Weak alkaline anion exchange fiber for Electrodeionization (EDI)

Ion exchange fiber is a fibrous ion exchange material. When it comes into contact with an electrolyte solution, the ions on the fiber can be selectively exchanged with the ions in the solution. Ion exchange fibers are divided into cation exchange fibers, anion exchange fibers and amphoteric ion-exchange fibers. In addition, ion exchange fibers have a certain strength, chemical resistance and other properties.

(1) The spacing of the diaphragm can be reduced. Usually, the spacing of the ED diaphragm is 0.8-1.0mm, while the electrodeionization is about 3mm. If the ion-filled fiber is filled, the diaphragm can be placed between the two, which is beneficial to shorten the reaction. Penetrate the sub-channels of the pure water treatment system of the electro-deionization device to increase the limiting current density.

(2) The ion-exchange fiber has a large specific surface area and a fast exchange rate, so it is more in line with the requirements of electrodeionization. The innovation of this project lies in the use of a self-developed new ion-exchange fiber material to develop high-end pure water products that can meet higher market demands and fill the gap in domestic high-end products.

Acid-base characteristics
So far, there have been many documents on the determination of the apparent acid-base characteristics of ion exchange fibers. It is closely related to the interface reactions such as coagulation and adsorption. It is one of the important characteristics of hydrated solids. Potentiometric titration The method is an important method to determine the acidity and alkalinity of fiber.
Chemical stability
The chemical stability of ion exchange fiber refers to the ability of the fiber to maintain the original physical and chemical properties under the action of chemical factors, and is determined by the backbone polymer and functional groups. The ion exchange fiber should have good chemical stability, for example, it should be kept in various acids (such as HCl, H2SO4), alkali (such as NaOH, Na2CO3, NH4OH), oxidizing substances (such as H2O2, K2Cr2O7, KMnO4), etc. Certain stability.
Mechanical behavior
The mechanical strength of ion exchange fiber depends on its preparation process, the number of chemical functional groups and the density of the network structure. Due to the multi-step chemical reaction during the preparation process, the fibril skeleton will undergo varying degrees of inter-chain cross-linking, branching, and destruction of orientation and crystal structure. Therefore, the mechanical strength of ion exchange fibers is generally lower than that of the original fiber. The strength of chemical synthetic fibers, but the appropriate strength is sufficient to meet the requirements of the general processing process. In short, the mechanical properties and exchange capacity of ion-exchange fibers should remain basically unchanged during the recycling process, so that the process can be stabilized.
Exchange adsorption performance
For ion exchange fibers, the exchange capacity is the number of exchangeable ions carried by a certain amount of fiber, which is one of the important indicators to measure fiber quality. The exchange capacity of ion exchange fibers depends on the number of active groups fixed on the macromolecular structure of the fiber and the degree of dissociation and accessibility. Due to many factors that affect ion exchange, the exchange capacity of different ion exchange fibers is also quite different.
Kinetic performance
Compared with granular ion exchange materials, ion exchange fibers have a larger specific surface area and a shorter mass transfer distance, so it has faster adsorption and desorption speeds, and its adsorption speed can be several times higher than the former, or even ten times higher. Several times

1. Ion-exchange fiber is used for the recovery and purification of waste acid, waste alkali, waste liquid and waste gas in the production process of iron and steel, chemical industry and light industry.
2. Ion-exchange fibers are widely used in seawater desalination, the preparation of industrial soft water, the production of ion-free pure water and the salt industry.
3. Ion-exchange fiber can also be used to adsorb heavy metals and pigments. The ion exchange rate is fast, easy to regenerate, and has a good decolorization effect on the difficult-to-treat reactive dye wastewater.

1. Chemical modification method
Chemical grafting is a commonly used grafting method, in which the free radicals generated by the thermal decomposition of chemical initiators initiate monomer grafting. At present, the main purpose of chemical grafting is to modify the fiber by introducing a small amount of functional monomers into the molecular chain. For example, polypropylene fiber introduces a small amount of acrylic acid through chemical grafting to improve its water absorption, and polypropylene fiber is used as the matrix. IEF is made by grafting vinyl monomers by chemical initiation method. Polypropylene fibers are thermally oxidized to produce peroxide or hydrogen peroxide. The latter decomposes to initiate graft polymerization. Add a suitable amount of reducing agent to produce hydroxyl anions as much as possible when hydrogen peroxide is decomposed. Homopolymer formation.
2. Polymer blending into fiber method
There are two types of polymer blending fiber forming methods: one is to disperse the ion exchanger into the spinning solution to form the fiber, and the content of the ion exchanger is 50%~60%; or it can be less than 100pum. Ion exchanger particles are dispersed in a fiber-forming polymer and a low-boiling solvent to make fibers, with a surface area of up to 1m/g. The other is to mix and spin two kinds of polymers, and then process the blended or composite fiber to make ion exchange fiber.
3, radiation grafting method
Radiation grafting is an important method for the modification of polymer materials. Compared with chemical grafting, it has the characteristics of advanced technology, high monomer utilization, low energy consumption, and no pollution. The production of IEF by radiation grafting method developed rapidly in the late 1990s. Radiation grafting is a free radical polymerization reaction. Due to the many conditions that affect the reaction, the raw materials used for grafting are different, and there is no complete theory and law to be found at present. According to the different reaction conditions, radiation grafting methods can generally be divided into: co-radiation grafting, anaerobic pre-radiation grafting and aerobic pre-radiation grafting.
4, monomer copolymerization method
The monomer copolymerization method is to directly copolymerize monomers that have or can be converted into ion exchange groups and monomers capable of forming fibers, and then spin them into fibers. The ion exchange fiber prepared by this method not only has a uniform distribution of functional groups on the molecular chain, but also has a relatively high content. However, since the functional group-containing monomers need to be protected during the copolymerization reaction, and the price of such monomers is expensive, the application of this preparation method is subject to certain restrictions.