Solid-polymer mixed matrix membranes for CO2/CH4 separation: metal organic frameworks and polyetherimide

Abstract

A mixed matrix membrane (MMM) consisting of a solid material dispersed in a polymer phase is considered a promising component in membrane-based technology for gas separation. In this work, a metal organic framework (i.e. MOF-199 and ZIF-8) and polyetherimide (Ultem) were employed as solid materials and polymer phase, respectively. The MMMs are fabricated via the solution casting technique by mixing 13 w t% Ultem in N-methyl-2-pyrolidone solvent with MOF loadings from 10 w t% to 30 w t% on a solvent free basis. The resulting MMM thickness was determined between 18 µm and 25 µm proportional to the MOF loading. The single gas permeability measurements of CO2 and CH4 were conducted at 50 psi and 100 psi using a membrane testing unit at room temperature. The incorporation of MOF-199 could improve the CO2 permeance and CO2/CH4 selectivity significantly as compared to the Ultem membrane because of the molecular sieving effect of MOF particles. In case of ZIF-8 MMMs, CO2 permeance was significantly higher than the Ultem membrane without a significant improvement in CO2/CH4 selectivity due to the sieve in a cage morphology between ZIF-8 particles and Ultem polymer. Nevertheless, an increase in differential pressure across a membrane resulted in an insignificant decrease in CO2/CH4 selectivity under the studied pressure range due to the dual-mode behavior of glassy polymers. The experimental gas permeances of both MOF-199 and ZIF-8 MMMs were in good agreement with those of predicted by the Maxwell model at their low loadings.