Acetic acid: Production route
How a rhodium catalyst won the whole industry
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.Methanol carbonylation has displaced almost every older route since the 1970s because it is cheap, selective and runs on methanol and CO, which can come from gas or coal. The main versions are Monsanto's rhodium process, Celanese's AO Plus (rhodium with lithium salts, lower water) and BP's Cativa (iridium). Older routes oxidise acetaldehyde from ethylene or oxidise butane and naphtha; they survive in a few plants. Fermentation makes food vinegar and a little bio-based acid.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| Methanol carbonylation (Rh or Ir catalyst) | most of world capacity, probably above 90% (indicative) | about 0.54 t methanol and 0.53 t CO per t (indicative) | 0.5-1.6 Mt a year per site; Celanese Clear Lake 1.6 Mt, Nanjing 1.2 Mt (ResourceWise, 2020); Jieyang 1.5 Mt single line (2026) | about 99% on methanol, 90-95% on CO (indicative) | propionic acid traces; off-gas | raw materials about $200/t at CFR China methanol of about $250/t and coal-based CO (indicative) |
| Acetaldehyde oxidation (from ethylene, Wacker) | small (indicative) | about 0.5 t ethylene per t (indicative) | 100-300 kt a year (indicative) | about 95% (indicative) | formic acid | higher than carbonylation (indicative) |
| Ethane or hydrocarbon direct oxidation | small (indicative) | not published | small | low selectivity (indicative) | formic and propionic acids, ethylene | not published |
| Fermentation (bio-acetic acid, vinegar) | food vinegar only; industrial share tiny (indicative) | about 0.77 t ethanol per t (stoichiometry) | small | about 85-90% (indicative) | biomass | well above carbonylation (indicative) |
How each route works
Methanol carbonylation (Rh or Ir catalyst)Methanol and carbon monoxide react with a methyl iodide promoter over rhodium (Monsanto, Celanese AO Plus) or iridium (Cativa) catalyst in a stirred reactor. Low-water processes cut distillation energy. CO comes from a dedicated syngas unit or coal gasifier on site.
Lowest cost and large scale; needs precious-metal catalyst and corrosion-resistant metallurgy.
ResourceWise (2020); Procurement Resource (2026); indicative process data Acetaldehyde oxidation (from ethylene, Wacker)Ethylene is oxidised to acetaldehyde and then to acetic acid. Once common in Europe and Japan; now marginal because ethylene costs more than methanol and CO.
Uses ethylene where methanol is scarce; uncompetitive today.
indicative Ethane or hydrocarbon direct oxidationEthane, butane or light naphtha is oxidised directly; SABIC has run an ethane-to-acetic acid process. Gives mixed acids and needs separation.
Uses cheap ethane; selectivity problems limit scale.
indicative Fermentation (bio-acetic acid, vinegar)Ethanol is oxidised by Acetobacter bacteria to vinegar; anaerobic routes and gas fermentation can make acetic acid directly. Food vinegar is typically 4-10% acid.
Bio-based and food-grade; dilute and costly to concentrate.
stoichiometry; indicative Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.