Thermal crosslinking membrane with enhanced CO2 separation performance derived from nitrile-containing phenolphthalein-based poly(arylene ether ketone)

Enhancing gas permeabilities of thermal crosslinking membranes while retaining adequate selectivity is of great significance for industrial applications. In this work, a novel and commercial polymer of nitrile-containing phenolphthalein-based poly (arylene ether ketone) (PEK-C(CN)) was introduced to prepare thermal crosslinking membranes via pretreatment in air and subsequent thermal crosslinking treatment in N2, and the high permselectivity for CO2/CH4 and CO2/N2 gas pairs was achieved. The ATR-FTIR and XPS results demonstrated that the nitrile groups might undergo thermal cyclotrimerization reaction with the formation of stable triazine rings across molecular chains during the pretreatment, which is conducive to the preparation of defect-free and highly permeable thermal crosslinking membranes. During thermal crosslinking treatment, the Cardo moieties decomposed and induced crosslinking with forming bulky biphenyl linkages between polymeric chains, accompanied with pyrolysis of some nitrile groups, which resulted in an increase in interchain distance and microvoid size. The CO2 permeability of the resulting thermal crosslinking membrane was increased to around 3 times without sacrificing CO2/CH4 and CO2/N2 selectivities due to the incorporation of nitrile groups, compared to the thermal crosslinking membrane derived from nitrile-free PEK-C. For equimolar binary mixture gases, the fully crosslinked membranes present the CO2 permeability of around 1300 Barrer with CO2/CH4 and CO2/N2 separation factors of 32.6 and 35.8, respectively, which offer a promising alternative in CO2 capture and separation.