simple diatomic molecules have only one bond and only one vibrational band. If the molecule is symmetrical, e.g. N2, the band is not observed in the IR spectrum, but only in the Raman spectrum. Unsymmetrical diatomic molecules, e.g. CO, absorb in the IR spectrum. More complex molecules have many bonds, and their vibrational spectra are correspondingly more complex, i.e. big molecules have many peaks in their IR spectra.

The atoms in a CH2 group, commonly found in organic compounds, can vibrate in six different ways: symmetric and antisymmetric stretching, scissoring, rocking, wagging and twisting:

Symmetrical Antisymmetrical Scissoring stretching stretching

Ro WaTw cki ggi isti ng ng ng

(These figures do not represent the "recoil" of the C atoms, which, though necessarily present to balance the overall movements of the molecule, are much smaller than the movements of the lighter H atoms).

Special effects

The simplest and most important IR bands arise from the "normal modes," the simplest distortions of the molecule. In some cases, "overtone bands" are observed. These bands arise from the absorption of a photon that leads to a doubly excited vibrational state. Such bands appear at approximately twice the energy of the normal mode. Some vibrations, so-called 'combination modes," involve more than one normal mode. The phenomenon of Fermi resonance can arise when two modes are similar in energy, Fermi resonance results in an unexpected shift in energy and intensity of the bands.

Practical IR spectroscopy

The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. Examination of the transmitted light reveals how much energy was absorbed at each wavelength. This can be done with a monochromatic beam, which changes in wavelength over time, or by using a Fourier transform instrument to measure all wavelengths at once. From this, a transmittance or absorbance spectrum can be produced, showing at which IR wavelengths the sample absorbs. Analysis of these absorption characteristics reveals details about the molecular structure of the sample. When the frequency of the IR is the same as the vibrational frequency of a bond, absorption occurs.

This technique works almost exclusively on samples with covalent bonds. Simple spectra are obtained from samples with few IR active bonds and high levels of purity. More complex

102 molecular structures lead to more absorption bands and more complex spectra. The technique has been used for the characterization of very complex mixtures.

Sample preparation

Gaseous samples require a sample cell with a long pathlength (typically 5–10 cm), to compensate for the diluteness.

Liquid samples can be sandwiched between two plates of a salt (commonly sodium chloride, or common salt, although a number of other salts such as potassium bromide or calcium fluoride are also used).[1] The plates are transparent to the infrared light and do not introduce any lines onto the spectra.

Solid samples can be prepared in a variety of ways. One common method is to crush the sample with an oily mulling agent (usually Nujol) in a marble or agate mortar, with a pestle. A thin film of the mull is smeared onto salt plates and measured. The second method is to grind a quantity of the sample with a specially purified salt (usually potassium bromide) finely (to remove scattering effects from large crystals). This powder mixture is then pressed in a mechanical press to form a translucent pellet through which the beam of the spectrometer can pass.[1] A third technique is the "cast film" technique, which is used mainly for polymeric materials. The sample is first dissolved in a suitable, non hygroscopic solvent. A drop of this solution is deposited on surface of KBr or NaCl cell. The solution is then evaporated to dryness and the film formed on the cell is analysed directly. Care is important to ensure that the film is not too thick otherwise light cannot pass through. This technique is suitable for qualitative analysis. The final method is to use microtomy to cut a thin (20–100 µm) film from a solid sample. This is one of the most important ways of analysing failed plastic products for example because the integrity of the solid is preserved.

It is important to note that spectra obtained from different sample preparation methods will look slightly different from each other due to differences in the samples' physical states.

Comparing to a reference

Schematics of a two-beam absorption spectrometer. A beam of infrared light is produced, passed through an interferometer (not shown), and then split into two separate beams. One is passed through the sample, the other passed through a reference. The beams are both reflected back towards a detector, however first they pass through a splitter, which quickly alternates which of the two beams enters the detector. The two signals are then compared and a printout is obtained. This "two-beam" setup gives accurate spectra even if the intensity of the light source drifts over time.

To take the infrared spectrum of a sample, it is necessary to measure both the sample and a "reference" (or "control"). This is because each measurement is affected by not only the light- absorption properties of the sample, but also the properties of the instrument (for example, what light source is used, what detector is used, etc.). The reference measurement makes it possible to eliminate the instrument influence. Mathematically, the sample transmission spectrum is divided by the reference transmission spectrum.

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The appropriate "reference" depends on the measurement and its goal. The simplest reference measurement is to simply remove the sample (replacing it by air). However, sometimes a different reference is more useful. For example, if the sample is a dilute solute dissolved in water in a beaker, then a good reference measurement might be to measure pure water in the same beaker. Then the reference measurement would cancel out not only all the instrumental properties (like what light source is used), but also the light-absorbing and light-reflecting properties of the water and beaker, and the final result would just show the properties of the solute (at least approximately).

A common way to compare to a reference is sequentially: First measure the reference, then replace the reference by the sample, then measure the sample. This technique is not perfectly reliable: If the infrared lamp is a bit brighter during the reference measurement, then a bit dimmer during the sample measurement, the measurement will be distorted. More elaborate methods, such as a "two-beam" setup (see figure), can correct for these types of effects to give very accurate results.

FTIR

Main article: Fourier transform infrared spectroscopy

An interferogram from an FTIR measurement. The horizontal axis is the position of the mirror, and the vertical axis is the amount of light detected. This is the "raw data" which can be Fourier transformed to get the actual spectrum.

Fourier transform infrared (FTIR) spectroscopy is a measurement technique that allows one to record infrared spectra. Infrared light is guided through an interferometer and then through the sample (or vice versa). A moving mirror inside the apparatus alters the distribution of infrared light that passes through the interferometer. The signal directly recorded, called an "interferogram", represents light output as a function of mirror position. A data-processing technique called Fourier transform turns this raw data into the desired result (the sample's spectrum): Light output as a function of infrared wavelength (or equivalently, wavenumber). As described above, the sample's spectrum is always compared to a reference.

There is an alternate method for taking spectra (the "dispersive" or "scanning monochromator" method), where one wavelength at a time passes through the sample. The dispersive method is more common in UV-Vis spectroscopy, but is less practical in the infrared than the FTIR method. One reason that FTIR is favored is called "Fellgett's advantage" or the "multiplex advantage": The information at all frequencies is collected simultaneously, improving both speed and signal-to-noise ratio. Another is called "Jacquinot's Throughput Advantage": A dispersive measurement requires detecting much lower light levels than an FTIR measurement.[2] There are other advantages, as well as some disadvantages,[2] but virtually all modern infrared spectrometers are FTIR instruments.

Absorption bands Main article: Infrared Spectroscopy Correlation Table

Wavenumbers listed in cm−1.

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Uses and applications

Infrared spectroscopy is widely used in both research and industry as a simple and reliable technique for measurement, quality control and dynamic measurement. It is also used in forensic analysis in both criminal and civil cases, enabling identification of polymer degradation for example.

The instruments are now small, and can be transported, even for use in field trials. With increasing technology in computer filtering and manipulation of the results, samples in solution can now be measured accurately (water produces a broad absorbance across the range of interest, and thus renders the spectra unreadable without this computer treatment). Some instruments will also automatically tell you what substance is being measured from a store of thousands of reference spectra held in storage.

By measuring at a specific frequency over time, changes in the character or quantity of a particular bond can be measured. This is especially useful in measuring the degree of polymerization in polymer manufacture. Modern research instruments can take infrared measurements across the whole range of interest as frequently as 32 times a second. This can be done whilst simultaneous measurements are made using other techniques. This makes the observations of chemical reactions and processes quicker and more accurate.

Infrared spectroscopy has been highly successful for applications in both organic and inorganic chemistry. Infrared spectroscopy has also been successfully utilized in the field of semiconductor microelectronics:[3] for example, infrared spectroscopy can be applied to semiconductors like silicon, gallium arsenide, gallium nitride, zinc selenide, amorphous silicon, silicon nitride, etc.

Isotope effects

The different isotopes in a particular species may give fine detail in infrared spectroscopy. For example, the O–O stretching frequency (in reciprocal centimeters) of oxyhemocyanin is experimentally determined to be 832 and 788 cm−1 for ν(16O–16O) and ν(18O–18O), respectively.

