Pore-scale investigation on the multi-component gas adsorption and diffusion in carbon xerogel microporous structure using molecular simulation methods

The atomic model of carbon xerogel microporous structure is reconstructed by a modified virtual porous carbon (VPC) model. The physical parameters of the reconstructed model, especially the predicted nitrogen adsorption isotherm, agree well with the experimental data. Then, the adsorption and diffusion of the gas in carbon xerogel microporous structure are investigated at the pore-scale. The results show that decreases of isosteric adsorption heat and the excess adsorption in carbon xerogel microporous structure are majorly contributed by the desorption of adsorbates in ultramicropores with the temperature increasing. The microporous structure appears a strong selectivity for oxygen in the air, due to the molecular sieving effect and the strong solid-fluid interaction between the pore wall and oxygen. As the desorption of oxygen in ultramicropores due to its increasing steric repulsion with the temperature rising from 298 K to 573 K, the selectivity of microporous structure for oxygen decreases, and the gap between isosteric adsorption heat for nitrogen and oxygen is narrowed. The systemic migration of gas molecules from the ultramicropores to the wider area is observed by the pore-scale analysis, and it makes the gas diffusivity appear an approximately linear relationship with the temperature. • The carbon xerogel microporous structure is reconstructed at atomic scale. • The properties of the reconstructed model agree well with the experimental data. • The influence of micropore structure on the gas adsorption and diffusion is studied. • Carbon ultramicropores show a steric repulsion to gas molecules at high temperature.