Molecular Simulation of CH4 Adsorption Characteristics under the Coupling of Different Temperature and Water Content

The adsorption characteristics of CH4 have an important influence on gas content prediction, gas extraction, and hazard prevention. Therefore, we explored the mechanism of CH4 adsorption under the action of water and temperature to grasp the influence of water and temperature on the adsorption characteristics of CH4. In this paper, a giant, regular-system Monte Carlo method is used to simulate the CH4 adsorption behavior at the molecular level under different temperatures, water contents, and the coupling of both. The results indicate that an empirical formula for the coupling effect of temperature and water content on CH4 adsorption was obtained. The impact of different effects on CH4 adsorption is as follows: coupling effect > single temperature effect > single water content effect. The optimal combination is at a temperature of 363 K and a water content of 8.31%. Compared with the CH4 adsorption capacity without water at room temperature, the CH4 adsorption capacity is reduced by 68.04% under the coupling effect of the optimal combination. Temperature has a negative effect on the adsorption of CH4, and temperature changes the adsorption capacity by changing the average molecular kinetic energy of CH4. The reason why the increase in H2O reduces the adsorption capacity of CH4 is that the interaction between H2O and the oxygen-containing functional groups of coal is stronger than that of CH4. As the water content increases, the adsorption heat decreases, thereby inhibiting the adsorption of CH4. In addition, H2O has a smaller molecular dynamics radius as compared to CH4; the larger the free volume and surface area in the pore structure, the more adsorption pores it occupies, resulting in a more significant reduction in the adsorption of CH4.