---11111111-•-----=------~S=i AIChE special section )
SEPARATIONS: A SHORT HISTORY AND A CLOUDY CRYSTAL BALL
PHIL WANKAT Purdue University eparations have always been and will continue to be still was invented by Jabir ibn Rayyan (aka Geber) in the late critically important in the processing of chemicals. 8th or early 9th century. Similar stills are currently in use in SIt is common to note that 40 to 70 % of both capital some whiskey distilleries and for distilling rose oil.[ 6l By the and operating costs in industry are due to separations_[!, P· lJ 14th century the production of strong alcoholic drinks had 4 18 It has been estimated that 15 % of the world's energy use become an industry. [ , P· l The first book on distillation was is required by separations.[2l Because of their industrial Hieronymus Brunschwig's Liber de arte distillandi published importance separations have always played an important in the early 1500s and translated into English in 1527_[7J part in chemical engineering education and in the chemical Brunschwig's book (Figure 1) is an apothecary with distilla engineering literature. tion used to produce various medicines from plants. Petroleum distillation was started in England in the 17th century and coal HISTORY OF SEPARATIONS tar distillation was first patented in 1746_[4, P· 35l Fractionation The beginning of separations apparently occurred before of coal tar into naphtha, kerosene, lubricating oil, and paraffin 3 recorded history. Egyptians used filtration to filter grape was patented in England in 1850. [ l The first oil refinery con 3 8990 juice over 5,000 years ago. [ , PP· l Aristotle mentioned that structed in 1860 in Pennsylvania used simple batch stills and 4 16 pure water can be obtained by evaporating sea water. [ , P· l A collected wide-boiling fractions as the distillation proceeded. combination of coagulation of impurities, evaporation, and crystallization used for salt manufacture were commonly in Phil Wankat has a joint appointment in 90 4 21 5 229 233 use by the 16th centuryY-P ' · PP ' · PP - l Similar practices Chemical Engineering and in Engineering 5 233 Education at Purdue University. He has a were still in use in India in 1980. [ , P· l Pressing, evaporation, B.S. ChE from Purdue, a Ph.D. from Princ and crystallization were commonly in use for sugar production eton, and an M.S. Ed from Purdue. He is by the 16th century.[4, P· 23 l the associate editor of GEE. Distillation, particularly batch distillation, has a long history. Mesopotamian clay distillation vessels with lids shaped to col lect the condensed volatile distillate have been dated to ~3500 BCE. [6l Alchemists in the first century AD in Alexandria used 4 16 a variety of simple batch stills or retorts_[ , P· l The alembic © Copyright ChE Division of ASEE 2009
286 Chemical Engineering Education ·_.~-/;;a~ ·. {J-ll/u£.,,,:: . ,..J}• ~o. ✓ •· 'L..~~ --P' - / ;;_/ ·;z,as (!~cJ,-~et roaren kun,t 3u t>jJt~niaen t,i~ j ., rCtmpofita -on frmplaaa/~nb bl ~aidt t~cfaurue pattpcnv!-cnt f~at3 ~ ~trne gt~ ,w«)ica.riw~ie b»famliri rtef41.len w be bii~ertt ~ 2lr~li1 lt'11b bur~ ~~petitnefl ~ mil: J~eeonfmo b:iif~wicf ~ff gcclnbc ~ii ~e.offmbatt ~ii not'f ~enc bic e6 begcrc+ Figure 1. Cover page to Hieronymus Brunschwig's Liber de arte distillandi. Courtesy of Donald F. and Mildred Topp Othmer Library of Chemical History, Chemical Heritage Foundation, Philadelphia, PA. Vol. 43, No. 4, Fall 2009 287 1 257 Horizontal stills with improved performance were used in the Davis,l1 · P· l who notes that safety valves are useful if they are early 19th century for alcohol purification. An improved still kept in working order. Packing was apparently first employed was developed in 1818 by Cellier in France who developed in 1820 and was patented in 1847.[16l The problem of breaking 4 35 a vertical bubble plate still for alcohol purification_[ , P· l the ethanol water azeotrope was solved by Young in 1902 with In Victorian times large estates often had batch distillation a batch, azeotropic distillation process using benzene as the systems to prepare drugs and concentrated liquors. Popular entrainer to produce the first observed ternary azeotrope as books on distillation were available for this market. [9l In his the distillate product. The batch process was converted to a Handbook ofChemical Engineering, published in 1901 and in continuous azeotropic distillation by Keyes in 1928Y7l an enlarged edition in 1904, George Davis clearly developed In the early 1920s petroleum refineries had not adopted 0 the unit operations idea (not by this name) for distillationY · more modem fractionation systems and were using horizon 100 103 11 PP· - , l Before this, the distillation of each chemical was tal stills directly heated on the bottom in conjunction with studied separately. It is notable that the 2nd edition of C. partial condensation to distil petroleum. These systems were 12 S. Robinson's The Elements of Fractional Distillation[ i not very efficient and considerable redistilling was required. has elements of both the unit operations generalization and Modernization of distillation in refineries occurred in the individual chapters for distillation of a number of chemicals 1920s when W.K. Lewis was hired as a consultant by the such as ethanol. By the fourth edition, extensively revised by Standard Oil Company of New Jersey and introduced vertical 3 Ed Gilliland,l1 l the unit operations approach dominated and 8 305306 fractionation systems.[ , PP· l By the 1920s and 1930s the distillation of specific chemicals were relegated to examples. 12 18 schematics of continuous distillation columns in textbooks[ ' ' 19 20 12 The Elements of Fractional Distillation may have been the l and in Perry's HandbooAf. · section i look fairly modem except first chemical engineering book to also become popular with a that valve trays and structured packings had not been invented nontechnical audience-it was very popular with bootleggers yet. Heat recovery in distillation was common by 1923Y-P 575l 14 85 in the 1920s and 1930s.