Detailed explanation of softening resin knowledge

Detailed explanation of softening resin knowledge

Water treatment resin is divided into cationic resin and anionic resin.

The cationic resin is subdivided into sodium type and hydrogen typy.

● Sodium resin exchanges calcium and magnesium ions in water into sodium ions to make the water soft.

● The hydrogen type resin is to exchange calcium and magnesium ions in the water with hydrogen ions to soften the water.

The anion resin contains replaceable hydroxide ions, which can replace the acid ions in the water, and the use of anion resin and hydrogen-type cationic resin can change the water into pure water.

In the water treatment industry, ion exchange is the reaction of equimolar molar amounts of ions in water and ions on ion exchange resins.

Resin trap is an indispensable equipment in this process, Huanzheng provides customized processing services for Johnson screen resin traps (https://www.zhehanfilter.com/news/johnson-screen-resin-trap-filter-for-water-treatment.html). 

Physical properties

The particle size and related physical properties of ion exchange resins have a great influence on its work and performance.

Resin particle size

Ion exchange resins are usually made into small beads, and their size is also important.

The smaller the resin particles, the greater the reaction speed, but the resistance of the fine particles to the passage of liquid is greater, requiring a higher working pressure.

Especially the concentrated sugar liquid has a high viscosity, and this effect is more significant.

Therefore, the size of the resin particles should be selected appropriately. If the resin particle size is below 0.2mm (about 70 mesh), it will significantly increase the resistance of fluid flow, reduce the flow rate and production capacity.

Resin particle size is usually determined by wet sieving method, the resin is sieved after fully swelled with water.
Accumulating the remaining amount on the 20, 30, 40, 50...mesh screen, 90% of the particles can pass through the corresponding diameter of the sieve, which is called the "effective particle size" of the resin.
The effective particle size of most general-purpose resin products is between 0.4 and 0.6 mm.

Whether the resin particles are uniform is expressed by a uniform coefficient.It is to determine the "effective particle size" of the resin and take the cumulative retention of 40% of the particles, and the ratio of the corresponding screen diameter to the effective particle size. For example, the effective particle size of a resin (IR-120) is 0.4 ~ 0.6mm, and the particles retained on the 20 mesh sieve, 30 mesh sieve and 40 mesh sieve are:

18.3%, 41.1%, and 31.3%, the calculated uniformity coefficient is 2.0.

The particle size of the resin is critical to the selection of the resin trap filter element, choose the right wedge wire screen slot size to carry out effective work. (https://www.zhehanfilter.com/sintered-wire-mesh/wedge-wire-screen.html)

Resin density

The density of the resin when it is dried is called true density.

The weight of the wet resin per unit volume (even the voids between particles) is called the apparent density. The density of the resin is related to its crosslinking degree and the nature of the exchange group. Generally, resins with a high degree of cross-linking have higher densities. The density of strongly acidic or strongly basic resins is higher than that of weakly acidic or weakly basic resins, while the density of macroporous resins is lower.

Solubility of resin

The ion exchange resin should be insoluble.

However, substances with a low degree of polymerization included in the resin during the synthesis process, and substances generated by the decomposition of the resin will be dissolved during the operation.

Resins with a low degree of crosslinking and many active groups have a greater tendency to dissolve.

Degree of swelling of resin

Ion exchange resins contain a large number of hydrophilic groups, which swell upon contact with water.

When the ions in the resin change, for example, the cationic resin changes from H+ to Na+, and the anion resin changes from Cl- to OH-, all expand due to the increase in ion diameter, increasing the volume of the resin.

Generally, resins with a low degree of crosslinking have a greater degree of swelling. When designing an ion exchange device, the degree of expansion of the resin must be considered to accommodate the resin volume change that occurs during ion conversion in the resin during production operation.

Durability of resin

Resin particles have transfer, friction, expansion and contraction changes during use. After long-term use, there will be a small amount of wear and tear, so the resin must have high mechanical strength and wear resistance. 

Generally, resins with a low degree of cross-linking are more fragile, but the durability of the resin is mainly determined by the uniformity and strength of the cross-linked structure.

Such as macroporous resins, those with a higher degree of cross-linking, the structure is stable and can withstand repeated regeneration.

Cationic resin

This type of resin contains a large number of strongly acidic groups, such as sulfonic acid group-SO3H, which is easily dissociated into H+ in solution, so it is strongly acidic.

After the resin dissociates, the negatively charged groups contained in the body, such as SO3-, can adsorb other cations in the binding solution.

These two reactions exchange H+ in the resin with cations in the solution. Strong acid resin has a strong dissociation ability, and can dissociate and produce ion exchange in acidic or alkaline solutions.

After the resin is used for a period of time, it needs to be regenerated, that is, the ion exchange reaction is carried out in the opposite direction with chemicals to restore the functional group of the resin to its original state for reuse.

As mentioned above, the cationic resin is regenerated with strong acid. At this time, the resin releases the adsorbed cation, and then combines with H+ to restore the original composition.

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