A molecular dynamics and grand canonical Monte Carlo study of silicalite-1 as a membrane material for energy-related gas separations

Hydrogen separation and combustion subsequent to coal gasification is highly attractive as an environmentally benign method of energy generation. Siliceous zeolites are thermally and chemically stable microporous materials that can satisfy the function of a gas separation membrane for such high temperature (>473 K) processes. Ensuing steam generation via hydrogen combustion can consequently occur without significant energy loss. Silicalite-1 is attractive for the separation of smaller H₂ (2.89 Å) from larger CO₂, CH₄, N₂ and O₂ molecules with kinetic diameters of 3.30, 3.80, 3.64 and 3.46 Å, respectively. The current study employs molecular dynamics and grand canonical Monte Carlo approaches to predict single-component gas diffusivities and adsorption isotherms for H₂, CO₂, CH₄, N₂ and O₂ in silicalite-1 at 273–1,073 K. The respective gas diffusivities and adsorption loadings determined in this study enable prediction of separation characteristics of silicalite-1 at relevant process conditions. Adsorption of all gases, excluding H₂, is relatively high at ambient temperature and significantly affects overall mass transport and separation selectivity. Hydrogen adsorption is relatively low even at ambient temperature, and at elevated temperatures (>473 K), adsorption of all gases is low, resulting in mass transport and separation selectivity that is dependent upon molecular diffusivity.