Alkylation and disproportionation of aromatic hydrocarbons over mesoporous molecular sieves

Abstract

Toluene alkylation with propylene and trimethylbenzene (TMB) disproportionation were investigated over mesoporous molecular sieves of MCM-41 type of different pore dimensions, possessing various Si/Al ratios or modified with heteropoly acids (HPA) of Keggin type. It was shown that the acid strength of (Al)MCM-41 was sufficient to activate propylene in the alkylation of toluene providing cymene selectivity over 96% while the rate of consecutive reactions was negligible. In contrast, TMB disproportionation proceeded at a significantly lower extent than over zeolites. Siliceous MCM-41 modified by HPA (HPA-MCM-41) exhibited a lower rate of cymene isomerization compared to (Al)MCM-41. Moreover, m-cymene was mainly formed at the expense of o-cymene. In TMB disproportionation over HPA-MCM-41 (HPA=H6PV3Mo9O12) significantly higher concentrations of xylenes were reached in comparison with (Al)MCM-41. m- and o-xylenes as primary products of TMBs disproportionation were preferentially formed.