CO₂ absorption and desorption in an aqueous solution of heavily hindered alkanolamine: Structural elucidation of CO₂-containing species

The pathways for the CO₂ absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(t-butylamino)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.