Polymer Electrolyte Membranes with Hybrid Cluster Network for Efficient CO2/CH4 Separation

Well-connected transport pathways play a critical role in high-performance CO2-facilitated separation membranes. Inspired by the ionic cluster network in polymer electrolyte membranes (PEMs) for fast ion transport, designing a unique CO2-philic cluster network structure is a promising strategy to construct efficient CO2 transport channels in membranes. Herein, a forced induction method is presented to construct a CO2-philic cluster network in membranes. Sulfobutylether-beta-cyclodextrin (sβ-CD) is introduced in a quaternary ammonium polysulfone (QAPSf) matrix. During the membrane formation process, the quaternary ammonium groups on QAPSf are attracted by the sulfonic acid groups on sβ-CD, assembling around and thus forming hybrid clusters. These clusters are swollen and interconnected by water under a humidified state. The hybrid cluster network acts as an effective CO2 transport pathway via clustering quaternary ammonium ion pairs as continuous CO2-facilitated transport sites. Simultaneously, the internal cavity of sβ-CD in hybrid clusters affords additional free volume in membranes, thus enhancing the CO2 permeability. The resultant QAPSf/sβ-CD membrane exhibits an optimal CO2 permeability of 1303 Barrer, a CO2/CH4 selectivity of 39, and good long-term operation stability for 30 days, surpassing the 2008 Robeson upper bound limit. This concept of constructing a hybrid cluster network for facilitated transport is expected to be applicable to explore more advanced PEMs for effective gas separation.