How sulfuric acid is made
The world's most-used industrial acid is made by burning sulfur and passing the smoke over a catalyst.
- stations
- 6
- things upstream
- 3
- raw sources
- 3
- step from the ground
- 1
The short version
Sulfuric acid is made by burning molten sulfur in dry air to form sulfur dioxide gas, then passing the cleaned gas over a vanadium catalyst so it picks up more oxygen. The resulting sulfur trioxide is absorbed into strong acid, and water is added to bring the acid to the grade a customer wants.
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Melt and spray the sulfur
Solid sulfur is melted, filtered to remove grit, and sprayed into a furnace as fine droplets. Spraying gives the liquid a huge surface so that it burns quickly.
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Burn it in dried air
Sulfur burns in a blast of air that has been dried first, producing sulfur dioxide gas and a lot of heat. Waste-heat boilers capture that heat as steam.
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Clean and dry the gas
Dust and moisture are stripped from the gas, and the gas is dried by sulfuric acid itself. Impurities would foul the catalyst and wreck the next step.
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Pass it over the catalyst
Inside a tall converter the gas flows through several beds of a vanadium oxide catalyst, which helps it pick up one more oxygen atom and become sulfur trioxide. The gas is cooled between beds.
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Absorb it in strong acid
Dropped into water, sulfur trioxide would make a hot acid mist, so it is fed into concentrated acid in an absorption tower, where it forms a fuming liquid called oleum.
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Dilute to the right grade
Water is added in controlled amounts to bring the acid to the strength a customer ordered. Plants that run the gas through the converter and absorber twice convert nearly all of it.
Goes in
Worth repeating
- Sulfuric acid dehydrates sugar and paper so aggressively that it pulls the water out of their molecules and leaves black carbon.
- Sulfuric acid's biggest customer is fertilizer manufacture, and it is also used in mineral processing, oil refining and lead-acid batteries.
- The contact process was patented in 1831 by a British vinegar merchant, and it replaced the lead chamber process.
Back to the ground
Follow every input upstream and sulfuric acid starts as these 3 raw sources.
Where it goes next
Sulfuric acid feeds 24 lines directly and reaches 404 things in total.
Further down the line
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Sources
Cite this page: "How sulfuric acid is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/sulfuric-acid