Products optimization by FeS2 catalyst for low-rank coal microwave pyrolysis

Catalytic microwave pyrolysis aims to improve the energy efficiency and perfect product distribution. In this work, ferrous disulfide (FeS2) is employed as a catalyst for low-rank coal microwave pyrolysis reaction. The catalytic effects on pyrolysis temperature, product yields, and three pyrolysis products are also discussed. Some key analytical techniques, such as SEM-EDS, FT-IR, and GC-MS, are used to compare the products of microwave pyrolysis and catalytic microwave pyrolysis. A catalytic mechanism of FeS2 is proposed based on the catalytic effects. Results showed that FeS2 catalyst improves the temperature-rising rate and final temperature of microwave pyrolysis, leading to the change of the distribution of pyrolysis products. When 12.0% FeS2 catalyst is added for the microwave pyrolysis, the yields of solid, liquid, and gaseous products are 64.10%, 27.20%, and 8.7%, respectively, and the yield of liquid product increases by 6.40% compared with microwave pyrolysis. The number of small particles on the surface of solid product obviously decreases, and a layered phenomenon appears in large solid product. Moreover, the mass fraction of light oil significantly increases, indicating that FeS2 catalyst can make coal tar "light". Catalytic microwave pyrolysis of low-rank coal can be divided into coal liquefaction and secondary reaction stages, and the FeS2 catalyst works better in the entire catalytic microwave pyrolysis.