Effects of variable amounts of volatiles in corncob on microwave co-pyrolysis of low-rank coal and corncob

Crop waste-assisted microwave pyrolysis of low-rank coal (LRC) can provide sufficient hydrogen for thermal decomposition reactions of LRC, which can change the pyrolysis reactions and product characteristics. To reveal the effect of crop waste as a hydrogen supply on the microwave pyrolysis of LRC, the temperature-rise characteristics, product distribution, and product characteristics of microwave co-pyrolysis of LRC and corncob (CR) with different amounts of volatiles were investigated in detail, and the crystal and chemical structures of char and tar were analyzed. The results showed that the volatiles in CR promoted the production of tar and inhibited the generation of pyrolysis gas within a certain range during microwave co-pyrolysis; however, the volatiles had the opposite effect beyond this range. With an increase in volatiles in CR, the yields of char and pyrolysis water gradually decreased and increased, respectively. CR with low amounts of volatiles at high final pyrolysis temperatures increased the specific surface area and total pore volume of the char obtained by microwave co-pyrolysis and improved the aromaticity and graphitization of char and the ordered structure of the crystal structure in char. Additionally, the formation of aromatic structures in the tar was promoted, and the contents of oxygen-containing functional groups and aliphatic hydrocarbons in the tar were reduced. The fraction of light oil in the tar increased by 18.49%, indicating that the lightness and stability of the tar significantly increased. These findings have provided a theoretical basis for microwave co-pyrolysis of LRC and crop wastes, as well as experimental evidence for regulating its product characteristics.