What kinds of ion exchange resins can be divided according to their functions and uses?

Water treatment resin is divided into cationic resin and anionic resin, and cationic resin is subdivided into sodium type and hydrogen type. Sodium resin exchanges calcium and magnesium ions in water into sodium ions to soften water. Hydrogen resin exchanges calcium and magnesium ions in water with hydrogen ions to soften the water. Anionic resin contains replaceable hydroxyl ions, which can replace acid ions in water. Using anionic resin and hydrogen cationic resin at the same time can change water into pure water. Pore structure can be divided into gel type and macroporous type. Any macroporous resin with physical pore structure is called macroporous resin, and the full name is preceded by "macroporous". If it is classified as acidic, add "Yang" before the name; If it is classified as alkaline, add "Yin" before the name. Such as macroporous strong acid styrene cation exchange resin. Ion exchange resin can also be divided into styrene resin and acrylic resin according to the type of its matrix. The types of chemically active groups in resin determine the main properties and types of resin. Firstly, it is divided into two categories: cationic resin and anionic resin, which exchange ions with cations and anions in solution respectively. Cationic resins are divided into strong acidity and weak acidity, and anionic resins are divided into strong alkalinity and weak alkalinity (or divided into medium strong acidity and medium strong alkalinity). Naming method of ion exchange resin: the model of ion exchange product consists of three Arabic numerals, the first numeral represents the classification of the product, the second numeral represents the difference of skeleton, and the third numeral is the sequence number to distinguish the difference of gene, crosslinking agent, etc. See table 8- 1 for the meanings of the first and second digits. Table 8- 1 Meaning code of one or two digits in resin model 0 1 2 3 4 5 6 Classification name Strong acid, weak acid and weak base coalesce amphoteric redox skeleton name Styrene acrylic acid, acetic acid, epoxy ethylene pyridine urea formaldehyde vinyl chloride macroporous resin model is preceded by "D", and Arabic numerals are connected with "×" after the model to indicate the crosslinking degree of gel resin. For example, D0 1 1×7 represents a macroporous strong acid styrene cation exchange resin with a crosslinking degree of 7. There are many manufacturers and varieties of ion exchange resins at home and abroad. There are dozens of domestic manufacturers, mainly including Shanghai Resin Co., Ltd., Nankai Chemical Plant, Zhejiang Zheng Guang Industrial Co., Ltd., Chen Guang Chemical Research Institute Resin Factory, Jiangsu Sikes Resin Co., Ltd., etc. More famous abroad, such as American Rohm &; Amberlite series produced by Hass Company, Ionresin series produced by Success Company, Dowex series produced by Dow Chemical Company, Duolite series and Asmit series in France, Diaion series, Ionac series and Allassion series in Japan, etc. The brand of resin is mostly decided by each manufacturer or host country. Some foreign products use the letter C to represent cationic resin (C stands for the initial letter of cation) and A stands for anionic resin (A stands for the initial letter of anion). For example, Amberlite's IRC and IRA stand for cationic resin and anionic resin respectively. According to the regulations of China Ministry of Chemical Industry (HG2-884-76), the model of ion exchange resin consists of three Arabic numerals. The first digit represents the product classification: 0 stands for strong acidity, 1 stands for weak acidity, 2 stands for strong alkalinity, 3 stands for weak alkalinity, 4 stands for chelation, 5 stands for amphoteric, and 6 stands for redox. The second digit represents different skeleton structures: 0 represents styrene system, 1 represents acrylic system, 2 represents phenolic system and 3 represents epoxy system. The third place is the serial number, which is used to distinguish the difference between matrix and crosslinking group. In addition, the letter D is in front of the macroporous resin, so D00 1 is a macroporous strongly acidic styrene resin. 2. Basic ion exchange resin (1) Strongly acidic cationic resin This kind of resin contains a large number of strongly acidic groups, such as sulfonic acid group-SO3H, which easily dissociates H+ in solution, so it is strongly acidic. After the resin is dissociated, the anion groups contained in the body, such as SO3-,can adsorb other cations in the binding solution. These two reactions make H+ in the resin exchange with cations in the solution. Strong acid resin has strong dissociation ability, which can dissociate in acidic or alkaline solution to produce ion exchange. After a period of use, the resin should be regenerated, that is, it should react with chemicals in the opposite direction, so that the functional groups of the resin can be restored to their original state and reused. The cationic resin is regenerated with strong acid, at