Biosynthetic Pathways for Biobased Ethylene

Introduction

Ethylene (C₂H₄) is the world’s most produced organic chemical, forming the backbone of plastics, solvents, textiles, and packaging. Traditionally derived from steam cracking of fossil hydrocarbons, ethylene production accounts for significant carbon emissions (~2 tonnes CO₂ per tonne of ethylene).

The shift toward biobased ethylene offers a sustainable alternative—leveraging biomass, bioethanol, and engineered microbes to replace fossil routes. With drop-in compatibility for existing infrastructure and a vast array of downstream uses, biobased ethylene is a high-impact molecule in the journey toward decarbonized chemistry.

What Products Are Produced?

• Ethylene (C₂H₄) – Primary monomer
• Bio-Polyethylene (Bio-PE) – Green plastics
• Ethylene oxide, ethylene glycol – Precursors for antifreeze, PET
• Vinyl acetate, styrene – Coatings and packaging resins
• Polyvinyl chloride (PVC), EVA – Flexible and rigid plastics

Pathways and Production Methods

1. Bioethanol-to-Ethylene (Dehydration Route)

• Fermentative production of ethanol from sugars or lignocellulosic biomass
• Catalytic dehydration of ethanol at 400–500°C to ethylene
• Catalysts: Al₂O₃, HZSM-5, silica-alumina

2. Direct Microbial Ethylene Production

• Engineered microbes express ethylene-forming enzyme (EFE) from Pseudomonas
• Conversion of α-ketoglutarate + arginine → ethylene + succinate + CO₂
• Works in E. coli, Synechococcus, and yeast systems under aerobic conditions

3. Photoautotrophic Routes Using Algae or Cyanobacteria

• Synechococcus elongatus and Chlamydomonas reinhardtii modified to fix CO₂ and emit ethylene
• Solar-driven process using photosynthesis and EFE
• Produces ethylene gas directly from light and CO₂

Catalysts and Key Tools Used

Fermentation:

• Saccharomyces cerevisiae, Zymomonas mobilis, Clostridium spp. for ethanol
• Lignocellulosic and 2G biomass used as feedstock

Catalysts for Dehydration:

• HZSM-5, SAPO-11, and phosphated alumina for high ethylene selectivity
• Operate in fluidized-bed or fixed-bed reactors

Genetic Engineering Tools:

• Ethylene-forming enzyme (efe gene) insertion
• Synthetic promoters for high EFE expression
• CO₂-fixation enhancements in photoautotrophs

Case Study: Braskem’s Green Ethylene from Sugarcane Ethanol

Highlights

• Uses bioethanol from sugarcane in Brazil
• Dehydrates it to ethylene using zeolite-based catalysts
• Produces over 200,000 tonnes/year of green ethylene
• Supplied to make bio-PE and green packaging for global brands like Coca-Cola and LEGO

Timeline

• 2010 – World’s first commercial green ethylene plant launched
• 2014 – Expansion of bio-PE offerings to global brands
• 2022 – Achieved 2 million tonnes of CO₂ saved milestone
• 2024 – Scaling green EVA and other co-polymers from biobased ethylene

Global and Indian Startups Working in This Area

Global

• Braskem (Brazil) – Leader in ethanol-based green ethylene
• LanzaTech (USA) – Exploring CO₂-to-ethanol-to-ethylene route
• Virent & Gevo (USA) – Biomass-to-ethylene via sugar intermediates
• Avantium (Netherlands) – Indirect ethylene via furanics and dehydration

India

• Praj Industries – Bioethanol-to-ethylene and downstream products
• Godavari Biorefineries – Ethanol-based biopolymer monomer exploration
• IIT Madras, CSIR-IIP – Dehydration catalysts for bioethanol
• IISER Pune & IIT Guwahati – Engineered E. coli and cyanobacteria for direct ethylene production

Market and Demand

The global ethylene market was valued at USD 165 billion in 2023, projected to reach USD 210 billion by 2030. Though biobased ethylene comprises less than 1% of current supply, it’s growing at a CAGR of ~10–12%, especially in packaging and consumer goods.

Major Use Segments:

• Packaging films and containers
• Construction materials (pipes, insulation)
• Textiles and fibers
• Automotive and electronics
• Green consumer products – bio-PE for branded goods

Key Growth Drivers

• Demand for fossil-free polyethylene and plastics
• Government mandates on bioplastic content and sustainability labeling
• Abundance of bioethanol from molasses, corn, and lignocellulose
• Industry shift toward carbon-negative materials
• Consumer push for eco-certified packaging

Challenges to Address

• Energy requirements of ethanol dehydration at high temperature
• Cost gap between fossil vs. bioethanol feedstocks
• Stability and productivity of EFE-based microbial systems
• Limited photoautotrophic ethylene production at scale
• In India: Need for public-private investments to scale 2G bioethanol-based ethylene

Progress Indicators

• 2008–2010 – First ethanol dehydration demo by Braskem
• 2014 – Start of engineered microbial ethylene research in cyanobacteria
• 2018 – Pilot photoautotrophic ethylene production
• 2022 – India’s ethanol surplus positions it for green ethylene scale-up
• 2024 – Green PE and EVA gaining traction in packaging and footwear sectors

Ethanol dehydration route: TRL 9 (commercial scale globally and demo-ready in India). Engineered microbial ethylene: TRL 4–6 (lab to early pilot). Photoautotrophic microbial ethylene: TRL 3–5 (proof-of-concept and small scale)

Conclusion

Biosynthetic pathways for biobased ethylene offer a powerful route to decarbonize one of the largest and most polluting petrochemical value chains. Whether through bioethanol dehydration or microbial photosynthesis, these innovations open the door to net-zero plastics, fibers, and chemicals.

With India’s ethanol economy expanding, and the world demanding low-carbon materials, biobased ethylene stands as a strategic molecule for green industrial transformation—one that blends biology, catalysis, and circular chemistry.

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