By considering the O–O bond as a spring, the wavenumber of absorbance, ν can be calculated:

where k is the spring constant for the bond, c is the speed of light, and μ is the reduced mass of the A–B system:

(mi is the mass of atom i).

The reduced masses for 16O–16O and 18O–18O can be approximated as 8 and 9 respectively. Thus

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Where ν is the wavenumber; [wavenumber = frequency/(speed of light)]

The effect of isotopes, both on the vibration and the decay dynamics, has been found to be stronger than previously thought. In some systems, such as silicon and germanium, the decay of the anti-symmetric stretch mode of interstitial oxygen involves the symmetric stretch mode with a strong isotope dependence. For example, it was shown that for a natural silicon sample, the lifetime of the anti-symmetric vibration is 11.4 ps. When the isotope of one of the silicon atoms is increased to 29Si, the lifetime increases to 19 ps. In similar manner, when the silicon atom is changed to 30Si, the lifetime becomes 27 ps.[4]

Two-dimensional IR

Two-dimensional infrared correlation spectroscopy analysis is the application of 2D correlation analysis on infrared spectra. By extending the spectral information of a perturbed sample, spectral analysis is simplified and resolution is enhanced. The 2D synchronous and 2D asynchronous spectra represent a graphical overview of the spectral changes due to a perturbation (such as a changing concentration or changing temperature) as well as the relationship between the spectral changes at two different wavenumbers.

Main article: Two-dimensional infrared spectroscopy

Pulse Sequence used to obtain a two-dimensional Fourier transform infrared spectrum. The time period τ1 is usually referred to as the coherence time and the second time period τ2 is known as the waiting time. The excitation frequency is obtained by Fourier transforming along the τ1 axis.

Nonlinear two-dimensional infrared spectroscopy[5][6] is the infrared version of correlation spectroscopy. Nonlinear two-dimensional infrared spectroscopy is a technique that has become available with the development of femtosecond infrared laser pulses. In this experiment, first a set of pump pulses are applied to the sample. This is followed by a waiting time, wherein the system is allowed to relax. The typical waiting time lasts from zero to several picoseconds, and the duration can be controlled with a resolution of tens of femtoseconds. A probe pulse is then applied resulting in the emission of a signal from the sample. The nonlinear two-dimensional infrared spectrum is a two-dimensional correlation plot of the frequency ω1 that was excited by the initial pump pulses and the frequency ω3 excited by the probe pulse after the waiting time. This allows the observation of coupling between different vibrational modes; because of its extremely high time resolution, it can be used to monitor molecular dynamics on a picosecond timescale. It is still a largely unexplored technique and is becoming increasingly popular for fundamental research.

As with two-dimensional nuclear magnetic resonance (2DNMR) spectroscopy, this technique spreads the spectrum in two dimensions and allows for the observation of cross peaks that contain information on the coupling between different modes. In contrast to 2DNMR, nonlinear two-dimensional infrared spectroscopy also involves the excitation to overtones. These excitations result in excited state absorption peaks located below the diagonal and cross peaks. In 2DNMR, two distinct techniques, COSY and NOESY, are frequently used. The cross peaks in the first are related to the scalar coupling, while in the later they are related to the spin transfer between different nuclei. In nonlinear two-dimensional infrared spectroscopy, analogs have been drawn to these 2DNMR techniques. Nonlinear two- dimensional infrared spectroscopy with zero waiting time corresponds to COSY, and nonlinear two-dimensional infrared spectroscopy with finite waiting time allowing vibrational 106 population transfer corresponds to NOESY. The COSY variant of nonlinear two-dimensional infrared spectroscopy has been used for determination of the secondary structure content proteins.[7]

References

1. ^ a b Laurence M. Harwood, Christopher J. Moody (1989). Experimental organic chemistry: Principles and Practice (Illustrated ed.). Wiley-Blackwell. p. 292. ISBN 0632020172. 2. ^ a b Chromatography/Fourier transform infrared spectroscopy and its applications, by Robert White, p7 3. ^ Lau, W.S. (1999). Infrared characterization for microelectronics. World Scientific. ISBN 9810223528. http://books.google.com/?id=rotNlJDFJWsC&printsec=frontcover. 4. ^ Kohli, K.; Davies, Gordon; Vinh, N.; West, D.; Estreicher, S.; Gregorkiewicz, T.; Izeddin, I.; Itoh, K. (2006). "Isotope Dependence of the Lifetime of the 1136-cm-1 Vibration of Oxygen in Silicon". Physical Review Letters 96 (22): 225503. doi:10.1103/PhysRevLett.96.225503. PMID 16803320. 5. ^ P. Hamm, M. H. Lim, R. M. Hochstrasser (1998). "Structure of the amide I band of peptides measured by femtosecond nonlinear-infrared spectroscopy". J. Phys. Chem. B 102: 6123. doi:10.1021/jp9813286. 6. ^ S. Mukamel (2000). "Multidimensional Fentosecond Correlation Spectroscopies of Electronic and Vibrational Excitations". Annual Review of Physics and Chemistry 51: 691. doi:10.1146/annurev.physchem.51.1.691. PMID 11031297. 7. ^ N. Demirdöven, C. M. Cheatum, H. S. Chung, M. Khalil, J. Knoester, A. Tokmakoff (2004). "Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary structure". Journal of the American Chemical Society 126 (25): 7981. doi:10.1021/ja049811j. PMID 15212548.

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Ultraviolet–visible spectroscopy

Beckman DU640 UV/Vis spectrophotometer.

Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry (UV-Vis or UV/Vis) refers to absorption spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent (near-UV and near-infrared (NIR)) ranges. The absorption in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum, molecules undergo electronic transitions. This technique is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.[1]

Applications

An example of a UV/Vis readout

UV/Vis spectroscopy is routinely used in the quantitative determination of solutions of transition metal ions and highly conjugated organic compounds.

• Solutions of transition metal ions can be colored (i.e., absorb visible light) because d electrons within the metal atoms can be excited from one electronic state to another. The colour of metal ion solutions is strongly affected by the presence of other species, such as certain anions or ligands. For instance, the colour of a dilute solution of copper sulfate is a very light blue; adding ammonia intensifies the colour and changes the wavelength of maximum absorption (λmax). • Organic compounds, especially those with a high degree of conjugation, also absorb light in the UV or visible regions of the electromagnetic spectrum. The solvents for these determinations are often water for water soluble compounds, or ethanol for organic-soluble compounds. (Organic solvents may have significant UV absorption; not all solvents are suitable for use in UV spectroscopy. Ethanol absorbs very weakly at most wavelengths.) Solvent polarity and pH can affect the absorption spectrum of an organic compound. Tyrosine, for example, increases in absorption maxima and molar extinction coefficient when pH increases from 6 to 13 or when solvent polarity decreases. • While charge transfer complexes also give rise to colours, the colours are often too intense to be used for quantitative measurement.

The Beer-Lambert law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species in the solution and the path length. Thus, for a fixed path length, UV/Vis spectroscopy can be used to determine the concentration of the absorber in a solution. It is necessary to know how quickly the absorbance changes with concentration. This can be taken from references (tables of molar extinction coefficients), or more accurately, determined from a calibration curve. 108

A UV/Vis spectrophotometer may be used as a detector for HPLC. The presence of an analyte gives a response assumed to be proportional to the concentration. For accurate results, the instrument's response to the analyte in the unknown should be compared with the response to a standard; this is very similar to the use of calibration curves. The response (e.g., peak height) for a particular concentration is known as the response factor.

The wavelengths of absorption peaks can be correlated with the types of bonds in a given molecule and are valuable in determining the functional groups within a molecule. The Woodward-Fieser rules, for instance, are a set of empirical observations used to predict λmax, the wavelength of the most intense UV/Vis absorption, for conjugated organic compounds such as dienes and ketones. The spectrum alone is not, however, a specific test for any given sample. The nature of the solvent, the pH of the solution, temperature, high electrolyte concentrations, and the presence of interfering substances can influence the absorption spectrum. Experimental variations such as the slit width (effective bandwidth) of the spectrophotometer will also alter the spectrum. To apply UV/Vis spectroscopy to analysis, these variables must be controlled or accounted for in order to identify the substances present.

