Triethylene glycol, often abbreviated as TEG, is a colorless, odorless and hygroscopic liquid widely used as a solvent, humectant and dehydration agent. Its melting point is a frequently asked question because the compound can supercool and different sources report slightly different values. This article gives the accepted melting point and the complete set of physical properties needed for engineering and formulation work.
What Is Triethylene Glycol?
Triethylene glycol is an alcohol with three hydroxyl groups and the formula HOCH2CH2OCH2CH2OCH2CH2OH, CAS number 112-27-6. It is completely miscible with water and ethanol and slightly soluble in diethyl ether. TEG is produced by the oligomerization of ethylene oxide and is used in natural gas dehydration, as a solvent, and as a humectant in industrial and consumer products.
Melting Point of Triethylene Glycol
The melting point of triethylene glycol is approximately -7°C. Published values vary slightly between -4.3°C and -7.2°C depending on purity, cooling rate and measurement method, and the compound is prone to supercooling, so it can remain liquid below its melting point. For design work, treat -7°C as the reference value and confirm the specification of the purchased grade.
Complete Physical Property Data
| Property | Value |
|---|---|
| CAS Number | 112-27-6 |
| Melting Point | About -7°C |
| Boiling Point | About 289.4°C at 101.3 kPa; about 134°C at 0.267 kPa |
| Density | About 1.1274 g/cm³ at 20°C |
| Viscosity | 49.0 mPa·s at 20°C |
| Surface Tension | 45.2 mN/m at 20°C |
| Flash Point | About 177°C, closed cup |
| Autoignition Temperature | About 412.8°C |
Chemical Properties of Triethylene Glycol
Although the physical behavior of TEG resembles that of water, its chemistry is governed by the three hydroxyl groups, which form hydrogen bonds and act as reactive centers. TEG undergoes typical alcohol reactions such as esterification and etherification, and its high boiling point and low volatility make it a safe solvent for processes requiring elevated temperatures. It is also an effective absorber for water vapor and certain acid gases.
Industrial Applications and Selection Notes
Natural gas dehydration: TEG removes water vapor from gas streams and is regenerated by heating.
Solvent and coupling agent: used in printing inks, coatings, cleaning formulations and chemical synthesis.
Humectant and plasticizer: found in textiles, tobacco, cork and certain polymer systems.
Heat transfer fluid: suitable for closed-loop systems operating at moderate temperatures.
When selecting TEG, verify the water content, color and purity against the process requirement, and store it in sealed containers to prevent moisture uptake.
Safe Handling and Storage
TEG has a high flash point and low vapor pressure, which reduces fire and inhalation risk compared with low-boiling solvents. Nevertheless, use adequate ventilation, avoid skin contact with hot material, and keep containers tightly closed because the product is hygroscopic. Refer to the supplier safety data sheet for first-aid and disposal guidance.
Frequently Asked Questions
What is the melting point of triethylene glycol?
The melting point of triethylene glycol is approximately -7°C, with published values ranging from about -4.3°C to -7.2°C depending on purity and measurement conditions.
What is the CAS number of triethylene glycol?
The CAS registry number of triethylene glycol is 112-27-6.
Is triethylene glycol soluble in water?
Yes, TEG is completely miscible with water and with ethanol, and slightly soluble in diethyl ether.
Why does triethylene glycol have a high boiling point?
The three hydroxyl groups form strong intermolecular hydrogen bonds, which raise the boiling point to about 289.4°C at atmospheric pressure.
What is triethylene glycol used for?
TEG is used for natural gas dehydration, as a solvent and humectant in industrial formulations, and as a heat transfer fluid in closed systems.