Studies on DEA and MDEA degradation

Aqueous diethanolamine ("DEA") is widely used for the removal of acid gases such as CO{dollar}sb2{dollar} and H{dollar}sb2{dollar}S while aqueous methyl diethanoamine ("MDEA") is primarily used for the selective removal of H{dollar}sb2{dollar}S in the presence of CO{dollar}sb2{dollar} from light hydrocarbon gases. In addition to normal absorption and desorption reactions, some side reactions occur between CO{dollar}sb2{dollar}, 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.; CO{dollar}sb2{dollar} 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 CO{dollar}sb2{dollar} solubility in aqueous MDEA and aqueous BHEP solutions were developed.; DEA degradation experiments under flow conditions were carried out in a coiled heat exchanger 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 CO{dollar}sb2{dollar} were carried out in a 600 mL stainless steel autoclave to study the effect of temperature, MDEA concentration and CO{dollar}sb2{dollar} 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.