Alkylation of Isobutane with Butenes: Effect of Sulfuric Acid

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Hunt, C. d’A., Hanson, D. N., Wilke, C. R., AIChE J., 1, 441 (1955). Malakoff , H. L., “Tray Efficiencies in Distillation Columns,” Research Committee Third Annual Progress Report, AIChE, Kew York, N Y (1955). Murphree, E. V., Ind. Eng. Chem., 17,747 (1925). Nord, hI., Trans. Amer. Inst. Chem. Eng., 42, 863 (1946). Prausnitz, J. hl., Eckert, C. A., Orye, R. V., O’Connell, J. P., “Computer Calculations for hlulticomponent VaporLiquid Equilibria,” Prentice-Hall, Englewood Cliffs, XJ (1967). Qureshi, A. K., Smith, W., J.Inst. Petrol., 44,137 (1958). Schoenborn, E. X I Plank, C. il., Winslow, C. E., “Tray Efficiencies in Distillation Columns,” final report from Korth Carolina State College, AIChE, Xew York, K Y (1959). Toor, H. L., Sebulsky, R. T., AIChE J.,7,558,565 (1961).

Walter, J. F., Sherwood, T. K., I d . Eng. Chem., 33, 493 (1941). Wilke, C. R., Chem. Eng. Progr., 46,95 (1950). Wilke, C. R., Lee, C. Y., Ind. Eng. Chem., 47, 1253 (1955). Williams, B., Begley, J. W., Wu, Chi-hua, “Tray Efficiencies in Distillation Columns,” final report from the University of Michigan, AIChE, New York, N Y (1960). 86, 127 (1964). Wilson, G. M.,J.Amer. Chem. SOC., Young, G. C., P h D dissertation, University of Nebraska, Lincoln, XB (1971). Zuiderweg, F. J., Harmens, A., Chem. Eng. Sci., 9, 89 (1958).

RECEIVED for review September 30, 1971 ACCEPTED February 14, 1972 This study was supported by the National Science Foundation under Grant No. GK-1748.

Alkylation of Isobutane with Butenes: Effect of Sulfuric Acid Compositions Lyle F. Albright,’ Lawrence Houle, Andrew M. Sumutka, and Roger E. Eckert School of Chemical Engineering, Purdue University, Lafayette, I N 47907

lsobutane was alkylated at 10°C in a continuous-flow stirred reactor with 2-buteneI 1 -butene, or isobutylene at conditions conducive to production of high-quality alkylates. Sulfuric acids containing 0-570 water and 0-1 5% acid-soluble hydrocarbons were used as the catalyst. With especially 2-butene and 1 -butene, the water content of the acid was found to be highly important in affecting the quality and yield of alkylate resulting in high-quality alkylates at acid strengths produced. The optimum water content i s about 0.5-1 as low as 85%. Most if not all commercial alkylation units currently do not control the water content of the acid within the recommended range. With proper control, the alkylate quality often could be increased as much as one octane number, and acid consumption reduced by at least 50%.

.OY0,

w h e n isobutane is alkylated with butenes, the composition of the sulfuric acid used as catalyst affects the composition and hence quality of the alkylate produced. Fresh sulfuric acids, containing 1-2% water, result in poorer quality alkylates than are produced using acids that contain several percent of acid-soluble hydrocarbons, as is indicated by plant data (Albright, 1966). Laboratory results of hlosby and Albright (1966) and Li e t al. (1970) have shown t h a t acid mixtures containing 94 to about 96% sulfuric acid produced the best alkylates as measured by the octane number. The mixtures used in their investigations were blends of discarded alkylation acids (about 89-90% acid) and concentrated fresh acid (98-99% acid). When sulfuric acid is used as an alkylation catalyst, it is diluted during the overall process by several components : (a) Conjunct polymers that are highly unsaturated, I iron ionized, and contain numerous Cs and CS rings (11’ and Lee, 1963). These polymers are by-products t h a t may be formed as olefins and tert-butyl (and possibly other) cations rearrange and polymerize (Deno et al., 1964). Albright and Li (1970) have suggested that olefins To whom correspondence should be addressed. 446

