Biocatalytic Synthesis of Biobased Acrylonitrile

Introduction

Acrylonitrile is a critical industrial monomer used in producing ABS plastics (Acrylonitrile Butadiene Styrene), carbon fiber precursors, nitrile rubber, and acrylamide polymers. It’s conventionally synthesized via the petroleum-based SOHIO process, which oxidizes propylene and ammonia over a bismuth-molybdate catalyst at high temperatures (~450°C).

This process is highly energy-intensive and carbon-intensive, driving the interest in biobased acrylonitrile via biocatalytic or hybrid fermentation-chemical approaches. Recent advances in metabolic engineering and chemo-enzymatic catalysis have made it possible to synthesize acrylonitrile from renewable feedstocks like glycerol, glucose, or 3-hydroxypropionic acid — offering a safer, cleaner, and climate-friendly pathway to this essential monomer.

What Products Are Produced?

Acrylonitrile – A key building block for:

• ABS plastics – Used in automotive parts, electronics
• Nitrile rubber (NBR) – Gloves, hoses, gaskets
• Carbon fiber precursors – Lightweight composites
• Acrylamide – Flocculants, paper chemicals, paints

Pathways and Production Methods

1. 3-Hydroxypropionic Acid (3-HP) Route

Sugar → 3-HP → Acrylonitrile

• Catalyzed by dehydration and ammoxidation steps
• Final conversion: 3-HP + NH₃ + O₂ → acrylonitrile + H₂O + CO₂
• Process can be chemocatalytic or enzymatic + thermal

2. Glycerol-Based Routes

Glycerol → Acrolein → Acrylonitrile

• Glycerol dehydrated to acrolein, then ammoxidation yields acrylonitrile
• Hybrid biocatalytic-chemical pathway with renewable glycerol as feedstock

3. Fermentative Glutamic Acid Pathway (Future Concept)

• Glucose → Glutamic acid → Acrylonitrile analogs (via deamination + dehydration)
• Theoretical; being explored for nitrogenated platform chemicals

Catalysts and Key Tools Used:

Key Enzymes & Catalysts

• Dehydratases – For converting 3-HP or glycerol to intermediates
• Ammoxidation catalysts – Vanadium, molybdate-based solid catalysts
• Hybrid enzymes + thermal steps – For eco-friendly reaction sequences

Engineering Approaches

• Pathway balancing for toxic intermediates
• Enzyme screening for stable dehydratases
• In situ ammonia control systems in fermentation
• Membrane reactors for intermediate removal

Feedstocks

• Crude glycerol (from biodiesel)
• Glucose, xylose (from lignocellulose)
• 3-HP (microbially produced from sugars or CO₂)

Case Study: DOE–Catalyst Partnership – 3-HP to Acrylonitrile Pilot

Highlights

• Produced acrylonitrile from 3-HP at ~80% yield
• Hybrid process: biological fermentation of 3-HP, then catalytic ammoxidation
• Used solid mixed oxide catalysts under milder conditions than SOHIO process
• Lower CO₂ emissions and energy consumption

Timeline

• 2015 – 3-HP platform identified as a biobased route to acrylonitrile
• 2017 – DOE pilot unit established with catalyst partners
• 2020 – Process validated at 1-ton scale
• 2023 – Licensing discussions for bio-acrylonitrile in carbon fiber production

Global and Indian Startups Working in This Area

Global

• Cargill & Rennovia (USA) – 3-HP to acrylonitrile via hybrid biocatalysis
• ADM – Glycerol-to-acrylonitrile valorization concepts
• BioAmber (legacy tech) – Biobased C3 intermediates
• LanzaTech – Syngas-based C3 routes to acrylonitrile analogs

India

• IIT Madras & CSIR-IICT – Glycerol-to-acrylonitrile feasibility
• IIT Guwahati – Metabolic pathways for 3-HP from sugars
• Praan Biosciences – Microbial catalysts for C3 acids
• Indian Oil R&D – Drop-in biobased acrylonitrile for rubbers

Market and Demand

The global acrylonitrile market was USD 12.4 billion (2023) and is projected to reach USD 17.3 billion by 2030, growing at a CAGR of ~5%. Biobased acrylonitrile, though currently under 2% of the market, is gaining interest in green automotive materials and carbon fiber composites.

Major End-Use Segments

• ABS resins and plastics – Automotive, electronics
• Acrylic fibers and composites
• Carbon fiber precursor resins
• Rubber and elastomers – Gloves, hoses
• Water treatment and adhesives

Key Growth Drivers

• Push for renewable ABS plastics and carbon fibers
• Rising glycerol surplus from biodiesel
• Toxicity concerns with propylene and SOHIO emissions
• Integration with biorefineries and C3 platforms
• Green composites in automotive and aerospace industries

Challenges to Address

• Thermal steps (ammoxidation) still required → hybrid process
• Low microbial tolerance to acrylonitrile and intermediates
• Catalyst degradation from byproducts or ammonia
• Uncertainty in industrial uptake due to cost and regulations
• India: Need for integration with glycerol valorization chains

Progress Indicators

• 2012–2015 – First microbial/catalytic 3-HP to acrylonitrile
• 2018 – Pilot trials for bio-acrylonitrile
• 2021 – Glycerol-based acrolein bioconversion improved
• 2023 – Enzymatic ammonia coupling research in India
• 2024 – Biobased acrylonitrile tested in electronics ABS

Globally, biobased acrylonitrile via 3-HP/glycerol is at TRL 6–7 (pilot validation). In India, it is at TRL 3–4 with academic and early tech-market efforts underway.

Conclusion

The biocatalytic synthesis of acrylonitrile is a promising route in the green transformation of polymers and fibers. Using glycerol and glucose as renewable sources can reduce emissions and fossil dependency.With strong C3 biotech R&D and biodiesel-derived glycerol, India has the potential to be a leader in biobased acrylonitrile innovation.