Various knowledge points about ion exchange resin

What factors affect the properties of ion exchange resins?

      Ion exchange resins should be insoluble substances. However, substances with lower polymerization degree mixed during the synthesis process, and substances generated by resin decomposition, will dissolve during operation. Resins with lower crosslinking degree and more active groups have a greater tendency to dissolve.

      Ion exchange resins contain a large number of hydrophilic groups and absorb water and swell upon contact with water. When the ions in the resin change, such as the cation resin from H+ to Na+ ，and the anion resin from Cl －to OH －, they all swell due to the increase in ion diameter, increasing the volume of the resin. Generally, resins with low crosslinking degree have a larger swelling degree. When designing ion exchange equipment, the swelling degree of the resin must be considered to adapt to the volume changes of the resin caused by ion conversion during production operation.

      Ion exchange resin particles undergo changes such as transfer, friction, expansion, and contraction during use. After long-term use, a small amount of loss and breakage will occur, so the resin must have high mechanical strength and wear resistance. Generally, resins with low crosslinking degree are more easily fractured, but the durability of the resin is mainly determined by the uniformity and strength of the crosslinking structure. For example, macroporous resins with high crosslinking degree have stable structures and can withstand repeated regeneration.

Principle of Ion Exchange Resins

      Ion exchange resins can be divided into cation exchange resins, anion exchange resins, and amphoteric ion exchange resins. Ion exchange resins are insoluble in water and common solvents. Most are made into granular form, and some are made into fibrous or powdery form. The size of the resin particles is generally in the range of 0.3 ～ 1.2mm ，most of them are between 0.4 ～ 0.6mm之间。它们有较高的机械强度( They have high mechanical strength ) and firmness, and are also chemically stable, with a long service life under normal conditions. According to the chemical active groups, they are first divided into two major categories: cation resins and anion resins. Cation resins are further divided into strong acid and weak acid types. The working principle of ion exchange resins: In the ion exchange process, cations in water, such as ( such as Na+ 、 Ca2+ 、 K+ 、 Mg2+ 、 Fe3+ etc. ) exchange with H+ on the cation exchange resin, the cations in the water are transferred to the resin, while H+ is exchanged into the water. Anions in water ( such as Cl-、HCO3- etc. ) exchange with OH- on the anion exchange resin, anions in the water are transferred to the resin, while OH- is exchanged into the water. And H+ and OH- combine to form water, thus achieving the purpose of desalination.

Precautions for Using Ion Exchange Resins

      Different types of ion exchange resins have different chemical compositions and structures, and therefore have different uses. When using resins, carefully select them according to their properties. In general, there are several points to note when using ion exchange resins.

    During winter storage and transportation, the temperature should be maintained at 5-40℃ to avoid excessive cold or heat, affecting the quality. If there is no insulation equipment in winter, the resin can be stored in brine, and the brine concentration can be determined according to the temperature. During the use of the resin, prevent contact with metals (such as iron, copper, etc.), oil stains, organic molecules, microorganisms, strong oxidants, etc., to prevent the ion exchange capacity from decreasing or even losing its function. Therefore, periodic activation treatment of the resin should be carried out according to the situation. The activation method can be determined according to the pollution situation and conditions. Generally, cation resins are easily contaminated by Fe during softening, and can be soaked in hydrochloric acid and then gradually diluted. Anion resins are easily contaminated by organic matter, and can be soaked or rinsed with 10%NaC1+2-5%NaOH mixed solution. If necessary, it can be soaked in 1% hydrogen peroxide solution for several minutes. Other methods include alternating acid-base treatment, bleaching treatment, alcohol treatment, and various sterilization methods.