Characteristic and performance of polyvinylidene fluoride membranes blended with different additives in direct contact membrane distillation

Membrane distillation (MD) is a thermal-driven membrane separation process which recently garners interest from academic and industry due to its low energy requirements and the ability to integrate with renewable energy. In this work, two different additives, i.e. polyethersulfone (PES) and ethylene glycol (EG), were added into dope solutions consisting of polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) to prepare membranes for MD applications. The membranes were characterized with respect to thickness, pore size, porosity, and water contact angle using scanning electron microscope and water contact goniometer. Compared with the membranes made from pure PVDF and PVDF-EG system, it is found that PVDF-EG-PES membrane displayed improved characteristics i.e. having optimum porosity, large pore size, and thin membrane thickness coupled with finger-like structure extended from both inner and outer layers of the membrane. In addition to this, the permeate flux of PVDF-EG-PES membrane during MD application was also reported to be the highest among all the membranes studied when tested under same process conditions. With respect to membrane performance stability, the results showed that PVDF-EG-PES membrane could achieve a very consistent permeate flux while maintaining high NaCl rejection throughout 20 h operation, indicating the potential of this membrane in MD process.