I n d . E n g . Chem. Res. 1988,27, 381-386
$(Pi,T),I)/, = deactivation functions defined by eq 1, 2, 3, 4, 18, 37a, 47, and 48, s-l $G', $G = deactivation functions defined by eq 17 and 20 or 46 and 49, s-*
Literature Cited Arandes, J. M.; Azkoiti, M. J.; Bilbao, J. Chem. Eng. J. 1985a, 31, 137. Arandes, J. M.; Romero, A.; Bilbao, J. Znd. Eng. Chem. Process Des. Deu. 1985b,24, 828. Barbier, J. Appl. Catal. 1985,13, 245. Carbucichio, M.; Forzatti, P.; Trifiro, F.; Tronconi, E.; Villa, P. L. Proceedings of the International Symposium o n Catalyst Deactiuation, Antwerp, 1980; Delmon, B., Froment, G. F., Eds.; Elsevier: Amsterdam, 1980. Corella, J.; Asiia, J. M. Znd. Eng. Chem. Process Des. Deu. 1982,21, 55. Corella, J.; Bilbao, J.; Aznar, M. P. Znt. Chem. Eng. 1985a, 25, 275. Corella, J.; Bilbao, R.; Molina, J. A.; Artigas, A. Znd. Eng. Chem. Process Des. Deu. 1985b,24, 625. Corella, J.; Menhdez, M. Chem. Eng. Sci. 1986,41(7), 1817. Corella, J.; Aznar, M. P.; Monzbn, A. An. Quim. 1987,83, 91. Corella, J.; Aznar, M. P.; Monzbn, A. Znt. Chem. Eng. 1988,in press. Corella, J.; Monzbn, A.; Butt, J. B.; Absil, R. P. L. J.Catal. 1986,100, 49. Evans, J. W.; Trim, D. L.; Wainwright, M. S. Znd. Eng. Chem. Prod. Res. Deu. 1983,22, 242.
38 1
Fitzharris, W.; Katzer, J. P.; Manogue, W. H. J . Catal. 1982,76, 369. Forzatti, P.; Buzzi-Ferraris, G. l n d . Eng. Chem. Process Des. Deu. 1982,21, 67. Frusteri, F.; Barcellona, V.; Mento, G.; Parmaliana, A.; Giordano, N. Ann. Chim. (Roma) 1985, 75, 441. Fuentes, G. A.; Boegel, J. V.; Gates, B. C. J. Catal. 1982, 78, 436. Fuentes, G. A. Appl. Catal. 1985, 15, 33. Haas, J.; Fetting, F.; Oubicza, L. Acta Phys. Chem. 1985, 31, 659. Hicks, R. F.; Bell, A. T. J. Catal. 1984,90, 205. Kittrell, J . R.; Tam, P. S.; Eldridge, J. W.Hydrocarbon Proc. 1985, Aug, 63. Mardaleishvili, R. E.; Rapoport, Yu. I. J. Catal. 1985, 95, 447. Nelder, J . A.; Mead, R. Comput. J . 1964, 7, 308. Orr, N . H.; Cresswell, D. L.; Edwards, D. E. Znd. Eng. Chem. Process Des. Deu. 1985,22, 135. Pal, A. K.; Bhowmick, M.; Srivastava, R. D. Znd. Eng. Chem. Process Des. Dev. 1986,25, 236. Papayannakos, N.; Marangozis, J. Chem. Eng. Sci. 1984,39, 1053. gethwisch, D. G.; PhilIips, J.; Chen, Y.; Hayden, T. F.; Dumesic, J. A. J . Catal. 1985, 91, 167. Shum, V. K.; Butt, J. B.; Sachtler, W. M. H. J . Catal. 1985,96,371. Soong, Y.; Krishna, K.; Biloen, P. J. Catal. 1986, 97, 330. Srivastava, R. D.; Guha, A. K. J . Catal. 1985,91, 254. Sudhakar, Ch.; Vannice, M. A. J . Catal. 1985, 95, 227. Trimm, D. L. Chem. Eng. Process. 1984,18, 137.
