Enhanced anti-wetting and anti-fouling properties of composite PFPE/PVDF membrane in vacuum membrane distillation

Composite hydrophobic PFPE/PVDF membranes were prepared by coating and UV-curing for vacuum membrane distillation (VMD). The water contact angle of PFPE/PVDF membrane reached 162.6°, while the decrease in pore size in comparison to the original membrane was insignificant. The effects of organic and inorganic foulants (including humic acid, sodium silicate and calcium carbonate) on membrane performance were investigated. As for this PFPE coating layer, it had an active mitigation effect on the scaling behavior and almost no membrane wetting occurred. In particular, the organic migration across the membrane was completely prevented. Then the membrane cleaning process was conducted to prove the stability under long-term operation of composite membranes when deionized (DI) water was used as cleaning agent after repeated cycles of VMD treatment of 2 M NaCl feed solutions containing 200 mg/L humic acid (HA). The results of a 30-h test indicate that the salt rejection was kept at a high level, exceeding 99.99% and the recovery of MD flux was around 90% of the initial flux after the second cleaning cycle. The promising anti-fouling and anti-wetting performance of the composite PFPE/PVDF membranes provides a high potential for further development of these membranes for membrane distillation and membrane crystallization applications.