[ ,p. l Batch distillation was important The histories of distillation equipment, distillation control, enough to attract the attention of Lord Rayleigh who appar and azeotropic and extractive distillation were reviewed by 5 ently did the first theoretical analysis of the methodY l Fair,l1 6l Buckley,l2 1l and Othmer,l1 7l respectively, for the 75th The first continuous distillation appears to have been de anniversary of AIChE. veloped by Aeneas Coffey in 1830. He developed a vertical Theoretical analysis of continuous binary distillation was 4 perforated plate column for alcohol purification (Figure 2). [ , PP· first achieved by Sorel, who was interested in the distillation 35 36 11 ' l This still was equipped to preheat the feed by exchange of alcoholP2l Sorel's method is accurate, but confusing and with the condensing distillate and the bottoms. Davis[lll shows laborious since a trial-and-error calculation was required on open-steam distillation systems and several examples of every stage. Binary distillation was analyzed graphically with methods to reduce energy. In 1900 vertical perforated plate out trial-and-error by Ponchon[23 J and Savarit[24l independently. columns quite similar to modem equipment were introduced Lewis[25J realized that in many cases the vapor and liquid molar 4 36 9 for distillation of tar. [ , P· ' al Safety in tar stills is discussed by flow rates are approximately constant-if they are assumed to Figure 2. "The Coffey still of 1830 for distilling alco hol from fermented mash, using perforated plates. 1. Boiler. 3. Stripping col umn. 4. Rectifying column. 6. Feed. 8. Condenser. " Reprinted with permission from Davies, J. T., "Chemi cal Engineering: How Did it Begin and Develop?" in Furter, WF. (Ed.), History of Chemical Engineering, American Chemical Soci ety, Washington, D.C., Ad- vances in Chemistry Series, 190, 15-43 (1980). Copyright 1980 American Chemical Society. 288 Chemical Engineering Education be constant Sorel's trial-and-error procedure is not required. Gibbs studied the thermodynamics of growing crystal surfaces The simplified Lewis method was converted to a graphical at equilibrium and realized that thermodynamics was often method by McCabe and Thiele. [26l Because McCabe-Thiele not sufficient to explain the crystal growth.[36l McCabe[37l plots clarified the physical reasons why column distillation found that the deposition rate/unit area is often linear in works, the method was rapidly adopted. While no longer used supersaturation and deposits grow at a uniform rate. Unfor for design, McCabe-Thiele diagrams are commonly used to tunately, McCabe's L law often does not holdY6l Industrial teach distillation. Solutions for multicomponent distillation scale crystallizers in 1934[33l do not look very different than are much more complicated, particularly if there are non-dis many modem crystallizers. The important theory of crystal tributing light and heavy non-keys. Initially, stage-by-stage size distribution was developed by Randolph and LarsonY9l 7 28 36 methods were adapted to multicomponent distillation,(2 ' l Hulbert[ l reviewed crystallization for the 75th anniversary but closure remained a problem. Numerous computer solution of AIChE, and more recent advances in crystal engineering methods were developed after Amundson and Pontinen[29J are reviewed by Doherty. [4oJ Precipitation is similar to crystal realized that distillation equations could be conveniently lization except the product is usually amorphous with a poorly solved after they were put into matrix form. One of the more defined shape and structure. Precipitation is often used as a robust and common methods still used in commercial simula first cut before crystallization. Early workers did not delineate tors was Naphtali and Sandholm's[30] linearization of all the between precipitation and crystallization and many early equations. The history of distillation models was reviewed by crystallizations would now be classified as precipitation. Holland[31 l for AIChE's 75th anniversary. Membrane filtration developed at least as early as 1600 Unlike distillation, which developed gradually over cen BC when the Arawak people of the West Indies used porous 4 turies, practical application of absorption appears to have stone filters to purify drinking water_[ ll With this exception, 4 29 11 190 the development of membrane separations is almost unique been developed solely by a single person in 1836.[ ,P· , ,P· l William Gossage used an old windmill as a tower to absorb since the science was developed before practical applica HCl in a downward-flowing stream of water. The column tions. The first studies of membrane phenomena were done was packed with gorse and brushwood. This inspiration by Abbe Nollet in 1748 who studied permeation through a 42 82 soon led to towers packed with various materials such as semipermeable membrane.[ · P· l In 1855 Fick studied dif twigs, broken brick, coke, and stone to absorb HCl. A next fusion and developed the laws of diffusion still used to study 42 82 43 membranes. [ , P· l Thomas Graham studied dialysis in 1854[ l step was the development of high efficiency CO2 absorption 4 29 3 and dialysis using parchment paper for the membrane was towers by Ernest Solvay for his Solvay process_[ , PP· - oJ The need for good distribution of the gas in the tower was practiced commercially for processing beet sugar at the end of 282 1 203 the 19th century. [ll, P· l The major current application - the ar known by 1902Y · P· l Theoretical analysis of absorption 42 was facilitated by Whitman's development of the two-film tificial kidney-was developed in 1944 by Kolff and Beck. [ 9597 44 PP· l Graham studied gas separations in 1863[ l but it was theory of mass transferY 2l not until 1954 that Kolff and Balzer developed a membrane Liquid-liquid extraction became an important laboratory lung oxygenator that was improved by the work of Clowes method in the mid 19th century, and the concept of partition 42 131 133 and coworkers.