Cyclohexanone, CAS 108-94-1, is a cyclic ketone used as a solvent and chemical intermediate. It is transported under the proper shipping name “Cyclohexanone,” UN 1915, hazard class 3, packing group III, as listed in 49 CFR 172.101. Cyclohexane, CAS 110-82-7, is an aliphatic hydrocarbon transported as “Cyclohexane,” UN 1145, hazard class 3, packing group II. The near-identical prefix and the shared Class 3 flammable liquid label create recurring confusion in shipping documentation, tank assignment, placard display, and limited-quantity packaging. The mix-up is not limited to spelling; the two substances occupy different packing groups, have different flash points, and trigger different packaging and placarding thresholds. This article addresses the main operational distinctions and common failure points in Cyclohexanone vs Cyclohexane Shipping: Common Mix-Ups.

What Distinguishes the Hazard Table Entries for UN 1915 and UN 1145?

The 49 CFR 172.101 entry for cyclohexanone assigns proper shipping name “Cyclohexanone,” UN 1915, hazard class 3, packing group III, and the flammable liquid label. The cyclohexane entry assigns “Cyclohexane,” UN 1145, hazard class 3, packing group II, and the same label. The packing-group difference follows from the flash-point and boiling-point criteria in 49 CFR 173.120. Cyclohexanone has a closed-cup flash point of approximately 44°C and a boiling point of 155.6°C at 101.3 kPa. Cyclohexane has a closed-cup flash point of approximately −18°C and a boiling point of 80.7°C at 101.3 kPa.

The molecular mass of cyclohexanone is approximately 98.15 g/mol; cyclohexane is approximately 84.16 g/mol. Density at 20°C is approximately 0.947 g/cm³ for the ketone and 0.779 g/cm³ for the hydrocarbon. Vapor pressure at 20°C is approximately 0.5 kPa for cyclohexanone and 12.7 kPa for cyclohexane. Flash point measurements are typically performed under ASTM D93-20 or ASTM D56-21a. The lower cyclohexane flash point places it in packing group II because the value is below 23°C and the boiling point is above 35°C. The cyclohexanone flash point places it in packing group III because the value falls between 23°C and 60°C.

At bulk transfer racks that share a positive-displacement pump skid for both products, a known failure mode is cross-contamination when the suction and discharge manifold is drained to a common slop tank and the pump casing is not purged with nitrogen between batches. The low-boiling cyclohexane residue raises the vapor pressure and lowers the flash point of the subsequent cyclohexanone lot. The receiving tank’s pressure/vacuum vent is often specified for the lower vapor pressure of cyclohexanone, so cyclohexane-residue vapor can increase venting demand beyond the original design. A tank truck that arrives with a product odour typical of the alkane rather than the ketone should be sampled at the top, middle, and bottom levels; a single top sample may miss a dense residue layer at the bottom if the previous cargo was cyclohexane and the tank was not drained completely.

Regulatory Consequences When UN 1915 Is Transposed to UN 1145 on Shipping Papers

A shipping-paper error that lists “Cyclohexane” on a cyclohexanone shipment changes the dangerous-goods declaration from a packing group III material to a packing group II material. Under 49 CFR 172.202(a)(2), the proper shipping name must appear exactly as listed in 49 CFR 172.101; the use of “cyclohexyl solvent,” “cyclohexanone/cyclohexane blend,” or “cyclic C6 solvent” is not acceptable as a substitute. A carrier receiving a bill of lading with the wrong UN number may reject the shipment at the gate, leading to demurrage and rework. In intermodal ports, the container booking system compares the UN number in the transmission against the dangerous-goods profile, and a mismatch between the shipper’s declared packing group and the port’s hazardous material code can block vessel loading.

The SDS Section 14 template is a common source of the error. A supplier that copies the cyclohexane SDS template and changes the product name without updating the transport information will issue a safety data sheet that lists UN 1145 for cyclohexanone. The error then propagates to the customer’s carrier declaration and to the vessel stowage plan. In many enterprise resource planning systems, the material master for cyclohexanone and cyclohexane are linked by a search string that returns both entries. A purchase order for the ketone can autocomplete to the hydrocarbon if the user enters “cyclohex” and selects the first row. The resulting transaction then sends the wrong CAS and UN number to the warehouse, and the shipping label is printed before the product is sampled. The control for this failure is to require the proper shipping name and UN number to be copied from the current SDS Section 14 rather than from the material master alone.

When the shipment is a parcel tanker or ISO tank container, the product name on the stenciled sheet must match the bill of lading and the heating system must be set for the correct vapor pressure. Cyclohexanone is sometimes heated to reduce viscosity in cold weather; cyclohexane is not heated under the same conditions because of its higher vapor pressure and lower flash point. A heating coil set for cyclohexanone can raise the cargo temperature above the flash point and increase vapor formation if the tank actually contains cyclohexane, creating a confined-space ignition hazard at the tank hatch.

If Cyclohexane Residue Lowers the Flash Point of a Cyclohexanone Tank, What Classification Rule Applies?

The classification of a contaminated cyclohexanone batch is controlled by 49 CFR 173.120 and the UN Manual of Tests and Criteria, Part III, Section 32. If the measured closed-cup flash point of the mixture falls below 23°C and the boiling point remains above 35°C, the material must be shipped as a packing group II flammable liquid rather than the original packing group III cyclohexanone. The shift is not linear across the full concentration range because a small addition of cyclohexane raises the vapor pressure disproportionately relative to its mass fraction. Published data for this specific configuration is limited, and the exact concentration at which the flash point drops below 23°C must be determined by ASTM D93-20 on a representative sample rather than by extrapolation from pure-component flash points.

