ACTIVITY AND CHARACTERIZATION OF ANION-MODIFIED IRON(III) OXIDES AS CATALYSTS FOR DIRECT LIQUEFACTION OF LOW PYRITE COALS

In previous papers, we reported on the catalytic activity of finely divided sulfated iron oxides for the direct liquefaction of coals containing between 0.2 and 2.5 wt % of pyrite (Energy Fuels, 1991, 5,497-507). The addition of small amounts of sulfated iron oxide catalysts (3500-7000 ppm relative to coal) significantly improved coal conversions and oil yields in the direct liquefaction of these coals. However, the large amounts of inherent pyrite present clouded the interpretation of catalyst composition, dispersion, and activity of the added sulfated iron oxide catalysts. In this paper, we address the quantification of catalyst activity and characterization, before and after reaction, of some previously reported and some newly synthesized anion-modified iron oxide catalysts by using two coals with very low inherent contents of pyrite. Information obtained on these anion-modified iron oxide/oxyhydroxide catalytic systems includes: physicochemical characterization of the sulfated catalysts before coal liquefaction; activity of small amounts of iron added as FeOOH/SO4, MO/FeOOH/SO4, Fe2O3/SO4, and Mo/Fe2O3/SO4 catalysts for direct liquefaction of a low-pyrite bituminous (Blind Canyon) and a subbituminous coal (Wyodak); and quantification of dispersion and composition of these catalysts after coal liquefaction and their transformation and sintering behavior under coal liquefaction conditions. The initially added sulfated iron oxides are completely converted to highly dispersed pyrrhotites (approximately 20 nm) essentially all as Fe7S8 in about 30 min under liquefaction conditions. These pyrrhotites maintained their state of high dispersion for long reaction times (120 min) without apparent agglomeration. The ability of sulfated iron oxide catalysts to form highly dispersed pyrrhotites under coal liquefaction conditions and to maintain them with little or no agglomeration renders these catalysts well suited for direct coal liquefaction reactions at low catalyst concentrations.