Applications of Ion Exchangers

Applications for ion exchange have many current forms, and some of these could expand as increased awareness of ion exchange processes continues. In addition, as the field of materials engineering continues to produce an ever-increasing variety of substances, the potential for creating new, useful ion exchange materials grows. Furthermore, the explosive growth in computer power during the last 15 years helps materials engineers work much more efficiently in developing useful compounds. If virtual reality technology materializes as it's proponents profess, materials development could be in for another burst of growth.

The current uses of ion exchange are long and numerous, and although I won't go into all of them here, I would like to point out several important applications. An application that can hit close to home is in the treatment of water for drinking, use (commercial, industrial, and residential), and wastewater treatment. Ion exchangers can soften the water, deionize it, and even be used in desalination. In industrial uses, pure water is often crucial for the successful development of a product. Preparation of various acids, bases, salts, and solutions is also aided by ion exchange. Analytical chemistry uses ion exchange in chromatography. The recovery of valuable metals is also possible with resins. Industrial drying of treatment of gases is accomplished often with ion exchange. The food industry uses ion exchange in a variety of ways, ranging from wine-making to sugar manufacture. In the medical world, dozens of important manifestations of the benfits of ion exchange can be found, from development and preparation of key drugs and antibiotics, such as streptomycin and quinine, to treatments for ulcers, TB, kidneys, and much more. Ion exchange is used to prevent coagulation in blood stores and in dextrose, as well. An ion exchange is also useful in death, as it plays a role in the treatment of formaldehyde.

The list goes on and on, but you get the picture. The list keeps growing with each passing year, as well, so stay tuned for updates on ion exchange applications.

Ion exchange resins applications A general overview

Contents

1. Water treatment

1.1. Softening 1.2. Dealkalisation 1.3. Demineralisation 1.4. Mixed bed polishing 1.5. Drinking water

2. Sugar industry

2.1. Softening of water used for sugar extraction 2.2. Softening of sugar juices before evaporation 2.3. The NRS softening process 2.4. The Gryllus softening process 2.5. Demineralisation of sugar juices before evaporation 2.6. Colour removal from sugar syrups after evaporation 2.7. The Quentin process 2.8. Sugar recovery from molasses 2.9. Sucrose inversion 2.10. Chromatographic separation 2.11. Glucose treatment

3. Other applications in the food industry

3.1. Dairy products 3.2. Beverages 3.3. Fruit juices 3.4. Recovery of polyphenols 3.5. Citric acid 3.6. Aminoacids 3.7. Sorbitol demineralisation 3.8. Gelatine demineralisation

4. Applications in the chemical industry

4.1. Recovery or removal of metals 4.2. Caustic soda and chlorine production 4.3. Phenol 4.4. Hydrogen peroxide purification 4.5. Selective removal of various elements

5. Catalysis

5.1. Alkylation 5.2. Condensation 5.3. Esterification 5.4. Etherification 5.5. Dehydration 5.6. Hydrogenation

6. Pharmaceutical industry

6.1. Extraction and purification of antibiotics 6.2. Slow-release formulations 6.3. Resins used as drugs 6.4. Taste-masking 6.5. Production chromatography

7. Miscellaneous applications

7.1. Mining industry 7.2. Enzyme immobilisation 7.3. Hydroculture

1. Applications of ion exchange resins in water treatment

Water softening and demineralisation are also described with chemical reactions in the IX basics page. Andregeneration methods are in another page.

1.1. Softening

A strongly acidic cation exchange resin is used here in the sodium form. The ions forming hardness, essentially calcium and magnesium, are exchanged for the sodium ions of the resin, and the softened water can be used for several purposes:

Laundries Domestic water boilers Low pressure industrial boilers Textile

Resins used:

AmberliteTM IR120 Na, AmberjetTM 1000 Na Amberlite SR1L Na for drinking water

Treated water quality: Residual hardness < 0.02 meq/L (1 mg/L as CaCO3) with reverse flow regeneration

Regeneration: brine (NaCl as a 10 % solution)

