How ethylene glycol is made

Your polyester shirt and your car's antifreeze share one sweet-tasting, toxic ingredient.

stations: 6
things upstream: 15
raw sources: 8
steps from the ground: 4

The short version

Ethylene gas is oxidized over silver to make ethylene oxide, a reactive three-membered ring. Water then pops the ring open, and a large excess of water keeps the molecules from reacting further. After the water is boiled off and heavier glycols are split away, the syrupy liquid goes to polyester plants and antifreeze blenders.

Oxidize over silver

Ethylene and oxygen pass over a silver catalyst in a closed reactor and form ethylene oxide. A part of the ethylene burns all the way to carbon dioxide. The oxide is a very hazardous substance and stays sealed inside the plant.

Goes in
Ethylene Oxygen gas
Open the ring with water

The oxide reacts with water, which breaks its strained ring and gives two hydroxyl groups. A large excess of water keeps the new glycol from reacting with more oxide. Yields reach 90% this way.

Goes in
Water
Or go through carbonate

Shell's OMEGA process first reacts the oxide with carbon dioxide, partly recovered from the first step, to make ethylene carbonate. Water then opens this with a base catalyst, reaching 98% selectivity.

Goes in
Carbon dioxide
Boil off the water

All that surplus water has to come off again, and this separation takes a lot of energy. It is the main drawback of the plain water route.
Split the glycol family

Columns separate the main product from its heavier cousins, diethylene, triethylene and tetraethylene glycol. The clean liquid boils at 198 °C.
Send it two ways

Most goes to polyester fiber and resin plants, and the rest largely to antifreeze blenders. A half-and-half mix with water freezes at −37 °C and boils at 129 °C, which suits car radiators.

End of the lineEthylene glycol Next it goes into pet plastic, spandex.

Worth repeating

Charles-Adolphe Wurtz first prepared ethylene glycol in 1856, and named it for its likeness to both ethyl alcohol and glycerin.
Ethylene oxide became industrially important in the First World War as a route to glycol coolant.
Ethylene glycol tastes sweet but is toxic in high concentrations.