Technology

INEOS' chlor-alkali technology is rooted in its BICHLOR™ membrane electrolyser system, a refinement of industrial electrolysis methods developed over 130 years. Here's a detailed technical breakdown:

Core Technology Origins

• Legacy foundation: Inherited infrastructure from ICI's 1897 Weston Point facility (UK), operational for over a century.
• Process evolution: Transitioned from mercury/diaphragm cells (phased out due to environmental concerns) to modern membrane technology.
• Key acquisitions: Expertise consolidated through historical assets, including ICI's electrolysis patents and operational know-how.

Technical Configuration

• Modular membrane cells:
  • Each module contains anode/membrane/cathode assemblies in a "zero-gap" design to minimize voltage loss.
  • Titanium anode pans with mixed metal oxide (MMO) coatings resist chlorine corrosion.
  • Nickel cathode pans with catalytic coatings enhance hydrogen evolution.
• Membrane materials: Fluorinated polymer cation-exchange membranes (e.g., Nafion™ derivatives) enable selective Na⁺ ion transfer.
• Pressure management: Operates at 0–400 mbarg via reinforced pan walls (1mm thickness vs. 0.8mm in competitors).

Performance Metrics

Operational Advantages

1. Maintenance efficiency:
   • Individual modules replaceable without full shutdowns.
   • External headers isolate hydrogen (cathode) and chlorine (anode) streams.
2. Safety features:
   • Fully wetted membranes prevent gas crossover and explosions.
   • Leak-resistant bolted seals on modules.
3. Material innovations:
   • Explosion-bonded titanium/nickel discs ensure electrical conductivity.
   • MMO anode coatings reduce chlorate byproduct formation.

Industrial Process Workflow

1. Brine Purification (ICI Legacy)

• Devices:
  • Dissolution tanks: Raw salt (NaCl) dissolved in water to form brine (25–28% NaCl)
  • Ion exchange columns: Removal of Ca²⁺, Mg²⁺, and heavy metals via chelating resins (ICI-developed process)
  • Settling tanks: Clarification to remove suspended solids

2. Brine electrolysis (BICHLOR™ Core):

• Modular cell design (ICI’s bipolar electrolyser patents → INEOS BICHLOR™):
  • Anode pan: Titanium substrate with mixed metal oxide (MMO) coating for chlorine evolution
  • Cathode pan: Nickel substrate with catalytic coating (16-year lifespan) for hydrogen evolution.
  • Cation-exchange membrane: Fluoropolymer-based (e.g., Nafion™) separating anode/cathode chambers.
  • Zero-gap configuration: Electrodes pressed directly against the membrane to minimize voltage drop.
• Process flow:
  1. Purified brine enters anode chamber via feed tubes, fully wetting the membrane.
  2. DC current (6–7 kA/m²) splits NaCl into Cl₂ (anode) and H₂ + NaOH (cathode):
     2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH
  3. Chlorine gas rises to anode chamber header; hydrogen and 32% NaOH catholyte exit cathode chamber.

3. Gas-Liquid Separation

• Anode side (Cl₂ handling):
  • Dechlorination towers: Stripping residual Cl₂ from depleted brine using vacuum or air.
  • Coolers/compressors: Chlorine gas cooled to 15–20°C for liquefaction or chemical synthesis.
• Cathode side (H₂/NaOH handling):
  • Gas separators: Hydrogen purified via catalytic recombination (O₂ removal) for fuel or ammonia production.
  • Evaporators: NaOH concentrated to 50% using multi-effect evaporation.

4. Product Finishing (ICI/INEOS Methods)

• Chlorine derivatives:
  • HCl synthesis: Combustion of H₂ and Cl₂ in quartz burners.
  • NaClO production: Absorption of Cl₂ in NaOH solution.​​​​​​​
• Caustic soda:
  • Crystallizers: Solid NaOH flakes/prills via cooling and drying.

References

1. INEOS Group > Electrochemical Solutions > The Chlor-Alkali Process. (Accessed 23rd May 2025) 
2. INEOS Group > Electrochemical Solutions > Modular Membrane Cell Electrolysers. (Accessed 23rd May 2025) 
3. INEOS Group > Electrochemical Solutions > INEOS Electrochemical Solutions. (Accessed 23rd May 2025)
4. INEOS Group > Electrochemical Solutions > BICHLOR™ ELECTROLYSER brochure. (Accessed 23rd May 2025) 
5. CloroSur, Technical Seminar, 18^th Nov 2014, CHLOR-ALKALI TECHNOLOGY, INEOS Technology.