High permeation flux polypropylene/ethylene vinyl acetate co-blending membranes via thermally induced phase separation for vacuum membrane distillation desalination

Abstract

Isotactic polypropylene (iPP)/ethylene vinyl acetate (EVA) co-blending hydrophobic microporous membranes for vacuum membrane distillation (VMD) were prepared via thermally induced phase separation (TIPS), and the membranes were supported by a nonwoven polyester fabric with special cellular structures. These special cellular structures consist of two parts: a thin dense cellular layer and a thick loose cellular layer. These structures markedly decreased the resistance of mass transfer and improved flux performance during VMD. The co-blending membranes used for VMD led to superior long-term stability and excellent durability relative to neat PP membranes. This result can be attributed to the addition of EVA that significantly reduced membrane crystallinity. The thickness of the dense cellular layer and voids of the loose cellular layer showed a minimum and a maximum at a PP/EVA co-blending ratio of 6:1, respectively. Aqueous NaCl solutions (0.5mol/L) were used in the VMD experiment at a feed temperature of 70°C and a permeate side absolute pressure of 3kPa. The flux of the iPP/EVA co-blending membranes was 27.6kg/(m2h) within 36h of continuous operation, whereas that of the iPP membranes was only approximately 16kg/(m2h) within 6h of continuous operation under the same condition.