[ · PP· - l Pauli developed electrodialysis in 33 ratios was introduced by Berthelot and Jungfleisch in 1872. [ l 4 1924[ ll and the multicell electrodialyzer was developed in Industrial applications started about this time. In 1883 Goering 42 98 99 4 1940 ,( · PP· ' oJ but electrodialysis did not become practical patented a countercurrent extraction process for recovery of until the 1950s with the development of synthetic ion-exchange acetic acid, and in 1898 Pfleiderer patented a stirred column 42 100 membranes.[ · P· J Currently, industrial applications of elec 3 extractorY l With the development of chemical engineering trodialysis are uncommon, but there is interest in use of it as as a profession in the early 20th century, extraction benefited part of a hybrid process. [45l The seminal development that led to from many of the improvements originally devised for distilla large-scale commercial applications of membranes for pressure tion and absorption. Development of new aqueous two-phase driven systems was the Loeb-Sourirajan method of producing extraction systems has allowed purification of proteins that 42 10 105 asymmetric membranes with a defect-free thin skin. [ · PP· 4- ' 34 35 475 are likely to be unstable in organic solvents. [ l Treybal[ , P· l 46l This method rapidly led to commercial reverse osmosis notes that extraction is "a relatively immature unit opera 42 104 47 systems in the 1960s.[ · P· ' l Loeb-Sourirajan membranes tion. It is characteristic of such operations that equipment could also be used for ultrafiltration (UF) if the membranes types change rapidly, new designs being proposed fre were not annealed. This led to commercial UF systems, but quently and lasting through a few applications only to be they were severely hampered by concentration polarization. replaced by others. Design principles for such equipment The eventual understanding of concentration polarization led are never fully developed ...." to the development of flow regimes and membrane modules Crystallization from solution was one of the key tools of that allowed for practical applications of UF in the mid to 36 42 117125 the alchemists,l l was an important unit operation at the end late 1960s.[ · PP· l After Henis and Tripodi at Monsanto 266 of the 19th century,[ll, P· l but remains partly art. In 1878 developed the Prism membrane separator for hydrogen pu- Vol. 43, No. 4, Fall 2009 289 42 129 133 48 rification in 1979/ , PP· - , l several other commercial gas Liquid chromatography in the form of column elution permeation systems were developed. [42J Pervaporation can be chromatography was first developed by Tswett in 1903. [62l He traced to the work of Graham, but the definitive studies were called the method "chromatography" because he observed col done by Binning and his co-workers in the late 1950s and ored bands moving down the column. Large scale applications early 1960s. [49l Pervaporation was first commercialized in the of very similar systems were commercialized in the late 1940s 1980s for breaking the ethanol-water azeotrope_[47l for separation of carotene, xanthophyll, and chlorophyll on an activated carbon column using gradient elution and backwash, Adsorption, particularly the use of charcoal to purify water, and in the 1950s the Arosorb process developed by Sun Oil has been known since Biblical times,[5°, Vol 1, P· 82l was used Co. was used to separate aromatics from alkyl hydrocarbons commercially in the late 18th century for the clarification of using silica gel. [5o, Vol 2, P· ll Currently, commercial applications 1 1075 raw sugar,[5 , P· l and was recommended for purifying water 2 4 9 ofliquid chromatography are common for bioseparations. Liq in an 1859 Western US guide book.l5 , P l Scheele studied the 3 548 uid-liquid chromatography (LLC) was developed by Martin adsorption of gases on charcoal in 1773 p , P· l and the ability and Synge[63l and gas-liquid chromatography was developed of charcoal to remove odors from air was extensively studied 64l 1 1087 by James and Martin. [ Although very successful in analytical by Hunter in the 1860s.l5 , P· l Clay was also extensively applications these methods are less successful in large-scale used with an early use in "fulling" (the removal of grease systems. LLC led to bonded phases that are used commercially from wool-hence the name fuller's earth) and processing in large-scale systems, however. Scale-up of size exclusion vegetable oils, and later applications in petroleum processing chromatography (SEC) was successful, and SEC was used with percolation processes_[5l , PP· 1059-1061 l Thermal desorption for large-scale separations shortly after it was invented.[65l including burning the adsorbates off of the adsorbent was the Although affinity (or bioaffinity) chromatography, which common regeneration method if the adsorbent was regener is used for purification of antibodies and proteins, has been ated. Solvent recovery with activated carbon followed by traced back to Starkenstein's isolation of a-amylase on starch steam desorption has been commercially practiced since the in 19I0,[66l modem applications started in the 1950s with the 50, Vol 1, P· 73 1920s with little change in the basic equipment.[ l 66 67 work of Lermann's group[ , l and were popularized by a Pressure swing adsorption (PSA) developed by Skarstrom[54l series of papers by Cuatrecasas and Anfinsen. [67l Large-scale at Esso in the 1950s and 1960s allowed for much faster applications (large-scale is a relative term and may refer to a cycles and thus higher productivity. PSA was rapidly com 50 mL column processing 15 liters of fluid) were started in mercialized for air drying, hydrogen purification, and air the early 1980s.[68l Although many commercial units are not separation. Simulated moving beds (SMB) were developed large, the value of the purified product can be significant. by Broughton and his coworkers at UOP during the same time frame to solve the attrition and mixing problems that Electrophoresis, which is also extensively used for protein 55 56 occurred in moving beds_[ , l This process is similar to the purification on a small scale, has a long history, but modem Shanks process ( 1841) used to simulate counter-current flow electrophoresis was initiated by the experimental work of Ame 35 723 724 in leaching. [ , P· - l Two major commercial applications of Tiselius in 1937 and the development of a theory for electro 69 70 the SMB have been purification of p-xylene and separation lytes by Debye and Htickel.