Frank J. Derbyshire, P. Varghese and D.Duayne Whitehurst
Mobil Research and Development Corporation, Central Research Division, PO Box 1025, Princeton, NJ 08540, USA
Abstract
The two-stage conversion of a subbituminous coal has been investigated using an autoclave reactor system. The overall performance of the reaction is found to be determined by the effectiveness of the first-stage operation and by the method of sequencing of the stages. The initial thermal products can undergo condensation reactions which render them unresponsive to subsequent catalytic conversion and which increase the light gas yield. This can occur during the first stage reaction, if there is limited capacity for free-radical stabilization, and upon storage and/or thermal cycling between stages. The latter effects are circumvented by operating the two stages in immediate sequence. Condensation is also reduced by increasing the solvent quality and the solvent:coal ratio. The presence of a catalyst during thermal decomposition of coal can greatly improve conversion and product stability even at short reaction time and can reduce constraints on solvent quality. The more feasible approaches to improving first-stage operation appear to be in controlling the solvent composition and in employing hydrogenation catalysts.