Preparation And Application Of PVDF Flat Sheet Hydrophobic Membrane

In this paper, the novel flat sheet hydrophobic membrane of polyvinylidene fluoride (PVDF) based on the support of non-woven fabric was prepared by phase inversion process to improve the flux and mechanical properties. During seawater desalination processes through direct contact membrane distillation (DCMD), the experimental results showed that the membrane had high permeate flux and solute rejection. The following conclusions were obtained:(1) The influence factors on membrane structures, such as solvent, the PVDF concentration, non-solvent additive, volatile time, non-woven fabric, knife gap, the temperature and components of coagulation bath were investigated. It was found that the PVDF flat sheet hydrophobic membrane based on the support of non-woven fabric with the mixture of H3PO4and acetone as non-solvent additive had a strong mechanical properties, a thin skin, a more porous network sponge-like layer and a narrow pore size distribution. The membrane structure had the advantage of enhancing the permeate flux and keeping a high salt rejection.(2) The influence of membrane distillation mode, temperature, flow rate and salt concentration on permeate flux was discussed by DCMD. The permeate flux of co-current flow mode was about10.5%higher than that of cross flow mode. It was helpful to enhance permeate flux by improving feed temperature and flow rate. With increase of salt concentration, the permeate flux would decline.(3) The laboratory study of seawater desalination was conducted by DCMD with self-prepared PVDF flat sheet hydrophobic membranes. The influence of antiscalant on water recovery was investigated with the seawater at50℃and the cold distillate water at20℃. It was found that the addition of antiscalant in the seawater can obviously improve the water recovery, it can reach as high as about85%and reduce the emission of seawater concentrate, the PVDF membrane had stable permeate flux and the conductivity of the obtained distillate remained below10μS/cm during the whole process. The continuous200h DCMD experiment results indicated that this emerging technology may be of great potential to be utilized in seawater desalination.