When reclassification occurs, the shipper must update the proper shipping name, UN number, packing group, placard, limited-quantity mark, and any material-safety data sheet Section 14 entries. The use of “Cyclohexanone” as the proper shipping name is no longer permitted if the mixture no longer meets the UN 1915 criteria; the appropriate mixture entry, such as “Flammable liquid, n.o.s.” or a technically correct n.o.s. entry under 49 CFR 172.101, may be required, depending on the composition.

For non-bulk shipments, the packing-group confusion changes limited-quantity thresholds under 49 CFR 173.150(b). A PG II flammable liquid is limited to 1 L inner packaging per package, while a PG III flammable liquid may use 5 L inner packaging, both with a gross package mass not exceeding 30 kg. If cyclohexane is packaged in 5 L inner containers because the shipper assumes cyclohexanone, the package is no longer a limited-quantity shipment and must be requalified with UN specification packaging under 49 CFR 178.503 or similar. In air transport, the IATA Dangerous Goods Regulations assign packing-instruction limits by packing group; a PG III allowance for cyclohexanone cannot be transferred to a misdeclared PG II cyclohexane shipment.

Cyclohexanone vs Cyclohexane Shipping: Common Mix-Ups in Non-Bulk and Bulk Packaging

Because both products are Class 3 flammable liquids, the Class 3 placard is visually identical. The UN number on the placard or on an adjacent orange panel is the first distinguishing mark. A cyclohexanone tank truck marked with UN 1145 or a cyclohexane tank truck marked with UN 1915 will fail a roadside inspection even if the Class 3 symbol is present. Placarding thresholds differ by packing group under 49 CFR 172.504(c), and a shipment of cyclohexanone that is incorrectly declared as cyclohexane may be placarded at a quantity where no placard is required for the actual PG III material. The reverse error can result in no placard where one is required for the PG II cyclohexane.

Segregation is not the primary issue because both materials are Class 3 and have no corrosive or toxic subsidiary hazards; however, emergency-response information under 49 CFR 172.602 must list the correct UN number and guide. A first responder using the wrong emergency-response guide for a spill may select incompatible firefighting or containment measures. Cyclohexane has a specific gravity below 1 and is water-insoluble, so it will float and spread on water; cyclohexanone has a specific gravity below 1 but is partially water-miscible, so runoff control and containment differ.

When an ISO tank container is shifted from cyclohexane service to cyclohexanone service, the cleaning procedure must include a heated water wash or solvent wash followed by a dry air purge and verification. Cyclohexane has a lower boiling point and higher vapor pressure, so it will evaporate faster than cyclohexanone; however, residual cyclohexane trapped in the bottom valve, sample line, or vapor return line may not be reached by a simple steam clean if the tank was not depressurized and drained completely. Tank inspection should include manway gasket replacement and a visual check of the sump because cyclohexanone may attack elastomer seals that were selected for cyclohexane service. Tank truck cleaning facilities that use a simple drain-then-rinse procedure without a solvent or steam cycle may leave a cyclohexane heel in the discharge line and pump. Because cyclohexane has a lower surface tension and lower heat of vaporization than cyclohexanone, it wets the interior of a stainless-steel tank differently and can be retained in dead zones such as the manway gasket groove and the pressure-relief valve seat. A pre-loading inspection that only checks the tank interior from the top hatch can miss these locations. The presence of residual cyclohexane can be confirmed by a photoionization detector calibrated to isobutylene at the sump or by a GC-FID headspace analysis.

At a terminal that loads both products through the same top-loading arm, a Raman verification system can compare the liquid fingerprint against a stored spectral library before the valve opens. The system rejects a cyclohexane delivery into a cyclohexanone tank by detecting the alkane C–H stretch pattern and the absence of the ketone carbonyl band at approximately 1715 cm⁻¹. The carbonyl band is a reliable marker because cyclohexane lacks a carbonyl group. When Raman verification is not installed, a simple density check at 20°C can detect bulk contamination because the density difference between the two liquids exceeds 0.1 g/cm³; however, low-level residue may require gas chromatography with flame ionization detection and a flash point test.

Bulk storage tanks for cyclohexanone are often nitrogen-blanketed and may be heated to maintain pumpability, but the set point is far below the boiling point. Cyclohexane storage requires more aggressive vapor control because the vapor pressure at 20°C is 12.7 kPa, roughly 25 times the cyclohexanone value of 0.5 kPa. If a plant discharges a cyclohexane truck into a cyclohexanone tank that is vented for the lower vapor pressure, the vapor flow through the pressure/vacuum vent may exceed the capacity of the vent and the tank may exceed its design pressure. Process engineers cross-check the tank vent sizing standard API 2000 or ISO 28300 before switching service.

Firefighting foam selection is another operational distinction. Cyclohexanone is a polar solvent and may require alcohol-resistant aqueous film-forming foam, while cyclohexane is nonpolar and can be extinguished with standard aqueous film-forming foam. A spill response plan drafted for cyclohexane may fail if the actual cargo is the ketone because standard foam can be degraded by polar solvents. The emergency-response information under 49 CFR 172.602 must therefore list the correct product name and UN number so the responder selects the correct foam type.

Terminals should retain a pre-loading sample from each truck compartment for at least 30 days after shipment. If the receiving customer reports off-spec cyclohexanone, the retained sample can be compared with the customer’s receiving sample by gas chromatography. The shipping-paper chain of custody under 49 CFR 172.602 does not itself prove the composition of the tank, but the retained sample tied to the bill of lading closes the evidentiary gap between the loading rack and the receiving tank.