INTERACTIVE EFFECTS BETWEEN SOLVENT COMPONENTS - POSSIBLE CHEMICAL ORIGIN OF SYNERGY IN LIQUEFACTION AND COPROCESSING

The traditional mechanism for coal liquefaction ties liquefaction ability of a solvent with its scavenging ability and cannot explain synergistic effects between solvent components. Such effects are naturally anticipated by mechanisms that involve interaction between components to generate reactive components. This paper discusses three recent papers, in which beneficial effects of adding nondonor species to the donor solvent were reported, in light of the solvent-mediated hydrogenolysis model for coal liquefaction-a model we have previously proposed. The nondonor species, which in these cases are polycyclic aromatic hydrocarbons, are good acceptors of hydrogen and react with hydroaromatic donors to give cyclohexadienyl radicals, which are capable of engendering hydrogenolysis, thereby increasing the overall rates. The PCAH species also help minimize wasteful transfer of hydrogen that would otherwise lead to reduced but uncleaved products. In this case the beneficial effect is reflected in the efficiency of hydrogen utilization. Finally, we extend this line of reasoning to the context of coprocessing coals and heavy oils. We use semiquantitative estimates for the fate of aliphatic radicals in the presence and absence of PCAH components to suggest that the PCAH components provided by coals convert aliphatic radicals, which are ineffective in causing bond scission, into cyclohexadienyl radicals that can do so.