Study On The Structure Control Of Pervaporation Composite Membrane Support Layer

The rapid growth of population and the rapid development of society lead to the serious shortage of fresh water resources.Desalination of brackish water,sea water and salt water is considered to be an effective way to solve this problem.Pervaporization(PV),as a new membrane separation technology,has attracted extensive attention from many scholars in the field of seawater desalination in recent years.At present,the main problem of desalination by pervaporization is that the infiltration flux is relatively low,which limits its practical application.In this paper,polyvinyl alcohol(PVA)as a dense layer material,through the non-solvent phase conversion method(NIPS)to prepare polyvinylidene fluoride(PVDF),polysulfone(PSF)support layer,the research focus on the control of the structure of the support layer,in order to obtain high performance pervaporation membrane.Specific research contents are as follows:(1)The effects of directional non-solvent phase conversion on the structure and properties of PTFE membrane were studied.The results show that compared with the non-directional phase transformation method,the membrane prepared by the directional phase transformation method has lower surface porosity,higher mass transfer resistance,and greater shrinkage during drying process.(2)The influences of polyvinylpyrrolidone(PVP)on the morphology and performance of PVDF membrane were studied.The results show that with the addition of PVP,the surface hydrophilicity of the membrane increases,the surface pore size decreases,the pure water flux and the overall porosity increase firstly and then decrease.When the amount of PVP was 5 wt%,the performance of PVDF membrane was the best.The water flux of PVDF/PVA composite membrane was 87.26 kg/(m2·h)at 70℃ for treating 35,000 ppm NaCl solution,and the salt cutting rate was 99.92%.(3)In order to further improve the membrane permeability efficiency,PSF was selected as the supporting layer material.Sulfonated polysulfone(SPSF)and propionic acid were added into the casting solution to improve the surface hydrophilicity of PSF membrane,thus enhancing the interface bonding force between PSF supporting layer and PVA separation layer,and improving the stability of the composite membrane.The influence of propionic acid content on PSF membrane was studied.The results showed that when the content of propionic acid was 15 wt%,the surface water contact Angle of PSF membrane reached 56.2°,and the pure water flux of the membrane reached 654.27 kg/(m2·h),and the BSA retention rate was 94.82%.Compared with PVDF/PVA composite membrane,the permeation flux of the composite membrane prepared by using this membrane as the supporting layer is greatly improved.The PV water flux of 35,000 ppm NaCl solution treated at 70℃can reach 114.25 kg/(m2·h),and the salt cutting rate is 99.90%.