Ind. Eng. Chem. Res. 2002, 41, 5627-5631
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Alkylation of Isobutane with C3-C5 Olefins: Feedstock Consumption, Acid Usage, and Alkylate Quality for Different Processes Lyle F. Albright School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47906
Commercial processes for alkylating isobutane with C3-C5 olefins often consume significantly different amounts of isobutane and olefin feeds when equal amounts of alkylate product are formed. Undesired byproducts, including light (C3-C5) paraffins and isoparaffins, acid-soluble oils (ASOs or conjunct polymers), and pseudo-alkylates (mixtures of C5-C16 isoparaffins having low octane numbers), are produced in variable amounts. About 0.6-3.0% of the olefins often reacts to produce ASOs and pseudo-alkylates. For alkylations with HF as the catalyst, isobutane consumptions are often 6-15% higher for production of a given amount of alkylate than for those with sulfuric acid. Several details pertaining to feedstock consumption are reported for what is thought to be the first time. Recent improvements that reduce feedstock demands, reduce byproduct formation, and increase the quality (or octane number) of the alkylate product are discussed. Introduction Often, 130-150 isoparaffins in the C5-C16 range are detected in alkylates produced in commercial alkylation units.1 Such alkylates are produced by reacting isobutane with mixtures of C3-C5 olefins using either sulfuric acid or HF as the catalyst. The lighter isoparaffins, as indicated by material balances of carbon and hydrogen atoms, consume relatively more isobutane on a mole basis than heavier isoparaffins. In the past 10 years, approximately 70% of all new alkylation plants built worldwide chose sulfuric acid as the catalyst.2 In the U.S., about 13-15% of the gasoline pool is alkylate depending, to some extent, on the season. Despite the importance of alkylation, relatively little quantitative information has been published on the following important aspects: first, increased isobutane consumption when HF is used as the catalyst and, second, increased olefin consumption as acid-soluble oils (ASOs or conjunct polymers) are produced during alkylations. Four different chemical mechanisms occur during alkylations.3,4 Mechanism 1 produces C7, C8, and C9 isoparaffins when propylene, a C4 olefin, and a C5 olefin, respectively, react with isobutane; basically, this mechanism is the only true alkylation sequence and the isobutane and olefin react in a 1:1 molar ratio. Trimethylpentanes (TMPs) are the preferred C8 isoparaffins, with research octane numbers (RONs) in the 100-109.6 range. Dimethylhexanes are less branched and much less desired C8 isoparaffins having RON values in the 55.5-76.3 range. Monomethylheptanes have even lower octane numbers. Dimethylpentanes are the predominant C7 isoparaffins produced, and they have RON values that average about 89-91. Trimethylhexanes are major C9 isoparaffins with RON values of about 90. Mechanism 2 produces numerous isoparaffins in the C4-C16 range. Heavy cations are first formed by polymerization-type reactions; these cations then fragment, and hydride transfer produces the numerous isoparaffins. Alkylates produced by mechanism 2 often have
RON values of about 92-93. Mechanism 3 results in the formation of heavy cations that are then converted to heavy isoparaffins. Material balances indicate that isobutane and olefins react on about a 1:1 molar ratio for the combined mixture of isoparaffins produced by mechanisms 1-3. Mechanism 4, often referred to as self-alkylation of isobutane, is quite different in that, when n-olefins are used, undesired light and normal paraffins (propane, n-butane, and n-pentane) are produced in addition to the alkylate (also a C4-C16 isoparaffin mixture). This alkylate contains high concentrations of C8 isoparaffins. About 2 mol of isobutane react with 1 mol of n-olefin. With n-butenes, the simplified reaction is often shown as follows
2i-C4H10 + n-C4H8 f n-C4H10 + i-C8H18
(1)
