Ion exchangers are solid, insoluble polyelectrolytes, natural or artificial (synthetic) materials widely used for water purification processes: from calcium and magnesium cations (softening), from organic acid anions, demineralization and some other special applications.

By chemical nature, ion exchangers are inorganic (mineral) and organic.

The most typical natural inorganic ion exchangers are zeolites. Clays, mica, graphite oxides, salts of polyacids of titanium, vanadium and many other compounds can also be attributed to ion exchangers.

Ion exchange resins

Synthetic, artificially obtained ion exchangers are called ion exchange resins.

Ion exchange resins are high molecular weight cross-linked compounds that form a polymer matrix containing functional groups acidic or basic type that dissociate or are able to ionize in water.

• functional groups of the acid type are: -COOH; -SO 3 H; -RO 4 H 2, etc.
• functional groups of the main type are: ≡N; =NH; -NH 2 ; -NR 3+ etc.

In appearance, ion-exchange resins are spherical material with a diameter of 0.3 to 2.0 mm (basic size within 0.5..0.8 mm), from almost colorless to yellow-brown, as a rule, slightly stuck together ( because wet).

By structure, ion-exchange resins can have a gel, macroporous, and intermediate structure, which is determined by the degree of cross-linking of polymer molecules. Gel ion exchange resin only has the ability to ion exchange when wet (swollen) because it lacks true porosity. Macroporous ion-exchange resin is characterized by the presence of pores with a developed surface, so it is capable of ion exchange both in swollen and not swollen state.

The grain diagram of an ion-exchange resin, anion exchanger and cation exchanger, respectively, in general terms looks like this:

1. polymer matrix
2. ionic functional groups of the polymer matrix
3. counterions

The functional groups mentioned above are capable of entering into ion exchange reactions with ions of dissolved substances (impurities - in relation to water). If the matrix of the ion exchange resin is designated as R, then the reaction of such an exchange looks like:

a) R - - H + + Na + + Cl - → R - - Na + + H + + Cl -

b) R + - OH - + Na + + Cl - → R + - Cl - + Na + + OH -

According to such a reaction, cations of hardness salts, iron and manganese ions are easily exchanged.

It can be seen from the above reactions that ion exchange resins can exchange cations (a) - in this case they are called cation exchangers, or exchange anions (b) - in this case they are called anion exchangers. In addition to the indicated ion-exchange reactions on ion-exchange resins, complex formation and redox reactions, as well as physical sorption, are possible.

The sorption properties of ion-exchange resins are determined not only by the nature of the functional groups, but also by the acidity (pH value) of the treated water.

Classification of ion exchange resins

Depending on the functional groups introduced into the polymer chain of the ion exchange resin, there are:

• -SO 3 H - strongly acidic cation exchanger,
• -COOH - weakly acidic cation exchanger.

A strongly acidic cation exchanger exchanges cations of any degree of dissociation in solutions at all possible pH values. A weakly acidic cation exchanger exchanges cations from acid solutions at pH >5.

• -NH 2, \u003d NH, ≡N - weakly basic anion exchanger,
• -NR 3 + Hal - - strongly basic anion exchange resin.

A strong base anion exchanger exchanges anions of any degree of dissociation in solutions at all possible pH values. A weakly basic anion exchanger exchanges anions from alkali solutions at pH values<8..9.

Characteristics of ion exchangers and ion exchange resins

The most important characteristics of ion exchangers are:

• total (total) exchange capacity- this is the maximum number of milligram-equivalents (mg-equiv) of ions of a substance absorbed by a unit of mass or volume of an ion exchanger in equilibrium with an electrolyte solution,
• dynamic (working) exchange capacity- this is the maximum number of mEq of ions absorbed by a unit of mass or volume under conditions of solution filtration through a layer of ion exchanger until the ions “leak through” into the filtrate.

The values ​​of the total exchange capacity of most ion-exchange resins are in the range of 2..5 meq/g (1..2.5 g-eq/dm3). The procedure for determining the exchange capacity is standardized.