[ , l Tiselius' original method, of fructose and glucose. [50, Vol 2, chapt 6] moving boundary electrophoresis, is limited by being able to collect pure samples of only the fastest positively and nega 3 549 Ion exchange can also be traced to biblical times.l5 , P· l tively charged components and convection caused by elec Scientific studies were first done by Thompson in 1850 using troosmosis often reduces the separation. Gel, membrane, and 57 58 63 naturally occurring clays_[ , , P· 1 l The first major application paper electrophoresis were developed to control convection. of ion exchange, water softening, occurred early in the 20th If the electrophoresis is done in the presence of a pH gradi 53 549 century. [ , P· l The major advance in ion exchange was the ent the result is isoelectric focusing, which has considerably development of synthetic polymeric ion exchange resins in more separation power. Isoelectric focusing was developed 59 England in 1935.[ l Synthetic polymer resins were used by by Kolin in the mid-1950s and further developed by Svens Frank Spedding and his coworkers for large-scale chromato 7 son. [ ll Preparative methods of electrophoresis and isoelectric graphic separation of the rare earths in the Manhattan project focusing often employ two-dimensional approaches po,71 l but 59 60 during and immediately following World War IF ' l and applications remain small-scale although a few researchers are currently used for almost all ion exchange applications continue to work to scale-up the systems. including home water softening. Moving bed systems with intermittent or pulsed solids movement have been used for After reviewing the historical development of separation large-scale ion exchange systems, particularly for water techniques, I conclude that the two most important long-term treatment, since the 1940s_[5o, Vol 2, PP· 68-76l Applications of developments were distillation and membrane separators. ion exchange for biochemical separations followed Moore 1. Distillation. Despite modest separation factors, dis and Stein's demonstration of the power of ion exchange tillation's ease of staging as a countercurrent process with chromatography.[61 ' 58, P· 163l extensive reuse of energy separating agent plus use of reflux 290 Chemical Engineering Education 6 85 86 and boil up allow one to obtain high purity and high recovery can be used for membrane systems.l7 ' l Spreadsheets,[ l without the addition of a mass separating agent. The major MATLAB, and Mathematica[37l are useful for solving prob downside for distillation is high energy use. Azeotropes and lems and helping students understand the equilibrium-staged low relative volatility limit applications, although the addi separation methods. If students have not been trained in these tion of a mass separating agent often allows circumvention tools, class time must be set aside to teach students how to of these limits. use the tools-preferably in a computer laboratory. Use of 2. Membrane separators. Asymmetric hollow-fiber these tools also helps graduates satisfy ABET's criterion 3k, membranes with high selectivity have an extremely high "an ability to use the techniques, skills, and modem engineer 33 area to volume ratio, very low energy use, and can achieve ing tools necessary for engineering practice."[ l Simulators 3 82 high purities. The downsides for membrane separators is the should also be used in dual level electives_[ o, l The "lecture" difficulty of staging and the lack of reuse of energy separat portion of the courses should use well known active learning 83 84 89 ing agent make achieving both high recovery and high purity methods[ ' ' l in addition to mini lectures. expensive. Concentration polarization and fouling currently limit applications for liquids. PREDICTIONS Where are industrial use, education, and research funding TEACHING SEPARATION PROCESSES for separations headed? My crystal ball is cloudy, but I will The key questions remain, What to teach? and, How to hazard predictions. These predictions assume that the one 72 73 great "killer" application that makes a host of existing separa teach it?[ ; l If we had as much time as was needed, we could teach all the separations in a separations-oriented ChE tion processes obsolete will not appear and that funding for academic research on separations will remain tight despite curriculum[73l that includes core courses in phase equilibrium, equilibrium-based separations, solids/mechanical separa the identification of a number of high-priority research areas in separations_[9oJ tions, and rate-based separations; and electives in advanced equilibrium-based separations and in novel/unusual separa First prediction: Distillation will remain the major industrial tions. This process-oriented curriculum uses separations as workhorse and a major, although probably slowly declining, the unifying theme, but it does not fit into current trends in part of education in separations. Education in distillation curriculum development. [74, 75l (including absorption and stripping) will increasingly focus With an overcrowded curriculum separation methods are not on the use of process simulators. Unfortunately, funding for going to receive significantly more time; thus, we must choose academic research on distillation will remain anemic in the which separations to include. At Purdue we currently have one United States. core course in separations. In this junior-level course I cover Rationale - Industrial Use: Distillation will continue to be flash distillation, normal and complex continuous distillation the industrial workhorse because: 1. Distillation is trusted. 2. (binary, multicomponent, extractive, and azeotropic), batch It is understood well enough that existing computer models will produce designs that work in about 80 % of cases. [9o, P· 25l distillation, absorption and stripping, liquid-liquid extraction, 3. Except for extractive and azeotropic distillation, mass and membrane separations. The course has two lectures and separating agents are not required and thus do not need to a two-hour, AspenPlus computer laboratory every week. To be recovered. 