this time, the resin releases adsorbed cations, and then combines with H+ to restore the original composition. (2) Weakly acidic cationic resins These resins contain weakly acidic groups, such as carboxyl-COOH, which can dissociate H+ in water and become acidic. After the resin is dissociated, the remaining anionic groups, such as R- COO (R is hydrocarbyl), can be adsorbed and combined with other cations in the solution, thus generating cation exchange. This kind of resin is weak in acidity, so it is difficult to dissociate and exchange ions at low pH value, and it can only work in alkaline, neutral or weakly acidic solutions (such as pH 5 ~ 14). This resin is also regenerated by acid (it is easier to regenerate than strong acid resin). (3) Strongly Basic Anionic Resin This kind of resin contains strongly basic groups, such as quaternary amino (also known as quaternary amino) -NR3OH (R is hydrocarbyl), which can dissociate OH- in water and become strongly basic. Cationic groups of this resin can be adsorbed and combined with anions in solution, thus generating anion exchange. This resin is highly decomposable and can work normally at different pH values. Regenerate with strong alkali (such as NaOH). (4) Weak Basic Anionic Resin This kind of resin contains weak basic groups, such as primary amino (also called primary amino) -NH2, secondary amino (secondary amino) -NHR, or tertiary amino (tertiary amino) -NR2, which can dissociate OH- in water and become weak basic. Cationic groups of this resin can be adsorbed and combined with anions in solution, thus generating anion exchange. In most cases, this resin absorbs 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 by Na2CO3 and NH4OH. (5) Conversion of ionic resins The above are the four basic types of resins. In practical use, these resins are often converted into other ion types to meet various needs. For example, strongly acidic cationic resins often react with NaCl and are converted into sodium resins for reuse. During operation, Na+ released from sodium resin exchanges and adsorbs with Ca2+, Mg2+ and other cations in the solution, and these ions are removed. H+ is not released during the reaction, which can avoid the decrease of pH value of the solution and the resulting side effects (such as sucrose conversion and equipment corrosion). After this resin is used in the form of sodium, it can be regenerated with brine (no strong acid). Another example is that anion resin can be converted into chlorine type for reuse, and Cl- is released when working, and other anions are adsorbed and exchanged, and its regeneration only needs saline solution. Chlorine resin can also be converted into bicarbonate (HCO 3-). Strong acid resin and strong base resin will no longer have strong acid and strong base after being converted into sodium type and chlorine type, but they still have other typical properties of these resins, such as strong dissociation and wide working pH range. Three. Composition of ion exchange resin matrix ion exchange resin matrix is mainly composed of styrene and acrylic acid (ester), which are polymerized with divinylbenzene, a cross-linking agent, respectively, to form a polymer with a long molecular skeleton and a cross-linked cross-linked network skeleton structure. First use styrene resin, then use acrylic resin. These two resins have good adsorption properties, but each has its own characteristics. Acrylic resin can exchange and adsorb most ionic pigments, with a large amount of decolorization, and the adsorbate is easy to elute and regenerate, so it can be used as the main decolorizing resin in sugar factories. Styrene resin is good at adsorbing aromatic substances and polyphenol pigments (including negatively charged or uncharged) in sugar juice; But it is difficult to elute during regeneration. Therefore, the advantages of the two methods can be fully exerted by using acrylic resin for rough decoloration and then using styrene resin for fine decoloration. The crosslinking degree of resin, that is, the percentage of divinylbenzene used in the polymerization of resin matrix, has great influence on the properties of resin. Generally, resins with high crosslinking degree are tightly polymerized, firm and durable, with high density, few internal gaps and strong ion selectivity; However, the resin with low crosslinking degree has larger pores, stronger decoloring ability and faster reaction speed, but it has greater expansibility, lower mechanical strength and is brittle when working. The crosslinking degree of industrial ionic resin is generally not less than 4%; The crosslinking degree of resin for decoloration is generally not higher than 8%; The cross-linking degree of the resin simply used for adsorbing inorganic ions can be higher. In addition to the above two series of styrene series and acrylic series, ion exchange resin can also be polymerized from other organic monomers. Such as phenolic resin (FP), epoxy resin (EPA), vinyl pyridine resin (VP), urea-formaldehyde resin (UA) and so on. Four. Physical structure of ion exchange resins Ionic resins are usually divided into