Ind. Eng. Chem. Process Des. Develop., Vol. 1 1 , No. 3, 1972

react with these polymeric compounds to form higher molecular weight materials. (b) Sulfate esters formed by reactions betrreen the acid and the olefins. The esters are often quite unstable regenerating the olefins and acid. Such olefins then enter into either alkylation or polymerization reactions. (e) Water that often increases in quantity in the acid as alkylation progresses. Small but nevertheless significant amounts of water are generally dissolved in the reactants, especially in the olefin feedstocks, and sulfuric acid is an effective dehydration agent. Some Rater and sulfur dioxide are also formed by oxidation reactions between sulfuric acid and the hydrocarbons. These latter reactions occur readily a t temperatures somewhat higher than those in commercial alkylation reactors, but it is doubtful t h a t much water is formed by such oxidation steps in a welloperated alkylation system. (d) Sulfur dioxide that is formed by oxidation reactions and that is dissolved in small amounts in the acid. The dissolved hydrocarbons, frequently called red oils or acid sludges, have a significant effect on the overall alkylation sequence (Albright and Li, 1970; Hofmann and Schriesheim, 1962). These hydrocarbons are intermediate reactants


to a t least some extent and are involved in hydride ion and proton transfer. Since the transfer step of isobutane from the hydrocarbon to the acid phase is generally, if not always, the rate-controlling step of the overall reaction, possibly these dissolved hydrocarbons have surfactant characteristics and hence affect the character of the emulsion formed between the t\yo liquid phases. The water content of the acid controls the level of ionization in the acid phase. Kramer (1967) has shown t h a t the rate of hydride transfer steps vary with the water level, and such a n explanation helps clarify the variations noted for alkylation when the water content of the acid changes Sormally used sulfuric acid from a n alkylation unit is discarded when the acid strength has dropped to about 88-91'%',. The water content generally varies from 3 to 5% and acid-soluble hydrocarbons account for 4-7%. Unfortunately, accurate analysis of the waste acid is generally not attempted. Relatively little has been reported till now on the relative importance of the water and the dissolved hydrocarbons in affecting the alkylation process. Information was obtained in the current investigation to clarify the role of these diluents.

Table 1. Typical Compositions of Families of lsoparaffins in Alkylates as Function of Octane Number Olefin

Colcd

O.N.

light ends

Trimethylpentanes

1-butene and 2-butene

98 97 96 95 94 93 92 91 90

5 8 10 13 16 20 23 26 28

87 79 72 66 61 55 51 45 40

Isobutylene

Dimethylhexanes

Heavy ends

4 7

io

12 13 14 15 16 17

4 6 8 9 10 11 11 13 15

found to be accurate within 0.1% or even better in experiments with fresh acid containing no dissolved hydrocarbons. The acid-soluble hydrocarbons in the used alkylation acids were determined by difference.

