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Studies on DEA and MDEA degradation Chakma, Amitabha


Aqueous diethanolamine ("DEA") is widely used for the removal of acid gases such as C0₂ and H₂S while aqueous methyl diethanoamine("MDEA") is primarily used for the selective removal of H₂S in the presence of C0₂ from light hydrocarbon gases. In addition to normal absorption and desorption reactions, some side reactions occur between C0₂, DEA and MDEA resulting in the formation of degradation compounds. Degradation not only represents a loss of valuable solvent, but may also lead to operational problems such as corrosion, foaming and fouling. C0₂ equilibrium solubility in aqueous MDEA solutions as well as in aqueous N,N-bis hydroxyethyl piperazine ("BHEP"), a major DEA and MDEA degradation product, were measured and mathematical models to predict equilibrium C0₂ solubility in aqueous MDEA and aqueous BHEP solutions were developed. DEA degradation experiments under flow conditions were carried out in a coiled heat exchnager tube heated by means of a constant temperature heat transfer fluid. A Mathematical model predicting DEA degradation in heat transfer tubes was developed. Carefully controlled MDEA degradation experiments with C0₂ were carried out in a 600 mL stainless steel autoclave to study the effect of temperature, MDEA concentration and C0₂ partial pressure. MDEA was found to degrade fairly rapidly at elevated temperature. The major MDEA degradation compounds were identified by gas chromatography and mass spectrometry. A kinetic model describing MDEA degradation was developed. Solution purification studies consisting of activated carbon adsorption of degradation compounds and reversal of degradation reactions by alkali addition were also studied. While activated carbon adsorption was found ineffective, alkali addition was found to be quite effective in reversing some of the major DEA degradation reactions. A purification process based on degradation reaction reversal technique was developed.

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