Evolution of methane adsorption characteristics in coal under N-Methylpyrrolidone treatment

The extraction of coalbed methane (CBM) from low-permeability coal beds is a key matter for coal mine safety. The microporous system of coal has a significant influence on its gas adsorption capacity. To reveal the evolution of the microporous system and methane adsorption characteristics of coal under solvent treatment, CO2 and methane isothermal adsorption experiments were carried out. The experimental results show that the N-Methylpyrrolidone (NMP) solvent significantly modifies the micropore structure of coal. After NMP treatment, the maximum reductions in the pore volumes of lignite, bituminous coal, and anthracite are 64.99%, 24.05%, and 11.29%, respectively. Their adsorption constant a values decrease by 55.13%, 27.48%, and 9.32%, respectively. and b values decrease by 52.14%, 21.47%, and 16.25%, respectively. The swelling of macromolecular polymers is the main contributor to the reduction in micropore volume. NMP has a significant impact on lignite and bituminous coal, while its effect on anthracite is slightly weaker. This indicates that NMP can help to solve the challenges of coalbed methane extraction.