A novel PVI-PVA/PS composite membrane modified by metal ions for CO2 separation: Effect and mechanism

The membrane process is potentially more energy-efficient than conventional separation technologies in the separation of carbon dioxide (CO2) /nitrogen (N2) from flue gas. In this work, a series of PVI (Polyvinylimidazole)-PVA (Polyvinyl alcohol) /PS (Polysulfone) membranes were prepared by co-blending two polymers, PVI and PVA, as the separation layer of the fixed carrier composite membrane. The separation performance increased by the dual action of PVA and the imidazole group in the PVI. Furthermore, Mg2+-PVI-PVA/PS and Cu2+-PVI-PVA/PS composite membranes were developed by adding Mg2+ and Cu2+, and the separation performance was considerably improved by complexing metal ions with PVA and PVI. Especially, Mg2+-PVI-PVA/PS demonstrated superior separation performance, with a CO2 permeation rate of 12 GPU and a CO2/N2 separation factor of 183 at a pressure of 1 bar. What's more, the mechanism study clarified that the prepared composite membrane mainly relies on the facilitated transfer mechanism to achieve the selective separation of CO2. The presence of water molecules significantly improved the CO2 permeability and separation selectivity, indicating that PVI-PVA and Mg2+ could promote the hydration reaction of CO2 and H2O, forming easily mobile HCO3- carriers.