To produce the same amount of gasoline-type isoparaffins, referred here as alkylate, isobutane consumption is essentially twice as great with mechanism 4 as with mechanism 1. Olefin consumption, however, is approximately identical for all four mechanisms. With branched olefins (namely, isobutylene and isopentenes), mechanism 4 was essentially unreported until about 1990. When isobutane and isobutylene react via mechanism 4, the overall reaction scheme involves the net consumption of essentially equal numbers of moles of isobutane and isobutylene. When isobutane and isopentenes react via mechanism 4, both increased isobutane consumption and increased isopentane production occur. Mechanism 4 is of minor importance with branched olefins when sulfuric acid is used. All of the C5, C6, and C7 isoparaffins produced when C4 olefins are used are formed via some combination of mechanisms 2 and 4; mechanism 2 type reactions are often part of mechanism 4. In all commercial processes, ASOs are also produced. Details of the chemical composition of these oils, as they exist in the acids, are not completely known. Miron and Lee5 separated most but not all of these oils from the
10.1021/ie020323z CCC: $22.00 © 2002 American Chemical Society Published on Web 10/17/2002
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acids. The oils that they separated from used sulfuric acid and HF had similar compositions and were insoluble in water. Spalding et al.6 later separated a very small amount of water-soluble oils. The water-insoluble oils have empirical compositions of about (C1.0H1.75)n, where n averages from about 10 to 30. In the laboratory, olefins have been employed to produce ASOs plus simultaneously a low-quality (low-octane-number) mixture of C4-C16 isoparaffins referred to here as pseudoalkylate. The olefins first react to form isoalkyl acid sulfates that are soluble in the acid; these sulfates then react in the acid phase to form the two byproducts. The ASOs remain dissolved in the acid, but the pseudoalkylates separate as a hydrocarbon layer. Laboratory and other evidence suggests that ASOs are also produced mainly from olefins in commercial units, often by the mechanism just described. The ASOs separated from the acids have numerous CdC double bonds. Such bonds react with sulfuric acid (or HF) to form sulfate (or fluoride) groups.6 Eastman et al.7 reported that the HF phase in a Phillips alkylation unit contained about 82-85 wt % HF, 8-12% ASOs, and 0.1% water. Hence, about 5-6% of the material in this HF phase was missed. They suggested that the missing material was dissolved isobutane. Calculations made here indicate that the double bonds in the ASOs when they react with HF would account for most, if not all, of the 5-6%. This latter explanation is preferred. In used sulfuric acids, several percent of the sulfuric acid has probably reacted to form dissolved conjunct polymer sulfates. Considerable information is presented and analyzed here, for what is thought to be the first time, to compare quantitatively significant differences in yields of alkylate and acid consumption in different commercial alkylation processes. Alkylate quality is also considered. Consumption of Isobutane The consumption of all feedstocks including isobutane and sometimes isopentane is considered first. A frequently used method for reporting yields of alkylate product is to give the weight of alkylate produced per 100 weight of olefin feed. When propylene, C4 olefins, and C5 olefins are used to alkylate isobutane, yields would be 238.1, 203.6, and 182.9, respectively, if only mechanism 1 occurred, i.e., only C7, C8, and C9 isoparaffins, respectively, would be produced. Although these values are frequently used by refineries, they do not address isobutane consumption (or yields). Mechanism 4 is always of significant importance when HF is used as the catalyst but normally not with sulfuric acid. For alkylations using propylene as the olefin and HF as the catalyst, Hutson and Hays8 reported in one case that 24.7% of the propylene reacted via mechanism 4 (and hence about 75.3% by the other three mechanisms). Calculations indicate that, in this case, almost 40% of the isobutane reacted by mechanism 4. They also reported that the relative importance of mechanism 4 increased greatly as both the isobutane/ propylene ratio and temperature increased. Other variables of probable importance include the composition of acid and the character of the HF/hydrocarbon dispersion (or interfacial area between the two liquid phases); no experimental information, however, is known on either. For alkylations using n-butenes and HF, Payne9 indicates that n-butane is produced but reported only
