REACTIVITY AND SELECTIVITY FOR THE HYDROCRACKING OF VACUUM GAS OIL OVER METAL-LOADED AND DEALUMINATED Y-ZEOLITES

Hydrocracking, hydrodenitrogenation (HDN), and hydrodesulfurization (H DS) of vacuum gas oil (VGO) were examined using Ni-, Co-, and Fe-loade d and dealuminated Y-zeolites at 300-380 degrees C under an initial hy drogen pressure of 5 MPa. The major fraction of the VGO was n-paraffin s (45 wt %), and the second major fraction was alkyl-substituted 3- an d 4-ring aromatics. Polar aromatics and 1- and 2-ring aromatics were m inor components. Paraffins of 15-32 carbon chains and aromatic compoun ds of 3-4 rings were efficiently hydrocracked into a gasoline fraction over Ni-HY-A (Si/2Al = 16.0) zeolite, which gave the least yield of g aseous byproducts among the catalysts examined. Extensively dealuminat ed Ni-HY-B zeolite (Si/2Al = 50.0) produced a large amount of middle d istillate fraction, while the yields of gas and coke that was deposite d on the catalyst were markedly suppressed. Both zeolites exhibited ex cellent HDN and HDS activities. The Co-HY and Fe-HY zeolites showed a similar hydrocracking activity as did the Ni-HY-A zeolite, whereas the Fe-HY produced more gaseous hydrocarbons. The Co-HY and Fe-HY zeolite s were inferior to the Ni-HY-A in HDS and HDN activities at 380 degree s C. The metal-free HY-A zeolite exhibited higher yields of gaseous hy drocarbons, 4-ring aromatics, coke, and hexane-insoluble fractions tha n did the metal-loaded catalysts. The HY-A zeolite had essentially no HDS and HDN activities, and the concentration of alkyldibenzothiophene s in the product oil was increased by condensation and transalkylation during cracking reaction. The excellent activities of the metal-loade d HY-zeolites apparently originated from the optimized acidity, as a r esult of dealumination, in addition to the highly dispersed metal sulf ides which enhanced hydrogenation activity. The acidic strength of the catalysts was a key factor in controlling the selectivity between gas oline and gas oil production.