In situ infrared study of the role of PEG in stabilizing silica-supported amines for CO2 capture

Abstract

The CO2 capture capacity, adsorption mechanism, and degradation characteristics of two sorbents, silica-supported tetraethylenepentamine (TEPA/SiO2) and polyethylene-glycol-modified TEPA/SiO2 (PEG/TEPA/SiO2), are studied by diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry. The CO2 capture capacities of TEPA/SiO2 and PEG/TEPA/SiO2 are determined to be 2087 and 1110μmol CO2g-1sorbent, respectively. Both sorbents adsorb CO2 as hydrogen-bonding species, NH2-O, and carbamate/carboxylate species. The CO2 adsorption half-time increases with the number of CO2 capture cycles. Infrared results suggest that the increased adsorption half-time is a result of diffusion limitation, caused by accumulation of TEPA and PEG species on the surface of the sorbent particles. The degradation of TEPA/SiO2 is found to correlate with the accumulation of carboxylate/carbamic species. The addition of PEG decreases the degradation rate of the sorbent and slows down the formation of carboxylate species. These carboxylate species can block CO2 capture on amine (NH2/NH) sites. The stabilizing role of PEG on TEPA/SiO2 can be attributed to hydrogen-bonding between TEPA (NH2/NH)and PEG (OH). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.