How potassium hydroxide is made

Caustic potash was once made by stirring potash into slaked lime. Now current through brine does it.

stations: 5
things upstream: 2
raw sources: 2
step from the ground: 1

The short version

Potassium hydroxide is produced by electrolysis of potassium chloride solution, in cells that keep the two electrodes apart. Hydrogen and chlorine form as by-products at the electrodes. The liquor is boiled down, and the product is sold as flakes, pellets or solution. About 2.5 million tonnes were made in 2023.

Dissolve potassium chloride

Potash salt is dissolved in water to make a brine. The brine is purified before it goes to the cells.

Goes in
Potash Water
Run current through the cell

Electrolysis gives potassium hydroxide in solution, hydrogen at the cathode and chlorine at the anode. The anode and cathode spaces must be kept apart.
Boil the liquor down

The caustic solution is evaporated to a stronger concentration. Most commercial grades are about 90 percent pure, with the rest water and carbonates.

about 90% pure
Melt-cast it into pellets

The molten caustic is cast into pellets or rods. They pick up moisture from air and turn tacky, so they are sealed in drums at once.
Pack by purity grade

Industrial and food uses need at least 90 percent purity. Food grade also has strict arsenic and lead limits.

End of the linePotassium hydroxide Next it goes into aa battery.

Worth repeating

Until the late 19th century caustic potash came from mixing potash with slaked lime and filtering off the chalk, a method electrolysis replaced.
Potassium hydroxide is the precursor to most soft and liquid soaps.
It is used in cocoa processing and to debitter olives.