semiquantitative information. Hayes and Hutson8 stated that n-butane is produced when C4 olefins are used but gave no quantitative information. Representatives of refineries using HF as the catalyst realize that propane is formed in relatively large amounts but frequently are unaware of the amount of n-butane produced, believing its production is small or even insignificant. One representative even claimed none was produced. Data obtained from a UOP brochure10 indicate that 1.0 bbl of C4 olefins reacts with 1.2 bbl of isobutane in the presence of HF to produce 1.8 bbl of alkylate. The data of Hammershaimb and Shah11 were also used. Using density values reported by Goyel,12 calculations suggest that slightly more than 6% of the olefins reacted to form n-butane; if 70% of the olefins were n-butenes, then about 9% of the n-butenes reacted to form nbutane. Data obtained from a commercial alkylation unit using HF also indicate a similar increase in isobutane consumption. The importance of mechanism 4 with C4 olefins likely follows the same trends relative to operating changes as reported by Hutson and Hays8 for propylene, i.e., isobutane/olefin (I/O) ratios, temperature, and HF composition have significant effects. For an alkylation unit using HF, the UOP brochure10 also reports that 1.0 bbl of C5 olefins react with 1.3 bbl of isobutane to produce 1.8 bbl of alkylate. Calculations indicate that 1.34 mol of isobutane reacts per mole of C5 olefins, i.e., about 34% increased isobutane consumption because of mechanism 4. Hence, about 34% of the olefin is converted by mechanism 4 to C5 paraffins (either n-pentane or isopentane). For an alkylation using HF, Abbott and Randolph14 report that 74.2% of 2-methyl-2-butene reacted by mechanism 4 to form isopentane. This information suggests that isopentenes react to a much higher extent by mechanism 4 than n-pentenes. Abbott and Randolph also discussed a method for minimizing the net production of isopentane. They recommended first separating the isopentane from the alkylate and then recycling this isopentane to the alkylation reactor. They did not quantitatively indicate how such recycling would affect the alkylate quality, but probably only rather low qualities would be obtained. Recycling would also significantly increase operating costs. Judging from the above information for industrial alkylations using HF, about 15-25% of propylene is often converted by mechanism 4 to propane, 6-10% of the C4 olefins to n-butane, and 25-35% of C5 olefins to n-pentane and isopentane. Mechanism 4 likely accounts for at least 6-20% increased isobutane consumption depending on the olefin feedstock. Assuming the same amounts of isobutane consumed, 6-20% more alkylate could have been produced if only mechanisms 1-3 had occurred, such as when sulfuric acid is used as the catalyst. Table 1 shows calculations for cases in which C4 olefins were used for alkylations where 0 and 7% of the olefins reacted by mechanism 4; such values are considered typical for C4 olefins when sulfuric acid and HF, respectively, are used as the catalysts. Olefin consumption, however, was unchanged. Mechanism 4 also has a significant effect on alkylate quality. Past literature13 often implies or even indicates that TMPs (and especially 2, 2, 4-TMP) are produced exclusively in addition to the light C3-C5 paraffins. Experimental results, including those of Hutson and Hays,8 suggest however that the alkylates produced contain significant quantities of dimethylhexanes (with
Ind. Eng. Chem. Res., Vol. 41, No. 23, 2002 5629 Table 1. Consumption of Isobutane and C4 Olefins withouta and withb Mechanism 4c without
with
pounds of olefin consumed/gallon of alkylate alkylation by mechanisms 1-3 2.815 2.618 alkylation by mechanism 4 0.197 total olefins consumed 2.815 2.815 pounds of isobutane consumed/gallon of alkylate alkylation by mechanisms 1-3 2.916 2.712 alkylation by mechanism 4 0.401 total isobutane consumed 2.916 3.113 a Basis: without; 0% of C4 olefins reacted by mechanism 4. Basis: with; 7% of C4 olefins reacted by mechanism 4. c Consumption of olefins to produce ASOs and pseudo-alkylate is assumed to be zero.
