Sulphur Trioxide (SO₃) — properties & hazards overview
Boiling point
≈ 45 °C (liquid → gas)
Melting point
≈ 17 °C
Vapour pressure (25 °C)
≈ 25 hPa
Water solubility
Reacts violently (forms H₂SO₄)
Flammability
Non-flammable
Corrosivity
Extreme (acid mist)
Toxicity
Severe respiratory irritant
Environmental
Acid-forming pollutant
| Property | Value / Note |
|---|---|
| Physical state | Colourless to slightly bluish liquid or gas; forms dense white fumes in humid air (H₂SO₄ aerosol). |
| Odour | Pungent, choking, acid-like; perceptible at very low concentrations. |
| Reactivity | Violently exothermic with water and organics; instantly hydrolyses to H₂SO₄. |
| Typical sources | Contact-process acid plants, oleum handling, sulphur burners, catalyst beds, or fume leaks in SO₃ piping. |
| Best analytical detection | Indirect aerosol sampling with ion-chromatographic sulfate analysis — SO₃ converts rapidly to H₂SO₄ mist; thus analysis is performed on collected aerosol (EPA Method 8, EN 14577). Direct FTIR/NDIR detection is unreliable due to rapid hydrolysis. |
*Indicative data; confirm with process safety data and regulatory measurement standards.