Iron-based catalysts, H/sub 2/S and liquefaction

One of the most promising advances of the past 50 years of coal liquefaction catalysis is learning of the iron and sulfur synergism. Now with the promotional effects of hydrogen sulfide demonstrated and its mechanism of action being unveiled, the interaction of hydrogen sulfide with iron needs to be understood for explaining the basis of presulfiding catalysts and for new catalyst design. Presulfiding metal oxide hydrogenation catalysts has long been known to enhance liquefaction yields. However, the chemistry-based reason(s) for the enhancement is unclear. The metal oxides are probably converted to a mixed oxide-sulfide under sulfur-rich conditions. Using differential thermal analysis under high pressure for coal hydrogenation, Takeya rates red mud + S at 297/sup 0/C as having better catalytic activity than red red mud at 429/sup 0/C. A combination of iron oxides and sulfur have been used for coal liquefaction effectively. In related studies, Beardon and Aldridge have patented the pretreatment of coal with hydrogen sulfide to enhance conversions. Gatsis utilized 4 to 8 volume percent hydrogen sulfide (based on hydrogen gas) to enhance the conversion of bituminous coal (Pittsburgh Seam Coal) into a more filterable, higher hydrogen content product using a solvent. The operating conditions in the extractionmore » zone were 250/sup 0/-500/sup 0/C and 500 to 5,000 psig with a solvent to coal weight ratio of 0.2 to and a residence time from 30 seconds to 5 hours.« less