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