Claus process
Recovering elemental sulfur from the hydrogen sulfide stripped out of natural gas and crude oil — the reason sulfur is a by-product of pollution control rather than a mined commodity.
Almost all the world's sulfur is now produced by cleaning it out of fossil fuels, and the Claus process is how. Natural gas and crude oil contain hydrogen sulfide, which is lethally toxic and which turns into sulfur dioxide when the fuel is burned. It has to be removed. The Claus process takes the removed gas and turns it into solid elemental sulfur instead of releasing it.
The result is a commodity produced in inverse proportion to demand for it. Sulfur output is set by how much oil and gas is processed and how strictly emissions are regulated, not by anyone's need for sulfuric acid — which is an unusual and occasionally awkward position for one of the most heavily used industrial chemicals in the world.
Processing
It runs in two stages. A third of the hydrogen sulfide is burned to sulfur dioxide in a furnace; the remaining two thirds then react with that sulfur dioxide over a catalyst to give elemental sulfur and water. Passing the gas through several catalytic stages in series, condensing out the sulfur between each, takes recovery above ninety-five per cent, and a tail gas treatment unit after them can push it beyond ninety-nine.
The sulfur is drawn off as a liquid and either shipped molten in heated tankers or poured into vast solid blocks at the plant. Those blocks, some of them visible from the air, are the stored surplus of a product that arrives whether or not anybody wants it.
Economic significance
Sulfur mining as an industry effectively ended because of this process. The Frasch process, which melted sulfur out of underground deposits with superheated water, could not compete with a material that refineries must produce anyway and would otherwise have to pay to dispose of.
What follows from that is a supply chain most people never trace: sulfuric acid is made from this sulfur, and phosphate fertiliser is made with that acid. A world that burns less fossil fuel produces less sulfur, and the fertiliser industry has a supply question it did not choose.
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
- Sulfur — element · recovered from the hydrogen sulfide stripped out of natural gas and crude oil — which is now almost the whole of world supply
Sources
- Material WorldOur own writing