Abstract

Solvent degradation during the CO₂ capture process is known to reduce capture capacity, increase corrosivity, emissions and solvent toxicity, and complicate operation of the plant. The wide variety in degradation compounds include charged species, typically referred to as heat stable salt (HSS), amides, acids, nitrosamines, small volatile organic compounds, ammonia, and more. To prolong the time in operation of an amine solution, solvent management strategies are implemented in the large-scale process, where thermal reclamation is among them. Thermal reclamation is typically performed by first adding sodium hydroxide (NaOH) to the degraded amine solution, prior to distillation of the solvent.^1–3 This is meant to hydrolyse the amides and recover non-degraded amine and an organic acid, hence reduce the loss of amine in the reclaiming process. Other degradation compounds, such as some nitrosamines are known to decompose to their corresponding amines at the elevated temperatures, either of the reclamation process itself, or even at stripper conditions.⁴

In this work we are performing alkaline hydrolysis and thermal stability testing of individual, known degradation compounds of ethanolamine (MEA). This is done inspired by the procedures described by Closmann et al. 2009⁵ and, Freeman and Rochelle 2012 ⁶, by mixing 1 part 5 M NaOH (aq.) to solutions with 1 part of a solution with MEA degradation compounds, such as the species shown in Table 1. The mixtures are then left at room temperature for 24 hours, and then heated to 140°C for 24 hours, and the composition of each solution is measured by LCMS before and after each treatment. The experiments will also be performed with fresh MEA and MEA that has been used and degraded in the SINTEF cyclic solvent degradation rig (SDR)^7,8, where more amides than those for which pure, individual standards were purchased. It is assumed that reactions analogous to that given in Scheme 1 will take place during the experiments, meaning that we should see both an increase in MEA, and possibly organic acid, as well as a decrease in amide concentrations. The experimental work will be extended to the CESAR1 solvent and its components once its degradation chemistry is better understood and analytical methods for its degradation products are in place.

Keywords: amine stability; reclamation; thermal reclaiming; alkaline hydrolysis

Authors: Vanja Buvik*, Andreas Grimstvedt, Kai Vernstad

*SINTEF Industry, NO-7465 Trondheim, Norway

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