Fabrication Of The Pervaporation Composite Membrane And Study Of The Effects Of The Membrane Structures To Pervaporation Performance

With the development of economy,the demand of fresh water is increasing.China is among one of the 13 countries,which is suffered from lacking of water,by the United Nations.Extracting fresh water from salty water,seawater and brackish water is considered as an effective way to solve this problem.Conventional seawater desalination technologies such as MED,MSF,RO and NF,have some disadvantages which limit their applications.Pervaporation desalination attracted many scholars' attention in recent years,but its low productivity limited the application in industrialization.In this study,Pervaporation desalination composite membrane using PVA as separating layer and UF membrane as supporting layer have been prepared,and the effects of structure,temperature,concentration and the degree of crosslinking on PV desalination performance have been studied.PVA has a good ability to form a film,and a good resistance to acid,alkali and oil.In this study,pervaporation desalination composite membrane using PVA as separating layer and PES UF membrane as supporting layer have been prepared.Because of the swelling problem of PVA in water which limits its application in PV.SPTA crosslink agent has been used and the effect of content of SPTA on PV properties has been studied.Specific discovers are shown below:1.The composite membrane has a good efficiency with a 15%SPTA content,the PV water flux was 13.27 L·m-2·h-1 and the rejection to NaCl was over 99.88%when the feed temperature was 70 ? and the NaCl concentration was 35000 ppm.The effects of temperature and concentration of the feed to membrane performance have been studied.And the membrane showed stable performance during a continuous running time for 12 h.2.SPTA-PVA composite membranes with different substrates have been prepared,the effect of hydrophilicity,surface pore diameter and porosity of the substrates on pervaporation has been studied.The result showed that a high hydrophilicity of the substrate is benefit for the transport of water molecule through the membrane;surface porosity has a great influence on the water flux,PAN UF membrane,using the casting solution of 18 wt.%PAN and 6 wt.%PEG 400,has a surface pore diameter of 17.90 nm and the porosity was as high as 6.175%.Using this substrate,the composite membrane has a flux of 44.02 L · m-2 · h-1 and a rejection of 99.98%to NaCl when the feed temperature was 70? with a salt concentration of 35000 ppm.3.PMDA-PVA/PAN composite membrane has been prepared by dip-coating method using PMDA as crosslinking agent.Crosslinking time and temperature have studied,the structure of PVA separating layer has been characterized to discuss the effect of the concentration of PMDA on pervaporation property.The result showed that the membrane with a concentration of 20%PMDA has a good salt rejection.When dealing with a 35000 ppm,70? NaCl solution,the water flux can reach to 32.26 L·m-2·h-1,and the rejection to the salt was 99.98%.