1.2. De-alkalisation

In a water containing bicarbonates — most waters in Western and Central Europe do — calcium and magnesium associated with bicarbonate ions are exchanged for hydrogen ions from a

weakly acidic cation exchange resin. This is called removal of temporary hardness. The treated water contains carbon dioxide that can be removed with a degasifier. The salinity of the treated water is lower than that of the feed water. Dealkalisation is used:

To treat water used to make beverages in breweries and soft drink plants

To soften drinking water supplies in municipalities At home, to filter, soften and partially demineralise

the water you use to make tea or coffee As a first demineralisation step For certain industrial processes

Resins used:

Amberlite IRC86 for industrial water Amberlite PWC13 for municipal drinking water ImacTM HP333 and HP335 for household filter

cartridges

Treated water quality Residual alkalinity = very low (endpoint at 10 % of the raw water alkalinity) Residual hardness = permanent hardness (TH – Alk)

Regeneration : Acid (preferably HCl at 5 % concentration)

1.3. Demineralisation

All ions must be removed from water. Therefore the water passes first through cation exchange resins in the hydrogen form, then through anion exchange resins in the hydroxyl or free base form. All cations are replaced by ions from the cation resin, and all anions for the ions of the anion resin. These H+ and OH— ions recombine to create new water molecules (H2O). The treated water contains only traces of sodium and silica.

Resins used:

Amberlite IRC86 (weakly acidic resin) Amberlite IR120 or Amberjet 1000 (strongly acidic

resin) Amberlite IRA96 or IRA67 (weakly basic resin) Amberlite IRA402 or Amberjet 4200 or 4600 (strongly

basic resin)

The use of weakly functional resins depends on the raw water analysis and plant size.

Treated water quality Conductivity: 0.2 to 1 µS/cm with reverse flow regeneration Residual silica 5 to 50 µg/L depending on the silica concentration in the feed water and the quantity of caustic regenerant. These values are lower than those obtained with other technologies, such as reverse osmosis or distillation. Note that the pH value should not be used as a process control, as it is impossible to measure the pH of a water with less than say 5 µS/cm conductivity.

Regeneration Cation exchange resins: strong acid (HCl or H2SO4) Anion exchange resins: caustic soda (NaOH)

1.4. Mixed bed units

1.4.1. Polishing mixed beds

When an even better treated water quality is required, close to that of totally pure water, a polishing vessel is installed after a primary demineralisation plant. It is filled with cation and anion exchange resins, which must be mixed during the loading run, but separated for regeneration. The separation is carried out with an upflow backwash step, and requires resins with appropriate particle sizes and densities.

Resins used:

Amberjet 1000 or 1500 (strongly acidic resin) Amberjet 4200 or 4400 (strongly basic resin)

For specific applications, such as ultrapure water or circuits in nuclear power plants, other highly purified grades are also used.

Treated water quality Conductivity: 0.055 to 0.1 µS/cm Residual silica: 1 to 10 µg/L. Note that the pH value should not be used as a process control, as pH meters are unable to operate at 1 µS/cm conductivity or below.

Regeneration Cation exchange resins: strong acid (HCl or H2SO4) Anion exchange resins: caustic soda (NaOH)

1.4.2. Working mixed beds

For low salinity waters, or when only moderate demineralised water volumes are required, mixed bed units can be installed and fed directly with city water or reverse osmosis permeate. These units are called "Working MBs". The resins used are essentially the same as those for polishing mixed bed units. A special case is Service De-Ionisation (SDI) — using mixed bed columns or cartridges regenerated off-site — described in a separate page.

1.5. Drinking water

Ion exchange is a valuable technology for the selective removal or certain contaminants from underground water. See details in a separate page.

2. Use of ion exchange resins in the sugar industry

2.1. Softening of water used for sugar extraction

The process it that described in point 1.1 (water softening).

2.2. Softening of beet sugar juices before evaporation

The hardness of beet sugar juices results in scaling of the heat exchanger in the evaporators. To prevent it, increase the thermal efficiency and save energy, it is usual to soften the sugar juice. The plant can then operate continuously, without frequent interruptions required for de-scaling the equipment.

