Industrial & Engineering Chemistry Research, Vol.51, No.42, 13609-13618, 2012
Chemical and Molecular Descriptors for the Reactivity of Amines with CO2
Amine-based solvents are likely to play an important role in CO2 capture applications in the future, and the identification of amines with superior performance will facilitate their use in CO2 capture. While some improvements in performance will be achieved through process modifications, modifying the CO2 capture performance of an amine also implies in part an ability to modify the reactions between the amine and CO2 through development of new fiinctionalized amines. We present a computational study of trends in the reactions between CO2 and functionalized amines with a focus on identifying molecular descriptors that determine trends in reactivity. We examine the formation of bicarbonate and carbamate species on three classes of functionalized amines: alkylamines, alkanolamines, and fluorinated alkylamines including primary, secondary, and tertiary amines in each class. These functional groups span electron-withdrawing to donating behavior, hydrogen-bonding, extent of functionalization, and proximity effects of the functional groups. Electron withdrawing groups tend to destabilize CO2 reaction products, whereas electron-donating groups tend to stabilize CO2 reaction products. Hydrogen bonding stabilizes CO2 reaction products. Electronic structure descriptors based on electronegativity were found to describe trends in the bicarbonate formation energy. A chemical correlation was observed between the carbamate formation energy and the carbamic acid formation energy. The local softness on the reacting N in the amine was found to partially explain trends of carbamic acid formation energy.