Experimental Details

Results

The continuous-flow stirred-tank reactor previously used by Li et al. (1970) was also used in this investigation. A11 runs were made a t conditions which had earlier been found to result in high-quality alkylates. These conditions are: 10°C, 3000 rpm for agitator, 5 min average residence time of reactants in the reaction vessel, 20: 1 wt ratio of isobutane to olefin in feed stream, and 1.6: 1 volumetric ratio of acid-tohydrocarbon phases. The acid-continuous emulsion product from the reactor system was collected in steel sample containers as had been done earlier by Li et al. Sufficient time was given to allow the phases to separate in this container. Then the mixture was refrigerated, and the hydrocarbon layer was analyzed by gas chromatography. The composition of the alkylate was next used to calculate the research octane number ( O X . ) of the product. Near the end of the current investigation, it was found that failure to decant the hydrocarbon layer from the acid layer as soon as possible was causing a 0.2-0.4 decrease in the calculated octane number. This decrease was relatively constant in all subsequent runs. d similar decrease is also undoubtedly occurring in many commercial units that do not immediately separate the two phases. The octane number results, as reported here, are hence on the conservative side in that slightly better quality alkylates were actually formed. Acids for this investigation were prepared by blending used alkylation acids, fresh sulfuric acids, and a red oil extract obtained from used acids. Two used acids were obtained from American Oil Co. The first, with an acid strength of 89.97,, contained 3.7% water and 6.4% red oil; the second, with a n acid strength of S8.7%, contained 2.6% water and 8.7% red oil. The term red oil as used here refers to acid-soluble hydrocarbons. The red oil extract was obtained by diluting used acids with ice (and water), and using a hexane extraction procedure to recover part of the acid-soluble hydrocarbons (Jliron and Lee, 1963). The strengths of the used alkylation acids in this investigation were determined by titration with 1 N NaOH using phenolphthalein as the indicator. I n such a procedure, monobutyl sulfates contribute some to the acid strength. The water contents of the acids were determined by mixing a fuming sdfuric acid (equivalent to 103 or 105 wt % sulfuric acid) with the acid until fuming just started; this technique was

Alkylation runs were made using sulfuric acids whose compositions varied from 83.2 to 100% titratable acidity, from 0 to 5.3% water, and from 0 to 15.7% dissolved hydrocarbons. Alkylation runs were made with all three C4 olefins, but the most extensive data were obtained using 2-butene. The specific acid compositions for the 2-butene runs were selected sequentially to explore the region of high-quality alkylate thoroughly. As subsets of these runs, factorial designs in the acid composition variables of water and red oil (R.O.) content were used. Some runs were also repeated to provide a n overall estimate of experimental error for judging significance of effects and adequacy of the mathematical models developed. Several runs were made using acids containing less than 0.5% water. -4lthough the qualities of the alkylates as measured by the octane numbers were frequently high, the yields of alkylates based on the amount of olefin used were in all cases low-significantly less than the theoretical yield. Since the acid strength also dropped significantly during these runs, it is obvious that olefins were forming acid-soluble hydrocarbons. I n all runs made with higher amounts of mater, the yields were essentially equal to the theoretical. These results clearly indicate t h a t water contents less than 0.5% are then of no commercial interest for alkylation, and most of the runs in this investigation were then limited to higher water contents. Alkylate Quality. Alkylates obtained when 1-butane and 2-butene were used had calculated octane numbers ranging from 93.9 to 98.2, while isobutylene alkylates varied from 89.7 to 92.7 O X . In general, as the octane number increased, the alkylate was found to have a higher trimethylpentane content but lower amounts of light ends (C6-C7 isoparaffins), dimethylhexanes, and heavy ends (C, and higher isoparaffins). Table I shows typical values for each family of compounds as a function of the octane number. Sufficient data are available for 2-butene alkylates to determine how alkylate compositions were affected by changes in the composition of the feed acid. The fraction of trimethylpentanes decreased appreciably and those of both the light ends and dimethylhexanes increased with increased amounts of water and of red oil for red oil contents above 67,. Trends for heavy ends are less certain, but the heavy end content increased with increased water and Ind. Eng. Chem. Process Des. Develop., Vol. 11, No. 3, 1972

447

,

I

3

I

~~

I

Table II. Regression Analysis for Equation 1 Sum of Deg. of mean F Source squares freedom sq. rdio Fo 9 g n Red oil-linear 4 07 1 4 07 31 13 7 Water-linear 11 50 1 11 50 85 13 7 Red oil-squared 11 55 1 11 55 86 13 7 Red oil X water 2 46 1 2 46 19 13 7 WEIGHT

