Ethylene glycol

The main difference between propylene glycol and ethylene glycol lies in toxicity: ethylene glycol is poisonous to humans and animals, whereas propylene glycol is considered low-toxicity and is even used in the food and pharmaceutical industries. From a chemical point of view, the differences lie in molecular structure, which affects physical properties: ethylene glycol provides slightly better heat transfer and a lower freezing point at the same concentration. When deciding which is better — ethylene glycol or propylene glycol — for closed heating systems and industrial refrigeration circuits, the former is usually chosen due to lower viscosity and lower cost, while for facilities with a risk of contact with drinking water or people, the latter is clearly preferable. The question of the difference between propylene glycol and ethylene glycol inevitably comes down to the field of application, and it is always assessed through the lens of safety and economics.

Monoethylene glycol and ethylene glycol are essentially the same substance, namely 1,2-ethanediol, and the difference between them comes down only to purity and terminology. Monoethylene glycol (MEG) is a chemically pure glycol with a minimal content of diethylene glycol and other impurities, which is why it is used in the production of polyester fibres and PET packaging. Commercial ethylene glycol under GOST 19710-83 is also MEG, but in price lists and technical documentation both names are often used interchangeably, so when asking what the difference is between monoethylene glycol and ethylene glycol, you can be sure: for heat-transfer fluids and antifreezes, it is the same thing.

When choosing which heat-transfer fluid is better — ethylene glycol or propylene glycol — engineers weigh several factors. Ethylene glycol fluids have higher thermal conductivity and lower viscosity at low temperatures, which gives better energy efficiency and reduces the load on pumps. Propylene glycol fluids, on the other hand, are inferior in thermal properties, but are completely safe in the event of possible leaks in domestic hot water systems and food production. Therefore, for large industrial circuits and boiler houses where contact with drinking water is excluded, the answer to which heat-transfer fluid is better is ethylene glycol, while for social facilities and greenhouses it is propylene glycol.

Neutralising ethylene glycol in laboratory and industrial conditions means its chemical breakdown into safe products. One common method is oxidation with strong oxidisers, for example potassium permanganate or ozone, down to oxalic acid and carbon dioxide. Ethylene glycol can also be neutralised by thermal incineration in special high-temperature furnaces, where the substance decomposes into water and carbon dioxide. In the case of small spills, adsorption with inert materials followed by disposal is effective, and pouring spent glycol into the sewer is strictly prohibited.

Ethylene glycol dissolves well in water, so what removes it, first of all, is plenty of warm water with added detergent. If a spill has occurred on metal or plastic, the surface is washed with water, then degreased with isopropyl alcohol or alcohol solutions, which remove the oily glycol film very well. For concrete floors in workshops, an aqueous solution with soda or alkaline detergents is used, after which the area is thoroughly rinsed. The main thing is not to let the liquid dry out, otherwise the oily trace is harder to remove.

Ethylene glycol is found in almost all engine coolants — antifreeze fluids — as well as in brake fluids and anti-icing additives for aviation fuel. In industry, ethylene glycol is found in heat-transfer fluids for heating and air conditioning systems, in textile processing formulations, in the production of varnishes and paints, and as a solvent in organic synthesis. In everyday life it can be found in window-washing fluids, in shoe care products and in some cosmetic products such as nail polish, where it is present in minimal doses.

The guaranteed shelf life of ethylene glycol under GOST 19710-83 is one year for the premium grade and three years for the first grade. The actual storage period of ethylene glycol can be significantly longer if the product is kept in sealed metal drums in a cool, unheated warehouse and does not come into contact with moisture. Over time, the acid number in samples can increase and iron impurities from the container can appear, so when purchasing large batches, logistics are arranged so that the reagent is used within the stated shelf life, and laboratory testing is carried out before filling it into the system.

Ethylene glycol is dangerous primarily if ingested: it acts as a neurotoxin and damages the liver and kidneys, with the first symptoms resembling mild intoxication, while severe poisoning occurs after 12–24 hours. It is compared to methanol because both are technical alcohols with high toxicity, and poisoning by either is treated with ethanol. However, what makes methanol and ethylene glycol dangerous individually is different metabolic pathways: methanol damages the optic nerve, while glycol forms calcium oxalate crystals in the renal tubules. Even inhaling the vapours over a long period is harmful, so working with the substance requires exhaust ventilation.

Pure ethylene glycol freezes at around –12°C. However, the question of the freezing temperature of ethylene glycol is more often asked in the context of aqueous mixtures: a 40% solution remains liquid down to –24°C, and an antifreeze concentrate with 60% glycol crystallises only at –49°C. The lowest freezing point is achieved in a mixture of approximately 67% ethylene glycol and 33% water, which remains fluid at –75°C, although in real formulations the properties are adjusted with a package of additives.

Disposal of ethylene glycol must be carried out through licensed enterprises that accept spent heat-transfer fluid and incinerate it in high-temperature furnaces with emissions cleaning. It is strictly forbidden to pour glycol into the sewer or onto the ground, since it easily migrates into water bodies, disrupting the water balance and causing the death of aquatic organisms. Therefore, the question of how to dispose of ethylene glycol at a production facility is resolved by collecting it in sealed containers and concluding an agreement with a regional hazardous waste operator.

Ethylene glycol is directly a dihydric alcohol, a raw material, while antifreeze is a ready-made coolant consisting of ethylene glycol, water, dye and a package of functional additives. Thus, the difference between ethylene glycol and antifreeze is exactly the same as between base oil and finished motor oil. If we consider carboxylate antifreeze and how it differs from ethylene glycol, the difference lies in the chemistry of the corrosion inhibitors: carboxylate formulations use organic acids and their salts, which are adsorbed only on metal surfaces and last longer than traditional silicate or phosphate additives, while the glycol itself remains the same.