Ethanolamine

Ethanolamine

[eth-uh-nol-uh-meen, -noh-luh-, -nuh-lam-in]
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Ethanolamine, also called 2-aminoethanol or monoethanolamine (often abbreviated as ETA or MEA), is an organic chemical compound that 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 that of ammonia. Refractive index of ethanolamine is 1.4539.

Ethanolamine is commonly called monoethanolamine or MEA in order to be distinguished from diethanolamine (DEA) and triethanolamine (TEA). Ethanolamine is the second-most-abundant head group for phospholipids, substances found in biological membranes.

Production

Monoethanolamine is produced by reacting ethylene oxide with aqueous ammonia; the reaction also produces diethanolamine and triethanolamine. the ratio of the products can be controlled by changing the stoichiometry of the reactants.

Applications

MEA is used in aqueous solutions for scrubbing certain acidic gases. It is used as feedstock in the production of detergents, emulsifiers, polishes, pharmaceuticals, corrosion inhibitors, chemical intermediates. For example, reacting ethanolamine with ammonia gives the commonly used chelating agent, ethylenediamine:

In pharmaceutical formulations, MEA is primarily used for buffering or preparation of emulsions.

Gas stream scrubbing

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.

pH-control amine

Ethanolamine is often used for alkalinization of water in steam cycles of power plants, including nuclear power plants with pressurized water reactors. This alkalinization is performed to control corrosion of metal components. ETA (or sometimes a similar organic amine, e.g., morpholine) is selected because it does not accumulate in steam generators (boilers) and crevices due to its volatility, but rather distributes relatively uniformly throughout the entire steam cycle. In such application, ETA is a key ingredient of so-called "all-volatile treatment" of water (AVT).

Ethanolamines

Ethanolamine also refers to a class of antihistamines containing an ethyl-amine group attached to a diphenylmethane 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 passing the brain-blood barrier (excluding Loratadine and other non-sedating antihistamines) 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. The effects of centrally-acting ethanolamine antihistamines and related drugs can in the case of some drugs create a type of euphoria, a euphoria which is particularly marked with orphenadrine, an antihistamine closely related to diphenhydramine which is used for low back pain, other disorders of skeletal muscle and some aspects of Parkinsonism; the euphoria is significant and reliable enough for orphenadrine to be considered a miscellaneous antidepressant and method for treating adverse effects of opioids.

References

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