The composition and classification of ion exchange resins

1. What is hydrogen cation exchange resin?

Hydrogen cation exchange resin (sometimes referred to as “hydrogen resin”) is a man-made organic polymer product. The most commonly used raw materials are: styrene or acrylic acid (ester). The polymer skeleton (resin matrix) with a three-dimensional three-dimensional network structure is formed through polymerization reaction, and then different “chemically active groups” are introduced into the skeleton. . Because its active groups, such as sulfonic acid group (-SO3H), carboxyl group (-COOH), etc., all contain active hydrogen ions, which can be dissociated in water for exchange with other cations, especially before the name of cationic resin Add the word “hydrogen type” to distinguish it from the “sodium type” of the same system. However, the “sodium type” can be treated with strong acid to become the “hydrogen type”, and the “hydrogen type” can also be treated with a “sodium hydroxide” solution to become the “sodium type”, that is, the two types of resins can actually be converted into each other. The hydrogen type cation exchange resin is insoluble in water and general solvents. Like other ion-exchange resins, it is often made into granules and looks a bit like fish eggs. The particle size is about 0.3 ~ 1.2 mm, but most of them are in the range of 0.4 ~ 0.6 mm. The chemical properties are quite stable, the touch is hard and flexible, and the mechanical strength is sufficient to withstand considerable pressure. The color ranges from white to almost black. When the color is light, it is transparent, when it is dark, it is translucent, and it has a bright resin luster. . The most common application of hydrogen-type cation exchange resins is the softening of hard water, that is, let hard water flow through the resin layer, and absorb the “hardness ions” in the hard water, such as calcium and magnesium ions, into the resin, which becomes non-hardness ions. This is also the main purpose of the initial manufacture of cation exchange resin, but it is not as much as the “sodium type” in industrial applications, because in the softening process, it will directly release hydrogen ions, making the water acidic. It may corrode related metal equipment. Depending on the needs, it can also be used in water pretreatment processes to soften water and lower pH.

2. Type

The difference between the main properties and types of resins lies in their chemically active groups. Therefore, hydrogen cation exchange resins can be divided into two types according to the types of active groups (a functional group): strong-acid cation exchange resins. anion exchange resin) and weak-acid anion exchange resin (weak-acid anion exchange resin). The strong acid cation exchange resin is named because its active hydrogen ions are easily dissociated in water. Its skeleton is all polystyrene system. The main product is the “sulfonic acid type” strong acid cation exchange resin. The skeleton is all polyacrylic acid system. The main product is “carboxylic acid type” weakly acidic cation exchange resin. Usually the color is white or light yellow spherical sub-exchange resin. Usually the color is darker, brown-yellow to multi-colored spherical particles, with comprehensive color The most common; on the contrary, the weakly acidic cation exchange resin is because its active hydrogen ions are relatively incapable of particles in water, and light yellow is the most common. If a chemical reaction is used to express the difference between these two resins, we can describe it as follows (R stands for resin matrix): Strong acidity: R-SO3H → R-SO3- + H+ (H+ is easy to dissociate and is strongly acidic in water) Weak acidity: R-COOH → R-COO- + H+ (H+ is not easy to dissociate, and is weakly acidic in water) Because of the strong dissociation ability of strong acid cation exchange resin, it can be dissociated in any acidic or alkaline solution Ion and produce ion exchange, and its pH range is 1-14. On the contrary, the dissociation ability of weakly acidic cation exchange resin is very weak, and it can only dissociate and produce ion exchange in weakly acidic to alkaline solutions, and its pH range is only 5-14.

A400 anion softener resin

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