Maintaining surface air layers for wetting prevention in membrane distillation
Sprache des Vortragstitels:
Englisch
Original Tagungtitel:
DECHEMA Jahrestreffen der Process-Net Fachgruppen Mechanische Flüssigkeitsabtrennung, Kristallisation, Phytoextrakte, Adsorption, Extraktion, Fluidverfahrenstechnik und Membrantechnik
Sprache des Tagungstitel:
Deutsch
Original Kurzfassung:
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.