Isolation and structural characterization of bicarbonate and carbonate species formed during CO₂ absorption/desorption by a hindered alkanolamine

The pathways for the CO₂ absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(tbutylamino) ethanol (TBAE) were elucidated by X-ray crystallographic and 13C NMR spectroscopic analysis. In the early stage of the CO₂ absorption, the formation of carbonate species ([TBAEH]2CO₃) was predominant along with the generation of small amounts of zwitterionic species. With the progress of the absorption, the carbonate species was rapidly transformed into bicarbonate species ([TBAEH]HCO₃), and the amounts of the zwitterionic species increased gradually. During desorption at elevated temperature in the absence of CO₂, [TBAEH]HCO3 was found to transform into [TBAEH]2CO₃, where CO₃ ^2-strongly interacts with two [TBAEH]+ via hydrogen bondings.