The dynamic (working) exchange capacity is always less than the static one due to the fact that it depends on the following factors:

• the nature of the ion exchange resin,
• its granulometric composition,
• the quality of the source water, and the dependence is determined not only by the total number of trapped ions, but also by their ratio with each other, the presence of iron, manganese, organic impurities in the source water,
• the pH value of the source water, its temperature and the temperature of the regeneration solution,
• uniformity of the passage of purified water through the ion exchanger layer,
• the nature of the regenerant, its purity, concentration, specific consumption,
• the required indicators of the quality of the resulting water after filtering through an ion-exchange resin,
• the height of the ion exchanger layer, the speed of working, regeneration and loosening filtration,
• specific consumption of wash water,
• filtration area (area of ​​the horizontal section of the filter),
• addition of complexing agents and other factors to the regeneration solution.

Some filter materials ( ion exchangers) are able to absorb positive ions (cations) from water in exchange for an equivalent amount of cation exchanger ions.

Water softening by cationization is based on the phenomenon of ion exchange (ion exchange technologies), the essence of which is the ability of ion exchange filter materials (ion exchangers - cation exchangers) to absorb positive ions from water in exchange for an equivalent amount of cation exchanger ions.

The main operating parameter of the cation exchanger is the exchange capacity of the ion exchanger, which is determined by the number of cations that the cation exchanger can exchange during the filter cycle. The exchange capacity is measured in gram equivalents of retained cations per 1 m 3 of a cation exchanger in a swollen (working) state after being in water, i. in a state in which cation exchanger is in the filtrate.

There is a full and working (dynamic) exchange capacity of the cation exchanger. The total exchange capacity of the cation exchanger is the amount of calcium Ca +2 and magnesium Mg +2 cations that can hold 1 m 3 of the cation exchanger in working condition until the hardness of the filtrate is compared with the hardness of the source water. The working exchange capacity of the cation exchanger is the amount of Ca +2 and Mg +2 cations that retains 1m 3 of the cation exchanger until the “breakthrough” of hardness salt cations into the filtrate.

The exchange capacity, related to the entire volume of the cation exchanger loaded into the filter, is called the absorption capacity of the water softener filter.

In the softener, the treated water passes through the cation exchanger layer from top to bottom. At the same time, at a certain depth of the filter layer, the maximum softening of water occurs (from hardness salts). The layer of cation exchanger that participates in water softening, is called the softening zone (the working layer of the cation exchanger). With further softening of water, the upper layers of the cation exchanger are depleted and lose their ion-exchange capacity. The lower layers of the cation exchanger enter into ion exchange and the softening zone gradually descends. After some time, three zones are observed: working, depleted and fresh cation exchanger. The hardness of the filtrate will be constant until the lower boundary of the softening zone coincides with the lower layer of the cation exchanger. At the moment of combination, the “leakage” of Ca +2 and Mg +2 cations and an increase in residual hardness begin until it becomes equal to the hardness of the original water, which indicates the complete depletion of the cation exchanger.

The operating parameters of the water softening system () are determined by the formulas:

E p \u003d QЖ and (g-equiv / m 3)
E p \u003d e p V k,
V to = ah to
e p \u003d QЖ and / ah to
Q \u003d v to aT to \u003d e p ah to / F and
T to \u003d e p h to / v to Zh and.

where:
e p - working capacity of the cation exchanger, meq / m 3
V to - the volume of the cation exchanger loaded into the softener in the swollen state, m 3
h k - height of the cation exchanger layer, m
W and - hardness of the source water, g-eq / m 3
Q - the amount of softened water, m 3
a - cross-sectional area of ​​​​the water softener filter, m 2
v to - the rate of water filtration in the cationite filter
T to - the duration of the water softener (inter-regeneration period)

Introduction

The total exchange capacity of the anion exchange resin is determined by its neutralization with a solution of HCl or H 2 SO 4 under static or dynamic conditions and is expressed in equivalents per 1 g of dry or swollen anion exchange resin.

Anion exchange reactions / A-anion exchange resin / have the form:

A. /OH/ +H /Cl = A.OH.Cl +HO;

A. /OH/ + H /SO = A.SO +2HO.

In addition to the exchange capacity, the main indicators of the anion exchanger suitability include: discoloration, swelling degree, aging ability, insolubility in water and organic solvents, ease of regeneration, thermal and mechanical strength.

