Effect of highly dispersed iron catalyst on direct liquefaction of coal

The effect of a highly dispersed γ-FeOOH catalyst on the liquefaction of Yallourn coal was examined using a rapid-heating autoclave equipped with an infrared-ray image furnace, in relation to its transformation into pyrrhotite (Fe1−xS), by comparison with a conventional pyrite catalyst. It was found that the γ-FeOOH catalyst promoted the activation of gaseous hydrogen remarkably during the heating stage up to 450°C, as it could be transformed into smaller size pyrrhotite at lower temperatures of around 250°C. As a result, the efficiency of hydrogen consumption on oil yield was significantly increased due to a lower yield of hydrocarbon gases, compared with the case where pyrite catalyst was used. Further continuous liquefaction tests were performed using a 0.1t/d Bench Scale Unit (BSU) with gas and bottom recycling, and the residual activities of the recycle catalysts in the coal liquid bottom (CLB) were examined using a batch type autoclave. It appeared that the oil yield increased with a decrease in the crystallite size of pyrrhotite among the fresh and recycle catalysts. Control of H2S at a concentration of approximately 1.0 vol.% in the gas phase by the addition of elemental sulfur was effective in maintaining the liquefaction activity of recycle catalyst because of the suppression of both troilite formation and the crystal growth of pyrrhotite. It was demonstrated that a high oil yield of over 60wt%daf was obtained in the liquefaction of Yallourn coal with a considerable reduction of γ-FeOOH catalyst loading.