Toward the Understanding of Chemical Absorption Processes for Post-Combustion Capture of Carbon Dioxide: Electronic and Steric Considerations from the Kinetics of Reactions of CO2(aq) with Sterically hindered Amines

The present study reports (a) the determination of both the kinetic rate constants and equilibrium constants for the reaction of CO2(aq) with sterically hindered amines and (b) an attempt to elucidate a fundamental chemical understanding of the relationship between the amine structure and chemical properties of the amine that are relevant for postcombustion capture of CO2 (PCC) applications. The reactions of CO2(aq) with a series of linear and methyl substituted primary amines and alkanolamines have been investigated using stopped-flow spectrophotometry and 1H NMR measurements at 25.0 °C. The specific mechanism of absorption for each of the amines, that is CO2 hydration and/or carbamate formation, is examined and, based on the mechanism, the kinetic and equilibrium constants for the formation of carbamic acid/carbamates, including protonation constants of the carbamate, are reported for amines that follow this pathway. A Bronsted correlation relating the kinetic rate constants and equilibrium constants fo...