RELEVANCE OF CLEAVAGE OF STRONG BONDS IN COAL-LIQUEFACTION

Almost ten years ago we proposed that cleavage of bonds too strong to undergo simple thermolysis but which are cleaved by the mediation of solvent or solvent-derived radicals may be an important contributor to the liquefaction of coals. In this paper we discuss the process implications of this revised view. We show how this picture continues to help rationalize many otherwise inexplicable observations in fossil fuel conversion technology. These observations include the breaking of nonhomolyzable bonds in grafted and doped coals, the ineffectiveness (in liquefaction) of nonhydroaromatic radical scavengers, the effectiveness of nondonor polycyclic aromatic hydrocarbons (PAH), the 'activation' of cyclic aliphatics by PAH, increasing hydrogen utilization efficiency observed with added PAH, and the decrease in gas formation observed at lower temperatures or with added PAH. We also discuss examples that show the importance of the solvent medium in transferring and transporting hydrogen in catalytic systems. Finally, we discuss how the solvent or solvent-derived radicals may also promote retrogressive reactions under certain conditions.