At 20 °C and 101.3 kPa, methyl tertiary-butyl ether (MTBE, CAS 1634-04-4) is a low-density flammable ether with a density of 0.7405 kg/L under ASTM D4052, a closed-cup flash point of −28 °C under ASTM D56, and a boiling point of 55.2 °C under ASTM D86. The vapour pressure at 20 °C is approximately 26.6 kPa by ASTM D5191. These values control the packaging boundary for MTBE drum and IBC packaging: 160 kg drums, 80 per FCL, and the Evonik benchmark. The standard pack is a 160 kg net carbon-steel tight-head drum, and 80 drums form a full-container load in a 20 ft ISO container. The IBC format is a 1,000 L single-unit alternative used where receiving terminals are arranged for intermediate bulk handling. Because MTBE is a Class 3, Packing Group II flammable liquid under UN 2398, packaging decisions are driven by ullage, closure permeation, electrostatic dissipation, and segregation rather than simple capacity.

How Does a 160 kg Steel Drum Meet Flammable-Liquid Ullage Requirements?

A 160 kg net fill corresponds to a liquid volume of 216.1 L at 20 °C when calculated from 160 kg ÷ 0.7405 kg/L. A nominal 200 L drum is therefore unsuitable; the specified container is a closed-head steel drum with a brimful capacity of at least 220 L, usually 225 L or 230 L, to retain the statutory vapour space. The drum body is a UN 1A1 carbon-steel unit with a double-seamed top and bottom, a 2-inch bung and a 3/4-inch bung. The gaskets are specified as PTFE or FFKM; ethylene-propylene diene monomer and natural rubber are excluded because low-molecular-weight ethers produce unacceptable swelling and permeation. The bung flange is not internally coated with a reactive phenolic lining unless the lot is intended for high-purity solvent delivery where iron pickup must be controlled below the customer threshold.

Thermal expansion is not controlled by the 160 kg weight alone. Using a coefficient of thermal expansion of 0.0014 K⁻¹, a 30 K temperature rise expands the 216.1 L fill by approximately 9.1 L. A 225 L drum leaves only 8.9 L of headspace at 20 °C, which is marginal if the package is exposed to solar radiation or a hot warehouse. A 230 L drum leaves 13.9 L of headspace and keeps the liquid below the bung gasket after the same temperature rise. The packing instruction in ADR 4.1.1.4 is therefore supplemented by the drum manufacturer’s ullage table, which for MTBE usually requires the fill to remain below 98% of brimful capacity at the maximum transport temperature.

On automated drum-filling lines equipped with Coriolis mass flow meters, the 160 kg target is controlled to ±0.2 kg, and the lance is lowered into the drum to maintain submerged filling. This reduces splash-generated mist and restricts the formation of a flammable headspace aerosol. Vapour recovery is held at a slight vacuum of 0.2 kPa to 0.5 kPa at the bung during filling. Orientation of the lance is interlocked with the drum weight signal; if the lance does not reach the bottom 200 mm before product flow begins, the fill cycle is aborted. Bung torque is set from the drum manufacturer’s certificate, commonly between 20 N·m and 25 N·m for PTFE-lined polyethylene bungs. Undertorque permits vapour loss at the closure, while overtorque has been recorded in drum rework logs as extruding the PTFE gasket into the chime and creating a false seal that passes a quick visual check but fails a pressure-decay test.

The 80-per-FCL Loading Matrix and Container Securement

The 80-drum FCL is obtained by packing a standard 20 ft ISO container with a 4 × 10 × 2 matrix: four drums across the internal width of approximately 2.35 m, ten drums along the internal length of approximately 5.90 m, and two vertical layers. The matrix is feasible only when the external diameter is at or below 585 mm and the drum height is at or below 930 mm, so that the upper layer clears the door header. The net payload is 12,800 kg; with a steel drum tare mass of 22 kg to 26 kg, the gross mass becomes 14,560 kg to 14,880 kg. This is not the limiting load for a 20 ft dry container. The limiting factor is stacking geometry and door clearance, not gross mass.

