Application of 15N-NMR spectroscopy to analysis of amine based CO2 capture solvents

Abstract

15N NMR spectroscopy is a useful tool for amine reactivity characterization since it can provide information about the availability of the lone pair of electrons on nitrogen through the measured chemical shift values, which depend on molecular structure and medium effects. Although the amino nitrogen is the focal nucleus of the carbon dioxide-amine reaction, 15N NMR measurements have so far received little attention in the field of amine-based chemical absorption of carbon dioxide. In this study, from one hand, through 15N NMR chemical shifts measurements, the effect of solvent on the electron density of the nitrogen of 2-methyl-2-amino-1-propanol (AMP) in solvent blends was investigated; from the other hand, 15N NMR chemical shifts of aqueous primary non-hindered and hindered alkyl amines were related to the corresponding carbamate forming and carbamate stability equilibrium constants as well as carbamate forming kinetic constants, showing linear relationships. Such correlations could be useful for predictive estimation of carbamate-related equilibrium and kinetic constants.