Received for review May 27, 1986 Accepted October 2, 1987
Alkylation of Isobutane with C4 Olefins. 1. First-Step Reactions Using Sulfuric Acid Catalyst Lyle F. Albright,* Mark A. Spalding, James A. Nowinski, Robert M. Ybarra, and Roger E. Eckert School of Chemical Engineering, P u r d u e University, W e s t L a f a y e t t e , I n d i a n a 47907
Considerable information has been obtained concerning the operating variables required for the first step of a two-step alkylation process t o produce high-quality gasoline blends. With n-butenes, sec-butyl sulfates are produced in the first step, and the alkylates can be produced in the second step with research octane numbers over 100. With isobutylene, however, low polymers form as intermediates that lead t o relatively poor-quality alkylates. The results of this investigation clarify the chemistry and provide important information for developing a two-step alkylation process. Two-step alkylation of isobutane can produce highquality alkylates with research octane numbers (RON'S) as high as 99-101 (Albright et al., 1977b). In this process, n-butenes are reacted in the first step, or first reactor, with sulfuric acid or HF to produce sec-butyl esters. In the second step, or second reactor, the sec-butyl esters are reacted with isobutane in the presence of excess sulfuric acid or HF to produce isoparaffin alkylates and to recover the acid catalyst. Alkylates containing 90% or more trimethylpentanes have been produced by the two-step process (Albright et al., 1977b);these alkylates had much higher quality than those produced in commercial alkylation plants. lko-step alkylations offer potential economic advantages including less recycle of isobutane, use of weaker sulfuric acid, and less agitation. The exothermic first-step reaction possibly can be operated without refrigeration which would be a significant energy saving. Trimethylpentanes (TMP's) are the most important and also most desired family of isoparaffins produced. Production of trimethylpentanes is generally more complicated than the simple chain mechanism proposed by Schmerling (1953, 1964). The mechanism which involves a trimethylpentyl cation (TMP') is 0888-5885/88/2627-0381$01.50/0
t-C4Hg++ 2-butenes or isobutylene TMP+ + isobutane
-
TMP
-
TMP+ (1)
+ t-C4H9+
(2)
The past mechanism fails to explain several key features (Albright, 1977). For example, butenes react or disappear from the hydrocarbon phase more rapidly than isobutane. The mechanism also does not adequately explain the production of dimethylhexanes (DMH's) and the relatively poor quality of alkylates produced from isobutylene. Appreciable amounts of sec-butyl sulfates are frequently produced from n-butenes, but all attempts to date to produce tert-butyl sulfates from isobutylene have been unsuccessful (Albright et al., 1977a; Faunce, 1978). The alkylation mechanisms for isobutylene and n-butenes obviously differ greatly. Previous investigations of the first-step reactions by Albright et al. (1977a) were limited to low temperatures, -30 to -10 "C, and the analytical techniques then employed were incomplete. Investigations are still needed at higher temperatures, different acid compositions, and a wider range of operating variables. Solubility of butyl sulfates in the hydrocarbon phase may be important; yet no solu0 1988 American Chemical Society
RERCTIW TIME ( M l N . 1
Figure 2. First-step hydrocarbon phase compositions for two runs at -20 O C , 1/0= 1.5 with 96.4% sulfuric acid.
First-Step Experiments with Liquid Mixtures of n -Butenes and Isobutane Both mono-sec-butyl sulfate (MBS) and di-sec-butyl sulfate (DBS) were produced by slowly adding sulfuric acid in measured amounts to liquid mixtures of n-butenes and isobutane:
-
n-C4H8+ H2S04 MBS Figure 1. Exploded view of alkylation reactor.
bility information is currently available. Considerable additional data have been obtained in the present investigation on the production of both monosec-butyl sulfate and di-sec-butyl sulfate. In contrast, at similar conditions isobutylene forms predominantly trimers, tetramers, and pentamers. Operating variables for the first step of a two-step n-butene alkylation process are suggested.
