The effect of operating conditions on the degradation of MEA−MDEA−H 2 O−CO 2, MEA−MDEA−H 2 O−O 2, and MEA−MDEA−H 2 O−O 2 −CO 2 systems (where MEA is momoethanolamine and MDEA is methyldiethanolamine) was evaluated in a stirred-cell reactor at temperatures of 55−120 °C using overall amine concentrations of 7 and 9 mol/L, a MDEA−MEA ratio and CO 2 loading of 0.1−0.4 and 0−0.502 mol/mol, respectively, and O 2 and/or CO 2 pressures of 250 kPa. The results showed that the extent of degradation and the number of products decreased in the order MEA−MDEA−H 2 O−O 2 > MEA−MDEA−H 2 O−O 2 −CO 2 >MEA−MDEA−H 2 O−CO 2, illustrating the detrimental influence of an increase in the O 2 concentration in the solvent. Also, higher total amine concentrations and CO 2 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−H 2 O−O 2 system. Furthermore, even in an O 2 -free environment, O 2 is produced as a byproduct of CO 2 -induced degradation at high temperatures, thereby generating an oxidative degradation environment. It also appears that MDEA degrades preferentially to protect MEA.
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Lawal et al. (2005) studied this question.