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Carbon dioxide (CO 2 ) emissions to the atmosphere have greatly contributed to climate change as the concentration has increased since the pre-industrial period. Various mitigation strategies have been developed to combat climate change with membrane being one of the growing alternatives. Pristine hollow fiber (HF) membrane typically exhibits lower selectivity as compared to dense flat sheet membrane. In this study, we developed an asymmetric HF polyethersulfone (PES) membrane with critical concentration at two different dope extrusion rate (DER) at 3 and 6 mL/min to be studied for CO 2 /N 2 and CO 2 / CH 4 gas separation for flue gas and biogas upgrading applications by testing the fabricated membrane with pure gas permeation test with variable pressure at room temperature. It was observed that HF membrane extruded with high DER exhibits finger-like structure beneath the skin layer with more pinholes compared to HF extruded with low DER. The gas permeance was observed to increase in linear fashion as function of upstream pressure while the gas selectivity appears to be relatively constant regardless of upstream pressure. Meanwhile, polydimethylsiloxane (PDMS) coated HF PES membrane shows lower gas permeance as compared to its pristine membrane with improved CO 2 /N 2 and CO 2 /CH 4 selectivity. HF PES membrane extruded at 3 mL/min shows relatively low gas permeance, CO 2 /N 2 and CO 2 /CH 4 selectivity as compared to HF PES extruded at 6 mL/min. Additionally, this study shows that sequential coating of PDMS layer does not improve gas selectivity performance of the fabricated asymmetric PES HF membrane while the gas permeance reduction was observed.

Carbon dioxide (CO2) concentration is now 50% higher than in the preindustrial period and efforts to reduce CO2 emission through carbon capture and utilization (CCU) are blooming. Membranes are one of the attractive alternatives for such application. In this study, a rubbery polymer polydimethylsiloxane (PDMS) membrane is incorporated with magnesium oxide (MgO) with a hierarchically two-dimensional (2D) nanosheet shape for CO2 separation. The average thickness of the synthesized MgO nanosheet in this study is 35.3 ± 1.5 nm. Based on the pure gas separation performance, the optimal loading obtained is at 1 wt.% where there is no observable significant agglomeration. CO2 permeability was reduced from 2382 Barrer to 1929 Barrer while CO2/N2 selectivity increased from only 11.4 to 12.7, and CO2/CH4 remained relatively constant when the MMM was operated at 2 bar and 25 °C. Sedimentation of the filler was observed when the loading was further increased to 5 wt.%, forming interfacial defects on the bottom side of the membrane and causing increased CO2 gas permeability from 1929 Barrer to 2104 Barrer as compared to filler loading at 1 wt.%, whereas the CO2/N2 ideal selectivity increased from 12.1 to 15.0. Additionally, this study shows that there was no significant impact of pressure on separation performance. There was a linear decline of CO2 permeability with increasing upstream pressure while there were no changes to the CO2/N2 and CO2/CH4 selectivity.

The current work predicted the permeance of CO2 across a ZIF-L@PDMS/PES composite membrane using two different models. The membrane was fabricated by dipping a PES hollow fiber membrane in a coating solution made using PDMS that contained ZIF-L. First, flat sheet ZIF-L@PDMS membranes were fabricated to verify the role of ZIF-L on the gas separation performance of the membrane. Based on the data, the presence of ZIF-L in the PDMS matrix allowed enhancement of both permeability and selectivity of CO2, where the maximum value was obtained at 1 wt% of ZIF-L. The performance of ZIF-L@PDMS layer, as a function of ZIF-L loading, was well-predicted by the Cussler model. Such information was then used to model the CO2 permeance across ZIF-L@PDMS/PES composite membrane via the correction factor, which was introduced in the resistance in series model. This work discovered that the model must consider the penetration depth and the inorganic loading (in the case of ZIF-L@PDMS/PES). The error between the predicted CO2 permeance and the experimental results was found to be minimal.