Infrared Study of Strongly and Weakly Adsorbed CO2 on Fresh and Oxidatively Degraded Amine Sorbents

• Published in: Journal of physical chemistry. C 2013-05, Vol.117 (18), p.9196-9205
• Main Authors: Srikanth, Chakravartula S, Chuang, Steven S. C
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp311232f

CO2 adsorption on fresh and oxidatively degraded tetraethylenepentamine (TEPA) and polyethylene glycol (PEG-200) supported on amorphous silica (SiO2) was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Fresh TEPA sorbents adsorb CO2 in the form of ammonium ions, carbamates, and carbamic acid of which infrared features and binding strength strongly depend on the type of amine sites (i.e., primary or secondary) and their densities. CO2 adsorbed on the primary amine sites exhibited a strong IR intensity of carbamate in the 1680–1200 cm–1 region, and CO2 adsorbed on the secondary amine sites showed a high IR intensity of ammonium ion in the 2800–2100 cm–1 region. Oxidative degradation of the fresh sorbents in the presence of air at 100 °C for 12 h converted a high fraction of secondary amines in TEPA to amide and imide species, isolating the primary amine sites and decreasing the overall density of amines in the sorbent. The isolated primary amine sites of the degraded sorbents bind weakly adsorbed CO2 in the form of carbamic acid and carbamate. Carbamic acid can be removed from the sorbent at a higher rate than carbamate by flowing inert gas or air at 25 °C. High amine density (i.e., loading) sorbents containing multilayers of amines bind strongly adsorbed CO2 which can only be thermally desorbed from the sorbents.