Acrylonitrile, prop-2-enenitrile, CAS 107-13-1, is a clear, low-boiling monomer shipped as the stabilized liquid under UN 1093, Class 3, Packing Group I. It is produced at industrial scale by propylene ammoxidation over bismuth molybdate fluidized-bed catalyst at 400–450 °C, then quenched, absorbed and distilled to separate acrylonitrile from acetonitrile and hydrogen cyanide. A standard 20 ft ISO tank container with a nominal shell volume of 24,000 L can carry approximately 18.8 tonnes of stabilized acrylonitrile at a 97% fill fraction and 20 °C. At geometric capacity, the same shell corresponds to 19.34 tonnes. Across common 21,000 L to 26,000 L tank containers, the practical loaded mass ranges from 16.4 tonnes to 20.3 tonnes under the same reference conditions.

Acrylonitrile is a major intermediate for acrylic fibres, acrylonitrile-butadiene-styrene and styrene-acrylonitrile resins, nitrile rubber, acrylamide and adiponitrile. Its transport and storage are dominated by three properties: density near 0.806 kg/L at 20 °C, a boiling point of 77.3 °C, and a closed-cup flash point below 0 °C. The following transport-relevant data are taken from standard safety data sheets and merchant monomer specifications.

How Many Tonnes of Acrylonitrile Fit in a 20 ft ISO Tank?

The loaded mass is calculated from the tank shell volume, the batch density at loading temperature, and the fill fraction permitted for the cargo. For a 20 ft ISO tank container, the shell volume is not defined solely by the frame length; it is certified under ISO 1496-3 and varies with barrel diameter, dished-end depth and valve-box design. Common chemical-service volumes are 21,000 L, 24,000 L, 25,000 L and 26,000 L. The mass equation is:

loaded mass = nominal shell volume × liquid density at loading temperature × fill fraction

For a 24,000 L tank at 0.806 kg/L and a 97% fill fraction, the loaded mass is 23,280 L × 0.806 kg/L = 18,765 kg, or 18.8 tonnes. Since a standard 20 ft ISO tank container typically has a maximum gross mass of 30,480 kg and a tare mass of 3,700–4,200 kg, the available payload exceeds 26,000 kg. The acrylonitrile load is therefore volume-limited, not weight-limited. A 10 °C decrease in loading temperature from 25 °C to 15 °C increases the liquid density by approximately 1.1% and raises the loaded mass by the same proportion.

The density should be measured on the batch certificate of analysis by a digital density meter according to ASTM D4052-22. Individual batches may vary slightly with water, acetonitrile or stabilizer content, and the actual loaded mass must be recalculated using the measured density and the tank capacity certificate.

Regulatory fill fraction, thermal expansion and tank selection

A 20 ft ISO tank used for UN 1093 is a frame-mounted pressure vessel marked under ISO 6346 with the size type code 22T6 for a typical liquid tank container. The shell is commonly designed for a maximum allowable working pressure of 4 bar to 6 bar, with a pressure-relief device set at or below the design pressure. Because acrylonitrile is a flammable, toxic liquid, the applicable transport provisions under ADR, RID and the IMDG Code restrict filling so that the liquid cannot fill the entire shell at the maximum service temperature. If a maximum service temperature of 50 °C is assumed and the liquid cubic expansion coefficient is taken as approximately 1.1 × 10⁻³ K⁻¹, the volume increase from 15 °C to 50 °C is about 3.8%. A fill fraction above 96.3% at 15 °C would reach the fully liquid condition at 50 °C. The 97% value used in the capacity table is therefore an operator reference, not a replacement for the dangerous-goods transport approval.

Loading and unloading are conducted through closed-loop vapour return or low-pressure nitrogen padding. Initial filling velocity is limited to approximately 1 m/s until the dip pipe is submerged, reducing static charge accumulation. Bonding and grounding are maintained throughout transfer according to API RP 2003. Top discharge is preferred, and any bottom outlet is arranged with independent shut-off devices as required for Packing Group I flammable toxic liquids. The tank shell is not heated in normal service because the viscosity is low and the cargo has sufficient pumpability at ambient temperature.

When inhibitor depletion raises polymerization hazard during transit

Stabilized acrylonitrile is inhibited with hydroquinone monomethyl ether at approximately 35–50 mg/kg. The inhibitor scavenges free radicals and prevents autocatalytic polymerisation during storage and transport. If the inhibitor is depleted by prolonged heating, contamination with peroxides, or exposure to strong bases, the monomer can begin radical auto-polymerisation. The heat of polymerisation is approximately 76 kJ/mol, which can raise the liquid temperature rapidly. Because the atmospheric boiling point is 77.3 °C, a thermal runaway can increase vapour pressure and exceed the tank relief capacity. For this reason tank shipments are monitored for temperature, and terminals typically avoid storage above 25 °C for extended periods. Contact with strong oxidisers, free-radical initiators and alkaline materials is incompatible with inhibited acrylonitrile.

The vapour space is flammable under most ambient conditions. The explosive limits are 3–17 vol% in air, and the vapour density of 1.83 means that acrylonitrile vapour can accumulate in low points and travel to ignition sources. The autoignition temperature is approximately 481 °C. Occupational exposure limits are 2 ppm as an 8-hour time-weighted average under OSHA, 1 ppm as a 10-hour time-weighted average under NIOSH, and 10 ppm as a short-term limit. Tank inspection and cleaning therefore require closed-loop sampling, calibrated photoionisation or detector-tube monitoring, and supplied-air respiratory protection until the vessel atmosphere is verified below the applicable exposure limit.

Acrylonitrile arriving in a 20 ft ISO tank is transferred to plant storage and then distributed to polymerisation processes. In acrylic fibre production, acrylonitrile is copolymerised with methyl acrylate or vinyl acetate and wet-spun or dry-spun. In ABS resin production, acrylonitrile and styrene are grafted onto polybutadiene latex or dissolved rubber in emulsion or continuous mass polymerisation lines. Nitrile rubber is produced by emulsion copolymerisation with butadiene, with bound acrylonitrile contents from approximately 18 wt% to 50 wt%. Higher acrylonitrile grades provide oil resistance for seals and fuel hoses; lower grades provide improved low-temperature flexibility. Polymerisation vessels are equipped with high-temperature interlocks, rupture discs, deluge systems and residual monomer stripping because acrylonitrile monomer remains hazardous until chemically incorporated or removed.

Transfer pumps are typically canned or magnetically coupled centrifugal units with double mechanical seals to limit fugitive emissions. Dead legs in piping are minimised because stagnant monomer can lose inhibitor and form polymer deposits. After unloading, the tank is gas-freed and rinsed. Rinse water and condensate are collected and managed as hazardous waste because acrylonitrile is toxic to aquatic life. Before entry, the tank atmosphere is tested for oxygen, flammability and acrylonitrile vapour. The representative load of 18.8 tonnes in a 24,000 L tank should be verified against the tank capacity certificate and the batch density at the measured loading temperature.