Equipment and Operating Techniques Two types of reactors were used in this investigation of the first-step reactions. The first reactor was a large glass test tube and was provided with a mechanical agitation (Nowinski, 1985). It was stoppered a t the top and provided with a gas-tight seal for the impeller shaft; a similar reactor was described earlier (Doshi, 1975; Ewo, 1976; Faunce, 1978). The second reactor was of similar design except it was constructed of steel and equipped with two thick-wall glass windows. It was used a t pressures up to 6 atm. Three agitator impellers and four baffles were provided in the second reactor to ensure vigorous agitation of the liquid phases. An exploded view of this reactor is shown in Figure 1. Several openings were used in each reactor for adding the acid and liquid hydrocarbons, to provide a helium blanket if desired, for sampling and for removing the products. For the steel reactor, liquid samples were withdrawn by using a hypodermic needle that penetrated the self-sealing silicone rubber septum on a top opening. In general, 5Ck250 mL of reactants was employed for each batch run. The steel reactor was immersed in a bath that was controlled to h0.5 "C a t temperatures as low as -30 OC. The volumes of feedstocks added to the reactor were determined with burets. As a check, the liquid volumes in the reactor were also determined from calibrations on the tube side walls or the glass windows. When agitation in the reactor was stopped, the liquid phases separated and the volume of each phase was measured. The liquid phases were analyzed by gas chromatography, NMR, infrared, and/or hydrolysis followed by acid titration. The Karl Fischer method was employed to measure the water content of the various liquids.
+ n-C4H8
MBS
(3)
DBS
(4)
Conditions investigated in this series of runs were as follows: temperature, -30 to 30 "C; acid-to-olefinmolar ratios (A/O), up to about 2 ; acid compositions, 92-96.7% acid, 1-8% water, 0-4.6% conjunct polymer, and traces of sulfur dioxide; isobutane-to-olefin molar ratios (I/O), 1 to 3. After several drops of acid were added to the hydrocarbon phase, two liquid phases formed. Figure 2 gives the combined data of two runs in which the A/O was successively increased by adding small amounts of acid at various time intervals. The hydrocarbon phase was always the continuous phase of the emulsion a t low A/O. DBS was formed almost exclusively a t A/O up to about 0.4. About 5-8% by weight DBS was dissolved in the hydrocarbon phase a t A/O of 0.282 and 0.564. Because of the low acidity of the resulting bottom phase, isobutane was inert in these runs. As will be discussed later, more DBS dissolved in the hydrocarbon phase at A/O of about 0.45. At higher A/O, the DBS content decreased since DBS was converted to MBS: DBS
-
+ H2S04
2MBS
(5)
When fresh acids were added, no color developed in either liquid phase. When used acids which contained dark conjunct polymers were added to produce A/O less than 0.6, the hydrocarbon phase was tinted brown. Apparently some dark conjunct polymers were extracted from the bottom phase, but the color disappeared at higher A/O's. MBS was found to be highly soluble in the acid phase but a t most only slightly in the hydrocarbon phase. Several tests confirmed that the sulfate dissolved in the hydrocarbon phase was predominantly if not exclusively DBS. In one test, the hydrocarbon phase was separated from the bottom phase and subjected to vacuum to remove most if not all of the isobutane and unreacted n-butene; a rather viscous clear liquid was obtained. The following evidence indicates that it is essentially pure DBS. (a) The NMR spectrum of this liquid, as shown on Figure 3, had relative signal areas and positions consistent with the predicted ones for DBS (Spalding, 1985). The same peaks were also obtained for the hydrocarbon phase that was a mixture of isobutane, n-butene, and the butyl sulfate. (b) The IR spectrum of the liquid, Figure 4,was also consistent with DBS (Spalding, 1985).
Ind. Eng. Chem. Res., Vol. 27, No. 3, 1988 383
g
40
Q
P I
z 0
m 30
a
90
a a
$
20
W
I if
IO
v)
m
a t' 6
5
4
3
2
1
06
Figure 3. 'H NMR spectrum of DBS.