Each layer is separated by plywood or HDPE drum boards placed over the lower drum chimes. The upper layer is offset so that each upper drum sits in the valley formed by two lower drums; this reduces the shear load on the lower bung closures. According to the IMO/ILO/UNECE CTU Code and the IMDG Code chapter 7.2, the container is secured with steel or polyester strapping anchored to the internal lashing points, and the void at the door is filled with timber or airbags. A loose 80-drum FCL can shift en bloc under repeated rail braking; rail operators often require additional longitudinal blocking at the floor level. Under the IMDG Code, UN 2398 must be segregated from Class 5.1 oxidisers and from Class 1 explosives according to the applicable segregation table. For consolidated container loads, 80-per-FCL packing avoids mixed-stowage incompatibility and simplifies emergency-response documentation.

When an IBC Replaces 160 kg Drums in Regional Solvent Distribution

Regional distribution may replace the 160 kg drum with a 1,000 L stainless steel 31A IBC or a rigid-plastic composite 31HA1 IBC, provided the UN approval is marked for Packing Group II flammable liquids. At 20 °C, a full 1,000 L IBC would contain 740.5 kg; commercial filling for MTBE is usually capped at 950 L, or 703 kg, leaving 50 L of headspace for thermal expansion and vapour collection. The IBC valve seat and closure gasket are specified as PTFE or FFKM. Composite IBC inner bottles must be tested for permeation resistance to low-viscosity ethers, because a standard uncoated HDPE bottle can retain the product but may allow gradual vapour loss through the wall if the barrier layer is absent. Published data for MTBE permeation through specific IBC barrier materials is limited; therefore the supplier’s UN certificate and test report must confirm compatibility with the actual batch composition and storage temperature.

Because MTBE is a low-conductivity flammable ether, the dominant failure mode in IBC handling is electrostatic discharge during top-up gravity filling or fast pneumatic transfer. Published conductivity data for MTBE is sparse; under IEC TS 60079-32-1, the product is treated as a low-conductivity flammable liquid. The IBC must be bonded to an earthing point with a resistance below 10 Ω before the valve is opened, and the fill line is specified as stainless steel or static-dissipative polymer. Splash filling is prohibited; the dip pipe must remain below the liquid surface. Nitrogen blanketing is applied when the IBC is stored for extended periods or when the MTBE grade is not inhibited. MTBE can form ether peroxides in contact with air, and the peroxide content should be confirmed by iodometric titration before any operation that could concentrate peroxides, such as distillation or drying. The receiving tank must not contain copper or copper-bearing alloys in continuous contact with uninhibited MTBE; stainless steel is the conservative selection for pump internals, valve seats, and transfer lines.

The Evonik Benchmark Specifies Container Integrity, Not Just Bulk Purity

The Evonik benchmark for MTBE drum and IBC packaging is applied as a logistics and container-integrity envelope rather than a single published specification. Published data for Evonik’s current packaged configuration is limited; the benchmark is therefore expressed through the verifiable parameters that remain after the bulk analytical specification is separated from the container. These parameters include 160 kg ± 0.2 kg net fill, 80 drums per FCL in a 20 ft container, UN 1A1 steel drum construction, PTFE or FFKM bungs, controlled closure torque, and a certificate of analysis that states the stabilizer and peroxide status. The benchmark does not replace the bulk assay; it supplements the assay by identifying whether the packaged unit can be moved through a solvent terminal without rework.

A drum load that meets the Evonik benchmark is therefore not automatically a high-purity product. It is a packaged lot whose closure type, ullage, container count, and gross-weight profile match the reference logistics envelope. Under CLP Regulation EC 1272/2008, packaged MTBE must carry the hazard statements H225, H315, H319, H335, and H411, with corresponding precautionary statements such as P210, P280, and P403+P235. The drum and IBC labels are not a substitute for the transport placard; UN 2398, Class 3, and the marine pollutant mark must appear on the transport unit when the packaged threshold is exceeded.

At the receiving terminal, drum loads are inspected before offloading for bung tamper marks, chime deformation, and rust bleeding around the 2-inch and 3/4-inch closures. A random drum is weighed; any net weight below 159.5 kg is isolated for leakage or loading damage. IBC units are examined for sight-glass haze, stress cracking at the base, and compression damage to the valve lock. Shipments that fail the container inspection are not released into the downstream storage system until the affected units are quarantined and the supplier’s batch record and UN test certificate are reviewed.