Involvement of light alkanes in direct synthesis of alkylbenzenes.

Ponomoreva O.A. , Smirnov A.V. , Mazin E.V. , Knyazeva E.E. , Nesterenko S.N. , and Ivanova I.I.

Proceedings of EUROPACAT-V, September 2-7, 2001, 10-P-29.

ABSTRACT. Benzene alkylation with ethane, propane and i-butane has been investigated over the wide range of catalysts including H-MFI zeolites with different SiO2/Al2O3; sulfated zirconia (ZrO2/SO4), Pt/oxides, mixed (H-MFI + Pt/oxides) or (ZrO2/SO4 + Pt/oxides) catalytic systems, Pt/H-MFI and Pt/ZrO2/SO4 bifunctional catalysts. Pt supported catalysts with Pt content of 0.02 and 0.3 % were prepared as described in [1]. Benzene alkylation was carried out at atmospheric pressure in the temperature range of 523 - 773 K, alkane/benzene molar ratio = 1 and WHSV = 0.2 - 7 h-1. The comparative study of benzene reaction with different alkanes over acidic catalysts has demonstrated that the alkylation ability of alkanes increases in the following order of reactants: C4H10 << C3H8 < C2H6, which is an opposite to their reactivity. The major products of benzene interaction with ethane are ethylbenzene, toluene, and methane. In the case of propane, the main products are propylbenzenes, toluene, ethylbenzene, methane, and ethane. On the contrary to ethane and propane, isobutane does not give any products of direct addition. The major reaction pathway in the latter case is oligomerization followed by isomerization, cracking and aromatization leading preferentially to C3-C4 alkanes, naphthalene and coke. Incorporation of Pt into the catalysts results in significant increase of overall conversion and selectivity towards the products of direct addition. The results point to complementary synergy between the actions of acidic and Pt sites in alkylation. The effect is more pronounced on the catalysts with direct deposition of Pt than on mixed catalytic systems, probably due to the shorter mean distance between the acidic and dehydrogenation sites on the former. To shift the reaction equilibrium and to increase the yields of the products of direct addition, hydride forming compounds have been added to the catalytic systems as H2-scavengers. The addition of H2-acceptors resulted in a twofold to tenfold increase of catalytic activity and up to two fold increase of selectivity.

Laboratory of Kinetics and Catalysis