The process of gelatin filtration by ion exchange method

Ion exchange is a way to separate and purify things based on the interaction of charges. We use resin in this process. The resin has exchangeable ions on it. These ions can react with the charged impurities in the gelatin solution. Things like metal ions, pigments, and small molecular organic compounds are among those charged impurities. They’ll have a displacement reaction. Thanks to this reaction, we can get rid of the impurities and make the gelatin much purer. It’s really a useful technique for improving the quality of gelatin.

The application of ion exchange in the purification of gelatin

1. Remove mental ions(deliming)

• Treatment of impurities: Residual Ca²⁺, Mg²⁺, Fe³⁺, etc. in the gelatin raw materials(from the ash of animal bones and skins)
• Resin selection: Strong acid cation exchange resin (such as sulfonic acid type resin)
• Operation conditions：
  • PH range: 4.0-5.5(near the isoelectric point of gelatin to reduce the adsorption of gelatin)
  • Flow rate: 1-2 BV/h
• Effect: The ash content is reduced from 2-5% to <0.1%, meeting the standards of pharmaceutical grade.

2. Decolorization and removal of organic acids

• Treatment of impurities: Pigments(sucha as melanoidins), small molecular organic acids(such as lactic acid).
• Resin selection: Macroporous anion exchange resin (such as acrylic resin)
• Principle: Pigments and organic acids are negatively charged and adsorbed by the resin, while adjusting the pH of the solution.
• Effect: Transmittance (660 nm) increased by 10-15%, odor significantly reduced.

3. Remove endotoxins and pyrogens

• Treatment of impurities: Endotoxins (lipopolysaccharide, negatively charged), microbial metabolites
• Resin selection: Strong basic anion exchange resins (such as quaternary ammonium resins)
• Operation conditions：PH: 6.0-8.0（Endotoxin has a high degree of ionization and is easily adsorbed）
• Effect: Endotoxin content <0.25 EU/mL (meeting injection grade standards)

Operation Procedures

Pretreatment

• The gelatin solution is subjected to microfiltration (0.45 μm) to remove suspended particles and prevent the resin bed from being blocked.
• Adjust the pH to the optimal working range of the resin (for example, use pH 4.5 for cationic resins and pH 7.0 for anionic resins).

Operation of the ion exchange column

• Column loading: The resin is soaked in water and swollen before loading, and the column height-to-diameter ratio is ≥5:1.
• Adsorption: The gelatin solution passes through the resin column at a flow rate of 1-3 BV/h, and the outlet conductivity or ion concentration is monitored.
• End point judgment: When the outlet impurity concentration reaches 10-20% of the inlet, stop feeding.

Resin regeneration

• Cationic resin: rinse with 5-10% HCl to replace adsorbed metal ions.
• Anion resin: rinse with 4-8% NaOH to remove pigments and organic acids.
• Water washing: rinse with deionized water until neutral and set aside.

Advantages and Limitations

Advantage

• High selectivity: Directed removal of specific ions (such as Ca²⁺, Fe³⁺) to avoid functional loss of gelatin.
• Deep purification: Deashing, decolorization, and pyrogen removal can be performed simultaneously to improve product grade.
• Renewability: The resin can be reused hundreds of times, reducing long-term costs.

Limitation

• High pretreatment requirements: suspended solids must be removed first to prevent resin contamination.
• PH sensitivity: PH must be strictly controlled to avoid gelatin denaturation or resin failure.
• Long operation cycle: The adsorption-regeneration process is time-consuming and suitable for intermittent production.

Application

Points for Attention

1. Prevention and control of resin contamination:

• Regularly disinfect with a 0.1% sodium hypochlorite solution to prevent the growth of microorganisms.
• Avoid contact between oily substances and the resin (which may lead to irreversible blockage).

2. Control of gelatin loss:

• Optimize the pH to reduce the non-specific adsorption of gelatin to the resin.

3. Environmental protection treatment:

• The regenerated waste liquid (containing acids and alkalis) should be neutralized before discharge.

Conclusion

The ion exchange method precisely removes ionic impurities in gelatin through the charge adsorption-release mechanism, and it is a key process for preparing high-purity gelatin, especially for pharmaceutical and injection-grade gelatin. Its core lies in:

• Selective adsorption: Select the appropriate resin type and operating conditions according to the target impurities;
• Regeneration cycle: Achieve the reuse of the resin through acid-base regeneration to reduce costs.
  In practical applications, it is often used in combination with processes such as membrane filtration and activated carbon adsorption to build an efficient purification chain.