Maintaining surface air layers for wetting prevention in membrane distillation

Description

Preventing the penetration of feed liquid in membrane pores (wetting) is still a challenge in making membrane distillation (MD) processes technically more feasible. In this work, a new method was developed to impede surfactant wetting in a full direct contact membrane distillation (DCMD) setup for desalination of saline brines. Gas recharging was introduced on the feed surface side of superhydrophobic and hydrophobic membranes and a mesh spacer for trapping air at the membrane surface was inserted in the feed side of membrane cell. This technique was examined against a representative surfactant, aqueous NaCl solution containing sodium dodecyl sulfate (SDS), to determine its capability for controlling membrane pore wetting. The results showed that despite the high concentrations of the SDS (up to 230 mg/l) in the feed solution, maintaining gas bubbles on the surface of the superhydrophobic membrane together with using a mesh spacer in the feed side prevented wetting in all conditions (~100% salt rejection) while no impact on the permeate flux was detected. Introduced air bubbles led to adsorption of SDS molecules at the interface of water/air, so that the hydrophilic headgroup of SDS remained in the liquid phase with no adhesion to the polymeric matrix of the membrane due to the presence of air layers as a barrier. Moreover, the existence of gas bubbles could enhance the liquid entry pressure of the membranes by 1.12 - 2.55 times, particularly more for less hydrophobic membranes. The experimental results indicate that utilizing gas bubbles improves the applicability of the MD processes where the liquid feed is capable of wetting the membrane pores.

Period	09 Mar 2017
Event title	DECHEMA Jahrestreffen der Process-Net Fachgruppen Mechanische Flüssigkeitsabtrennung, Kristallisation, Phytoextrakte, Adsorption, Extraktion, Fluidverfahrenstechnik und Membrantechnik
Event type	Conference
Location	GermanyShow on map