Catalytic liquefaction of coal with highly dispersed Fe₂S₃ impregnated in-situ

Daliuta subbituminous coal, from Shenfu, Shanxi province of China, was liquefied in a 50 mL micro-autoclave apparatus at 440 °C, initial hydrogen pressure of 6.0 MPa, soaking time of 30 min, using a mixture of tetralin and cyclohexane as solvent. The experiments were carried out to investigate the effects of in-situ impregnated Fe₂S₃ on the liquefaction conversion, oil and gas yields of the coal, and the aromatic, aliphatic, and polar compounds fraction content in the oil. The effect of surfactant treatment during catalyst impregnation was also studied using hexadecyl-trimethylammonium bromide. Gradient elution chromatography (GEC), GC, and GC-MS were used to characterize and quantify the coal liquids. XRD and TEM were used to characterize the catalyst. The results indicate that without catalyst the conversion and oil yield are 43.2 and 37.4 wt %, respectively. At the same reaction condition but with the addition of 1.0 wt % Fe (based on daf coal), the conversion and oil yield reach 62.6 and 54.2 wt %, respectively. When the surfactant was used during the 1 wt % Fe catalyst impregnation, the conversion and oil yield became 68.8 and 59.5 wt %, respectively. The catalyst is dispersed in nanometer size particles in amorphous phase that transforms to pyrrholite phase during the liquefaction. The addition of 9.2 × 10^-4 M surfactant changes the ζ-potential of the coal particles from -15 mV to +29 mV, decreases the size of catalyst particle on the coal surface from 30-40 to 15-20 nm. The oil products are complex aromatics with 2 to 3 rings.