Pollution Prevention and Abatement Handbook WORLD BANK GROUP Effective July 1998 Removal of Lead from Gasoline: Technical Considerations

The Effects of Lead in Gasoline ment. Thus, the marginal cost of octane from lead addition increases as the lead level increases. Refiners add tetraethyl lead (TEL) and tetra- me- In addition to its octane benefit, TEL also pro- thyl lead (TML) to gasoline to increase octane. In vides engine lubrication benefits. Lead in gaso- most situations, adding lead is the least expen- line prevents the wear of engine parts (valve seat sive means of providing incremental octane to recession) under severe driving conditions such meet gasoline specifications. At sufficiently high as prolonged high speed, towing, and hilly ter- levels, addition of lead can increase octane as rain for vehicles—typically older models—manu- much as 10 to 15 control octane numbers factured with soft valve seats. Consequently, a (Figure 1). Lead susceptibility (the gasoline’s pro- mandate for lead removal is often accompanied pensity to increase in octane with lead addition) by requirements for gasoline additives designed is a function of the gasoline’s composition and to prevent valve seat recession. Sodium-based blending properties. In general, the higher a base additives, for example, can be blended into gaso- gasoline’s clear octane (before lead addition), the line for this purpose.1 lower is its lead susceptibility. Lead addition is subject to decreasing returns to scale: each incre- Gasoline Octane Number ment of lead added to a gasoline blend provides a smaller octane boost than the previous incre- Octane number is a measure of a gasoline’s pro- pensity to knock (ignite prematurely, before the piston reaches the top of the stroke) in standard Figure 1. Octane Improvement from Addition test engines. The higher a gasoline’s octane is, the of Lead: 92, 87, and 82 Octane (CON) Gasolines better is its antiknock performance. Gasolines have two octane ratings. The research octane num- 20 ber (RON) measures antiknock performance at low engine speeds; the motor octane number 15 (MON) measures antiknock performance at high engine speeds. For any gasoline, RON is higher than MON, usually by 8 to 12 numbers. The differ- ence between the two is called octane sensitivity. 10 Most countries set specifications (minimum levels) for both RON and MON by gasoline grade. The

United States, however, sets specifications for the Octane gain (CON) gain Octane 5 control octane number (CON), the arithmetic aver- age of RON and MON.

0 Oil-Refining Processes 0.00 0.20 0.40 0.60 0.80 Oil refineries transform crude oils into numer- Grams of lead/liter ous coproducts. Refined coproducts fall into four 92 octane 87 octane 82 octane broad categories in the order of increasing spe-

240 Removal of Lead from Gasoline: Technical Considerations 241 cific gravity and decreasing volatility: liquefied refiner can vary the octane level of reformate over petroleum gas (LPG) and refinery gases; gasoline; a wide range (90–102 RON clear) by controlling distillate (kerosene, jet fuel, diesel fuel, and heat- the “severity” of the reformer, primarily by drop- ing oil); and residual oil (fuel oil, bunker oil, and ping pressure or increasing temperature, or both. asphalt). In virtually all situations, light prod- No other refining process allows the refiner com- ucts—gasoline and distillate—are the most valu- parable control of blendstock octane. The combi- able, and heavy products (residual oil) are the nation of high-octane blendstock and operating least valuable. The following main oil refining flexibility usually makes reforming the process processes play key roles in gasoline production. of choice for controlling octane level and produc- 1. Crude distillation splits crude oil into discrete ing incremental octane-barrels in response to lead fractions suitable for further processing. It is the phase-out. However, reformate is high in aromat- indispensable process in any refinery, the precur- ics and benzene: the higher the reformer sever- sor for all others. Of the many crude fractions ity, the higher the aromatics and benzene content. produced in the crude distillation unit, two, light (For example, increasing reformer severity from naphtha and medium to heavy naphtha, are espe- 90 to 100 RON increases the aromatics content of cially important in gasoline blending. Both are in reformate by roughly 15 percentage points.) the gasoline boiling range, and both have low Isomerization upgrades light naphtha (70–78 octane, making them unattractive as gasoline RON) to isomerate, a high-quality, moderate-oc- blendstocks. tane blendstock (85–90 RON). Light naphtha (boiling range, 15o–70oC) has Alkylation combines light olefins (propylene, three alternative dispositions: (a) direct blending n-butenes, and isobutene), which are produced to gasoline in small proportions; (b) direct blend- mainly by the FCC unit, and isobutane, coming ing in larger proportions (as present in the crude from hydrocracking, FCC, reforming or straight- oil mix), with attendant addition of lead to the run, and NG processing, to form alkylate, a high- gasoline pool; or (c) upgrading by isomerization quality, high-octane blendstock (92–97 RON). followed by blending. Alkylation can be employed only in refineries Medium and heavy naphtha (boiling range, with an FCC unit. o o 160 –375 F) is the primary feed to catalytic re- Polymerization converts light olefins (propy- forming, the workhorse of the upgrading process. lene and butenes) to form polygasoline, an ole- 2. Conversion processes convert heavy feeds into finic, high-octane blendstock (97 RON). This lighter materials for further processing or direct process relies on the same olefin feeds as alkyla- blending. Fluid catalytic cracking (FCC) is the most tion and can be employed only in refineries with important conversion process. The FCC unit is the an FCC unit. Polymerization increases the olefin heart of a conversion refinery, the most impor- content of gasoline; tant single determinant of the refinery’s profit margin. The FCC unit converts heavy refinery • Etherification processes produce oxygenate streams, in the residual oil range, into a spectrum blendstocks such as methylterbutylether of lighter, more valuable refinery streams, includ- (MTBE), ETBE, TAME and DIPE. Of these ing (a) a moderate-quality, high-octane gasoline blendstocks, MTBE is the most widely used. It blendstock (91–93 RON clear) called FCC gasoline; has exceptionally high octane (115 RON) and and (b) refinery gases, which may be sold or used other desirable blending properties as well. In as feed to alkylation and oxygenate production. the refinery, MTBE is produced using pur- 3. Upgrading processes improve the octane of chased methanol and isobutene produced crude fractions already in the gasoline boiling mainly by the FCC unit. As with alkylation, range. refinery-based etherification can be employed Catalytic reforming is the most important and only in refineries with an FCC unit. most universal upgrading process for gasoline • Blending mixes blendstocks and additives to manufacture. In most refineries, reforming is the produce finished products that meet specifi- primary source of additional octane. Reforming cations. Merchant MTBE, for example, can be upgrades heavy naphtha (35–55 RON clear) to a purchased on world oil markets. Because of prime gasoline blendstock, called reformate. The its high octane, blending merchant MTBE is a 242 PROJECT GUIDELINES: POLLUTANT CONTROL TECHNOLOGIES

