Thermodynamic characteristics of methane adsorption about coking coal molecular with different sulfur components: Considering the influence of moisture contents

Abstract Sulfur groups are very susceptible to adsorption onto coking coal. In this study, three major organic sulfides of coking coal were extracted and identified by experiments. Then, coal molecules containing sulfide groups were respectively constructed via simulation. The adsorption isotherm curves of methane under different moisture contents were created. The experimental results show that thiophanthren, methyl-dibenzothiophene and dimethyl-naphthothiophene are the main organic sulfides found in coking coal. The simulation results indicate that the presence of moisture will cause the methane adsorption capacity to decrease sharply, which is mainly affected by the H/C ratio. With increasing of moisture content, the adsorption capacity of water molecules to coal molecules is stronger than that of methane molecules. The heat of methane adsorption, meanwhile, has no obvious relationship with moisture contents, but is mainly affected by S/C ratio. The adsorption heat of coal with an appreciable moisture content is less than that of coal without moisture. When the moisture content reaches a certain limit value (4%), its influence on the heat of methane adsorption is very small. The order of the heat of methane adsorption is dense medium component (DMC) > heavy component (HC) ＞ loose medium component (LMC). Water molecules easily combine with the chemical bonds on the surface of coal molecules and the hydrophilic functional groups inside. The heat of adsorption is mainly influenced by differences in the degree of coalification, but not by the various components extracted. When water is present, the adsorption capacity of methane is reduced to some extent, causing the adsorption system to methane coal molecules to reach equilibrium and release less heat. The results of this study were offer a quantitative understanding of the adsorption and thermodynamic properties of coal molecules with complex structures after extraction.