Basic types of ion exchange resins
(1) Strong acid cation resin
This kind of resin contains a large number of strong acidic groups, such as sulfo SO3H, which is easy to dissociate H+in solution, so it is strongly acidic. After the resin is dissociated, the negative group contained in the body, such as SO3 -, can adsorb other cations in the bound solution. These two reactions make the H+in the resin exchange with the cation in the solution. Strong acidic resin has strong dissociation ability, which can dissociate and produce ion exchange in acidic or alkaline solutions.
After a period of use, the resin shall be regenerated, that is, the ion exchange reaction shall be conducted in the opposite direction with chemicals to restore the functional groups of the resin to the original state for reuse. For example, the above cation resin is regenerated with strong acid. At this time, the resin emits the adsorbed cation, and then combines with H+to restore the original composition.
(2) Weak acid cation resin
These resins contain weak acidic groups, such as carboxyl COOH, which can dissociate H+in water and become acidic. The remaining negative groups after the resin dissociation, such as R-COO - (R is a hydrocarbon group), can be adsorbed and combined with other cations in the solution to produce cation exchange. This kind of resin is weak in acid or dissociation. It is difficult to dissociate and conduct ion exchange at low pH, and can only function in alkaline, neutral or slightly acidic solutions (such as pH5-14). This kind of resin is also regenerated with acid (easier to regenerate than strong acid resin).
(3) Strong base anion resin
This kind of resin contains strong basic groups, such as quaternary amino group (also called quaternary amino group) - NR3OH (R is hydrocarbon group), which can dissociate OH in water and become strongly alkaline. The positive group of the resin can combine with the anion adsorption in the solution to produce anion exchange.
This kind of resin has strong dissociation and can work normally at different pH. It is regenerated with strong alkali (such as NaOH).
(4) Weakly basic anion resin
These resins contain weakly basic groups, such as primary amino (also called primary amino) - NH2, secondary amino (secondary amino) - NHR, or tertiary amino (tertiary amino) - NR2. They can dissociate OH - in water and become weakly alkaline. The positive group of the resin can combine with the anion adsorption in the solution to produce anion exchange. In most cases, this resin will adsorb all other acid molecules in the solution. It can only work under neutral or acidic conditions (such as pH1-9). It can be regenerated with Na2CO3 and NH4OH.
(5) Transformation of ionic resin
These are the four basic types of resins. In practical use, these resins are often converted to other ionic types for operation to meet various needs. For example, the strong acidic cation resin is often used to react with NaCl and change into sodium resin for reuse. During operation, the sodium resin emits Na+to exchange with Ca2+, Mg2+and other cations in the solution to remove these ions. No H+is released during the reaction, which can avoid pH drop of solution and side effects (such as sucrose conversion and equipment corrosion). After the resin is used in sodium type, it can be regenerated with brine (without strong acid). For another example, the anion resin can be converted to chlorine type for reuse, releasing Cl - while adsorbing and exchanging other anions during operation, and its regeneration only requires salt aqueous solution. Chlorine resin can also be converted to hydrogen carbonate (HCO3 -) for operation. After the strong acid resin and strong basic resin are converted to sodium type and chlorine type, they no longer have strong acid and strong basic, but they still have other typical properties of these resins, such as strong dissociation and wide working pH range.
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