In this process, the type of resin used is the same as that for water softening, but the resins must be approved for use with

food and resist specific stress due to the temperature and concentration of the juice.

The calcium and magnesium ions present in the sugar juice are exchanged for sodium ions from the resin. The process is applied to thin juice, i.e. after carbonation. In general, several columns operate in parallel to ensure continuous operation.

Resins used:

Amberlite FPC14 Na

2.3. The NRS process

This is a clever process where the resin is regenerated with a solution of caustic soda diluted in thin juice. The basic idea is that whilst calcium hydroxide is insoluble in water, the calcium ions make a soluble complex with sucrose. The spent regenerant is recycled upstream, before the carbonation step, so that the production of waste is negligible. Moreover, the juice is not diluted in water as in the traditional softening process, because the NRS process does not include sweetening-off and sweetening-on steps. The energy balance is favourable and results in steam saving.

Resins used:

Amberlite FPC14 Na

2.4. The Gryllus process

This is an older process in which the softening resin is regenerated with thick juice, which contains high concentrations of sodium. The salt consumption is thus reduced, and again, no waste is produced, since the spent regenerant is recycled.

Resins used:

Amberlite FPC22 Na

2.5. Demineralisation of sugar juices before evaporation

In this process, "non-sugars" are removed from thin juice to increase the efficiency of crystalllisation, i.e. the sugar yield. In general, each kilogram of removed non-sugar produces 1.4 kg of additional sugar. Otherwise, the process is similar to water demineralisation: a strongly acidic cation exchange resin and a weakly basic anion exchange resin are used, regenerated respectively with acid and caustic soda.

Resins used:

Amberlite FPC14 Na (strongly acidic) Amberlite FPA53 (weakly basic)

2.6. Colour removal from cane sugar syrups after evaporation

Cane syrups usually contain many organic compounds imparting colour to the crystallised sugar and reducing the crystallisation yield. The colour removal process uses strongly basic anion exchange resins, regenerated with a sodium chloride solution. These resins are macroporous, so that high molecular mass compounds can be removed. The most efficient method uses two columns in series, the first one filled

with acrylic resin, the second, polishing column with styrenic resin.

Resins used:

Amberlite FPA98 Cl (acrylic) Amberlite FPA90 Cl (styrenic)

2.7. The Quentin process

Crystallisation of beet sugar is partially inhibited by the potassium and sodium ions contained in the juice, so that large quantities of sugar remain in the molasses after crystallisation. Magnesium being less "melassigenous" than sodium or potassium, the idea is to pass the thin juice through a column of strongly acidic cation exchange resin in the magnesium form. This increases the production of whit sugar and reduces the quantity of molasses.

Resins used:

Amberlite FPC23 H (must be first converted to the Mg++ form with magnesium chloride)

2.8. Sugar recovery from molasses

This process is based on ion exclusion, a kind of ion exchange chromatography using fine mesh, uniform particle size resins. It separates sugar from non-sugars and increases the recovery of sugar contained in the molasses.

Resins used:

Amberlite CR1220 K

2.9. Sucrose inversion

Sucrose (common sugar) is a di-saccharide. In an acidic environment, the sucrose molecule splits into two mono-saccharides: glucose and fructose, in equal proportions. Invert sugar has a more powerful sweetening power than sucrose (1.15 vs. 1.0) , and a lower tendency to crystallise, an important feature for some industrial food products. Inversion is produced by passing sugar syrup through a low cross-linked strongly acidic cation exchange resin in the H+ form.

Resins used:

Amberlite FPC12 H

2.10. Chromatographic separation

As fructose has a higher sweetening power than glucose (1.3 vs. 0.7), invert sugar syrups can be enriched with fructose by passing the syrup through a fine mesh, very uniform strongly acidic cation exchange resin in the calcium form. As the syrup stream moves down the column, fructose moves more slowly than glucose. This results in separated bands of higher purity of each component within the column. The fructose fraction is recovered separately in view of its commercial value. The glucose fraction can be either sold as a glucose syrup, or isomerised enzymatically to produce more fructose.

