Probing the Adsorption/Desorption of CO2 on Amine Sorbents by Transient Infrared Studies of Adsorbed CO2 and C6H6

CO2 diffusion limitations and readsorption of desorbed CO2 during removal from immobilized amine sorbents could significantly reduce the effectiveness of CO2 capture processes. To decouple CO2 diffusion from desorption/readsorption on silica and tetraethylenepentamine (TEPA)/silica sorbents, a new transient diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) method was carried out by using benzene as a surrogate probe molecule. Comparison of the infrared intensity profiles of adsorbed CO2 and Si–OH (which adsorbs benzene) revealed that slow rates of CO2 uptake and desorption are a result of (i) CO2 diffusion through an interconnected network produced from CO2 adsorbed inside of the amine/silica sorbent pores and (ii) readsorption of CO2 on the amine sites inside of the pores and at the external surface of the sorbents. High rates of CO2 adsorption/desorption onto/from the immobilized amine sorbents could be achieved by sorbents with low amine density at the external surfaces and pore mouths.