What n-Hexane (CAS 110-54-3) Is
n-Hexane is a straight-chain saturated aliphatic hydrocarbon with the formula C6H14 and a molecular weight of 86.18. It is a colourless, volatile liquid with a faint petroleum odour, practically insoluble in water and miscible with most organic solvents. Commercial hexane is not a single substance but a narrow distillation cut that contains n-hexane together with its branched isomers, methylcyclopentane and cyclohexane; the n-hexane content of an extraction grade parcel is typically 95% or higher, and that figure is the first line item on any specification sheet.
Typical Specification Sheet
| Property | Typical value | Reference method |
|---|---|---|
| n-Hexane content | 95 % minimum, extraction grade | Gas chromatography |
| Distillation range at 101.3 kPa | 66 - 70 degrees C | ASTM D86 |
| Density at 20 degrees C | 0.659 g/cm3 | ASTM D4052 |
| Flash point, closed cup | minus 22 degrees C | ASTM D93 |
| Water | 0.01 % maximum | ASTM D1364 (Karl Fischer) |
| Colour | 10 Pt-Co maximum | ASTM D1209 |
| Residue on evaporation | 10 ppm maximum | Gravimetric |
| Transport classification | UN 1208, Class 3, Packing Group II | UN Model Regulations |
Why Extraction Processes Choose Hexane
The selection is a combination of thermodynamics and plant economics. Hexane has a low boiling point near 68.7 degrees C, so the solvent can be stripped from the extracted oil at modest temperature and low energy cost, which protects heat-sensitive oils and keeps the thermal load on the desolventiser low. Its narrow boiling range means that the recovered solvent returns to the extraction circuit with a consistent composition, avoiding the build-up of heavy ends that would change the extraction equilibrium. It is chemically inert towards triglycerides and does not react with the oil, and its low water solubility limits emulsion formation and the load on the water-removal stage. Its low latent heat of vaporisation and low viscosity also reduce pumping and condenser duties.
On the other side of the balance, hexane is highly flammable and is classified as a hazardous air pollutant in many jurisdictions, so modern plants use closed loops, vapour recovery units and solvent-loss monitoring as primary operating indicators rather than afterthoughts.
Regulatory Status in Food and Feed Processing
Hexane is recognised as an extraction solvent for food use. Under Regulation (EU) No 2009/32/EC it is a permitted extraction solvent for the production of fats and oils and for the removal of contaminants, subject to maximum residue limits that vary by commodity. In the United States, 21 CFR 173.270 permits hexane as a solvent for the extraction of oil from oilseeds and oilseed-derived ingredients, again subject to purity and residue conditions. Compliance therefore depends on both the purity of the solvent delivered and the desolventising performance of the buyer's plant, and buyers in food supply chains should request solvent documentation that states the residue profile.
Occupational and Environmental Controls
The critical health concern is neurotoxicity. n-Hexane is metabolised to 2,5-hexanedione, which damages peripheral nerves; prolonged exposure above occupational limits causes numbness in the hands and feet and progressive loss of motor function. Controls are engineering-led: closed transfer, local extraction at filling points, specified respiratory protection for maintenance tasks, and biological monitoring of 2,5-hexanedione in urine where the exposure assessment requires it. Because the flash point is minus 22 degrees C, the liquid produces flammable vapour at any normal ambient temperature, so bonding and grounding of containers and lines, flameproof electrical equipment and static-dissipative clothing are mandatory in the extraction area.
Frequently Asked Questions
Q: Why is n-hexane used instead of other solvents for oil extraction?
A: It combines a low boiling point near 68.7 degrees C for cheap solvent recovery, a narrow boiling range for a stable extraction circuit, chemical inertness towards oils, and low water solubility. Those properties together give high oil yield at low energy cost.
Q: What purity should be ordered for food oil extraction?
A: A hexane content of 95% or higher with a controlled distillation range of about 66 to 70 degrees C, water at 0.01% maximum, residue on evaporation at 10 ppm maximum, and a low aromatic content, so that solvent residues left in the oil are within the applicable limits.
Q: How is n-hexane stored and transported?
A: As a flammable liquid under UN 1208, Class 3, Packing Group II, in grounded steel drums, IBCs or road tankers, under nitrogen where moisture control is needed, away from heat and oxidisers. Vapour space is kept inert or vented through vapour recovery.
Q: What are the health hazards of working with hexane?
A: Inhalation of vapour can cause dizziness and headache at high concentrations, and repeated overexposure can cause peripheral neuropathy through the metabolite 2,5-hexanedione. Engineering controls, exposure monitoring and, where required, biological monitoring are the standard safeguards.
Q: Can hexane be recovered and reused in the plant?
A: Yes. The solvent distilled from the oil is condensed and returned to the circuit. The recycled stream is monitored for heavy ends, water and acid build-up, and a purge is taken so that the composition of the circulating solvent stays within the range used to set the extraction process.