Mmif-Based Mixed-Matrix Membranes for CO2 Separation

Metal organic frameworks (MOFs) are promising candidates for separation and purification applications due to their tunable chemistry. Hence, MOFs are considered promising candidates as dispersive phase in mixed matrix membranes (MMMs). The organic linkers in MOFs have affinity to polymer chains so the control of MOF/polymer interface is easier than zeolite/polymer interface. Zeolite based MMMs have been studied for the last two decades and much effort has been spent to ensure good adhesion between organic and inorganic phases.

The molecular simulation studies in the literature revealed several possible MOF structures as outstanding candidates for MOF-based MMMs. One of these MOFs, which became prominent for CO₂/CH₄separation, is microporous metal–imidazolate framework (MMIF) [1]. However, no experimental data is available in the literature to confirm the predicted performances of these MOFs, in particular no MMM studies using these MOFs are reported.

In this study, first, MMIF has been synthesized and characterized in order to experimentally verify its capability of CO₂ capture. Then, it is incorporated into polyimides to prepare MMMs. Membranes are characterized with SEM, XRD, TGA, DSC and pure and mixed-gas permeability tests for CO₂/CH₄ and CO₂/N₂separations.

Contrary to simulation results and Maxwell model predictions reported in the literature, pure gas permeability measurements at 35°C and 4 bar showed that Matrimid based MMMs containing 10% MMIF improved the permeability of Matrimid by 15% and no improvement in selectivity was observed. The permeability and selectivity remained stable with an increase in MMIF loading to 20%. On the other hand, mixed gas selectivity for CO₂/CH₄improved significantly to 88 for 10% loading.

This work is supported by TUBITAK (Turkish Scientific and Technological Research Council) through Project No. 113M776.

Reference:

1. Erucar, I, Keskin, S., “Screening Metal Organic Framework-Based Mixed-Matrix Membranes for CO₂/CH₄ Separations”, Ind. Eng. Chem. Res., 50 (22), pp. 12606–12616 (2011).