What Is Propylene Glycol Made From? Tracing Its Production Roots

Propylene glycol is primarily made from propylene oxide, a key petrochemical. This is because propylene oxide undergoes a hydration reaction to form propylene glycol efficiently, making it the dominant starting material in industrial processes.
Industrially, the main raw material is propylene oxide, derived from propylene (a hydrocarbon from petroleum or natural gas). Minor routes may use glycerol (a byproduct of biodiesel production) via hydrogenolysis, though this is less common due to higher costs.
Biosynthetically, propylene glycol can be produced by certain microorganisms. For example, bacteria like Lactobacillus or yeast can ferment sugars (e.g., glucose) to form lactic acid, which is then reduced to propylene glycol under anaerobic conditions. This bio-based method offers a renewable alternative to petrochemical routes.

The answer is ​​propylene glycol (PG) is primarily synthesized from propylene oxide​​, a derivative of petroleum or natural gas, though emerging bio-based methods use renewable feedstocks like glycerin or plant sugars. What raw materials power its industrial production, and how can microorganisms create this versatile chemical? Here’s a detailed look at PG’s manufacturing origins and the science behind its biological synthesis.

​​Industrial Production: Petrochemical Route (90% of Global Supply)​​
​​Primary Feedstock​​:
​​Propylene oxide (PO)​​: Derived from propylene (C₃H₆), a byproduct of oil refining/natural gas processing
​​Hydrolysis Reaction​​:
C
3
​
H
6
​
O+H
2
​
O
acid/base catalyst
​
C
3
​
H
8
​
O
2
​
(PG)
​​Conditions​​: 150-200°C, 10-20 bar pressure
​​Byproducts​​: Dipropylene glycol (DPG) and tripropylene glycol (TPG)
​​Purification​​:
Distillation separates PG (99.5% purity) from heavier glycols
​​Alternative Feedstocks​​:

​​Glycerin​​: Byproduct of biodiesel production (cheaper but lower yield)
​​Acetol​​: Intermediate from biomass pyrolysis
​​Bio-Based PG: Sustainable Production Pathways​​
​​1. Microbial Fermentation​​
​​Organisms​​: Genetically modified E. coli, Saccharomyces cerevisiae
​​Pathway​​:
Glucose→Dihydroxyacetone phosphate→Methylglyoxal→Acetol→PG
​​Yield​​: Up to ​​135 g/L​​ in optimized bioreactors
​​2. Enzymatic Conversion​​
​​Substrate​​: Glycerin + ​​glycerol dehydratase​​ enzyme
​​Process​​:
C
3
​
H
8
​
O
3
​
→C
3
​
H
6
​
O
2
​
(PG)+H
2
​
O
​​Advantage​​: 85% energy savings vs. petrochemical route
​​Comparison of Production Methods​​
​​Parameter​​

​​Petrochemical PG​​

​​Bio-Based PG​​

​​Feedstock​​

Propylene (fossil fuel)

Glycerin/glucose (renewable)

​​CO₂ Footprint​​

2.5 kg CO₂/kg PG

0.8 kg CO₂/kg PG

​​Purity​​

99.9%

99.5% (requires extra filtration)

​​Cost​​

$1,200/ton

$1,800/ton (2024 prices)

Propylene glycol (PG) is typically produced from propylene oxide, a compound derived from petroleum or natural gas. The manufacturing process involves the hydration of propylene oxide in the presence of a catalyst to form propylene glycol. This chemical reaction can proceed via different methods, including non-catalytic high-temperature processes or catalytic processes at lower temperatures. Advances in technology and environmental concerns have led to more efficient and cleaner production methods.

The versatility of propylene glycol stems from its properties, including low toxicity, excellent solubility in water and many organic compounds, and its ability to retain moisture. These characteristics make it an essential ingredient in a variety of applications. For instance, in the food industry, PG serves as a solvent and preservative, often used in flavorings, colorings, and as a humectant to keep foods moist. It's also found in pharmaceuticals as a solvent for oral, topical, and injectable medications, ensuring their stability and effectiveness.

In cosmetics and personal care products, PG is used for its moisturizing and skin conditioning properties, making it a common component in lotions, creams, and deodorants. Additionally, its low toxicity and excellent performance in heat transfer applications make it a preferred choice over ethylene glycol in antifreeze formulations where there is a risk of accidental ingestion by pets or humans.

Safety considerations are paramount when using propylene glycol, given its widespread application across industries that directly impact human health, such as food and pharmaceuticals. Proper handling and adherence to regulatory guidelines ensure its safe use. By focusing on keywords like production, safety, and versatility, this overview emphasizes not only how propylene glycol is made but also its critical role in various everyday products and the importance of responsible usage.