Applied Catalysis A: General, 91 (1992) 125-129 Elsevier Science Publishers B.V., Amsterdam
125
APCAT A2316
Alkylation of benzeng with propene to produce cumene over a nickel/y-alumina catalyst Jian Panming, Wang Qiuying, Zhu Chao and Xu Yanhe Department of Chemistry, Lunzhou University, Lanzhoy Gansu 730000 (People’s Republic of China) (Received 4 May 1992, revised manuscript received 19 June 1992)
Abstract
The alkylation of benzene with propene to produce cumene over a Ni/y-AlaOa catalyst has been investigated in a fixed-bed continuous-flow reactor. At 70°C 1.5 MPa, a molar ratio of 3: 1 (benzene/ propene), and a weight hourly space velocity of 2.0 h-l, the conversion of propene is 99.91, the selectivity of cumene is 98.7%)and no n-propylbenzene is formed. In terms of lifetime and catalyst utilization value, the Ni/pAl,Os catalyst yields an optimum performance of 1500 h and 1120 g cumene/g catalyst. Keywords: alkylation, benzene, nickel/alumina, propene.
INTRODUCTION
In the past, Ni/y-AlzOa catalysts have been mainly used for the hydrogenation of unsaturated hydrocarbons and petroleum hydrogenation cracking. More recently, many attempts have been made to use supported nickel catalysts in the oligomerization of alkenes, such as ethene [ 11, propene [2,3], and n-butene [ 41. No report, however, has been made of the alkylation of benzene with propene to produce cumene over a Ni/y-A&OS catalyst. The alkylation of benzene with propene to produce cumene is a well-know reaction. Commercial production began in May 1942 to supply high-performance fuel for military aircraft. A vapor-phase process with phosphoric acid on a kieseguhr catalyst and a liquid-phase alkylation in the presence of sulfuric acid were used [ 51. Other Friedel-Crafts catalysts, especially aluminum chloride, have also been used for alkylation reactions [ 6,7]. In the last few years, zeolite catalysts have been tested in the alkylation reaction [8-111 .Conditions of reaction were optimized with HZSM-5 zeolite to give 66-94% cumene selecCorrespondence to: Dr. P. Jian, Department of Chemistry, Lanzhou University, Lanzhou, Gansu 730000, People’s Republic of China. Tel. ( +86-931)28111539, fax.( +86-931)417576.
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0 1992 Elsevier Science Publishers B.V. All rights reserved.
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P. Jian et al./Appl. Catal. A 91 (1992) 125-129
tivity, 27-67% conversion of propene [ 111, and a reaction temperature over 200” C was used. In the present study, the alkylation of benzene with propene to produce cumene over a Ni/y-AlzOs catalyst has been examined in a fixed-bed stainless steel reactor. The conversion of propene and the selectivity of cumene were found to be 99.9 and 98.7% respectively, at 70°C. The effect of reaction temperature, benzene/propene molar ratio and weight hourly space velocity (WHSV) upon the conversion of propene and the selectivity of cumene are reported. EXPERIMENTAL
The procedure for the synthesis of a Ni/y-AlzOa catalyst has been described in a previous paper [ 21. y-AIPOBwas macerated with nickel salt solution, then dried and calcined to obtain the catalyst samples. Catalytic experiments were performed under 1.5 MPa in a fixed-bed continuous-flow microreactor. The reactor was an 8 mm I.D. stainless steel tube surrounded by an electrical heater equipped with a TW-72 thermoregulator. The reactor products were passed through cold water condensers to remove the liquid fraction and the volume of the remaining gas was measured by a wet test meter. The cumene product was analysed on a SP-2305E gas chromatograph using a 4 mm stainless steel column packed with 12% SE-30 on a 60-80 mesh white supportor. Benzene ( A.R. ) and propene (99.6% ) were used without further treatments. RESULTS AND DISCUSSION
The alkylation of benzene with propene produces cumene and diisopropylbenzene, transalkylation reactions occur simultaneously. n-Propylbenzene is also produced by secondary isomerization of cumene (see eqns. 1-4).
. Q +
C3H6
\ 0
+ 2 c3ns
CH3-p-CH3
(1)
\
-
0/
_
c5-?-cH3 Q
FH"3
(2)
\CH3 CH3-PH-CH3
(3)
127
P. Jian et al./Appl. Catal. A 91(1992) 125-129
CH3-
l-I-m3
6
(4)
.