The total exchange capacity of various grades of anion exchangers used in the sugar industry can be 1–10 meq/g. The domestic macroporous anion exchange resin AV-17-2P used for bleaching sugar solutions has a total exchange capacity of 0.1 N. HCl solution 3.8 mg-eq / g, and 0.1 n. NaCl solution 3.4 mg-eq/g.

Purpose of analysis - evaluate the quality of the anion exchange resin for decolorization of sugar solutions.

Principle of analysis method is based on the titration of a 0.1 N acid solution not absorbed by the anion exchanger. NaOH solution.

Reagents:

0.1 N HCl and NaOH solutions.

Devices and materials:

A glass column with a diameter of 18 mm, a height of 250 mm, with an end drawn in the lower part, on which a rubber tube with a screw clamp is put on;

glass funnel;

Volumetric flask for 500 cm 3;

Burette for titration;

Beaker;

anion exchange resin.

Definition progress

10 g of the anion exchanger prepared for analysis in OH - form is transferred with water into a glass column with a diameter of 18 mm with a glass wool swab at the bottom, and excess water is drained through a rubber tube with a screw clamp.

After that, 400 cm 3 of 0.1 n. HCl solution, maintaining the level of the solution above the anion exchanger layer equal to 1 cm. Then it is washed with double the volume of the anion exchanger with water. The filtrate and washings are collected in a volumetric flask and brought to a volume of 500 cm 3 . Selected from the total volume in a glass of 50 cm 3 and titrated with 0.1 N. NaOH solution.

Calculations:

1. To obtain comparable results, the exchange capacity of the anion exchanger is expressed in the same way as the cation exchanger in terms of mg-eq / g of dry ion exchanger.

Therefore, if 1 g of absolutely dry anion exchanger absorbs

cm 3 0.1 n. HCl solution, and 1 cm 3 of this solution contains 0.1 mg-eq / g, then the total exchange capacity of the anion exchange resin E A can be calculated from the formula

,

where E A- total exchange capacity of the anion exchanger, mg-eq/g of absolutely dry ion exchanger;

a- amount of filtrate collected for titration, cm 3 ;

V O - the amount of 0.1 n. HCl solution passed through the anion exchanger, cm 3;

Vb- total amount of filtrate, cm 3 ;

g- the amount of dry anion exchange resin taken to determine its capacity, g;

W is the moisture content of the anionite, %. Determined by drying for 3 hours at 95-100˚С.

2. The capacity of the anion exchanger can also be expressed as a percentage of HCl. In this case, take into account the fact that 1 cm 3 0.1 n. HCl solution contains 0.0036 g HCl, calculation of E is carried out according to the formula

6.3. Regeneration of ion exchange resins

Introduction

The ion-exchange resins spent in the working cycle are subjected to regeneration (recovery) after they are washed with water.

Cation exchangers are reduced with weak solutions of HCl and HSO

K.Na + H /SO = K.H + Na /SO;

KNa + HCl = KH + NaCl.

For the reduction of anion exchangers, weak solutions of NaOH, KOH, NaCl, etc. are used.

A.OH.Cl + Na /OH = A./OH/ + Na /Cl.

At the end of the regeneration cycle, the acidity of the regenerate from the cation exchanger or the alkalinity of the regenerate from the anion exchanger should approach the acidity and alkalinity of the regeneration solutions. The end of regeneration is determined by titration.

Purpose of analysis - restore the exchange capacity of ion exchangers.

Principle of analysis method based on the titration of regeneration solutions from a cation exchanger 0.1 N. NaOH solution, and from the anion exchanger - 0.1 n. HCl solution.

Reagents:

5% HCl solution;

4% NaOH solution;

0.1 N NaOH solution;

0.1 N HCl solution.

Devices and materials:

Glass columns with cation exchange resin and anion exchange resin.

Definition progress

After washing the resin with water, regeneration is carried out in the columns: cation exchanger - with 5% HCl solution, and anion exchanger - with 4% NaOH solution, passing them at a rate of 20 cm 3 /min.

The end of the regeneration of the cation exchanger is established by titration of its regeneration solutions with 0.1 N. NaOH solution, and an anion exchanger - 0.1 n. HCl solution.

