Study On Superhydrophobic Modification Of Polyvinylidene Fluride (PVDF) Membrane For Membrane Distillation

Membrane distillation (MD) is a new kind of membrane separation method,which is driven by a vapor pressure drop through a porous hydrophobic membrane.Having various advantages, such as high separating efficiency, low operatingtemperature and low energy consumption, MD process has been widely used inseawater desalination, fruit juice and traditional Chinese medicine concentration.However, membrane fouling is one of the tough problems against the widespread useof this membrane technology. The feed solution is gradually concentrated to saturationand there are crystallization phenomena observed on the membrane surface, which isresulted from temperature polarization and concentration polarization during the MDprocess. Therefore, membrane was wetted and fouled. In this paper, superhydrophobicpoly (vinylidene fluride)(PVDF) membrane was fabricated by the surfacemodification technology to improve the membrane fouling issue in MD process.In this paper, PVDF membranes have been prepared using nonsolvent inducesphase separation (NIPS) method. The optimum conditions was found to be12wt.%PVDF,5wt.%LiCl in casting solutions and60wt.%DMF in coagulation bath.In this paper, PVDF membranes modified with water-, oil-and stain-proofingmaterial were investigated. The effects of the concentration of water-, oil-andstain-proofing material, treating time and treating temperature on the membranemorphologies and properties were studied. The results showed that the membranemodified under the condition of2.0g/L water-, oil-and stain-proofing,2h treatingtime and70°C treating temperature expressed the biggest water contact angle of126°。In this paper, PVDF membranes modified with nanoparticles were alsoinvestigated. Based on the hydrophobic property of nanoparticles and its intrinsicproperties, the superhydrophobic PVDF membrane was fabricated by the way ofspray-deposition. The effects of the concentrations of nanoparticles and adhesive onthe modified membranes morphologies and properties were studied. The resultsshowed that the superhydrophobic membrane with a water contact angle of156°wasfabricated under the condition that the nanoparticle content was1wt%and thenanoparticle to adhesive mass ratio was4:5. A series of membrane distillationexperiments were studied with original and modified membranes. The results showed that the superhydrophobic PVDF membrane had an excellent anti-fouling propertycompared with the original one.