The difference between the above two substances in antifreeze is due to their toxicity and efficiency. Ethylene glycol shows high efficiency in heat transfer but propylene glycol has lower toxicity. In the following, we will further study these two substances and their application in antifreeze.

what is glycol?

Glycol is an organic chemical compound that belongs to the family of alcohols. In glycols (also called diols), the molecule contains two groups of hydroxyl attached to carbon atoms. These substances are classified as alcohols.

The following figure shows the molecular structure of these two substances

Note that ethylene glycol is available in three forms: monoethylene glycol, diethylene glycol and triethylene glycol. But monoethylene glycol is more widely used as an antifreeze among other types of ethylene glycols.

Propylene glycol has heat transfer properties in the temperature range of -50 degrees Fahrenheit to 350 degrees Fahrenheit. Although both propylene glycol and ethylene glycols (mono, di and triethylene glycol) have a variety of applications in industry, for example in cosmetics (propylene glycol), the preparation of resins, inks, polyethylene terephthalate (ethylene glycol) But both are used in the preparation of antifreeze and cooling mixtures and have a common application in this field.

What is antifreeze?

Antifreeze is a mixture of distilled water and another base product (ethylene or propylene glycol). Some formulations for antifreeze also add a special inhibitor to protect metals from corrosion. Corrosion inhibitors increase the range of these antifreezes for common metals such as carbon steel, copper as well as aluminum. In general, the use of antifreeze serves a dual purpose: lowering the freezing point as well as increasing the boiling point of liquids in cooling systems. Based on this feature, antifreeze can prevent cooling systems from freezing and prevent possible problems due to overheating.

Differences between propylene glycol and ethylene glycol:

The main difference between these two substances is their toxicity. Monopropylene glycol is a non-toxic compound used in cosmetics. However, due to its high toxicity, ethylene glycol is not usually used directly with human-based products.Propylene glycol is excreted in the urine after consumption or converted to lactic acid and other normal metabolic products. But ethylene glycol, previously mentioned as toxic, decomposes into oxalic acid. The formation of oxalic acid may lead to the deposition of calcium oxalate crystals in the blood vessels, lungs, myocardium, and.. This substance and its toxic by-products first affect the central nervous system (CNS), then the heart, and finally the kidneys. Drinking some of this substance can also be fatal.

Why not use only propylene glycol in antifreeze?

Although this material is slightly toxic, but it should be noted that ethylene glycol can provide a lower freezing point, and to reach the same freezing point, more propylene glycol is needed. It also has a lower viscosity and viscosity and can be much more effective in heat transfer. However, the choice of which of these materials to use as antifreeze depends on their application and the extent of their contact with the environment, human contact, and so on. For example, in aircraft, propylene glycol is used to prevent snow from freezing and shrinking in winter. It is also found in antifreeze in supermarkets. But monoethylene glycol is used in closed systems and in controlled industrial applications In general, propylene glycol has received more attention in the food industry and water pipes due to its low toxicity. Because these cases are directly related to human health and can affect people's health.