Process optimization for fabrication of PVDF - TiO2 hydrophobic membrane using phase inversion method for desalination application using VMD

Abstract

The properties of membranes are significantly influenced by process parameters. To understand the impact of operating parameters on membrane characteristics, a design of experiments was conducted using response surface methodology (RSM). The gradient descent method was employed to determine the optimal conditions for desired membrane characteristics. This study involved the preparation of a hydrophobic flat sheet membrane made of Polyvinylidene fluoride (PVDF) using central composite design (CCD) arrays. The operating variables considered for developing the PVDF flat sheet hydrophobic membrane were polymer concentration, additive concentration, evaporation time, and ethanol concentration in the coagulation bath. The responses, such as contact angle, membrane porosity, and tensile strength, were measured using the sessile drop method, gravimetric method, and universal testing machine. Nonlinear regression models were developed for contact angle, porosity, and tensile strength using minimization of the sum of square errors in CCD, which were found to be in good agreement with experimental data. The results indicated that polymer concentration had the highest synergistic influence on the surface contact angle, but had an antagonistic effect on membrane porosity. The tensile strength of the fabricated membrane increased with polymer concentration but declined with additive concentration. It was important to determine the optimal conditions for the trade-off between the operating parameters and membrane characteristics. The theoretical desired membrane characteristics were determined to be 109 ± 2°, 59.9 ± 2%, and 78.7 ± 1 MPa under optimal conditions of 16.0 wt% polymer concentration, 1.676 wt% TiO2 concentration, 29.09 min of evaporation time, and 39.59 wt% coagulation bath concentration. The experimental values of membrane characteristics under optimal conditions were measured to be 108.2 ± 2°, 58.9 ± 2 %, and 77.3 ± 1 MPa. The fabricated membrane was employed for desalination using vacuum membrane distillation.