Influence of Microwave-Assisted Supercritical Carbon Dioxide Treatment on the Pore Structure of Low-Rank Coal.

CO₂ injection into coal seams not only enhances coalbed methane (CBM) extraction but also allows for CO₂ sequestration. Microwave irradiation is considered to be an effective technology to enhance CBM extraction. In this paper, the effects of microwave irradiation and supercritical CO₂ immersion on the pore structure of low-rank coals were investigated by scanning electron microscopy (SEM), mercury-in-pressure (MIP), low-temperature nitrogen adsorption (LTN₂GA), and carbon dioxide isothermal adsorption/desorption (CO₂IA/D) of coal samples. The results showed that the macropores and micropores of the coal samples were more developed after microwave irradiation. After carbon dioxide immersion, the coal samples showed huge fissures, and the meso- and micropores were reduced. In contrast, microwave-assisted carbon dioxide not only reduced the specific surface area in the meso- and microporous stages and decreased the adsorption sites of methane but also enhanced the pore connectivity in the macroporous stage instead of the appearance of huge fissures. This study illustrates the potential of microwave-assisted supercritical carbon dioxide for enhanced coalbed methane extraction and carbon dioxide sequestration.