Study On Anti-Fouling PVDF Membrane For Membrane Distillation

Membrane distillation(MD) uses water solution as hot feed solution, water vapor pressure is in the role of impetus so that water vapor of the feed solution can pass through the microporous membrane and condensed in the cold fluid, and bring about good separation performance. The study of MD membrane focuses on improving the hydrophobic capability, because the super-hydrophobic membrane has the capability of inorganic pollution anti-fouling. But in the actual application process of the membrane distillation(MD), most waste water contains not only inorganic salt, but also organic compound so that improving the comprehensive ability of anti-pollution is very important to the MD membrane. In this paper, the super-hydrophobic membrane was obtained by coating the homemade poly vinylidene fluoride(PVDF) membrane, and then it was hydrophilic modified so that composite hydrophilic/ super-hydrophobic membrane was made. Later those membranes were used in the direct contact membrane distillation(DCMD) to test their ability of pollution anti-fouling. The purpose of this research is to investigate a method of making anti-fouling MD membrane.In this paper, by adjusting the ratio of N,N-Dimethylformamide(DMF) and N-methyl-2-pyrrolidone(NMP) cotents in casting solution, finding that the best ratio of DMF/NMP in casting solution for the formation of the PVDF membrane was 3:1, the average pore size of PVDF membrane was 0.364 ?m, the porosity was 67.54% and the contact angle was 112.94°.In this paper, the surface coating method was used to make super-hydrophobic modification of the surface of the PVDF membrane. It was told by the result that the biggest contact angle of super-hydrophobic modified membranes were achived when the PVDF content was 2%, PG content was 39%, temperature of casting solution was 50°, evaporation time the was 10 s, and temperature of coagulation bath was 60°. The result of the DCMD test indicated that capabilities of anti-wetting, inorganic pollution anti-fouling and composite pollution(inorganic and organic pollution) anti-fouling of super-hydrophobic membranes were improved better in comparison with the original one.In this paper, the super-hydrophobic membranes were hydrophilic modified so that composite hydrophilic/ super-hydrophobic membrane was made. And it was indicated by the result that the best PVDF hydrophilic/ super-hydrophobic membrane was obtained when the content of nanoparticle TiO2 was 43.6mg/L. The result of the DCMD test indicated that the capabilities of anti-wetting and inorganic pollution anti-fouling of the PVDF hydrophilic/ super-hydrophobic membranes were as good as the super-hydrophobic membranes, and the capabilities of composite pollution anti-fouling were improved better in comparison with the super-hydrophobic membranes. Results of this study pointed out the correct way of making anti-fouling PVDF membrane for membrane distillation.