Ind. Eng. Chem. Res. 1994,33, 712-717
712
Alkylation of Isobutane by Ethylene: A Thermodynamic Study Jean-Michel Goupil, Jean-Luc Poirier, and Daniel Cornet'
Laboratoire Catalyse et Spectrochimie, URA, CNRS DO414 ZSMRa, University of Caen, 6 Bd. Markchal Juin, 14050 Caen, France Alkylation of isobutane by ethylene produces mainly hexanes, but a variety of other compounds, alkanesor alkenes, may be formed by secondary reactions such as successive alkylations, isomerization, and ethylene polymerization. The equilibrium distribution of products is evaluated in the temperature range 280-680 K and at various initial compositions and pressures. Isomer groups are treated using Alberty's formulation. Calculations show that alkenes are thermodynamically unstable under usual reaction conditions. The equilibrium amounts of alkanes are such that c6 >> c8 >> Clo and heavy alkanes also appear unstable. The selective formation of particular isomers (dimethylbutanes, trimethylpentanes) is also integrated in the equilibrium equations. T h e calculated compositions (C6:c&lO) are compared with experimental data. 161
1. Introduction
Alkylation of isobutane by light alkenes CuHzU with the help of an acid catalyst produces a mixture of alkanes with high octane index. The reaction proceeds at about 0 "C in the liquid state. The acids H2S04 or HF are the preferred catalyst (Albright, 1990),but A1C13has also been mentioned (Roebuck and Everett, 1970). Branched ab kanes are the main products, and the selectivity for Cv+4 is high, but never reaches 100%. For instance, the reaction of isobutane with n-butenes catalyzed by HzS04 at -20 "C yields 90 % octanes, 4 % and 6 % of heavier products Cg+; the C8 cut contains up to 97% trimethylpentanes (TMP). However when the reaction is carried out at 10 "C, the amount of octanes is down to 46%, with only 81% TMP among the c8 (Albright et al., 1988). Similarly, reacting ethylene and isobutane with an AICb catalyst produces an alkylate with 73 % hexanes and 15% octanes, and the CS cut contains 95% 2,3-dimethylbutane (Dickenson and Reveal, 1971). Various solid catalysts with a high surface acidity, such as BF3/Si02, were patented for this process (Child et al., 1990). We examined chlorinated alumina as a potential catalyst for the reaction of isobutane with ethylene at 273373 K (Goupy et al., 1993). Results were generally similar to those observed with AlC13 in a liquid medium; for a ratio CY = isobutane/ethylene equal to 20 (mol/mol), the alkylate contained 85% hexanes and 12% octanes. The (26 cut was very rich in 2,3-DMB (up to 97%), while the c!3 cut contained dimethylhexanes (DMH) as well as trimethylpentanes (TMP). However, when the catalyst was not optimized, more than 50% heavy products Cg+ could be found in the alkylate. Oligomerization of the alkene CUHzv (Weitkamp, 1980),followed by alkylation of isobutane by the oligomers, may explain the appearance of alkanes higher than Cu+4. This paper goal is to establish the thermodynamic distribution of products expected when ethylene reacts with isobutane. Calculations will be performed in the temperature range 280-680 K, at pressures from 0.5 to 2.5 MPa and with a dilution ratio a = 5-20. Ideal gas behavior will be assumed for all compounds.
* To whom correspondence should be addressed. FAX: (33) 31 45 28 7 7 .
260
360
460
560
660
760
T/K
Figure 1. Equilibrium constants for the reactions 1-3. Key: solid lines, selective reactions; dotted lines, nonselective reactions.
