Influence Mechanism of Different Weathering Degrees on Conversion of Coal to Biogas

To investigate the influence mechanism of weathering in the biogas production from coal, the characteristics of three coal samples with different weathering degrees obtained from the Wuhai mining area in Inner Mongolia and from the Xishan and Jincheng mining areas in Shanxi province were analyzed using the following methods: humic acid (HA) extraction, three-dimensional fluorescence spectroscopy, X-ray photoelectron spectroscopy and X-ray diffractometry. The results showed that the HA content in weathered coal increased with an increase in weathering degree. The content of dissolved organic matter in moderately and intensively weathered coals was clearly higher than that in slightly weathered coals. Meanwhile, the C–C and C–H in the aromatic ring was broken under the action of weathering, thus decreasing the aromaticity. Additionally, the weathering process also intensified the disordering of the directional arrangement of the macromolecular structure, causing the crystallinity of the coal to decrease. These conditions facilitated the degradation and utilization of coal by microorganisms and can be helpful to produce more biogas from coal.