Using ammonia as an additive to fabricate a high performance PVDF hollow membrane for distillation

Highly hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane with high porosity is specially desired to meet the requirements of distillation. Here, a novel approach was proposed to fabricate a hydrophobic PVDF hollow fiber membrane by using aqueous ammonia (NH3 center dot H2O) as an additive. Adding NH3 center dot H2O to the PVDF spinning solution increased the porosity, enhanced the thermal stability, improved the water contact angle, and reduced the vapor transport resistance of the fabricated membranes. The membranes achieved nearly 99% salt rejection when they were used to desalinate a 3.5 wt% sodium chloride solution, and the maximum transmembrane permeate flux was similar to 32 kg/(m(2).h) when the hot feed solution and cold distillate were 80 degrees C and 20 degrees C, respectively. In addition, the PVDF hollow fiber membrane exhibited good stability in desalination. The method of utilization NH3 center dot H2O described here provides an operable route to the production of highly hydrophobic PVDF hollow fiber membrane with high porosity.