Ethylene Glycol vs. Diethylene Glycol — What's the Difference?

Ethylene glycol (EG) is a simple, colorless, odorless, and sweet-tasting organic compound widely used in antifreeze formulations and industrial applications. It is highly toxic to humans and animals, even in small quantities, leading to acute poisoning and potentially fatal consequences. On the other hand, diethylene glycol (DEG) is a related chemical compound that is produced by the partial hydrolysis of ethylene glycol. Though still toxic, DEG has a lower toxicity level compared to EG, making it somewhat safer for use in various industrial applications.

EG's primary use is in the manufacture of antifreeze and de-icing solutions for vehicles and aircraft, due to its ability to depress the freezing point of water. It is also used in hydraulic and brake fluids. Conversely, DEG is used in a broader range of applications, including as a solvent for dyes, in the manufacture of brake fluid, and in some cases, as a humectant in tobacco, glue, and cosmetics, showcasing its versatility beyond just antifreeze and de-icing solutions.

The toxicity of EG is a major concern, as ingestion of even small amounts can cause serious health issues, including kidney failure, neurological damage, and death. Its sweet taste can unfortunately lead to accidental ingestions, particularly by children and pets. DEG, while also toxic, tends to cause less severe acute health effects, but exposure or ingestion in larger quantities can still lead to serious health complications, including renal failure and neurological damage.

In terms of chemical structure, EG is the simplest diol (a compound with two hydroxyl groups), consisting of two carbon atoms connected by a single bond, each bonded to a hydroxyl group. DEG is formed from two EG molecules joined together, resulting in a slightly more complex structure with four carbon atoms and two hydroxyl groups. This structural difference accounts for their varying physical properties and applications.

While both compounds are used in the production of polyester fibers and resins, EG is particularly crucial in the manufacture of polyethylene terephthalate (PET) used for plastic bottles and containers. DEG, due to its lower volatility and higher boiling point compared to EG, finds use in applications requiring a stable and less volatile solvent, including certain types of brake fluids and as a conditioning agent in textiles and paper.