How hydrochloric acid is made

Most hydrochloric acid is a by-product of making other chemicals, caught and dissolved in water.

stations: 5
things upstream: 8
raw sources: 5
steps from the ground: 3

The short version

Hydrochloric acid is hydrogen chloride gas dissolved in water. Since 2000 most has been made by absorbing hydrogen chloride that other chemical plants give off, and a smaller share is made directly from hydrogen and chlorine. The solution is stored in lined tanks and shipped, and steel mills use much of it to clean rust.

Collect the gas

Making plastics and other organic chemicals releases hydrogen chloride gas. Plants capture it rather than vent it.

Goes in
Chlorine
Burn hydrogen in chlorine

Direct synthesis burns hydrogen in chlorine to make hydrogen chloride. This is often tied to the chloralkali process, which produces chlorine and hydrogen together.

Goes in
Hydrogen Chlorine
Recover it from spent pickle liquor

Steel mills regenerate spent acid by pyrohydrolysis, which drives hydrogen chloride back out of the used liquid. The iron oxide that remains is sold.
Dissolve it in water

The gas is absorbed in water to produce the acid. Dissolving it is highly heat-releasing, so absorbers are cooled.

Goes in
Water
Store and ship in lined tanks

The strong acid is stored and moved in tanks lined with resistant materials. A common technical grade for steel cleaning is about 18 percent.

End of the lineHydrochloric acid Next it goes into deodorant, silicone, polysilicon and 4 more.

Worth repeating

Only about 3 million of the roughly 20 million tonnes of hydrochloric acid made each year come from direct synthesis.
Steel mills dip steel in it to remove rust and scale before rolling or galvanizing.