In silico screening of zeolite membranes for CO2 capture

The separation of CO2/H2, CO2/CH4, and CO2/N2 mixtures is of practical importance for CO2 capture and other applications in the processing industries. Use of membranes with microporous layers of zeolites, metal–organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) offer considerable promise for use in such separations. In view of the extremely wide variety of available microporous structures, there is a need for a systematic screening of potential candidates in order to obtain the best permeation selectivities, Sperm. The permeation selectivity is a product of the adsorption selectivity, Sads, and the diffusion selectivity, Sdiff, i.e. Sperm = Sads × Sdiff. For maximizing Sperm, we need to choose materials for which Sads and Sdiff complement each other.For a wide variety of zeolites, we have used Configurational-Bias Monte Carlo (CBMC) simulations of mixture adsorption isotherms, along with Molecular Dynamics (MD) simulations of diffusivities for three binary mixtures, CO2/H2, CO2/CH4, and CO2/N2, to calculate Sads, Sdiff, and Sperm. These simulation results provide insights into the influence of pore size, pore topology and pore connectivity that influences each of the three selectivities. In particular, we emphasize the important role of correlations in the diffusion behaviors within microporous materials. Furthermore, we have constructed Robeson plots for each of the separations in order to provide generic guidelines to the choice of materials that offer the appropriate compromise between Sperm and the membrane permeability.