Monoethanolamine (MEA), 2-aminoethan-1-ol, CAS 141-43-5, molecular formula C₂H₇NO, molar mass 61.08 g/mol, is consigned as the proper shipping name Ethanolamine under UN 2491, hazard Class 8, Packing Group III. Under the United Nations Model Regulations and modal instruments such as ADR/RID/ADN, the IMDG Code, and 49 CFR 172.101, the classification is fixed; a consignor may not reclassify MEA as a non-corrosive commodity solely on the basis of pH. The GHS/CLP block for MEA includes Skin Corr. 1B, Eye Dam. 1, Acute Tox. 4 by the oral, dermal, and inhalation routes, and STOT SE 3 for respiratory irritation; hazard statements are H302, H312, H332, H314, and H335. At 101.3 kPa the normal boiling point is 170°C, the closed-cup flash point is 93°C when tested to ASTM D93, and the autoignition temperature is 410°C. Because the flash point is above 60°C, MEA does not meet the Class 3 flammable-liquid criteria; however, it remains a combustible liquid that can sustain combustion at elevated temperatures in confined spaces. Aqueous solutions are strongly alkaline, with a 100 g/L solution pH in the range 11.8–12.0 at 20°C.

How Does Packing Group III Modify the UN 2491 Packaging and Quantity Regime?

Class 8 packing groups are assigned by the UN Manual of Tests and Criteria, Part III, Section 37.4. Packing Group I describes full-thickness skin necrosis within a 60-minute observation period after an exposure of up to 3 minutes; Packing Group II covers necrosis within 14 days after an exposure of 3–60 minutes; Packing Group III covers necrosis within 14 days after an exposure of 60 minutes–4 hours, or a substance that is corrosive to steel or aluminium at a rate exceeding 6.25 mm/year at 55°C without producing full-thickness skin necrosis. Published dermal corrosivity data for MEA in open regulatory SDSs are limited; the Dangerous Goods List assigns Packing Group III to UN 2491, and the consignor should not perform a reclassification without the in vivo or in vitro corrosion data specified in Part III of the UN Manual. For packagings, PG III allows performance level Y rather than X for UN specification packagings, and the non-bulk packing instruction is P001. Under ADR subsection 3.4.1, the limited-quantity inner package limit for a PG III liquid is 5 L, and the gross package mass must not exceed 30 kg. In the IMDG Code, the same 5 L/30 kg thresholds apply, but the package must bear the limited-quantity mark. 49 CFR 173.202 and ADR Packing Instruction P001 govern the construction and testing of combination packagings; steel drums marked 1A1/Y, plastic drums marked 1H1/Y, and composite jerricans marked 3H1/Y are typical outer packagings. For intermediate bulk containers, instruction IBC03 applies; portable tank instruction T4 and tank provision TP1 are assigned in the Dangerous Goods List.

At the interface between the liquid phase and the container wall, material compatibility controls the choice of seals, gaskets, pump casings, and transfer lines. MEA is hygroscopic and absorbs carbon dioxide from air, forming carbamate species that increase viscosity and may precipitate at low temperature. The freezing point is 10.3°C, density is 1.012 g/cm³ at 20°C, and vapour pressure is approximately 0.4 hPa at 20°C. In production-scale bulk storage, 316L stainless steel and passivated carbon steel are commonly used for tanks; copper, copper alloys, zinc, and galvanized steel are unsuitable because the alkaline amine phase attacks these metals. Gasket selection is validated by immersion testing to ASTM D471; PTFE, graphite, or FFKM materials are preferred in continuous transfer service. The melting point temperature means that external heat tracing on suction lines and drains may be required in unheated loading areas; steam heating should be limited to avoid local overheating because MEA mists are corrosive to the respiratory tract. The occupational exposure limit published by ACGIH is 3 ppm as an eight-hour time-weighted average with a 6 ppm short-term exposure limit; OSHA’s permissible exposure limit is 3 ppm with a skin notation. These values drive closed-loop loading with vapour return and local exhaust ventilation on manual sampling points. A corrosive vapour breakthrough at a pump seal or valve packing does not require a Class 3 electrical classification, but the area should be classified for corrosive exposure and cleaned with water because MEA is fully miscible with water.