4. A complete binary separation is possible, cover this significant amount of material, extraction is taught which means a component can be recovered with high at a purely equilibrium level with no design, and membranes purity and high recovery. 5. In many cases distillation is the are usually limited to gas permeation (but including all flow most economical separation process. 6. Currently, 90-95% patterns). I use my own textbook,[76l although there are other of all separations in the chemical process industry are done by distillation. [l, P· 11 l good textbooks available_[e.g., 53 ' 77' 78l [The outline of this course is available from the author at [email protected].] Rationale - Education: Because of the broadening of posi Obviously, this choice of material leaves out many important tions that graduates accept, most schools want to prepare separation processes. Some of these are included in senior students for jobs outside the traditional chemical and laboratory (e.g., drying and chromatography) or senior petroleum industries. Thus, there is considerable pressure design courses, but the students rarely have the same level to teach other separations, but additional time is rarely al of understanding of theory. It is also important, if possible, located to separation processes. Process simulators will be used because they prepare students for industrial practice, to have dual-level (graduate and undergraduate) electives they are now readily available at most schools, they are sup 9 80 available on topics such as particulates,l7 l rate separations,l l ported by textbooks, ABET encourages the use of modern 81 82 bioseparations,l l or advanced distillation.[ l tools, and they help students learn. For distillation and the other equilibrium-staged separations, Rationale - Research Funding: The U.S. funding agencies process simulators are used for design and simulation in indus have to a considerable extent apparently decided that distil 83 84 try and thus should be used in undergraduate courses.[ ; l The lation is a known art and that companies or Fractionation particular process simulator used is not critical. Spreadsheets Research Inc. (FRI) should conduct any research needed. Vol. 43, No. 4, Fall 2009 291 This reasoning ignores that even small advances in distil membrane separators remain the only separation sys lation can be economically important, and that a paradigm tems that are funded at close to a reasonable level. shift, although perhaps unlikely, would have enormous economic impact. Fourth prediction: Adsorption, ion exchange, and chromato graphic separation processes will slowly become more impor Second prediction: Mechanical separations such as flota tant in industry and will continue to receive modest research tion, filtration, centrifugation and settling will continue to be support, particularly for biological applications. These pro ignored in the ChE core at most schools although they will cesses will be taught mainly at the graduate level. Their lack remain critically important in industry. Funding for research of coverage at the undergraduate level will continue to serve in particulates will remain reasonably secure. as a barrier to their wider application in industry. Research Rationale - Industrial Use: Because unwanted solids must funding will remain tight although it will be somewhat more be removed and many products are sold as solids, particu available for biological applications. late separations will remain industrially important. Rationale - Industrial Use: Adsorption, ion exchange, and Rationale - Education: Unfortunately, at the time that the chromatographic separation processes can often accomplish engineering science revolution changed chemical engineer separations more economically than other methods. This is ing education, many steps in handling and processing solids particularly true in biological applications where distilla were art not science. These unit operations were often tion is not applicable. Because most engineers with a B.S. dropped from the curriculum since they were not considered degree are unfamiliar with these processes, however, they to be scientific. Many schools have added these processes will be unlikely to consider sorption separations for new back into the curriculum, but in an elective course on par applications. [9o, P· 16l ticulates instead of in the core. Because of time pressures on Rationale - Education: Since the sorption separations are the core, mechanical separations are unlikely to be added to batch processes that require mass transfer calculations, they the core in a meaningful way. are inherently more difficult to understand than steady Rationale - Research Funding: The mechanical separa state, equilibrium processes. Because many undergraduate tions have found a home in the general area of funding for chemical engineers have considerable difficulty understand particulates. Although not overly generous, this funding is ing them, these processes will be taught mainly to graduate probably secure. students. Third prediction: Membrane separation processes will con Rationale -Research Funding: Money will be available for tinue to find industrial applications, but at a slower rate than materials applications to make new sorbents, particularly if the research can be tied to nanotechnology. Biological predicted by researchers. Membrane research will continue to applications have more sources of funding available than benefit from support that is modest, but robust compared to nonbiological applications such as gas processing. that received by other areas of separation. Membrane separa tions will become an increasingly common part of separation Fifth prediction: Crystallization (and precipitation) will courses in the ChE core. continue to be used in many industries where it is critically important. Crystallization will remain an orphan