gel type and macroporous type. The polymer skeleton of the gel resin has no pores when it is dried. It expands after absorbing water, forming pores between macromolecular chains, which are usually called micropores. The average pore size of wet resin is 2 ~ 4 nm (2×10-6 ~ 4×10-6 mm). These resins are suitable for adsorbing inorganic ions, and their diameters are relatively small, generally 0.3 ~ 0.6 nm. This resin can't absorb macromolecular organic matter, because the size of the latter is relatively large, for example, the diameter of protein molecules is 5 ~ 20nm, so it can't enter the micropores of this resin. Macroporous resin is made by adding pore-forming agent in the polymerization process to form a porous sponge skeleton with a large number of permanent micropores inside, and then introducing exchange groups. It has both big holes and big holes. The pore size of wetting resin is 100 ~ 500 nm, and its size and quantity can be controlled in the manufacturing process. The surface area of pores can be increased to more than1000 m2/g. Jiangsu Sikes Resin Co., Ltd. not only provides good contact conditions for ion exchange, shortens the distance of ion diffusion, but also adds many chain-like active centers, which can adsorb various nonionic substances like activated carbon, and expand its functions through intermolecular van der Waals force and molecular adsorption. Some macroporous resins without exchange functional groups can also adsorb and separate many substances, such as phenols in chemical plant wastewater. Macroporous resin has many pores, large surface area, many active centers, and fast ion diffusion and exchange, which is about ten times faster than gel resin. When in use, it has quick response and high efficiency, and shortens the required treatment time. Macroporous resin also has many advantages: it is resistant to swelling, not easy to break, oxidation, wear, heat, temperature change and easy to adsorb and exchange organic macromolecules, so it has strong anti-pollution ability and is easy to regenerate. V. Ion exchange capacity of ion exchange resin The performance of ion exchange resin in ion exchange reaction is its "ion exchange capacity", that is, the number of milliequivalents 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 milligram equivalents is the number of milligram molecules (for divalent or multivalent ions, the former is the latter multiplied by the ionic valence). It has three forms: total exchange capacity, working exchange capacity and regenerative exchange capacity. 1, total exchange capacity, indicating the total number of chemical groups that can undergo ion exchange reaction per unit amount (weight or volume) of resin. 2. Working exchange capacity refers to the ion exchange capacity of resin under certain conditions, which is related to the type and total exchange capacity of resin, and also to specific working conditions such as solution composition, flow rate, temperature and other factors. 3. The regeneration exchange capacity refers to the regeneration exchange capacity of the resin obtained under a certain regeneration dose, indicating the regeneration and recovery degree of the original chemical groups in the resin. The regeneration exchange capacity is generally 50 ~ 90% of the total exchange capacity (generally controlled at 70 ~ 80%), while the working exchange capacity is 30 ~ 90% of the regeneration exchange capacity (used for resin regeneration). The latter ratio is also called resin utilization rate. In practical use, the exchange capacity of ion exchange resin includes adsorption capacity, but the proportion of the latter varies with the structure of the resin. At present, it cannot be calculated separately. In the specific design, it needs to be revised according to the empirical data, and tested in the actual operation. The determination of exchange capacity of ionic resin is generally carried out with inorganic ions. These ions are small in size and can freely diffuse into the resin and react with all exchange groups inside the resin. However, in practical application, the solution often contains high molecular organic compounds, which are large in volume and difficult to enter the micropores of the resin, so the actual exchange capacity will be lower than the value measured by inorganic ions. This situation is related to the type of resin, the structural size of the hole and the substance to be treated. 