Alkylation reactions over ion-exchanged molecular sieve zeolite catalysts. Part 2.—Alkylation of toluene with methanol: consideration of the effects of catalyst deactivation on the primary product distribution

Abstract

The primary product distribution arising from the methylation of toluene with methanol over a range of catalysts under non-isomerizing conditions has been studied. It was found that over partially deactivated catalyst samples the primary product xylene isomer distribution consisted of 25–27%para, 14–16%meta and 55–61%ortho, which is similar to that occurring in homogeneous catalysis and in heterogeneous systems that lack the small pore structure of zeolite catalysts. The selectivity for m-xylene formation remained constant at 14–16% irrespective of the catalysts used, the reaction conditions or the length of time on stream. For the NH₄Y and LaY-88.9 samples the selectivity for para formation was high initially but decreased rapidly with increasing catalyst deactivation, reaching a constant value which was similar for all the partially deactivated samples. It is shown that the methylation data for the partially deactivated catalysts can be explained on the basis of the reactivity of the methylating agent. In the case of the NH₄Y and LaY-88.9 samples the high para selectivity at the beginning of the reaction is considered to be due to an added orientating effect associated with catalysis occurring on zeolites with a restricted pore size.