Anion exchange resin 阴离子交换树脂

There are many ionizable and exchangeable groups on the skeleton of its network structure, such as sulfonic acid group (- SOH), carboxyl group (- COOH) and quaternary amine group (- NROH). It is the existence of these groups that makes the resin have ion exchange ability.

There are many kinds of ion exchange resin, polystyrene type ion exchange resin is commonly used. It is polymerized with styrene and divinylbenzene to form a spherical network structure, in which divinylbenzene is a cross-linking agent. After sulfonation with concentrated sulfuric acid, polystyrene sulfonic acid cation exchange resin is prepared.

If other groups are used instead of sulfonic groups, a series of cation exchange resins can be obtained. For example, - COOH, - OH, etc. The hydrogen ions on these groups can be exchanged by cations in the sample solution.

Ion exchange resin contains a certain amount of water, which shall be kept as much as possible during transportation and storage. If the resin is dewatered during storage, it should be soaked with concentrated salt water (- 10%) first, and then gradually diluted. It should not be directly put into water to prevent the resin from being broken due to rapid expansion.

During long-term storage, strong resin shall be transformed into salt type, weak resin can be transformed into corresponding hydrogen type, free alkali type or salt type, and then soaked in clean water. During storage or transportation, the resin shall be kept at a temperature of 5-40 ° C to avoid supercooling or overheating, which may affect the quality. If there is no thermal insulation equipment in winter, the resin can be stored in salt water. The temperature of salt water can be determined according to the temperature.

The anion exchange resin has the same organic skeleton as the cation exchange resin, except that dissociatable basic groups, such as - NH, - NH, - NHR, are introduced into the skeleton. If this kind of resin is treated with NaOH solution, exchange reaction will occur and it will be transformed into OH type anion exchange resin. The reaction is as follows:

R—N(CH)Cl + OH ====== R—N(CH)OH + C1

The hydroxyl ions on these groups can be exchanged by anions in the sample solution.

Cation resin is divided into weak resin and strong resin. The molecular formula is H-R (of course, it can also be Na-R type), and H is hydrogen ion. The height of resin is about 0.8m to 1.6m. When the water passes through the resin layer from top to bottom, the cation in the water exchanges with the H ion of the resin. The top layer of the resin is iron calcium magnesium ion, followed by potassium sodium ammonia ion.

The effluent quality is acidic, and the PH value is generally less than 3. When operating for about one day, sodium ions begin to appear in the effluent, indicating that the reaction has reached the end point, and acid (HCl) backwashing is required to replace sodium and calcium ions.