Benefits of Propylene Glycol as Coolant | Compared to Ethylene Glycol

In recent years, propylene glycol as coolant has gained popularity because of the advancement of automobile industry and people’s awareness of environmental issues. This is because propylene glycol has almost all of the same properties as ethylene glycol that can be used as an antifreeze coolant, while propylene glycol is non-toxic and biodegradable.

Physical and chemical properties of propylene glycol

Propylene glycol has two isomers; if not specified, it is commonly referred to as 1,2-propanediol. 1,2-Propanediol is an organic molecule that has the chemical formula C₃H₈O₂. Under normal conditions, it is a colorless, viscous liquid that is nearly odorless and mildly sweet to the nose. It is miscible with water, ethanol, and many organic solvents.

Physical Properties

Propylene Glycol is a colorless, viscous, stable, absorbent liquid with essentially no taste or odor. It is flammable, and has a low toxicity level. Propylene glycol's solubility allows it to be miscible with water, ethanol, ether, chloroform, acetone, and other organic solvents. Propylene glycol is less soluble in hydrocarbons, chlorinated hydrocarbons, oils, and fats than ethylene glycol, but it is more stable.

Chemical properties

Propylene glycol is a flammable liquid. It is hygroscopic and has no corrosive effects on metals.1,2-Propylene glycol dehydrates to become propylene oxide or polyethylene glycol. Propylene glycol is quite low in toxicity and irritation, and no victims have been identified. In rats, the LD50 is 7000-8000 mg/kg via intravenous and intraperitoneal routes, and 2800 mg/kg orally. However, it has been noted that when large amounts of propylene glycol are added to foods and beverages in a single dose, it can produce catastrophic slumber as well as renal damage. Propylene glycol can be found in tobacco leaves and smoke.

Comparing ethylene glycol and propylene glycol as coolant

Since the 1950s, almost every country has employed ethylene glycol as antifreeze. So, what is the difference between ethylene glycol and propylene glycol as coolants?

Basic physical and chemical properties

Ethylene Glycol, commonly known as "Glycol", "1,2-Ethylene Glycol", or EG for short, is the most basic diol, with the chemical formula (CH₂OH)₂. Ethylene glycol is a colorless, odorless, pleasant liquid with toxicity. It is miscible with water and acetone, but less soluble in ether. Its melting point is -13.2℃.

Propylene glycol, with the chemical formula C₃H₈O₂, is a colorless, viscous, stable absorbent liquid. Its melting point is -59℃. Ethylene glycol outperforms propylene glycol in terms of both cold transport and freezing resistance.

Toxicity

Both these two coolants have equivalent heat conduction, freezing point protection, and rubber compatibility. However, propylene glycol as coolant performs better than ethylene glycol in terms of corrosion resistance, toxicity, and biodegradation.

Propylene glycol is classified as low toxicity, with little toxicity and irritation. Ethylene glycol, on the other hand, is very poisonous and poses a greater risk to human health. The human body's lethal dose for an adult is approximately 1.6g/kg. An application of more than 200ml ethylene glycol will be life-threatening.

Fields of application

Glycol-based coolants are often available in industrial, automotive antifreeze, and other varieties. Only carbon steel, stainless steel, copper, and other anti-corrosion treatments are covered by the general industrial type of ethylene glycol coolant. Propylene glycol antifreeze coolant is commonly used in automobile antifreeze, food, beverage, and other low-toxicity applications.

Benefits of propylene glycol as coolant

With the comparison above, the benefits of propylene glycol as coolant can be summarized as follows:

Environmental protection

Propylene glycol is less harmful to the environment than ethylene glycol. Because propylene glycol decomposes oxidatively to produce carbon dioxide and water, no hazardous chemicals are produced. However, the degradation of ethylene glycol antifreeze produces hazardous gasses that cause pollution.

Good Compatibility

Propylene glycol as coolant works well with a variety of metals, rubbers, and plastics. Propylene glycol can help safeguard the car's engine and cooling system.

Anti-corrosion

Propylene glycol as coolant possesses sterilizing and rust-prevention properties that can significantly increase the life of automotive engines and cooling systems.

However, as a coolant, propylene glycol has lower heat conductivity and frost resistance than ethylene glycol. In addition, propylene glycol is more expensive and it requires special handling for closed storage because it absorbs moisture from the air.

Conclusion

The advantages of propylene glycol as coolant lie in its nontoxicity and good compatibility. However, propylene glycol still cannot beat ethylene glycol in several aspects. As a result, the formulation of propylene glycol as a coolant cannot simply copy the formulation of ethylene glycol. New formulations must be improved appropriately based on the properties of propylene glycol, so as to broaden the applications of propylene glycol coolants in the cooling systems of automobiles, ships, large cooling towers, solar energy, and other equipment.