Temperature-Dependent Corrosivity and Bulk Transfer Equipment

Elevated temperature raises both the vapour concentration and the corrosion rate of MEA in carbon steel. Field transfer lines operating above 50°C should use 316L or 304 stainless steel because carbon steel can release iron into the alkanolamine stream, producing off-spec colour and heat-stable salts. Loading pumps should be sealless or mechanically sealed with PTFE/graphite glands; elastomeric linings degrade when amine solutions penetrate the polymer matrix. A rupture in a suction line upstream of a positive-displacement pump can draw air into the MEA stream, and the resulting carbamate solids can scour pump rotors and plug filter elements. Published data for the specific carbamate loading of MEA under shipping temperatures are limited; however, the stoichiometric loading of carbon dioxide in a primary alkanolamine is approximately 0.5 mol CO₂ per mole of amine, which is the design basis for gas-treating absorbers. The same chemistry operates unintentionally in container headspaces. Bulk ISO tank containers should therefore be nitrogen-blanketed and kept closed when not transferring; the nitrogen pressure should remain below the pressure-relief set point but above atmospheric pressure. For overland tank vehicles, a pad of inert gas prevents moisture ingress and reduces the formation of a crust in the vent line. A thermal expansion allowance must be calculated under ADR 4.3.2.2 for the applicable tank capacity and temperature rise; the filling degree at 20°C should not exceed the tank code limit.

During cargo loading and stowage, segregation requirements for UN 2491 follow the Class 8 corrosive liquid provisions in the applicable modal code. Under 49 CFR 177.848, Class 8 liquids are segregated from acids, oxidizers, and cyanide compounds when the potential for toxic gas release exists. The IMDG Code requires that alkaline corrosive liquids such as MEA be stowed away from acids, foodstuffs, and living quarters. On cargo vessels, the EmS emergency schedule for UN 2491 in the IMDG Code is F-A, S-B; that schedule directs fire-fighting with water and the control of spills by containment and dilution. The transport document must show the dangerous goods description in the sequence prescribed by ADR 5.4.1.4: UN 2491, ETHANOLAMINE, Class 8, Packing Group III, followed by the number and type of packagings and the total quantity. Where the consignment is a limited quantity under ADR 3.4.1, no Class 8 label and no dangerous goods declaration are required, but the limited-quantity mark must be affixed. Empty packagings that still contain residue are not exempt from classification; under 49 CFR 173.29, a residue-containing drum must be offered and transported as UN 2491 unless cleaned to a non-hazardous condition and purged of vapour. Cylindrical drums should be chocked and strapped in transport units to prevent shifting; drums in ISO containers are often loaded with a minimum of two straps per row and dunnage of non-absorbent material.

When Monoethanolamine Is Tendered as a Limited Quantity or Excepted Quantity

Under the limited-quantity provisions of ADR 3.4.1, a PG III corrosive liquid in an inner packaging of not more than 5 L may be placed in an outer package not exceeding 30 kg gross mass. The outer package must meet the general packaging standards in ADR Part 6, and the limited-quantity mark must have a minimum side dimension of 100 mm. Limited quantities are exempt from the dangerous goods transport document, placarding, and Class 8 labelling requirements under ADR but remain subject to general packaging quality and training provisions. For excepted quantities, the Dangerous Goods List assigns code E1 to UN 2491. The E1 code permits 30 mL of liquid in each inner packaging and 1 L in the outer package. The excepted quantity package must be marked with the E1 mark and is exempt from the dangerous goods transport document and Class 8 label; however, the outer package must be securely closed and capable of retaining the inner packagings under normal conditions of transport. Air transport differs: IATA Dangerous Goods Regulations Packing Instruction 852 governs Class 8 liquids in limited quantities, and the operator-approved net quantity limits must be checked against the edition in force at the time of consignment. The package must not be consolidated with incompatible goods, and no more than one limited-quantity or excepted-quantity package may be placed in an outer packaging that carries other dangerous goods if the mixing would increase the hazard.

Bulk process experience with MEA derives mainly from gas-sweetening and chemical intermediate operations where the same storage and transfer hazards appear. In post-combustion carbon-dioxide capture, aqueous MEA at 15–30 wt% is circulated through packed absorbers and crossflow heat exchangers; the regenerator bottom is typically maintained at 121–127°C. The absorber pressure varies with feed gas composition; published design data for coal-fired flue-gas systems indicate near-atmospheric operation, while natural-gas units operate above 10 bar. Heat-stable salts form from reaction with trace oxygen and organic acids, and these salts contribute to foaming, corrosion, and reboiler fouling. Reclaiming units remove a bleed stream, but the recovered amine still contains residual salts. In shipping, a bulk tank that has previously carried another product must be washed and dried before loading MEA; residual acid or aldehyde impurities can generate exothermic reactions and off-gassing. Water rinse should be followed by a nitrogen dry and a visual inspection of sumps and drains. The tank pressure-relief valve and vents should be isolated from moisture and carbon dioxide. For ISO tank containers, the lining and gasket set must be compatible with strongly alkaline liquids; unlined carbon steel is accepted for short-duration transport but may require passivation. ISO tank containers for liquid chemicals are designed to ISO 1496-3; the loading terminal should verify the tank approval and lining against Class 8 service before transfer begins.