INFLUENCE OF CATALYSTS UPON HYDROGEN TRANSFER PATHWAYS DURING HYDROLIQUEFACTION OF COAL

Several mechanisms are involved in the transfer of hydrogen from the gas phase to coal during hydroliquefaction, according to the nature of the solvent. The impact of various catalysts on the respective pathways has been investigated at low catalyst-to-coal ratio in a batch reactor. The examined catalytic materials include: iron oxide, metallic tin and lead, in oxide and supported nickel-molybdenum as a reference. The contribution of mineral matter from coal to hydrogenation reactions has been evaluated; sulfur causes some catalytic effect. With a non donor solvent, direct incorporation of gaseous hydrogen is predominant. Tetralin (1,2,3,4-tetrahydronaphthalene) donates hydrogen in the absence of added catalyst; when used with a catalyst, the net result is an increase of the contribution of gaseous hydrogen consumption. Shuttle mechanisms involving the solvent or coal liquids cannot be ruled out. Coal liquids produce some inhibition effect on the activity of iron oxide which is partly restored by the elimination of volatile products; other interactions between coal liquids and catalysts probably affect the sulfidation of iron oxide. The hydrogeneration activity of metallic tin and lead may originate from the formation of hydrides of intermetallic compounds.