Beer-Lambert law Main article: Beer-Lambert law

The method is most often used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer-Lambert law:

−, where A is the measured absorbance, I0 is the intensity of the incident light at a given wavelength, I is the transmitted intensity, L the pathlength through the sample, and c the concentration of the absorbing species. For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, and has units of 1 / M * cm or often AU / M * cm.

The absorbance and extinction ε are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm.

The Beer-Lambert Law is useful for characterizing many compounds but does not hold as a universal relationship for the concentration and absorption of all substances. A 2nd order polynomial relationship between absorption and concentration is sometimes encountered for very large, complex molecules such as organic dyes (Xylenol Orange or Neutral Red, for example).

Practical considerations

The Beer-Lambert law has implicit assumptions that must be met experimentally for it to apply. For instance, the chemical makeup and physical environment of the sample can alter its extinction coefficient. The chemical and physical conditions of a test sample therefore must match reference measurements for conclusions to be valid.

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Spectral bandwidth

A given spectrometer has a spectral bandwidth that characterizes how monochromatic the light is. If this bandwidth is comparable to the width of the absorption features, then the measured extinction coefficient will be altered. In most reference measurements, the instrument bandwidth is kept below the width of the spectral lines. When a new material is being measured, it may be necessary to test and verify if the bandwidth is sufficiently narrow. Reducing the spectral bandwidth will reduce the energy passed to the detector and will, therefore, require a longer measurement time to achieve the same signal to noise ratio.

Wavelength error

In liquids, the extinction coefficient usually changes slowly with wavelength. A peak of the absorbance curve (a wavelength where the absorbance reaches a maximum) is where the rate of change in absorbance with wavelength is smallest. Measurements are usually made at a peak to minimize errors produced by errors in wavelength in the instrument, that is errors due to having a different extinction coefficient than assumed.

Stray light See also: Stray light

Another important factor is the purity of the light used. The most important factor affecting this is the stray light level of the monochromator [2] . The detector used is broadband, it responds to all the light that reaches it. If a significant amount of the light passed through the sample contains wavelengths that have much lower extinction coefficients than the nominal one, the instrument will report an incorrectly low absorbance. Any instrument will reach a point where an increase in sample concentration will not result in an increase in the reported absorbance, because the detector is simply responding to the stray light. In practice the concentration of the sample or the optical path length must be adjusted to place the unknown absorbance within a range that is valid for the instrument. Sometimes an empirical calibration function is developed, using known concentrations of the sample, to allow measurements into the region where the instrument is becoming non-linear.

As a rough guide, an instrument with a single monochromator would typically have a stray light level corresponding to about 3 AU, which would make measurements above about 2 AU problematic. A more complex instrument with a double monochromator would have a stray light level corresponding to about 6 AU, which would therefore allow measuring a much wider absorbance range.

Absorption flattening

At sufficiently high concentrations, the absorption bands will saturate and show absorption flattening. The absorption peak appears to flatten because close to 100% of the light is already being absorbed. The concentration at which this occurs depends on the particular compound being measured. One test that can be used to test for this effect is to vary the path length of the measurement. In the Beer-Lambert law, varying concentration and path length has an equivalent effect—diluting a solution by a factor of 10 has the same effect as shortening the path length by a factor of 10. If cells of different path lengths are available, testing if this relationship holds true is one way to judge if absorption flattening is occurring.

110

Solutions that are not homogeneous can show deviations from the Beer-Lambert law because of the phenomenon of absorption flattening. This can happen, for instance, where the absorbing substance is located within suspended particles.[3] The deviations will be most noticeable under conditions of low concentration and high absorbance. The reference describes a way to correct for this deviation.

Ultraviolet-visible spectrophotometer

The instrument used in ultraviolet-visible spectroscopy is called a UV/Vis spectrophotometer. It measures the intensity of light passing through a sample (I), and compares it to the intensity of light before it passes through the sample (Io). The ratio I / Io is called the transmittance, and is usually expressed as a percentage (%T). The absorbance, A, is based on the transmittance:

A = − log(%T / 100%)

The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction grating or monochromator to separate the different wavelengths of light, and a detector. The radiation source is often a Tungsten filament (300-2500 nm), a deuterium arc lamp, which is continuous over the ultraviolet region (190-400 nm)— or more recently, light emitting diodes (LED) and Xenon arc lamps[4] for the visible wavelengths. The detector is typically a photodiode or a CCD. Photodiodes are used with monochromators, which filter the light so that only light of a single wavelength reaches the detector. Diffraction gratings are used with CCDs, which collects light of different wavelengths on different pixels.

Diagram of a single-beam UV/Vis spectrophotometer.

A spectrophotometer can be either single beam or double beam. In a single beam instrument (such as the Spectronic 20), all of the light passes through the sample cell. Io must be measured by removing the sample. This was the earliest design, but is still in common use in both teaching and industrial labs.

In a double-beam instrument, the light is split into two beams before it reaches the sample. One beam is used as the reference; the other beam passes through the sample. The reference beam intensity is taken as 100% Transmission (or 0 Absorbance), and the measurement displayed is the ratio of the two beam intensities. Some double-beam instruments have two detectors (photodiodes), and the sample and reference beam are measured at the same time. In other instruments, the two beams pass through a beam chopper, which blocks one beam at a time. The detector alternates between measuring the sample beam and the reference beam in synchronism with the chopper. There may also be one or more dark intervals in the chopper cycle. In this case the measured beam intensities may be corrected by subtracting the intensity measured in the dark interval before the ratio is taken.

Samples for UV/Vis spectrophotometry are most often liquids, although the absorbance of gases and even of solids can also be measured. Samples are typically placed in a transparent cell, known as a cuvette. Cuvettes are typically rectangular in shape, commonly with an internal width of 1 cm. (This width becomes the path length, L, in the Beer-Lambert law.) Test tubes can also be used as cuvettes in some instruments. The type of sample container used must allow radiation to pass over the spectral region of interest. The most widely applicable cuvettes are made of high quality fused silica or quartz glass because these are 111 transparent throughout the UV, visible and near infrared regions. Glass and plastic cuvettes are also common, although glass and most plastics absorb in the UV, which limits their usefulness to visible wavelengths.[5]

A complete spectrum of the absorption at all wavelengths of interest can often be produced directly by a more sophisticated spectrophotometer. In simpler instruments the absorption is determined one wavelength at a time and then compiled into a spectrum by the operator. A standardized spectrum is formed by removing the concentration dependence and determining the extinction coefficient (ε) as a function of wavelength.

Notes

1. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole. 2007, 169-173. 2. ^ "Beer's Law - Alisdair Boraston". http://www.brewingtechniques.com/brewingtechniques/beerslaw/boraston.html. Retrieved 2009-02-06. 3. ^ Wittung, Pernilla; Johan Kajanus, Mikael Kubista, Bo G. Malmström (8 August 1994). "Absorption flattening in the optical spectra of liposome-entrapped substances" (pdf). FEBS_Lett_352_37_1994.pdf (application/pdf Object). http://www.img.cas.cz/ge/FEBS_Lett_352_37_1994.pdf. Retrieved 2009-02-06. 4. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole. 2007, 349-351. 5. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole. 2007, 35 NMR spectroscopy

A 900MHz NMR instrument with a 21.2 T magnet at HWB-NMR, Birmingham, UK

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique that exploits the magnetic properties of certain nuclei. For details regarding this phenomenon and its origins, refer to the nuclear magnetic resonance article. The most important applications for the organic chemist are proton NMR and carbon- 13 NMR spectroscopy. In principle, NMR is applicable to any nucleus possessing spin.

Many types of information can be obtained from an NMR spectrum. Much like using infrared spectroscopy (IR) to identify functional groups, analysis of a NMR spectrum provides information on the number and type of chemical entities in a molecule. However, NMR provides much more information than IR.

The impact of NMR spectroscopy on the natural sciences has been substantial. It can, among other things, be used to study mixtures of analytes, to understand dynamic effects such as change in temperature and reaction mechanisms, and is an invaluable tool in understanding protein and nucleic acid structure and function. It can be applied to a wide variety of samples, both in the solution and the solid state.

