TRANSFORMATION OF AN ETHYLBENZENE-O-XYLENE MIXTURE ON HMOR AND PT-HMOR CATALYSTS - COMPARISON WITH ZSM-5 CATALYSTS

The transformation of pure ethylbenzene and of an ethylbenzene (20 wt. -%)-o-xylene (80 wt.-%) mixture is carried out on acid and bifunctiona l HMOR catalysts under the following conditions: fixed bed reactor, te mperature 410 degrees C, 0.96 MPa pressure of hydrogen and 0.24 MPa pr essure of hydrocarbons, weight of hydrocarbon injected per weight of c atalyst and per hour between 10 and 110. On both catalysts the main re action of pure ethylbenzene is disproportionation, this reaction occur ring mainly through diphenylethane intermediates. The main effect of p latinum is to allow the bifunctional isomerization of ethylbenzene. In addition to disproportionation reactions, ethylbenzene in mixture wit h xylene is also transformed through similar mechanisms into dimethyle thylbenzene (transethylation) and into ethylmethylbenzene (transmethyl ation). o-Xylene is rapidly transformed into m- and p-isomers. Large d ifferences exist between MOR and ZSM-5 catalysts, ZSM-5 catalysts are very active for ethylbenzene dealkylation and C-8 naphthenes hydrocrac king while MOR catalysts are more active for xylene isomerization and disproportionation, and ethylbenzene hydroisomerization. Disproportion ation 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 intermediate s at channel intersections and diffusion limitations are responsible f or the particular behaviour of ZSM-5 catalysts.