| Summary: | The unique properties of polyvinyl alcohol (PVA) and polysulfone (PSf), such as good membrane-forming ability and adjustable structure, provide a great opportunity for CO<sub>2</sub>-separation membrane development. This work focuses on the fabrication of PVA/PSf composite membranes for CO<sub>2</sub>/N<sub>2</sub> separations. The membranes prepared by coating a 7.5 wt% PVA on top of PSf substrate showed a relatively thin selective layer of 1.7 µm with an enhanced CO<sub>2</sub>/N<sub>2</sub> selectivity of 78, which is a ca. 200% increase compared to the pure PSf membranes. The CO<sub>2</sub>/N<sub>2</sub> selectivity decreases at a rapid rate with the increase of feed pressure from 1.8 to 5 bar, while the CO<sub>2</sub> permeance shows a slight reduction, which is caused by the weakening of coupling transportation between water and CO<sub>2</sub> molecules, as well as membrane compaction at higher pressures. Increasing operating temperature from 22 °C to 50 °C leads to a slight decrease in CO<sub>2</sub> permeance, but a significant reduction in the CO<sub>2</sub>/N<sub>2</sub> selectivity from 78 to 27.1. Moreover, the mass transfer coefficient of gas molecules is expected to increase at a higher velocity, which leads to the increase of CO<sub>2</sub> permeance at higher feed flow rates. It was concluded that the CO<sub>2</sub> separation performance of the prepared membranes was significantly dependent on the membrane operating parameters, and process design and optimization are crucial to bringing CO<sub>2</sub>-separation membranes for industrial applications in post-combustion carbon capture.
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