What distinguishes DEA, MEA and MDEA in an Amine Treating unit?

DEA (Diethanolamine), MEA (Monoethanolamine), and MDEA (Methyldiethanolamine) are all types of amines used in amine treating units to remove acid gases (H2S and CO2) from natural gas, but they differ in their chemical structure and, consequently, their performance characteristics. MEA is a primary amine, meaning it has one carbon-containing group and two hydrogen atoms attached to the nitrogen atom. It is highly reactive and has a strong affinity for both H2S and CO2, making it effective for achieving very low levels of acid gas in the treated gas. However, MEA also reacts irreversibly with CO2 to form heat-stable salts, which reduces its effective capacity and increases operating costs. It also has a higher corrosion potential compared to DEA and MDEA. DEA is a secondary amine, meaning it has two carbon-containing groups and one hydrogen atom attached to the nitrogen atom. It is less reactive than MEA but still effective for acid gas removal. DEA is less prone to forming heat-stable salts with CO2 than MEA, making it a more economical option in some cases. MDEA is a tertiary amine, meaning it has three carbon-containing groups and no hydrogen atoms attached to the nitrogen atom. It reacts more readily with H2S than with CO2, making it a selective solvent for H2S removal. MDEA also has a lower tendency to form heat-stable salts with CO2 and has a lower corrosion potential than MEA and DEA. MDEA is often preferred when selective removal of H2S is desired or when CO2 slippage is acceptable. The choice of amine depends on the specific requirements of the application, including the concentration of acid gases in the feed gas, the desired level of acid gas removal, and economic considerations.