(447e) Modeling MOF/Polyimide Interfaces in Mixed Matrix Membranes for CO2 Separation

The separation of CO2 from industrially important gas mixtures like natural gas, syngas and flue gas is an enormously crucial issue in chemical industry. An attractive class of material is mixed-matrix membranes (MMMs) where metal organic frameworks (MOFs) are incorporated into polymer matrices. The principle issue in these applications is the plasticization of the polymers at high partial pressures of CO2, which can lead to reduced membrane selectivity and unpredictable transport properties at the polymer/MOF interfaces.

In this molecular simulation study, we focused on the interfacial interactions between the polymer chains and MOF particles. For this purpose, the ZIF-8-Matrimid® 5218 MMM was modeled and the interfacial interactions of polymer-MOF were investigated via Molecular Dynamics (MD) and Monte Carlo (MC) simulations. First, Matrimid® 5218 was modeled alone and the model was validated by reproducing experimental CO₂ sorption data. CO₂ sorption was simulated by a series of Grand Canonical MC (GCMC) runs and subsequent MD runs to simulate chain relaxation and swelling of the polymer during gas uptake. Generalized AMBER Force Field (GAFF) was used to model the polyimide while atomistic charges were calculated using Semi-Empirical methods via B3LYP functional. The MMM model was constructed with the smallest possible crystal structure of ZIF-8 and 2 polymer chains. CO₂sorption runs were performed up to 30 bar in order to investigate the plasticization of MMM's and subsequent changes at the polymer/ZIF-8 interfaces. Simulation results indicated that the interactions between the functional groups of the polymer and ligands at the MOF surface may have significant contribution on the gas transport through the interface.

Acknowledgment: This work was supported by TUBITAK trough grant no. 113M776.