After regeneration, the cation exchanger is washed with water until a neutral or slightly acidic reaction, and the anion exchanger - until a neutral or slightly alkaline reaction.

test questions

1. What is ion exchange?

2. What are ion exchange resins?

3. What ion exchange resins are used in sugar production?

4. Tell us about the static and dynamic exchange capacity of ion exchangers?

5. What determines the total exchange capacity of ion exchangers?

6. In what units is the total exchange capacity expressed?

7. What is the purpose of using ion exchangers in sugar production?

8. On what principle is the determination of the total exchange capacity of ion exchangers based?

9. Why is ion exchange resin regenerated?

10. On what principle is the regeneration of ion exchangers based?

11. How is the end of the ion exchanger regeneration process determined?

Lab #7

Waste water analysis of sugar production

Introduction

In the food industry, the largest amount of water is consumed by sugar factories. If only pure water from natural reservoirs is used for the needs of a sugar beet plant, without returning part of the waste water to production, then the total consumption of industrial (fresh) water will be 1200-1500% by weight of beets. It is possible to reduce the consumption of fresh water to 150-250% by weight of the beet, provided that waste water is used in many areas of the sugar plant according to the circulating water supply scheme. Artesian water is used only for washing granulated sugar in centrifuges, for pumping the massecuite Ι crystallization and for the needs of the factory laboratory.

Waste (waste) waters of sugar factories are diverse in their physical and chemical composition, the degree of pollution and the method of required purification. According to the degree of pollution, they are classified into three categories. Each category is divided into two subgroups: A and B, of which the water of subgroup A is better in quality than subgroup B.

Waste water from sugar production contains a large amount of organic matter, and their treatment in natural conditions is associated with certain difficulties, requires significant land areas and can have a negative impact on the environment. In recent years, a number of biological treatment methods and appropriate equipment for their implementation have been developed. The currently proposed purification methods are mainly based on anaerobic and aerobic processes for the decomposition of sewage impurities from sugar and starch factories.

Modern wastewater treatment technology consists in the sequential separation of impurities contained in them by mechanical, anaerobic and aerobic methods. At the same time, the anaerobic method is a new process in wastewater treatment technology. The anaerobic purification process requires maintaining temperatures in the range of 36-38 0 С for its implementation, which is associated with additional heat consumption. Its difference from the widespread aerobic method lies primarily in the minimal growth of biosludge and the conversion of carbohydrate-containing impurities into biogas, the main component of which is methane.

Aerobic process

C 6 H 12 O 6 + O 2 ---- CO 2 + H 2 O + Bioprecipitate + Heat (6360 kJ).

anaerobic process

C 6 H 12 O 6 ---- CH 4 + CO 2 + Bioprecipitate + Heat (0.38 kJ).

Anaerobic methods are divided into four main groups according to the type of reactors used in the purification processes:

With recirculation of biosludge (activated sludge):

With a layer of anaerobic sediment and its internal sedimentation;

With inert fillers for biosludge;

Special.

Wastewater subjected to anaerobic treatment should contain as little as possible mechanical impurities and substances that inhibit the methanogenic process. A hydrolysis-acid phase must pass in them, and in addition, wastewater must have a certain pH value and a temperature in the range of 36-38 0 С.

It is believed that the anaerobic treatment method is economically beneficial for wastewater with pollution of more than 1.2-2.0 g/dm 3 BOD 5 (biological oxygen demand). The upper limit of pollution is not limited. It can be equal to 100 g / dm 3 COD (chemical oxygen demand).

These include:

A) Excess fresh water from the pressure tank, from the cooling of the massecuite in massecuite mixers, from pumps and other installations with a temperature below 30 ° C. These waters do not require treatment to be returned to production;

B) Barometric, ammonia and others with temperatures above 30°C. To return these waters, pre-cooling and aeration is required.

To wastewater category II include conveyor-washing water from hydraulic conveyors and beet washers. For the reuse of these waters in production, their preliminary mechanical purification is required by settling in special settling tanks.

To wastewater category III include: pulp press water, its sludge, laver water, conveyor-washing water sediment, liquid filtration sediment, household, fecal and other harmful waters. Category III water treatment requires biological and combined treatment methods in appropriate sedimentation tanks and filtration fields.

At existing sugar factories, the following main indicators of water balance (% by weight of beets) are taken as a basis: fresh water intake from a reservoir - 164; the number of recycled waters of category I - 898; II category -862; wastewater of category III - 170 or 110, provided that the suspension of the conveyor-washing sludge is settled in vertical settling tanks-thickeners Sh1-POS-3 and the decantate is returned to the category II water recirculation circuit.