112

Contents

Basic NMR techniques

The NMR sample is prepared in a thin-walled glass tube - an NMR tube.

When placed in a magnetic field, NMR active nuclei (such as 1H or 13C) absorb at a frequency characteristic of the isotope. The resonant frequency, energy of the absorption and the intensity of the signal are proportional to the strength of the magnetic field. For example, in a 21 tesla magnetic field, protons resonate at 900 MHz. It is common to refer to a 21 T magnet as a 900 MHz magnet, although different nuclei resonate at a different frequency at this field strength.

In the Earth's magnetic field the same nuclei resonate at audio frequencies. This effect is used in Earth's field NMR spectrometers and other instruments. Because these instruments are portable and inexpensive, they are often used for teaching and field work.

Chemical shift

Main article: Chemical shift

Depending on the local chemical environment, different protons in a molecule resonate at slightly different frequencies. Since both this frequency shift and the fundamental resonant frequency are directly proportional to the strength of the magnetic field, the shift is converted into a field-independent dimensionless value known as the chemical shift. The chemical shift is reported as a relative measure from some reference resonance frequency. (For the nuclei 1H, 13C, and 29Si, TMS (tetramethylsilane) is commonly used as a reference.) This difference between the frequency of the signal and the frequency of the reference is divided by frequency of the reference signal to give the chemical shift. The frequency shifts are extremely small in comparison to the fundamental NMR frequency. A typical frequency shift might be 100 Hz, compared to a fundamental NMR frequency of 100 MHz, so the chemical shift is generally expressed in parts per million (ppm).[1] To detect such small frequency differences the applied magnetic field must be constant throughout the sample volume. High resolution NMR spectrometers use shims to adjust the homogeneity of the magnetic field to parts per billion (ppb) in a volume of a few cubic centimeters.

By understanding different chemical environments, the chemical shift can be used to obtain some structural information about the molecule in a sample. The conversion of the raw data to this information is called assigning the spectrum. For example, for the 1H-NMR spectrum for ethanol (CH3CH2OH), one would expect three specific signals at three specific chemical shifts: one for the CH3 group, one for the CH2 group and one for the OH group. A typical CH3 group has a shift around 1 ppm, a CH2 attached to an OH has a shift of around 4 ppm and an OH has a shift around 2–3 ppm depending on the solvent used.

Because of molecular motion at room temperature, the three methyl protons average out during the course of the NMR experiment (which typically requires a few ms). These protons become degenerate and form a peak at the same chemical shift. 113

The shape and size of peaks are indicators of chemical structure too. In the example above— the proton spectrum of ethanol—the CH3 peak would be three times as large as the OH. Similarly the CH2 peak would be twice the size of the OH peak but only 2/3 the size of the CH3 peak.

Modern analysis software allows analysis of the size of peaks to understand how many protons give rise to the peak. This is known as integration—a mathematical process which calculates the area under a curve. The analyst must integrate the peak and not measure its height because the peaks also have width—and thus its size is dependent on its area not its height. However, it should be mentioned that the number of protons, or any other observed nucleus, is only proportional to the intensity, or the integral, of the NMR signal, in the very simplest one-dimensional NMR experiments. In more elaborate experiments, for instance, experiments typically used to obtain carbon-13 NMR spectra, the integral of the signals depends on the relaxation rate of the nucleus, and its scalar and dipolar coupling constants. Very often these factors are poorly known - therefore, the integral of the NMR signal is very difficult to interpret in more complicated NMR experiments.

J-coupling

Main article: J-coupling Some of the most useful information for structure Multiplicity Intensity Ratio determination in a one-dimensional NMR spectrum comes Singlet (s) 1 from J-coupling or scalar coupling (a special case of spin- spin coupling) between NMR active nuclei. This coupling Doublet (d) 1:1 arises from the interaction of different spin states through the Triplet (t) 1:2:1 chemical bonds of a molecule and results in the splitting of Quartet (q) 1:3:3:1 NMR signals. These splitting patterns can be complex or Quintet 1:4:6:4:1 simple and, likewise, can be straightforwardly interpretable or Sextet 1:5:10:10:5:1 deceptive. This coupling provides detailed insight into the connectivity of atoms in a molecule. Septet 1:6:15:20:15:6:1

Coupling to n equivalent (spin ½) nuclei splits the signal into a n+1 multiplet with intensity ratios following Pascal's triangle as described on the right. Coupling to additional spins will lead to further splittings of each component of the multiplet e.g. coupling to two different spin ½ nuclei with significantly different coupling constants will lead to a doublet of doublets (abbreviation: dd). Note that coupling between nuclei that are chemically equivalent (that is, have the same chemical shift) has no effect of the NMR spectra and couplings between nuclei that are distant (usually more than 3 bonds apart for protons in flexible molecules) are usually too small to cause observable splittings. Long-range couplings over more than three bonds can often be observed in cyclic and aromatic compounds, leading to more complex splitting patterns.

For example, in the proton spectrum for ethanol described above, the CH3 group is split into a triplet with an intensity ratio of 1:2:1 by the two neighboring CH2 protons. Similarly, the CH2 is split into a quartet with an intensity ratio of 1:3:3:1 by the three neighboring CH3 protons. In principle, the two CH2 protons would also be split again into a doublet to form a doublet of quartets by the hydroxyl proton, but intermolecular exchange of the acidic hydroxyl proton often results in a loss of coupling information.

Coupling to any spin ½ nuclei such as phosphorus-31 or fluorine-19 works in this fashion (although the magnitudes of the coupling constants may be very different). But the splitting patterns differ from those described above for nuclei with spin greater than ½ because the spin 114 quantum number has more than two possible values. For instance, coupling to deuterium (a spin 1 nucleus) splits the signal into a 1:1:1 triplet because the spin 1 has three spin states. Similarly, a spin 3/2 nucleus splits a signal into a 1:1:1:1 quartet and so on.

Coupling combined with the chemical shift (and the integration for protons) tells us not only about the chemical environment of the nuclei, but also the number of neighboring NMR active nuclei within the molecule. In more complex spectra with multiple peaks at similar chemical shifts or in spectra of nuclei other than hydrogen, coupling is often the only way to distinguish different nuclei.

Second-order (or strong) coupling

The above description assumes that the coupling constant is small in comparison with the difference in NMR frequencies between the inequivalent spins. If the shift separation decreases (or the coupling strength increases), the multiplet intensity patterns are first distorted, and then become more complex and less easily analyzed (especially if more than two spins are involved). Intensification of some peaks in a multiplet is achieved at the expense of the remainder, which sometimes almost disappear in the background noise, although the integrated area under the peaks remains constant. In most high-field NMR, however, the distortions are usually modest and the characteristic distortions (roofing) can in fact help to identify related peaks.

Second-order effects decrease as the frequency difference between multiplets increases, so that high-field (i.e. high-frequency) NMR spectra display less distortion than lower frequency spectra. Early spectra at 60 MHz were more prone to distortion than spectra from later machines typically operating at frequencies at 200 MHz or above.

Magnetic inequivalence

More subtle effects can occur if chemically equivalent spins (i.e. nuclei related by symmetry and so having the same NMR frequency) have different coupling relationships to external spins. Spins that are chemically equivalent but are not indistinguishable (based on their coupling relationships) are termed magnetically inequivalent. For example, the 4 H sites of 1,2-dichlorobenzene divide into two chemically equivalent pairs by symmetry, but an individual member of one of the pairs has different couplings to the spins making up the other pair. Magnetic inequivalence can lead to highly complex spectra which can only be analyzed by computational modeling. Such effects are more common in NMR spectra of aromatic and other non-flexible systems, while conformational averaging about C-C bonds in flexible molecules tends to equalize the couplings between protons on adjacent carbons, reducing problems with magnetic inequivalence.

