Cyclohexanone (CAS 108-94-1) is shipped in dedicated 20 ft ISO tank containers under the proper shipping name “Cyclohexanone,” UN 1915, Class 3, Packing Group III. ISO tank shipping for cyclohexanone: loading and care is governed primarily by the closed-cup flash point of 44 °C (ASTM D93), which places the material in the upper-temperature band of Packing Group III but still requires ignition-source control, static bonding, and oxygen displacement for safe transit. The liquid has a density of 0.9478 g/cm³ at 20 °C and a dynamic viscosity of 2.2 mPa·s at 20 °C. The freezing point is approximately -47 °C, so heating is not required for pumpability on most routes. Vapour pressure at 20 °C is reported in the range 0.5 kPa to 0.7 kPa, keeping the saturated vapour concentration below the lower explosive limit under cool ambient conditions. Solar heating of an uninsulated tank, however, can raise the upper-shell temperature above 40 °C and create a flammable headspace unless the tank is nitrogen-blanketed.

Flammability and vapour-pressure boundaries within a 20 ft ISO frame

The lower explosive limit of cyclohexanone is commonly cited as 1.1 vol %, and the upper explosive limit is approximately 9.4 vol %. At 44 °C, the vapour pressure is sufficient to generate a headspace concentration at the lower explosive limit at 101.325 kPa total pressure. Because the difference between a safe cool-loading condition and a flammable transit condition is only 4 K to 6 K when the liquid is near 40 °C, the loading terminal applies a nitrogen blanket with residual oxygen below 4 vol %. Nitrogen purity of 99.0 vol % or higher is specified; lower purity may leave enough residual oxygen to support ignition after the vapour space becomes enriched with ketone. The standard 20 ft chemical tank is built to ISO 1496-3:2019 as Type T11, with a test pressure of 4.0 bar and a working pressure of 1.8 bar. This construction exceeds the minimum IMDG Code portable tank instruction T2 test pressure of 1.5 bar for UN 1915. The shell material is usually 316L stainless steel rather than carbon steel because trace iron can discolour the ketone and accelerate oxidative acidity build-up during long transit.

Table 1 summarises the primary parameters relevant to ISO tank loading and care.

Under the IMDG Code, cyclohexanone is assigned to Class 3, Packing Group III, and is not listed as a marine pollutant in the IMDG Code index. The transport flash point of 44 °C permits bottom loading in many jurisdictions, but closed-loop vapour return is still required by terminal permits where ketone emissions are regulated. The product is only partially water-soluble; at 20 °C approximately 8.7 g/100 mL dissolves in water. This limited solubility means that free water appears only after the solubility limit is exceeded, and free water may extract oxygenated impurities from the cyclohexanone layer. A dedicated stainless-steel tank with 316L wetted surfaces is preferred. Manifold gaskets and valve seats are constructed of PTFE or a fluoropolymer-facing material because cyclohexanone can extract plasticiser and swell nitrile or natural-rubber elastomers.

What pre-loading checks are required after a nonketone last cargo?

Pre-loading acceptance starts with the last-cargo record and wall-wash certificate. Acceptable preceding cargos for industrial-grade cyclohexanone include ketones, light esters, and aromatic hydrocarbon streams; unacceptable prior cargos include isocyanates, amines, epoxides, chlorosilanes, and strong oxidizers. When the last cargo is outside the approved matrix, the tank is washed with a mild alkaline detergent and rinsed with demineralized water until the final rinse conductivity is below 10 µS/cm. Caustic residues are controlled to below 0.01 wt % because cyclohexanone undergoes base-catalysed aldol condensation; dimer and oligomer formation produces turbidity and shifts the acidity profile in downstream oxidation. After washing, the tank is dried with heated nitrogen at 60 °C until the vent gas dew point is below -30 °C. The manway is then closed, and the oxygen content is verified at the top dome to be below 4 vol % with a portable zirconia or paramagnetic analyser. A wall-wash non-volatile residue limit of 10 mg/m² is applied for high-purity cyclohexanone; solvent-grade shipments may accept up to 50 mg/m² when documented on the cleaning certificate. The bottom outlet valve is inspected for heel retention and is closed with a blind flange and locking bar before the loading arm is connected.

