Effect of water on CO2 adsorption and diffusion in low-rank coal nanopores

In this study, the nanopore structure of low-rank lignite was obtained using scanning electron microscopy, N 2 and CO 2 adsorption methods. Based on these data, the nanopore models of lignite with varying moisture volume fractions were constructed. Then, CO 2 adsorption and diffusion performances on lignite were researched. The findings indicate that moisture is the dominant factor limiting CO 2 storage capacity. Water molecules can preferentially occupy high-energy adsorption centers and form dense water films, creating a significant “shielding effect” that substantially reduces CO 2 adsorption density. With increasing moisture volume fraction, CO 2 interaction energy distribution shifts from a heterogeneous “high-energy long-tail” pattern under dry condition to a homogenized low-energy distribution, accompanied by a marked decrease in thermodynamic stability. As moisture volume fraction enhances, the CO 2 diffusion coefficient shows a non-monotonic variation under the present simulation conditions, which can be attributed to the difference between surface-energy smoothing at low-to-moderate moisture volume fraction s and water-film blocking at high moisture volume fraction moisture volume fraction.