without a Rationale - Industrial Use: In applications where they work well (high selectivity and high flux, commercially available, home, however, in the core of most undergraduate curricula. high purity or high recovery is required, minimal foul- Crystallization research is currently underfunded and is un ing occurs, and the membrane has a long life) membranes likely to receive large increases. are often the most energy efficient and least expensive Rationale - Industrial Use: Since many products are sold separation method by far. Unfortunately, these limitations in a solid form, the final processing step is often crystal currently limit use of membranes, but additional research is lization. In addition, many products such as salts and other likely to slowly broaden the range of applications. nonvolatile materials use very large-scale crystallization. Rationale - Education: Since industry is using membrane These processes are not going to disappear. separations more and since many academics are doing Rationale - Education: Crystallization can be analyzed membrane research, there is a desire to cover this material. as an equilibrium staged separation, but the equilibrium Membrane separators are now included in many textbooks, is not the VLE that undergraduates and professors are and the level of presentation is accessible to undergraduate familiar with. A complete analysis that predicts the crystal chemical engineering students. size distribution requires a mass transfer analysis coupled Rationale - Research Funding: Funding agencies appear with population balances. This material is accessible to undergraduates, but because population balances are usually to believe that the major membrane successes in water not covered elsewhere in the undergraduate curriculum, treatment and medical applications can be repeated considerable time needs to be devoted to the topic. Even even though the context may be different. So far, complete coverage of population balances only begins to the tendency of membrane researchers to be overly cover the idiosyncratic nature of crystallization. Because of optimistic about the rate of commercialization of new competing pressures to cover other material, most schools membrane applications has not cut into support, and will not carve out the time required in the undergraduate 292 Chemical Engineering Education core despite a call to make crystalline solids one of the core themes in the curriculum.[4oi Thus, at most schools thorough analysis of crystallization will only be done in elective courses when there is a professor interested in teaching this material. Most ChE graduates have a weak background in 90 19 crystallization and solids handling in general/ - P- J and this unfortunate condition is predicted to continue. First prediction: Rational - Research Funding: Much of the funding for crystallization was based on the promise of applications in space. This source appears to have largely dried up and no large-scale replacement sources have materialized. Distillation will Sixth prediction: Extraction will continue to be important in industry and to be covered in un remain the major dergraduate courses, but not enough time and energy will be focused on the unique extraction design issues in education. No prediction will be made on research funding. industrial work Rationale - Industrial Use: Extraction is very useful for cases where distillation does not work. Many of these applications of extraction such as separation of nonvolatile compounds are industri horse and a major, ally important. Rationale - Education: Although crystallization is probably the most idiosyncratic equilibrium although probably staged separation process, extraction is a close second. Important content such as third-phase (or rag) formation and design of different types of extractors receives minimal or no coverage in most slowly declining, undergraduate programs. Complete coverage of the methods used industrially would require a separate course. Because of time pressures on the curriculum, this will not happen in the required core. In addition, most current textbooks do not cover, and most professors teaching separations part of education are not familiar with, these details. in separations. IS THERE A BETTER WAY TO ALLOCATE RESEARCH FUNDING? Education in A rational way to allocate funding for separations research could be based on the potential for impact. Impact can certainly come from major advances such as the Loeb-Sourirajan method of distillation producing asymmetric membranes, but it can also come from relatively small advances that are very widely applied. Hypothesize that impact potential can be approximated as, (including absorp Impact Potential a (potential research advances) x (market for separation method) (1) tion and stripping) The market is the current use of the separation method measured in value of products or in cost of the separation units. In either case market can be estimated reasonably accurately will increasingly for separation methods currently in use. [Other evaluation methods would have to be used to analyze rare proposals for separation methods that are totally novel where there is no cur focus on the use of rent use.] Potential for research advances is much more difficult to estimate. Perhaps a start can be obtained by using an updated version of George Keller's plot of use maturity versus 9 process simulators. technological maturity_[ ll If technological maturity is normalized to scale from Oto 1, then we can hypothesize that Unfortunately, Potential for research advances a (1 - Technological Maturity) (2) funding for Then, Impact Potential a (1 - Technological Maturity) x (market for separation method) (3) academic research This model is a guide for setting funding levels but still leaves significant room for individual on distillation will judgments and modifications such as the use of weighting factors for potential and market. . . . Let's qualitatively consider how three industrial separation methods would fare with this remain anemic in approach. According to Keller,[91 l distillation is technologically mature and is close to the technology asymptote; thus, the potential for research advances is low. Since the market is the United States. huge, however, Eq. (3) shows that the impact potential of additional research is relatively large. Thus, funding should be increased from its current very low level. Membrane systems have a lower technological maturity (higher potential) than distillation[91 l and a significant market; thus, funding for membrane research will remain high. Solvent extraction has a somewhat lower technological maturity than distillation,[91 l which implies a somewhat Vol. 43, No. 4, Fall 2009 293 higher potential, but the market is about I/20th as large in posium Series, 79 (235), 90 (1983) the process industries[9o, r. 29l; thus, funding would be lower 18. Walker, WH., WK Lewis, and WH. McAdams, Principles of Chemical Engineering, McGraw-Hill, New York (1923) than for distillation. 