Stability of Solvents for Gas Purification
Doctoral thesis
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https://hdl.handle.net/11250/3101326Utgivelsesdato
2023Metadata
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Sammendrag
The main objective of this work was to increase the understanding of the chemical processes occurring as solvents used in gas purification degrade. Amine systems for CO2 capture and glycol systems for gas dehydration were in focus. The work included a literature review, oxidative and thermal degradation studies of both amines and glycols and development of analytical methods.
In thermal degradation experiments with MEA, the concentration of CO2 was found to increase the degradation rates, while the water and amine concentrations had no effect. Replacing water with TEG resulted in increased thermal degradation rates for MEA, AP, MMEA, and EAE. Also changing the cosolvent to organic diluents, DEG, MEG, THFA, NFM/water, and NMP resulted in increased thermal degradation of MEA.
In oxidative degradation experiments of MEA, increasing the concentration of MEA in loaded solutions resulted in increased degradation rates when the CO2 concentration was kept constant. The same was not seen when the CO2 concentration was increased simultaneously with the MEA concentration. Independent analytical techniques were developed for the quantification of small glycols and small organic acids. GC-FID and quantitative 13C NMR were successfully used to quantify the glycols. HPLC-UV and HSS analysis were successfully used to quantify the acids.
Thermal degradation experiments of TEG show that the added impurities, water and formic acid, reduced the thermal stability of TEG. DEG and MEG were confirmed as thermal degradation products of TEG. Gas bubbles were observed in the degraded solutions, but no other degradation components were identified.
The oxidative stability of TEG was reduced both by an increase in temperature and oxygen available. The degradation products identified and quantified were DEG, MEG, formic, acetic, glycolic, glyoxylic, and oxalic acid, formaldehyde and acetaldehyde, water, and CO2. Identification of additional degradation compounds, tetraethylene glycol, pentaethylene glycol, and diethylene glycol monoethyl ether was achieved by a GC-MS analysis. Oxidative degradation experiments with MEG showed that the stability of MEG is considerably higher than TEG under the given conditions.