For newly built sugar beet factories, the consumption of fresh water for production needs should not exceed 80% by weight of beets, and the amount of treated industrial wastewater discharged into natural water bodies should not exceed 75% by weight of beets.

When analyzing the quality of industrial and waste water, their temperature, color, odor, transparency, sediment characteristics, suspended solids content, dry residue, pH, total alkalinity (acidity), oxidizability, biochemical oxygen demand (BOD), chemical oxygen demand (COD) are determined , concentration of ammonia, nitrates, chlorides and other indicators.

Objective - master the methods of quality control of industrial (fresh) and waste water.

A significant number of processes occurring in nature and carried out in practice are ion-exchange processes. Ion exchange underlies the migration of elements in soils and organisms of animals and plants. In industry, it is used for the separation and production of substances, water desalination, wastewater treatment, concentration of solutions, etc. Ion exchange can occur both in a homogeneous solution and in a heterogeneous system. In this case, under ion exchange understand the heterogeneous process by which an exchange takes place between ions in solution and in a solid phase called ion exchanger or ion exchanger. The ion exchanger sorbs ions from the solution and in return gives the ions that are part of its structure into the solution.

3.5.1. Classification and physico-chemical properties of ion exchangers

Ion exchange sorbents, ion exchangers are polyelectrolytes that are composed of matrices- immobile groups of atoms or molecules (high-molecular chains) with active ionogenic groups atoms that provide its ion exchange capacity. Ionic groups, in turn, consist of immobile ions bound to the matrix by chemical interaction forces, and an equivalent number of mobile ions with the opposite charge - counterions. Counterions are able to move under the action of a concentration gradient and can be exchanged for ions from a solution with the same charge. In the system ion exchanger - electrolyte solution, along with the distribution of exchanging ions, there is also a redistribution between these phases of the solvent molecules. Together with the solvent, a certain amount of coions(ions of the same name in charge with fixed ones). Since the electrical neutrality of the system is preserved, together with the coions, an additional amount of counterions, equivalent to them, passes into the ion exchanger.

Depending on which ions are mobile, ion exchangers are divided into cation exchangers and anion exchangers.

Cation exchangers contain immobile anions and exchange cations, they are characterized by acidic properties - a mobile hydrogen or metal ion. For example, cation exchanger R / SO 3 - H + (here R is a structural base with a fixed functional group SO 3 - and counterion H +). According to the type of cations contained in the cation exchanger, it is called H-cation exchanger, if all its mobile cations are represented only by hydrogen, or Na-cation exchanger, Ca-cation exchanger, etc. They are denoted RH, RNa, R 2 Ca, where R is the frame with the fixed part of the active group of the cation exchanger. Cation exchangers with fixed functional groups -SO 3 -, -PO 3 2-, -COO -, -AsO 3 2-, etc. are widely used.

anion exchangers contain immobile cations and exchange anions, they are characterized by the main properties - a mobile hydroxide ion or an ion of an acid residue. For example, the anion exchanger R / N (CH 3) 3 + OH -, with the functional group -N (CH 3) 3 + and the counterion OH -. The anion exchanger can be in different forms, as well as the cation exchanger: OH-anion exchanger or ROH, SO 4 - anion exchanger or RSO 4, where R is a frame with a fixed part of the active group of the anion exchanger. The most commonly used anion exchangers with fixed groups - +, - +, NH 3 +, NH +, etc.

Depending on the degree of dissociation of the active group of the cation exchanger, and accordingly on the ability to ion exchange, cation exchangers are divided into strongly acidic and weakly acidic. So, the active group -SO 3 H is completely dissociated, therefore, ion exchange is possible in a wide pH range, cation exchangers containing sulfo groups are classified as strongly acidic. Medium strength cation exchangers include resins with phosphoric acid groups. Moreover, for dibasic groups capable of stepwise dissociation, only one of the groups has the properties of an acid of medium strength, the second behaves like a weak acid. Since this group practically does not dissociate in a strongly acidic medium, it is therefore expedient to use these ion exchangers in slightly acidic or alkaline media, at pH4. Weakly acidic cation exchangers contain carboxyl groups, which are little dissociated even in weakly acidic solutions, their operating range at pH5. There are also bifunctional cation exchangers containing both sulfo groups and carboxyl groups or sulfo and phenolic groups. These resins work in strongly acidic solutions, and at high alkalinity they sharply increase their capacity.

