Air separation
Liquefying air and distilling it into its components — the source of industrial oxygen, nitrogen and every noble gas but helium.
Air separation works because the gases in air boil at different temperatures. Compress air, cool it until it liquefies, and then let it warm in a distillation column: nitrogen comes off first, then argon, then oxygen, each drawn from the height in the column where its boiling point puts it.
The economics are unusual. The feedstock is free and unlimited, so the entire cost is the energy of compression and cooling, and the plant is generally built next to whatever consumes the product rather than shipping it. A steelworks has an air separation unit because moving oxygen is more expensive than making it.
Processing
The rare components are collected in proportion to how much air is processed, which is what sets their price. Neon, krypton and xenon are present in air at a few parts per million or less, so they are recovered as side-streams from plants running at scale for oxygen and nitrogen — never on their own account.
That dependence has consequences. When neon supply is disrupted, it is usually because the large steel and chemical plants whose air separation units yield it as a by-product have stopped, not because anybody stopped wanting neon.
Uses
Oxygen for steelmaking is the largest single output by tonnage, followed by nitrogen used as an inert blanket in chemical plants, food packaging and electronics manufacture.
Argon goes to welding and to metallurgy, where an inert atmosphere prevents a hot metal from reacting with air. Neon, krypton and xenon go to lighting, lasers and specialist optics in quantities small enough that a single plant's side-stream supplies a large share of world demand.
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.
produces
- Oxygen — element · the largest output by tonnage, and the reason air separation units sit beside steelworks
- Nitrogen — element · the most abundant component of air and the first to boil off
- Argon — element · drawn from an intermediate height in the column, between nitrogen and oxygen
- Neon — element · recovered as a side-stream in proportion to the air processed, never on its own account
- Krypton — element · present in air at about one part per million
- Xenon — element · the rarest of the stable noble gases in air, and priced accordingly
takes as input
- Air — material · the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it
Sources
- Material WorldOur own writing