b
low octane numbers). The alkylate product obtained by mechanism 4 is often in the 94-95 RON range. When propylene is used as the olefin feed, mechanism 4 results in higher octane numbers as compared to alkylates produced using mechanisms 1-3. Mechanism 1 in this case produces considerable amounts of dimethylpentanes (with RONs in the 89-91 range). The combination of alkylates produced via mechanisms 2 and 3 probably have RONs of about 91-93. To promote mechanism 4 and the highest-quality alkylate, higher I/O ratios can be used, but operating costs to recover and recycle the unreacted isobutane increase; also isobutane consumption (and costs) increases. For mixed C4 olefins with HF as the catalyst, mechanism 4 can sometimes produce a slightly higher-quality alkylate as compared to mechanism 1. 1-Butene in the mixed olefin feed produces alkylates via mechanism 4 containing considerable TMPs, whereas it produces more DMHs via mechanism 1. If increased I/O ratios are used to promote mechanism 4, both increased isobutane consumption and higher separation (distillation) costs result. With commercial HF-type units, I/O ratios are often in 13:1 to 15:1 range, whereas these ratios with sulfuric acid are in 8:1 to 10:1 range. Alkylations using mixed C4 olefins and sulfuric acid are often preferred because high-quality alkylates are produced using lower I/O ratios and lower isobutane consumption. Sulfuric acid has the advantage that 1-butene first isomerizes and then produces mainly TMPs with high octane numbers.15 Commercial alkylation units using HF as the catalyst tend to use C5 olefins to only a very limited extent because of the importance of mechanism 4. In such cases, n-pentane production to form low-quality fuels and excessive production of isopentane are undesired. Further isobutane consumpton is increased to a significant extent. Isopentane is also readily alkylated with C3-C5 olefins via mechanisms 1-4. Although only limited experimental evidence is available, the kinetics of alkylations appear to be similar for both isobutane and isopentane. Isopentane is sometimes deliberately introduced as a feed. Of course, isopentane is always produced during alkylation via mechanism 2 and sometimes mechanism 4. The qualities of the alkylates formed from isobutane are always greater than those formed from isopentane. When isopentane is alkylated with propylene, the predominant C8 isoparaffins produced are dimethylhexanes (with low octane numbers). Alkylating isopentane with C4 and C5 olefins results in alkylates containing high concentrations of C9 and C10 isoparaffins, both of which have rather low octane
Table 2. C4 Olefin Consumption for Desired Alkylate, ASOs, and Pseudo-Alkylate as Function of Sulfuric Acid Consumption acid consumption (lb/gal) 0.2 0.3 0.4 0.5 1.0
% C4 olefin consumed to produce: alkylate ASOs pseudo-alkylate 98.76 98.16 97.55 96.95 94.04
0.62 0.92 1.23 1.53 2.98
0.62 0.92 1.23 1.53 2.98
numbers. Mechanism 4, which is of high importance with HF as the catalyst, would result in high concentrations of C10 isoparaffins in addition to the light nparaffins. Alkylation plants using HF as a catalyst generally have little or no incentive to use feedstocks containing high concentrations of isopentane or C5 olefins. Consumption of Olefins In addition to producing the desired alkylate, olefins also react to form ASOs and simultaneously pseudoalkylate, which often have research octane numbers in the low 80s.6 The pseudo-alkylate contains relatively high concentrations of C8 isoparaffins, but its TMP/ DMH ratio is much lower than that of conventional alkylates. The C/H atomic ratio of the pseudo-alkylate is about 2.25. Conjunct polymers, however, typically have C/H ratios of about 1.75.5 The olefins have C/H ratios of 2.0. With these assumptions, carbon and hydrogen balances indicate that the weight of pseudoalkylate is 50.9% of the weight of olefin that reacts. Because the exact C/H ratios of both the conjunct polymers and pseudo-alkylate