Preparation of PFSA/PSf hollow fiber composite membranes with recovered PFSA for the pervaporation separation of EtOH/H2O

Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration (UF) membrane as substrate with recovered PFSA. The composite membranes were applied to the pervaporation separation of 95% ethanol (EtOH)/H₂O mixture. SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm, much thinner than those of other PFSA composite membranes revealed in the literatures. Effects of annealing temperature, coating solution concentration and counter-ions of PFSA on the pervaporation performances of the composite membranes were investigated. The total flux decreases and separation factor increases with the increase of annealing temperature. The highest permeation flux of 3230 g m^?2 h^?1 and a separation factor of 5.4 is obtained for the composite membrane annealed at 80°C. The lowest permeation flux of 396 g m^?2 h^?1 and a separation factor of 27.7 is obtained for the composite membrane annealed at 160°C. The permeation performances of the PFSA/PSf composite membrane are evidently influenced by the counter-ions of PFSA. The flux sequence of the PFSA/PSf composite membranes with different counter-ions is H⁺>Li⁺>Ca²⁺>Mg²⁺>Na⁺>K⁺>Ba²⁺>Fe³⁺>Al³⁺, and the separation factor sequence is H⁺<Li⁺<Al³⁺<Na⁺<Mg²⁺<Ca²⁺<K⁺<Ba²⁺<Fe³⁺. The apparent activation energy ΔE _app values of the composite membranes with different counter-ions were calculated by Arrhenius law. The sequence of ΔE _app values for the membranes with monovalent counter-ions is Li⁺>Na⁺>K⁺. There are very little variations of ΔE _app values between the composite membranes with three divalent counter-ions (Mg²⁺, Ca²⁺ and Ba²⁺), and the ΔE _app values of the composite membranes with two trivalent counter-ions (Fe³⁺ and Al³⁺) are relatively high.