% RED O I L


Figure 1 . O.N. as a function of feed acid composition using 2-butene as olefin

probably with decreased amounts of red oil in the range from 0 to 7% red oil. Trimethylpentanes are major components of alkylates, and their composition also varied with acid composition. Lower fractions of 2,2,4-trimethylpentane and higher fractions of 2,3,3- and 2,3,4-trimethylpentanesJ in general, occurred with increased amounts of water and red oil; these three isomers comprised most of the trimethylpentanes in all cases. The results of 30 runs using 2-butene in which high yields were obtained (acid contained over 0.5% water) were analyzed using full quadratic models in water and red oil content. For the octane number, the following model was found to have all terms significant, and the deviations about the predicted values are essentially equal to the experimental error estimated from duplicates: O X . = 97.0

+ 0.50 (ojOR.0.) - 0.35 (%H?O) 0.037 (%Reo.)* - 0.067 (%R.O.)(%HzO)

(1) Figure 1 shows the contours calculated from Equation 1; the 30 experimental data points are also given on this graph. A summary of the statistical calculations for establishing that Equation 1 is a valid representation of the results is presented in Table 11. Only the results of the final regression analysis for octane number are given although various models and terms were considered for octane number and the detailed composition responses (Sumutka, 1971). Figure 1 clearly indicates t h a t the water content should be maintained in the range of 0.5 to 1.0% to obtain the highest quality alkylate for a n acid with any given red oil content. As the water content increases above this level, the alkylate quality decreases rapidly. Some dissolved hydrocarbons are needed to obtain the maximum quality alkylates. As the red oil content increases above 6-870 however, the quality of the alkylate slowly decreases. It is of interest t h a t a 95-96 O.N. alkylate was produced for a n acid such as is commonly discarded from a commercial alkylation process; such a n acid might often contain 4 4 % water and 5-7% red oil. Yet the same quality alkylate is produced with acids having acidities as low as 84-86Y0 if the water content is reduced to 0.5-1.0%. Less extensive data (see Table 111) were obtained for alkylations using 1-butene as the olefin feed. The results for five runs of Li et al. (1970) are available, and a n additional eight runs were made in the present investigation. Four of these latter runs can be compared directly with 2-butene runs. When acids containing no red oil were used, the quality of the 1-butene alkylates were often slightly greater than those of 2-butene alkylates; this finding confirms earlier results (Shlegeris and Albright, 1969; Li et al., 1970). However, when several percent red oil was present in the acids, the alkylates for comparable runs produced from 1-butene were generally poorer in quality by about 0.6 O X . than alkylates produced from 2-butene. 448

Ind. Eng. Chem. Process Des. Develop., Vol. 11, No. 3, 1972

Due to regression Deviation about regression Error from duplicates a Critical value of

29 58

4

7 40

3 28

25

0 13

57

9 2

0 77 6 0 13 F ratio at 99% significance level.

I n such cases, slightly greater amounts of dimethylhexanes and heavy ends were present in 1-butene alkylates. Although the data for 1-butene alkylations are less extensive, the general trends relative to the w-ater and red oil contents of the acid are the same as for 2-butene alkylations. For isobutylene alkylations, the data for 11 runs are available for evaluating the effects of acid composition, as shown by Table IV. Five of these runs were made by Li et al. (1970). The qualities of the isobutylene alkylates were always much poorer (by 3 to 6 O X . ) than for corresponding runs using 2-butene. The qualities of isobutylene alkylates were, however, less affected by changes in acid composition than they were for the other two alkylates, and no clear trends have yet been established. Changes in Composition of Dissolved Hydrocarbons. I n this investigation, all acid-soluble hydrocarbons were grouped and treated as if they were essentially a single compound. Such an assumption is probably a good first approximation. Some preliminary information has been obtained that helps clarify this point. First, used alkylation acids darken significantly as they age a t ambient temperatures. Oxidation reactions also occur, and some sulfur dioxide is evolved. Storing used acid in a refrigerator minimizes color changes and oxidation. On several occasions, runs mere made with an old and dark acid a t operating conditions identical to those used earlier when the acid was new and lighter colored. For each comparison, no significant changes were noted for the composition and qualit,\; of the alkylates produced. The method employed for recovery of red oil from used sulfuric acids only yielded a t most 50% of the acid-soluble hydrocarbons. It seems obvious that the recovered hydrocarbons would not have the same composition (and molecular weight) as the hydrocarbons present in the original used acid. The color of the red oil recovered from the used acid was also found to vary. I n some cases, a light yellow liquid with a relatively low viscosity was obtained; on standing a t ambient conditions, this liquid darkened and became more viscous. With older and darker used acids, poorer yields of red oil were obtained, and the recovered red oil was darker and more viscous. Three runs were made in which extracted red oil was mixed with fresh acid to produce synthetic used acid blends containing up to 3.2% red oil. These runs were compared to runs with acids of similar composition, except in the latt'er case, the acid mixtures were obtained by blending used acids, fresh concentrated sulfuric acid, and red oil extract. Essentially identical alkylation results were obtained for the two types of acid blends. When the results for several corresponding runs using different used acids obtained from American Oil Co. were compared,


