Commercial monoethanolamine (MEA; CAS 141-43-5; EINECS 205-483-3) is a primary alkanolamine supplied as a hygroscopic liquid with a nominal assay of ≥99.0 wt%. Its molecular weight is 61.08 g/mol, normal boiling point is 170.0 °C at 101.3 kPa, and freezing point is 10.3 °C. At 20 °C, density is 1.016 g/cm³ and dynamic viscosity is 21.0–24.0 mPa·s; at 25 °C, viscosity is 18.5–19.0 mPa·s. Vapour pressure at 20 °C is 0.4 mmHg (0.053 kPa), and the closed-cup flash point is 93 °C. A 10 wt% aqueous dilution produces a pH of approximately 12.0. These properties establish the material as a strong alkanolamine base with volatility intermediate between ammonia and diethanolamine. Unblanketed storage will absorb carbon dioxide from headspace and form carbamate salts that increase viscosity. Bulk tanks are therefore maintained under nitrogen with a dew point of −40 °C or lower, and transfer lines are constructed of 304L or 316L stainless steel with centrifugal pumps sized for the 21–24 mPa·s cold-product viscosity.

Incoming quality control should include Karl Fischer water and Pt-Co colour because water above 0.3 wt% or colour above 25 can indicate contaminated returnable containers or exposure to carbon steel. The refractive index is used as a rapid confirmation of assay because MEA and diethanolamine refractive indices differ; however, refractive index alone does not resolve oligomeric degradation products. Ethanolamine homologues diethanolamine and triethanolamine are controlled at ≤0.5 wt% and ≤0.1 wt% respectively in high-purity grades; chloride and iron are controlled at ≤1 mg/kg and ≤0.5 mg/kg for applications where corrosion or catalysis sensitivity is present. Incoming pH of a 10 wt% dilution should fall between 11.9 and 12.2; values below 11.5 indicate carbonation or contamination with acid gases.

What Limits Loaded Amine Corrosion Rates in Acid Gas Removal Units?

Aqueous MEA at 15–20 wt% is charged to packed absorber towers for removal of CO₂ and H₂S from natural gas, refinery fuel gas, and syngas. The absorber is normally operated at 30–45 °C and pressures from 5 to 70 barg; the rich amine leaves the bottom with an acid gas loading of 0.35–0.45 mol CO₂/mol amine. Regeneration is conducted in a steam-reboiled stripper at 105–120 °C, and reboiler duty for primary amines is generally 3.5–4.5 GJ/tonne CO₂ stripped. Carbon steel piping is accepted for lean solvent below 93 °C, but hot lean/rich exchangers, rich letdown valves, and reboiler tube bundles require stress-relieved AISI 316L or 304L. The failure mode at these points is acid gas breakout during carbamate decomposition, which lowers the local pH to 5.5–6.5 and promotes iron carbonate scale spallation and wall thinning. Corrosion rates on carbon steel can exceed 0.1 mm/year when temperature exceeds 95 °C and loading exceeds 0.4 mol/mol; NACE SP0408 describes inspection and corrosion-control practices for such amine units. Heat-stable salts such as formate, acetate, oxalate, and thiosulfate are controlled to ≤1.0 wt% as formate equivalent by ion exchange or vacuum reclamation. Filtration with 10 µm full-flow cartridges and a 5–10 wt% activated carbon slipstream removes hydrocarbon and degradation products. Copper alloys and galvanized steel are incompatible; cupric ions accelerate oxidative degradation and promote localized corrosion. A unit operating at 30 wt% MEA instead of 20 wt% may reduce circulation rate but increases corrosion tendency and thermal degradation because reboiler tube-wall temperatures increase with acid gas loading. Downstream of the regenerator, lean amine is cooled through aerial coolers and trim coolers to 35–40 °C before returning to the absorber; the cooling-water side of the lean amine cooler must be treated for ammonia and amine breakthrough.