Correlation spectroscopy

Correlation spectroscopy is one of several types of two-dimensional nuclear magnetic resonance (NMR) spectroscopy or 2D-NMR. This type of NMR experiment is best known by its acronym, COSY. Other types of two-dimensional NMR include J-spectroscopy, exchange spectroscopy (EXSY), Nuclear Overhauser effect spectroscopy (NOESY), total correlation spectroscopy (TOCSY) and heteronuclear correlation experiments, such as HSQC, HMQC, and HMBC. Two-dimensional NMR spectra provide more information about a molecule than one-dimensional NMR spectra and are especially useful in determining the structure of a molecule, particularly for molecules that are too complicated to work with using one- 115 dimensional NMR. The first two-dimensional experiment, COSY, was proposed by Jean Jeener, a professor at Université Libre de Bruxelles, in 1971[citation needed]. This experiment was later implemented by Walter P. Aue, Enrico Bartholdi and Richard R. Ernst, who published their work in 1976.[2]

Solid-state nuclear magnetic resonance

A variety of physical circumstances does not allow molecules to be studied in solution, and at the same time not by other spectroscopic techniques to an atomic level, either. In solid-phase media, such as crystals, microcrystalline powders, gels, anisotropic solutions, etc., it is in particular the dipolar coupling and chemical shift anisotropy that become dominant to the behaviour of the nuclear spin systems. In conventional solution-state NMR spectroscopy, these additional interactions would lead to a significant broadening of spectral lines. A variety of techniques allows to establish high-resolution conditions, that can, at least for 13C spectra, be comparable to solution-state NMR spectra.

Two important concepts for high-resolution solid-state NMR spectroscopy are the limitation of possible molecular orientation by sample orientation, and the reduction of anisotropic nuclear magnetic interactions by sample spinning. Of the latter approach, fast spinning around the magic angle is a very prominent method, when the system comprises spin 1/2 nuclei. A number of intermediate techniques, with samples of partial alignment or reduced mobility, is currently being used in NMR spectroscopy.

Applications in which solid-state NMR effects occur are often related to structure investigations on membrane proteins, protein fibrils or all kinds of polymers, and chemical analysis in inorganic chemistry, but also include "exotic" applications like the plant leaves and fuel cells.

NMR spectroscopy applied to proteins Main article: Protein nuclear magnetic resonance spectroscopy

Much of the recent innovation within NMR spectroscopy has been within the field of protein NMR, which has become a very important technique in structural biology. One common goal of these investigations is to obtain high resolution 3-dimensional structures of the protein, similar to what can be achieved by X-ray crystallography. In contrast to X-ray crystallography, NMR is primarily limited to relatively small proteins, usually smaller than 35 kDa, though technical advances allow ever larger structures to be solved. NMR spectroscopy is often the only way to obtain high resolution information on partially or wholly intrinsically unstructured proteins. It is now a common tool for the determination of Conformation Activity Relationships where the structure before and after interaction with, for example, a drug candidate is compared to its known biochemical activity. Proteins are orders of magnitude larger than the small organic molecules discussed earlier in this article, but the basic NMR techniques and some of the NMR theory also applies. Because of the much higher number of atoms present in a protein molecule in comparison with a small organic compound, the basic 1D spectra become crowded with overlapping signals to an extent where direct spectra analysis becomnes untenable. Therefore, multidimensional (2, 3 or 4D) experiments have been devised to deal with this problem. To facilitate these experiments, it is desirable to isotopically label the protein with 13C and 15N because the predominant naturally occurring isotope 12C is not NMR-active, whereas the nuclear quadrupole moment of the predominant naturally occurring 14N isotope prevents high resolution information to be obtained from this nitrogen isotope. The most important method used for structure determination of proteins 116 utilizes NOE experiments to measure distances between pairs of atoms within the molecule. Subsequently, the obtained distances are used to generate a 3D structure of the molecule by solving a distance geometry problem.

117

Laboratories of Organic Chemistry

Work A

Cleaning of organic substances by crystallization

ROLE: Selecting suitable solvent for crystallization and recrystallized unknown organic substances.

OBJECTIVE: To learn the correct technique for crystallising substances.

PRINCIPLE OF WORK: See Section 2.4 Add:

Area of life, and brief description of the crystallization properties of solvents selected for crystallization

WORKING PROCEDURE

1. Selection of a suitable solvent for crystallization: Approximately 0.1 grams of a model substance for crystallization is gradually mixed in tubes with 0.5 to 1 ml solvent, room temperature (dropwise addition) and is gradually heated to boiling.

The solvent is suitable for crystallization: -

if the substance is dissolved in 1 ml of solvent at room temperature or under moderate heating - if the substance is dissolved by boiling or by adding another 2 ml solvent - if the substance is dissolved at the boiling point solvent, but after cooling exclude crystals, respectively. is not precluded by strong supercooling (ice-NaCl-water), shaking the walls peel rod tube below the surface of the solution The solvent is suitable for crystallization: - if the substance is in the hot solvent-soluble and cooling the solution, the crystals only where the substance is well soluble at room temperature in a solvent and a minimum, may be the crystallization of this sample use a mixture of these solvents. Solvents must be miscible with each other.

2. Build your apparatus as shown.

Fig. 1 Apparatus for the crystallization of organic substances from different solvent A - B electric Bank - the condenser (Liebig, ball) C - D Bath - cooker

3. Practical implementation of the crystallization residue tested sample is weighed (too large crystals are broken), transferred to a flask and add a small amount (about 10 ml) of the selected solvent. In the crystallization of water only built on a boiling beaker. Content Bank (after adding boiling chips) is heated (usually in a water bath), stirring occasionally until boiling. The water level in the bath should be taking about 0.5 cm below the surface of the solution in the bank to its walls exclude crystallized substance. If the substance in that quantity of solvent at the boiling point to dissolve, add more gradually through the cooler (measured) amount of solvent to obtain a saturated solution at boiling point. For reasons of practical implementation of the crystallization is recommended that this solution slightly diluted The de-inking, clean and clarifying solution (after it cooled very marginal) to him Rida charcoal (1 / 50 to 1 / 20 weight of the sample). P contents of the flask boil 2-3 minutes. Hot is filtered (through a folded filter) into a beaker and allowed to cool gradually. If that does not exclude the filtrate from the solid, the filtrate vessel is immersed in a cooling bath (ice-NaCl-water), scratch beneath the surface of vessel wall solution, esp. be used other ways of crystallization (Chapter 2.4.3). r precipitated crystals are separated from the filtrate by suction (the residue in the flask is washed first share fitr), washed on filter with cold solvent and dried in air. L pieces over and consider the calculate the force of crystallization. If the substance in the amount of solvent to dissolve at the boiling point, add progressively cooler over other (measured) amount of solvent to obtain a saturated solution at boiling point. For reasons of practical implementation of the crystallization is recommended that this solution slightly diluted If it is necessary to crystallize the substance from a mixture of solvents proceed as follows: For almost boiling solution of the substance in a small amount of solvent in which the substance dissolves well, and gradually added to a permanent haze hot solvent in which the substance is insoluble or poorly soluble. Turbidity to remove the heating, or adding a few drops of the first reagent. Next, we proceed as in the above example by adding activated charcoal and subsequent laboratory operations as described. R precipitated crystals are separated from the filtrate by suction (the residue in the flask is washed first share fitr), washed on filter with cold solvent and dried in air . L pieces over to consider and calculate the force of crystallization. If the substance in the amount of solvent to dissolve at the boiling point, add progressively cooler over the other (measured) amount of solvent to obtain a saturated solution at boiling point. For reasons of practical implementation of the crystallization is recommended that this solution slightly diluted.

4. Own knowledge at work:

Solubility of substances in different solvents

+ = Substance is soluble - = insoluble substance

5. Evaluation work

Work B

Separation of organic substances by distillation at atmospheric pressure

ROLE: Separation of a model mixture consist of components with different boiling points. Aim: To obtain data on boiling single fractions, the best to separate the individual components, remains a distillation curve.

PRINCIPLE OF WORK: see chapter 2.5.1 and 2.5.3 Add: Basic terms:

Definition and mathematical expression of the parameters affecting the efficiency of separation: see chapter 2.5.1 and 2.5.3 Complete: Basic concepts:

WORKING PROCEDURE:

1. Assemble the distillation apparatus as shown (Fig. 2)

2. Distillation flask to fill 2 / 3 (up to 3 / 4) volume of the sample. Add 2-3 boiling stones, which will prevent bumping boil.

