Monoethylene glycol, commonly abbreviated as MEG, is the simplest and most widely produced glycol. With CAS number 107-21-1, it is a key raw material for polyester fibers and PET resin, and a familiar antifreeze and heat transfer fluid. This article reviews the physical and chemical properties of monoethylene glycol and their practical consequences.
What Is Monoethylene Glycol?
Monoethylene glycol, also called ethylene glycol or ethane-1,2-diol, has the formula C2H6O2 and the structure HOCH2CH2OH. It is a colorless, practically odorless, hygroscopic liquid with low volatility and a viscosity higher than water. MEG is completely miscible with water and with many polar organic solvents, which underlies most of its applications.
Physical Properties of MEG
| Property | Value |
|---|---|
| CAS Number | 107-21-1 |
| Molecular Formula | C2H6O2 |
| Boiling Point | About 197.3°C |
| Melting Point | About -12.9°C |
| Density | About 1.113 g/cm³ at 20°C |
| Solubility | Miscible with water, ethanol and acetone |
| Viscosity | Increases significantly at low temperature |
Pure MEG freezes at about -12.9°C, but aqueous solutions remain liquid far below this temperature, which is the basis of its antifreeze function.
Chemical Properties and Reactivity
The two hydroxyl groups of MEG undergo typical alcohol reactions including esterification, etherification and oxidation. Condensation with dicarboxylic acids such as terephthalic acid produces polyester, the basis of PET bottles and polyester fibers. Reaction with nitric acid forms glycol dinitrate esters, and the strong hydrogen bonding of the hydroxyl groups gives MEG its high hygroscopicity and water solubility.
Freezing Point Depression and Heat Transfer Fluids
When MEG is mixed with water, it strongly depresses the freezing point while raising the boiling point. A 40 percent aqueous solution freezes at about -25°C and a 60 percent solution at about -49°C, which makes MEG-water mixtures effective low-temperature heat transfer fluids for automotive cooling systems, solar thermal collectors and industrial chillers. The same property is used in aircraft deicing and runway deicing fluids.
Major Industrial Applications
Raw material for polyester fibers, PET resin and films.
Antifreeze and engine coolant formulations.
Heat transfer and deicing fluids for industrial and aviation use.
Humectant and dehydrating agent in gas processing and textile finishing.
Solvent and chemical intermediate in organic synthesis.
Safety Considerations and Storage
MEG is toxic if ingested: it can cause severe metabolic poisoning affecting the kidneys and nervous system, so it must be stored away from food and drink and kept out of reach of children. Prolonged skin contact may cause mild irritation, while its low volatility makes inhalation risk minimal at room temperature. Store MEG in sealed containers to prevent moisture absorption and follow the safety data sheet for handling and disposal.
Frequently Asked Questions
What are the properties of monoethylene glycol?
MEG is a colorless, hygroscopic liquid with a boiling point of about 197.3°C, a melting point of about -12.9°C and complete miscibility with water.
What is the CAS number of monoethylene glycol?
The CAS registry number of monoethylene glycol is 107-21-1.
Why is monoethylene glycol used as antifreeze?
MEG-water mixtures depress the freezing point well below 0°C, for example about -49°C at a 60 percent concentration, which prevents coolant freezing.
Is monoethylene glycol toxic?
Yes, MEG is toxic if ingested and can cause severe kidney and nervous system damage; it must be stored safely away from food and children.
What is monoethylene glycol used to make?
MEG is the main raw material for polyester fibers and PET resin, and is also used in antifreeze, heat transfer fluids, humectants and deicing products.