Chemical and Molecular Descriptors for the Reactivity of Amines with CO2
2012
Lee, Anita S. | Kitchin, John R.
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 functionalized 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.
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