3. Injected into the water cooler and we start to warm up carefully (if observed var secret, never Do not dispose of boiling stones in superheated liquids. We must remove the heat and wait until the liquid has cooled, and then add boiling stones and continue heating. Otherwise, the liquid contents can surge, thermometer hit of equipment and cause injury and fire)

4. When the sample begins to distil, takes the spirit after 2 ml and shares for each share apiece its boiling point. Of

5 The record also construct a distillation curve as the dependence of boiling bjeme. On the 6th The chart TV subtract individual components and medzifrakcií NB.: A.) An important parameter influencing the quality of the separation of components is heat. Must be a slow, steady and controllable. To heat the distilled samples will be used heating nest, where the temperature is gradually added under the lights on the nest. At the beginning of the heat so we choose to give us light lit up the heating nest, light goes out once again add to the warm- up, but just enough to light lit up again and so we proceed until the entire volume of distilled evydestiluje samples. N b.) distillatively one component of the mixture to a decrease in temperature on the thermometer in the cooler Claisen, slowing and stopping the distillation. This applies only if the force is sufficiently high and cutting fluids in the mixture forming azeotrope see Chap. 2.5.4). (C) distilled off after the second component of the mixture can become the third component has such a high boiling point that exceeds the temperatures reached in the column. In this case the distillation is interrupted, the bath was removed, the flask is cooled and the apparatus was removed by puncture column. The paper then continues with a simplified apparatus. Schematic diagram of apparatus:

Fig. 2 Apparatus for fractional distillation under atmospheric pressure - flask B - puncture column C - Claisen condenser D - E thermometer - measuring cylinder F - heating nest

EVALUATION OF THE TRIAL:

WORK C

Cleaning substances by distillation under reduced pressure

TASK: distillation of a sample with high boiling point components.

OBJECTIVE: To build the apparatus for distillation of organic substances under reduced pressure. Capture a fraction of constant boiling point and using a nomogram to determine the boiling temperature of the collected fractions and atmospheric pressure. Z

WORKS PRINCIPLE:i See chapter 2.5.1 and 2.5.2.2 lowering the pressure of the rectification will reduce the boiling point of components with high boiling points, preventing degradation of substances, and also escape the health damaging fumes in air. Distillation under reduced pressure distillation required in comparison simple changes in an apparatus .

Basic concepts:

Sources vacuum: Safety at work: Due to work with glass sets of the apparatus under vacuum is a real danger of implosion. Therefore throughout the work to protect your eyes or glasses. face shield. WORKING PROCEDURE: 1 Determine the approximate boiling point of an unknown sample of our machinery to measure the boiling point. To the tube for that purpose by the Pasteur pipette is spread over 0.5 cm samples, which you insert into the capillary with a sealed end upwards. Temperature range of the device is set from 120 to 210 ° C and the temperature gradient of 20 ° C (at a time can be measured two Samples). Detailed procedure for measuring the BP, see the work of E. 2 Build the drawing apparatus for distillation under reduced pressure (Fig. 3). In Tavannes forget all ground joints carefully cleaned and painted in their fat. With the third Put on your goggles or face shield and throughout their distillation immediately.

4. Turn on the vacuum pump and sealing apparatus investigate "dry" without pouring samples. Failure to reach the desired pressure reduction is controlled by sealing apparatus away from the pumps to apparatus the fifth After examining the tightness of bank fill up. to half the volume of sample 6. Turn on the vacuum pump and observe the pressure drop gauge. After reaching the desired vacuum begin with heating bath. Using the nomogram and around the TV set device, we will determine at what temperature should distil our sample with a pressure gauge shows us. Then set the bath temperature about 30 ° C or more. If the sample of non-distilled after reaching the set temperature in the bath, gradually adding warm-up in the bath (after 5 to 10 ° C) until the sample begins to distil.

7. During the distillation temperature monitor and check the pressure. After stabilization of temperature and pressure Data write. S 8th After distillation heating is switched off, remove the oil bath apparatus and gently aerate. 9th Turn off the vacuum pump 10. The resulting data back can be determined from a monogram designed t our experimental samples.

Schematic diagram of apparatus:

Fig. 3 distillation apparatus under reduced pressure - magnetic stirrer, oil bath, thermometer B - flask with stirrer C - D Claisen condenser - pressure reducing valve plug or E - Thermometer F - G Alonzo vacuum - Bank of alcohol consumption - connect to the pump

The evaluation experiment: Approximate determination of BP at atmospheric pressure: Expected BP under reduced pressure:

H donate obtained in the distillation under reduced pressure: values calculated from the monogram:

WORK D

Steam distillation and extraction

TASK:

By steam distillation divide mixture of xylene and aniline.

OBJECTIVE: To use the apparatus for steam distillation and know it to practical use in conjunction with a simple chemical reaction. Determine the presence of xylene and aniline mixture model and manage methodology for extraction.

The PRINCIPLE OF WORK: see chapter 2.5.4. Steam distillation 2.7 Extraction 2.7.1. Extraction of particulate matter 2.7.2. Extraction fluid

WORKING PROCEDURE:

1 Assemble the apparatus as shown in the steam distillation (Fig. 4)

2. We have a sample that is a model mixture of xylene and aniline. The two compounds are insoluble in water, shall not be mixed with water, have high tv, that are suitable for steam distillation. Our task is to separate them to each other. Before processing, we measure the volume of sample and place it in the distilling flask.

3 Dilute hydrochloric acid (1:1), using INDICATOR PAPER acidify sample to pH 2 Xylem with hydrochloric acid (HCl) reaction, but gives the lowland HCl anilíniumchlorid. And

Anilínium chloride is a crystalline substance in water-soluble, which doesn’t evaporate with the steam. This allows the separation of xylene.

4. Distillation flask with the sample attached to the apparatus to an acidic environment with steam distilled xylene by distillation receiver. Aniline in the form Aniliniumchloridu remained in the distilling flask dissolved in water. N 5th Distillation flask and cooled slightly by adding conc. NaOH solution (may be added solid NaOH) distillation residue basified to pH 11 to release the aniline salt. z

6. In steam distillation continued until alkaline environment distilled into a second master aniline. D 7 Both distilled saturated NaCl solutions, the resulting layer is separated in a separating funnel. Of the remaining layers of water separately extracted with xylene and aniline in ether. The simplest form of extraction is mixing and separating, it is done in a separating funnel. Before extraction is necessary to examine the tightness of the stopper and tap the funnel. If necessary, tap gently clean it again and then top with grease. Aqueous solution of the substance to extract transferred to a separating funnel and add it to the extraction solvent in an amount of 1 / 3 the volume of extracted solution (in our case only 10 ml ether). Funnel extraction hold with both hands. With one hand, adhering to the stopper and the second tap. Mixture in the funnel shacked slightly, then turn the tap funnel topand opening the resulting pressure will be released. Shake for 1-2 seconds then back in balance and pressure. Repeat the process until no further stops in the funnel formed pressure. Content separating funnel even then thoroughly shaken for a few minutes to contact the two phases was the most perfect. Funnel with a relaxed stopper mounted in rack and let stand until the publication of two sharply defined layers. The bottom layer is deleted from the dropping funnel into a beaker and pour the top layer of dry-mouthed funnel into Adobe. If necessary, the extraction is repeated with fresh portions of solvent. N 8th The combined organics transferred to a dry flask, add the appropriate amount of drying agent (anhydrous Na2SO4), and the bank will conclude with occasional stirring ECHAM stand 5 to 10 min. After drying agent, filtered off. N9. Build a simple distillation apparatus at atmospheric pressure (p. 22) with a magnetic stirrer and oil bath 10. First set the bath temperature to distillatively ether (tv ether 37 ° C) and after ydestilovaní raise the temperature of the bath distillatively xylene (xylene tv 139-140 ° C). At 11 Aniline processed by analogy with the difference that the ether evaporated on a rotary evaporator and pass on aniline as the raw product.

