Ethanolamine

Overview
Ethanolamine, also called 2-aminoethanol or monoethanolamine (often abbreviated as MEA), is an organic chemical compound which is both a primary amine (due to an amino group in its molecule) and a primary alcohol (due to a hydroxyl group). Like other amines, monoethanolamine acts as a weak base. Ethanolamine is a toxic, flammable, corrosive, colorless, viscous liquid with an odor similar to ammonia. Refractive index of ethanolamine is 1.4539.

Ethanolamine is commonly called monoethanolamine or MEA to distinguish it from diethanolamine (DEA) and triethanolamine (TEA). Monoethanolamine is produced by reacting ethylene oxide with ammonia. Further treatment with ethylene oxide can yield DEA and/or TEA. Ethanolamine is the second most abundant head group for phospholipids, substances found in biological membranes.

Ethanolamine also refers to a class of antihistamines containing an ethyl-amine group attached to a diphenyl structure. Examples of drugs within this class include diphenhydramine (Benadryl), phenyltoloxamine (Percogesic), and doxylamine (Unisom Sleep Tablets). They are one of the oldest classes of antihistamine drugs, yet remain the most effective for treating allergy symptoms, even exceeding the effectiveness of new OTC and prescription antihistamines such as loratadine (Claritin) and Fexofenadine (Allegra). However, all ethanolamines are extremely sedating, even more so than many barbiturates. For this reason, they are not always desirable drugs for treatment, and less-effective drugs are indicated to avoid the substantial drowsiness inherent in ethanolamines. On the other hand, they are such effective sedatives that they are marketed as over-the-counter sleep-aids in addition to anti-allergy medications.

Uses of monoethanolamine (MEA)
MEA is used in aqueous solutions for scrubbing certain acidic gases and is also used in surface active agents, emulsifiers, polishes, pharmaceuticals, corrosion inhibitors, chemical intermediates. In pharmaceutical formulations, MEA is primarily used for buffering or preparation of emulsions.

Aqueous solutions of MEA (solutions of MEA in water) are used as a gas stream scrubbing liquid in amine treaters. For example, aqueous MEA is used to remove carbon dioxide (CO2) from flue gas. Aqueous solutions can weakly dissolve certain kinds of gases from a mixed gas stream. The MEA in such solutions, acting as a weak base, then neutralizes acidic compounds dissolved in the solution to turn the molecules into an ionic form, making them polar and considerably more soluble in a cold MEA solution and thus keeping such acidic gases dissolved in this gas-scrubbing solution. Therefore, large surface area contact with such a cold scrubbing solution in a scrubber unit can selectively remove such acidic components as hydrogen sulfide (H2S) and CO2 from some mixed gas streams. For example, basic solutions such as aqueous MEA or aqueous potassium carbonate can neutralize H2S into hydrosulfide ion (HS-) or CO2 into bicarbonate ion (HCO3-).

H2S and CO2 are only weakly acidic gases. An aqueous solution of a strong base such as sodium hydroxide (NaOH) will not readily release these gases once they have dissolved. However, MEA is rather weak base and will re-release H2S or CO2 when the scrubbing solution is heated. Therefore, the MEA scrubbing solution is recycled through a regeneration unit which heats the MEA solution from the scrubber unit to release these only slightly acidic gases into a purer form and returns the regenerated MEA solution to the scrubber unit again for reuse.