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 Xbp 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.