CATALYTIC CRACKING OF CANADIAN NONCONVENTIONAL FEEDSTOCKS .1. CRACKING CHARACTERISTICS OF GAS OILS DERIVED FROM COPROCESSING DISTILLATE AND SHALE OIL

Two nonconventional vacuum gas oils (VGO's) featuring high nitrogen concentrations were obtained by vacuum distillation of a coal-oil coprocessing product and a shale oil, respectively. Analyses showed that the coprocessing VGO was more aromatic whereas the shale VGO contained more polar components. The two VGO's were cracked in a microactivity test (MAT) unit at different temperatures and catalyst/oil ratios over three commercial catalysts containing rare earth-exchanged or ultrastable Y zeolite (REY or USY). Similar to most products from primary upgrading processes, these two VGO's showed comparatively poor cracking results in terms of conversion, gasoline, and coke yields. This was attributed to nitrogen poisoning of catalysts during cracking of either of the two gas oils and also to the relatively high polynuclear aromatic (PNA) content of the coprocessing VGO. Cracking results improved when nitrogen and PNA compounds were partially removed from the VGO's by solvent extraction or clay adsorption. The treated VGO's can be considered as potential fluid catalytic cracking (FCC) feedstocks. Additive coke resulting from the basic nitrogen and the Conradson carbon residue in the gas oils was found to be dependent only on the temperature. The effect of severity on product distribution and the performance of the three catalysts with respect to nonconventional gas oil cracking are demonstrated and discussed.