Screening tests of aqueous alkanolamine solutions based on primary, secondary, and tertiary structure for blended aqueous amine solution selection in post combustion CO2 capture

Abstract

In this work, hindered primary, secondary and tertiary aqueous alkanolamine solutions with different numbers of hydroxyl groups were investigated for their initial rates of absorption and desorption which show how fast the amine solution will reach equilibrium and will be regenerated, respectively, and also investigated pKa, equilibrium solubility of CO2, heat duty (Qreg) for solvent regeneration, and heat of CO2 absorption (ΔHabs). These experimental data were used as a screening tool to enable the selection of the best amine components for designing an optimal blended aqueous amine solution system. The absorption experiments were performed at 313K and atmospheric pressure using 15% CO2 (in N2 balance) as feed gas whereas desorption experiments were performed at 363K and atmospheric pressure. Alkanolamines with a larger number of hydroxyl groups exhibited lower performance in all the CO2 capture activities because of the negative electron withdrawing effect of the hydroxyl group. Consequently, based on the results of individual primary, secondary, and tertiary aqueous alkanolamine solutions, the ones with only one hydroxyl group (2-amino-2-methyl-1-propanol (AMP), 2-(ethylamino) ethanol (EAE), and 2-(dimethylaminoethanol) (DMAE)) were selected for formulation into aqueous amine blends. Two binary aqueous amine blends of AMP/DMAE and EAE/DMAE and one ternary aqueous amine blend of AMP/EAE/DMAE at various molar ratios were tested. All solvent combinations showed better performance than 5M MEA, especially in the initial desorption rate and energy efficiency. Of these aqueous amine blends, the 2.5M AMP/2.5M DMAE exhibited the best performance with an equilibrium CO2 solubility of 0.56mol CO2/mol amine, initial absorption rate of 0.26×10−2mol CO2/min, initial desorption rate of 2.62×10−2mol CO2/min, and heat duty of 53.81kJ/mol.