Preparation Of Anion Exchange Membranes For Diffusion Dialysis And Their Performance

In recent years,with the rapid development of metal processing,mining engineering,electroplating and other chemical industries,it inevitably discharges a large amount of acid waste liquid during the process,which not only wastes resources but also greatly damages the environment.So how to efficiently separate and recycle acid waste liquid becomes the urgent issue to deal with.Diffusion dialysis technology refers to the ion in the solution selectively pierces through anion exchange membrane with the driving of the osmotic pressure in solution to achieve the aim of separation and recovery.The technology attracts the attention of the researchers because it contains many unique properties,such as low energy consumption,easy operation,high efficiency and environmental friendly.Click chemistry has many advantages,such as mild reaction conditions,quick and thorough reaction,products three-dimensional,stereo-selectivity and so on.So it is widely used in the fields of sugar compounds,biological macro-molecules and synthesis of drug-lead compounds.In this paper,we compound three different types of homogeneous anion exchange membranes by click chemistry and apply them to the field of diffusion dialysis.We research the relationship between polymer structure and performance.A series of homogeneous anion exchange membranes,in which trimethylamine（TMA）salt and hydrophobic P（styrene-butadiene-styrene）block co-polymer（SBS）respectively serve as alkaline functional group and polymer matrix,have been successively combined into compound SBS-TMA-X by click chemistry with casting film-forming method.Then with the 1,2-ethanedithiol（EDT）as cross-linking agent,we successively obtained different cross-linking degree of modified membranes TSBS-Y.At last,with propiolic acid（PA）served as the auxiliary groups,we successively obtained the modified membranes TSBS-COOH-Z by one-pot-click process.The structure and thermal stability of SBS-TMA-0.09 were characterized with the help of 1H-NMR spectroscopy（1H-NMR）and Thermo-Gravimetric（TG）analyzer.With the help of Scanning Electron Microscopy（SEM）、 Dynamic Mechanical（DM）analyzer 、Exact Balance（EB）analyzer 、 Diffusion Dialysis（DD）analyzer and Potentiometric Titrator（PT）analyzer,its morphology 、 mechanical strength、acidic stability and the performance of diffusion dialysis were studied.The cross linking degree of TSBS-Y were quantitatively studied by means of Organic Element（OE）analyzer.The relationship between performance of diffusion dialysis and temperature were studied by means of Variable Temperature Water-bath（VT-W）analyzer.The results show that: three kinds of anion exchange membranes all have good appearance.Their appearance hasn’t been obviously changed with the introduction of modifying agent.In addition,their initial decomposition temperature is about 200 oC.The thermal degradation temperature of the main-chain is about 490 oC.The mass-fraction remains 97% after being soaked in acidic solution about 7 days.Above all,their diffusion dialysis performance has nothing to do with immersion time.Mechanical strength of membranes TSBS-Y is superior to SBS-TMA-X and TSBS-COOH-Z,and the tensile strength（Ts）of membranes TSBS-0.3 can reach 42.2 MPa.At room temperature,TSBS-COOH-0.10 with hydrogen bond structure has the best performance of diffusion dialysis,whose dialysis coefficient（U_H⁺）value is 3.43×10^-2 m/h,separation factor（S）value is 28.3,and the core performance is much better than commercial membrane（DF-120）.For all samples,U value increases with temperature and S value is falling at high temperature.TSBS-COOH-0.10 corresponds to the lowest temperature when its S value suddenly drops.