Enhanced properties of the PVDF membrane with carboxylated MWCNT and sodium alginate for membrane distillation

Abstract

The use of nanomaterials to modify membrane distillation membranes enhances their performance by avoiding wetting and fouling. This study plans a critical analysis of the advancement made in the use of multi-walled carbon nanotubes and sodium alginate for PVDF membrane modification and further, the developed membrane has been analyzed for water desalination through the direct contact membrane distillation process. Using the phase inversion method polyvinylidene fluoride (PVDF, N1) and polyvinylidene fluoride/ multi-walled carbon nanotubes/sodium alginate (PVDF/MWCNT/SA, N2) membranes were prepared. Taguchi L16 array has been developed to find out optimum conditions. In this Taguchi method, four parameters with four levels are mainly; Feed temperature (55 °C, 60 °C, 65 °C, 70 °C), feed flow rate (0.8 LPM, 1 LPM. 1.2 LPM, 1.4 LPM), feed concentration (5 wt%, 10 wt%, 15 wt%, 20 wt%), and permeate temperature (9 °C, 12 °C, 15 °C, 18 °C) and optimum conditions (feed temperature-70 °C, feed flow rate-1.4 LPM, feed concentration-5 wt%, permeate temperature-15 °C) were found. The changes in hydrophobicity, morphology, surface roughness and chemical composition of the pure and modified membranes before the experiment and after fouling were analyzed by the contact angle, scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transformation infrared microscopy (FTIR), respectively. The effect of four operating parameters on permeate flux and rejection has also been evaluated. It was determined that carboxylated MWCNT and sodium alginate incorporated membrane gave the highest permeate flux, 6.38 kg/m2.h for MgSO4 salt at operating parameters, which is 25 % higher than the pure PVDF membrane (flux - 5.13 kg/m2.h). A 100 h long run experiment was conducted on the N1 and N2 membranes. The modified N2 membrane showed high stability.