Schematic diagram APPARATUS

Fig. 4 Apparatus for steam distillation A - B nest heating - steam generator C - core tube with olive and D - extension to rain. By steam E - F flask - Liebig condenser G - Alonzo H - collecting vessel

ASSESSMENT AND RECORD ATTEMPT own observations: C Elkova volume model mixture in ml: volume in ml distilled xylene About bjem aniline after evaporation of ether in ml: The ratio of both components in the mixture:

WORK E

Determination of physical constants and chromatography

ROLE: a.) Determine the melting point of solid b.) Determine the boiling point of liquid unknown sample c.) analyzed by thin layer chromatography and mixture model to determine the standards of quality organic ingredients

OBJECTIVE: a.) To master the basic methods for the determination of physicochemical constants characterizing the chemical compound. B.) To master basic techniques of thin layer chromatography

PRINCIPLE OF WORK: see chapter 2.8, 2.8.1, 2.8.2, 2.8.3, 3.1 and 3.2

The melting and boiling point are estimated by Büchi B-540th

Melting point measurement

Procedure P: Preparing the sample to the melting temperature: Granulated crystalline and non-homogeneous samples were first homogenized in a mortar. Capillary for the determination of tt to fill up 4-6 mm. To obtain comparable results it is important that the capillary filled to the same amount, and the sample was compact. Sample is obtained by tapping the capillary on a hard surface A

Approximate Melting temperature:

1 Turn on your device and determine the approximate melting point of our unknown sample. Temperature range of the device is set from 80 to 200 ° C and the temperature gradient of 20 ° C / min. For both samples an approximate indication tt do at once. Detailed description of settings parameters is attached to the device.

2. Measurement start pressing START. The display device will appear graphic design during measurement, which informs about the current phase measurement.

3 The first phase of measurement is Warm-up phase, when the device is heated to the starting temperature (SETPOINT) from which we pursue our sample, in this case 80 ° C. Reaching this temperature and start the next phase of the device notified beep.

4 After the beep, enter one of the samples at the respective positions of the melting temperature of the device (middle three positions) and press START.

5. The next stage is measured by itself t temperature rises at a rate, what the temperature gradient was determined at the beginning. In this case, 20 ° C / min. Through a magnifying glass in the monitor device embedded with capillary samples. When the substance begins to melt, press the corresponding button, with which the position of the first sample in a capillary. When the sample is completely melted, press the button (with the position of the sample) for the second time. Subsequently press STOP button. If you press Stop before it reaches the maximum temperature (MAXPOINT) is necessary to press this button twice, the device began to cool and the initial temperature.

6. After pressing STOP, the display appears at approximately the melting temperature of our samples, which we will record.

The precise determination of melting point:

7. If we can determine the temperature approaching melting point, the whole measurement is repeated so that the capillary preparing two melting temperature of one sample and instrument parameters set so that the initial temperature (SETPOINT) will be about 50 to 10 ° C lower than the approximate determination of the melting point , temperature gradient set to 2 ° C. / min and maximum temperature (MAXPOINT) is automatically set to 15 º C above the initial, the temperature is only confirmation. Make sure that the height of the sample in the capillary was the same and compact

8. Furthermore, longer follow the above procedure and the same way we set the melting point of the second sample.

Determination of BOILING TEMPERATURE

Determination of boiling by Silowopova.

Procedure : Approximate boiling point :

1 first, pulled out three thin capillaries about 10 to 12 cm long, which sealed a oniec.

2 Unknown liquid sample is placed in a microfuge up to 5-10 mm and immersed it into a capillary to the upper end sealed. (Use a Pasteur pipette for easy filling microfuge liquid.)

3. Turn on the device to measure temperature and determine the approximate boiling point of our unknown sample. Temperature range of the device is set from 40 to 150 ° C and the temperature gradient of 20 ° C / min (at a time can be measured two samples, so an approximate indication bv students can do two at once). Detailed description of the parameter settings when the device is attached

4. Measurement start pressing START. The display device will appear graphic showing during measurement, which informs about the current phase measurement.

5 The first phase of measurement is Warm-up phase, when the device is heated to the starting temperature (SETPOINT) from which we pursue our sample, this case 40 ° C. Achieving this temperature and start the next phase of the device notified beep.

6. After the beep, place a sample on one of the positions for measuring the boiling temperature of the device (the two most extreme position) and press START. In the 7th The next stage is determined BP itself temperature rises at a rate, what the temperature gradient was determined at the beginning. In this case, 20 ° C / min. Through a magnifying glass

Fig. 6 Determination of boiling point

The device monitor embedded samples. The boiling point is reached when bubbles begin to escape from the bottom of the capillary rapidly and continuously (see Fig. 6).

Fron the disply read the aproximate point boil one and the second sample and then press STOP button. If you press Stop before it reaches the maximum temperature (MAXPOINT), it is necessary to press this button twice, the device began to cool initial temperature. P P as to the precise determination of boiling point:

8. If we determine the approximate boiling point of the whole measurement is repeated so that the preparing two microfuge our sample parameters and set the device so that the initial temperature (SETPOINT) will be about 5 degrees lower than some specified point, boiling point, the temperature gradient set to 2 ° C / min and maximum temperature (MAXPOINT) is automatically set to 15 ° C higher than the initial, the temperature has only confirmed. Make sure that the Height of liquid in the tubes was the same.

9 Furthermore, longer follow

THIN-LAYER CHROMATOGRAPHY

The qualitative analysis of the model will use a mixture of commercial thin-layer chromatography plates for chromatography with SiO2 layer formed. The composition of the sample can be determined for standard delivery expenses. Of operation: the above procedure. Working procedure:

1. Prepare a solution of the sample examined in that it dissolved in 0.5 ml of ethanol

2. On silufolovej plate using a ruler and a pencil to lightly outline the regions start at a distance of about 1.5 cm from the bottom. The distance between the sample application from the edges of the plate should be about 0.5 to 1 cm

3. Using a fine glass capillary Streak individual samples plate so that the spots not greater than 2-3 mm diameter. Each standard is applied special capillary.

4. Prepare a chromatography chamber, in our conditions, we will serve the beaker covered with watch glass, which is inserted a strip of filter paper placed in a beaker and tenách after reaching its peak.

5 Pour it into the developing solvent mixture so that the water level was about 0.5 cm from the bottom.

6. Chromatogram of sample application put in a chromatographic chamber so that the tart was above the solvent.

7. When rising, the solvent reaches a distance of about 1 cm from the top, chromatogram out of the chamber, mark the solvent front in pencil (the interface between wet and dry part of the plate) and chromatogram let air-dry

8. Separated substances in our sample are colored spots on the chromatogram without visible detection. From the chromatogram of visual evidence of the composition of the samples and confirm dentitu individual components of the standards by comparing their R and F values

9. RF retarding factor is calculated by the formula:

RF = a / b

a = distance from start center spots in cm

b = distance of solvent front from the start in cm

10. When we worked exactly as the standard RF and RF spots in the sample are equal.

Fig. 7 Chromatogram

A - Start

B - Solvent front

Results VALUATION:

Observations on the determination of the melting temperature: melting point samples: Sample # 1 Sample # 2

1...... 1...... 2...... 2…………………….

Observation in determining the boiling point: Temperature boiling samples: Pressure: ...... Boiling Point:

1...... 2nd ......

E VALUATION thin layer chromatography:

Drawing chromatograms:

2

1.5-Diphenyl-1 ,4-pentadiene-3-one (dibenzalacetón) is prepared by condensation of benzaldehyde with acetone in the presence of bases.

Necessary chemicals: 2.65 g benzaldehyde (2.5 ml, 0.25 mol) acetone 0.75 g (1.0 ml, 0.013 mol) ethanol, 20 ml sodium hydroxide

Workflow:

The flask with a magnetic stirrer, mix 25 ml cold 10% solution of NaOH with 20 ml of ethanol. Stirring on a magnetic stirrer are added sequentially 2.5 ml distilled mixture of benzaldehyde and 1.0 ml of acetone. For 15 min. maintain the reaction mixture with stirring at room temperature. The reaction mixture was cooled in a water bath, the precipitated product filtered through a Buchner funnel and washed with cold water until neutral washings. The crude product is purified by crystallization from ethanol with addition of activated charcoal. We obtain yellow crystals with mp ~ 112 ° C.

N-Benzylidénanilín (benzanilín)

is prepared by condensation of benzaldehyde with aniline.

