Achieving Premium Brine Quality in Chlor-Alkali Production through Chelating Resins

The quality of brine in chlor-alkali production is crucial. Traditional primary brine purification does not meet the required standards, so secondary purification of the brine is necessary. In the secondary brine purification process, ion exchange resins are generally used to remove Ca²⁺, Mg²⁺, and heavy metals. These devices utilize the selectivity and equilibrium reaction principles of anion and cation exchange resins to remove electrolyte ions from water. This process is essential for producing high-purity water. After the brine is refined through the ion exchange filter, the secondary brine can achieve a total mass fraction of Ca²⁺ and Mg²⁺ of less than 20 ppb.

Working Principle：

In the ion-exchange membrane process for caustic soda production, the typical reactions for removing cations from brine are:

 

Service Cycle：

RCH₂N(CH₂COONa)₂ + Ca²⁺ → RCH₂N(CH₂COO)₂Ca + 2Na⁺

 

Regeneration:

RCH₂N(CH₂COO)₂Ca + 2HCl → RCH₂N(CH₂COOH)₂ + CaCl₂

 

Conditioning:

RCH₂N(CH₂COOH)₂ + 2NaOH → RCH₂N(CH₂COONa)₂ + 2H₂O

 

In these reactions, the chelating resin RCH₂N(CH₂COOH)₂ reacts with divalent metal ions such as Ca²⁺, Mg²⁺, and Sr²⁺, forming stable chelate complexes RCH₂N(CH₂COO)₂Ca and releasing hydrogen ions (H⁺) or sodium ions (Na+)in case of resin operated in sodium form. This process effectively removes these hardness ions from the brine, thus purifying it to meet the stringent quality requirements for ion-exchange membrane caustic soda production.

 

Selectivity Order：

• Under Acidic Conditions: Pb2+ > Cu2+ > U4+ > Zn2+ > Al3+ > Mg2+ > Sr2+ > Ca2+ > Na+ > Ba2+
• Under Alkaline Conditions: Mg2+ > Ca2+ > Sr2+ > Al3+ > Ba2+ ≥ Na+ > K+

 

SEPLITE® LSC750 Chelating Resin

SEPLITE® LSC750 chelating resin is a macroporous, uniformly sized resin with weakly acidic aminophosphonic acid active groups, cross-linked with styrene and divinylbenzene. This chemical structure facilitates the formation of chelates with metal ions. Compared to iminodiacetic acid resins, aminophosphonic acid chelating resins exhibit a higher affinity for divalent cations and form more stable chelates with low atomic weight and low-valence cations. Therefore, SEPLITE® LSC750 aminophosphonic acid chelating resin is more suitable for secondary brine purification in ion-exchange membrane caustic soda production, whereas iminodiacetic acid type chelating resins are better suited for removing heavy metal ions.

SEPLITE® LSC750 Resin Structural Formula

 

Working Principle：

In the ion-exchange membrane process for caustic soda production, the typical reactions for removing hard ions from brine are:

 

Service Cycle:

RCH₂NHCH₂PO₃Na₂ + Ca²⁺ → RCH₂NHCH₂PO₃Ca + 2Na⁺

 

Regeneration:

RCH₂NHCH₂PO₃Ca + 2HCl → RCH₂NHCH₂PO₃H₂ + CaCl₂

 

Conditioning:

RCH₂NHCH₂PO₃H₂ + 2NaOH → RCH₂NHCH₂PO₃Na₂ + 2H₂O

 

Selectivity Order：

• Under Acidic Conditions (pH acidic): Pb2+ > Cu2+ > U4+ > Zn2+ > Al3+ > Mg2+ > Sr2+ > Ca2+ > Na+ > Ba2+
• Under Alkaline Conditions (pH basic): Mg2+ > Ca2+ > Sr2+ > Al3+ > Ba2+ ≥ Na+ > K+

 

IV. Application of Uniform Particle Size Chelating Resins

To adapt to developments in the ion-exchange membrane caustic soda industry, Sunresin has developed SEPLITE® LSC750 (aminomethylphosphonic acid) and SEPLITE® LSC710 (iminodiacetic acid) chelating resins. Building on this foundation, Sunresin has obtained a full set of patents for the production equipment of uniform particle size chelating resins. Sunresin has introduced the improved SEPLITE® Monojet™ LSC7100 iminodiacetic acid and SEPLITE® Monojet™ LSC7500 aminomethylphosphonic acid uniform particle size chelating resins.

 

Sunresin is currently the only company in China with the capability to produce uniform particle size chelating resins, filling the domestic gap in this area. These advancements effectively enhance the efficiency and extend the lifespan of ion-exchange membranes.

 

SEPLITE® Monojet™ LSC7100 and SEPLITE® Monojet™ LSC7500 Chelating Resins

SEPLITE® Monojet™ LSC7100 and SEPLITE® Monojet™ LSC7500 are macroporous, uniform particle size chelating resins developed and produced by Sunresin. These resins have a styrene backbone and feature iminodiacetic acid and aminophosphonic acid groups, respectively. Their chemical structures are conducive to forming chelates with metal ions, enabling selective adsorption.

 

Both iminodiacetic acid chelating resins and aminophosphonic acid chelating resins exhibit high affinity for metal cations and easily form stable chelates with divalent metal cations. Consequently, SEPLITE® Monojet™ LSC7100 and SEPLITE® Monojet™ LSC7500 uniform particle size chelating resins are suitable for secondary brine purification in the ion-exchange membrane process for caustic soda production.

 

• Faster Exchange Speed and Higher Working Exchange Capacity: These resins demonstrate more efficient ion exchange processes and can handle larger volumes of metal ions.
• Better Hydraulic Characteristics During Operation: Improved flow dynamics result in lower system pressure drops during operation.
• Significant Improvement in Brine Treatment Volume and Efficiency: They can process greater quantities of brine more efficiently in each cycle.
• Higher Resistance to Osmotic Shock: Lower breakage rates under similar operating conditions, reducing the need for resin replenishment and replacement
• Longer Lifespan with Advanced Granulation Technology: Manufactured using internationally leading jet granulation technology, these resins offer enhanced durability.
• Excellent Uniformity and Larger Effective Void Volume: The resins' uniform particle size provides greater effective porosity, improving overall performance.