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Avoidance of oxidative degradation brought by the addition of inorganic salts to aqueous 30 %wt. MEA

https://doi.org/10.1016/j.cesx.2021.100096

Fig. 6 shows the amount of amine degradation avoided by employing the SAS. There are three important things to notice in this image. The first one is that the degradation avoided with the use of potassium iodide does not reach a maximum, or a plateau, in the course of the 21 days of oxidation experiments. Such a plateau would have been expected in case of KI consumption, as eventually one would observe iodide depletion in the solvent. For comparison, a plateau does start to appear for the NaCl SAS, though very incipiently. Incidentally, the second point of notice is that, if salt was indeed being consumed in this reaction, one would expect to see different curves for 2.0 %wt. and 7.5 %wt. NaCl – which clearly have very distinct amounts of “reactants”. Finally, the SAS prepared in these experiments have very small molar amounts of NaCl and KI. Let us suppose that KI reacts with oxygen in a 1:1 molar basis, shielding MEA that would otherwise react with oxygen following an assumed 1:1 stoichiometry. By the end of day 21, having avoided the loss of almost 2 mol kg−1 MEA in the SAS containing 2.0 %wt. KI, one could expect to have instead lost 2 mol kg−1 KI. However, this SAS contains merely 0.120 mol kg−1 of KI. If potassium iodide is indeed being consumed by oxygen, it is doing so in a basis far below 1:1 and indeed experiencing no reduction in inhibition capacity, as the lack of a plateau demonstrates. For these three reasons, we do not believe that salt consumption explains the differences in degradation behaviors alone, though it might certainly contribute with them to some extent. Contrary to the previous studies of halides as degradation inhibitors (Lee and Rochelle, 1987), we cannot see that it is a scavenging effect that is seen in these experiments, as the degradation rate is stable over time and iodide concentration is preserved. Conversely, our results agree with the observation by Sjostrom et al. (2020) that iodide is not consumed in this process.”

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Fig. 6. Avoidance of oxidative degradation brought by the addition of inorganic salts to aqueous 30 %wt. MEA. Error bars represent standard deviations of calculated values with sets of parallel experiments.”

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