Perfluorocyclobutyl polymer thin-film composite membranes for CO2 separations

The role of carbon emissions on global warming has fueled widespread interest in mitigation strategies. Thin-film composite membranes are a promising technology for carbon capture; however, only membranes with high and stable permeance (>3000 GPU) and moderate CO2/N2 selectivity (>20) potentially could decrease CO2 capture costs to $20US/ton. In many cases, practical problems such as membrane plasticization and physical aging rule out promising new materials from commercial consideration. The present contribution is part of a larger effort to develop fundamental structure–property relationships for perfluorocyclobutyl (PFCB) polymers that provide a foundation for PFCB-based membranes with resistance to plasticization and physical aging. A focus of this part of the study was to develop procedures to fabricate PFCB thin-film composite membranes with reproducible performance characteristics. Biphenylvinylether–perfluorocyclobutyl (BPVE–PFCB) polymer was used as a model for the family of PFCB polymers. The thickness of the PFCB selective layer was controlled by changing processing conditions. Results show that uniform PFCB layers were coated successfully on support membranes to produce thin-film composites with reproducible permeance and selectivity values. Membranes prepared with the thinnest BPVE–PFCB films yielded CO2 permeance of 1000 GPU with CO2/N2 selectivity around 15. Estimated CO2 permeance through the PFCB thin layer alone was up to 1700 GPU, with CO2/N2 selectivity close to the bulk film intrinsic selectivity of 20. The use of other PFCB polymers and copolymers with superior separation characteristics may be used to prepare composite membranes with improved performance.