When bottom-loading at ambient temperatures, the loading arm is bonded before the hose is coupled, and the tank chassis is grounded to a resistance of less than 10 Ω in accordance with NFPA 77. Initial fill velocity is limited to 1 m/s until the dip leg outlet is submerged, after which the rate can be raised to a maximum of 7 m/s as recommended by API RP 2003. The fill line is a stainless-steel dip leg extending to the bottom sump; splash loading is not permitted because mist formation increases static charge and airborne exposure. Vapour displaced from the tank is returned to the supply vessel through a closed balance line, or routed to a scrubber or thermal oxidizer if the terminal does not permit vapour return. Product temperature is recorded at the loading arm. A loading temperature of 20 °C to 30 °C is typical; if the incoming product temperature exceeds 40 °C, the loading supervisor stops the operation until the tank has been re-inerted and the source tank is sampled for flash point and water. The fill ratio is calculated to allow thermal expansion to 50 °C; at a loading temperature of 20 °C, a standard outage of 5 vol % is maintained. Samples are drawn from the top and bottom after loading for density by ASTM D4052, water by ASTM E203, and appearance against a retained reference.

Pressure relief, inert padding, and transit monitoring

After the tank is sealed, a nitrogen pad is applied at 0.2 bar to 0.5 bar above atmospheric. The pressure-relief valve on a Type T11 tank is typically set at 1.8 bar; the 4.0 bar test pressure provides margin for surge and thermal expansion. A falling pad during transit indicates a vapour leak or thermal contraction; the tank should be inspected with a portable combustible-gas detector at the dome fittings rather than opened. If the tank skin temperature approaches 45 °C, the upper shell may exceed the liquid flash point and the headspace should be assumed flammable. In such conditions, route changes, shaded parking, or water-spray cooling of the shell are used to reduce skin temperature. The tank is not equipped with internal baffles, so surge loads in a partially filled tank are controlled by keeping the outage within the calculated expansion limit and by avoiding abrupt braking or high-speed lane changes.

Elastomer seals in the loading line and tank fittings are inspected for swelling and compression set before each loading. PTFE envelope gaskets and perfluoroelastomer O-rings are preferred over EPDM in ketone service; nitrile swells significantly and loses sealing force after prolonged contact with cyclohexanone. Mechanical pump seals are specified with silicon-carbide faces and fluoropolymer secondary seals. The tank relief valve is tested at intervals required by the tank container CSC inspection and ISO 1496-3 periodic inspection; shell thickness is measured by ultrasonic testing at the 2.5-year or 5-year inspection interval according to the tank certificate. Pressure-test records are retained for the life of the tank.

Table 2 consolidates the loading and transit care checklist.

At the discharge terminal, the tank is grounded, and the vapour return line is connected before the liquid line. Unloading is performed by nitrogen pressure up to 2.0 bar or by a centrifugal pump; compressed air is not used because oxygen addition accelerates oxidation to acidic and coloured by-products, especially if the tank has been heated by transit. After discharge, the tank is drained with a slope toward the bottom outlet and stripped with nitrogen for at least 30 minutes before cleaning or inspection. Residual liquid in the bottom valve recess is sampled for density and water by ASTM D4052 and ASTM E203; if the water content exceeds 0.10 wt %, the tank must be dried before return to service. Spill response uses alcohol-resistant foam because water dilution alone is ineffective once the solubility limit of 8.7 g/100 mL is exceeded. The 8-hour occupational exposure limit used for open handling is 20 ppm as a TWA; supplied-air or cartridge respirators are required where vapour concentrations exceed this value. Cyclohexanone is incompatible with strong oxidizers, nitric acid, and strong bases; cleaning agents must be completely removed before the next loading to prevent aldol condensation and colour formation.