Vapour phase alkylation of ethylbenzene with t-butyl alcohol over mesoporous Al-MCM-41 molecular sieves

The alkylation of ethylbenzene with t-butyl alcohol was studied over Al- MCM-41 (Si/Al = 50 and 90) and Al, Mg-MCM-41 (Si/(Al + Mg) = 50) in the vapour phase from 200 to 400C. The products were p-t-butylethylbenzene (p-t-BEB), p-tbutylvinylbenzene (p-t-BVB) and m-t-butylethylbenzene (m-t-BEB). Ethylbenzene conversion decreased with increase in temperature and increase in the ethylbenzene content of the feed. The reaction between the freely diffusing ethylbenzene in the channel and the t-butyl cations remaining as charge compensating ions yielded p-t- BEB. p-t-BVB, an unexpected product in this investigation, was produced by dehydrogenation of p-t-BEB over alumina particles present in the channels of the molecular sieves. Adsorption of ethylbenzene on Brønsted acid sites and its subsequent reaction with very closely adsorbed t-butyl cations proved to be necessary to obtain m-t-BEB. Though m-t-BEB was obtained, the corresponding m-t-butylvinylbenzene was not observed in this study. Study of time durations indicated rapid and slow catalyst deactivation at lower and higher streams respectively.