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

Abstract

CO 2 diffusion limitations and readsorption of desorbed CO 2 during removal from immobilized amine sorbents could significantly reduce the effectiveness of CO 2 capture processes. To decouple CO 2 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 CO 2 and Si–OH (which adsorbs benzene) revealed that slow rates of CO 2 uptake and desorption are a result of (i) CO 2 diffusion through an interconnected network produced from CO 2 adsorbed inside of the amine/silica sorbent pores and (ii) readsorption of CO 2 on the amine sites inside of the pores and at the external surface of the sorbents. High rates of CO 2 adsorption/desorption onto/from the immobilized amine sorbents could be achieved by sorbents with low amine density at the external surfaces and pore mouths.