What Is Triethylene Glycol (TEG)?
Triethylene glycol, known by the CAS number 112-27-6 and commonly abbreviated TEG, is a straight-chain glycol with the molecular formula C6H14O4 and a molar mass of 150.17 g/mol. It is a colourless, odourless, hygroscopic and low-volatility liquid at room temperature. The molecule contains two hydroxyl groups and two ether linkages, which together give TEG high water solubility, humectant behaviour and good solvent power for many organic compounds.
These properties explain why TEG is the preferred desiccant in natural gas dehydration and why it appears in humectant, plasticiser, lubricant and resin applications. The same low volatility also means that inhalation exposure under normal handling is limited to mists rather than to vapour.
Is TEG Hazardous?
TEG is not classified as a highly hazardous substance under most regulatory frameworks, and its acute toxicity is low. It is nevertheless a substance that requires respect in industrial use. Under the Globally Harmonised System it carries the hazard statements H319 for serious eye irritation and H335 for respiratory tract irritation, and it should be labelled accordingly.
On flammability, TEG is not classified as a flammable liquid because its flash point is far above the usual 60 °C threshold, but it is a combustible liquid that can burn when heated. It should therefore be kept away from strong oxidising agents and open flames, and heated systems should be designed so that leaks do not reach ignition sources. In transport, TEG is generally not classified as dangerous goods, and it is not regarded as a marine pollutant, but national rules should always be checked before shipment.
Physical Properties of TEG
| Property | Typical value |
|---|---|
| Molecular formula | C6H14O4 |
| Molar mass | 150.17 g/mol |
| Density at 20 °C | approx. 1.124 g/mL |
| Melting point | approx. -7 °C |
| Boiling point at 101.3 kPa | approx. 285 °C |
| Boiling point under reduced pressure | approx. 125 to 127 °C at about 0.1 mmHg |
| Flash point | commonly reported between 165 °C and 177 °C |
| Vapour pressure at 20 °C | below 0.01 mmHg |
| Relative vapour density | approx. 5.2, air equals 1 |
| Solubility | Miscible with water and alcohol, slightly soluble in ether, essentially insoluble in petroleum ether |
The figure of 125 to 127 °C is often quoted out of context: it is a reduced-pressure boiling point measured at roughly 0.1 mmHg and must not be confused with the atmospheric boiling point of about 285 °C.
Main Industrial Uses
Natural gas dehydration: TEG absorbs water vapour from wet gas streams in glycol contactors, controlling dew point and preventing hydrate formation and pipeline corrosion.
Plasticisers and resins: TEG acts as an intermediate in plasticiser manufacture and in unsaturated polyester and polyurethane systems.
Solvent: it is used as a process solvent in textile and coating operations where a high-boiling, water-miscible liquid is needed.
Humectant and conditioning agent: TEG retains moisture in inks, paper, textiles and air-treatment formulations.
Brake fluids and lubricants: TEG contributes to hydraulic brake fluid and lubricant formulations, where water tolerance and high boiling point are important.
Health Effects and Exposure Routes
The most relevant exposure route in industrial practice is eye contact, because TEG is a viscous liquid that is easily transferred from gloved hands and because it is classified as a serious eye irritant. Inhalation of mists or aerosols can irritate the respiratory tract and, at high concentrations, may cause headache or drowsiness. Skin contact may produce mild irritation, particularly on repeated or prolonged exposure. Ingestion is unlikely in normal handling, but TEG must not be swallowed; it is not intended for consumption and should be kept away from food, drink and children.
Repeated very high dose studies in animals have been associated with effects on some organs, but the exposure levels involved are far above those encountered in well-ventilated industrial operations with standard personal protective equipment.
Safe Handling and First Aid
Wear chemical-resistant gloves and safety goggles, and use local exhaust ventilation where mists can be generated.
Do not eat, drink or smoke while handling, and wash hands after work and before breaks.
Keep containers sealed when not in use to limit moisture pickup and to avoid contamination of the product.
Inhalation: move the person to fresh air, keep them warm and at rest, and seek medical attention if symptoms persist.
Eye contact: rinse with plenty of water for at least 15 minutes with the eyelids held open, then obtain medical attention.
Skin contact: remove contaminated clothing and wash the affected area with soap and water.
Ingestion: do not induce vomiting unless directed by medical staff; seek medical attention and show the safety data sheet.
Storage, Transport and Spill Response
Store TEG in sealed containers in a cool, dry and well-ventilated area, away from strong oxidisers, ignition sources and open flames. Because the liquid is hygroscopic, tanks and drums should be kept closed and, for long-term storage of large volumes, blanketed with dry nitrogen. Carbon steel and stainless steel are the usual materials of construction; sampling points should be designed to minimise moisture ingress.
In the event of a spill, stop the source if it is safe to do so, contain the liquid with inert absorbent material or a bund, and prevent it from entering drains, sewers and watercourses. Collect the absorbed material into labelled containers for disposal through an approved waste contractor, and ventilate the area. Report spills that exceed the reporting threshold set by local environmental regulations.
Frequently Asked Questions
Q: Is TEG hazardous?
TEG has low acute toxicity and is not classified as highly hazardous under most regulations, but it can irritate the eyes and respiratory tract, with the GHS statements H319 and H335.
Q: What is the boiling point of TEG?
The atmospheric boiling point is about 285 °C. The value of 125 to 127 °C corresponds to a reduced pressure of about 0.1 mmHg.
Q: What is TEG mainly used for?
TEG is mainly used for natural gas dehydration, and also as a plasticiser, solvent, humectant, brake fluid component and resin raw material.
Q: Is TEG flammable?
TEG is not classified as flammable; its flash point is commonly reported between 165 °C and 177 °C, but it can burn at high temperatures.
Q: What should I do if TEG contacts my eyes?
Rinse the eyes with plenty of water for at least 15 minutes with the eyelids held open, and seek medical attention.
Q: How should TEG be stored?
Store TEG in a sealed container in a cool, dry and ventilated area, away from strong oxidisers, ignition sources and open flames.