Diethanolamine solutions corrosion

Activated tertiary amines such as triethanolamine (TEA) and methyl diethanolamine (MDEA) have gained wide acceptance for CO2 removal. These materials require very low regeneration energy because of weak CO2 amine adduct formation, and do not form carbamates or other corrosive compounds (53). Hybrid CO2 removal systems, such as MDEA —sulfolane—water and DIPA—sulfolane—water, where DIPA is diisopropylamine, are aqueous alkaline solutions in a nonaqueous solvent, and are normally used in tandem with other systems for residual clean-up. Extensive data on the solubiUty of acid gases in amine solutions are available (55,56). 

In an amine system, one way to increase absorption is to increase amine concentration. A higher amine concentration requires 1) more extensive filtration to keep the solution clean and 2) the addition of corrosion inhibitors and to minimize corrosion. Another option is to change from monoethanolamine (MEA) to methyl diethanolamine (MDEA)86. 

Winterization is the provision of design features, procedures, or systems for air-cooled heat exchangers to avoid process-fluid operating problems resulting from low-temperature inlet air. These include fluid freezing, pour point, wax formation, hydrate formation, laminar flow, and condensation at the dew point (which may initiate corrosion). Freezing points for some commonly encountered fluids in refinery service include benzene, 5.6°C (42°F) p-xylene 15.5°C (55.9°F) cyclohexane, 6.6°C (43.8°F) phenol, 40.9°C (105.6°F) monoethanolamine, 10.3°C (50.5°F) and diethanolamine, 25.1°C (77.2°F). Water solutions... 

Reaction 3-19 implies that corrosion rates should increase in proportion to the concentration of alkanolammonium ions, and generally this is true. Richer solutions are more corrosive than leaner, other things being equal. Also, undegraded lean MEA solutions are more corrosive than undegraded lean diethanolamine (DEA) solutions, because MEA, the stronger base, retains a higher concentration of alkanolammonium cations and, thoefore, forms a more corrosive solution. 

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