What Monoethanolamine Is
Monoethanolamine (MEA, CAS 141-43-5) is the simplest ethanolamine, formula C2H7NO and molecular weight 61.08 g/mol. It is a clear, colourless, viscous liquid with an ammoniacal odour, completely miscible with water and with most polar organic solvents. Key physical data are a boiling point of 170 °C at 101.3 kPa, a melting point of about 10.5 °C, a density of 1.012 g/cm³ at 25 °C, a closed-cup flash point of about 85 °C and a vapour pressure of roughly 0.5 hPa at 20 °C. A 1 % aqueous solution is distinctly alkaline, with pH near 11.5.
The molecule contains both a primary amine and a primary alcohol, so it behaves as a bifunctional building block. The amine reacts with acids to form salts and amides, with carbon dioxide to form carbamates, and with alkylating agents or fatty acids to give surfactants; the hydroxyl group gives it water solubility and allows ester formation.
Typical Specification of Industrial MEA
| Parameter | Typical value | Test reference |
|---|---|---|
| Assay (total amine) | ≥ 99.5 % w/w | Titrimetric amine value |
| Water | ≤ 0.30 % w/w | ASTM E203 |
| Colour | ≤ 15 Pt-Co units | ASTM D1209 |
| Density at 25 °C | 1.010–1.015 g/cm³ | ASTM D4052 |
| Distillation range | 168–172 °C | ASTM D1078 |
| Flash point | about 85 °C, closed cup | ASTM D93 |
| Transport classification | UN 2491, Class 8, Packing Group III | UN Model Regulations |
Typical commercial offers are a technical grade at 99.5 % minimum and a distilled, low-colour grade. Colour is the usual reason buyers move up a grade, because MEA discolours on contact with air and with carbon dioxide, and colour bodies formed in storage carry into downstream cosmetic or pharmaceutical products.
Principal Industrial Uses
Gas treating is the largest single outlet. Aqueous MEA at 15 to 30 % strength absorbs acidic gases in refinery, natural gas and ammonia plant service; the amine reacts with carbon dioxide to form a carbamate and with hydrogen sulphide to form a bisulfide salt, and both are reversed in the regenerator with steam. Understandingamine degradation - oxidation to organic acids, reaction with carbonyl sulfide and carbon disulfide - is the core of solvent management in such units.
In surfactants, MEA is amidated with fatty acids to give monoethanolamides and amide ether sulfates, which are used as foam boosters and viscosity builders in shampoos and liquid detergents. The same amidation chemistry serves corrosion inhibitors, emulsifiers and textile auxiliaries. Other outlets include cement grinding aids, where MEA salts improve mill throughput; pH control and neutralisation in metalworking fluids and water treatment; and synthesis of ethylene diamine derivatives and pharmaceutical intermediates.
Corrosion, Exposure and Segregation
MEA is corrosive and carries Class 8 transport status. The concentrate causes severe skin burns and serious eye damage, so filling, sampling and drum handling are done with face shield, chemical goggles, nitrile or butyl gloves and an acid-resistant apron, with eyewash and safety shower at the point of work. The workplace exposure limit commonly applied is 3 ppm as an 8-hour time-weighted average, measured as the amine; local exhaust ventilation at vents, sampling points and pump seals keeps airborne amine below that level. MEA attacks copper and its alloys, so stainless steel, carbon steel for inhibited dry service, and polyethylene or polypropylene for small containers are the usual materials of construction.
Product quality degrades through two mechanisms: carbon dioxide uptake from air, which lowers the assay and raises colour, and oxidation, which generates aldehydes. Storage is therefore closed, dry and between 15 and 30 °C, with nitrogen padding preferred for long-term or pharmaceutical-bound parcels, and drums rotated on a first-in, first-out basis. The melting point near 10.5 °C means cold-weather parcels can solidify; they are re-melted gently and mixed before sampling so that the assay and water results are representative.
Frequently Asked Questions
Q: What are the CAS number, formula and molecular weight of MEA?
A: Monoethanolamine is CAS 141-43-5, formula C2H7NO, molecular weight 61.08 g/mol.
Q: Is monoethanolamine miscrible with water?
A: Yes, MEA is fully miscible with water in all proportions and also with methanol, ethanol, acetone and glycerol; it is only partly soluble in long-chain hydrocarbons.
Q: Why does MEA colour rise in storage?
A: Air contact causes oxidation and carbon dioxide uptake, both of which generate colour bodies. Nitrogen padding, closed containers and stock rotation keep colour at the 15 Pt-Co level or below.
Q: What exposure limit applies to MEA in the workplace?
A: A commonly applied limit is 3 ppm as an 8-hour time-weighted average, with local exhaust ventilation used to control amine vapour at vents, seals and sampling points.
Q: How is MEA packed and shipped?
A: In 200 litre steel or plastic drums, intermediate bulk containers, or stainless steel ISO tanks and road tankers, classified as UN 2491, Class 8, Packing Group III, sometimes under nitrogen for colour-critical grades.
Q: What happens if MEA freezes in cold weather?
A: It solidifies near 10.5 °C. The parcel is warmed gently, mixed thoroughly and re-sampled before use, because stratified liquid can give an unrepresentative assay result.