Metabolic Engineering for Renewable Propylene Glycol

Introduction

Propylene glycol (PG) is a widely used chemical intermediate in industries like cosmetics, pharmaceuticals, food, plastics, and antifreeze. Conventionally derived from petroleum-based propylene oxide, its production contributes to fossil fuel consumption and greenhouse gas emissions.

In response to rising environmental concerns, scientists are exploring renewable routes to propylene glycol, especially using metabolic engineering. By modifying microbial metabolic pathways, renewable feedstocks like glucose, glycerol, and agricultural waste can be converted into biobased PG via biosynthetic processes that are cleaner, safer, and more sustainable.

What Products Are Produced?

• 1,2-Propylene Glycol (1,2-PG) – Main target for antifreeze, solvents, and food additives
• Acetol – An intermediate in some engineered biosynthetic pathways
• Renewable derivatives – Including polyester precursors and humectants

Pathways and Production Methods

1. Glycerol-Based Pathways

• Glycerol is converted to dihydroxyacetone (DHA) → acetol → 1,2-PG
• Enzymes involved: Glycerol dehydratase, aldehyde reductase

2. Glucose-Based Routes (via Pyruvate)

• Glucose → pyruvate → lactate or acetol → propylene glycol
• E. coli and Corynebacterium glutamicum engineered to express lactate reductase, methylglyoxal synthase

3. Reductive Acetol Pathway

• Glycerol/glucose converted to acetol via engineered keto intermediates
• Acetol is reduced by alcohol dehydrogenase to 1,2-PG

Catalysts and Key Tools Used

Microbial Hosts:

• E. coli, C. glutamicum, Saccharomyces cerevisiae, Bacillus subtilis

Key Enzymes:

• Glycerol dehydratase
• Methylglyoxal synthase
• Alcohol dehydrogenase
• Lactaldehyde reductase

Synthetic Biology Tools:

• CRISPR-Cas for gene editing
• Metabolic flux analysis
• Promoter and operon engineering
• Redox balancing for cofactor efficiency (NADH/NADPH)

Case Study: Renewable PG from Glycerol by DuPont Tate & Lyle

Highlights

• Utilizes corn-based glycerol as feedstock
• Fermentation followed by catalytic hydrogenolysis to propylene glycol
• Produces over 100,000 tonnes/year of bio-PG
• Used in cosmetics, food, and automotive sector

Timeline

• 2006 – Technology demonstrated at pilot scale
• 2010 – Commercial plant established in Tennessee, USA
• 2015 – Certified biobased PG launched for industrial markets
• 2023 – Expanded applications in bioplasticizers and green solvents

Global and Indian Startups Working in This Area

Global

• DuPont Tate & Lyle Bio Products (USA) – Bio-PG from renewable glycerol
• ADM (USA) – Glucose-to-PG bioprocesses
• Oleon (Belgium) – Bio-PG for personal care
• Metabolic Explorer (France) – Biointermediates from glycerol

India

• Praj Industries – Bio-PG from 1G and 2G sugars
• Godavari Biorefineries – Glycerol valorization platforms
• IISc Bangalore & ICT Mumbai – Engineered E. coli and C. glutamicum for PG
• CSIR-IICT – Biocatalysis research for renewable glycols

Market and Demand

The global propylene glycol market was valued at USD 4.5 billion in 2023 and is expected to reach USD 6.8 billion by 2030, with a CAGR of ~5.5%. The biobased PG market is growing faster, with a CAGR of ~9–10%, due to demand in:

Key Use Segments:

• Cosmetics & personal care – Moisturizers, creams, fragrances
• Pharmaceuticals – Drug carriers and stabilizers
• Food industry – Humectants and flavor solvents
• Antifreeze & de-icing fluids – Automotive and aircraft safety
• Plastics & resins – Polyester polyols and bio-PET

Key Growth Drivers

• Abundant glycerol from biodiesel production
• Rising demand for non-toxic, food-grade glycols
• Push for green solvents and safer cosmetic ingredients
• Industrial switch to bio-based antifreeze
• Favorable REACH and FDA regulations on bio-PG

Challenges to Address

• Enzyme efficiency and stability under industrial conditions
• Yield optimization from glucose vs. glycerol
• Cost competitiveness vs. petrochemical PG
• Downstream purification of PG from fermentation broth
• In India: Need for scale-up infrastructure and glycerol valorization policies

Progress Indicators

• 2008–2010 – Glycerol-to-PG fermentation demonstrated
• 2012 – Engineered E. coli achieves >80% yield in lab
• 2017 – First commercial bio-PG applications in food and pharma
• 2021 – Indian labs develop glucose-to-PG pathways
• 2024 – Dual-feedstock (glycerol + lignocellulose) platforms under test

Bio-PG via fermentation is at TRL 9 globally (DuPont, ADM). In India, glycerol-based routes are at TRL 6–7, while glucose-to-PG metabolic engineering efforts are at TRL 4–5 with ongoing pilot studies.

Conclusion

Metabolic engineering for renewable propylene glycol presents a high-potential opportunity to decarbonize a key industrial chemical. With versatile applications across consumer, industrial, and pharmaceutical sectors, bio-PG enables a drop-in, safer, and more sustainable alternative to its fossil-derived counterpart.

As India grows its biofuel and glycerol streams, and strengthens its synthetic biology capabilities, it is well-positioned to become a regional hub for biobased glycol production, contributing to green chemistry and climate-smart industrial growth.

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