Study On Modification Of Ion Exchange Membrane With High Selective Permeation

In recent years,with the deepening of people's research on membrane technology,ion-exchange membrane technology is gradually maturing and has been widely applied in many fields.The choice of permeability as a basic property of the most essential features of ion exchange membranes has been favored by many researchers.Due to the monopoly of advanced foreign technologies,although China is the largest country in the production of heterogeneous ion exchange membranes,the production of ion exchange membranes is difficult to apply to high-tech fields.Nowadays,most of the ion exchange membranes in the market have a selective permeability of about 90%.How to improve the selective permeability of ion exchange membranes has become a problem that needs to be solved in the ion exchange membrane industry in China.In this experiment,from the viewpoint of modifying the ion exchange membrane,it is intended to obtain a highly selective ion exchange membrane through the modification of existing commercial membranes.The hole transfer theory proposed by Wang et al.et al.overcomes the disadvantage that the South-South equilibrium is applicable only when there is no external electric field force.This theory believes that the reason for ion leakage is that the membrane surface is As a result of the potential effect,ion leakage occurs when the diameter of the pore is greater than 2 times the membrane potential.Based on this,the experiment modified the membrane by blocking the macropores on the surface of the cation exchange membrane and increasing the surface potential of the anion exchange membrane.It was hoped that a highly selective permeation ion exchange membrane with a selective permeability above 98%would be obtained.And finally through its application in the double-film three-cell cobalt electrowinning process to verify.First,the conductive polymer polypyrrole was selected to surface-coat the cation exchange membrane.The experiment chose L₁₆?4⁵?orthogonal test with five factors including reaction time,reaction temperature,type of doping acid,concentration of doping acid and concentration ratio of monomer and oxidant.The experiment finally determined that the reaction temperature was 20°C,the reaction time was 30 min,the concentration ratio of pyrrole monomer to oxidant was 4,the dopant was concentrated nitric acid and the concentration of dopant was 1 mol/L.best effect.The properties of the membrane were characterized by SEM,Fourier infrared spectroscopy,chloride ion leakage,ion exchange capacity,membrane resistance and water content of the modified membrane and the original membrane.The large pores on the surface of the modified membrane were blocked and uniformly dense,the chloride ion leakage rate decreased from 14%to 2.47%,and the selective permeability reached nearly 98%;the membrane resistance decreased from8.8?·cm-2 to 6?·In cm^-2,the moisture content also decreased by 10%.Based on the analysis of the reasons,it is believed that the polypyrrole film coated on the surface of the membrane successfully seals the larger pores on the surface of the membrane,thereby blocking the passage of counter ions;and the polypyrrole,due to the nature of its conductive polymer,helps reduce the membrane surface resistance.The ultimate cation exchange membrane's selective permeability has been greatly improved.Second,the polymer polyelectrolyte polyethyleneimine was selected to perform plasma graft modification of the anion exchange membrane.The effects of the concentration of polyethyleneimine solution,the plasma glow discharge power,the duration of the discharge,and the discharge gas atmosphere on the experimental results were analyzed by single factor method.It was finally determined that when the discharge time was 5 minutes,the concentration of the PEI aqueous solution was 50%.The discharge gas atmosphere is vacuum,and the glow discharge power is 0.5w/cm²,the best modification effect is achieved.The performance of the film is characterized by SEM scanning electron microscopy,anion migration number,ion exchange capacity and membrane resistance.After the modification,the number of ion migration in the anion membrane increased from 90%to 97%,and the ion exchange capacity also increased to some extent.The reason for the analysis was that the successful grafting of polyethyleneimine resulted in the introduction of bases on the membrane surface.The concentration of active groups is increased to increase the surface potential of the membrane of the anion exchange membrane,thereby expanding the range of action of the membrane potential,suppressing the passage of the cation exchange membrane,and eventually achieving the effect of improving the selective permeability.Finally,in order to verify the effect of the modified membrane in practical applications,it was used in a double-membrane three-cell cobalt electrowinning process.The membranes before and after the modification were placed in a membrane module for parallel testing.By comparing the production of metallic cobalt and the generation rate of chlorine in the two groups of experiments,it was found that the cobalt deposition efficiency of the electrolytic cell using the modified ion exchange membrane module increased by nearly 20%,and it had a lower chlorine generation rate.This verified the effectiveness of the ion exchange membrane modification.The success of the ion exchange membrane modification experiment not only promotes its own selective permeability,but also suppresses the production of chlorine while increasing the production efficiency of cobalt.Finally,the enriched hydrochloric acid can also be recycled and reused.It is truly economical and environmentally friendly.The coordinated development.Although this experiment successfully produced highly selective permeation ion exchange membranes,some problems were found during the modification process.Since it is difficult to store pyrrole monomers for a long period of time,it is worth further study whether other conductive polymers can be replaced.However,in this experiment,higher concentrations of polyethyleneimine were not used for the experiments,and therefore the selectivity of the anion exchange membranes was greatly improved.The space;in the application process also found that the heat resistance and durability of ion exchange membranes need to be further improved.