2. Competition between Alkylation and Polymerization The primary alkylation i-C4H,o
+ C2H4 S C6H14
(1)
is likely to compete with ethylene dimerization 2C2H4s C4H, Then isobutane may be alkylated by the butenes imC4H10 + C4H8 S C8H18
(2)
(3) The equilibrium constants of these reactions are easily deduced from thermodynamic data (Kilpatrick et al., 1946). They were first evaluated in the conditions of the low-temperature alkylation, i.e. when selective reactions occur. A t full selectivity, reaction 1 produces 2,3-DMB only, and reaction 3, three TMP isomers, the 2,2,3-TMP being absent. Then dimerization 2 is likely to give the linear butenes. The quantities log K for reactions 1, 2, and 3 are plotted as solid lines in Figure 1. The equilibrium constants were also determined for completely unselective reactions, i.e. giving all of the hexanes, butanes, and octanes. Nonselective reactions
OSSS-5S85/94/2633-0712~0~.5QIO 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 3, 1994 713 Table 1. Standard Gibbs Energies of Formation AGOf (J/mol)
ethylene isobutane A
B A'
B' butenes (linear) 2,2 + 2,3-DMB 2,3-DMB TMP + DMH TMP (3 isomers)
c,,
u'=exp(
+ c,T + c,T(ln 27
Cn
C1
c2
59426 -117840 -47411 -19422 78254 -21163 2594.1 -164380 -154980 -199450 -201880
-114.42 -19.626 -62.079 42.297 -162.82 36.075 -53.933 125.35 64.31 207.73 244.28
25.219 60.522 9.2329 8.0811 5.2917 8.6652 44.609 69.697 78.471 84.911 83.419
appear to be more favored than the selective ones. Inspection of Figure 1 shows that in any event, reactions 1 and 2 are favored at temperatures up to 650 K. But below 500 K, the butenes may obviously disappear through reaction 3, and the amount of octanes produced in this way also complies with the equilibrium C6H14
+ C2H4
* C6H18
3. Unlimited Alkylations and Polymerizations Any process occurring in the system is a combination of successive alkylations (5) i-C4H10 + mC2H4 e C2m+4H4m+10 with equilibrium constant K, (m 1 l),and polymerizations
*
nC2H4 C2nH4n (6) with equilibrium constant K', (n I2). Molecules with an odd carbon number are nearly absent from the alkylate, sothat neither cracking nor metathesis need be considered. There is however a huge number of possible isomers. Calculations will be simplified when reactions are nonselective, i.e. all isomers are formed in mutual equilibrium. Then, the alkanes Csm+4can be considered as a single entity denoted as group (m); similarly, the alkenes Czn build up a group (n). Following Alberty (Alberty, 1983), the standard Gibbs energies of formation for hydrocarbon groups may be expressed as linear functions of the carbon number N:
+ BN, with N = 4 + 2m for alkane group (m) (7)
AGO, = A'
where PO is the reference pressure (0.1 MPa). The equilibrium constants of reactions 5 and 6 are now:
K, = .(TU)P O , K', = u'($v')"'
(11)
The partial pressure of any particular compound, or group, is a function of the fractional conversion of ethylene through each reaction. Starting with 1 mol of ethylene, we get at equilibrium mol of CzHd converted alkane group ( m ) all alkanes alkene group (n) all alkenes
x, x = Z&lX,
mol produced Xmlm
P = %-dx,/m) Yn I n q = Z&z(Yn/n)
yn
Y = E - 2 Yn
Then the unreacted fraction of ethylene is r = 1 - x - y. Equilibrium relationships for reactions 5 and 6 now read
and Yn
PO
+ Q + r)
( ~ y
= K', withn 2 2
(13)
Let
U = u(a - p ) , U' = ru', rv V=
and V' = "' (14) a+q+r' a+q+r The quantities x,/m and y,ln form geometric series (Alberty et al., 1986) ""= m UPwithmI 1
(15)
and Yn
= U'(V')"-l n
with n I2
(16)
Summing the series yields p
=
4=-
uv
m
U'V'
Then x, y and r are easily derived:
+ B'N, with N = 2n
for alkene group (n) (8) The quantities A, B, A', and B' were deduced from the data published for alkanes C4-Clo (Alberty and Gehrig, 1984)and alkenes C4-C8 (Alberty and Gehrig, 1985).Their variation with temperature was represented by A = co + c,T + c,T(ln T ) (9) Values appropriate to temperatures from 260 to 760 K are listed in Table 1, including the AGOf for ethylene (AGO,) and isobutane (AGO& From these, the following quantities may be evaluated u=exp(
RT
(4)
by which hexanes are alkylated by ethylene. Then octanes may be alkylated, etc. Therefore, equilibrium calculations in the ethylene + isobutane system should take into account all successive polymerization and alkylation steps.