Resins used:

Amberlite CR1320 Ca

2.11. Glucose demineralisation

Glucose syrups are demineralised to increase purity. The principle is identical to that of water or sugar demineralisation. In view of the high concentration and high temperature of the syrups, resins with a good resistance to these stresses must be used.

Resins used:

DowexTM 88 (strongly acidic resin) Dowex 66 (weakly basic resin)

3. Examples of other applications in the food industry

3.1. Whey demineralisation

Whey, a by-product of cheese production, contains valuable proteins and is used in the food industry. It is demineralised to increase purity. Again, the principle is the same as that of water or sugar demineralisation.

Resins used:

Amberlite FPC14 (strongly acidic resin) Amberlite FPA51 (weakly basic resin)

3.2. Beverages

There are several applications in this area:

Treatment of the water used to make beer or soft drinks (see chapter 1)

De-acidification of beverages with Amberlite FPA51 (weakly basic anion resin)

Removal of metals Removal of bad taste or smell Colour and turbidity removal with non-ionic

adsorbents

3.3. Treatment of fruit juices

Acid removal with Amberlite FPA51 (weakly basic anion resin)

Removal of bitterness from orange juices with a non-ionic adsorbent resin, Amberlite FPX66

Colour removal with an adsorbent resin

3.4. Recovery of polyphenols

Polyphenols are praised today for their anti-oxidant properties. They are found in many types of fruit, such as berries or red grape. Anthocyanins are polyphenols that can be recovered from grape must.

Resins used:

Amberlite FPX68 (non-ionic adsorbent resin)

3.5. Citric acid

This acid is used as a preservative in many industrial food products. It is produced by fermentation. Its purification requires ion exchange demineralisation.

Resins used:

Amberlite FPC22 H (strongly acidic) Amberlite FPA51 (weakly basic)

3.6.Aminoacids

L-lysine and other essential aminoacids (not produced by the human body) are produced by fermentation. Lysine is recovered from the fermentation broth with a cation exchange resin in ammonium form.

Resins used:

Amberlite FPC14 (strongly acidic)

3.7. Sorbitol demineralisation

Sorbitol is a polyol, a powerful sweetener and emollient used for instance in chewing gum. It can be produced by hydrogenation of glucose or by enzymatic processes. The final product often requires demineralisation.

Resins used:

Amberlite FPC22 (strongly acidic) Amberlite FPA51 (weakly basic) Amberlite FPC52 and FPA90 in a polishing mixed bed

3.8. Gelatine demineralisation

Gelatine is produced from the collagen present in pig skin and bones. To produce high purity gelatine, demineralisation is required.

Resins used:

Amberlite FPC14 or FPC22 (strongly acidic) Amberlite FPA53 (weakly basic acrylic)

4. Some applications in the chemical industry

4.1. Recovery and removal of metals

In surface finishing and plating shops, metals can be recovered or removed:

Gold recovery from industrial jewelleries as cyanide complexes, with Amberlite IRA402

Recycling of various rinse water streams in plating shops, with Amberlite 252 (for cation removal), IRA96 (for chromate), and IRA410 (for cyanide)

Copper and iron removal from chromium plating shops with Amberlyst 15Wet

Chromic acid recovery in plating shops with Amberlite IR120 and Amberlite IRA96

Removal of iron from zinc baths with Amberlite IRC748

Purification of pickling baths, removing iron and zinc as chloride complexes with Amberlite IRA402. Elution is done simply with water.

Other examples:

Recovery of silver as a thiosulphate complex from photographic baths with Amberlite IRA67 or IRA402

Selective mercury removal in various industries with AmbersepTM GT74, a resin with thiol functionality.

Cadmium can be removed with the same resin Recovery of vanadium and copper catalysts in the

production of adipic acid (a precursor of nylon) with AmberlystTM 40Wet

4.2. Production of chlorine and caustic soda

These chemicals are produced by electrolysis of saturated brine. In the production process, the absence of divalent metals is critical. A selective chelating resin is thus used to remove them (principally calcium), which reduces the initial calcium concentration from 10 – 20 mg/L down to a very low level, smaller than 20 µg/L.

