Aspects of degradation of monoethanolamine solutions\ud during Co2 absorption
The most common technique for carbon dioxide removal from gaseous streams\ud is amine scrubbing, a proven technology in the oil and gas industries. The use of\ud this route in coal fired power plants is not fully understood and the likelihood of\ud solvent degradation is high. Decreased absorption efficiency, undesirable byproducts,\ud the environmental impact of their disposal and increased process costs\ud are the main consequences.\ud In this study, two experimental rigs were designed and commissioned to explore\ud the effects of gas composition and temperature on monoethanolamine\ud degradation. Analytical procedures to detect and quantify its major thermal and\ud oxidative degradation products were also developed.\ud It became apparent early on that solvent degradation, under actual plant\ud conditions, is a slow phenomenon, thus, it was decided to focus on thermal\ud degradation. The present study uniquely enabled the absorption/desorption\ud behaviour of thermally degraded solvents to be evaluated. The major thermal\ud degradation products were quantified.\ud After 14 full absorption/stripping cycles at the presence of 16% oxygen and 15%\ud carbon dioxide, significant concentrations of nitrites and nitrates were detected in\ud the samples. Thermal degradation at 160 oC for 8 weeks reduced\ud monoethanolamine concentration by almost 95%, as evidenced by the chemical\ud analysis, but the remaining solvent retained 22% of its capacity to remove carbon\ud dioxide. Therefore, although not fully quantified, the requirement for\ud monoethanolamine make-up may not be quite as serious as initially believed.\ud There is some evidence to support that the rate of thermal degradation was\ud enhanced as carbon dioxide loading increased and a 20% higher MEA loss was\ud determined in the samples with the rich initial molar loading. A range of\ud degradation products were quantified that correspond to those cited in the\ud literature. 1-(2-hydroxyethyl)-2-imidazolidinone was indicated as the most stable\ud MEA degradation product in the degraded samples at concentrations of up to\ud 17% v/v.
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