A Comparison of FeS, FeS + S and solid superacid catalytic properties for coal hydro-liquefaction

Catalyst plays an important role in direct coal liquefaction. This paper focuses on the catalytic behavior of a novel SO42-/ZrO2 superacid catalyst in coal hydro-liquefaction. A series of hydro-liquefaction experiments were conducted under mild conditions – 400 °C, 30 min and H2 initial pressure 4 MPa in a batch autoclave with a volume of 100 ml. The catalytic property of SO42-/ZrO2 was compared with FeS and FeS + S by Shenhua coal. The liquefaction products catalyzed by different catalysts were analyzed by FTIR spectrum, 1H NMR spectrum and element analysis. In addition, the SO42-/ZrO2 solid superacid was characterized. The results indicated that the SO42-/ZrO2 solid superacid shows outstanding catalytic property for direct liquefaction of coal and gives the highest coal conversion and gas + oil yield compared to other two catalysts. The THF conversion and the extraction yield of CS2/NMP mixed solvent of liquefied coal catalyzed with SO42-/ZrO2 are 76.3%, daf and 81.2%, daf respectively, and the yield of gas + oil is 62.5%, daf under the condition used in this study. The pyrolysis of coal macromolecular clusters can be promoted by catalysts such as FeS, FeS + S and SO42-/ZrO2. There may be only the pyrolysis of volatile matter and the relaxation of the structure of coal macromolecular clusters in non-catalytic liquefaction at 400 °C. Added sulfur in FeS can improve the catalytic activity of hydrogenation. SO42-/ZrO2 is a notable catalyst in the study of coal direct liquefaction because it shows excellent catalytic activities for the pyrolysis and the hydrogenation. In addition, it has been found that the C–O bond is the most stable group in coal liquefaction reaction except for the covalent bond between carbon and carbon.