Enhanced conversion of heavy feedstock through the circulation of catalytic components in tail oil derived from coal liquefaction

Abstract

The co-hydroprocessing of lignite and heavy residue generates a substantial amount of tail oil, compromising the technical efficiency and posing significant environmental hazards. We proposed a cascade utilization scheme via the combination of tail-oil cycling and tail-oil co-hydrocracking, to maximize the utilization of catalytic components and enhance the conversion of heavy feedstock. At a cycling ratio of 50 wt%, the conversion efficiency of carbonaceous solids increased from 88 % to over 95 % after 5 cycles. The effluent tail oil also represented a favorable hydrocracking performance when mixed with Merey atmospheric residue. The spent catalysts and iron-containing minerals gradually accumulated in solid residues, which provided additional catalytic components for hydrogenation and coke inhibition in the co-hydroprocessing and co-hydrocracking systems. Moreover, the cycling process improved the colloidal stability and enhanced the hydrogenolysis of heavy components, effectively curbing the degradation tendency within the reaction system and producing more light oils.