High-Performance Polyimide CO2 Separation Membrane Prepared by Zn(II) Coordination Cross-Linking

Chemical modification of polyimide membranes is employed to achieve “trade-off” breakthrough or improve the plasticization resistance in CO 2 separation. However, harsh reaction conditions restrict the application of traditional chemical modifications. In this work, a simple chemical modification method─the coordination cross-linking between hydroxyl groups on polyimide (6FSPI) and Zn(II)─was investigated. Because of the reversible complexation of Zn(II) in the modified membrane as a transport carrier with CO 2, and the addition of Zn(II) disrupts coiled chain of spiro moiety or intrachain cross-linking to induce more quantities of ultrafine micropores, the CO 2 permeability coefficient of the modified membrane is 2.97 times that of the pristine 6FSPI. Simultaneously, there is improvement in diffusion selectivity of the modified membrane, resulting in the CO 2 /CH 4 selectivity improvement. The overall CO 2 /CH 4 separation performance of the modified membrane reaches up to the 2008 Robeson limit. In addition to serving as facilitated transport carriers, Zn(II) can also be used as cross-linking points. The modified membrane maintains a stable CO 2 permeability coefficient beyond 4000 kPa. Our work suggests that the Zn(II) coordination cross-linking is a facile chemical modification method that can enhance long-term performance and separation performance of polyimide membranes simultaneously.