Modeling of MEA degradation

Abstract

Background: Degradation of monoethanolamine (MEA) is a problem in CO2 absorption due to loss of solvent and potential environmental issues associated with the degradation products. The aim of this project was to increase the understanding of the degradation of MEA in order to further improve a recently suggested model of the degradation process. Method: Experimental data sets were used to create reaction rate equations for a set of suggested degradation reactions. The degradation products considered were ammonia, formaldehyde, formic acid, N-(2-hydroxyethyl)formamide (HEF), glyoxal, N-(2-hydroxyethyl)imidazole (HEI), oxalic acid, N,N-bis(2-hydroxyethyl)oxalamide (BHEOX) and N-(2-hydroxyethyl)glycine (HEGly). By utilizing the experimental data available and an Arrhenius expression for the temperature dependency, an extended model for the degradation of MEA and formation of the compounds listed above as a function of temperature and oxygen concentration in the gas phase was developed. The reaction rate coefficients and reaction orders for the reactions considered were found by fitting the reaction rate equations to the experimental data. This was done by using model equations for a semi flow batch reactor to represent the experimental set up. The optimization routine used was a standard particle swarm optimization combined with a trial and error approach. To generate the model, several approaches were tried. The large uncertainties associated with the system and the lack of experimental data for some components made it necessary to make assumptions without justification regarding some issues.Conclusion: The model developed for the oxidative degradation of MEA in CO2 capture is able to predict the development of the degradation products to some extent. Substantial work remains before the model can predict the degradation of MEA and the production of the chosen degradation products to a satisfactory degree. The results presented in this thesis may be utilized as a valuable starting point for further development of a temperature and oxygen concentration dependent model for oxidative degradation of MEA.