Effects of electrostatic interactions on gas adsorption and permeability of MOF membranes

We examined the effects of electrostatic interactions on gas adsorption and permeability of metal organic framework (MOF) membranes and MOF-filled mixed matrix membranes (MMMs) for CO2/CH4, CO2/N2 and H2/CO2 separations using molecular simulations. Adsorption isotherms and diffusion rates of CO2, CH4, N2 and H2 in several MOFs were computed using grand canonical Monte Carlo and equilibrium molecular dynamics simulations, respectively. Gas permeability and selectivity of pure MOF membranes and MOF-filled MMMs were then evaluated using theoretical permeation models. The accuracy of our molecular simulations was validated by comparing theoretical predictions for gas permeability and selectivity of MOF-filled MMMs with the available experimental data. We then used the same modelling approach to predict the performance of new MOF-filled MMMs in CO2/CH4, CO2/N2 and H2/CO2 separations. Promising MOF/polymer combinations which offer high selectivity and permeability relative to pure polymer membranes were identified. Our results showed that including electrostatic interactions between adsorbate molecules and MOF atoms is crucial for modelling pure MOF membranes but has less significance for modelling MOF-filled MMMs whenever the MOF volume fraction, ≤ 0.30. This result suggests that preliminary screening studies of MOF-filled MMMs can be carried out without assigning partial charges to MOF atoms.