Enzymatic Conversion of Biomass to Adipic Acid

Introduction

Adipic acid is a key dicarboxylic acid used in the production of nylon-6,6, polyurethanes, plasticizers, and coatings. Globally, over 3 million tons of adipic acid are produced annually, primarily from petrochemical routes involving benzene, nitric acid, and cyclohexane, processes that emit significant amounts of nitrous oxide (N₂O)—a potent greenhouse gas.

To decarbonize this supply chain, researchers have turned to biomass-derived sugars and lignin as feedstocks and enzymes as eco-friendly catalysts. The enzymatic conversion of biomass to adipic acid represents a green alternative that avoids harsh chemicals and reduces CO₂ emissions, using biocatalysis to replace energy-intensive steps.

What Products Are Produced?

• Bio-based Adipic Acid – Used in:
• Nylon-6,6 fibers and plastics
• Thermoplastic polyurethanes (TPUs)
• Plasticizers and resins
• Performance coatings and sealants
• Co-products/Intermediates – Glucaric acid, muconic acid, 2-oxoadipic acid

Pathways and Production Methods

1. Glucose to Adipic Acid via Muconic Acid

• Glucose → Shikimate pathway → Muconic acid → Adipic acid
• Muconate is enzymatically hydrogenated using enoate reductases or whole-cell catalysts

2. Oxidation of 5-HMF or Glucaric Acid

• Biomass sugars → 5-hydroxymethylfurfural (5-HMF) or glucaric acid
• Enzymatic ring-opening and hydrogenation lead to adipic acid

3. Lignin Valorization Pathway

• Lignin → Aromatic intermediates (e.g., catechol, vanillin) → Muconic acid → Adipic acid
• Enzymes and microbial cascades convert aromatic units to linear dicarboxylic acids

Catalysts and Key Tools Used

Key Enzymes:

• Cis,cis-muconate cycloisomerase
• Muconolactone isomerase
• Reductive enoate reductases
• Aldehyde/alcohol dehydrogenases (for HMF intermediates)

Microbial Hosts:

• E. coli, Pseudomonas putida, Saccharomyces cerevisiae (engineered for pathway steps)

Tools:

• CRISPR-Cas9 for metabolic rewiring
• Immobilized enzymes for stepwise reactions
• Co-culture systems for multistep bioconversions
• Computational protein engineering for enzyme specificity

Case Study: Verdezyne’s Muconic Acid to Adipic Acid Process

Highlights

• Engineered Candida tropicalis and E. coli to produce muconic acid from sugars
• Used biocatalytic hydrogenation to convert muconate to adipic acid
• Product passed performance tests for nylon-grade specifications

Timeline

• 2011 – Proof-of-concept for bio-adipic acid via muconate
• 2014 – Pilot plant operation in Malaysia using palm-based sugars
• 2017 – Produced over 20 tons/year of bio-adipic acid
• 2020 – Operations paused; IP licensed to global chemical producers

Global and Indian Startups Working in This Area

Global

• Verdezyne (USA/Malaysia) – Sugar to adipic acid via muconate
• Genomatica (USA) – Biosynthetic pathways for C6 dicarboxylic acids
• Cargill – Exploring adipic acid via enzymatic and fermentation platforms
• DSM & Evonik – R&D in green nylon intermediates

India

• IIT Bombay & ICT Mumbai – Enzymatic oxidation of 5-HMF and sugar acids
• IIT Guwahati – Lignin to muconate via Pseudomonas strains
• NCL Pune – Enzyme cascade design for dicarboxylic acid synthesis
• DBT-supported consortia – Working on microbial fermentation and enzyme screening for nylon monomers

Market and Demand

The global adipic acid market was valued at USD 6.3 billion in 2023, projected to reach USD 8.7 billion by 2030, with a CAGR of ~4.8%. The bio-based segment, though small, is growing at over 12% CAGR, fueled by nylon and polyurethane applications.

Major Use Segments:

• Textiles and clothing (nylon fibers)
• Automotive and electronics (engineering plastics)
• Footwear and sportswear (TPUs)
• Construction and coatings

Key Growth Drivers

• Demand for green nylon and polyurethane
• Environmental regulations on nitrous oxide emissions
• Shift toward lignocellulosic biorefineries
• Brand interest in sustainable packaging and textiles
• Integration with sugar and lignin supply chains

Challenges to Address

• Low enzyme activity or specificity for key steps
• Thermodynamic bottlenecks in hydrogenation reactions
• High product recovery costs due to downstream purification
• In India: Lack of pilot-scale continuous bioprocessing systems

Progress Indicators

• 2010–2013 – Enzymatic muconate conversion demonstrated
• 2015 – Pilot bio-adipic acid production in Asia
• 2018 – Lignin valorization routes gain global interest
• 2021–2023 – Indian research focuses on modular biocatalysis
• 2024 – India sees DBT and DST grants in nylon bio-feedstocks

Sugar to adipic acid (muconate route): TRL 6–7. HMF and lignin-based routes: TRL 4–6. In India: Work ongoing at TRL 3–5, with enzymatic cascades in development

Conclusion

The enzymatic conversion of biomass to adipic acid provides a sustainable alternative to petroleum-based nylon monomers. Using green biocatalysts, researchers can unlock pathways that reduce emissions, enable circular carbon use, and promote biobased materials in textiles, plastics, and automotive sectors.

India’s biomass abundance and growing bioeconomy support a promising future for bio-adipic acid manufacturing, especially with ongoing research in enzymatic valorization, lignin chemistry, and bioreactor design.

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