Binary Gas Transport with Multilayer Adsorption in Nanoporous Media

Abstract We investigate binary gas transport with multilayer adsorption in nanoporous media by merging pore-scale properties obtained via multicomponent simplified density theory (MSLD) with continuum-scale transport modeling. Accordingly, we propose a diffusion-based gas transport model that considers the free and sorbed phases and multilayer multicomponent adsorption in the nanoporous media and incorporates a dynamic sorbed-phase density. Bulk, Knudsen, and viscous diffusion are considered in the free phase, while surface diffusion and multilayer adsorption are considered in the sorbed phase. The proposed model is utilized to investigate the impact of fluid-solid interactions and pore size on gas transport and storage using different fluid-solid systems. It was also used to perform gas transport simulation and a comparison with monolayer adsorption model was made. The results show that the pressure and composition diffusion coefficients are smaller in strong adsorption affinity systems due to increased adsorption and reduced free-phase volume fraction. The pressure and the composition capacity factors are higher for stronger adsorption affinity systems. The results also reveal that the sorbed phase occupies a significant fraction of the pore space and can occupy the entire pore volume for sufficiently small nanopores, depending on pressure and fluid-solid interactions. Accordingly, the mass transport is dictated by the sorbed phase, with its influence increasing as the fluid-solid interaction increases. Furthermore, the free phase contribution to mass transport increases with pore size. On comparing the mass flux obtained using the proposed model with the mass flux obtained using a monolayer adsorption model, a slightly lower contribution of the sorbed phase to total mass flux was observed for the multilayer model. The proposed model incorporates pertinent multicomponent gas transport and storage mechanisms in nanoporous media on a continuum scale but informed by pore-scale phenomena.