How chlorine is made
Table salt dissolved in water and hit with a huge electric current gives off chlorine.
- stations
- 5
- things upstream
- 5
- raw sources
- 4
- steps from the ground
- 2
The short version
Chlorine is made by passing electric current through salt brine in a cell split by a membrane. Chlorine gas collects at one electrode. At the other, hydrogen gas and caustic soda form. The chlorine is cooled, dried and compressed into a liquid. Every tonne made brings along a fixed amount of caustic soda.
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Dissolve salt into brine
Salt is dissolved in water to make a saturated brine. Some plants dissolve rock salt underground and pump the brine out to the surface.
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Purify the brine
Chemicals precipitate calcium, magnesium and other contaminants, and filters and ion-exchange beds take out the rest. Dirty brine ruins the cell membranes.
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Run current through the cells
In each membrane cell, chloride ions give up electrons at the anode and become chlorine gas. Only sodium ions can pass through the membrane, and at the cathode water breaks into hydrogen gas and hydroxide.
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Cool and dry the chlorine
Hot, wet chlorine leaves the cells and is cooled to remove most of its water. It is then dried by contact with concentrated sulfuric acid.
Goes in -
Compress and liquefy it
The dry gas is compressed and chilled until it condenses. Liquid chlorine is stored in pressure tanks and shipped in tank cars, or piped to plants next door.
Worth repeating
- Splitting salt water also gives off hydrogen, one mole of it for every mole of chlorine.
- The process uses about 2,500 kWh of electricity for each tonne of caustic soda it makes.
- Roughly two-thirds of chlorine ends up in organic chemicals such as PVC, and the finished products often contain no chlorine at all.
Back to the ground
Follow every input upstream and chlorine starts as these 4 raw sources.
Where it goes next
Chlorine feeds 15 lines directly and reaches 311 things in total.
Further down the line
Keep walking
Sources
Cite this page: "How chlorine is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/chlorine