Chemical and molecular descriptors for the reactivity of amines with CO 2

Abstract

Amine-based solvents are likely to play an important role in CO 2 capture applications in the future, and the identification of amines with superior performance will facilitate their use in CO 2 capture. While some improvements in performance will be achieved through process modifications, modifying the CO 2 capture performance of an amine also implies in part an ability to modify the reactions between the amine and CO 2 through development of new functionalized amines. We present a computational study of trends in the reactions between CO 2 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 CO 2 reaction products, whereas electron-donating groups tend to stabilize CO 2 reaction products. Hydrogen bonding stabilizes CO 2 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. © 2012 American Chemical Society.