Fabrication of a super hydrophobic polyvinylidene fluoride–hexadecyltrimethoxysilane hybrid membrane for carbon dioxide absorption in a membrane contactor

Abstract

To obtain a super hydrophobic hollow fiber membrane for using in membrane contact absorption of carbon dioxide (CO2), hybrid polyvinylidene fluoride-hexadecyltrimethoxysilane (PVDF–HDTMS) membranes were fabricated via the non-solvent induced phase-inversion method with ammonia water as the non-solvent additive and dehydrofluorination reagent, and HDTMS as the hydrophobic modifier. The membranes exhibited super-hydrophobicity which was attributed to the formation of rough nanoscale microstructure and low surface free energy of the outer surface. The largest contact angle of water and diethanolamine (DEA) on the membrane outer surface attained 150°. Scanning electron microscopy images revealed that the membrane outer surfaces consisted of rough microscale hierarchical spherulitic particles with a nanoscale stereoscopic coralliform microstructure. Attenuated total reflectance–Fourier transform infrared spectroscopy of the membranes indicated that the HDTMS chains grafted in the PVDF were mainly located on the outer layer of the hollow fiber membranes. The membranes showed excellent CO2 mass transfer flux compared to our previously fabricated membrane with 8 wt % of phosphoric acid as the non-solvent additive in the dope (PVDF-PA-8). The membrane contactor with the membrane obtained by adding 1.5 wt% of HDTMS in the dope achieved the maximum CO2 mass transfer flux of 2.23 × 10−3 mol/m2s with the inlet gas (CO2/N2 = 19/81, v/v) at a flow rate of 20 mL/min and the absorbent liquid (1 mol/L DEA) at a flow rate of 50 mL/min. CO2 mass transfer flux of this membrane decreased by 17% after 17 days of operation and then remained stable.