Organic Acids (e.g. acetic acid) — class summary
Volatility
C₁–C₆ volatile; longer chains as aerosol
Water solubility
High for short chains; falls with chain length
pKa
3.7 – 4.9
Odour threshold
ppb range (butyric, valeric)
Toxicity
Irritant; corrosive when concentrated
Flammability
Combustible liquids
Chronic risk
Respiratory irritation
Environmental
Odour; COD load
| Property | Value / Note |
|---|---|
| Scope | Formic (HCOOH), acetic (CH₃COOH), propionic, butyric, valeric and caproic acid; the fatty acid family from fermentation and protein breakdown. Formic acid has its own sheet. |
| Physical state | Volatile liquids; the C₂–C₄ acids are the ones normally found in the gas phase. |
| Solution chemistry | Weak acids. At pH > pKa + 2 they are fully dissociated and effectively non-volatile — that is what makes alkaline scrubbing work. |
| Corrosivity | Attack carbon steel, zinc and many elastomers; glacial acetic acid is classified as corrosive (danger). |
| Typical sources | Potato and vegetable processing, fermentation, rendering, silage, anaerobic digestion, metal degreasing baths. |
| Best analytical detection | FTIR for speciation of the individual acids in the stack; pH and conductivity in the liquor for control; ion chromatography of the blow-down to confirm the captured load. |
*Class summary — check the individual SDS. Concentrated acetic acid (≥ 25%) is classified as corrosive; this sheet describes the dilute vapour phase.