0
a
0 0
0.2
iz
0.4
0.6
0.0
1.0
A / O RATIO
Figure 5. DBS contents in the hydrocarbon phases for first-step runs with used alkylation acid of 93.9% acidity.
Figure 4. Infrared absorption spectrum of the sulfate phase for A/O = 0.45.
(c) The density of the liquid was 1.05 g/cm3; the density of di-n-butyl sulfate as a comparison is 1.062 (Druckey et al., 1970). (d) The liquid was hydrolyzed by refluxing. Titration indicated the resulting liquid contained 45.0% by weight H2S04. The predicted value for complete hydrolysis of DBS is 46.6%. Some isobutane or n-butene was perhaps still in the liquid. DBS liquid was stored for extended periods at -20 "C, and no instabilities were noted. Even at room temperature, DBS appeared stable for a t least several hours. Gas chromatographic analyses of mixtures of DBS, isobutane, and n-butenes are complicated by reactions in the vaporization hot block. DBS decomposes to produce H2S04and an equilibrium mixture of n-butenes by the reverse reactions of eq 3 and 4. Doshi (1975),who had used similar chromatographic techniques, was unaware of these decomposition reactions. He consequently mistakenly concluded that some 1-butene was isomerized to 2-butenes in the first-step reactor. The hydrolysis results of this investigation confirmed the presence of DBS in the hydrocarbon phase since the resulting acid-to-olefin molar ratio was essentially 0.5. The DBS concentration in this phase decreased as expected when the isobutane-to-olefin (I/O) ratio in the liquid feedstock increased. A series of runs was made to investigate the effect of temperature and of A/O on DBS production for first-step experiments using an acid that contained 93.9% H2S04, 4.6% conjunct polymer, 1.2% water, and 0.3% sulfur dioxide. This acid was produced by adding fuming sulfuric acid to a used acid from a commerical alkylation unit. Figure 5 shows the results at -15, -10, 0, and 10 "C. The amount of DBS dissolved in the hydrocarbon phase at each temperature passed through a maximum below A/O = 0.5. These maxima increased from about 18% a t -15 "C to about 40% a t 10 "C. For the bottom phase, the following conclusions can be made. At A/O up to 0.4, this phase was mainly DBS; small amounts of MBS, water, and conjunct polymers were also
0
0.2
0.4
0.6
0.0
A / O RATIO
Figure 6. Effect of acid composition on bottom-phase (sulfate) volume for first-step reactions between 2-butenes and various fresh acids.
always present. Most of the water and conjunct polymer in the feed acid likely remained in the heavy phase. A t about A/O = 1.0, the bottom phase was mainly MBS. Some water, conjunct polymer, sulfuric acid, and DBS were also present. These latter conclusions are based on Karl Fischer analysis for water and on acid titrations before and after hydrolysis of the sulfates. In runs with fresh acids that contained no conjunct polymers, separations of the two liquid phases were rapid and essentially complete after 15 min. With used acids however, separation was often slow; variations by as much as f10% occurred in measured acidities of the acid (or sulfate) phase before and after refluxing. In some cases, separation was apparently still occurring after 1or 2 days.
First-Step Experiments with Pure 2-Butenes Five fresh acids with acidities varying from 91.8% to 99.6% were dripped into liquid mixture of 2-butenes at -10 "C. At low A/O, two liquid phases formed for all acids. Figure 6 shows the large effect of both the water content of the acid and the A/O on the volume percent of the bottom (sulfate) phase in the two-phase mixture. The percent decreased greatly as the water content decreased. With 0.4% water (in 99.6% acid), only a trace of heavy phase was noted; at A/O greater than 0.19, there was only a single phase which contained primarily butene. It also contained dissolved DBS and a small amount of water. With 95.1% H2S04, the bottom or sulfate phase reached a maximum at about A/O = 0.5. As more acid was added,
384 Ind. Eng. Chem. Res., Vol. 27, No. 3, 1988 15 W
z +
\2
0
- c,=
W
60 W
a IX
2
40
W
3 20
0
0
0.2
0.0
0.6 A / O RATIO
0.4
I0
A/O RATIO
Figure 7. Hydrocarbons and single-phase compositions for first-step reactions between 2-butenes and 95.1% fresh acid a t -10 O C .
