Glycols are a type of organic compound belonging to the alcohol family. They’re characterized by having two hydroxyl groups in their molecular structure.
This article will compare and contrast two common glycols: propylene glycol and ethylene glycol.
While they sound similar, it’s important to understand the differences between propylene glycol vs ethylene glycol because they have different properties and uses. Crucially, they also differ in toxicity, which is a critical factor when choosing the right glycol for a specific application.
What are glycols?
Glycols are organic compounds that contain two hydroxyl groups. That means they have a wide range of uses, from the production of cosmetics and resins to the creation of antifreeze.
Antifreeze is a substance that prevents liquids from freezing in cold temperatures and keeps them from boiling when it’s hot.
Key Differences Between Ethylene Glycol and Propylene Glycol
While both ethylene glycol and propylene glycol serve as antifreeze, coolants, and solvents, their properties and uses differ significantly.
Ethylene Glycol
- Ethylene glycol excels at heat transfer, working more effectively to prevent freezing and move heat in closed systems.
- Because it’s toxic when ingested, ethylene glycol is primarily used in closed-loop systems and in industrial applications.
Propylene Glycol
- Propylene glycol has lower toxicity, which makes it more appropriate for applications where it might come into contact with people.
- It’s often used in open-loop systems and in applications like de-icing, preventing ice buildup, and in some supermarket freezers.
- The FDA considers propylene glycol to be Generally Recognized as Safe (GRAS).
- Propylene glycol is often derived from renewable sources.
In short, ethylene glycol is a workhorse for industrial applications, while propylene glycol is the go-to choice in situations that demand a safer, less toxic substance.
Applications in HVAC Systems
Both ethylene glycol and propylene glycol can be used in heating, ventilation, and air conditioning (HVAC) systems, but each has its own strengths and weaknesses.
Ethylene Glycol in HVAC
Ethylene glycol is a good choice for closed-loop HVAC systems, where efficiency in transferring heat is key. However, due to its toxicity, it’s not recommended for systems that might leak or where humans or animals could be exposed.
Propylene Glycol in HVAC
Propylene glycol is the better option for open-loop HVAC systems, geothermal systems, or any system where it might come into contact with drinking water. It’s the go-to choice when safety and low toxicity are the main considerations.
Factors to Consider When Choosing
When deciding between the two, think about:
- The type of system (open vs. closed loop)
- How well it needs to transfer heat
- How concerned you are about toxicity and the chance of exposure
Toxicity and Safety
Here’s where the two glycols really differ: ethylene glycol is toxic, whereas propylene glycol is much less so.
If you’re using ethylene glycol, you need to be extremely careful about storing and disposing of it. It can be deadly if ingested.
Propylene glycol is generally considered the safer choice if there’s any chance a human or animal could be exposed. When deciding between the two, always think about how toxic they are and how likely it is that someone could get hurt.
Frequently Asked Questions
Which is better, propylene glycol or ethylene glycol?
Neither is inherently “better” – it depends on the application. Ethylene glycol has superior antifreeze properties, but its toxicity limits its use. Propylene glycol is less effective as an antifreeze but is much safer, making it suitable for food and pharmaceutical applications. The best choice hinges on balancing performance and safety requirements.
Is ethylene glycol banned in the US?
No, ethylene glycol is not banned in the US. It’s widely used in industrial applications, particularly as antifreeze in vehicles. However, its use is strictly regulated due to its toxicity, and it’s not allowed in applications where human consumption is possible.
Why is propylene glycol banned in Europe?
That’s a common misconception! Propylene glycol is not banned in Europe. It’s approved for use in various food, cosmetic, and pharmaceutical products within the European Union. There might be specific restrictions on its concentration in certain products, but a complete ban isn’t in place.
Is ethylene glycol more toxic than propylene glycol?
Yes, ethylene glycol is significantly more toxic than propylene glycol. Ethylene glycol is highly poisonous and can cause severe kidney damage, neurological problems, and even death if ingested. Propylene glycol is considered much safer and is generally recognized as safe (GRAS) by regulatory agencies for use in food and other products.
In Conclusion
Ethylene glycol and propylene glycol are both antifreeze agents, but they have some key differences. Ethylene glycol provides better heat transfer, while propylene glycol is less toxic.
When deciding which one to use, consider the specific application, the heat transfer requirements, and the potential risks of toxicity. For closed-loop systems where humans and animals won’t be exposed, ethylene glycol can be a good choice. But for situations where there’s a risk of exposure, propylene glycol is the better bet.
It’s always a good idea to consult with HVAC professionals or chemical experts to determine the best choice for your specific system requirements. And if you’re not sure which type of glycol is already in your system, test the fluid. Specific gravity and refractive index tests can help you identify the glycol type.