Transformation of an ethylbenzene-o-xylene mixture on HMOR and Pt-HMOR catalysts. Comparison with ZSM-5 catalysts Original Research Article

The transformation of pure ethylbenzene and of an ethylbenzene (20wt.-%)-o-xylene (80 wt.-%) mixture is carried out on acid and bifunctional HMOR catalysts under the following 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 reaction of pure ethylbenzene is disproportionation, this reaction occurring mainly through diphenylethane intermediates. The main effect of platinum is to allow the bifunctional isomerization of ethylbenzene. In addition to disproportionation reactions, ethylbenzene in mixture with xylene is also transformed through similar mechanisms into dimethylethylbenzene (transethylation) and into ethylmethylbenzene (transmethylation). o-Xylene is rapidly transformed into m-andp-isomers. Large differences exist between MOR and ZSM-5 catalysts. ZSM-5 catalysts are very active for ethylbenzene dealkylation and C8 naphthenes hydrocracking while MOR catalysts are more active for xylene isomerization and disproportionation, and ethylbenzene hydroisomerization. Disproportionation of ethylbenzene occurs mainly on H-ZSM-5 through a deethylation-ethylation mechanism and on HMOR through diphenylethane intermediates. Steric constraints on the formation of bulky bimolecular intermediates at channel intersections and diffusion limitations are responsible for the particular behaviour of ZSM-5 catalysts.