Resins used:

Amberlite IRC747 when strontium removal is not necessary

Amberlite IRC748 when strontium must also be removed

4.3. Phenol

Two applications:

Removal of sulphuric acid and organic acids from process streams in phenol production. A special weak base resin with a phenol-formaldehyde matrix is used.

Removal of phenol from industrial waste. Phenol is removed on a non-ionic adsorbent resin. Regeneration is done with acetone.

Resins used:

Amberlyst A23 for acid removal Amberlite XAD4 for phenol removal from waste

4.4. Hydrogen peroxide purification

Resins are used in two different processes:

Removal of anthraquinone derivatives. These organic compounds can be removed on a non-ionic adsorbent. Regeneration is done with methanol.

Removal of metal traces such as iron, with a strongly acidic resin. The treatment is done at a very high specific flow rate.

In both cases, the product quality is excellent, with residuals of just a few µg/L. Caution: hydrogen peroxide (H2O2) is a powerful oxidant, and serious steps must be taken in both processes to avoid accidents.

Resins used:

Amberlite XAD4 for organic contaminants Amberlyst 15Wet for metals

4.5. Selective removal of various elements

I have built up a periodic system of the elements (Mendeleev table) with brief information about the removal of several ions (mostly metals) with resins.

5. Catalysis

A catalyst is a substance that increases the rate of approach to equilibrium of a chemical reaction without being substantially consumed in the reaction.

In the majority of processes where a mineral acid was previously used as a catalyst — notably in the petrochemical industry — a strongly acidic cation exchange resin in the H+ form is now used instead. These resin must operate under stressful conditions — often at temperatures between 130 and 170 °C — and display an acidity as high as possible.

A few typical examples are shown below.

5.1. Alkylation

Product OctylphenolReactants Octane +

phenolCatalyst Amberlyst

15DryTemperature 100 – 120 °C

5.2. Condensation

Product Bisphenol AReactants Acetone +

phenolCatalyst Amberlyst 131Temperature 60 – 80 °C

5.3. Esterification

Product Dimethyl maleate

Reactants Maleic anhydride

Catalyst Amberlyst 46Temperature 110 °C

5.4. Etherification

Product Methyl-ter-butyl ether (MTBE)

Reactants Isobutylene + methanolCatalyst Amberlyst 35Temperature 40 – 80 °C

5.5. Dehydration

Product IsobutyleneReactant IsobutanolCatalyst Amberlyst

35Temperature 70 – 80 °C

5.6. Hydrogenation

Product Methyl isobutyl ketone (MIBK)Reactant AcetoneCatalyst Amberlyst CH28 (palladium-doped

catalyst)Temperature 130 – 140 °C

6. Pharmaceutical industry

There are various and complex applications. As the pharmaceutical industry is intrinsically secretive, few details are known. Nevertheless, let us mention a few examples:

6.1. Extraction and purification of antibiotics

Various antibiotics use ion exchange and adsorbent resins in their production process. The objective is to purify them after extraction from fermentation broths. Examples: streptomycin, gentamycin, cephalosporin, tetracyclin.

Resins used:

Amberlite XAD1600 (non-ionic styrenic adsorbent) Amberlite XAD7HP (non-ionic acrylic adsorbent)

6.2. Slow-release formulations

Powdered, highly purified ion exchange resins are used as excipients in pharmaceutical formulations. The active ingredient is adsorbed on the resin and is released more slowly in the body than it would if it were present in their original state.

Resins used:

Amberlite IRP64 (weakly acidic) Amberlite IRP69 (strongly acidic) Amberlite IRP88 (weakly acidic in potassium form) DuoliteTM AP143 (strongly basic)

6.3. Resins used as drugs

The same resin types can be used as active substances in the medicine. It is obvious that they must meet very stringent specifications and be approved by health authorities. Let us mention two examples:

Cholestyramine, a drug used to reduce the cholesterol level, is a powder based on a strongly basic anion resin in the choride form.