AGO,= A
AGO, -A' - 2B'
AGOi - A - 4B RT
)
AGO -2B '=;["p(
dT
)I
Y=
U'V'(2 - V') (1 - V')2
(20)
Finally, U , V, U',and V' may be substituted into eqs 17, 18, and 21: uur(a - p )
= Ly
+ q + r(1- v)
(22)
alkanes
Table 2. Calculated Equilibrium Composition of the Alkylate (wt %): Indefinite Alkylations and Polymerization (Nonselective)
overall
wt%
T=
T=
T=
P(MPa) 280K 10 2.5 hexanes 93.6 octanes 6.0 decanes 0.36 ... butenes hexenes octenes ... 5 2.5 hexanes 87.3 octanes 11.1 decanes 1.3 butenes ... 20 2.5 hexanes 96.8 octanes 3.1 decanes 0.1 ... butenes
380K 92.9 6.7 0.45
480K 93.2 6.3 0.41 0.03 0.01
0
c
VI C
x 8
6
...
-0,l
0.75-
Y
VI
octanes
C
" U VI
ttecpnesxl 0
cy
C c
8 d6decanesxlOO
480
580
T/K
Figure 2. Indefinite alkylation and polymerization for nonselective reactions. cy = 10; P = 2.5 MPa. Key: (a, top) left scale, overall conversion of ethylene and fractional conversions into total alkanes andhexanes;rightscale,octanes,decanes(XlO)anddodecanes (XlOO); (b, bottom) fractional conversions of ethylene into total alkenes, butenes, hexenes (X2), and octenes (X4).
r+
+ q + r) a + q + r(1- u ) p(a
+
+ + r) - 2u'rl
Q[~((Y
a
+ q + r(1-
u')
=1
(24)
Numerical solutions of the system in @, q, r) are obtained by iteration for a set of temperatures. The equilibrium conversions into alkanes ( x ; XI;x2; x3; x4) and alkenes (y; y1; y2; y3) are plotted in Figure 2 for a = 10 and P = 2.5 MPa. Equilibrium allows complete conversionof ethylene at all temperatures under 600 K, giving alkanes as the only stable products. Figure 2a shows that hexanes constitute the main part of the alkylate, and the conversions to higher alkanes rapidly decrease with m: hexanes (XI) >> octanes ( x 2 ) >> decanes ( x g ) , etc. The calculated weight distributions appear in Table 2. They do not vary much with temperature between 280 and 580 K, as all alkanes decrease in a regular way above 550 K. Results in Table 2 show that the weight ratios p = c6/c8 and p' = cS/clO are very sensitive to the dilution a. At 280 K,
... ...
...
T=
1.1 0.8 96.7 2.9 0.1 0.2
increases from 7.8 to 31 as a is raised from 5 to 20. A change in total pressure has comparatively little effect on the calculated distribution, but the domain of stability of the alkanes is shifted: at a = 10, the temperature of 99 % ethylene conversion is lowered by 100 K when Pgoes from 2.5 down to 0.5 MPa. Alkenes start to appear at about 550 K and steadily increase with temperature (Figure 2b). At T = 680 K and P = 2.5 MPa, they reach 1.2% by weight for a = 20 and 6% for a = 5. At any temperature, the conversion into alkene group (n)decreases with n: at a = 10, the weight ratio butenedhexenes is about 4 (Table 2) and there are hardly any octenes. However the amounts of butene, etc., are only indicative since propene and pentenes, which have not been included in the calculation, would actually appear above 550 K as a result of cracking. Therefore, calculations involving unlimited alkylations and polymerizations predict that neither alkenes nor heavier alkanes will be found at equilibrium as soon as a 2 5 and T < 550 K. That the heavier alkanes or alkenes are unstable at any temperature was not obvious since, at the actual pressures and with the help of a strongly acidic catalyst, alkenes are readily polymerized, yielding a maximum of products in the range COO-CIH) (Tabak et al., 1986). In the present case, dilution with a large excess of isobutane favors the production of light alkanes. The thermodynamic prediction is to be compared with some alkylation experiments performed in a flow reactor with A1203-Cl catalysts (Goupy et al., 1993). Initially, the conversion of ethylene was complete, but it declined steadily after a few hours on line. The alkylate contained exclusively alkanes, mainly hexanes and octanes, in good agreement with the thermodynamic prediction. The amount of Cg slowly decreased with time on line, whereas the c8 and heavier alkanes were nearly constant. Within the c6, a high isomer selectivity was obtained at the end of the initial period. Therefore, alkylate compositions are presented in Table 3 at the same degree of ethylene conversion (50% ), Experimental distributions comply with thermodynamics as far as hexanes and octanes constitute the main part of the alkylate. But at 273 K, we measured a weight ratio p = c6/c8 equal to 8.9 at a = 20 and about 5 at a: = 10. This is notably under the predicted values, respectively p = 31 and 15.6. Also the p'ratio (CdClo) was found under prediction, specially at a = 10. Discrepancies between experimental and calculated distributions might be due to the selectivity of the reaction. p
380
...
