Process Degradation of Amines

“Lab-scale single-condition experiments (thermal and oxidative degradation experiments) are important for identifying new potential solvents for CO2 capture and the identification of degradation compounds. Although both oxidative and thermal degradation conditions separately produce many of the compounds found in large-scale pilot plants, neither of them can produce the same degradation profile as observed in pilot samples. Some of the most prominent degradation products formed in pilot-scale CO2 capture plants are not found to any considerable extent under any of the single condition experiments. Therefore, several lab-scale cyclic degradation setups have been built and are now available for solvent testing. Here, the solvent circulates between low and high temperatures. Oxygen is available in the low-temperature part of the cycle. A detailed description of two cyclic degradation rigs can be found elsewhere. (11,87) These setups mimic the CO2 capture process and provide more realistic conditions. For example, the SINTEF solvent degradation rig (11) has been shown to give a more similar degradation profile as seen in pilot samples for MEA than in the single condition experiments. The cyclic experiments are needed in the scaling-up of solvent technologies, as it allows the identification of prominent degradation compounds before taking the solvent to the pilot scale. This will ensure that the most critical degradation compounds, either influencing the operation, emission, or operation of flue gas wash sections, can be monitored during piloting. Only a few studies and amines have been investigated in cycled laboratory setups. One reason for the low abundance of cyclic degradation studies is the complexity of these rigs, in effect increasing the experimental cost. The following amines have been studied in cycled systems: MDEA, MEA, AMP, Pz, 2-methylpiperazine (2-MPZ), and MDEA/Pz. (11,45,87,90,103,104) Mostly, the main focus of these studies has been assessing the solvents’ chemical stability when repeatedly exposed to low and high temperatures. However, one study also investigated how different inhibitors behave under these conditions. (45)

Buvik et al. give an overview of degradation studies at the pilot scale. (105) The review points to the importance of flue gas pretreatment technologies, such as the removal of SOX, NOX, and particulates, to increase solvent lifetime and reduce amine degradation. Another main conclusion is the fact that no single degradation compound of the ones studied stands out as the only one to monitor and to assess solvent degradation.”

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