19. Badger, WL and WL McCabe, Elements of Chemical Engineering, New York, McGraw-Hill (1931) CLOSURE 20. Perry, J.H. (Editor-in-Chief), Chemical Engineers' Handbook, Mc Since reactors and separators are the core of chemical Graw-Hill, New York (1934) 21. Buckley, PS., "History of Distillation Control, " AIChE Symposium engineering, these aspects are important in the history, the Series, 79 (235), 46 (1983) current practice, and the future of chemical engineering. The 22. Sorel, E., La Retification de /'Alcohol, Gauthier-Villars, Paris (1893) history of separations helps explain how the current practice 23. Ponchon, M., "Graphical Study of Fractional Distillation (in French)," of chemical engineering separations and of separations in Tech. Moderne, 13, 20, and 53 (1922) 24. Savarit, R., "Definition of Distillation, Simple Discontinuous Distil chemical engineering education evolved, and the history lation, Theory and Operation of Distillations Columns (in French)," provides a useful, but probably limited, crystal ball to predict and "Exhausting and concentrating Columns for Liquid and Gaseous the future. Mixtures and Graphical Methods for their Determination (in French)," ArtsetMetiers, 65,142,178,241, and307(1922) 25. Lewis, WK, "The Efficiency and Design of Rectifying Columns for ACKNOWLEDGMENT Binary Mixtures," Ind. Engr. Chem., 14,492 (1922) A shorter version of this paper was presented at the AI ChE 26. McCabe, W.L and E.W. Thiele, "Graphical Design of Fractionating 100th Anniversary Meeting in November 2008. Columns, " Ind. Engr. Chem., 17, 960 (1925) 27. Lewis, W.K, and G.L Matheson, "Studies in Distillation. Design of Rectifying Columns for Natural and Refinery Gasoline," Ind. Engr. REFERENCES Chem., 24, 494 (1932) 1. Humphrey, J.L, and G.E. Keller II, Separation Process Technology, 28. Thiele, E.W, and RL Geddes, "Computation of Distillation Apparatus McGraw-Hill, New York (1997) for Hydrocarbon Mixtures," Ind. Engr. Chem., 25, 289 (1933) 2. Korns, WJ., reported in article by L Guterman, The Chronicle of 29. Amundson, N.R, andAJ. Pontinen, "Multicomponent Distillation Calcu Higher Education, pp. Al and A6 (June 20, 2008) lations on a Large Digital Computer, " Ind. Engr. Chem., 50, 730 (1958) 3. Hougen, O.A., "Seven Decades of Chemical Engineering, " Chem. 30. Naphtali, LM., and D.P Sandholm, "Multicomponent Separation Engr. Frog., 73(1), 89 (January 1977) Calculations by Linearization, " AIChE Journal, 17(1), 148 (1971) 4. Davies, J.T, "Chemical Engineering: How Did it Begin and Develop?" 31. Holland, CD., "History of the Development of Distillation Computer in Furter, W.F (Ed.), History of Chemical Engineering, American Models," AIChE Symposium Series, 79(235), 15 (1983) Chemical Society, Washington, D.C, Advances in Chemistry Series, 32. Whitman, WG., Chem. Met. Engr., 29(4), 147 (July 23, 1923) 190, 15-43 (1980) 33. Frank, TC, L Dahuron, B.S. Holden, W.D. Prince, AF Seibert, and 5. Barker, D.H., and CR Mitra, "A History of Chemical Technology LC Wilson, "Liquid-Liquid Extraction and Other Liquid-Liquid and Chemical Engineering in India," in Furter, WF (Ed.), History of Operations and Equipment, " in D.W. Green and R.H. Perry (Eds.), Chemical Engineering, American Chemical Society, Washington, D.C, Perry's Chemical Engineers' Handbook, 8th Ed., McGraw-Hill, New Advances in Chemistry Series, 190, 227-248 (1980) York, Section 15 (2008) 6. RT, "Distillation through the Ages," Chemical Heritage, 25(2), 40 34. Albertsson, P-A, G. Johansson, and F Tjerneld, "Aqueous Two-Phase (Summer 2007) Separations, " in Asenjo, J.A (Ed.), Separation Processes in Biotechnol 7. Stanwood, C, "Found in the Othmer Library," Chemical Heritage, ogy, Marcel Dekker, New York, chapter 10 (1990) 23(3), 34 (Fall 2005) 35. Treybal, RE., Mass Transfer Operations, 3rd Ed., McGraw-Hill, New 8. Gornowski, E.J., "The History of Chemical Engineering at Exxon, " York (1980) in Furter, W.F (Ed.), History of Chemical Engineering, American 36. Hulburt, H.M., "Perspectives on Crystallization in Chemical Process Chemical Society, Washington, D.C, Advances in Chemistry Series, Technology, " AIChE Symposium Series, 79(235), 77 (1983) 190, 303-311 (1980) 37. McCabe, WL, Ind. Engr Chem., 21, 30, and 112 (1929) 9. Monzert, L, Monzert's Practical Distiller, Dick & Fitzgerald, New 38. McCabe, WL, "Crystallization," in Perry, J.H. (Editor-in-Chief), York (1889) Chemical Engineers' Handbook, McGraw-Hill, New York, 1467-1492 10. Freshwater, D.C, "George E. Davis, Norman Swindin, and the Empiri (1934) cal Tradition in Chemical Engineering," in Furter, WF (Ed.), History 39. Randolph, AD. and MA Larson, AIChE J., 8, 639 (1962) of Chemical Engineering, American Chemical Society, Washington, 40. Doherty, M.F, "Crystal Engineering: From Molecules to Products," D.C, Advances in Chemistry Series, 190, 97-111 (1980) Chem. Engr. Educ., 40(2), 116 (Spring 2006) 11. Davis, G.E., A Handbook of Chemical Engineering Illustrated by 41. Krantz, WB., "Membrane Science and Technology in the 21st Century," Working Examples, Vol. II, Davis Bros., Manchester (1902) Chem. Engr. Educ., 38(2), 94 (Spring 2004) 12. Robinson, CS., Elements ofFractional Distillation, 2nd Ed., McGraw 42. Lonsdale, H.K, "The