improvement of hollow fiber membrane characteristics and performance by using of chloride salt additives

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by the dry/wet jet spinning phase inversion technique. Fibers used for MD process must have at least one hydrophobic surface and high overall porosity with small pore sizes. DiMethylACetamide (DMAC) was used as polymer solvent and several chloride salts (NaCl, KCl, CaCl2 and BaCl2) are not dissolved by DMAC were used as pore forming additive in dope solution that improved porosity in fibers structure. Four experiments were performed for determination of optimum salt between these salts that increase the overall porosity while keep pore sizes in hollow fiber structure smaller than 0.4 micrometer. Other spinning parameters were maintained the same at these experiments. Salt particle sizes in DMAC were measured by Dynamic Light Scattering (DLS). The prepared membranes were characterized through Scanning Electron Microscope (SEM) observation and contact angle test. Finally the optimum membrane were tested for desalination by direct contact membrane distillation and compared with fiber that produced at same spinning parameters and without salt additive. An optimal hollow fiber membrane was fabricated using the BaCl2 particles with contact angle of 93.8, overall porosity of 85% and pore size of 0.29μm. This optimum membrane exhibits the highest permeate flux (16.902 Kg/m2hr compared to 11.015) and salt rejection factor of 99.9%.

Keywords:

Hollow Fiber Membrane , Phase Inversion , Polyvinylidene Fluoride , Membrane Distillation (MD) , Salt Additive , Desalination