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Explain in detail the structure and performance of ion exchange resins

Jul 20, 2020

 Ion exchange resin and sulfonated coal are mainly used for ion exchange in water treatment. Among them, ion exchange resins are widely used and have many types, and sulfonated coal is a cation exchanger with both strong acid type and weak acid type exchange groups.


   ion exchange resins are divided into gel type, macroporous type and isoporous type according to their structural characteristics;


  According to the type of resin matrix, it is divided into: styrene, phenolic and acrylic, etc.;


  According to the nature of the exchange group, it is divided into: strong acid type, weak acid type, strong base type and weak base type.


  ⑴The structure of ion exchange resin


   is an insoluble polymer compound composed of a spatial network structure skeleton (ie the matrix) and many active groups attached to the skeleton. The active group ionizes in water and is divided into two parts: the fixed part, which is still firmly bound to the skeleton and cannot move freely. It constitutes the so-called fixed ion. The movable part can move freely within a certain range and carry out with the other same ions in the surrounding solution. The exchange reaction is called exchangeable ion.


  ⑵Basic performance


  ①Appearance


   is transparent or semi-transparent spherical, and the colors are milky white, light yellow, yellow, brown, tan, etc.,


  ②Crosslinking degree


"" refers to the percentage of the crosslinking agent in the total weight of the resin raw material. It has a decisive influence on many properties of the resin such as exchange capacity, water content, swelling, mechanical strength, etc. Generally, the crosslinking degree of resin in water treatment is 7% to 10%.


  ③Water content


   refers to the percentage of moisture per gram of wet resin, generally 50%. The greater the degree of crosslinking, the smaller the pores and the lower the moisture content.


  ④Swelling


   refers to the phenomenon that the volume of dry resin becomes larger by soaking in water. Generally speaking, the smaller the degree of cross-linking, the easier it is for the active groups to ionize. The larger the hydrated ion radius of exchangeable ions, the greater the swelling degree; the higher the electrolyte concentration of the solution surrounding the resin, the smaller the resin swelling rate.


   In production, try to ensure that the ion exchanger has a long working cycle, reduce the number of regenerations, and extend the service life of the resin.


  ⑤Density


   is divided into dry true density, wet true density and wet apparent density


  ⑥Exchange capacity


   is the most important performance of the resin. It is the data necessary for the design of the ion exchange process device, and it quantitatively indicates the size of the resin exchange capacity. Divided into full switching capacity and working switching capacity.


  ⑦effective ph range


   Since the exchange group of the resin is divided into strong acid and strong base and weak acid and weak base, the pH value of water will affect its ionization and affect its working exchange capacity. Weak bases can only have higher exchange capacity in acidic solutions and weak acids in alkaline solutions.


  ⑧selective


   is the ability of ion exchange resin to preferentially exchange certain ions in water. In addition to the type of resin, it is also related to the humidity and ion concentration in the water.


  ⑨Ion exchange balance


   The ion exchange reaction is a reversible reaction, subject to the law of mass action and the law of equivalents. After a certain period of time, the ion exchange reaction between the solid resin phase and the solution phase in the ion exchange system reaches equilibrium, and the equilibrium constant is also called the ion exchange selectivity coefficient. Reducing the concentration of reaction products is beneficial to the exchange reaction.


  ⑩Ion exchange rate


   is mainly affected by the ion diffusion process in the ion exchange process.

Source:https://www.up-resin.com/

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