Diffusion Dialysis And Electrodialysis Application Of Ion Exchange Membranes Made By ATRP

Large amount of waste acids or alkali are often produced in wrought iron, metallurgy and other modern industrial processes. Direct discharge of these effluents without any treatment not only results into waste of the useful resources, but also brings forward serious contamination of the environment and water resources. Diffusion dialysis (DD) is a separation process with low operation cost. The driving force of the ions is the concentration difference between permeate and diffusion side, which leads to low energy consumption. Other advantages of DD are its clean nature and the easiness to operate and hence DD is an effective, economical and environment-friendly method to treat waste water. In addition, ion exchange membrane with special selectivity is urgently needed in specific seperation fields in recent years. For instance, specific ions need to be separated from complex aqueous salt solutions for the comprehensive utilization of ocean resource. Electrodialysis(ED) is a process that ions migrate through ion exchange membrane (IEM) under direct current field, with low energy consumption, easiness to operate, long working life and no pollution. Permselective membrane can achieve separation of different ions through ED process because of the difference of the ions’transmission performance. Therefore, the preparation of permselective membrane is significant for separation of monovalent and divalent ions.Traditional atom transfer radical polymerization(ATRP) and electronic transfer activate regeneration atom transfer radical polymerization(ARGET-ATRP) are important controlled/living radical polymerization processes and have been rapidly developed in recent years. These methods can control not only molecular weight and polydispersity of polymeric chains, but also composition, structure and terminal functional groups of polymers. With these methods, we can prepare block and graft copolymers with predetermined order and structure.This thesis is divided into five chapters. The first chapter is the introduction, describing the harm and conventional treatment of industrial waste liquor, theory and application of diffusion dialysis and electrodialysis, mechanism of ATRP, ARGET ATRP, and surface initiated atom transfer radical polymerization (SI-ATRP). In addition, the application and preparation of monovalent selective membranes are presented.The second chapter explores several methods of preparing poly(sodium-p-styrene-sulfonate) (PSSS) by ATRP, including:(1)polymerization of sodium-p-styrene-sulfonate (SSS) with the initiation of EBiB by traditional ATRP, (2) polymerization of SSS with the initiation of PPO-CH2Br from BPPO by ARGET ATRP, (3) polymerization of SSS with the initiation of EBiB by ARGET ATRP. The former two methods have some disadvantages, while PSSS can be successfully prepared through the third method.In the third chapter, polyelectrolyte PSSS is mixed with PVA, cross-linked with silane cross-linking agent, and then cast, dried and heat-treated to yield cation exchange membranes. The membranes are characterized in the respect of water uptake, swelling in 65 ℃ water, and ion exchange capacity, and then taken for application in DD process of simulative industrial waste liquor (NaOH/Na2WO4). The high hydrophilicity and abundant -OH groups from PVA can endow the membranes with high OH’ permeability, while the ion exchange groups of PSSS can endow the membranes with high permeability and selectivity. Furthermore, cross-linking with silane can overcome the disadvantage of high swelling.The forth chapter describes the preparation of monovalent anion selective membranes by grafting SSS onto brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) with SI-ATRP method, followed by quaternization of BPPO. Therefore, the main body of the membrane contains positively charged -N+(CH3)3 groups and the surface is grafted with negatively charged -SO3- groups. The membranes are characterized in the respect of water uptake, thermal stability, transport number and ion exchange capacity, and also taken for application in ED process of NaCl/Na2SO4 system.The last chapter is a summary of the whole thesis. Meaningful conclusions about the preparation and applications of the ion exchange membranes with the method of ATRP are drawn through summary of the experimental and theoretical analyses.