Growth of Membrane Technology," J. Membrane Hill, NewYork(1930) Sci., 10(2+3), 81 (1982) 13. Robinson, CS., and E. R Gilliland, Elements ofFractional Distillation, 43. Graham, T, Phil. Trans., Roy. Soc., (London), 144, 177 (1854) 4th Ed., McGraw-Hill, New York (1950) 44. Graham, T, "On the Molecular Mobility of Gases, " Phil. Trans., Roy. 14. Weber, H.C, "The Improbable Achievement: Chemical Engineering Soc. (London), 153, 385 (1863) at M.LT, " in Furter, W.F (Ed.), History of Chemical Engineering, 45. Xu, T, and C Huang, "Electrodialysis-Based Separation Technologies: American Chemical Society, Washington, D.C, Advances in Chemistry A Critical Review, " AIChE J., 54(12), 3147 (2008) Series, 190, 77-96 (1980) 46. Loeb, S., and S. Sourirajan, "High flow porous membranes for sepa 15. Rayleigh, Lord (J. Strutt), "On the Distillation of Binary Mixtures, " rating water from saline solutions," U. S. Pat 3,133,132 (May 12, Phil Mag., 4(23), 521 (1902) 1964) 16. Fair, J.R, "Historical Development of Distillation Equipment," AIChE 47. Baker, RW, E.L Cussler, W Eykamp, W.J. Korns, R.L Riley, and H. Symposium Series, 79 (235), 1 (1983) Strathmann, Membrane Separation Systems -A Research & Develop 17. Othmer, D. F, "Azeotropic and Extractive Distillation," AIChE Sym- ment Needs Assessment, US Dept Energy, Contract No. DE-AC0l- 294 Chemical Engineering Education 88ER30133 (April 1990) 70. Ivoiy, C.F., "Electrically Driven Separation Processes: Analytical and 48. Henis.J_M.S .. and M.K. Tripodi. "A Novel Approach to Gas Separation Preparative Methods," in Asenjo, J.A. (Ed.), Separation Processes in Using Composite Hollow Fiber Membranes." Separ. Sci. Technol .. 15. Biotechnology, Marcel Dekker, New York, chapter 16 (1990) 1059 (1980) 71. Righetti, PG., Isoelectric Focusing: Theory, Methodology and Ap 49. Binning. R.C.. R.J. Lee. J.F. Kennings. and E.C. Martin. Ind. Engr. plications, Elsevier Biomedical, Amsterdam (1983) Chem .. 53. 45 (1961) 72. Wankat, PC., RP Hesketh, K.H. Schulz, andC.S. Slater, "Separations. 50. Wankat. PC.. Large Scale Adsorption and Chromatography. 2 vols .. What to Teach Undergraduates," Chem. Engr. Educ., 28(1), 12 (Winter CRC Press. Boca Raton. FL (1986) 1994) 51. Mantell. C.L.. "Adsorption. "in Periy. J.H. (Editor-in-Chief). Chemical 73. Wankat, PC., "Teaching Separations: Why, What, When, and How?" Engineers' Handbook, McGraw-Hill, New York, section 11 (1934) Chem. Engr. Educ., 35(3), 168 (Summer 2001) 52. Marcy, RB., The Prairie Traveler, US War Department, Washing 74. Cussler, E.L., D.W. Savage, A.PJ. Middelberg, and M. Kind, "Refo ton, D.C. (1859). Reprint edition, Applewood Books, Bedford, MA cusing Chemical Engineering, Chem. Engr. Frog., 98(1), 26S (Januaiy (1989) 2002) 53. Seader, J.D., and E.J. Henley, Separation Process Principles, 2nd Ed., 75. Armstrong, R.C., "A Vision of the Curriculum of the Future," Chem. Wiley, New York (2006) Engr. Educ., 40(2), 104 (Spring 2006) 54. Skarstrom, C.W., "Use of Adsorption Phenomena in Automatic Plant 76. Wankat, PC., Separation Process Engineering, 2nd Ed. of Equilibrium Type Gas Analyzers," Ann. NY Acad. Sci., 72(13), 751 (1959) Staged Separations, Prentice-Hall, Upper Saddle River, NJ (2007) 55. Broughton, D.B., and Carson, D.B., "The Molex Process," Petrol 77. Geankoplis, C.J., Transport Processes and Separation Process Prin Refiner, 38(4), 130 (1959) ciples (Includes Unit Operations), 4th Ed., Prentice-Hall, Upper Saddle 56. Broughton, D.B., and C.G. Gerhold, U.S. Patent 2,985,589 (May 23, River, NJ (2003) 1961) 78. McCabe, W.L., J.C. Smith, andP Harriott, Unit Operations of Chemical 57. Thompson, H.S., J. Roy. Agr. Soc. Eng., 11, 68 (1850) Engineering, 7th Ed., McGraw-Hill, New York (2005) 58. Dechow, F.J., Separation and Purification Techniques in Biotechnology, 79. Peukert, W., and H.-J. Schmid, "Novel Concepts for Teaching Particle Noyes, Park Ridge, NJ, (1989) Technology," Chem. Engr. Educ., 36(4), 272 (Fall 2002) 59. Ettre, L.S., "Preparative Liquid Chromatography and the Manhattan 80. Wankat, PC., "Using a Commercial Simulator to Teach Sorption Project," LCGC, 17(12), 1104 (December 1999) Separations," Chem. Engr Educ., 40(3), 165 (Summer 2006) 60. Spedding, F.H., E.L., Fulmer, T.A. Butler, E.M. Gladrow, M. Gobush, 81. Belter, PA., E.L. Cussler, and W.-S. Hu, Bioseparations: Downstream PE. Porter, J.E. Powell, and J.M. Wright, "The Separation of Rare Processing for Biotechnology, Wiley, New York (1988) Earths By Ion Exchange III. Pilot plant scale separations," J. Am. 82. Doherty, M.F., and M.F. Malone, Conceptual Design of Distillation Chem. Soc., 69, 2812 (1947) Systems, McGraw-Hill, NewYork(2001) 61. Moore, S., and W.H. Stein, J. Biol. Chem., 211, 893 (1954) 83. Wankat, PC., "Integrating the Use of Commercial Simulators into 62. Ettre, L.S., and A. Zlatkis (Eds.), 75 Years of Chromatography-A Lecture Courses," J. Engr. Educ., 91, 19 (2002) Historical Dialogue, Elsevier, Amsterdam (1979). 84. Dahm, K.D., "Process Simulation and McCabe-Thiele Modeling: 63. Martin, A.J.P, and R.L.M. Synge, "A New Form of Chromatogram Specific Roles in the Learning Process," Chem. Engr. Educ., 37(2) Employing Two Liquid Phases," Biochem. J., 35, 1358 (1941) 132 (Spring 2003) 64. James, A.T., andA.J.P Martin, "Gas Liquid Partition Chromatography: 85. Coker, D.T., B.D. Freeman, and G.K. Fleming, "Modeling Multicom the Separation and Microestimation of Volatile Fatty Acids. Formic ponent Gas Separations Using Hollow-Fiber Membrane Contactors," Acid to Dodecanoic Acid," Biochem. J., 50, 679 (1952) AIChE J., 44, 1289 (1998) 65. Janson, J.-C., and Dunnill, P, "Factors Affecting Scale-Up of Chro 86. Burns, M.A., and J.C. Sung, "Design of Separation Units Using matography," in Industrial Aspects of Biochemistry, Vol. 30, Part I, Spreadsheets," Chem. Engr. Educ., 30(1), 62 (Winter 1996) Spencer, B., (Ed.), North-Holland/ American Elsevier, Amsterdam and 87. Binous, H., "Equilibrium-Staged Separations Using MATLAB and NewYork, 81 (1974) Mathematica," Chem. Engr. Educ., 42(2), 69 (Spring 2008) 66. Turkova, J., Bioa.ffinity Chromatography, 2nd Ed., Elsevier, Amster 88. Vol. 43, No. 4, Fall 2009 295