Temperature- and Pressure-Dependent Methane and Carbon Dioxide Adsorption on Coal: Insights for Carbon Storage in Deep Coal Seam

Summary In this study, we explore the adsorption behaviors of methane (CH4) and carbon dioxide (CO2) on coal at pressures up to 2,000 psi and 800 psi, respectively, and temperatures ranging from 30°C to 80°C, as applied to enhanced coalbed methane (ECBM) recovery and CO2 sequestration (CS). Combined ECBM and CS can be used to enhance energy production while reducing the carbon footprint. CH4 adsorption measurements within the tested pressure range decrease sublinearly with increasing temperature; however, the Langmuir volume derived from modeling remains relatively stable across the same temperature range, indicating a limited sensitivity of coal’s maximum adsorption capacity to temperature. This suggests that higher temperatures may favor gas extraction due to lower pressure requirements, though this increases the challenges for CS, for which higher CO2 adsorption is desired. CO2 adsorption shows a distinctive pattern: Capacities decrease linearly with increasing temperature but unexpectedly increase beyond the CO2 critical temperature (31.2°C), especially near 40°C. This suggests that supercritical CO2, due to its enhanced mass transfer properties, can more effectively displace CH4 in coal seams. However, at higher temperatures, the CO2 sorption capacity reduces, complicating ECBM operations. Through this study, we also reveal a reduced CO2/CH4 sorption ratio at supercritical conditions, indicating a stronger influence of the coal physical structure on adsorption. These findings provide critical insights into optimizing thermodynamic conditions for balancing CH4 recovery and CO2 storage, contributing to sustainable energy production and global carbon management efforts.