Effect of benzoic acid content on aging of 6FDA copolyimides based thin film composite (TFC) membranes in CO2/CH4 environment

Abstract

Abstract 6FDA based polyimides possess outstanding properties, with a high free volume fraction entailing in high permselectivity properties for gas separation processes. However, they are very sensitive to aging process. Copolyimdes 6FDA–DAM:DABA were synthesized using different ratios of diamines: (9:1), (3:1) and (2:1) and the homopolyimide 6FDA–DAM. Thin Film Composite membranes were prepared and thermally annealed at 300\u202f°C for 1\u202fh to improve CO 2 induced plasticization resistance. For exploring the future applications of these polymers, long–term performance studies of TFC membranes are absolutely needed. For this purpose, TFC membranes were tested for 180\u202fh at 35\u202f°C using a 50/50 vol./vol. CO 2 /CH 4 feed composition at 8 bars of transmembrane pressure and aging was done under similar conditions. As a result, a more accurate behavior of long–term performance under working conditions can be disclosed. Overall, the drop of performance of all TFC membranes was minor, if it is compared with other studies of aging under ambient conditions. It is explained because polymeric materials experience certain swelling under continuous working conditions due to the presence CO 2 and they cannot rearrange themselves as fast as under ambient conditions. 6FDA based polyimides are optimal candidates for industrial applications without losing their properties over extended period of time.