Ethylene
The highest-tonnage organic chemical made anywhere, and a plant hormone that ripens fruit — the same molecule doing both.
Ethylene is two carbons joined by a double bond, and that bond is the whole of its industrial usefulness: it is strained enough to open under a catalyst and join to the next molecule, indefinitely. More of it is made than any other organic chemical — well over two hundred million tonnes a year — and most becomes polyethylene.
It is also a plant hormone. Fruit ripens in response to it, which is why one ripe apple ripens the others in a bowl, and why bananas are shipped green and gassed with ethylene on arrival. The industrial chemical and the signalling molecule are the same substance, discovered independently and reconciled late.
Processing
Made by steam cracking — naphtha in Europe and Asia, ethane from natural gas in North America and the Middle East. The feedstock choice decides the by-product slate, and an ethane cracker's near-exclusive ethylene output is why propylene has periodically been in short supply while ethylene was not.
Uses
Polyethylene takes the largest share. The rest goes to ethylene oxide (antifreeze, surfactants), ethylene dichloride and on to PVC, ethylbenzene and on to styrene, and to alpha-olefins for detergents and co-monomers.
And to ripening rooms, in quantities that are trivial industrially and decisive commercially — the entire global trade in bananas and avocados depends on being able to postpone ripening and then trigger it.
History
Isolated in the eighteenth century and long a laboratory curiosity. Its polymer was found by accident at ICI in 1933, when a high-pressure experiment left a waxy white solid in the vessel; the reaction turned out to depend on a trace of oxygen leaking in, which is why it had not been reproducible.
Polyethylene's first significant use was as radar cable insulation in the Second World War, where its low dielectric loss was a genuine military advantage and its existence was classified.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is produced by
- Steam cracking — process · the principal product, and the largest-tonnage organic chemical made anywhere
is a source for
- Styrene — compound · via ethylbenzene: ethylene alkylates benzene, and the product is dehydrogenated
- Polyethylene — material · the monomer the polymer is named for, and essentially the only input
- Polyvinyl chloride — material · via ethylene dichloride and vinyl chloride — the chlorine comes from the chlor-alkali industry, and PVC is where about a third of world chlorine production ends up
is an input to
- Polymerisation — process · into polyethylene, and via ethylene dichloride into PVC — the two highest-tonnage plastics between them
contains
is commonly confused with
- Propylene — compound · one carbon apart, made in the same plant, and the difference decides whether the product is polyethylene or polypropylene
Sources
- Material WorldOur own writing
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)