Mass Transfer Studies of Carbon Dioxide Absorption into Aqueous Solutions of 4-(Diethylamine)-2-Butanol, Blended Monoethanolamine with 4-(Diethylamine)-2-Butanol, and Blended Monoethanolamine with Methyldiethanolamine

Abstract

One of the parameters used to characterize the performance of a solvent for carbon dioxide (CO2) capture is the mass transfer performance of CO2 absorption in the solvent. In this study, a newly developed amino alcohol solvent, 4-(diethylamino)-2-butanol (DEAB), was evaluated for its mass transfer performance as a single or blended solvent in comparison with existing commercially available amine solvents. Consequently, the mass transfer performance characteristics of the absorption of CO2 in aqueous solutions of a primary alkanolamine (e.g. monoethanolamine, MEA), a tertiary amine (e.g. methyldiethanolamine, MDEA) and DEAB were compared using a bench-scale absorber packed with high efficiency DX structured packing at atmospheric pressure using a feed gas mixture containing 14.9% CO2 and 85.1% nitrogen. The mass transfer performance characteristics of CO2 absorption in aqueous blended MDEA/MEA solution with total concentrations of 30 g/L and weight ratios of 27/03, 25/05, and 23/07, as well as aqueous blended DEAB/MEA solution with concentrations of DEAB+MEA (g/L) of 3.5+30.23, 7.18+30.23, 14.43+30.23, 17.96+30.23, 21.82+30.23, 25.15+30.32, and 29.38+30.23 were also compared using the same experimental conditions. Specific absorption performance criteria used for this study were CO2 removal efficiency, absorber height requirement, the effective interfacial area for mass transfer, and the overall mass transfer coefficient (KGav). The results show that the new tertiary aqueous chemical solvent, DEAB, has a much higher removal efficiency for CO2 along the height of the column than aqueous MDEA, another tertiary solvent. The results for blended aqueous MDEA/MEA system and blended aqueous DEAB/MEA system showed that the ratios of 23/07 (g/L) MDEA/MEA system and 17.96/30.23 of DEAB/MEA system respectively has the highest CO2 removal efficiencies along the height of the column, highest KGav values and highest cyclic capacities compared with other ratios tested, with the blended aqueous DEAB/MEA system having extremely superior performance. Interestingly, the results of the new blended amine solution demonstrate that the height of the column can be reduced substantially by up to 32.5% compared even to pure aqueous MEA (30.23 g/L), which before now, has been credited with providing the shorter column height.