Enhanced CO2 permeability of thermal crosslinking membrane via sulfonation/desulfonation of phenolphthalein-based cardo poly(arylene ether ketone)

Abstract

Thermal crosslinking membranes for gas separation have excellent plasticization resistance compared to polymeric membranes. Their low gas permeability, however, is not high enough for industrial application at low cost. In this study, a method, called the sulfonation/desulfonation of the polymeric precursor, was proposed to enhance the CO2 permeability of thermal crosslinking membranes without significantly sacrificing the CO2/CH4 selectivity. The effects of the degree of sulfonation (DS) on the polymeric chain rigidity, interchain distance, and gas separation performance of thermal crosslinking membranes were investigated using dynamic mechanical thermal analysis, a thermal gravimetric analyser coupled with a mass spectrometer, wide-angle X-ray diffraction, and gas permeation tests. Results indicated that the sulfonation/desulfonation of the polymeric precursor significantly influenced the microstructure and gas separation performance of the derived thermal crosslinking membranes. The interchain distance and microvoids of the thermal crosslinking membranes were greatly enlarged by the sulfonation and desulfonation reaction. The rigidity of the polymeric chain was improved by the formation of interchain hydrogen bonding induced by –SO3H groups, which prevent the melting of the polymeric membrane during heat treatment. The gas permeability of the thermal crosslinking membrane was markedly enhanced while the CO2/CH4 selectivity decreased as the DS increased. The CO2 permeability was up to 2.3 times higher than that of the non-sulfonated thermal crosslinking membrane. The separation performance of the derived crosslinking membranes for CO2/CH4 was positioned near or above the 2008 Robeson upper bound.