6. Adsorption Selectivity of Ion Exchange Resin Ion exchange resins have different affinities for different ions in solution and are selective for their adsorption. The degree of exchange adsorption of various ions by resins has a general law, but different resins may be slightly different. The main rules are as follows: (1) High-valent ions usually have priority adsorption, while low-valent ions have weak adsorption. Among the ions with the same valence, the ions with larger diameter are strongly adsorbed. The adsorption order of some cations is: Fe3+>; Al3+>； Pb2+>； Ca2+>； Mg2+>； k+& gt； na+& gt； Adsorption of anions by H+ (2) The general order of adsorption of inorganic acid radicals by strongly basic anion exchange resin is SO42->; NO3->； cl->； HCO 3-& gt； The general order of anion adsorption by OH- weakly basic anion exchange resin is: OH->; Citrate 3->; SO42->； 2-> tartrate; Oxalate II->; PO43->； NO2- & gt； cl->； Acetate->; HCO3- (3-(3)) absorbs colored substances. Strong basic anion exchange resin is often used to decolorize sugar solution. It has strong adsorption on melanin (the reaction product of reducing sugar and amino acid) and alkaline decomposition product of reducing sugar, but weak adsorption on caramel pigment. This is thought to be because the first two are usually negatively charged, while caramel has a weak charge. Generally, resin with high crosslinking degree has strong ion selectivity, while resin with macroporous structure has lower ion selectivity than gel resin. This selectivity is larger in dilute solution and smaller in concentrated solution. Seven. Physical properties of ion exchange resin The particle size and related physical properties of ion exchange resin have great influence on its work and performance. (1) resin The particle size of ion exchange resin is usually made into beads, and the size is also very important. The reaction speed of resin particles is high, but the resistance of particles to the passage of liquid is large, which requires higher working pressure; Especially, the concentrated sugar solution has high viscosity, and this effect is more significant. Therefore, the size of resin particles should be properly selected. If the particle size of resin is below 0.2 mm (about 70 mesh), it will obviously increase the resistance of fluid passing through and reduce the flow and production capacity. The particle size of resin is usually determined by wet sieve method. After fully absorbing water and swelling, the resin is sieved, and its retention on the sieve of 20, 30, 40 and 50 meshes is accumulated, so that 90% of the particles can pass through its corresponding sieve hole diameter, which is called the "effective particle size" of the resin. The effective particle size of the most common resin products is between 0.4 and 0.6 mm, and whether the resin particles are uniform or not is expressed by the uniformity coefficient. According to the "effective particle size" coordinate diagram of the measured resin, the corresponding ratio of the particle with cumulative retention of 40% and the mesh diameter to the effective particle size is taken. For example, the effective particle size of a resin (IR- 120) is 0.4 ~ 0.6 mm, and the particles retained on the 20-mesh sieve, 30-mesh sieve and 40-mesh sieve are 18.3%, 4 1. 1% and 3/kloc-respectively. (2) Density of resin The density of resin when it is dry is called true density. The weight of wet resin per unit volume (even the gap between particles) is called apparent density. The density of resin is related to its crosslinking degree and the properties of exchange groups. Generally, resins with high crosslinking degree have higher density, resins with strong acidity or alkalinity have higher density than resins with weak acidity or alkalinity, and macroporous resins have lower density. For example, the true density of styrene gel-type strong acid cationic resin is 1.26g/mL, and the apparent density is 0.85g/mL；; However, the true density of acrylic gel weak acid cationic resin is 1. 19g/mL, and the apparent density is 0.75g/mL. (3) The resin of soluble ion exchange resin should be insoluble. However, substances with low polymerization degree mixed in the process of resin synthesis and substances produced by resin decomposition will dissolve in the process of operation. Resins with lower crosslinking degree and more active groups have a greater tendency to dissolve. (4) Swelling ion exchange resin contains a large number of hydrophilic groups, which will swell in water. When the ions in the resin change, such as the cation resin changes from H+ to Na+, and the anion resin changes from Cl- to OH-, they all expand due to the increase of ion diameter, which increases the volume of the resin. Generally, resins with low crosslinking degree have higher swelling degree. When designing ion exchange device, the expansion degree of resin must be considered to adapt to the change of resin volume caused by ion transformation in resin during production and operation. (5) Durable resin particles have changes such as transfer, friction, expansion and contraction when used, and there will be a little loss and damage after long-term use, so the resin should have high mechanical strength and wear resistance. Generally, the resin with low crosslinking degree is easy to break, but the durability of the resin mainly depends on the uniformity and strength of the crosslinked structure. Such as macroporous resin with high crosslinking degree, stable structure and repeated regeneration resistance. 8. Application field of ion exchange resin: 1) There is a great demand for ion exchange resin in the field of water treatment, accounting for about 90% of the output of ion exchange resin, which is used to remove various anions and cations in water. At present, the largest consumption of ion exchange resin is pure water treatment for thermal power plants, followed by atomic energy, semiconductor and electronics industries. 