What Are Monoethylene Glycol and Diethylene Glycol?
Monoethylene glycol, or MEG, is the simplest diol produced from ethylene oxide, with the CAS number 107-21-1. Diethylene glycol, or DEG, is formed by the reaction of two molecules of ethylene glycol, giving a larger molecule with an ether linkage, and it has the CAS number 111-46-6. Both are clear, hygroscopic, odourless liquids that are fully miscible with water, but their molecular structures give them different physical properties and different industrial roles.
Key Chemical Differences
| Item | Monoethylene Glycol MEG | Diethylene Glycol DEG |
| CAS Number | 107-21-1 | 111-46-6 |
| Molecular Formula | C2H6O2 | C4H10O3 |
| Molecular Weight | 62.07 g/mol | 106.12 g/mol |
| Boiling Point | 197 degC | 245 degC |
| Melting Point | -13 degC | -10 degC |
| Density | 1.113 g/cm3 | 1.118 g/cm3 |
| Typical Purity | 99.8 percent min | 99.5 percent min |
MEG has a lower molecular weight, a lower boiling point and lower viscosity than DEG. DEG has two hydroxyl groups plus an ether oxygen, which changes its solvency and its behaviour in polymer formulations. These differences translate directly into different application profiles.
Applications of Monoethylene Glycol and Diethylene Glycol
MEG is the most widely traded glycol in the world. Its main applications include:
PET resin production for bottles and packaging.
Polyester fibre and filament for textiles.
Antifreeze and engine coolants for vehicles and industrial cooling systems.
Heat-transfer fluids and de-icing formulations.
Natural gas dehydration and as a general industrial solvent.
DEG is produced in smaller volumes than MEG and serves different markets, including:
Unsaturated polyester resins used in fibreglass and composites.
Plasticizers for polymers.
Industrial solvents for dyes, inks and textile processing.
Lubricants and hydraulic fluids.
Natural gas dehydration, where its higher boiling point is an advantage.
How to Choose Between MEG and DEG
Choose MEG when the application requires a low-viscosity diol for polyester polymerisation, antifreeze or coolant systems. Choose DEG when a higher-boiling glycol with different solvency is needed, such as in unsaturated polyester resins, plasticizers and specialty solvent blends. In both cases, verify the required specification, purity and documentation with the supplier, and confirm that the product grade matches the intended end use.
Safety and Compliance Notes
Both MEG and DEG are toxic if ingested, and neither is permitted in food or pharmaceutical products. DEG in particular has a history of accidental poisonings when it was wrongly used in pharmaceutical or food applications, so buyers must ensure that glycol supplies are clearly labelled and traced to their intended industrial use. Handle both products with standard industrial hygiene practices, avoid skin contact, and store them in clearly marked containers away from incompatible materials. Always consult the current Safety Data Sheet for each product.
Frequently Asked Questions
What is the difference between MEG and DEG? MEG, CAS 107-21-1, is the simplest ethylene glycol with the formula C2H6O2, while DEG, CAS 111-46-6, has the formula C4H10O3 and a higher molecular weight and boiling point.
What is MEG mainly used for? MEG is mainly used to produce PET resin, polyester fibre, antifreeze and engine coolants.
What is DEG mainly used for? DEG is mainly used in unsaturated polyester resins, plasticizers, solvents and lubricants.
Can DEG be used in food or pharmaceuticals? No, DEG is toxic if ingested and is not permitted in food, beverage or pharmaceutical applications. It must only be used in clearly controlled industrial applications.
What are the CAS numbers of MEG and DEG? The CAS number of MEG is 107-21-1 and the CAS number of DEG is 111-46-6.
Which glycol has a higher boiling point? DEG has a higher boiling point of about 245 degC, compared with about 197 degC for MEG.