Performance of PVDF flat membranes and hollow fibers in desalination by direct contact membrane distillation at high temperatures

Numerous studies have been conducted on desalination by direct contact membrane distillation (DCMD) through microporous hydrophobic membranes. The hot brine temperature in such studies is usually in the range of 40–90 °C. In steam assisted gravity drainage (SAGD) process, the brine obtained as the produced water however comes out at a high temperature of as much as 160 °C + . Reverse osmosis desalination can be employed only after such a brine is cooled down substantially. Two studies were conducted on DCMD-based desalination of such brines at a brine temperature up to 130 °C using flat sheet and hollow fiber membranes of polytetrafluoroethylene (PTFE). This investigation is focused on similar desalination studies with high temperature brines using much less expensive microporous hydrophobic membranes of polyvinylidene fluoride (PVDF). One flat sheet membrane and two different hollow fiber membranes of PVDF were employed with 1% salt-containing solution as the feed over a temperature range of 80–125 °C. The flat sheet membrane and one hollow fiber membrane-based module achieved desalination without any salt leakage. The value of the water vapor flux achieved through the flat sheet membrane of 0.1 μm pore size was very high around 270 kg/m²-h at 124 °C. Since the brine is at above-atmospheric pressure (2–3 atm), much larger pore sizes or any defects in the membrane will lead to salt leakage.