undoubtedly vary slightly, it is assumed that the weights of the two are identical; experimental evidence indicates that this assumption is a good one.6 Material balance calculations made here indicate how the percentages of the C4 olefins that react to form the alkylate (desired alkylate), ASOs, and pseudo-alkylate vary as the sulfuric acid consumption varies in the range of 0.2-1.0 lb of acid/gal of alkylate. The following assumptions were made: (1) The feed sulfuric acid to the alkylation unit has an acidity of 99.5% and a water content of 0.5%. Weaker feed acids are sometimes used in commercial units, but acid consumption values are then higher. (2) The used acid rejected from the alkylation unit has an acidity of 90% with ASOs and water contents of 8 and 2%, respectively. The water content of the acid increases during alkylation for at least two reasons: first, sulfuric acid is an effective drying agent for the feedstocks, and second, some sulfuric acid acts as an oxidizing agent for many isoparaffins, and particularly trimethylpentanes (TMPs), plus ASOs. During such oxidations, both water and SO2 form.16 The above composition of used acid is typical. (3) No undesired contaminants are present in the olefin and isobutane feedstocks. Such contaminants include acetylene, conjugated dienes, cyclopentene, and water. Table 2 indicates that over 4.7% less of the olefin reacts to form these undesired byproducts as acid consumption is reduced from 1.0 to 0.2 lb/gal. It should be emphasized that much, but not all, of the pseudoalkylates mix with true alkylates, as will be discussed later. Values such as those shown in Table 2 are probably published for the first time here. Propylene and C5 olefins also react to form ASOs and pseudo-alkylates; the formation reactions are similar to
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those occurring with C4 olefins. With propylene, acid consumption values have in the past often been reported as 0.8-1.2 lb/gal. The higher values are, however, caused in part by the relatively high stability of the isopropyl sulfates, as compared to sec-butyl sulfates. Often, a rather high percentage of the isopropyl sulfates fails to react with isobutane in the alkylation reactor to form alkylates; instead, these sulfates dilute the acid, thereby reducing the catalytic activity. C5 olefins in the past resulted in fairly high acid consumption. In the past five years, considerable evidence has been reported on how sulfuric acid consumption can be lowered with all olefins.17-19 (a) Use lower reaction temperatures such as 5-7 °C for alkylations using C4 and C5 olefins. In one comparison using C4 olefins,19 acidity drops per volume of alkylate produced decreased by a factor of about 3 as the temperature was decreased from 20° to 5 °C, i.e., acid consumption would also be reduced by a factor of 3. Higher temperatures, such as 15-20 °C, are, however, often preferred for alkylations using propylene because of the high stability of the isopropyl sulfates. A combination of higher temperature, longer residence time in the reactor, and stronger acid is often recommended for alkylations with propylene. (b) Branched olefins (isobutylene and isopentenes) produce more ASOs (and pseudo-alkylate) as compared to n-olefins. Cyclopentene is a particularly undesired feedstock. Reduced use of branched olefins, and especially of cyclopentene, is desired. (c) The composition of the sulfuric acid is highly important relative to acid consumption. Stratco, Inc.,18 has alkylated isobutane with mixed C4 olefins and collected information on how the acidity of the acid decreases per volume of alkylate produced as a function of acidity. These acidity decreases are a measure of the byproduct formation and can be used to calculate acid consumption. The smallest decreases often occur at 9293% acidity. In one test by Stratco, the acidity decreases were higher by the following factors at different acidities as compared to the decreases at 93% acidity: