CATALYTIC CRACKING OF VACUUM GAS OIL ON THE DEALUMINATED MORDENITES

Catalytic cracking of vacuum gas oil was carried out at 500 degrees C over two series of mordenites treated by either steam/HCl or HF. Secon dary mesopores were formed in the mordenite by these treatments and th eir volumes increased with the degree of dealumination, whereas the mi cropore volumes decreased proportionately. The conversion of gas oil a nd the yield of gasoline and kerosene + diesel were correlated with th e acid-amount/mesopore-volume ratio. A maximum conversion and yield we re observed at a point of acid-amount/mesopore-volume ratio. This maxi mum point was interpreted as an optimum condition for the cracking act ivity between two inverse tendencies. The one is the decreasing tenden cy of cracking activity with reducing acid density. The other is the o ne increasing in activity with an increasing volume of the mesopore wi th silica/alumina ratio for both conversion of VGO and yields of gasol ine and kerosene + diesel. On the treated mordenite of higher silica/ alumina ratio, more olefins were formed due to a low rate of hydrogen transfer reaction. Aromatics are found to be formed via cyclization of olefins which can occur inside an enlarged mesopore of dealuminated m ordenite. The largest content as an alkyl-aromatic compound in the pro duced gasoline was toluene, which was possibly interpreted as the diff usion limitation in the formation of higher alkyl-branched aromatics. (C) 1998 Academic Press.