Investigation of ZIF-8, amine-modified ZIF-8 and polysulfone based mixed matrix membranes for CO2/CH4 separation

Abstract

Membrane separation is one of the techniques used for biogas upgradation. Mixed matrix membranes (MMMs) are currently being explored to overcome the trade-off of selectivity-permeability inherent in polymer membranes used for gas separation. A significant challenge associated with MMMs is the poor polymer-metal–organic framework (MOF) filler interfacial compatibility, reducing the selectivity or permeability of gas. To address this issue, the present study focuses on the effect of the amine functionalization of ZIF-8 to enhance the CO2 gas permeation without reducing the CO2/CH4 selectivity. MMMs were fabricated using unmodified ZIF-8 and amine-modified ZIF-8 nanofillers dispersed in polysulfone at 5, 10, and 15 wt% loadings. MMMs were characterized by FTIR, DSC, TGA, and FESEM. X-ray diffraction and FTIR analysis was conducted to verify the amine modification of ZIF-8. Further, the performance of MMMs was tested with pure gasses (CO2 and CH4) and a model mixture of CO2 and CH4. In the mixed gas permeation test, the 10 wt% ZIF-8 MMM exhibited the highest CO2 permeability of 25.4 Barrers, while 15 wt% NH2-ZIF-8 MMM exhibited the highest selectivity of 13.5. Notably, the ZIF-8 MMMs demonstrated a 148% increase in CO2/CH4 selectivity, whereas the NH2-ZIF-8 MMMs exhibited a 155% increase compared to the pure polysulfone membrane.