CHAPTER 23. The Nature of Hydrogen Bonding in Adsorbed CO2 and H2O on Solid Amines in CO2 Capture

CO2 capture from fossil fuel (coal and natural gas) power plants has been considered a key strategy in mitigating global climate changes. One promising approach under development is the use of solid amine sorbents to bind CO2 in the form of ammonium carbamate from the flue gas of coal-fired power plants in a CO2 capture process. The CO2 capture process by solid amines consists of a number of steps: CO2 adsorption, diffusion and desorption. These steps are governed by the nature of the hydrogen bonding between the ammonium cation and the carbamate anion. This chapter discusses the sources of greenhouse gas emissions, basic principles governing the trapping of infrared energy by greenhouse gases, especially CO2, and the mechanistic step involved in the thermal swing CO2 capture process by solid amines. Infrared spectroscopy is used to illustrate the nature of hydrogen bonding in adsorbed CO2 (i.e. ammonium carbamate) and co-adsorbed CO2/H2O (i.e. hydronium carbamate). In situ infrared spectroscopy shows that hydrogen bonding interactions among these adsorbed species shift the stretching band of N–H and O–H to lower wavenumbers. The extent of hydrogen bonding is reflected in the degree of shift and broadness of the N–H and O–H stretching bands. Fine tuning solid amine (immobilized amine) sorbents for CO2 capture processes requires controlling the structure of amine sites to facilitate CO2 adsorption, diffusion and desorption.