Insight into product characteristics from microwave co-pyrolysis of low-rank coal and corncob: Unraveling the effects of metal catalysts

Microwave pyrolysis of low-rank coal can provide high yield and quality of valuable products. Coupling with hydrogenated and catalytic pyrolysis is considered to achieve the selective or targeted generation of pyrolysis products. In this study, three metal catalysts KCl, Fe2O3, and CaO were used in the microwave catalytic co-pyrolysis of low-rank coal and corncob to investigate their effects on the temperature rise, product distribu-tion, and product structure characteristics. The results showed that the maximum and final temperatures of microwave co-pyrolysis with the addition of a metal catalyst increased, and the corresponding yield and quality of tar were considerably improved. The porous structure of the char with the added metal catalyst was signif-icantly enhanced, and the carbon microcrystal structure became significantly strong, but the change in thickness was minimal. The formation of aliphatic hydrocarbons and C--O functional groups in both char and tar was inhibited when Fe2O3 and CaO were added. Among the three metal catalysts, CaO had the most obvious effect on the pyrolysis products, resulting in a maximum tar yield of 10.89 % and the highest light oil of 17.20 %. The char had a more regular and integrated porous structure; its Aar/Aal ratio reached a maximum of 12.603, showing the highest aromaticity. In addition, the total of valuable gas component and heat value of the pyrolysis gas arrived at 84.81 vol% and 14.93 MJ/m3, which showed excellent yield and performance. This work provides sufficient evidences for clean and efficient utilization of low-rank coal using catalytic microwave pyrolysis technology.