Effect of tetralin dissociation on coal liquefaction: Tubing bomb versus batch autoclave

The extent of coal hydroliquefaction in the presence of a good catalyst (impregnated ammonium heptamolybdate) and a hydrogen-donor solvent (tetralin) can be substantially greater in a tubing bomb than in a stirred autoclave, under nominally identical liquefaction conditions. This difference may be associated with the typically lower gas:liquid volume ratio existing under reaction conditions in a tubing bomb, relative to the ratio in an autoclave. If equilibrium is reached in the catalysed dissociation of tetralin, the extent of dissociation is less, and the hydrogen partial pressure is substantially higher, in the tubing bomb than in the autoclave. Calculations and measurements have been made for the equilibrium conditions in tetralin dissociation when coal is absent but a good catalyst (ammonium heptamolybdate dispersed on alumina) is present. For the calculation, the molar volumes and vapour pressures of tetralin and naphthalene must be known, together with the dissociation constant. Agreement was good between calculated and experimental values of dissociation in both tubing bomb and autoclave. The results permit prediction that increasing the gas:liquid volume in a tubing bomb liquefaction experiment should decrease the conversion; this effect was observed.