What is the Difference Between Ethylene and Propylene Glycol?

Ethylene glycol and propylene glycol are two types of glycols with different properties and uses. The main differences between them include:

1. Toxicity: Ethylene glycol is toxic, while propylene glycol is not. This distinction allows propylene glycol to be used as a food-grade antifreeze, making it suitable for applications where human or environmental contact is expected.
2. Physical Properties: Propylene glycol solutions have a higher viscosity and a higher freezing point than ethylene glycol solutions. This makes ethylene glycol more thermally efficient, especially at lower temperatures. For example, a 50% propylene glycol solution freezes at -31°F, while a 50% ethylene glycol solution freezes at -36°F.
3. Cost: Propylene glycol is generally more expensive than ethylene glycol.
4. Applications: Ethylene glycol is commonly used in applications where efficiency is important and there is no human contact, such as ice rinks, plastic molding, and in-line heaters. It is also the predominant fluid used for automotive antifreeze formulations. Propylene glycol, on the other hand, is used in food and pharmaceutical applications, as well as in HVAC systems, solar thermal heat transfer, and other process cooling and heating applications.
5. Environmental Impact: Propylene glycol is considered more environmentally friendly than ethylene glycol because it is biodegradable and can be derived from renewable plant sources.

Comparative Table: Ethylene vs Propylene Glycol

Ethylene glycol and propylene glycol are both used as antifreeze, but they have some differences in their properties and applications. Here is a table comparing their key characteristics:

Ethylene glycol has superior heat transfer properties due to its lower viscosity, making it more effective in freeze point depression. However, it is toxic and should not be used in any drinking water or food processing systems. Propylene glycol is less toxic than ethylene glycol and is often used in aircraft de-icing and other applications where human or environmental exposure is a concern.