Diamine crosslinked polyimide membrane to enhance stability and selectivity for CO2/CH4 separation

Polyimides with intrinsic microporosity are promising materials for gas separation, but their industrial application is hindered by poor long-term stability. This study proposes diamine modification of a polyimide membrane with diamines, such as p-phenylenediamine (p-PD), to enhance both membrane stability and selectivity for separating gas pairs such as CO 2 /CH 4 . Various characterization techniques confirmed the crosslinking reaction between the diamine and imide groups, which restricted the movement or rearrangement of polymer chains, resulting in improved membrane anti-plasticization performance and stability. Meanwhile, CO 2 -philic emeraldine base and quinone structures were formed due to the in-situ oxidation of p-PD during the crosslinking process, which significantly boosted CO 2 /CH 4 selectivity. The maximum selectivity (44.5), which is 66.0 % higher than that of the pristine membrane, was achieved using a p-PD-modified polyimide membrane for the separation of pure single CO 2 /CH 4 . Additionally, the separation of other gas pairs (such as CO 2 /N 2 ) and the effect of pressure on the separation of a CO 2 /CH 4 mixture were investigated using the p-PD-modified polyimide membrane, which demonstrated improved performance. Thus, this study provides a reference for enhancing the selectivity and stability of polyimide membranes through diamine modification using p-PD and its analogues.