Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures...

In order to further elucidate the thermodynamic mechanism of CH₄/CO₂ adsorption by coal molecules, the adsorption behavior of a molecular model of coal (C₂₀₆H₁₂₈O₃₆N₂) at Wucaiwan, Zhundong was investigated by applying Materials Studio 2020 and Monte Carlo (GCMC) simulation methods, and the adsorption behavior of CH₄ and CO₂ was studied from the thermodynamic point of view under the conditions of different temperatures, pressures, and moisture contents. The results showed that at different temperatures or moisture contents, CH₄ molecules had a low-density scattering distribution and CO₂ molecules had a high-density polymerization distribution. Temperature and moisture content and adsorption constants a and b were negatively correlated. Under the same conditions, the relationship between single- and binary-component adsorption amounts was CO₂ > CH₄ and the relationship between heat of adsorption was CO₂ > CH₄. When adsorption potential energy or entropy of adsorption was the same, the adsorption capacity was CO₂ > CH₄. Temperatures and moisture contents were negatively correlated with the total adsorption capacity of CH₄/CO₂; pressure was positively correlated with the total adsorption capacity of CH₄/CO₂. The effect of temperature on the equivalent heat of adsorption was greater than that of pressure at different temperatures, and the entropy of adsorption was positively correlated between temperature and CH₄/CO₂, while the amount of adsorption was negatively correlated with the entropy of adsorption. The effect of moisture content on the equivalent heat of adsorption was greater than that of pressure at different moisture contents, and the entropy of adsorption was negatively correlated between moisture content and amount of adsorption. The adsorption entropy of CH₄/CO₂ was negatively correlated, and the adsorption amount was positively correlated to the adsorption entropy. At a temperature above 318 K or moisture content above 10%, the total CH₄/CO₂ adsorption decreased significantly and the CO₂ adsorption decreased significantly. From a thermodynamic point of view, the presence of a large amount of H₂O had a much greater effect on CO₂ than on CH₄, and an increase in temperature or moisture content was unfavorable for CO₂ sequestration, CO₂ stripping of CH₄, and control of CH₄ diffusion and desorption, whereas at low temperature, high pressure, and moisture content <1%, the effect of stripping, sequestration, and control was good.