Research on CO2/CH4/N2 competitive adsorption characteristics of anthracite coal from Shanxi Sihe coal mine

Abstract

This study aims to solve the problem of unsatisfactory development and utilization of coalbed methane and CO₂ storage efficiency. It is focused on the adsorption behavior of CO₂, CH₄, and N₂ in the macromolecular structure model of Shanxi Sihe coal mine anthracite, as well as the competitive adsorption behavior of CO₂/CH₄ and CH₄/N₂ binary gas mixtures with different ratios. Experimental analysis such as elemental analysis, solid ¹³C nuclear magnetic resonance (¹³C NMR), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis were used to construct the Shanxi Sihe coal mine model of the macromolecular structure of anthracite coal. The Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods were used to study the adsorption capacity and heat characteristics of CO₂, CH₄, and N₂ at different temperatures using a molecular model of anthracite coal from Shanxi Sihe coal mine, as well as the competitive adsorption characteristics of CO₂/CH₄ and CH₄/N₂ binary mixtures. The mechanism of the influence of temperature and gas properties on the adsorption capacity and heat of adsorption was revealed from a microscopic perspective. The results indicated that the aromatic carbon content of anthracite in the Sihe coal mine, Shanxi is 81.19%, and the ratio X_bp of aromatic bridgehead carbon to surrounding carbon is 0.489. The aromatic structure is mainly composed of pyrene and anthracene. The molecular formula of the macromolecular structure model of anthracite in Shanxi Sihe coal mine is C₂₃₃H₁₅₇O₁₃N₂. The adsorption capacity and equivalent adsorption heat of the macromolecular model for adsorbing single-component gas CO₂/CH₄/N₂ decrease with the increase in temperature. The temperature has the greatest impact on CO₂ adsorption capacity and adsorption heat, followed by CH₄ and N₂. Under the competitive adsorption conditions of CO₂/CH₄ and CH₄/N₂ binary mixtures, the higher the partial pressure of a single-component gas in the mixture, the greater the adsorption capacity of the gas. The difference in the adsorption heat of CH₄ and N₂ is smaller than that of CH₄ and CO₂. The conclusions obtained from the study can provide technical and theoretical support for formulating reasonable drainage methods for coalbed methane wells.