common method of adding octane to gasoline Technical Options for Replacing Lead without capital investment. Certain gasoline in Gasoline additives such as MMT and DurAlt are also known to increase gasoline octane. Various technical options are available for replac- ing lead when it is removed from a gasoline pool: Refinery Categories • Increasing the octane of reformate by increas- ing reformer severity (within the limits of sus- Refineries can be categorized into two main tainable operations). In some instances, groups (see Table 1). achieving the necessary increase in reformer severity will call for revamping and modern- • Skimming refineries are relatively simple, com- izing the reformer. prising crude distillation, treating, upgrading • Increasing refinery production of high-octane (catalytic reforming in hydroskimming refin- blendstocks—FCC gasoline, reformate, eries only), and blending. Skimming refiner- isomerate, alkylate, polygasoline, and ethers ies produce refined products in proportions (MTBE)—by increasing the utilization of ex- determined mainly by the proportions of boil- isting process units and, if necessary, expand- ing-range fractions in the crude oil mix. For ing or revamping existing process units or example, a skimming refinery’s gasoline out- adding new units. As noted above, alkylate, put can be no greater than the aggregate vol- polygasoline, and ethers can be produced only ume of the crude oil fractions in the gasoline in conversion refineries. Increasing their pro- boiling range (about 60o–400oF). duction from existing units calls for increas- • Conversion refineries are relatively complex, ing the output of the refinery’s FCC unit; comprising crude distillation, treating, upgrad- • Reducing the volume of light naphtha in the ing (at least catalytic reforming and usually gasoline pool, by (a) increasing the volume of other processes as well), conversion (at least light naphtha upgraded to isomerate; (b) in- one conversion process and often more than creasing the volume of light naphtha sold to one), and blending. Conversion refineries pro- the petrochemical sector; or (c) reforming a part duce more light products and less heavy prod- (the higher boiling range materials) of he light ucts than is indicated by the distribution of naphtha stream. boiling range fractions in the crude oil mix. • Blending high-octane blendstocks, such as Some deep conversion refineries produce an merchant MTBE, or octane enhancing addi- all-light product slate containing no residual tives, such as MMT—into the gasoline pool. oil products. Conversion refineries shift the • Blending additional butanes into the gasoline product slate toward light products by crack- pool. (This, however, will increase the volatil- ing (converting) heavy crude oil fractions into ity of gasoline.) gasoline blendstocks, distillate blendstocks, and refinery gases. Conversion refineries of- These technical options may be applied in any fer more options for lead removal than skim- combination that is technically feasible in a given ming refineries. refinery. Each refinery has its own capital stock

