BENZYLATION OF TOLUENE BY BENZYL-CHLORIDE OVER PROTONIC ZEOLITES

The benzylation of toluene with benzyl chloride was studied at 383 K i n the liquid phase on different protonic zeolites: H-ZSM-5, H-BETA and HY. Monobenzylation to benzyltoluenes is the main reaction, usually h igher than 90% selectivity when a toluene/benzyl chloride molar ratio of 5 is used. Secondary. reactions to dibenzyl- and tribenzyltoluenes occur to various extent depending on the reaction conditions and catal ysts. The most active catalysts, and the most selective to monobenzyla tion, are those possessing mesopores in the 30-200 angstrom range: H-B ETA and dealuminated HY (Si/Al=20). On these zeolites it is proposed t hat intracrystalline catalysis occurs, shape selectivity then preventi ng secondary reactions. At variance, on the other zeolites, H-ZSM-5 an d nondealuminated HY, the reaction takes place at the external surface of the grain yielding a lower activity and selectivity to monobenzyla tion.