The experiments were carried out at 70°C and 1.5 MPa. It was found that the selectivity of cumene decreased and a greater amount of diisopropylbenzene was produced (15-26.7% ), when the benzene/propene molar ratio was lower than 3 : 1. Additionally, at a ratio higher than 3 : 1, only O-0.8% diisopropylbenzene was produced and oligomer formation increased proportionately (see Table 1). Obviously the production of diisopropylbenzene and the selectivity of cumene were influenced by the amount of propene in the reactants. Indeed, as the benzene/propene molar ratio was varied from 8: 1 to 1: 1, the selectivity of cumene fell from 100 to 67.4%. WHSV affected the production of diisopropylbenzene (see Table 2). At a 3 : 1 molar benzene/propene feed ratio and 70” C, the amount of diisopropylbenzene produced was reduced with an increase of WHSV. This might have been caused by the transalkylation reaction (eqn. 3). It is advantageous to the TABLE 1 Effect of benzene/prope& molar ratio on selectivity WHSVz2.0
h-l, T=70”C, P=1.5 MPa. Time-on-stream (TOS) =4 h
99.9
3/l 99.9
4/l 100
8/l 100
Selectivity of products (wt.-% au. for TOS range) Cumene 67.4 82.3 DIPB 26.7 15.3 Oligomer 5.9 2.4 Total 100 100
98.7 0.8 0.5 100
99.8 0.1 0.1 100
100 0 0 100
G&/W6
(molar)
Conversion of CBHB( % )
l/l
99.9
211
TABLE 2 Effect of WHSV on reaction properties T=70”C, P=1.5 MPa, CBHB/CBHIratio=3: 1. TOS=8 h WHSV (h-l) Conversion of CzHB ( % )
1.0 100
1.5 100
2.0 99.9
3.0 96.0
4.0 90.2
Selectivity ofproducts (wt.-% au. for TOS range) Cumene 84.6 97.3 DIPB 14.7 2.2 Oligomer 0.7 0.5 Total 100 100
98.7 0.8 0.5 100
99.9 0 0.1 100
99.9 0 0.1 100
P. Jian et al./Appl. Catal. A 91(1992) 125-129
128 TABLE 3 Effect of reaction temperature on cat&tic
T (“Cl
60 99.0
70 99.9
(wt.-% au. for TOS range) 98.5 98.8 99.0 0.6 0.5 0.2 0.9 0.7 0.8 0 0 0 100 100 100
98.7 0.8 0.5 0 100
Conversion of CsHs ( % ) Selectivity ofproducts Cumene DIPB Oligomer n-Propylbenzene Total
activity and selectivity
40 63.7
50 85.4
80 100
90 100
100 100
99.3 0.5 0.2 0 100
99.1 0.6 0.3 0 100
99.7 0.1 0.1 0.1 100
Fig.
1. Effect of time-on-stream on the akylation of benzene with propene (T= 7O”C, P= 1.5 MPa, CeH&Hs ratio=3: 1, WHSV=2.0 h-l). (a) Conversion of propene, (b) selectivity of cumene, (c) selectivity of DIPB, (d) selectivity of oligomer.
transalkylation reaction when the reaction time (contact time) is longer. In addition, the conversion of propene also dropped with an increase of WHSV. When the WHSV increased from 1.0 to 4.0 h-l, the conversion of propene decreased from 100 to 90.2%, while the selectivity of cumene increased from 84.6 to 99.9%, and that of diisopropylbenzene reduced from 14.7 to 0%. Table 3 presents the effect of reaction temperature on catalytic activity and selectivity. At 7O”C, the conversion of propene and the selectivity of cumene are 99.9 and 98.7%, respectively. No n-propylbenzene was produced at reaction temperatures between 40 and 90’ C, and at 100’ C only 0.1% n-propylbenzene was produced. This was expected because of the low-strength acid sites in the catalyst and the low temperature used. Our previous paper has pointed out that alkylbenzene isomerization occurred on stronger acid sites on the catalyst [ 121. Kaeding has suggested that n-propylbenzene becomes a major product, 36% selectivity at high temperatures (300’ C ), presumably by the subsequent iso-
P. Jim et al./Appl. Catal. A 91 (1992) 125-129
129
merization of cumene (eqn. 4). At temperatures below 250” C, cumene isomerization was not a favorable reaction since there was a wide departure from the thermodynamic equilibrium ratios calculated for propylbenzenes [ 111. In this work, the stability of the catalyst was also examined, as shown in Fig. 1. The Ni/y-AlsO3 catalyst was very stable in the alkylation of benzene with propene. The conversion of propene was over 96%, and the selectivity of cumene was over 98% for a total time of 1500 h. It is interesting that the oligomer selectivity reduced with an increase of TOS. This might have been due to the formation of coke which occupied the active sites for oligomer formation with increasing TOS. The catalyst lifetime was over 1500 h or 1120 g cumene/g catalyst. From this study, it would appear that the Ni/y-AlsO3 catalyst is a better catalyst for the alkylation of benzene with propene than existing ones. Benzene was alkylated with propene over a Ni/y-Al,03 catalyst to produce cumene with 98% selectivity, 96% conversion of propene and a 1500 h catalyst lifetime under conditions of 70°C and 1.5 MPa. Our paper shows that the application of Ni/y-AlpO3 catalyst to produce cumene would be of momentous current significance to industry, and would save on both energy and raw materials. ACKNOWLEDGEMENT
This work was supported by Grants for Scientific Research from Lanzhou University.
REFERENCES 1 F.X. Cai, C. Lepetit, M. Kermarec and D. Olivier, J. Mol. Catal., 43 (1987) 93. 2 P. Jian, Q. Wang, Y. Xu, C. Zhu, Z. Yan and X. Zhang, J. Mol. Catal. (China), 6 (1992) 52. 3 S.J. Miller, US Patent, 4 465 788 (1984). 4 D. Kiessling, G. Wendt, K. Hagenau and R. Schoellner, Appl. Catal., 71 (1992) 69. 5 S.H. Mcallister, J. Anderson, E.F. Bullard, Chem. Eng. Prog., 43 (1947) 189. 6 H. Miki, US Patent, 4 347 393 (1982). 7 R.C. Canfield and T.L. Unruh, Chem. Eng., 21 (1983) 32. 8 P.B. Venuto, L.A. Hamilton and P.S. Landis, J. Catal., 5 (1966) 484. 9 T. Yashima, H. Ahmad, K. Yamazaki, M. Katsuta and N. Hara, J. Catal., 16 (1970) 273. 10 T. Yashima, K. Yamazaki, H. Ahmad, M. Katsuta and N. Hara, J. Catal., 17 (1970) 151. 11 W.W. Kaeding and R.E. Holland, J. Catal., 109 (1988) 212. 12 Q. Wang, P. Jian, X. Xu, Y. Xu, Q. Gao and Q. Yang, J. Lanzhou Univ., 26 (1990) 81.