Polacrilin potassium, a medicine used to regulate the potassium level in the blood, is a powder based on a weakly acidic resin with a methacrylic matrix.

Resins used:

Duolite AP143 (cholestyramine) Amberlite IRP88 (polacrilin potassium)

6.4. Taste-masking

Similar resins are used to mask the unpleasant taste oir smell of a drug.

6.5. Production chromatography

The chromatographic separation of various molecules used as active ingredients can be done with very fine particle size resins instead of silica gels or other media.

Resins used:

A whole range of products available as Amberchrom resins.

7. Miscellaneous applications

7.1. Mining industry

The most significant application, involving thousands of cubic metres of resin, is uranium extraction. The crushed ore is treated with sulphuric acid, which brings the uranium in solution as uranium sulphate. The pregnant solution is passed through beds of strongly basic anion exchange resins, which displays a high affinity for the uranium sulphate complex.

Resins used:

Amberjet 4400 Ambersep 920U

7.2. Enzyme immobilisation

In enzymatic reactions, it is more convenient to immobilise the enzyme on a support rather than add it to the reaction medium. Ion exchange resins are particularly suitable for this application.

Resins used:

AmberzymeTM oxirane Duolite A568 (weakly basic resin with a phenol-

formaldehyde matrix)

7.3. Hydroculture

Cation and anion exchange resins are used to retain plant nutrients in hydroponic culture: ammonium, potassium, iron, zinc (cations) as well as nitrate and phosphate (anions). Oligoelements are also loaded unto the resin. This technique allows the nutrients to be released slowly as a function of the plant requirements. An overdose of fertilizer is made impossible.

Resins used:

LewatitTM HD5

Adsorption finds extensive applications both in research

laboratory and in industry. A few applications are discussed below:

In preserving vacuum: 

In Dewar flasks activated charcoal is placed between the walls of the

flask so that any gas which enters into the annular space either due to

glass imperfection or diffusion though glass is adsorbed.

In glass masks:

All gas masks are devices containing suitable adsorbent so that the

poisonous gases present in the atmosphere are preferentially

adsorbed and the air for breathing is purified.

In clarification of sugar:

Sugar is decolorized by treating sugar solution with charcoal powder.

The latter adsorbs the undesirable colors present.

In paint industry:

The paint should not contain dissolved gases as otherwise the paint

does not adhere well to the surface to be painted and thus will have a

poor covering power. The dissolved gases are therefore, removed by

suitable adsorbents during manufacture. Further, all surfaces are

covered with layers of gaseous, liquid or solid films. These have to be

removed before the paint is applied. This is done by suitable liquids

which adsorbs these films. Such liquids are called wetting agents. The

use of spirit as wetting agent in furniture painting is well known.

In chromatographic analysis:

The selective adsorbent of certain substances from a solution by a

particular solid adsorbent has helped to develop technique for the

separation of the components of the mixture. This technique is called

chromatographic analysis. For example: in column chromatography a

long and wide vertical tube is filled with a suitable adsorbent and the

solution of the mixture poured from the top and then collected one

by one from the bottom.

In catalysis:

The action of certain solids as catalysts is best explained in terms of

adsorption. The theory is called adsorption theory. According to this

theory, the gaseous reactants are adsorbed on the surface of the solid

catalyst. As a result, the concentration of the reactants increases on

the surface and hence the rate of reaction increases. The theory is

also able to explain the greater efficiency of the catalyst in the finely

divided state, the action of catalyst promoters and poisons.

In adsorption indicators:

Various dyes which owe their use to adsorption have been introduced

as indicators particularly in precipitation titrations. For example: KBr is

easily titrated with AgNO3 using eosin as an indicator.

In softening of hard water:

The use of ion exchangers for softening of hard water is based upon

the principle of competing adsorption just as in chromatography.

In removing moisture from air in the storage of delicate instruments:

Such instruments which may be harmed by contact with the moist air

are kept out of contact with moisture using silica gel.