Preparation of hydrophobic flat sheet membranes from PVDF-HFP copolymer for enhancing the oxygen permeance in nitrogen/oxygen gas mixture

In this study, poly(vinilydene fluoride-co-hexafluoropropylene) (PVDF-HFP) was used for preparation of hydrophobic membranes using non-solvent induced phase inversion (NIPS) technique. PVDF-HFP copolymer with concentrations of 10 wt% and 12 wt% was prepared to investigate the effect of polymer concentration on pore structure, morphology, hydrophobicity and performance of prepared membranes. Besides, the use of two coagulation baths with the effects of parameters such as coagulant time, polymer type and concentration, and the amount of nonsolvent were studied. The performance of prepared membranes was evaluated based on the permeability and selectivity of oxygen and nitrogen from a gas mixture of nitrogen/oxygen under operating conditions of feed flow rate (1-5 L·min^-1), inlet pressure to membrane module (0.1-0.5 MPa) and temperatures between 25 and 45℃. The results showed that the use of two coagulation baths with different compositions of distillated water and isopropanol, coagulant time, polymer type and concentration, and the amount of non-solvent additive have the most effect on pore structure, morphology, thickness, roughness and crystallinity of fabricated membranes. Porosity ranges for the three fabricated membranes were determined, where the maximum porosity was 73.889% and the minimum value was 56.837%. Also, the maximum and minimum average thicknesses of membrane were 320.85 μm and 115 μm. Besides, the values of 4.7504×10^-7 mol·m^-2·s^-1·Pa^-1, 0.525 and 902.126 nm were achieved for maximum oxygen permeance, O₂/N₂ selectivity and roughness, respectively.