2) Ion exchange resin in food industry can be used in industrial devices such as sugar making, monosodium glutamate, wine making and biological products. For example, high-fructose syrup is to extract starch from corn, then hydrolyze it to produce glucose and fructose, and then carry out ion exchange to produce high-fructose syrup. The consumption of ion exchange resin in food industry is second only to water treatment. 3) Ion exchange resin in pharmaceutical industry plays an important role in developing a new generation of antibiotics and improving the quality of original antibiotics. The successful development of streptomycin is a prominent example. In recent years, it has also been studied in the Chinese Medicine Committee. 4) In synthetic chemistry and petrochemical industry, acids and bases are often used as catalysts for esterification, hydrolysis, transesterification and hydration. It is also more advantageous to use ion exchange resin instead of inorganic acid and alkali to carry out the above reaction. For example, the resin can be reused, the product is easy to separate, the reactor will not be corroded, the environment will not be polluted, and the reaction is easy to control. Methyl tert-butyl ether (MTBE) was prepared by the reaction of isobutylene and methanol with macroporous ion exchange resin as catalyst, which replaced tetraethyl lead which caused serious environmental pollution. 5) Environmental-friendly ion exchange resin has been applied to many environmental problems that have attracted much attention. At present, many aqueous or non-aqueous solutions contain toxic ions or non-ionic substances, which can be recovered by resin. Such as removing metal ions from electroplating waste liquid and recovering useful substances from film production waste liquid. 6) Hydrometallurgy and other ion exchange resins can separate, concentrate and purify uranium from depleted uranium ore, and extract rare earth elements and precious metals. Other supplements: ion exchange technology has a long history, and some natural substances such as zeolite and sulfonated coal made from coal sulfonation can be used as ion exchangers. However, with the rapid development of modern organic synthesis industry technology, people have researched and developed a variety of ion exchange resins with excellent performance and developed many new application methods. Ion exchange technology has developed rapidly and is widely used in many industries, especially in high-tech industries and scientific research fields. In recent years, hundreds of resins have been produced at home and abroad, with an annual output of several hundred thousand tons. In industrial application, the advantages of ion exchange resin are mainly large capacity, wide decolorization range, high decolorization ability, ability to remove various ions, long service life and low operating cost (although the one-time investment cost is large). Many new technologies based on ion exchange resin, such as chromatographic separation, ion exclusion, electrodialysis, etc. , has its own unique function, can perform various special tasks, which is difficult to achieve by other methods. The development and application of ion exchange technology are still developing rapidly. The application of ion exchange resin is a key research topic in sugar industry at home and abroad in recent years, and it is an important symbol of sugar modernization. The application of membrane separation technology in sugar industry has also been widely studied. Ion exchange resins are all organically synthesized. The commonly used raw material is styrene or acrylic acid (ester), which generates a skeleton with a three-dimensional network structure through polymerization, and then introduces different types of chemically active groups (usually acidic or basic groups) into the skeleton. Ion exchange resin is insoluble in water and general solvents. Most of them are made into granules, and some are made into fibers or powders. The particle size of resin is generally in the range of 0.3 ~ 1.2 mm, mostly in the range of 0.4 ~ 0.6 mm, with high mechanical strength (fastness), stable chemical properties and long service life under normal conditions. Ion exchange resin contains one (or several) chemically active groups, that is, exchange functional groups, which can dissociate some cations (such as H+ or Na+) or anions (such as OH- or Cl-) in aqueous solution and adsorb other cations or anions in the solution. That is, the ions in the resin exchange with the ions in the solution, so as to separate the ions in the solution. There are many kinds of ion exchange resins, which have different functions and characteristics due to different chemical compositions and structures, and are suitable for different purposes. Appropriate resin types and varieties should be selected according to process requirements and material properties. Luanhe river water treatment