a I-
r
40
5?
s
t
20
0
0
0.1
0.2
0.3
0.4
0.5
0.6
A/O RATIO
Figure 8. Bottom-phase compositions for first-step reactions between 2-butenes and 95.1% fresh acid a t -10 O C .
the bottom phase disappeared a t A/O = 0.56, resulting in a single phase that was a mixture of butene, DBS, MBS, H2S04,and water. The run with 91.8% acid showed a different phenomena; the fraction of bottom phase increased as more acid was added until the top phase disappeared a t A/O of about 0.77. Figures 7 and 8 report the compositions of the hydrocarbon-rich and bottom phases, respectively, with 95.1% acid as a function of A/O. The DBS content of the hydrocarbon phase passed through a maximum at a A/O of about 0.5. The DBS was obviously highly soluble in the unreacted 2-butenes and the mixture contained over 60 w t % DBS. At A/O = 1.0, only a single phase was present, and the MBS content reached a maximum of 62%. The bottom phase was rich in MBS as shown in Figure 8. Similar shaped curves were generated for all acid concentrations, and DBS maxima occurred for all acids tested a t about A/O = 0.5. The DBS maxima decreased from about 67% with 99.6% acid to about 61% with 95.1% acid. A run was made a t -10 "C, and 99.6% acid was added to obtain A/O = 0.43. As shown in Figure 6, only a single phase was present. Water was then added to the resulting liquid to provide the same amount of water that would have been present if 95.1 % feed acid had been used. Two phases formed with a volume ratio comparable to that shown in Figure 6 for 95.1% acid. Slightly more DBS was, however, present after the addition as compared t o that of the run with 95.1% acid. Several runs were made with synthetic used acid. Such acids were produced by bubbling 1-butene through fresh acids. The results of these runs were similar to those using fresh acids. Analyses of the resulting bottom phases were
Figure 9. Effect of temperature on bottom-phase (sulfate) volume for first-step reactions between 2-butenes and 97.3% fresh acid.
Table I. DBS Concentration in Solvent Phase (First-Step Experiments) H20 in DBS in temp, fresh acid, Solv/O: A/O,b solvent, solvent O C wt % wt ratio mole ratio wt % 2,2,4-TMP -10 0.4 1.0 0.52 19 -10 2.1 0.9 0.50 44 -10 4.9 0.9 0.45 45 -10 9.0 1.0 0.50 34 2,2,4-TMP -20 0.4 1.0 0.49 13 -20 2.7 0.9 0.47 34 2,2,4-TMP -10 4.9 0.45 0.50 56 n-pentane -10 0.4 1.0 0.50 21 -10 2.1 0.58 0.50 52 isobutane -10 3.8 1.0 0.45 23 -10 9.2 1.0 0.45 17 Solvent/olefin. *Acid/oleAn.
difficult because of the conjunct polymers. Perhaps slightly more DBS was formed and dissolved in the top (or butene-rich) phase. Figure 9 shows a comparison of runs at -20 and -10 "C when 97.3% fresh acid was used. There is less bottom phase at higher temperatures; obviously DBS solubility in 2-butenes increased with temperature.
First-Step Experiments with Solvents A series of fmbstep runs was made in which the starting hydrocarbon liquid was a mixture of solvent and 2-butenes. Solvents investigated include 2,2,4-TMP (an important product in alkylation), isobutane, and n-pentane. Two phases occurred as the A/O increased to 1. A t A/O up to about 0.5, the volume of the bottom phase was less than the volume of acid added since the DBS produced dissolved to a significant extent in the top phase. At higher ratios, MBS was predominant, and it partitioned primarily to the bottom phase. Hence, the volume of the bottom phase became greater than the volume of the acid added. A t an A/O of about 0.5, seven runs were made using 2,2,4-TMP as a solvent, two with n-pentane, and two with isobutane. The several acids investigated had water contents varying from 0.4% to 9%. Table I indicates the DBS content for these runs in the solvent or hydrocarbon phase. (a) With 2,2,4-TMP and using a solvent-to-olefin (S/O) weight ratio of about 1.0 a t 10 "C,the DBS content in the hydrocarbon phase passed through a maximum a t an intermediate water amount in the acid. (b) Lower temperatures significantly decreased the DBS concentration in the hydrocarbon phase as shown by runs made at -20 and -10 "C.