factors of 2.7, 1.9, 1.1, 1.0, 1.1, 1.6, and 2.2 at acidities of 97.5, 95.5, 93.5, 93, 91.5, 89.5, and 87.5% respectively. In the case of propylene and C5 olefins, the acidities that normally result in minimal acidity decreases occur at higher acidities and at about 87-90% acidities, respectively.17,18 Because sec-pentyl sulfates are the least stable of C3-C5 sulfates, acids with rather low acidities have adequate catalytic activities for alkylations using C5 olefins. No information is currently known that compares the relative importance of ASOs and water dissolved in the acid concerning the rates of formation of more ASOs during alkylation. Water is known to have a larger effect than ASOs on alkylate quality.21 Hence, decreased water contents in the acid would probably often reduce acid consumption. High levels of agitation promote larger interfacial areas in the acid/hydrocarbon dispersions; the result is less ASO and less pseudo-alkylate plus higher-quality alkylate.15 Other variables of importance are the acid/ hydrocarbon ratio in the dispersion, the isobutane/olefin ratio, and the residence time. An important finding of the past several years is that the preferred operating conditions differ for different olefins.22 When two or more reactors are used in a refinery, there are preferred arrangements of series and/or parallel acid flows to the
reactors. Graves18 reports an example of acid consumption values for two, three, and four reactors. With four reactors, acid consumption values were sometimes less than 0.2 lb/gal of alkylate. Several years ago, alkylations using mixed C4 olefins and sulfuric acid often experienced acid consumptions of 0.45-0.7 lb/gal. Acid consumption values as low as 0.25-0.3 are currently obtained in at least one commercial unit. Even lower consumption values likely can be obtained in the future. Such reductions result in much reduced operating costs plus improved-quality alkylates. Considerably less information has been published on the production of ASOs and pseudo-alkylate when HF is used as the catalyst. Investigators with experience with this catalyst have suggested that the fractions of the olefins that react to form these byproducts are similar to those for alkylations using sulfuric acid. The isoalkyl acid sulfates dissolved in the acid react to form ASOs and pseudo-alkylate in the following three units of the alkylation plant: first, the alkylation reactor; second, the decanter used to separate the liquid-liquid dispersion leaving the reactor; and third, the storage tanks for used acids. The pseudo-alkylate formed in the first two units mixes with the true alkylate. As a result, the quality of the product mixture is reduced, by perhaps as much as 0.1 octane number. In the storage tanks for used sulfuric acid, a layer of pseudo-alkylate often forms on top of the acid phase within several days. Potential hazards in these storage tanks are similar to those in a tank filled with gasoline. Provisions should be made to remove the hydrocarbon liquid from these storage tanks. In addition, sulfuric acid acts in the storage tank as an oxidant of the dissolved ASOs to produce water and sulfur dioxide.16 Similar undesired reactions also occur in tank cars or trucks used to transport used acids. After several days at summer heat, a solid coke-like deposit sometimes forms; provisions are needed to vent the sulfur dioxide to prevent excessive pressures. Comparative Processes Producing Alkylate-like Hydrocarbons Solid catalysts for the alkylation of isobutane have been extensively investigated in the past 25 years, but all known results to date have not indicated that such processes will be superior or even comparable to current commercial processes. Two major faults are yet to be solved: (a) Diffusions of reactants into the pores of the catalyst and especially of heavier isoparaffins out of the pores are relatively slow, even with supercritical fluids. (b) Hydrocarbons and especially the heavier ones adsorb on the