Competitive adsorption of EL and IAST in the context of separation factor in CO2-ECBM process

CO2 is the potent greenhouse gas and continuously increasing in the earth's atmosphere due to anthropogenic activities. CO2 sequestration in coal seams provides a dual advantage as the mitigation of CO2 emission is achieved through enhanced coalbed methane (ECBM) recovery, which can offset the cost of CO2 sequestration. The competitive or preferential adsorption of CO2 and CH4 is a crucial step to comprehend CO2-ECBM process in coal. In this study, pure gas isotherm was first evaluated using the manometric method. Then the preferential adsorption was studied using Extended Langmuir (EL) and Ideal Adsorption Solution Theory (IAST) models. The selectivity or separation factor was later evaluated using both models. Furthermore, the sweeping efficiency and recovery factor were calculated using the EL and IAST models. Due to higher affinity propensity, coal CO2 is preferred over CH4 for the adsorption on coal. The selectivity ratios calculated are higher than 1, which implies that CH4 would be replaced by adsorbed CO2. The values for one sample are more than 4, indicating the displacement of methane is effective. The Henry constant computed adds additive information in the competitive adsorption of CO2/CH4. The recovery factor of CH4 calculated using EL and IAST models are 85% and 90%, respectively. This study comparatively analyzes the results of both EL and IAST models, which add new perspectives for understanding the complex mechanism of CO2-ECBM process in coalfields.