Similarly to cation exchangers, anion exchangers are divided into high basic and low basic. Highly basic anion exchangers contain well-dissociated quaternary ammonium or pyridine bases as active groups. Such anionites are capable of exchanging anions not only in acidic, but also in alkaline solutions. Medium and low basic anion resins contain primary, secondary and tertiary amino groups, which are weak bases, their operating range at pH89.

Amphoteric ion exchangers are also used - ampholytes, which include functional groups with properties of both acids and bases, for example, groups of organic acids in combination with amino groups. Some ion exchangers, in addition to ion-exchange properties, have complexing or redox properties. For example, ion exchangers containing ionogenic amino groups give complexes with heavy metals, the formation of which occurs simultaneously with ion exchange. Ion exchange can be accompanied by complexation in the liquid phase, by adjusting its pH value, which allows the separation of ions. Electron-ion exchangers are used in hydrometallurgy for the oxidation or reduction of ions in solutions with their simultaneous sorption from dilute solutions.

The process of desorption of an ion absorbed on an ion exchanger is called elution, while the ion exchanger is regenerated and it is transferred to its initial form. As a result of the elution of the absorbed ions, provided that the ion exchanger is sufficiently "loaded", eluates are obtained with an ion concentration 100 times higher than in the initial solutions.

Some natural materials have ion-exchange properties: zeolites, wood, cellulose, sulfonated coal, peat, etc., however, they are almost never used for practical purposes, since they do not have a sufficiently high exchange capacity, stability in the treated media. The most widespread are organic ion exchangers - synthetic ion-exchange resins, which are solid high-molecular polymer compounds, which contain functional groups capable of electrolytic dissociation, therefore they are called polyelectrolytes. They are synthesized by polycondensation and polymerization of monomers containing the necessary ionic groups, or by adding ionic groups to individual units of a previously synthesized polymer. Polymeric groups are chemically bonded to each other, crosslinked into a framework, that is, into a spatial three-dimensional network called a matrix, with the help of a substance interacting with them - a watercress agent. Divinylbenzene is often used as a crosslinker. By adjusting the amount of divinylbenzene, it is possible to change the size of the resin cells, which makes it possible to obtain ion exchangers that selectively absorb any cation or anion due to the "sieve effect", ions larger than the cell size are not absorbed by the resin. To increase the cell size, reagents with larger molecules than those of vinylbenzene are used, for example, dimethacrylates of ethylene glycols and biphenols. Due to the use of telogens, substances that prevent the formation of long linear chains, an increased permeability of ion exchangers is achieved. In places where the chains are broken, pores appear, due to this, the ion exchangers acquire a more mobile frame and swell more upon contact with an aqueous solution. Carbon tetrachloride, alkylbenzenes, alcohols, etc. are used as telogens. The resins obtained in this way have gel structure or microporous. To receive macroporous ionites in the reaction mixture add organic solvents, which are higher hydrocarbons, such as isooctane, alcohols. The solvent is captured by the polymerizing mass, and after the formation of the framework is completed, it is distilled off, leaving large pores in the polymer. Thus, according to the structure, ion exchangers are divided into macroporous and gel ones.

Macroporous ion exchangers have better kinetic exchange characteristics compared to gel ones, since they have a developed specific surface of 20-130 m 2 /g (unlike gel ones, which have a surface of 5 m 2 /g) and large pores - 20-100 nm, which facilitates the heterogeneous exchange of ions that takes place on the surface of the pores. The exchange rate significantly depends on the porosity of the grains, although it usually does not affect their exchange capacity. The larger the volume and grain size, the faster the internal diffusion.

Gel ion-exchange resins consist of homogeneous grains, which in dry form do not have pores and are impermeable to ions and molecules. They become permeable after swelling in water or aqueous solutions.

