Technology Type

The SOHIO process is a catalytic ammoxidation method for producing acrylonitrile from propylene, ammonia, and air. Developed by Standard Oil of Ohio (SOHIO) in the 1950s, it remains the dominant industrial method, accounting for ~90% of global acrylonitrile production. Below is a technical breakdown^[1],[2].

Process Overview

The process involves vapor-phase catalytic oxidation of propylene with ammonia and oxygen in a fluidized bed reactor. Key features include:

• Feedstock: Propylene (C₃H₆), ammonia (NH₃), and air (O₂ source)^[1],[3]
   
• Catalyst: Bismuth phosphomolybdate (BiPMo₁₂O₄₀) or similar mixed metal oxides^[2],[4]
   
• Key Reaction:  C₃H₆ + NH₃ + ²/₃ O₂ → C₃H₃N + 3 H₂O (ΔH= −515 kJ/mol)^[1]
   
• Byproducts: Acetonitrile (CH₃CN), hydrogen cyanide (HCN), CO₂, and water^[1],[5]

Process Flow and Steps

Reaction Section

• Reactor Type: Fluidized bed reactor^[3]
   
• Operating Conditions: 
  • Temperature: 400–510°C^[3],[6]
  • Pressure: 0.3–2 atm (gauge)^[1]
  • Residence Time: 2–20 seconds^[1]
     
• Feed Ratios:
  • NH₃/Propylene molar ratio: 1.1:1
    Excess NH₃ ensures reaction completion^[1]
  • Air/Propylene molar ratio: 8.1:1
    Excess air regenerates the catalyst^[1]

Quench and Neutralization

• Quench System: Reactor effluent is cooled in a countercurrent water scrubber to ~30°C, dissolving ACN, HCN, and acetonitrile^[1],[5]
   
• Neutralization: Residual NH₃ is neutralized with H₂SO₄ to form (NH₄)₂SO₄^[1],[5]

Product Recovery

• Absorption: Non-condensables (N₂, CO, CO₂) are vented or incinerated
   
• Distillation:

  1. Recovery Column: Separates crude ACN/HCN from acetonitrile and water^[3],[5]

  2. Extractive Distillation: ACN is purified to 99% using water as an entrainer^[1]

  3. HCN Removal: Stripped via fractionation^[5]

Key Performance Metrics

• Propylene Conversion: ~98%^[1]
   
• Acrylonitrile Selectivity: 75-80%^[1]
   
• Acrylonitrile Yield: ~1.05 kg acrylonitrile/kg propylene^[1]
   
• Byproduct Distribution: HCN (6%), Acetonitrile (3%)^[5]

Environmental and Economic Considerations

• Emissions: CO₂, NO_x, and unreacted hydrocarbons are incinerated^[1],[5]
   
• Byproduct Recovery: Acetonitrile (solvent) and HCN (adhesives) are optionally recovered^[2],[5]
   
• Energy Efficiency: Waste heat is recovered for steam generation^[1]

Advantages Over Alternatives

• Single-Step Process: Eliminates intermediate synthesis steps^[1]
   
• Scalability: Fluidized bed design allows continuous operation^[3],[4]
   
• Cost-Effective: ~50% lower operating costs vs. ethylene cyanohydrin routes^[1]

References

1. Deepa H. A, Anusha R, Asha P, 2016, Evaluation on Production and Economics of Acrylonitrile by Sohio Process, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH & TECHNOLOGY (IJERT) ICRET – 2016 (Volume 4 – Issue 21).
2. Wikipedia, Ammoxidation. (accessed 21^st Mar 2025)
3. IGTPAN (Instituto Granado de Tecnologia da Poliacrilonitrila), The SOHIO Process. (accessed 21^st Mar 2025)
4. R. K. Grasselli, Chapter 5: Ammoxidation of Propylene and Propane to Acrylonitrile, in Nanostructured Catalysts: Selective Oxidations, ed. C. Hess and R. Schlögl, The Royal Society of Chemistry, 2011, ch. 5, pp. 96-140.
5. Gizem Baran, 24^th Jul 2018, Acrylonitrile Production - Academia.edu.
6. Brent E. Basham, Richard T. Stimek,US20090223804A1, Process to co-manufacture acrylonitrile and hydrogen cyanide, Priority 2008-03-05.