surfaces of the solid catalyst. Relatively high temperatures are required to desorb these molecules. As a result, undesired reactions are promoted that form materials that deactivate (or cover) the catalytic surfaces. Choi et al.23 has recently reviewed surface diffusion in porous media and condensation regimes in these pores. These two faults contribute to rapid deactivation of the solid catalysts employed. Isoparaffins that do diffuse out of pores of the catalyst are often essentially limited to C5-C9 isoparaffins. In addition, significant amounts of C8 olefins are often produced (and hence lesser amounts of C8 isoparaffins). Heavier hydrocarbons apparently have a propensity to form deactivating species that remain in the catalyst pores; yields of
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alkylate based on the isobutane and olefin feedstocks are hence very low. In the past several years, both UOP and Snamprogetti have publicized processes to produce alkylate-like mixtures of hydrocarbons.24-27 The UOP process designated as InAlk has various modifications. Considering the version starting with isobutane, three reactors are used in series: first, a reactor to dehydrogenate the isobutane; second, a reactor to dimerize and to some extent trimerize isobutylene plus other C4 olefins; and third, a reactor to hydrogenate the dimers and trimers. Significant amounts of undesired byproducts are produced in especially the first and second reactors, including light ends (C2 and lower) and heavy ends (heavier than C8’s). Calculations based on the results reported by Frame et al.28 indicate that 87.4% of the isobutane is converted to a gasoline fraction and 12.6% to hydrogen and gaseous fuel hydrocarbons. Other modifications of InAlk appear to give even lower yields. Furthermore, this gasoline fraction often contains a weight ratio of C8 to C12 isoparaffins of 2.96. Such a low ratio would likely have an adverse effect on both the volatility and the quality of the liquid fuel. Conclusions Many refinery personnel do not realize that large differences occur in different industrial alkylation processes relative to the consumption (or demand) of both isobutane and olefins for the production of a given amount of alkylate product. Isobutane consumption is always greater, often by 6-20%, for processes using HF as the catalyst as compared to processes using sulfuric acid. With HF-type processes, undesired propane, nbutane, n-pentane, and sometimes much greater amounts of isopentane are produced, depending on the olefin feed. Modification of the operating variables can be used to lower the quantity of the undesired byproducts, but this simultaneously causes a reduced quality of the alkylate. Olefins are the predominant feedstocks for producing undesired ASOs and pseudo-alkylate. The accumulation of ASOs in the acid phase (sulfuric acid or HF) is the main cause of loss of catalytic activity. Calculations indicate that, in the case of sulfuric acid, 1.2-6% of the olefin reacts to form these two byproducts. Similar amounts of olefins likely react in units using HF. Recent methods have been developed to decrease acid consumption significantly and, hence, to lower olefin consumption. Sulfuric acid consumption has been reduced from about 0.5-0.7 lb/gal as of 5-10 years ago to values as low as 0.25-0.3 in one commercial unit. Simultaneously, alkylate quality has increased. Literature Cited (1) Albright, L. F.; Wood, K. V. Alkylation of Isobutane with C3-C4 Olefins: Identification and Chemistry of Heavy-End Production. Ind. Eng. Chem. Res. 1997, 36, 2110. (2) Pryor, P. Stratco, Inc., Leawood, KS. Personal communications, 2001. (3) Albright, L. F.; Spalding, M. A.; Faunce, J.; Eckert, R. E. Alkylation of Isobutane with C4 Olefins: Two-Step Process Using Sulfuric Acid as Catalyst. Ind. Eng. Chem. Res. 1988, 27, 391. (4) Albright, L. F. Updating Alkylate Gasoline Technology. CHEMTECH 1998, 28, 6, 40. (5) Miron, S.; Lee, R. J. Molecular Structure of Conjunct Polymers. J. Chem. Eng. Data 1963, 8, 150. (6) Albright, L. F.; Spalding, M. A.; Nowinski, J. A.; Eckert, R. E. Alkylation of Isobutane with C4 Olefins: Production and
