271977 Mixed-Matrix Membranes with Zeolite-Like MOFs for CO2/CH4 Separation

Monday, October 29, 2012: 4:21 PM
401 (Convention Center )
Ayse Kiliç, Cigdem Atalay-Oral, Ahmet Sirkecioglu, S. Birgül Tantekin-Ersolmaz and M. Göktug Ahunbay, Department of Chemical Engineering, Istanbul Technical University, Istanbul, Turkey

The separation of CO2 from industrially important gas mixtures like natural gas, syngas and flue gas is an enormously crucial issue in chemical industry. Zeolite-like metal organic frameworks (ZMOFs) are promising candidates for separation and purification applications. They have anionic frameworks and extra-framework ions in the pores of molecular dimensions increasing the interactions with guest molecules and improving their separation, storage, or ion-exchange capability. The charge-compensating extra-framework ions inside the cavities of ZMOFs can be ion-exchanged with alkali metals and this is expected to increase their affinity for CO2 and improve natural gas (CO2/CH4) purification performance.

In the present study, sod-ZMOF crystals having a sodalite topology were synthesized under solvothermal conditions. Following characterization of the crystals (XRD, TGA, SEM analyses), they were incorporated into Matrimid® polyimide (PI) matrix to form  dense mixed-matrix membranes (MMMs) by solvent-casting method. Although several gas adsorption studies with ZMOFs have been reported in the literature, they are used as fillers in mixed-matrix membranes and their gas separation properties are investigated for the first time in this work. SEM images of the MMMs, showed no apparent voids or defects at the filler/polymer interface and that ZMOF particles were dispersed homogenously in the polymer matrix. Physical and thermal properties of the prepared membranes (e.g. film density, Tg) were analyzed. The CO2/CH4 separation performances of the membranes were determined by measuring pure gas permeabilities. As-synthesized sod-ZMOF samples were also ion-exchanged with Na and K cations to examine the effect of ion-exchange on the material characteristics and gas separation properties of the MMMs. The contribution of ion-exchanged alkali cations is observed to change gas separation performance of sod-ZMOF significantly.

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