MEG - Mono Ethylene Glycol — Frequently Asked Questions

Fibre grade is high-purity MEG made for polyester production, with tight limits on diethylene glycol, water, acidity, iron, aldehydes and ultraviolet transmittance, because trace impurities cause yellowing and spinning faults in PET. Industrial grade has looser limits and suits antifreeze, heat-transfer fluids and chemical uses. Fibre grade can be used for industrial purposes, but not the other way round.

Ultraviolet transmittance at 220, 275 and 350 nm is a sensitive test for trace impurities, such as aldehydes and unsaturated or aromatic compounds, that are hard to measure individually. These impurities cause colour and haze in polyester, so polymer producers use UV transmittance as a quick screen. It matters for fibre grade; industrial buyers rarely need it.

A 50:50 mixture by volume of MEG and water protects to roughly −37 °C and is the usual coolant strength. Higher concentrations give more protection only up to around 60–70% glycol, beyond which the freezing point rises again. Commercial coolants also need corrosion inhibitors, because plain glycol and water corrode some metals. Check your equipment maker's requirements before formulating.

Yes. Under CLP it is harmful if swallowed (H302) and may cause kidney damage through prolonged or repeated oral exposure (H373). Its sweet taste makes accidental ingestion by people and animals a real risk, so label containers clearly. It is not regulated as dangerous goods for transport, but check the safety data sheet for the material supplied.

For fibre grade, yes, where possible. MEG absorbs water from the air, and oxygen at elevated temperature can form aldehydes and acids that reduce ultraviolet transmittance and raise colour. A dry nitrogen blanket in stainless steel, aluminium or lined tanks preserves polymer-grade quality. For industrial grade, closed containers in a dry store are usually sufficient.