Naphtha
The refinery cut that becomes plastic. Everything between petroleum gas and kerosene, and the single most important feedstock in the chemical industry.
Naphtha is a fraction rather than a chemical: the part of crude oil boiling roughly between 30 and 200 °C, made mostly of hydrocarbons with five to ten carbon atoms. It is the feedstock a steam cracker consumes to make ethylene and propylene, and therefore the origin of most of the world's plastic.
In North America and the Middle East, cheap ethane from natural gas has largely displaced it as a cracker feed. In Europe and much of Asia it has not. That geographical split decides which polymers are cheap where, because an ethane cracker makes almost only ethylene while a naphtha cracker makes propylene and aromatics too.
Processing
Separated by distillation, then usually hydrotreated to remove sulfur — which is not an environmental courtesy at this stage but a necessity, because sulfur poisons the catalysts downstream.
From there it goes to a steam cracker for olefins, or to a catalytic reformer for the aromatics that become polystyrene, polycarbonate and PET.
Uses
Overwhelmingly as cracker feed. Also as a solvent — lighter fluid and white spirit are naphtha fractions — and as a diluent for heavy crude so it can be pumped.
History
The word is ancient and has meant several things: a flammable liquid in Akkadian and Greek, and one of the candidate ingredients of Greek fire. Its modern meaning dates from the refining industry, and its modern importance from the 1940s, when steam cracking turned a middling fuel fraction into the starting point of the plastics age.
Environmental impact
Cracking is among the most energy-intensive processes in the chemical industry — the furnaces run above 800 °C — and naphtha cracking is more so than ethane cracking. That energy, rather than the carbon locked into the polymer, is the larger share of a plastic's production footprint.
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 sourced from
- Crude oil — material · the fraction boiling between about 30 and 200 °C, separated by distillation rather than made
is an input to
- Steam cracking — process · the European and Asian cracker feed; North American crackers mostly run on ethane from natural gas instead, and make a different product slate as a result
contains
is produced by
- Steam cracking — process · consumed rather than produced: it is the feed the cracker is designed around, and the choice of feedstock fixes the plant's whole product slate
is a source for
- Plastic — material · the cracker feed in Europe and Asia; North American crackers mostly run on ethane from natural gas instead
Sources
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- Material WorldOur own writing