Competitive adsorption of CO2, N2, and CH4 in coal-derived asphaltenes, a computational study

Abstract

Abstract Greenhouse gases are major contributors to global warming, and their concentration is increasing due to the widespread use of fossil fuels. Coal bed methane (CBM) offers a potential solution to this issue. However, the gas adsorption mechanisms of CBM, particularly in the context of coal-derived asphaltenes, are not fully understood. This study provides a comprehensive theoretical investigation of the competitive adsorption of carbon dioxide (CO $$_2$$ 2 ), methane (CH $$_4$$ 4 ), and nitrogen (N $$_2$$ 2 ) in the processes of CO $$_2$$ 2 - and N $$_2$$ 2 -enhanced coalbed methane recovery, with a focus on coal-derived asphaltenes functionalized with CH $$_4$$ 4 , NH, O, and S groups. Using the Grand Canonical Monte Carlo (GCMC) simulation method and performing Molecular Dynamics (MD) simulations, we studied the adsorption process. To investigate the electronic effects and nature of the interactions, we performed density functional theory (DFT) calculations. The adsorption energy values and non-covalent interactions (NCI) for the adsorption of gases signify the physical adsorption (van der Waals interaction), with CO $$_2$$ 2 exhibiting the highest (absolute) adsorption energy. The Monte Carlo results indicated that elevated temperatures led to a reduction in adsorption capacity. Coal-derived asphaltenes demonstrated greater selectivity for CO $$_2$$ 2 compared to CH $$_4$$ 4 and N $$_2$$ 2 in competitive adsorption, especially at elevated temperatures. Our findings highlight the significant potential of our asphaltene model, not only in mitigating CO $$_2$$ 2 greenhouse gas emissions but also in recovering CH $$_4$$ 4 , which is a valuable resource.