Ind. Eng. Chem. Res., Vol. 27, No. 3, 1988 385 Table 11. Solubility of DBS in Three Solvents
solvent 2,2,4-TMP n-pentane n-octane
temp, "C 0 -10 0 -10 0
S/DBS,
lsobutane
DBS in solvent, w t
wt ratio
%
0.75 0.97 0.72 0.75 0.98
28.0 23.6 27.0 8.9 13.8
(c) A decrease in S/O ratio from 1to 0.5 caused the DBS concentration in the hydrocarbon to increase from 45% to 56%. As also indicated in Table I, DBS was about equally soluble on a weight basis in n-pentane and 2,2,4-TMP. It is, however, much less soluble in isobutane; these results are considered preliminary. Tests indicated that the method of adding 2,2,4-TMP to the reaction mixture was unimportant. In the first method, the solvent was added to the 2-butenes before the acid was added. In the other method, 2,2,4-TMP was added after the acid was contacted with the 2-butenes, and no significant differences in results were noted. Three liquid phases were noted simultaneously in several runs when either 2,2,4-TMP or n-pentane was used as the solvent. In each case, low temperatures, -20 " C or less, and either 96.0% or 97.3% acid were used. In two cases, systems with three liquid phases were agitated and then heated by about 5-10 OC. As a result the two lighter phases were solubilized into a single phase; recooling the mixture once again resulted in three phases. When three phases were present, the bottom phase apparently contained mainly water, unreacted HzS04, and MBS; the middle phase was rich in DBS; and the top phase was rich in solvent. More investigations are needed to clarify the phenomena. DBS was prepared as already explained, and a solvent was then added to determine solubility. The weight ratio of solvent to DBS employed was, in general, in the range 0.72-0.98. The results obtained with 2,2,4-TMP, n-pentane, and n-octane are shown in Table 11. The solubilities of DBS in 2,2,4-TMP and n-pentane were again found to be similar. Solubilities in n-octane were, however, much less. DBS solubility increased slightly with increased temperature, which is also in agreement with the earlier results.
First-Step Runs with Isobutylene The results of first-step runs with isobutylene were greatly different than corresponding runs with n-butenes. When acid was added even in small amounts to liquid isobutylene or liquid mixtures of isobutane and isobutylene, large exothermicities were noted. The predominant reactions were polymerization to form mainly C12, CIS,and Cmunsaturated hydrocarbons as indicated by gas chromatographic analyses. Relatively small amounts of acid-soluble hydrocarbons (probably conjunct polymers), sulfur dioxide, and water were also produced. A t A/O as little as 0.05, trace amounts of alkylate were produced in addition to the C12-C2,, unsaturated hydrocarbons. The hydrocarbon phase was clear, but the minute amount of the bottom phase was yellowish brown. Probably up to several percent of the isobutylene was converted to conjunct polymers. There is no indication that tert-butyl sulfates were formed; if they did form, they were apparently very unstable. Figure 10 indicates the analysis of the hydrocarbon phase for the runs at -20 "C in which 96.4% fresh acid was added to a 5050 mixture of isobutane and isobutylene.
40 W
I soparaff ins
a
=I-
clz=
6.01
01
IO
IO
A / O RATIO
Figure 10. Hydrocarbon-phase compositions for first-step runs using isobutylene and 96.4% sulfuric acid at -20 OC.
