Effect of low temperature catalytic hydrogenation on pyrolysis and hydropyrolysis of a bituminous coal

The effect of coal pre-hydrogenation under relatively mild conditions (400 °C, 7 M Pa hydrogen pressure) using a dispersed sulphided molybdenum catalyst on fluidized bed (flash) pyrolysis at atmospheric pressure and fixed-bed hydropyrolysis was investigated for a UK bituminous coal (82% dmmfC). In pyrolysis at 600 °C, the catalytic pre-treatment raised the overall conversion and tar yield by ≈ 20 wt% daf coal giving nearly 50 wt% tar with little extra gas. The effect of the pre-treatment in fixed-bed hydropyrolysis at 500 °C and 15 M Pa pressure is even more pronounced with the overall conversion increasing from approximately 40 to 80 wt% daf coal, which included less than a 5 wt% rise in gas yield. The same level of conversion was achieved in hydropyrolysis using the catalyst impregnated coal without pre-hydrogenation, indicating that the chemical transformations occurring in catalytic hydrogenation and in the early stages of hydropyrolysis are broadly similar. However, the fact that the conversion in hydropyrolysis is significantly higher than that in flash pyrolysis for the catalytically hydrogenated coal indicates that further hydrogenation occurs during hydropyrolysis.