Ultem®/ZIF-8 Mixed Matrix Membranes for Gas Separation: Transport and Physical Properties

Daniel Eiras,Luiz Antonio Pessan,Ying Labreche

doi:10.1590/1980-5373-mr-2015-0621

Daniel Eiras, Luiz Antonio Pessan + Show 1 more

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https://doi.org/10.1590/1980-5373-mr-2015-0621

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Abstract

Mixed matrix membranes are promising options for improving gas separation processes. Zeolitic imidazolate frameworks (ZIFs) have a porous structure similar to conventional zeolites, being capable in principle of separating gases based on their differences in kinetic diameter while offering the advantage of having a partial organic character. This partial organic nature improves the compatibility between the sieve and the polymer, and a combination of the mentioned characteristics makes these hybrid materials interesting for the preparation of mixed matrix gas separation membranes. In this context the present work reports the preparation of Ultem®/ZIF-8 mixed matrix membranes and their permeabilities to pure CO2, N2 and CH4gases. A significant increase in permeability with increase in CO2/N2 selectivity was observed for the mixed matrix systems as compared to the properties of the neat Ultem®. Sorption results allowed to speculate that the ZIF-8 framework is not completely stable dimensionally, what influences the separation process by allowing gases with higher kinetic diameter than its nominal aperture to be sorbed and to diffuse through the crystal. Sorption and diffusion selectivities indicate that the higher separation performance of the mixed matrix membranes is governed by the diffusion process associated with the influence of gas molecule's geometry.

Highlights

Mixed matrix membranes are promising alternative for the development of gas separation new materials membranes
Since Zeolitic imidazolate frameworks (ZIFs)-8 particles are not able to avoid the gas molecules from accessing its porosity the overall separation capacity of the mixed matrix membranes will be affected in a negative fashion
A direct consequence of the high sorption capacity and relatively high diffusion coefficients of these gases in the ZIF-8 crystal is that the permeability of both nitrogen and methane increase with the addition of ZIF-8, which may be considered a direct consequence of its high sorption capacity and relatively high diffusion coefficients of these gases in the ZIF-8 crystal

Summary

Introduction

Mixed matrix membranes are promising alternative for the development of gas separation new materials membranes. Mixing polymeric materials with zeolites or other types of molecular sieving media creates membranes with properties that overcome the properties of the polymeric matrix. Such hybrid materials can offer the advantage of low cost and better mechanical properties of the polymer when compared to typical inorganic membranes[1,2,3]. For glassy polymers the formation of defect-free membranes can be achieved by the compatibilization of the two phases with silanes as reported in the literature[3,5]. High performance membranes are more complex to obtain, due to difficulties in avoiding the formation of interfacial defects between the dispersed and continuous matrix phases[6,7,8,9,10]

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