Swelling of ion exchangers

swelling called the process of gradual increase in the volume of the ion exchanger placed in a liquid solvent, due to the penetration of solvent molecules deep into the hydrocarbon frame. The more the ion exchanger swells, the faster the exchange of ions takes place. Swelling characterized weight swelling- the amount of absorbed water per 1 g of dry ion exchanger or swelling ratio- the ratio of the specific volumes of swollen ion exchanger and dry. Often, the volume of the resin in the process of swelling can increase by 10-15 times. The swelling of a high-molecular resin is the greater, the lower the degree of cross-linking of its constituent units, that is, the less rigid its macromolecular network. Most standard ion exchangers contain 6-10% divinylbenzene in copolymers (sometimes 20%). When long-chain agents are used for crosslinking instead of divinylbenzene, well-permeable macroreticulated ion exchangers are obtained, on which ion exchange occurs at a high rate. In addition to the structure of the matrix, the swelling of the ion exchanger is affected by the presence of hydrophilic functional groups in it: the ion exchanger swells the more, the more hydrophilic groups there are. In addition, ion exchangers containing singly charged counterions swell more strongly, in contrast to two- and three-charged counterions. In concentrated solutions, swelling occurs to a lesser extent than in dilute ones. Most inorganic ion exchangers do not swell at all or almost, although they absorb water.

Ion exchanger capacity

The ion-exchange capacity of sorbents is characterized by their exchange capacity, depending on the number of functional ionogenic groups per unit mass or volume of the ion exchanger. It is expressed in milliequivalents per 1 g of dry ion exchanger or in equivalents per 1 m 3 of ion exchanger and for most industrial ion exchangers is in the range of 2-10 meq / g. Full exchange capacity(POE) - the maximum number of ions that can be absorbed by the ion exchanger when it is saturated. This is a constant value for a given ion exchanger, which can be determined both in static and dynamic conditions.

Under static conditions, in contact with a certain volume of electrolyte solution, determine full static exchange capacity(PSOE), and equilibrium static exchange capacity(PCOE), which varies depending on the factors affecting the equilibrium (solution volume, composition, concentration, etc.). Equilibrium ion exchanger - solution corresponds to the equality of their chemical potentials.

Under dynamic conditions, with continuous filtration of the solution through a certain amount of ion exchanger, determine dynamic exchange capacity- the number of ions absorbed by the ion exchanger before the breakthrough of sorbed ions (DOE), full dynamic exchange capacity until the complete development of the ion exchanger (PDOE). The capacity before breakthrough (working capacity) is determined not only by the properties of the ion exchanger, but also depends on the composition of the initial solution, the rate of its passage through the ion exchanger layer, the height (length) of the ion exchanger layer, the degree of its regeneration and the size of the grains.

The operating capacity is determined from the output curve fig. 3.5.1

S 1 - working exchange capacity, S 1 +S 2 - full dynamic exchange capacity.

When elution is carried out under dynamic conditions, the elution curve has the form of the curve shown in fig. 3.5.2

Typically, the DEC is greater than 50% of the PDOE for strongly acidic and strongly basic ion exchangers and 80% for weakly acidic and weakly basic ion exchangers. The capacity of strongly acidic and strongly basic ion exchangers remains practically unchanged in a wide range of pH solutions. The capacity of weakly acidic and weakly basic ion exchangers largely depends on pH.

The degree of use of the exchange capacity of the ion exchanger depends on the size and shape of the grains. Usually the grain sizes are in the range of 0.5-1 mm. The shape of the grains depends on the method of preparation of the ion exchanger. They may be spherical or irregular in shape. Spherical grains are preferable - they provide better hydrodynamic conditions and high process speed. Ion exchangers with cylindrical grains, fibrous and others are also used. The finer the grains, the better the exchange capacity of the ion exchanger is used, but at the same time, depending on the equipment used, either the hydraulic resistance of the sorbent layer increases or the removal of small grains of the ion exchanger by the solution increases. Carryover can be avoided by using ion exchangers containing a ferromagnetic additive. This allows you to keep the fine-grained material in suspension in the zone - the magnetic field through which the solution moves.

Ion exchangers must have mechanical strength and chemical resistance, that is, they must not be destroyed as a result of swelling and operation in aqueous solutions. In addition, they should be easily regenerated, thereby retaining their active properties for a long time and working without a change for several years.

Thank you in advance for your response.

