Methyl diethanolamine, also known as N-methyl diethanolamine and more commonly as MDEA, is the organic compound with the formula CH3N(C2H4OH)2. It is a, colorless liquid with an ammonia odor. It is miscible with water, alcohol and benzene. A tertiary amine, it is widely used as a sweetening agent in chemical, oil refinery, syngas production and natural gas.

Similar compounds are monoethanolamine (MEA), a primary amine, and diethanolamine (DEA), a secondary amine, both of which are also used for amine gas treating. MDEA’s defining characteristic when compared to these other amines is its ability to preferentially remove H2S (and strip CO2) from sour gas streams.

MDEA’s popularity as a solvent for gas treating stems from several advantages it has when compared to other alkanolamines. One of these advantages is a low vapor pressure, which allows for high amine compositions without appreciable losses through the absorber and regenerator. MDEA is also resistant to thermal and chemical degradation and is largely immiscible with hydrocarbons. Lastly, MDEA has a relatively low heat of reaction with hydrogen sulfide and carbon dioxide, which allows for lower reboiler duties, thus lower operating costs.