(704e) Investigation of MOF/Polyimide Interactions 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 of ZIF-8/Matrimid® 5218 and ZIF-8/Ultem® 1000 MMMs for CO₂/CH₄ separation. Polyimides were constructed using Accelrys Materials Studio 5.0® software and equilibrated by a series of Molecular Dynamics (MD) run using LAMMPS package. Polymer Consistent Force Field (PCFF) was used for simulations and density, Fractional Free Volume (FFV) and Glass Trasition Temperature (Tg) of the polymers were compared with experimental values and the force-field was validated considering the agreement within these values. Monte Carlo (MC) and MD simulations were applied for estimating CO₂ and CH₄ sorption and diffusion in the polymers to validate the models.

In order to build model MMMs, a ZIF-8 cage and two polymer chains with 40 monomer units were packed in a simulation box by using Amorphous Cell Module in Materials Studio 5.0®. This corresponded to 15% per weight ZIF-8 content in the mixed matrix. The same equilibration steps were applied to the mixed matrixes, and their sorption and diffusion characteristics were investigated via MC and MD simulations.

Gas permeabilities up to 30 bar was estimated 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 dangling 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. 113M336.