Effect of internal coagulant on effectiveness of polyvinylidene fluoride membrane for carbon dioxide separation and absorption

Asymmetric hollow fiber membranes with inner skinless structures are favourable for carbon dioxide (CO2) separation and absorption in gas–liquid membrane contactors by reducing gas transport resistance. In this study, polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated by using different internal coagulants, which include water, ethanol–water, and dimethylacetamide (DMAc)–water solutions. The spinning dope solution was prepared with DMAc as the solvent, lithium chloride and polyvinylpyrrolidone (PVP) as the non-solvent additives. The resultant membranes were examined by scanning electron microscopy (SEM). The examination of membrane cross-sections indicated that the composition of internal coagulants had significant impacts on the thickness and structures of the inner skin layer. Results showed that an inner skinless surface could be formed using a 30 wt.% water–DMAc mixture. Gas permeation tests demonstrated that PVDF hollow fibers with an inner skinless surface had a higher CO2 absorption rate than other PVDF and polypropylene (PP) membranes and attained performance levels equivalent to a polytetrafluoroethylene (PTFE) membrane. PVDF membranes could be a cost-effective alternative for gas–liquid membrane contactors in applications of CO2 separation and absorption.