T=
580K 680K 93.5 92.6 5.6 4.6 0.32 0.21 0.4 2.13 0.1 0.39 0.02 0.06 87.0 10.2
Ind. Eng. Chem. Res., Vol. 33, No. 3, 1994 715 Table 3. Composition of Alkylates (wt %) Obtained with Chlorided Alumina Catalysts (Goupy et al., 1993)
1,oo
0,50
wt%
P(MPa) 2.5
(Y
10
20
2.5
hexanes octanes Ce+ hexanes octanes cs+
T=273K 76 15
T=323K 75 19
9
6
89 10 1
84 14
1
T=373K 73 21 3 73 23 3
Except for a very short initial period, the C g fraction contained more than 95% 2,3-DMB, and 2,2-DMB for most of the remaining, whereas all hexane isomers were considered in equilibrium calculation. Therefore, calculations should treat the case of selective reactions. This is especially important at low temperature where the primary products, i.e. highly branched alkanes, are isomerized very slowly. 095do
4. Alkylation Limited to CS a n d Dimerization
Thermodynamics predict very small equilibrium amounts of Clo and heavier alkanes at any practical temperature. Although the results of experiments at a = 10 do not exactly agree with this, equilibrium calculations may be carried out with the system restricted to its five main components, i.e. ethylene, isobutane, butenes, hexanes, and octanes. Thus, three independent reactions only need to be considered imC4H10 + CzH4 s
(1)
CCH14
2C2H4S C4H8 i-C,Hlo
(2)
+ 2C2H4* C&8
(25)
Selectivity in any of these requires that the relevant equilibrium constant K be restricted to the AGOt of the isomers under consideration: again, those are assumed to be in mutual equilibrium and may be treated as a single component. Using the same notations as before, equilibrium constants will be called K1 for reaction 1; K’2 for 2, which is a special case of 6 with n = 2; and K2 for eq 25, which is eq 5 for m = 2. When partial pressures are expressed by means of the fractional conversionsof ethylene into hexanes (XI) octanes ( x 2 ) and butenes (y), three independent equations are obtained:
p
AGoi+AGo,-
RT
exp(
y ( l + - x1 - x2 - 0 . 5 ~ ) p = -POK’2= 2(1- x1 - x 2 - y ) 2 P exp( 2AGoe PO RT x2(l + CY - x1 - x2 - 0 . 5 ~ ) ~ 2(a -
a($)
- 0.5x2)(1- x1- - x 2- - Y ) ~
(
$)2
(26)
(27)
2
K2=
exp( AGO, + 2AGoe RT - AGO’)
(28)
Here AGO1, AGO2 and AGob stand for the standard Gibbs energies of formation of (respectively) hexane, octane, and butene groups. The above equations are easily solved upon
380
480 T/K
580
Figure 3. Competition between alkylation (limited to Ce) and dimerizationfor fully selectivereactions (a= 10;P = 2.5 MPa). Key: left scale, overall conversion of ethylene and fractional conversions into 2,3-DMB;right scale, conversion into TMP (three isomers) and linear butenes.
