What are the advantages of propylene glycol over ethylene glycol?
Lower toxicity:
safe for animals, children and adults
For vehicles:
will not damage paint
less pump circulation to get same heat transfer
Non Hazardous Waste: avoid disposal costs
and with Classic Coolant inhibitors avoids main bearing damage if a gasket blows
Classic Coolant
has Safer Propylene Glycol for Antifreeze and Higher Boiling Point
together with Water for efficient Heat Transfer
and Conventional IAT Inhibitors to prevent Corrosion
In contrast to ethylene glycol, a potent cause of acute toxicity in humans, propylene glycol is a “generally recognized as safe” (GRAS) additive for foods and medications
It is widely used in food and tobacco products, pharmaceuticals, and cosmetics (the main ingredient in deodorant sticks).
In certain medicines, cosmetics, and food products, propylene glycol acts as
- a humectant food additive, labeled as E number E1520
- an emulsifying agent in Angostura and orange bitters
- industrial drying agent,
- surfactant, and
- solvent.
Propylene glycol is sometimes used as a de-icing agent; however, ethylene glycol is used more often because it costs less, even though it is a poison. Propylene Glycol has been the safe alternative for vehicle antifreeze coolant in the USA and France for many years. In the UK only ethylene glycol antifreeze coolant was available for retail in January 2010. Switzerland banned the sale of products containing ethylene glycol in 1972.
The industrial norm is to replace ethylene glycol with propylene glycol when safer properties are desired.
Biological Fate
Propylene glycol is metabolized in the liver by alcohol dehydrogenase to
- lactic acid, and then
- pyruvic acid
Both of these metabolites are normal constituents of the citric acid cycle and are further metabolized to carbon dioxide and water
About 45% of an absorbed propylene glycol dose is excreted by the kidneys unchanged or as the glucuronide conjugate.
Key Points
- Propylene glycol is used in various foods, cosmetics, and pharmaceutical products.
- Propylene glycol is metabolized to compounds that are normal constituents of the citric acid cycle.
- Unlike ethylene glycol, propylene glycol does not produce nephrotoxicity in humans caused by calcium oxalate in humans.
- Unlike ethylene glycol, propylene glycol is not metabolized to oxalic acid, so calcium oxalate is not deposited in the kidneys
- Propylene glycol (PG) is traditionally produced from petroleum-derived propylene oxide. However, Archer Daniels Midland Company has a proprietary glycols technology that uses a catalytic process known as hydrogenolysis to convert glycerin and sorbitol into propylene glycol. The process includes reacting glycerin and hydrogen in the presence of a catalyst under conditions of high temperature and pressure. The products resulting from this process include propylene glycol and water. ADM’s expertise in separation technology comes into use after the reaction when the propylene glycol is purified to both industrial standard and United States Pharmacopeia (USP) excipient grades. So we now have a sustainable propylene glycol.
Footnote
If scientific data are presented that show a health risk to animals of an ingredient or additive, the FDA’s Center for Veterinary Medicine (CVM) can act to prohibit or modify its use in pet food. For example, propylene glycol was used as a humectant in soft-moist pet foods, which helps retain water and gives these products their unique texture and taste. It was affirmed Generally Recognized As Safe (GRAS) for use in human and animal food before the advent of soft-moist foods. It was known for some time that propylene glycol caused Heinz Body formation in the red blood cells of cats (small clumps of proteins seen in the cells when viewed under the microscope), but it could not be shown to cause overt anemia or other clinical effects. However, reports in the veterinary literature of scientifically sound studies have shown that propylene glycol reduces the red blood cell survival time, renders red blood cells more susceptible to oxidative damage, and has other adverse effects in cats consuming the substance at levels found in soft-moist food. In light of these new data, CVM amended the regulations to expressly prohibit the use of propylene glycol in cat foods.