In metalworking fluid concentrate manufacturing, MEA is introduced at 0.1–1.5 wt% to establish reserve alkalinity and maintain diluted sump pH between 9.2 and 9.7. ASTM D4627 iron chip corrosion testing at 5 vol% dilution in 100 ppm hard water shows no ferrous corrosion above 0.3 wt% MEA when the formulation also contains a dimer acid or phosphorus ester inhibitor. For copper-containing alloys, ASTM D130 immersion at 50 °C in 3 wt% MEA without an azole inhibitor tarnishes copper beyond 1b; addition of tolyltriazole at 50–100 mg/L maintains 1a. The same amine buffering effect raises pH in hard water, but overdosing above 1.5 wt% MEA can accelerate cobalt leaching from cemented carbide tool grades at pH above 9.8; published data for specific ISO tool substrate grades is limited. In high-speed grinding operations, mist and foam control become the controlling process variables; defoamer dosage, fluid velocity, and sump turnover are adjusted before MEA concentration is used to correct alkalinity drift.

When MEA Replaces Ammonia in Detergent Neutralization at 40–60 °C

MEA neutralizes linear alkylbenzene sulfonic acid to yield the corresponding monoethanolamine alkylbenzene sulfonate. The exotherm is controlled at 40–60 °C in a jacketed 316L or 304L reactor by metered addition of LABSA to a dilute MEA heel. The target stoichiometry is 0.98 mol MEA per mol acid, producing a final pH of 7.0–7.5 in 10 wt% active solution. Localized acid pockets below pH 2.5 initiate sulfonic acid hydrolysis and darkening; too slow an addition permits atmospheric CO₂ absorption at the liquid surface and forms carbamate haze. Heat removal is usually the rate-limiting step rather than reaction kinetics. In production vessels, the neutralization batch is discharged through a positive-displacement pump because the finished paste at 25 °C may reach 2,000–4,000 mPa·s at 20 rpm on Brookfield spindle 4. In-line pH probes with tolerance of ±0.1 pH and temperature-compensated electrodes are used for endpoint control. The MEA sulfonate surfactant produced from 1 tonne of LABSA retains water solubility and is used in liquid laundry and hard-surface formulations at 3–10 wt% active matter.

Post-combustion CO₂ capture with 30 wt% MEA operates under a narrower solvent-management window than natural gas treating. Reboiler duty in demonstration plants is 3.2–4.0 GJ/tonne CO₂ captured when lean loading is 0.25–0.30 mol/mol and rich loading is 0.45–0.50 mol/mol. Flue gas is cooled to 40–50 °C before the absorber; SO₂ slip above 10 ppmv reacts with MEA to form sulfite and sulfate heat-stable salts, while oxygen partial pressure drives formation of formic and acetic acids. These degradation products are removed by thermal vacuum reclamation at 145–150 °C and 0.2–0.5 bar absolute. Reclaimer bottoms are handled as hazardous waste because they contain nitrosamines, heavy metals, and organic degradation compounds. Elevated solvent temperature in the stripper, especially above 125 °C, increases thermal degradation and amine slip to the water wash. Dissolved oxygen in the amine loop is controlled below 0.5 mg/L by blanketing surge tanks and using deaerated makeup water. Materials of construction for rich solvent lines, heat exchangers, and the stripper include 316L or 2205 duplex stainless steel; carbon steel is limited to cool, lean, low-oxygen sections. Water wash columns with structured packing and demister pads reduce aerosol amine emissions, and continuous solvent filtration removes iron sulfide and fly ash fines above 5 µm.

Request an MEA Quote: Spec Sheet, Lead Time and Documents

Procurement packages for monoethanolamine should be structured around the specification sheet, lead time, and document bundle. The specification sheet includes assay, water, colour, ethanolamine homologues, iron, chloride, and packaging. Lead times from regional terminals for 20–25 tonne tank truck quantities are typically 5–10 working days after order confirmation and clean truck inspection; drummed material in 200 kg or 210 L packages may add 2–3 working days for repackaging and palletization. The document bundle should include the lot-specific certificate of analysis, safety data sheet compliant with 29 CFR 1910.1200 and REACH Annex II, transport document for UN 2491 Ethanolamine, Class 8, Packing Group III, and REACH/TSCA statements. Supply-chain documents should also include certificate of origin, insurance certificate, ADR/RID transport form, container cleanliness certificate for tank trucks, and lot traceability from the production batch record.

Bids should identify the terminal or manufacturing origin because transit carbonation can shift pH and alkalinity on receipt; receiving inspection should compare the delivered 10 wt% pH against the specification sheet before the material is released to storage.