Amylation of Toluene by Solid Acid Catalysis

The solid acids SiO2-Al2O3 and zeolites Y and (beta) were investigated as catalysts for the alkylation of toluene with 1-pentene at temperatures in the range of 100-200 (degree)C. The alkylate product, a mixture of amyltoluene isomers, is a useful solvent in applications requiring a low vapor pressure. A reaction network is presented to represent the alkylation catalyzed by the amorphous solid acid, as well as side reactions such as oligomerization and isomerization. It indicates that alkylation is probabilistic, with the alkylation products being formed in the same ratio as the substrate aromatics in the reaction mixture. The presence of Ni and W promoters in the amorphous solid acid catalyst (Ni/W-SiO2-Al2O3) did not affect the alkylation appreciably. This catalyst, normally used for hydrocracking, performed well as an alkylation catalyst, with better than 90% conversion and 81% selectivity to the monoalkylated product at 150 (degree)C, 0.9 MPa, and 1 h-1 space velocity. It is suggested that benefits could be derived from metal promotion by co-feeding hydrogen, such as diene saturation, suppression of coke formation, and product polishing. In contrast to the amorphous catalyst, the zeolites, with their constrained pore geometries, gave improved selectivity to the monoalkylated product, but exhibited insufficient lifetimes for commercial application.