Problems of Alkaline Degreaser in Winter

by Dr E. Ramanathan , Coating Consultant

Alkaline degreasers based on caustic soda (NaOH) face several issues in winter, particularly with oil removal:

Challenges of Caustic-Based Alkaline Degreasers in Winter:

1. Poor Oil Emulsification in Cold Conditions:
   • In low temperatures, oils and greases become more viscous and harder to remove.
   • Caustic-based degreasers rely on saponification (reaction with fats to form soap) and emulsification, which slow down in cold temperatures.
2. Oil Floating on Subsequent Baths:
   • When oil is not effectively emulsified, it remains floating in degreasing and rinsing baths.
   • This leads to contamination of subsequent processes like phosphating or electrocoating.
3. Incomplete Cleaning on High-Oil Loads:
   • In cases where the material has excessive oil, the degreaser struggles to break it down, leading to redeposition and poor bath life.

Possible Remedies and Reformulation Approaches

To improve performance in winter and prevent floating oil issues, we can adjust the formulation and process:

1. Improve Oil Emulsification

✅ Add Nonionic Surfactants:

• Nonionic surfactants help emulsify oil better at low temperatures.
• Examples:
  • Alkylphenol ethoxylates (e.g., NP-9, NP-10)
  • Fatty alcohol ethoxylates (C12-C14 ethoxylates)
  • EO/PO block copolymers

✅ Use Solvent Boosters:

• Glycol ethers (e.g., Butyl Cellosolve) can improve oil solubility.
• Helps prevent oil from floating by better dispersing it in the bath.

2. Optimize Alkalinity Source

✅ Reduce Excess Caustic Soda (NaOH):

• High NaOH can lead to excessive saponification, forming floating soap scum.
• Instead, balance with Sodium Metasilicate (Na₂SiO₃) or Borates for improved emulsification.

✅ Use Sodium Carbonate or Sodium Metasilicate Instead of Pure NaOH:

• Sodium carbonate (Na₂CO₃) maintains alkalinity but is milder.
• Metasilicate improves wetting and prevents redeposition.

3. Add a Sequestrant to Improve Stability

✅ Use Chelating Agents Like EDTA or Phosphonates:

• These prevent soap scum formation and improve bath stability.
• Helps in water hardness control.

4. Use a Surfactant Blend for Cold Conditions

✅ Cold Degreasing Formulation:

• NaOH: 2–5% (Reduced to prevent floating soap)
• Sodium Metasilicate: 3–6% (Improves wetting)
• Nonionic Surfactants (NP-9, C12-C14 EO/PO): 1–3%
• Glycol Ether Solvent: 2–4% (Enhances oil removal)
• Sequestering Agent (EDTA, NTA, Phosphonates): 0.5–2%

5. Mechanical and Process Modifications

✅ Increase Bath Agitation:

• Use air sparging or mechanical circulation to keep oil dispersed.

✅ Pre-Wash with Warm Water or Light Solvent Spray:

• A warm pre-rinse (40–50°C) can reduce oil viscosity before alkaline degreasing.

✅ Use Oil Skimmers or Coalescers in the Bath:

• Helps remove floating oil and extends bath life.

Consultant’s Suggestion:

For winter operation, modify the degreaser by adding surfactants, reducing NaOH, and introducing solvents or chelating agents. If floating oil remains a problem, install an oil skimmer and improve bath circulation.

There are some misconcepts of LABS as sulphuric acid. It is not sulphuric acid, it is linear alkyl benzene sulphonate.

For solving heavy oil floating issues in an alkaline degreasing bath, a nonionic surfactant with excellent emulsification properties in a powder form is recommended. The best options include:

1. Sodium Lauryl Sulfate (SLS) Powder – A strong emulsifier that helps break down heavy oil.
2. Sodium Dodecylbenzenesulfonate (SDBS) Powder – Effective in alkaline solutions for oil dispersion.
3. Ethoxylated Nonylphenol (NP-9 or NP-10) in Powder Form – Good for emulsifying heavy oils in high pH environments.
4. Sodium Alkyl Ether Sulfate (AES) Powder – Enhances solubility and wetting properties.
5. Sodium Salt of Sulfosuccinate Esters – Works well as a detergent and dispersant in alkaline degreasing.
6. Sodium Stearate or Sodium Oleate – Soap-based emulsifiers that work in high alkalinity.

Among these, SDBS (Sodium Dodecylbenzenesulfonate) in powder form is widely available and works efficiently in high-alkaline baths, offering excellent oil emulsification and preventing floating oil accumulation.

Additional Notes

Mechanical Oil Skimmers available in the market