Investigating the Performance of Ethanolamine and Benzylamine Blends as Promising Sorbents for Postcombustion CO2 Capture through 13C NMR Speciation and Heat of CO2 Absorption Analysis

Aiming at formulating efficient sorbents for carbon capture and separation (CCS) processes, in this work, we evaluated the CO2 capture performance of aqueous blends of two primary amines, namely, ethanolamine (MEA), the benchmark for any capture process, combined with benzylamine (BZA), which has intriguing characteristics for industrial use, such as low corrosivity and good resistance to thermal and oxidative degradation. The CO2 loading, the CO2 absorption rate, and the CO2 heat of absorption were determined at 313 K for three different formulations of aqueous BZA/MEA blends, all with the same overall amine concentration (6 M) but with different amine molar ratios (1/2, 1/1, 2/1) by treating a gas mixture containing 15% CO2 (by volume) mimicking a fossil-derived flue gas. Furthermore, through an accurate 13C NMR study, the species present in solution during the CO2 absorption process were identified and quantified to understand the capture mechanism and to evaluate the interactions of the two primary amines when present together in different molar ratios. As a result, the three tested blends show similar high CO2 absorption rates, and their final loading values decrease in the order BZA/MEA 1/2 > BZA/MEA 1/1 > BZA/MEA 2/1, suggesting that a greater relative amount of MEA in the blend is advantageous to achieve a relatively higher CO2 loading. The 13C NMR analysis confirmed that the greater alkalinity of MEA leads to a greater formation of bicarbonate in solution and consequently higher loading. Finally, the CO2 absorption heat of all tested mixtures, measured using a high-precision microcalorimeter, was found to be comparable, if not even higher, to that of each individual amine.