What Is Monoethanolamine (MEA)?
Monoethanolamine, CAS 141-43-5, is the simplest ethanolamine, combining one hydroxyl group and one primary amine in a small molecule of formula C2H7NO and molecular weight 61.08 g/mol. It is a colourless, viscous liquid with a mild ammonia-like odour and is completely miscible with water and with most polar organic solvents. Aqueous solutions are strongly alkaline, with a pH above 11 in dilute solution, and the compound readily absorbs acidic gases. MEA is produced industrially by reacting ethylene oxide with a large excess of ammonia; the same process also yields diethanolamine (DEA) and triethanolamine (TEA), and the product distribution is controlled by the ammonia-to-ethylene oxide ratio followed by distillation.
Typical Physical and Chemical Properties
| Property | Typical value |
|---|---|
| Chemical name | 2-Aminoethanol (monoethanolamine) |
| Chemical formula | C2H7NO |
| CAS number | 141-43-5 |
| Molecular weight | 61.08 g/mol |
| Appearance | Colourless, viscous liquid |
| Odour | Mild ammonia-like |
| Boiling point | Approximately 170 °C at 101.3 kPa |
| Melting point | Approximately 10 °C |
| Density at 20 °C | Approximately 1.01 g/cm3 |
| Flash point (closed cup) | Approximately 85 °C |
| Water solubility | Miscible in all proportions |
| pH of dilute solution | Above 11 |
| Technical grade assay | 99.0 % minimum |
Acid Gas Treating and Process Applications
MEA is one of the classic solvents for amine gas treating, also called gas sweetening. In natural gas, refinery off-gas and synthesis gas service it absorbs hydrogen sulfide and carbon dioxide in an absorber column, and the reaction is reversible: the amine forms a hydrosulfide salt with hydrogen sulfide and carbamate or bicarbonate species with carbon dioxide. The rich solution is then heated in a regenerator, where the acid gases are released as a concentrated stream that can be routed to sulfur recovery or to a carbon dioxide capture train, and the lean amine is recycled. Because MEA is a primary amine, it reacts quickly and offers a high acid gas capacity per unit mass, which suits lean, low-pressure streams. It also forms heat-stable salts with oxygen-bearing contaminants and with some sulfur species, so formulated solvents are often preferred in heavily loaded or high-oxygen service.
Beyond gas treating, MEA is used as a neutralising amine and pH control agent in water circuits, as a component of metalworking fluids and boiler water treatment programmes, and as an intermediate in the manufacture of ethylenediamine, piperazine and various hydroxyethyl derivatives through catalytic amination.
Surfactants, Personal Care and Agrochemical Uses
MEA is a key raw material for nonionic surfactants. Reacted with fatty acids it forms ethanolamides such as coconut fatty acid monoethanolamide, which are widely used in liquid detergents, shampoos, body washes and industrial cleaners for foam boosting, viscosity building and mildness. In personal care formulations MEA acts as a pH adjuster, emulsifier and humectant, and it is also used in hair waving and straightening products and in hair colour developers. In agriculture, MEA is used as a salt-forming agent for acidic herbicide actives, which improves water solubility and formulation stability, and as an emulsifier for pesticide concentrates. MEA reacted with phosphoric acid gives ethanolamine phosphates that serve as foliar fertilisers supplying nitrogen and phosphorus, and the same chemistry supports dispersing agents, cement grinding aids and metal cleaning formulations.
Quality Control, Packaging and Handling
Commercial MEA is released against a specification that normally covers assay by gas chromatography, water content by Karl Fischer titration, colour in Pt-Co units, specific gravity, and residue on ignition. Typical practice is to ship the product in drums, intermediate bulk containers, ISO tank containers or bulk road tankers. Carbon steel and stainless steel are suitable construction materials; aluminium, copper, zinc and galvanised surfaces should be avoided because the amine attacks them. Containers must be kept closed, since MEA absorbs carbon dioxide and moisture from air and darkens as a result. Store indoors between roughly 15 °C and 30 °C: the product solidifies near 10 °C, so trace heating or a heated warehouse is needed in cold climates. MEA is corrosive to skin and eyes and is harmful if swallowed, so eye protection, gloves, aprons and good ventilation are required during handling.
Frequently Asked Questions
Q: What is monoethanolamine used for?
Its largest use is acid gas treating in natural gas, refinery and synthesis gas plants; it is also used in surfactants and personal care, agrochemical formulations, metalworking fluids, water treatment and as an intermediate for ethylenediamine and piperazine.
Q: What is the CAS number of MEA?
CAS 141-43-5, corresponding to 2-aminoethanol with the formula C2H7NO.
Q: How does MEA remove hydrogen sulfide and carbon dioxide?
The primary amine reacts reversibly with acidic gases to form salts. The loaded solution is regenerated with heat, which releases a concentrated acid gas stream and returns lean amine to the absorber.
Q: What is the difference between MEA, DEA and TEA?
They are the mono-, di- and tri-ethanolamine members of the same family, produced together from ammonia and ethylene oxide. MEA is the most reactive and the most alkaline, DEA and TEA are increasingly used where lower volatility and different solubility are preferred.
Q: How should MEA be stored?
In closed carbon steel or stainless steel containers, indoors, between about 15 °C and 30 °C, away from acids and oxidising agents, with protection against freezing and with nitrogen blanketing where colour stability is critical.
Q: Can MEA be used in fertilisers?
Yes. Reaction with phosphoric acid produces ethanolamine phosphates used as foliar nutrient sprays that supply nitrogen and phosphorus and improve uptake of trace elements.
Q: Why does MEA change colour during storage?
Because it absorbs carbon dioxide and oxygen from air and forms degradation products. Keeping vessels closed, minimising headspace and blanketing with dry nitrogen limits both colour formation and heat-stable salt build-up.