Influence of platinum on the transformation of an ethylbenzene- o-xylene mixture on H-ZSM-5

Abstract

The transformations of pure ethylbenzene and of an ethylbenzene (20wt.-%)- o-xylene (80 wt.-%) mixture were carried out on acid and bifunctional ZSM-5 catalysts under the following operating conditions: fixed bed reactor, temperature 410°C, 0.96 MPa pressure of hydrogen and 0.24 MPa pressure of hydrocarbons, weight of hydrocarbon injected per weight of catalyst and per hour between 10 and 110. On both catalysts the main reactions of pure ethylbenzene are dealkylation and disproportionation, this latter reaction occurring through a dealkylation-alkylation scheme. The main effect of platinum is to increase the rate of dealkylation and to decrease that of disproportionation, which is due to the rapid hydrogenation of ethylene. In addition to dealkylation and disproportionation, ethylbenzene mixed with xylenes is also transformed into dimethylethylbenzene (transethylation), this latter reaction decreasing considerably in the presence of platinum. On the acid and bifunctional catalysts o-xylene is very rapidly transformed into p-andm-xylenes. Xylenes are also transformed through disproportionation and transethylation. Platinum increases slightly the rate of disproportionation at the expense of transethylation.