The isobutane was quite reactive during the entire run. The composition of the hydrocarbon phase can be accounted for by the formation of acid-soluble hydrocarbons that are highly unsaturated and that provide hydride ions to produce isoparaffins. As A/O increased, the degree of unsaturation of the hydrocarbon phase decreased; a t A/O = 0.05, its iodine value was 175; and a t A/O = 8, it was 42. A run with 100% sulfuric acid resulted in exceptionally high exothermicities, apparently because of both polymerization and oxidation reactions.
Discussion of Results Both DBS and MBS can be produced readily in high yields by reacting limited amounts of sulfuric acid with either 1-butene or 2-butenes. It is thought that sec-butyl fluoride can also be produced from HF in a similar manner. Valuable new information has been obtained on the solubilities of DBS in hydrocarbons including isobutane and 2,2,4-TMP and of MBS in sulfuric acid. Either MBS or DBS can be produced in the first-step reaction and then transferred to the second-step reaction for eventual production of alkylate. Transfer of relatively pure DBS to the second-step reactor is one possibility since it is one of the three liquid phases that can be produced simultaneously in a first-step reaction. The current results further confirm the significant differences in the basic alkylation chemistry of n-butenes versus isobutylene. Large differences also obviously occur during conventional alkylations (Albright, 1977; Albright and Li, 1970).
Acknowledgment The National Science Foundation provided generous financial support of this project by means of Grant 8120306. Registry No. MBS, 3004-76-0; DBS, 63231-73-2; 1-butene, 106-98-9; isobutene, 75-28-5; 2-butene, 107-01-7; sulfuric acid, 7664-93-9.
Literature Cited Albright, L. F. In Industrial and Laboratory Alkylations; Albright, L. F., Goldsby, A. R., Eds.; ACS Symposium Series 55; American Chemical Society: Washington, D.C.; 1977; Chapter 8. Albright, L. F.; Li, K. W. Znd. Eng. Chem. Process Des. Deu. 1970, 9, 447. Albright, L. F.; Doshi, B. M.; Ferman, M. A.; Ewo, A. In Industrial and Laboratory Alkylations; Albright, L. F., Goldsby, A. R., Eds.; ACS Symposium Series 55; American Chemical Society: Washington, D.C., 1977a; Chapter 6. Albright, L. F.; Doshi, B. M.; Ferman, M. A.; Ewo, A. In Zndustrial and Laboratory Alkylations; Albright, L. F.; Goldsby, A. R., Eds.; ACS Symposium Series 55; American Chemical Society: Washington, D.C., 1977b; Chapter 7.
386
Ind. Eng. Chem. Res. 1988,27, 386-391
Doshi, B. M. Ph.D. Dissertation, Purdue University, West Lafayette, IN, 1975. Druckey, H.; Kruse, H.; Preussmann, R.; Nashed, N.; Ivankovic, S.; Landschutz, C. 2. Krebsforsch 1970, 74, 241. Ewo, A. M. S. Dissertation, Purdue University, West Lafayette, IN, 1976.
Faunce, J. M. S. Dissertation, Purdue University, West Lafayette, IN, 1978. Nowinski. J. M. S. Dissertation. Purdue Universitv. West Lafavette. IN, 1985.
Schmerling, L. Znd. Eng. Chem. 1953,45, 1447. Schmerling, L. 'Alkylation and Related Reactions". In FriedelCrafts and Related Reactions; Olah, G . A., Ed.; Interscience: New York, 1964; Vol. 11. Spalding, M. A. Ph.D. Dissertation, Purdue University, West Lafayette, IN, 1985.
