Technology Type

Historical Background

• Discovery: Phosgene was first synthesized in 1812 by John Davy, who combined carbon monoxide and chlorine under the influence of sunlight.
• Early Uses: Originally investigated for chemical synthesis, phosgene saw notorious use as a chemical weapon in World War I, causing the majority of chemical-related fatalities.
• Industrial Adoption: Post-war, phosgene became an indispensable intermediate in the global chemical industry, especially for the synthesis of polyurethanes (via isocyanates like TDI and MDI), polycarbonates, pesticides, pharmaceuticals, and dyes.

Technology Summary

• Core Reaction: The primary method for industrial phosgene production is the catalytic, gas-phase reaction of carbon monoxide (CO) and chlorine (Cl₂) over activated carbon or charcoal:
  CO(g) + Cl₂(g) → COCl₂(g)    ΔH = -107.6 kJ.mol^-1
  
• Process Type: The process is typically continuous, with high degrees of automation and stringent safety provisions due to phosgene’s acute toxicity.
• Alternative Routes: While laboratory and atmospheric photochemical or pyrolytic routes exist, all commercial-scale production today relies on the carbon-catalyzed process.
• Reaction parameters: Typical operating temperatures are 80°C to 200°C for activated carbon catalysts; reaction can occur up to 300°C but lower temperatures minimize detrimental byproducts and improve selectivity.

Detailed Process Description

Raw Material Preparation

CO and Cl₂ are purified to remove moisture, oxygen, and organic impurities:

• CO: ≥99% purity, dried via molecular sieves or similar
• Cl₂: ≥99.8% purity, obtained via brine electrolysis (chlor-alkali process)

Gas Mixing & Metering

• Precise metering ensures a slight excess of CO to prevent Cl₂ breakthrough and maximize conversion
• Gases are mixed using in-line mixers or packed beds (e.g., coke/Raschig rings)

Catalytic Reaction

• The gas mixture is passed through a fixed-bed reactor charged with high-surface-area activated charcoal
• Process Conditions:
  • Temperature: 80–180°C (industrial range); higher for special catalysts but <300°C for modern processes
  • Pressure: typically atmospheric, but can be up to 2–12 atm to increase throughput
  • Space velocity: optimized for full Cl₂ conversion and minimal by-product (CCl₄, CO₂)
• Hot-spot temperatures can approach 500–600°C near the reactor inlet due to the exothermic reaction, but catalyst bed exit temperatures are managed to 150–200°C.

Product Recovery & Purification

• The reaction effluent is condensed; non-condensable gases are sent to absorbers
• Phosgene is condensed (for storage or direct use), while unreacted gases and phosgene are captured via solvent scrubbing and activated carbon beds
• Final purification of phosgene is achieved by fractional distillation (removing COCl₂ from Cl₂, CO₂, HCl, and heavier compounds

Waste Treatment & Safety

• Effluents and phosgene-containing gases are neutralized using caustic soda (NaOH) systems achieving >99.99% destruction efficiency
• Multiple redundant scrubbers and real-time phosgene detectors are used for worker/environmental safety

Generic Process Flow Example

Simplified Phosgene Process Flow Diagram

• Feed: High-purity, dried CO and Cl₂.
• Mixer: Inline or packed bed mixer for even gas distribution.
• Primary Reactor: Fixed bed of activated charcoal (typically coconut shell type).
• Secondary Reactor: Completes conversion and manages temperature profile
• Condenser & Separation: Cools product, condenses phosgene, vents to absorber.
• Wash Columns & Distillation: Removes residual Cl₂, HCl, and byproducts, distills final product
• Caustic Scrubbers: Destroy residual phosgene by NaOH neutralization; incinerator or activated carbon beds as end-of-pipe controls.

Reaction Selectivity, Yield & Efficiency

• Selectivity: Highly selective toward phosgene so long as CO is in slight excess; side reactions such as CCl₄ (from insufficient CO) and CO₂ (from oxygen or high temperatures) are minimized with process optimization.
• Yields: Modern plants achieve near-quantitative yields (>99%) with <0.05% residual Cl₂
• Catalyst Performance: Catalyst (often coconut-shell activated carbon) is high surface area (1000–1200 m²/g), with 2–5 tons phosgene per kg of catalyst before reactivation is required
• Process Control: Key is rapid removal of reaction heat to avoid phosgene decomposition and catalyst fouling

Global Market Size & Deployments

• Market Size: The phosgene market was valued at $1.68 billion (2023) and is projected to reach $2.56 billion by 2032 (CAGR 4.6%)
• Volume: World production exceeds 2.7 million metric tonnes annually. Over 85% is used captively in polyurethane (isocyanates) and polycarbonates production
• Key Uses: Polyurethanes (TDI, MDI), polycarbonates, specialty chemicals (pesticides, dyes, pharmaceuticals), and carbonates
• Regional Highlights: Asia-Pacific leads demand (one-third of market share), followed by Europe and North America
• Major Producers: Covestro, BASF, Wanhua Chemical, Dow, Bayer, Paushak...

Technology Licensors & Providers

• Proprietary Processes: Most large producers have in-house, proprietary process details (e.g., Covestro, BASF, Dow), but the core technology (activated carbon catalysis) is open art and patent-free due to expired original patents
• BUSS ChemTech AG (Ciba-Geigy derivation): phosgene generators with single-train capacities up to 13,000 kg/h (28,600 lbs/h).
• General engineering firms: The basic gas-phase CO + Cl₂ over carbon catalyst process is public domain; many improvements relate only to catalyst life, safety, heat management, and emissions.

References

1. ScienceDirect. Phosgene.
2. Wikipedia. Phosgene.
3. Sarah Everts. May 12, 2015. A Brief History of Chemical War. Science History Institute.
4. National Library of Medicine. Emergency and Continuous Exposure Limits for Selected Airborne Contaminants: Volume 2. Phosgene. National Research Council (US) Committee on Toxicology. Washington (DC): National Academies Press (US); 1984.
5. National Library of Medicine (PubChem). Phosgene. 
6. Market Research Future. Phosgene Market Research Report.  
7. T. Anthony Ryan et al.. 4: Industrial manufacture and uses. Pergamon, Volume 24, 1996, Pages 167-221, ISSN 0082-495X, ISBN 9780444824455, DOI: 10.1016/S0082-495X(07)80009-6.
8. Walter Vladimir Cicha, Leo E. Manzer. European Patent EP0881986A1: Phosgene manufacturing process. Priority date: Nov 01, 1996. Assignee: EIDP Inc. 
9. Z. Csuros et al.. May 2, 1969. Investigation of the reaction conditions of phosgene production. Periodica Polytechnica Chemical Engineering, 1970, Vol. 14, Pages 3-11.
10. R. Hughes et al.. Aug 25, 2023. Operational parameters relevant to the examination of phosgene synthesis catalysis.  React. Chem. Eng., 2023, 8, 3150-3161. DOI: 10.1039/D3RE00354J.
11. United States Environmental Protection Agency. Sep 1985. EPA-450/4-84-007i: Locating and Estimating Air Emissions from Sources of Phosgene.
12. Data Insight Market. May 2, 2025. Phosgene: Growth Opportunities and Competitive Landscape Overview 2025-2033.
13. Allied Market Research. Jun 2022. Phosgene Market, by Derivative and Application: Global Opportunity Analysis and Industry Forecast, 2022-2031.