Necessary chemicals: benzaldehyde 3.2 g (0.03 mol) aniline 2.8 g (0.03 mol) ethanol, 5 ml

Workflow:

Banks to place a 3.2 g of benzaldehyde. Within 15 minutes, stirring constantly to it gradually add 2.8 g distilled aniline. The reaction is exothermic. After addition of aniline reaction mixture pour into a beaker and add to it 5 ml of ethanol. Cooling the reaction mixture in an ice bath to exclude the product crystals, which evacuated and dried. The crude product crystallized from ethanol. Tem of product is 52 ° C

Brombutan is prepared by the action of a mixture of sodium bromide and sulfuric acid to butane-1-ol.

Necessary chemicals: butane-1-ol 11.2 g (0.15 mol) NaBr 17.8 g (0.17 mol) of sulfuric acid concentration. 15 ml NaHCO3, Na2SO4

Preparation:

The Bank NaBr Dissolve 17.8 g in 20 ml of water and add to it distilled butane-1-ol. Stirring slowly add 15 ml conc. sulfuric acid when the reaction temperature rises above 90 ° C, contents of the flask cool down in a water bath. After adding the whole amount, we will give the bank a magnetic stirring bar and reflux with continuous vigorous stirring the mixture is heated in an oil bath at t reaction mixture (about 130 ° C in bath) for 1 hour. If we do not work in the hood, we modify the apparatus so that the unreacted bromo-hydrogen leaking into the air. On the upper end of the radiator hose to water the funnel, the extended part is immersed in a beaker of water, just below the surface. After an hour of heating contents of the flask cool down, reversing the downward and the mixture distilled until oily droplets of the crude product (about 30 min). Destilávlejeme into a separating funnel, add to it 30 ml of ether and shaken obsalievika well. Funnel mounted on the stand Let stand, sour appears sharp interface between layers. Separate the ether layer gradually in a separating funnel Wash the water, conc. HCI (2-3 ml), water, 5% sodium bicarbonate solution and finally IR

again with water. For use after washing 10 ml of water and other reagents except conc. HCl. After separating the aqueous layer éterickpodiel Dry the small amount of crack. Sodium sulphate is filtered to Claisen distillation flask. After the first completisation of apparatues ether distilled from the reaction mixture at given temperature oil bath and subsequently raise the temperature of bath and we distillate the product. We capture share in the 100 to 103 ° C.

4-Phenyl-3-butene-2-one (benzalacetón)

Preparing Claisen-Schmidt reaction of benzaldehyde with acetone.

Necessary chemicals:

benzaldehyde 4.2 g (4.0 ml, 0.04 mol) acetone 6.7 g (8.5 ml, 0.115 mol) NaOH 10% Solution for crack. Na2SO4, ether (diethyl ether), HCl

Workflow:

The round bottom flask, mix 4 ml distilled benzaldehyde, 8.5 ml of acetone and 1 ml of 10% NaOH. Contents of the flask while stirring on a magnetic stirrer was heated in an oil bath at 25-30 ° C for 1.5 hours. Then the solution is acidified with dilute HCl 1:1 to the indicator paper and pour into a separating funnel. The organic layer is separated, the aqueous layer extract 5-10 ml ether. Add to extract the organic layer. Wash the combined organic layers with a little water and dried crack. sodium sulfate. Drying agent was filtered, the filtrate distilled ether and distilled under reduced pressure lujeme. We capture fraction distilling at 133-134 ° C and pressure 2.13 kPa, or at a temperature of 100-108 ° C and pressure 0:26 kPa. Properly distilled benzalacetón solidifies and has mp 38-39 ° C. Crystallization from petroleum ether mp increased to 42 ° C.

2-nitrophenol and 4-nitrophenol

They are prepared phenol nitration with dilute nitric acid. After reaction, the 2-isomer is distilled from the reaction mixture with water vapor and 4-isomer remains in the distillation residue.

Necessary chemicals:

Phenol 9.4 g (0.1 mol)

HNO3 19.0 g (14.5 ml, 0.3 mol)

Preparation:

Combine 14.5 ml HNO3 with 40 ml of water. To establish a small beaker 9.4 g of molten phenol and add to it 2 ml of water to remain liquid. (Phenol liquefies immersing the container in which it is located in a warm water bath). Prepared dilute nitric acid to pour 500 ml flask and add 2 ml of phenol. Components begin to react, resulting dims and heating solution. Phenol add further so that the reaction temperature remained in the game-destroying 45-55 ° C. After adding the whole amount of phenol (about 5 min), the contents of the flask cooled, the mixture of nitrophenol resin was washed with 2x100 ml of ice-cold water to remove acid residues. Oily layer containing nitrate next product also decomposition products of oxidation, is subjected to steam distillation. Distillation is finished after separating the 2-isomer share (so we find that

cooler has condensation 2-nitrophenol and distilled water only). If the 2-isomer (mp 45 ° C) in the distillate solidifies, it is cool spirit. Conversely, if already starts to solidify in the condenser during the distillation, it is occasionally shut down the supply of cooling water. The alcohol 2-nitrophenol evacuated between filter paper and dried thoroughly and complete drying in air. 4-nitrophenol evaporate with the steam and remained in the distillation flask. The contents of the flask charcoal, warm up to boiling and filtered through a folded filter. Beaker containing 400 ml plunge into ice bath. Pour into it a few ml of hot filtrate. Solution was stirred until the rod is eliminated by the crystals of 4-nitrophenol. Add another portion (2 ml) and the filtrate again quickly blended. Thus the whole process a filtrate. Excluded odsajeme crystals and dried. Tt 4-nitrophenol

Cooler has condensation 2-nitrophenol and distilled water only).

If the 2-isomer (mp 45 ° C) in the distillate solidifies, it is cool spirit. Conversely, if already starts to solidify in the condenser during the distillation, it is occasionally shut down supply Fenylamid cN-acetic acid (acetanilide) is prepared by condensation of aniline with acetic anhydride.

Necessary chemicals: aniline 4.6 g (4.5 ml, 0.05 mol)

acetic anhydride 7.2 g (6.6 ml, 0.07 mol)

activated charcoal Working procedure: The Erlenmeyer flask mix aniline with 40 ml of water if the suspension under vigorous stirring often added acetic anhydride. After adding all the acetic anhydride, the reaction was shaken for 10 min, the reaction can be observed spontaneous secretion of crystalline product. On completion of the reaction the reaction mixture was allowed to stand for 30 min. Excluded crystals on a Buchner funnel, filter cake from the mother liquor and print it Wash the can with a little cold water. The next reaction use 5 grams of crude acetanilide well washed and the residue crystallized from water using activated carbon. In the event of dissolution in hot water to create a layer of oily, it is necessary to add small doses of hot water while stirring rod until the layer disappears. Product was dried at room temperature (mp = 113-114 ° C)

Note: Acetic anhydride is irritating to eyes and skin. We work in the hood with protective gloves.

4-nitroaniline, 4-nitroacetanilid

Preparing nitration of acetanilide, followed by acid hydrolysis intermediate.

Necessary chemicals: acetanilid 4 g (0.03 mol)

HNO3 (65%) 2.9 g (2.2 ml, 0.03 mol) conc

. H2SO4, conc. HCl, NH3 (aq)

Working procedure: The Erlenmeyer flask mix 5 g of crude acetanilide (See note.) With conc. H2SO4 (9 ml). After the dissolution of almost all the contents of the flask cooled acetanilide and carefully added dropwise nitration mixture prepared by carefully mixing 2.2 ml 65% HNO3 with 2.2 ml conc. H2SO4. The reaction mixture vigorously stirred. Nitration maintain the temperature below 35 ° C. After adding the entire volume of the nitration mixture flask from the cooling bath and let stand at room temperature 10 minutes. Then pour the reaction mixture to quadruple the volume of ice and water. 4-nitroacetanilid precipitated after mixing Wash the filtered and little water. Intermediate wet transferred to the boiling flask, add 30 ml water and 20 ml conc. HCl, fit a reflux condenser and the reaction mixture is heated to the boiling sky bath 30 minutes. The resulting solution pour into a beaker with 30 g of ice. 4-Nitroaniline isolate the mixture basified with ammonia water. The precipitated 4- nitroaniline is evacuated on a Buchner funnel and dried. The product after crystallization from ethanol forms yellow needles with mp

Note:

Raw acetanilide use of the previous reaction. It is a raw and wet acetanilid, so use it in excess (5 g), approximately 4 g of pure, dry acetanilide.