Liquefaction tests of Yallourn coal with iron based catalyst and elemental sulfur were carried out by using 0.1t/d BSU (Bench Scale Unit) to investigate the influence of the decrease in catalyst loading on oil yield. The properties of iron sulfide in CLB (Coal Liquid Bottom), recovered from the reactor after the coal liquefaction, were analyzed by powder X-ray Diffraction method with ldeg./min of scanning rate. It appeared that H2S concentration above lvol% in the gas phase was required to suppress the troilite (FeS) formation, keeping the pyrrhotite (Fe1-xS) on a smaller crystallite size. The liquefaction activities among the fresh and used catalyst (CLB-THFI) were strongly dependent on the crystallite size of pyrrhotite, indicating that the troilite was less active than pyrrhotite.
γ-FeOOH catalyst had an excellent catalytic activity among the iron based catalysts due to the transformation into pyrrhotite with smaller crystallite size. It was concluded that the catalyst deactivation was suppressed by keeping the H2S concentration at lvol% in the gas phase, resulted in a successful reduction of γ-FeOOH catalyst loading down to 0.3 wt% daf as Fe through the bottom recycle in the BCL (Brown Coal Liquefaction) process.
