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What Are The Types And Applications Of Ion Exchange Resins

Jul 20, 2020

Ion exchange resins are commonly used in raw water treatment with sodium-type cation exchange resins and anion exchange resins. The full names are composed of classification names, skeleton (or gene) names, and basic names. According to the acidity and alkalinity of the resin, add "positive" before the name if it is acidic. The strong acid cation resin reacts with NaCl to convert it into sodium-type resin, which is called "sodium-type cation exchange resin". Add "yin" before the name if it is alkaline.

   Ion exchange resins are commonly used in raw water treatment with sodium-type cation exchange resins and anion exchange resins. The full names are composed of classification names, skeleton (or gene) names, and basic names. According to the acidity and alkalinity of the resin, add "positive" before the name if it is acidic. The strong acid cation resin reacts with NaCl to convert it into sodium-type resin, which is called "sodium-type cation exchange resin". Add "yin" before the name if it is alkaline.


  1, strong acid cationic resin


   This type of resin contains a large number of strong acid groups, such as sulfonic acid group -SO3H, which easily dissociates H+ in the solution, so it is strongly acidic. After the resin dissociates, the negatively charged groups contained in the body, such as SO3-, can adsorb and bind other cations in the solution. These two reactions exchange the H+ in the resin with the cations in the solution. Strong acid resin has strong dissociation ability, and can dissociate and produce ion exchange in acid or alkaline solution.


After using for a period of time, the resin needs to be regenerated, that is, the ion exchange reaction is carried out in the opposite direction with chemicals to restore the functional groups of the resin to its original state for reuse. The above-mentioned cationic resin is regenerated with strong acid. At this time, the resin releases the adsorbed cations, and then combines with H+ to restore the original composition.


  2, weakly acidic cationic resin


   This kind of resin contains weakly acidic groups, such as carboxyl -COOH, which can dissociate H+ in water and become acidic. After the resin dissociates, the remaining negatively charged groups, such as R-COO- (R is a hydrocarbon group), can be combined with other cations in the solution to produce cation exchange. The acidity of this resin is weak, and it is difficult to dissociate and perform ion exchange at low pH. It can only work in alkaline, neutral or slightly acidic solutions (such as pH 5-14). This kind of resin is also regenerated with acid (it is easier to regenerate than strong acid resin).


  3, strong basic anion resin


   This kind of resin contains strong basic groups, such as quaternary amine group (also known as quaternary amine group) -NR3OH (R is a hydrocarbon group), which can dissociate OH- in water and become strongly basic. The positively charged groups of this resin can adsorb and combine with the anions in the solution to produce anion exchange.


  This kind of resin has strong dissociation and can work normally under different pH. It uses strong alkali (such as NaOH) for regeneration.


  4, weakly basic anion resin


This type of resin contains weakly basic groups, such as primary amino groups (also known as primary amino groups) -NH2, secondary amino groups (secondary amino groups) -NHR, or tertiary amino groups (tertiary amino groups) -NR2, They can dissociate from OH- in water and become weakly alkaline. The positively charged groups of this resin can adsorb and combine with the anions in the solution to produce anion exchange. In most cases, this resin adsorbs all other acid molecules in the solution. It can only work under neutral or acidic conditions (such as pH 1-9). It can be regenerated with Na2CO3 and NH4OH.


   Ion exchange capacity of ion exchange resin


The performance of ion exchange resin for ion exchange reaction is manifested in its "ion exchange capacity", which is the number of milligram equivalents of ions that can be exchanged per gram of dry resin or per milliliter of wet resin, meq/g (dry) or meq/mL (Wet); When the ion is monovalent, the number of milliequivalents is the number of milligrams (for divalent or multivalent ions, the former is the latter multiplied by the valence of the ion). It also has three expressions: "total exchange capacity", "working exchange capacity" and "regeneration exchange capacity".


  1. Total exchange capacity means the total amount of chemical groups that can undergo ion exchange reaction per unit quantity (weight or volume) of the resin.


  2. Working exchange capacity means the ion exchange capacity of the resin under certain conditions. It is related to the type of resin and total exchange capacity, as well as specific working conditions such as the composition of the solution, flow rate, temperature and other factors.


  3. Regeneration exchange capacity means the exchange capacity of the regenerated resin obtained under a certain amount of regeneration, indicating the degree of regeneration of the original chemical groups in the resin.


Generally, the regeneration exchange capacity is 50-90% of the total exchange capacity (generally controlled 70-80%), and the working exchange capacity is 30-90% of the regeneration exchange capacity (for recycled resin). The latter ratio is also called Utilization rate of resin.


  In actual use, the exchange capacity of the ion exchange resin includes the adsorption capacity, but the proportion of the latter varies depending on the resin structure. It is still not possible to calculate separately. In the specific design, it needs to be corrected based on empirical data and rechecked in actual operation.


"The measurement of ion resin exchange capacity is generally performed with inorganic ions." These ions are small in size and can diffuse freely into the resin body and react with all the exchange groups inside it. In practical applications, the solution often contains high molecular weight organic compounds, which are large in size and difficult to enter the micropores of the resin, so the actual exchange capacity will be lower than the value measured with inorganic ions. This situation is related to the type of resin, the size of the pore structure and the material being processed.


   Application fields of ion exchange resin:


  1) Water treatment


  The demand for ion exchange resins in the water treatment field is very large, accounting for about 90% of the output of ion exchange resins, which are used to remove various anions and cations in water. At present, the largest consumption of ion exchange resins is used in pure water treatment in thermal power plants, followed by atomic energy, semiconductors, and electronics industries.


   2) Food industry


   ion exchange resin can be used in sugar, monosodium glutamate, wine refining, biological products and other industrial equipment. For example, the production of high fructose syrup is to extract starch from corn, and then undergo hydrolysis to produce glucose and fructose, and then undergo ion exchange treatment to produce high fructose syrup. The consumption of ion exchange resin in the food industry is second only to water treatment.


  3) Pharmaceutical industry


  The ion exchange resin in the pharmaceutical industry plays an important role in the development of a new generation of antibiotics and the quality improvement of the original antibiotics. The successful development of streptomycin is a prominent example. In recent years, research has also been done on the commission of Chinese medicine.


  4) Synthetic chemistry and petrochemical industry


"In organic synthesis, acids and bases are commonly used as catalysts for esterification, hydrolysis, transesterification, hydration and other reactions. Using ion exchange resins instead of inorganic acids and bases can also carry out the above reactions, and has more advantages. For example, the resin can be used repeatedly, the product is easy to separate, the reactor will not be corroded, the environment will not be polluted, and the reaction can be easily controlled.


   Methyl tert-butyl ether (MTBE) is prepared by using a macroporous ion exchange resin as a catalyst, which is formed by the reaction of isobutylene and methanol, instead of the original tetraethyl lead, which can cause serious environmental pollution.


  5) Environmental protection


   Ion exchange resins have been applied to many environmental protection issues that are of great concern. At present, many aqueous or non-aqueous solutions contain toxic ions or non-ionic substances, which can be recycled with resin. Such as removing metal ions in electroplating waste liquid, and recovering useful substances in film production waste liquid.


  6) Hydrometallurgy and others


   Ion exchange resin, cation exchange resin, and anion exchange resin can separate, concentrate, purify uranium and extract rare earth elements and precious metals from depleted uranium ore

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

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