Hydrochloric acid: Production route
Three ways acid appears, mostly as someone else's leftovers
Three ways acid appears, mostly as someone else's leftovers What this tab covers How it is made: the main production routes or, for product families, the main product types and technologies, compared on share of supply, inputs per tonne, plant scale, yield, co-products and unit cost.Hydrochloric acid comes from three main sources. Most is by-product from chlorination and phosgenation, which makes HCl in proportion to chlorine consumed. Chlor-alkali producers also burn chlorine with their own hydrogen to make synthetic acid of high purity. A smaller share comes from the Mannheim process (salt plus sulphuric acid, making potassium or sodium sulphate). Much by-product HCl is recycled to chlorine or used in oxychlorination.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| By-product from isocyanates, chlorinated organics and fluorocarbons | majority of HCl (indicative) | not applicable (by-product) | 100-500 kt/yr at large MDI sites | not applicable | not applicable | near zero or negative: producers pay to dispose of surplus |
| Direct synthesis from chlorine and hydrogen | a large share in India and China (indicative) | about 0.97 t Cl2 and 0.028 t H2 per t of 100% HCl | 50-200 TPD units at chlor-alkali plants | near 100% | heat | opportunity cost of chlorine; often near zero when chlorine is negative |
| Mannheim process (salt plus sulphuric acid) | small | about 2.0 t KCl (or 1.6 t NaCl) and 1.34 t H2SO4 per t HCl (stoichiometric) | small | high | potassium or sodium sulphate (the main product) | set by sulphate market |
How each route works
By-product from isocyanates, chlorinated organics and fluorocarbonsPhosgenation for MDI, TDI and polycarbonate, chlorination of methane and aromatics, and HCFC/fluoropolymer production each release HCl gas, which is purified and absorbed or recycled.
cheap; purity varies (organics, fluorides)
indicative Direct synthesis from chlorine and hydrogenChlorine is burned with excess hydrogen in a graphite or silica burner and absorbed in water. This turns surplus chlorine into a saleable product and gives high-purity acid for food, pharma and electronics.
pure product; ties up chlorine
stoichiometry; indicative Mannheim process (salt plus sulphuric acid)Potassium or sodium chloride reacts with sulphuric acid in a furnace, giving sulphate of potash or sodium sulphate and HCl.
HCl is a co-product of SOP fertiliser
stoichiometry Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.