the alkylate produced with the second acid was lower by about 1 O.N. than t h a t produced with the first acid. A full quadratic model with a n added term was used for a regression analysis of the data. A significant effect of 0.9 0.3. was found by this procedure. This factor was applied to correct the results of the six runs made with the second acid so t h a t these results can be combined with the results of the 24 runs made with the first acid. The validity of this correction is further demonstrated by the fact t h a t the residual from the final model for Equation 1 is essentially equal to t h e value expected for a valid model, namely, the estimate of experimental error based on duplicated runs. It is thought t h a t the differences between the two acids may have been caused by variations of the butyl sulfate composition. Such a variation would also affect the calculated red oil composition t h a t is determined by difference. Secondary Reactions. I n numerous runs, secondary reactions were investigated by the technique first used by Li e t al. (1970). I n each case, the exit line from the reactor was closed after steady-state operation had been obtained. I n this way, the flow system vas suddenly converted to a batch system, and maintained as a batch system for several additional minutes. These runs were primarily made with feed acids containing 0.9-2.6% water and 0- 17.3% red oil. I n all six runs with 2-butene, the concentration of trimethylpentanes in the alkylate increased during 5 min allowed for secondary reactions. Furthermore, the quality of the alkylate also increased by 0.3 to 1.0 O X . with an average value of 0.6 O X . Runs for 1-butene and isobutylene were with acids containing 4- 13.8y0 red oil. The alkylate quality increased in all five 1-butene runs by 0.1-0.9 O X . with a n average increase of 0.5 O.N.; 5-10 min time was provided for the secondary reactions. Increases (average of 0.4 O N . ) of alkylate quality were noted in three runs with isobutylene, and a decrease of 0.3 O.N. was noted in the other run. The acid strength tended to increase slightly during the secondary reactions as noted by the strength before and after the secondary reactions. Calculations based on the alkylate yields and the composition of alkylates before and after the secondary reactions confirm, as shorn-n earlier by Li et al. (1970), t h a t acid-soluble hydrocarbons were reacting with isobutane to form primarily trimethylpentanes. Acid Consumption During Alkylation. Acidity measurements xere made of the feed acid and of the exit acid from alkylation system. Insufficient information was obtained to measure the acid consumption accurately, but the decrease in acid strength during the run should give a quantitative indication of the probable consumption. Unfortunately, it was not easy to measure accurately the acidity of some used acids containing considerable red oil because of the dark color of the acid. The decrease in acid strength during a run seems to be relatively constant for acids containing approximately 1% water regardless of t h e red oil content. Such information implies t h a t the rate of hydrocarbon buildup in the acid is then reasonably constant. The acid strength decreased, however, to a much greater degree during all runs using acids with less than 0.5% water. There are preliminary indications t h a t the decreases may also be quite high with acids containing 4% or higher water. Role of Water and Dissolved Hydrocarbons

The shape of the octane number contours, such as shown in Figure 1, can be explained by a combination of chemical and physical factors t h a t change with the acid composition.