introducing as a new variable the equilibrium partial pressure of ethylene (z,dimensionless):
p z=-
1-x,-x2-y (29)
PO 1 + a - x1 - x 2 - 0 . 5 ~
Upon elimination of all other quantities, a fourth degree equation holds for z:
+ z2[Kl + K’,Jl + 2 4 + ~P K ~ ( -2113a + z [ l + a + ~PK ~ ( a - l ) -p=O ] (30) P O
The first two terms in this equation appear to be very small, and if they are omitted, the positive root of the quadratic equation affords an excellent approximation of the desired z. Then higher accuracy is readily obtained. To cope with the selective alkylation occurring at the lowest temperatures, only the linear butenes were considered in reaction 2, but two hypothesis were examined for the hexanes and octanes: (a) Fully selective reactions, where reaction 1 produces only 2,3-DMB and reaction 25 produces three isomers, 2,2,4-,2,3,3-, and 2,3,4-TMP; (b) Partly selective reactions, where reaction 1 produces the two DMB isomers and reaction 25 produces the complete set of TMP (five isomers) and DMH (ten isomers). Case a represents “ideal” selectivities when reactions 1 and 2 are carried out separately. But in actual alkylation with ethylene, the hexanes consist of about 97 % 2,3-DMB and 3 % 2,2-DMB;and at least 40%DMH is found among the CSS(Goupy et al., 1993). Thus, case b was also considered. Calculations made use of the data in Table 1. The overall and fractional conversions of ethylene at a = 10 and P = 2.5 MPa are plotted against temperature in Figures 3 and 4. The general features are the same as for unselective reactions, except that inversion of the alkylation equilibrium occurs a t a lower temperature: the downward shift is about 70 K in case a and 40 K for case
Again the ratio p is rather insensitive toward pressure, but loweringP from 2.5 to 0.5 MPa shifta by 80 K downward the curve of ethylene consumption. Comparing the data in Tables 3 and 4 shows that the observed ratio p = CdCg conforms more with hypothesis a. In practice however, selective alkylation produces slightly more hexanes than allowed by this highly restricted equilibrium. Furthermore, according to Table 4, the calculated p will increase with temperature in case a, and decrease in case b. As the experimental p slightly decreases between 280 and 380 K, the quantity of octanes gets closer to the thermodynamic value (a) and stands away from the prediction in the other models.
over-
5. Conclusions
I O%O 5
8 380
8 480 T/K
’
580
0
0
Figure 4. Competition between alkylation (limited to CS) and dimerization for partly selective reactions (a = 10; P = 2.5 m a ) . Key: left scale, overall conversion of ethylene and fractional conversion into 2,2 + 2,3-DMB; right scale, conversions into TMP DMH and linear butenes.
+
Table 4. Calculated Equilibrium Composition of the Alkylate (wt %): Alkylation (Limited to Ca) and Dimerization wt%
a
P(MPa)
5
2.5
10
2.5
10
0.5
20
2.5
5
2.5
10
2.5
20
2.5
T = 280K 380K 480K 580K (a) Full Selectivity 2,3-DMB 60.0 69.7 TMP 40.0 30.3 lin butenes 2,3-DMB 72.0 80.5 TMP 28.0 19.5 lin butenes 2,3-DMB 72.0 80.5 TMP 28.0 19.5 lin butenes 2,3-DMB 81.8 88.3 18.2 11.7 TMP lin butenes (b) Incomplete Selectivity 2,2+2,3-DMB 91.5 81.2 T M P + DMH 8.5 18.8 lin butenes 2,2+2,3-DMB 95.7 89.3 TMP +DMH 4.3 10.7 lin butenes 2,2+2,3-DMB 97.9 94.2 2.1 5.8 TMP+DMH lin butenes
73.4 25.7 0.9 83.5 16.0 0.5 82.5 15.1 2.4 90.4 9.3 0.3
69.7 16.1 14.2 79.8 11.1 9.1 68.4 6.3 25.4 87.5 7.0 5.5
13.4 26.6 0.06 83.4 16.5 0.04 90.4 9.6 0.02
67.6 30.7 1.8 78.6 20.3 1.1
86.9 12.5 0.6
b. As hexanes are restricted to one or two isomers, their Gibbs energy of formation is higher than for the full group, and their stability appears lower. However, hexanes are readily isomerized above 550 K, so that selective models become unrealistic in this domain. More significant are the equilibrium amounts of alkanes at low temperature (Table 4). Dimethylbutanes are still favored over the Cg: at T = 280 K and a = 10, the ratio p = c6/cg is 2.6 (a) or 22.2 (b), compared with p = 15.6 in the nonselective case. Again, the dilution a has a major effect on the amount of octanes: for instance in case a at 280 K, p increases from 1.5 to 4.5 as a increases from 5 to 20.
