Caustic soda
Caustic soda (sodium hydroxide) is the world's main industrial alkali, co-produced with chlorine and essential for alumina, pulp, soaps and chemicals.
Commodity chemicals · Acids & alkalis · No. 6
- Single chemical
- Feedstock: Minerals and salts
- about 90 Mt a year (100% NaOH basis, 2025, indicative, derived from about 80 Mt chlorine x 1.13; no Euro Chlor or World Chlorine Council world total is published)
- 0.9 t CO₂e per t
- HS 281511, 281512
Caustic soda is chlorine's twin, so a PVC boom floods its market; US export prices roughly halved from 2022 to 2025.
Chart: Illustration: Caustic soda
Where it comes from
Chart: Map of where it comes from
Caustic soda is made by passing electricity through salt brine, with chlorine and a little hydrogen alongside; membrane cells give about 32% solution, then evaporated to 50%.
Three things to know
- Every tonne of chlorine brings 1.13 t of caustic, so strong PVC demand floods the market with caustic and pushes its price down.
- US Gulf export caustic fetched about $850/dmt in October 2022, but only $390-440/dmt three years later.
- India's capacity rose from 4.4 Mt in FY2019 to 6.40 Mt in FY2024-25, turning it into a small net exporter.
The journey
- 1 Salt brineAbout 1.5 t salt per tonne
- 2 ElectrolysisMembrane cells split brine, chlorine alongside
- 3 EvaporationConcentrated to 50% liquid lye
- 4 FlakesDried to 98-99% solid for distance
- 5 End useAlumina, pulp, soap and chemicals