Optimization of morphology and perf ormance of PVDF hollow fiber for direct contact membrane distillation using experimental design

Non-solvent induced phase inversion technology has been applied to develop porous poly (vinylidene fluoride) (PVDF) hollow fiber membranes in this study and structural characteristics of resultant membranes and their performance in direct contact membrane distillation (DCMD) were examined. Application of Taguchi experimental design with three level L9 orthogonal array (OA) and statistical analyses was attempted for identifying the relationship between the hollow fiber membrane formation conditions selected and the membrane performance and further making predictions. Membrane morphologies and microstructures were examined using FESEM, gas permeation and XRD; mechanisms for the membrane morphologies observed were discussed. Similar pattern of the plots of gas permeation and DCMD flux gave the hint that the skin resistance was not negligible in DCMD for these membranes. Analysis of variance (ANOVA) showed that among the three fabrication variables, content of non-solvent additive (i.e. glycerol) in the dope had the most significant effects on both membrane distillation coefficient Cm and thermal efficiency EE, while external coagulant composition is least influential. The observed responses at selected combination of spinning conditions were in agreement with those predicted based on the same fabrication conditions. The highest water flux achieved in the current work in desalinating 3 wt% NaCl aqueous solution was higher than 20 kg/m2-h at average feed temperature of 64.5 °C with 99.9% rejection.