Study On The Preparation And Desalination Performance Of PVDF/PI Cation Exchange Membrane

In chemical production,a lot of high salinity wastewater is often produced with complex components.In addition to the nearly saturated salt?sodium chloride?,there are also some organic impurities,water-soluble reactants,products and by-products.The treatment of high salinity wastewater is always a difficulty in the field of chemical industry and environmental protection.It is very important to treat high salinity wastewater with low energy consumption and low equipment requirements in chemical industry and environmental protection.With the development of membrane separation technology,electrodialysis technology has been widely used in the treatment of salty wastewater.The core of electrodialysis technology is ion exchange membrane,so it has become a research hotspot at home and abroad to develop an ion exchange membrane with large ion exchange capacity,good mechanical properties,small membrane surface resistance and anti pollution.In this paper,PVDF and PI were blended to prepare flat membrane by immersion precipitation phase transformation,and 4,4'-diaminostilbene-2,2'-disulfonic acid?DASD?was used to modify the surface of the membrane.The sulfonic acid group was introduced into the polymer framework by chemical bond to prepare homogeneous cation exchange composite membrane with enhanced ion selective permeability.In order to find out the optimal conditions for membrane preparation,the effects of soaking time,temperature and concentration of dasd-tea solution,concentration of PI and PVDF in casting solution and thickness of membrane preparation on the desalination performance of ion exchange membrane were investigated.The results showed that the optimal conditions for membrane preparation were:19.0 wt%PVDF,1.0 wt%PI,soaking time of 10 min,soaking temperature of 50?,concentration of DASD-TEA solution of 0.03 wt%?0.03 wt%4,4'-diaminostilbene-2,2'-disulfonic acid,0.03 wt%triethylamine,99.94 wt%deionized water?.The performance parameters of the ion exchange membrane were determined by testing the water content,ion exchange capacity and membrane surface resistance.Its water content is 38.6%,pure water permeability is 50 L·m^-2·h^-1·bar^-1,contact angle is 81.9°,ion exchange capacity is 0.32mmol·g^-1,membrane surface resistance is 2.96?·cm².In order to further prove the use value of PVDF/PI cation exchange membrane,the commercial polyethylene heterogeneous ion exchange membrane?commercial membrane?was desalted with a self-made electrodialysis device in the laboratory.The differences between PVDF/PI cation exchange membrane and commercial membrane were comprehensively analyzed by changing the applied voltage,feed flow rate,feed concentration and other conditions.The experimental results show that PVDF/PI cation exchange membrane is superior to commercial membrane in different applied voltage,feed flow rate and feed concentration.In the 120 min desalting experiment under the optimal working parameters of electrodialysis device?voltage 4 V,feed flow rate 40L/h?,the desalting rate of PVDF/PI cation exchange membrane is 1.33 times that of commercial membrane.