Characterization of Conjunct Polymers. Ind. Eng. Chem. Res. 1988, 27, 386. (7) Eastman, A. D.; Randolph, B. B.; Moore, W. P.; Heald, R. L. Consider Online Monitoring of HF Acid When Optimizing Alkylation Operations. Hydrocarbon Process. 2001, 80 (9), 95. (8) Hutson, T.; Hayes, G. E. Reaction Mechanisms with Hydrofluoric Acid Alkylation in Industrial Laboratory Alkylations; Albright, L. F., Goldsby, A. R., Eds.; ACS Symposium Series 55; American Chemical Society: Washington, DC, 1977; pp 27-56. (9) Payne, R. E. AlkylationsWhat You Should Know About This Process. Pet. Ref. 1958, 37, 8, 316. (10) UOP LLC, Pamphlet HF Alky Rev. 1, 1/99. (11) Hammershaimb, H. U.; Shah, B. P. Trends in HF Alkylation. Hydrocarbon Process. 1985, 64 (6), 73. (12) Goyl, O. P. Liquefied Petroleum Gas: Description, Properties, Recovery. In Testing in Encyclopedia of Chemical Processing and Design, McKetta, J. J., Ed.; Marcel Dekker: New York, 1988; Vol. 28, pp 226-227. (13) Schmerling, L. Alkylation of Saturated Hydrocarbons. In Chemistry of Petroleum Hydrocarbons; Brooks, B. T., Kurtz, S. S., Board, C. E., Schmerling, L., Eds.; Reinhold Publishing Co.: New York, 1955; Vol. 3, p 363. (14) Abbott, R. G.; Randolph, B. B. Control of Synthetic Isopentane Production During Alkylation of Amylenes. U.S. Patent 5,382,744, Jan 17, 1995. (15) Li, K. W.; Eckert, R. E.; Albright, L. F. Alkylation of Isobutane with Light Olefins: Operating Variables Affecting Physical Phenomena Only. Ind. Eng. Chem. Process Des. Dev. 1970, 9, 434. (16) Sung, S.; Szechy, G.; Albright, L. F. Decomposition of Spent Sulfuric Acid to Produce Sulfur Dioxide and Water. Ind. Eng. Chem. Res. 1993, 32, 2490. (17) Kranz, K.; Graves, D. C. Olefin Interactions in Sulfuric Acid-Catalyzed Alkylation. Presented at the National Meeting of the American Institute of Chemical Engineers, Dallas, TX, Mar 1998. (18) Graves, D. C. Acid Consumption and Acid Runaway in a Sulfuric Acid Alkylation Unit. Presented at the Stratco Seminar, Phoenix, AZ, Sep 1999. (19) Buckler, D. Alkylation Chemistry. Presented at the Stratco Seminar, Phoenix, AZ, Sep 1999. (20) Albright, L. F.; Kranz, K. E. Alkylation of Isobutane with Pentenes Using Sulfuric Acid as a Catalyst: Chemistry and Reaction Mechanisms. Ind. Eng. Chem. Res. 1992, 31, 475. (21) am Ende, D. J.; Eckert; R. E.; Albright, L. F. Interfacial Areas of Dispersions of Sulfuric Acid and Hydrocarbons. Ind. Eng. Chem. Res. 1995, 34, 4343. (22) Graves, D. C.; Kranz, K. E.; Millard, J. K.; Albright, L. F. Alkylation by Controlling Ratios. U.S. Patent 5,841,014, Nov 24, 1998, and U.S. Patent 6,194,625, Feb 27, 2001. (23) Choi, J. G.: Do, D. D.; Do, H. D. Surface Diffusion of Adsorbed Molecules in Porous Media: Monolayer, Multilayer, and Capillary Condensation Regimes. Ind. Eng. Chem. Res. 2001, 40, 4005. (24) Meister, J. M.; Black, S. M. ; Muldoon, B. S.; Wei, D. H.; Roeseler, C. M. Optimize Alkylate Production for Clean Fuels. Hydrocarbon Process. 2000, 79 (5), 63. (25) Wei, D. H.; Hammershaimb, H. U.; Meister, J. M.; Abrevaya, H. New Route to Produce High Octane Gasoline. Presented at the National Meeting of the American Institute of Chemical Engineers, Atlanta, GA, Mar 5-9, 2000. (26) Stine, L. O.; Vorn, B. V.; Hammershaimb, H. U. Process for Integrated Oligomer Production and Saturation. U.S. Patent 5,847,252, Dec 8, 1998. (27) Trotta, R.; Marchionna, M. The Combined Use of Snamprogetti’s Isoether DEP and LCN DET Technologies. Presented at Solid Acid/Base ‘97, New Orleans, LA, Jun 10−11, 1997. (28) Frame, R. F.; Stine, L. O.; Hammershaimb, H. W.; Muldoon, B. S. High-Octane Gasoline from Field Butenes by UOP Indirect Alkylation (InAlk) Process. Presented at the DGMK Conference, Aachen, Germany, Oct 6-7, 1997.
Received for review April 29, 2002 Revised manuscript received September 3, 2002 Accepted September 5, 2002 IE020323Z
