Application of polypropylene membranes hydrophilized by plasma for water desalination by membrane distillation

Abstract

Oil contaminants adsorbed on the hydrophobic membranes during water desalination by membrane distillation (MD) resulted in accelerated membrane wetting. To mitigate wetting problem, the surface modifications by plasma treatment have been developed to enhance polypropylene membrane hydrophilicity without changing its bulk properties. Argon and argon/oxygen gas plasma were applied for this purpose. The surface wetting properties of the membranes were evaluated by measurement of a water contact angle and fluorescein dye adhesion. The long-term studies of membrane distillation were carried-out for resistance test of membrane wettability. Plasma treatment caused etching of the membrane surfaces, which significantly increased the surface porosity, hence, the permeate flux increased over two times without a deterioration of distillate quality. A significant reduction of oil fouling for membranes modified by plasma treatment was confirmed. Desalination of lake water and Baltic Sea water carried out for several months revealed, that the membranes, despite the surface hydrophilization, retained a good resistance to wetting and scaling.