Alkylation reactions over ion-exchanged molecular sieve zeolite catalysts. Part 1.—Alkylation of toluene with methanol: consideration of the effects of reaction parameters on catalyst deactivation and the extent of polysubstitution

Abstract

The alkylation of toluene with methanol under non-isomerizing conditions has been studied over a range of ion-exchanged zeolite catalysts. Rapid deactivation with increasing time on stream was observed in the case of LaY and NH4Y catalysts, whereas a NiY and a range of Ni,SnY samples manifested a high steady-state activity; the catalytic activity at the steady state could be related to the chemical composition of these latter samples. Catalyst deactivation was always associated with the formation of polysubstituted products. From a detailed study of the systems at the steady state it was concluded that (i) methylation of toluene is always associated with the formation of tri- or tetra-methylbenzenes to a greater or lesser extent over the partially deactivated catalysts; (ii) the origin of the polymethylated products is a weakly adsorbed o-xylene species; (iii) the selectivity towards polysubstitution varies with time on stream. This results from a change in the strength of interaction between the xylenes and the catalyst surface as shown by studies of the heats of immersion of the catalysts.