Nonequilibrium Simulation of Gas Transport in Glassy Polymer Membranes

Chemical separations account for a large fraction of global energy usage, much of which can be curbed by a transition from thermal distillation processes to membrane-based separations. In this work, we utilize atomistic molecular simulation to study the permeability and selectivity of both pure- and mixed-gas feeds to glassy polymer membranes. Hybrid molecular dynamics/Monte Carlo simulations are used to generate gas sorption isotherms that account for structural relaxation. Nonequilibrium molecular dynamics simulations with applied external fields are then used to calculate gas diffusion coefficients, both for single-gas diffusion and in the case of mutual diffusion between competing species. Changes in both solution and diffusion selectivity for important gas pairs such as CO2/CH4 from the pure- to mixed-gas systems demonstrate the importance of modeling these processes under conditions relevant to the desired separations end-use case. These methods can be applied to probe the origins of observed phenomena from experiments, or to evaluate the performance of proposed polymer membrane candidates.