Table 111. Effect of Acid Composition on Alkylate Quality for Runs Using 1-Butene as Olefin Acid comDosition

% Water

% Dissolved hydrocarbons

Research O.N. (calcd)

0.0 0.7 0.9 0.9 1.0 1.2 1.3 1.7 1.8 2.1 2.6 2.6 3.6

0.0 0.0 7.6 12.2 4.0 1.7 8.7 3.2 0.0 4.8 6.4 8.7 0.0

94.7 96.8 96.3 95.1 96.1 97.2 96.0 97.2 96.7 96.7 96.0 93.9 93.9

Table IV. Effect of Acid Composition on Alkylate Quality for Runs Using Isobutylene as Olefin Acid composition

% Water

% Dissolved hydrocarbons

Research O.N. (calcd)

0.8 0.9 1.0 1.2 1.7 2.1 2.5 2.6 2.6 2.6 5.2

0.0 7.6 4.0 1.7 2.2 4.8 0.0 6.4 8.7 13.8 0.0

91.8 91.6 92.5 92.2 91.3 91.5 92.7 91.3 90.5 89.7 91.8

The water content of the acid probably affects the chemical factors to a considerable extent. Ionization and the rate of hydride transfer both change as the water content is varied. It should be realized t h a t G a m e r (1967) who investigated hydride transfer limited his investigation to sulfuric acids that contained no dissolved hydrocarbons. Additional inforniatioii is needed with used alkylation acids since hydride transfer is affected by dissolved hydrocarbons (dlbright, and Li, 1970). Water, in addition, affects both the viscosity of the acid phase and the solubility of isobutane in the acid. Cupit et nl. (1961) report t h a t isobutane solubilit'y decreases slightly as the water content is raised. The overall importance of water on the physical steps of t'lie alkylation sequence is probably relatively small, however. Hydrocarbons dissolved in the acid phase undoubtedly have significant effects on both physical and chemical steps of the alkylation reaction. The red oil ~ o u l dbe expected to affect isobutane solubility and to have some surface-active properties in the two-phase system. Furthermore, preliminary observations in this investigat'ion showed that tlie viscosity of the acid increased as the amount' of dissolved hydrocarbons in it increased. A11 of the above factors would affect the cliaracter of t h e emulsion in the reactor, and the rate of transfer of the isobutane to the acid phase. Li et al. (19iO) have reported extensive data indicating t h a t this transfer step is the most controlling step of the entire process. Dissolved hydrocarbons in the acid phase also react in intermediate steps in the alkylation sequence (Albright and Ind. Eng. Chem. Process Des. Develop., Vol. 1 1 , No. 3, 1972

449


Li, 1970; Hofmann and Schriesheim, 1962). Sufficient amounts of these hydrocarbons are required to obtain the desired highquality alkylates. With those facts, the shape of the curves of Figure 1 can be explained. At rather low red oil levels, additional amounts of red oil are beneficial since the desired chemical effects of the red oil predominate. At higher levels of red oil, those physical effects that are detrimental to the reaction begin to predominate. A less effective level of agitation occurs in a given reaction system as the viscosity of the acid increasesLe., a t higher red oil contents. M7ith higher amounts of red oil, some of the red oil may also accumulate a t the interface betxeen the phases and hence have some effect on the transfer step of isobutane to the acid phase. The water content of the acid should be maintained between rather narrow limits. With insufficient water, adequate ionization does not occur to give high yields of alkylate. Jl'ith too much mater, undesired reactions are appreciable, as evidenced by increased light ends, dimethylhexanes, and heavy ends, and these reactions compete with the desired alkylation reactions. Recommendations for Commercial Plants

