The resins consist of pores on the surface. The ions are both released and trapped by this system that is why whole system is termed as ion exchange system. There are different types of resins that caters to different types of ions. These resins are used in various types of industrial and commercial processes like purification, decontamination etc.
Styrene copolymerized with Divinylbenzene Resins are more popular. Apart from this, conventional ion exchange resins based on anion (chloromethylated, aminated) and cation (sulfonated) are used for multi-bed demineralization, mixed-bed condensate polishing, etc. As the Styrene Divinylbenzene has good capacity they offer significant stability.
Types of Ion Exchange Resin
On the basis of properties, ion exchange resins are of following types:
Strong Acid Cation Resins
Behaving like strong acid, these strong acid cation resins are highly ionized in both the acid (R-SO3H) and salt (R-SO3Na) form. Metal salt can be converted to the corresponding acid. The process reaction is as follows:
Weak Acid Cation Resins
Carboxylic acid (COOH) acts as the ionizable group in weak acid cation resins. They show more affinity for hydrogen ions. This results in the regeneration of the hydrogen form with less acid than is required for strong acid resins.
Strong Base Anion Resins
They are suitable for entire pH range. They deionize water in hydroxide (OH) form. Acidic nature of the water can be removed and purewater can be obtained. The reaction can be put forward as:
In weak base resins, intensity of ionization is affected by pH. They are incapable to split salts but can absorb acids.
Principle of Operation
Ion exchange resin consist of three-dimensional network of hydrocarbon chains of irregular macromolecules. For cation and anion exchangers following are ionic functional groups:
| Cation Exchangers (Carrying functional groups) | -COO- -PO32- -AsO32- -SO3- |
| Anion exchangers: (Carrying functional groups) | =S+- -NH3+ =NH2+ =N+= |
In cation and anion resins, ion exchange takes place in the following reactions:
| Cation exchange: | R-H+ + X+ « R-X+ + H+ |
| Anion exchange: | R+OH- + Y- « R+Y- + OH- |
| Neutralization: | H+ + OH- « H2O |
Properties
Ion exchange resins are mostly crosslinked polystyrene which is achieved by adding 0.5-25% of divinyl benzene to styrene at the polymerization process. Some of the properties that are related to cross linkage are:
- As the cross linkage is changed, the moisture content of the ion
exchange resin also gets altered. As cross linkage is increased the
moisture content get decreased:
- Chemical equivalents available for exchange per some unit weight
of resin is defined as capacity. Introduction of additional
functional becomes difficult if the resin is highly cross linked.
- The time required for an ion to reach equilibrium is affected by
crosslinkage. More is cross linkage time taken too reach equilibrium
is longer.
Ion exchange resins find applications in following processes and industries:
Processes
- Softening
- Dealkalizing
- Demineralizing
- Organic compound removal
- Nitrate removal
- Degasification.
- Water softening
- Water purification
- Juice manufacturing
- Sugar manufacturing
- Pharmaceutical industries
- Electronic industry
- Municipal water conditioning
- Boiler feed water conditioning
Removing Organics With Ion Exchange Resin: DeSilva, Francis J
Ion exchange or electrodialysis
