Enhancement of CO2 Separation Performance of a Polymeric Membrane by adding MOF

This thesis investigates the performance of novel Mixed-Matrix Membranes (MMMs) incorporating Metal-Organic Frameworks (MOFs) molecular sieving properties and amine-based facilitated transport mechanisms for the efficient separation of carbon dioxide (CO2). The experimental work involved the fabrication of MMMs using different MOF loadings and varying membrane thicknesses. Membrane samples were prepared using a combination of polyvinyl alcohol (PVA) and 2-(2-aminoethylamino)ethanol (AEEA), a diamine known for its superior CO2 separation properties, with different MOFs as filler material (ZIF-8, HKUST-1, and UiO-66). Gas permeation experiments were conducted under controlled conditions (40 °C, 90% relative humidity, and CO2/CH4 feed ratios of 50/50), CO2 and CH4 permeabilities were measured, and the selectivity of CO2 over CH4 was calculated. The results reveal that zinc 2-methylimidazole (ZIF-8) is the most promising MOF in terms of CO2 permeability and CO2/CH4 selectivity. With an optimal loading of 0.5 wt% ZIF-8 and the addition of 50 wt% AEEA, the membrane demonstrated excellent CO2 separation performance. Additionally, membrane thickness was found to influence permeability and selectivity, with thicker membranes generally exhibiting higher CO2 permeability due to the greater presence of AEEA and improved selectivity due to the increased diffusion barrier for CH4. However, incorporation of ZIF-8 and UiO-66 into the polymer matrix has posed challenges related to particle suspension, membrane homogeneity, and defect formation. At higher loadings of ZIF-8 (>=5 wt%), the membranes exhibited a decrease in both permeability and selectivity due to the presence of unsuspended ZIF-8 fragments and defects in the membrane structure. At any rate, the introduction of AEEA into the membrane system significantly improves CO2 separation performance through the reversible reaction of CO2 with the amine groups, forming carbamates that facilitate CO2 transport across the membrane. This facilitated transport mechanism complements the standard sorption-diffusion model traditionally used to describe gas permeation in polymeric membranes. The combined effects of MOF inclusion and amine-facilitated transport result in membranes that offer both high permeability and high selectivity, and with continued advances, membrane separations have the potential to revolutionize areas such as natural gas processing, carbon capture and storage (CCS), and hydrogen recovery. Furthermore, future work should focus on further optimizing the suspension of MOFs within the polymer matrix, as well as exploring additional MOF structures and functional groups to enhance membrane stability and performance over operating periods.