Investigation of the improvement of the CO2 capture performance of aqueous amine sorbents by switching from dual-amine to trio-amine systems

Mixing amines with different properties is considered a smart strategy for developing efficient aqueous solutions for reversible CO2 capture. Specifically, dual-amine blends containing the tertiary amine 2-dimethylamino-2-methyl-1-propanol (2DMA2M1P) have proven to be particularly advantageous due to significantly lower regeneration costs compared to conventional sorbents. With the aim of formulating high-efficiency sorbents, in this work we evaluated the improvement in the CO2 capture performance of such dual-amine blends by adding a further amine to form trio-amine systems: the use of three amines with different characteristics could further emphasize the advantages obtainable during both absorption and desorption. We formulated three new different aqueous solutions prepared by mixing 2DMA2M1P with the reaction rate promoter ethanolamine (MEA) and the absorption capacity promoter 2-amino-2-methyl-1-propanol (AMP) in different molar ratios. For each blend, the CO2 solubility at equilibrium, the CO2 absorption rate from a gaseous mixture, the regeneration rate at T = 373 K and the energy requirement for desorption were determined experimentally. In addition, to better understand the capture mechanism, 13C NMR spectroscopy was employed to evaluate the speciation of each blend during the CO2 absorption. Their CO2 capture performance was compared with that of the benchmark aqueous MEA and two 2DMA2M1P-based dual-amine mixtures, obtained with the same procedure. As a finding, all formulated trio-amine blends have superior CO2 equilibrium solubility and desorption performance compared with MEA 5 M. Noteworthy, the comparison with similar dual-amine systems highlighted the role of a suitable third amine in order to obtain enhance both absorption and desorption efficiencies. Among the formulated systems, MEA-2DMA2M1P-AMP (1:2:2) is potentially the most suitable to replace MEA in CO2 capture processes after a careful cost-benefit analysis on larger scale systems.