How polystyrene is made

Foam cups and clear CD cases come from the same molecule, styrene, which is built from ethylene and benzene.

stations: 6
things upstream: 10
raw sources: 4
steps from the ground: 6

The short version

Polystyrene is made from styrene, which is built from benzene and ethylene. Styrene is linked into long chains in a reactor, then the leftover monomer is stripped out and the melt is cut into pellets. Foam versions are made by soaking beads in a gas and expanding them with steam.

Extract benzene from naphtha

A refinery reforms naphtha to make aromatic compounds, and benzene is distilled out. It is the ring-shaped heart of styrene.

Goes in
Naphtha
Attach ethylene to the ring

Benzene and ethylene react over a catalyst to give ethylbenzene. Almost all ethylbenzene made in the world goes on to become styrene.

Goes in
Ethylene Benzene
Strip off hydrogen

Ethylbenzene is heated with steam over a catalyst, which pulls off two hydrogen atoms. The product is styrene, a liquid that is distilled clean.
Link styrene into chains

Styrene is heated in a reactor and polymerizes into polystyrene, thickening as the chains grow.

Goes in
Styrene
Remove leftover monomer

A vacuum chamber pulls unreacted styrene out of the thick melt, and it is recycled to the reactor. The polymer is then ready to shape.
Pellet it or foam it

Clear general-purpose polystyrene is extruded and cut into pellets. Foam beads are soaked with a blowing agent and puffed with steam, which fuses them into a block that is full of trapped air.

End of the linePolystyrene Next it goes into surfboard, bike helmet, ballpoint pen and 5 more.

Worth repeating

Polystyrene turns glassy at room temperature and flows when heated above its glass transition temperature of about 100 °C.
Roughly 35 million tonnes of styrene were produced worldwide by 2018.