Thermodynamics show that addition of ethylene onto isobutane may be complete and irreversible at least up to 550 K, as ethylene oligomersare unstable. The equilibrium amounts of hexanes, octanes, and decanes rapidly decrease with molecular weight, heavier alkanes also being unstable. The high selectivity for 2,3-DMB actually observed is likely due to a kinetic control. When this particular selectivity is introduced as a restriction to equilibrium, a C6/Cg ratio may be deduced, which nearly agrees with the experimental value. Octanes and higher alkanes are likely produced by addition of ethylene to the DMB, rather than by alkylation of isobutane with ethylene oligomers. However, when palladium is added onto the alkylation catalyst, ethylene oligomerization is fastened, and octanes become the main products (Timurzieva et al., 1990). Similarly, large amounts of octanes, decanes and heavier were observed over certain A1203-Cl catalysts, particularly after a long time on line (Goupy et al., 1993). Alkylation probably decays faster than oligomerization,but isobutane may still be alkylated by the butenes, hexenes, etc., so that selectivity changes with time on line. Finally, the above calculations were performed for ideal gases, and corrections would be necessary for a liquidphase process. These should be important for ethylene only. The main conclusions concerning the instability of alkenes and heavier alkanes would not be changed, and the composition of the alkylate, which is highly diluted in isobutane, would hardly be modified. Acknowledgment The authors thank TOTAL-France for financial aid. Literature Cited Alberty,R. A. Chemical ThermodynamicProperties of Isomer Groups. Znd. Eng. Chem. Fundam. 1983,22,318-321. Alberty, R. A.; Gehrig, C. A. Standard Chemical Thermodynamic Properties of Alkane Isomer Groups. J. Phys. Chem. Ref. Data 1984,13, 1173-1189. Alberty, R. A.; Gehrig, C. A. Standard Chemical Thermodynamic Properties of Alkene Isomer Groups. J. Phys. Chem. Ref. Data 1985,14,803-820. Alberty, R. A.; Oppenheim, I. Analytic Expressions for the Equilibrium Distributions of Isomer Groups in Homologous Series. J. Chem. Phys. 1986,84,917-920. Albright, L. F. Modern Alkylation. Part 1. Oil Gas J. 1990,Nov 12, 79-92. Albright, L. F. Modern Alkylation. Part 2. Oil Gas J. 1990, Noo 26, 70-77. Albright, L. F.; Spalding, M. A.; Faunce, J.; Eckert, R. E. Alkylation of Isobutane with CCOlefins. Part 3. Znd. Eng. Chem. Res. 1988, 27,391-397.
Ind. Eng. Chem. Res., Vol. 33, No. 3, 1994 717 Child, J. E.; Chou, T. S.; Huss, A.; Kennedy, C. R.; Ragonese, F. P.; Tabak, S. A. Heterogeneous Isoparaffin/Olefin Alkylation. U.S. Pat. 4,956,518,1990. Dickenson, R. L.;Reveal, W. S. Shell Produces Ethylene Alkylate. Oil Gas J. 1971,May 17, 120-123. Goupy,J.; Szabo,G.; Goupil,J. M.; Poirier, J. L.; Cornet, D. Alkylation of Isobutane using Solid Friedel-Crafts Catalysts. Abstracts of Papers. First European Congress on Catalysis, European Federation of Catalysis Societies: Montpellier, France, 1993;Paper A2. Kilpatrick, J. E.; Prosen, E. J.; Pitzer, K. S.; Rossini, F. D. Heats, Equilibrium Constants, and Free Energies of Formation of the 1946, MonoolefinHydrocarbons. J.Res. Natl. Bur. Stand. (US.)
Tabak, S. A.; Krambek, F. J.;Garwood,W. E. Conversion of Propylene and Butylene over ZSM-5 Catalysts. AZChE J. 1986,32,1526-
1531. Timurzieva, M. A.; Khadjiev, S. N.; Timurzieva, M. A.; Bdbourski, V. L.; Alexandrova, I. L. Isobutane-Ethylene Alkylation with PdCaHREHY Zeolite Catalysts. Neftekhimia 1990,30, 35-39. Weitkamp, J. Isobutane/Butene Alkylation on Cerium Exchanged X and Y Zeolites. In Catalysis by Zeolites; Imelik, B., et al. Eds.; Elsevier Scientific Publishing Co.: Amsterdam, 1980;pp 65-75.
Received for review June 15, 1993 Revised manuscript received November 1, 1993 Accepted November 11, 1993"
36,559-612. Roebuck, A. K.; Evering, B. L. Isobutane-Olefin Alkylation with Inhibited Aluminum Chloride Catalysts. Ind. Eng. Chem. Prod. Res. Dev. 1970,9,76-82.
Abstract published in Advance ACS Abstracts, January 15,
1994.
