(627c) Non-Equilibrium Molecular Dynamics Simulations of Composite MOF/Polymer Membranes

We recently developed a new non-equilibrium molecular dynamics simulation method [1] in order to simulate the permeation of pure fluids and separation of mixtures through membranes, namely "Concentration Gradient Driven Molecular Dynamics" (CGD-MD). This new method works by employing bias forces to fix the concentration of fluids (pure or mixture) at the inlet and outlet of a membrane in order to create and maintain a concentration gradient and drive the diffusion of molecules through the membrane. This is aimed at mimicking membrane separation experiments; for instance, high concentration/pressure at the feed side and vacuum at the permeate side. CGD-MD addresses two main shortcomings of previous non-equilibrium MD methods used for simulating membrane separation processes at the molecular scale. First, it avoids the feed depletion issue and allows running steady state and continuous simulations for unrestricted simulation times, and second, it maintains the feed composition at a target value without the need of any complex Monte Carlo-MD coupling. In this study we extend our method to include gas transport and separation in composite MOF/Polymer membranes. Accurate structural models of Polymer of Intrinsic Microporosity(PIM)-1 and ZIF-8 layers have been assembled and the separation of CH₄/H₂ mixture has been modeled by using the CGD-MD method.

[1] Ozcan, A., Perego, C., Salvalaglio, M., Parrinello, M., Yazaydin, O.*; "Concentration gradient driven molecular dynamics: a new method for simulations of membrane permeation and separation", Chemical Science, 2017, 8, 3858–3865.