Effects of Operating Variables on the Product Distribution and Reaction Pathways in the Oxidative Degradation of CO2-Loaded Aqueous MEA-MDEA Blends during CO2 Absorption from Flue Gas Streams

The effect of operating conditions on the degradation of MEA-MDEA-H2O-CO2, MEA-MDEA-H2O-O2, and MEAMDEA-H2O-O2-CO2 systems (where MEA is momoethanolamine and MDEA is methyldiethanolamine) was evaluated in a stirred-cell reactor at temperatures of 55-120 (degree) C using overall amine concentrations of 7 and 9 mol/L, a MDEAMEA ratio and CO2 loading of 0.1-0.4 and 0-0.502 mol/mol, respectively, and O2 and/or CO2 pressures of 250 kPa. The results showed that the extent of degradation and the number of products decreased in the order MEA-MDEA-H2O-O2 > MEA-MDEA-H2O-O2-CO2 >MEA-MDEA-H2O-CO2, illustrating the detrimental influence of an increase in the O2 concentration in the solvent. Also, higher total amine concentrations and CO2 loadings resulted in fewer products, whereas higher temperatures had the opposite effect. In addition, changes in the MDEA-MEA ratio altered the formation pathways of some products in the MEA-MDEA-H2O-O2 system. Furthermore, even in an O2-free environment, O2 is produced as a byproduct of CO2-induced degradation at high temperatures, thereby generating an oxidative degradation environment. It also appears that MDEA degrades preferentially to protect MEA.