Received for review July 29, 1986 Accepted September 24, 1987
Alkylation of Isobutane with C4 Olefins. 2. Production and Characterization of Conjunct Polymers Lyle F. Albright,* Mark A. Spalding, Christopher G. Kopser, and Roger E. Eckert School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907
Conjunct polymers, which are byproducts formed during the alkylation of isobutane with C3-C5 olefins, dilute the acid catalyst used so that it eventually loses effectiveness. For alkylations involving both n-butenes and sulfuric acid, decomposition of sec-butyl sulfates produces conjunct polymers, liquid hydrocarbons rich in heavy isoparaffms and olefins, sulfur dioxide, and water. During alkylation the polymers are present as conjunct polymer sulfates that contain sulfone, sulfonic acid, or sulfonic acid ester groups. NMR and IR spectroscopies were used to elucidate the structure of the conjunct polymers. Conjunct polymers are often referred to as acid-soluble polymers or as red oil. They are minor byproducts formed during the alkylation of isobutane with C3-C5olefins. They have molecular weights mainly in the range 300-500, contain C5 and maybe C6 ring groups, and are highly unsaturated with both conjugated and nonconjugated double bonds (Ipatieff and Pines, 1936; Miron and Lee, 1963). When dissolved in acids, they likely react with the acids to form esters, sulfones, etc., but no conclusive evidence to prove this postulate is yet known. A small amount of dissolved conjunct polymers is desired in the acid in order to improve the quality of the alkylate, as indicated by higher octane numbers (Hofmann and Schriesheim, 1963; Mosby and Albright, 1966; Li et al., 1970). When different acid compositions were compared, the best quality alkylate was produced using an acid containing 4-5% conjunct polymer and 1-1.5% water (Albright et al., 1972). Conjunct polymers likely serve as excellent sources of hydride ions for production of isoparaffins from branched cations (Albright, 1977). When acids are diluted with too much conjunct polymer and/or water, the acids are ineffective as catalysts and must be replaced with stronger acids. In commercial alkylation plants, 0.2-0.5 lb of sulfuric acid are often consumed per gallon of alkylate, i.e., about 0.025-0.06 weight of acid per weight of alkylate. Feed acids typically contain 98-999'0 acid (and the remainder water); the used or discard acids have 90-92% acidity and contain 4-6% conjunct polymers, 3-5% water, and small amounts of dissolved SOz. Used sulfuric acids are currently regenerated by relatively expensive energy-consumingprocesses. There is hence considerable economic incentive to develop processes with lower acid consumption. Less acid consumption is normally obtained with the following: lower operating temperatures; hydrocarbon feedstocks that are free of butadiene, sulfur-containing compounds, and water; olefin feedstocks low in propylene, amylenes, and isobutylene; improved agitation; and higher isobutane-toolefin ratios of the feed hydrocarbons.
Table I. Composition of Hydrocarbons Resulting from Decomposition of sec-Butyl Sulfates Dissolved in Used Acid" 10 20 20 temp, "C
AI0
LE'S
TMP's DMH's HE'sb RON hydrocarbon yield, % iodine no.
soz, wt
%
1.2 9.2 33.3 18.9 38.6 88.8 10 170 0.03
12 13.6 7.7 7.9 70.8 86.4 12 7 0.04
1.2 12.7 37.2 13.0 37.2 91.2 20 180 0.03
Industrial used acid was mixed with fuming sulfuric acid; final acid contained 93.9% acid, 1.2% water, and 4.6% conjunct polymers. Some HE'S were unsaturated.
Conjunct polymers are produced, in part a t least, by decomposition of mono-sec-butyl sulfate that is dissolved in sulfuric acid (Albright et al., 1977). Oxidation reactions also occur with sulfuric acid acting as the oxidant (Doshi and Albright, 1976); sulfur dioxide and water are also produced simultaneously. When used acids containing some butyl sulfates are stored for several days a t room temperature, more conjunct polymers, a small amount of poor-quality gasoline fraction, SOz, and water are produced. The objectives of the present investigation were to study reactions of sec-butyl sulfates that produce conjunct polymers and other undesired products and to clarify the structure of the polymers especially when dissolved in the acid. The results indicate that the polymers contain appreciable sulfur atoms and have ,formed sulfates.
Decomposition of sec -Butyl Sulfates Dissolved in Acid Solutions of mono-sec-butyl sulfate (MBS) in sulfuric acid were prepared a t conditions reported by Albright et al. (1988). When such a solution was stored at -15 "C or lower, the solution was stable for at least several weeks.
0888-5885/S8/2627-0386~0~~50/00 1988 American Chemical Society