C100E is a gel type strong acid cation exchange resin with high exchange capacity, chemical and physical stability and excellent performance. C100E effectively retains suspended particles, and also, in acidic (H +) form, removes iron and manganese ions.

The high exchange capacity makes it possible to obtain water with a total hardness of the order of 0.05 meq/l, and the excellent ion exchange kinetics make it possible to achieve high flow rates. When using C100E, the slip of ions that cause water hardness under normal operating conditions, as a rule, does not exceed 1% of the total hardness of the source water. In this case, the exchange capacity of the resin practically does not change, provided that the proportion of monovalent ions does not exceed 25%.

C100E is insoluble in acid and alkali solutions and in all common organic solvents. The presence of residual oxidizing agents (such as free chlorine or hypochlorite ions) in the water can reduce the mechanical strength of the cation exchange resin particles. C100E is thermally stable up to a temperature of 150°C, however, at high temperatures, the exchange capacity of the cation exchange resin in the acid (H+) form decreases.

Specifications

Physical Properties
	transparent spherical particles of yellowish color
Delivery form
Bulk weight, g/cm3
Specific gravity, g/cm3
Uniformity coefficient
Granule size, mm (mesh)
Exchange capacity, g-eq/l
Swelling Na + → H + , max, %
Swelling Ca 2+ → Na + , max, %
Application conditions
	6 - 10 (Na-form)
Maximum operating temperature, °C
Layer Height, cm (in)
Operating flow rate, resin volume/hour
Layer expansion in backwash mode, %
Concentration of NaCl solution, %
Salt consumption for regeneration, gr. NaCl /l resin

A BRIEF DESCRIPTION OF
free space above download - 50%
grain size 0.6mm up to 90%
Bulk weight 820gr/l
Water content (humidity) 42-48%
Total capacity up to 2 g eq/l
operating temperature from 4 - 120 0 С
water pH 0 - 14
transition of Na ions to H - 8%
layer height from 0.8 - 2m
service speed from 5 - 40m/h
specific speed of service 20oz/hour
backwash speed at 20 C from 10 - 12m/h
volume of water for backwashing with a new load 20oz
backwash water volume 4oz
volume of water for slow washing of salt 4oz
salt consumption during regeneration per 1 liter of load - 150g
residual hardness - 0.5mg equiv/l
specific pressure loss in kPa m 2 loading height - 1
pressure loss of 11mbar at 4°C per 1m loading height
regeneration speed - 5m/h
speed when washing salt with water - 5m/h

APPLICATION CONDITIONS
lack of oxidized iron (Fe 3+) in water
lack of dissolved oxygen in water
lack of organic matter in water
the absence of any oxidizing agents in the water
after sodium - softening, the total alkalinity and dry residue will increase.
strong oxidizing agents such as nitric acid can cause violent reactions
suspended solids in source water up to 8 mg/l
color of source water up to 30 0 С
turbidity of source water up to 6 mg/l
total hardness of source water up to 15 mg equiv/l

Below are the methods for calculating the exchange capacity and other parameters of the cation exchanger.

The working exchange capacity of the cationite E f g÷eq / m3, can be expressed by the following formula:

E f \u003d Q x W; Ep = ep x Vk.

The volume of the cationite loaded into the filter in the swollen state is expressed by the formula:

The formula for determining the working exchange capacity of the cation exchanger ep, g÷eq / m 3:

ep \u003d Q x W / S x h;

where W is the hardness of the source water, g÷eq/m3; Q - the amount of softened water, m 2; S is the area of ​​the cationite filter, m 2 ; h is the height of the cationite layer, m.

Denoting the speed of movement of water in the cation exchanger as v k , the amount of softened water Q can be found using the following formula:

Q \u003d v k x S x Tk \u003d ep x S x h / W;

from which it is possible to calculate the duration of the operation of the cationite filter Tk:

Tk = ep x h/v k x W.

It is also possible to calculate the exchange capacity of the cation exchanger using correlating graphs.

Based on approximate practical data, your filter will be able to clean no more than 1500 liters. water. For more accurate calculations, you need to know the amount (volume) of resin in your filter and the working capacity of your resin (for cation exchange resins, the working capacity varies from 600 to 1500 meq/l). Knowing these data, you can easily calculate the exact amount of softened water using your formulas.