CATALYTIC CRACKING OF VACUUM GAS OIL OVER THE MODIFIED MORDENITES ANDY-TYPE ZEOLITES MIXED WITH ALUMINA

Catalytic cracking of vacuum gas oil has been studied over pure zeolit es modified by steaming and acid treatment, and zeolite/alumina cataly sts containing any of the former zeolite (35 wt %) and alumina (65 wt %) with a different pore size distribution. The conversion of vacuum g as oil (VGO) over zeolite/alumina catalysts with a wide pore size dist ribution is almost the same as that over pure zeolites, but less coke is formed over zeolite/alumina compared to that over pure zeolites. Th e catalysts containing zeolite Y show higher conversion of VGO than on the catalysts containing mordenite. In addition, the catalysts contai ning modified mordenite, resulting in the development of mesopores, ha ve improved activity and selectivity for gasoline compared to those co ntaining mordenite with a micropore structure. Selectivity of olefin i s higher on the catalysts containing mordenites compared to the cataly sts containing zeolite Y because of low-bimolecular hydrogen-transfer reaction rates. The distribution of paraffin and olefin in gasoline pr oducts does not depend on the addition of alumina in mixed catalysts b ut rely on mainly the zeolite type. The influence of shape selectivity on products distribution causes the catalysts containing zeolite Y wi th large kinetic diameter to produce more branched aromatics than thos e containing mordenites. The modified mordenite catalysts having mesop ores in the 4-nm range yield more aromatics compared to the catalysts containing mordenite with mostly micropore. Catalysts containing zeoli te Y give the highest yield of xylene whereas the catalysts containing mordenites produce a maximum yield of toluene.