Collect. Czech. Chem. Commun. 1997, 62, 337-346

Zeolite Silylation for the Enhancement of para-Selectivity in Toluene Alkylation with Ethylene

Jan Krtil, Jiří Čejka and Blanka Wichterlová

J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,182 23 Prague 8, Czech Republic


The effect of zeolite silylation using tetraethyl and tetramethyl orthosilicate on the enhancement of para-selectivity and of yields of p-ethyltoluene in toluene alkylation with ethylene was investigated for different Si loadings. It was found that zeolite silylation caused a substantial increase in the selectivity and yield of p-ethyltoluene. Data on changes in sorption capacity, in the number of surface and inner strong acid OH groups, in the rate of uptake of p-ethyltoluene together with the catalytic activity of zeolite and its deactivation indicate that the silylation is restricted to surface and subsurface zeolite layers. The enhancement of para-selectivity and yield of p-ethyltoluene are controlled predominantly by changes in geometry of pore openings and thus by transport rates of ethyltoluenes.

Keywords: Zeolite silylation; Toluene alkylation; Ethylene; Tetraethyl orthosilicate; Transport of products; para-Shape-selectivity.