The results of this investigation indicate that the water content of the acid phase is most important to obtain the highest quality alkylate products. Most, if not all, refineries do not adequately dry their feedstocks nor control the level of water in the acid phase. I n such cases, the acid is normally discarded when only several percent acid-soluble hydrocarbons have been formed in the acid. Sufficient water has, however, accumulated so that the undesired reactions leading to light ends, dimethylhexanes, and heavy ends begin to become quite important. Furthermore, the rather high level of water causes the acid to approach the so-called i'runaaay'' conditions a t which acid strengths drop rapidly during alkylation. If the water content of the acid is maintained a t levels of about 0.5 to 1.0%, the acid could be used until acid strengths as l o x as 85% or even lower a e r e obtained. I n such a case, the dissolved hydrocarbon can be as high as 14%, which is a t least double that of most acids presently being discarded. Since the rate of formation of these hydrocarbons is thought to be as low and perhaps even lower than that of commercial units, the acid could be recycled twice as many times as in current units. K i t h effective water control, there will be no danger of a runaway reaction as the acid strength decreases. It is estimated that acid consumption can then be reduced by 50% or more if the water content of the acid is adequately controlled. For large alkylation plants with several reactors and employing series flow of the acid through the reactors, higher quality alkylates can be expected in the first reactors of the series than is currently obtained. With a system having three reactors, the acid strength in the three reactors would prob-

450

Ind. Eng. Chem. Process Des. Develop., Vol. 11, No. 3, 1972

ably be about 95, 90, and 85%, respectively. Estimates based on Figure 1 indicate overall alkylate qualities that are about 1.0 0.N. higher. Higher overall quality alkylate can also be expected in a n alkylation unit containing only a single reactor if the acid is handled batchwise-allowing a batch of acid to gradually become diluted with acid-soluble hydrocarbons until a strength of about 85y0 is reached. Corrosion would not appear to be a problem since the water content is controlled a t low levels. Thus, 85% acid contains mainly dissolved hydrocarbon and little Tr-ater, and the sulfuric acid strength in the water-acid combination is sufficiently high to avoid corrosion problems. T o maintain a low level of water in the acid phase, two recommendations are made. First, the feedstocks should be dried and care should be taken to prevent any water addition to the system such as by leaky heat exchangers. Second, the water content of the feed acid must be carefully controlled. It will in general be necessary to use more concentrated feed acids than is currently done. The results of the secondary reactions indicate that increased amounts of trimethylpentanes may often be produced in the alkylate if provisions are made for a n auxiliary or secondary reactor system. I n such a case, the alkylate quality will be increased. Acknowledgment

American Oil Co. supplied the used alkylation acid. literature Cited

Albright, L. F., Chem. Eng., 73 (21), 209 (1966). Albright. L. F.. Li. K. IT., Ind. Ena. Chem. Process Des. Deielop., 9, 447 (1970). ' Cupit, C. R., Gwyn, J. E., Jerigan, E. C., PetrolChem. Eng., 33, 214 (December 1961). Deno, N. C . , Boyd, D. B., Hodge, J. D., Pittman, C. G., Turner, J. O., J . Amer. Chem. Soc., 86, 1745 (1964). Hofmann. J. E.. Schriesheim. A , ibid.. 84.953. 957 (1962). Kramer, G. AI., J . Org. Chem., 32,920 (1967). Li, K. R., Eckert, R . E., Albright, L. F., Ind. Eng. Chem. Process Des. Develop., 9,434,441 (1970). Rliron, S., Lee, R. J., J . Chem. Eng. Data, 8,150 (1963). RIosby, J. F., Albright, L. F., Ind. Eng. Chem. Prod. Res. Develop., 5 , 183 (1966). Shlegeris, R. J., Albright, L. F., Ind. Eng. Chem. Process Des. Develop., 8, 92 (1969). Sumutka, A. AI., AIS thesis, Purdue Univ., Lafayette, I N , 1971. RECEIVEDfor review October 12, 1971 ACCEPTED April 3, 1972 Presented a t the Division of Petroleum Chemistry a t the 162nd Meeting, ACS, Washington, DC, September 1971, Cities Service Corp. and E. I. d u Pont de Xemours & Co., Inc. provided financial support with fellowships.

Alkylation of Isobutane with Butenes: Effect of Sulfuric Acid

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