PYROLYTIC DESULFURIZATION OF SOME HIGH-SULFUR COALS

The extent of sulfur removal achieved in coal pyrolysis and hydropyrolysis at 520-degrees-C in a fixed-bed reactor has been compared for three high-sulfur coals, namely a Spanish and a Turkish lignite and a US hvc bituminous coal (PSOC 1495) containing significantly different amounts of pyritic and organic sulfur. For all three coals, the level of desulfurization increased with conversion and was thus higher in hydropyrolysis than in pyrolysis at 150 bar. The use of a sulfided molybdenum catalyst in hydropyrolysis gave rise to levels of desulfurization in excess of 90% excluding unreacted sulfatic sulfur. However, a number of subtle differences were found for the coals investigated. The ease of reduction of pyrite to pyrrhotite correlated with increasing grain size for the three coals investigated. The Spanish lignite tar prepared at low pressure contained significant amounts of thiophenes but, in going to hydropyrolysis, the concentrations of thiophenes decreased relative to those of benzo-and dibenzothiophenes as anticipated from the relative rates of hydrodesulfurization.