Table 1. Refinery Categories and Processes Skimming Conversion Process Topping Hydroskimming Coking Catalytic cracking Deep conversion

Crude distillation •••• • Treating •••• • Blending •••• • Upgrading • • •• •• Conversion • •• ••• Oxygenate production •• Removal of Lead from Gasoline: Technical Considerations 243 and cost structure and faces a unique set of costs additives; (b) cumulative refining costs; (c) invest- and technical requirements when it seeks to re- ment requirements; (d) changes in gasoline move lead from its gasoline pool. Determining composition; and (e) the potential costs and in- the optimal combination of technical options, vestment requirements of other constraints on therefore, calls for detailed refinery analysis. refinery operations, such as limits on certain gaso- line properties (e.g., aromatics content, benzene The Cost of Lead Phase-Out content, and volatility). Refinery analysis gener- ally consists of the following steps: The cost of lead phase-out depends on a number • Development of technical data on the refinery. Ac- of factors, including: the initial lead concentra- tual process capacities and yields (and the po- tion in gasoline, the processing capabilities of the tential for upgrading), crude oil slate, product refinery, planned refinery modernization or slate, lead use, gasoline grade splits, prices for modification to meet evolving product demands, crude oil and refined products, and product and limits on other gasoline properties (e.g., vola- specifications for the time period of interest are tility, aromatics, and benzene). established. The cost of lead removal is generally in the range of US$0.02–$0.03/liter of gasoline with ini- • Development of crude oil assays. If not already tial lead levels of 0.6 g/liter or more and about incorporated in the refinery model, distillation US$ 0.01–$0.02/liter for initial lead levels of about curves for the crude oils processed by the re- 0.15 g/liter. Complex refineries with conversion finery are constructed. capacity tend to have lower lead removal costs • Adjustment of capital costs and required rates of than do technically less-advanced refineries with return. The costs of new process capacity are limited process options. Refinery modernization, adjusted and incorporated in the refinery therefore, generally facilitates the phase-out of model, along with the rate of return used to lead. annualize capital costs, to reflect the economic conditions faced by the refinery of interest. Analysis of Lead Phase-Out • Calibration of the refinery model. The refinery model is configured so as to yield reasonable Analyzing lead phase-out alternatives can be car- values for key measures of refinery operations: ried out by a combination of detailed engineer- marginal refining costs at observed product ing analysis and refinery modeling. This volumes, marginal costs of meeting product approach exploits detailed information that en- specifications, gasoline blend recipes, lead use, gineers can develop regarding the refinery of in- and capacity utilization of various refining pro- terest and makes it possible to assess numerous cesses. The calibration case serves as the base alternatives for lead removal and their effects on for comparing the results of subsequent “lead refinery economics and gasoline quality. Refiners reduction” cases. A well-calibrated refinery customarily rely on refinery models (linear pro- model increases confidence in the results of gramming models configured to represent their subsequent model runs. operations) to optimize refining and blending • Evaluation of various lead reduction cases for the operations and as planning tools to assess the projected product slate. Once the refinery model necessary changes in operations, the required pro- is calibrated to represent baseline operations, cess additions, and the blendstock or additive further model runs are made to assess the fea- purchases needed to phase lead out of gasoline. sibility and cost of progressively lower lead Modeling provides a quick and relatively in- limits for gasoline. These model runs are de- expensive method of assessing the economic signed to evaluate the effects of various ap- and technical aspects of lead reduction, such proaches for reducing lead use on refinery as: (a) alternative technical approaches for lead operations, such as changes in operating se- phase-out, including process upgrading, process verity, the addition of new process capacity additions, changes in operating procedures, and (reforming, pen-hex isomerization, and so on), the use of purchased high-octane blendstocks or and the use of additives. 244 PROJECT GUIDELINES: POLLUTANT CONTROL TECHNOLOGIES

Note pared for the Office of Policy, Planning, and Evalu- ation, U.S. Environmental Protection Agency, Wash- 1. One such additive is Lubrizol’s Powershield 8164. ington, D.C. At the recommended concentration of 0.7 grams per Chem Systems. 1994. “Study to Assess the Capability liter (g/l), bulk blending of Lubrizol’s additive in gaso- of the Bulgarian Refining Industry to Produce Un- line costs about US$0.003 per liter. leaded Gasoline.” Report prepared for the U.K. Know How Fund on Behalf of the World Bank, Sources Washington, D.C.

ABT Associates, Inc. 1996. “Costs and Benefits of Re- Lefler, W. 1985. Petroleum Refining for the Non-Technical moving Lead from Gasoline in Russia.” Report pre- Person. Tulsa, Okla.: PennWell Publishing Co.