Hydrophobic PVDF hollow fiber membranes with narrow pore size distribution and ultra-thin skin for the fresh water production through membrane distillation

Polyvinylidene fluoride (PVDF) hydrophobic asymmetric hollow fiber membrane was fabricated through the dry-jet wet phase inversion process. It is found that the PVDF hollow fiber has an ultra-thin skin layer and a porous support layer from the morphology study. The fully porous membrane structure has the advantage of decreasing the vapor transport resistance and enhancing the permeation flux. The fabricated PVDF membrane has a mean pore size of 0.16 μ m in diameter and a narrow pore size distribution. The rough external surface produces an advancing contact angle of 112 ± 3^{{ring operator}}with water. During direct contact membrane distillation (MD) of 3.5 wt% salt solution, PVDF hollow fibers produced a water permeation flux of 41.5 kg m^{- 2}h^{- 1}(based on the external diameter of hollow fiber) and a NaCl rejection of 99.99% with a hot salt solution at 79.3 °C and cold distillate water at 17.5 °C. This performance is comparable to or superior to most of commercially available PVDF hollow fiber membranes, indicating that the newly developed PVDF may be suitable for MD applications.