Assessing the Chemical Speciation during CO2 Absorption by Aqueous Amines Using in Situ FTIR

During amine scrubbing of CO2 from flue gas, carbamate and bicarbonate species are formed, the amount of which is directly related to the process performance. In this study we present a fast calibration-free spectroscopic technique for determining the speciation of CO2–H2O–alkanolamine systems and in turn the amine protonation and carbamate thermodynamic equilibrium constants. The method is based on in situ infrared monitoring of the liquid phase during CO2 absorption by an aqueous amine solution in a stirred vessel, combined with mathematical hard modeling of the reaction mechanism. The species concentrations are calculated by fitting of a thermodynamic model to multivariate spectroscopic measurements using nonlinear regression. Successful applications include the determination of the amine protonation and carbamate equilibrium constants of one primary (MEA), one secondary (DEA), and one sterically hindered primary (AMP) amine at 40 °C.