T. Odedairo, S. Al-Khattaf / Catalysis Today 204 (2013) 73–84
83
Table 8
Correlation matrix for parameters of benzene alkylation with methanol over mordenite catalyst.
kM1
EM1
ꢀ
kM2
EM2
ꢀ
kM3
1.0000
EM3
ꢀ
kM1,2,3
EM1,2,3
ꢀ
1.0000
0.2170
0.7975
0.2170
1.0000
0.7975
0.3258
1.0000
1.0000
0.1263
0.7895
0.1263
1.0000
0.4990
0.7895
0.4990
1.0000
−0.0482
1.0000
0.2072
0.6283
0.2072
1.0000
−0.0482
0.6283
energy for benzene methylation over mordenite with the energy
of activation for toluene isopropylation (37.3 kJ/mol) over another
12 ring zeolite [62], slightly lower apparent energy of activation is
still observed in the benzene methylation reaction over morden-
ite, even though the aromatic compound is expected to be more
reactivity in case of the isopropylation reaction.
reaction temperature, while the low temperature favors the acti-
vation of ethanol over both catalysts. Isopropanol presents higher
difficulty to be activated as compared with other alcohols at the
higher temperature. Therefore, for the purpose of implementing
an alkylation process for benzene content reduction in gasoline,
and considering the real feedstock, mordenite will be a suitable
catalyst for this particular process, under the present experimen-
tal conditions. Kinetic parameters of the benzene methylation
(E1), toluene methylation (E2) and xylene methylation (E3) with
methanol were calculated using the catalyst activity decay function
based on reactant-converted (RC). The apparent activation energies
were found to decrease as follows: E1 > E2 > E3. Additional stud-
ies involving catalyst preparation are needed for optimizing the
Apparent activation energies of 23.9 and 18.7 kJ/mol were
obtained for benzene methylation and toluene methylation,
respectively, over the catalyst based on ZSM-5 (Table 6). Similar
ite, the reactivity of the alkylbenzenes increased with increasing
methyl group per benzene ring over the ZSM-5 based catalyst.
Lower apparent activation energy was obtained for benzene ethy-
lation (17.1 kJ/mol) [40] over ZSM-5 based catalyst, as compared
with the activation energy reported for benzene methylation reac-
´
BrØnsted and Lewis acid acid properties of these materials.
´
tion (23.9 kJ/mol) in this present study. Although, the BrØnsted to
Acknowledgements
Lewis acid ratio of the ZSM-5 based catalyst used in this present
´
study is higher than the BrØnsted to Lewis acid ratio of the ZSM-
We are grateful for the support from Ministry of Higher Educa-
tion, Saudi Arabia for the establishment of the Center of Research
Excellence in Petroleum Refining and Petrochemicals at King Fahd
University of Petroleum and Minerals (KFUPM). Mr. Mariano Gica
also is acknowledged for his help during the experimental work.
5 catalyst used previously, the reaction temperature might have
played its part in the difference in apparent activation energy. It
is a well established fact that the intrinsic activation energy is a
function of catalyst acidity; however, the ethylation reaction over
ZSM-5 based catalyst previously reported was carried out at a much
lower reaction temperatures (250–300 ◦C) as compared with the
reaction temperatures used in this present study.
References
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equations were solved numerically using the fourth-order-Runge-
Kutta routine. Graphical comparisons between experimental and
model predictions for reactant-converted model (RC) based on the
optimized parameters for Scheme 3 is shown in Fig. 1.
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5. Conclusions
Zeolite mordenite and ZSM-5 are active catalysts for the syn-
thesis of toluene, xylene and ethylbenzene by alkylation of benzene
with methanol and ethanol in the vapor phase. By studying the alky-
lation of benzene with alcohols of different chain length, it has been
found that as the alkyl size (i.e. methyl, ethyl, and propyl) increases,
the optimum temperature for alkylation reaction decreases. The
high reaction temperatures strongly favor the yields of xylenes
and toluene with mordenite in benzene methylation, while low
yield of cumene was noticed over both catalysts in benzene iso-
propylation. In the ethylation reaction, the catalyst based on ZSM-5
showed higher ethylbenzene selectivity, while comparable diethyl-
benzene selectivity was noticed over both catalysts at constant
conversion level. When benzene is to be alkylated, there is no com-
petitive reaction apart from the alkylation reaction and the effect
of these alcohols as an alkylating agent plays an important role.
´
The reaction temperature and the BrØnsted to Lewis acid ratio
of the catalysts, play a significant role in the alkylation reactions.
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