Coal liquefaction by molybdenum catalyzed hydrogenation in the absence of solvent

Abstract

Dry catalytic hydrogenation, using an impregnated molybdenum catalyst, has been used to explore the processes of coal liquefaction and their relation to coal structure. It was found that for high activity the molybdenum must be present as MoS 2 and that the conditions used for impregnation can strongly influence catalyst dispersion and activity. At temperatures of 400°C and lower, a subbituminous coal was more readily converted to liquid products and gases, than a coal of bituminous rank. The low-rank coal products were comparatively richer in hydrogen, possessed higher oil to asphaltene ratios and were more aliphatic than the bituminous coal liquids. It is considered that the higher reactivity of the low-rank coal is attributable to the initial reactions being conducted under conditions which promote hydrogenation while minimizing condensation and cracking reactions. Examination of reacted coals by reflected fluorescent light microscopy showed a close correlation between the yield of extractable liquids and the maximum intensity of vitrinite fluorescence. The fluorescence appears to be directly related to the liberation of relatively low molecular weight species within the coal structure. Coal pretreatment by low-temperature dry hydrogenation, prior to higher temperature liquefaction in the presence of solvent, improved the overall conversion and product selectivity of both bituminous and subbituminous coals. It is suggested that subtle control of the initial conversion reactions can lead to more efficient liquefaction of coals of different rank.