A new look to the old solvent: Mass transfer performance and mechanism of CO2 absorption into pure monoethanolamine in a spray column

Abstract

The most mature CO₂ capture technology is absorption of monoethanolamine (MEA) in packed or spray columns. Typically, an aqueous 30 wt.% MEA solution is used. High MEA concentrations are believed to hinder mass transfer rate due to high viscosity of MEA. We worked, for the first time, on the effects of using pure MEA on overall mass transfer coefficient (K_Gɑ) and absorption efficiency in a spray column by varying several operational parameters. Image analysis results suggested that interfacial area increased with increasing liquid flow rate. As a result, K_Gɑ increased. As opposed the belief in literature, K_Gɑ also increased with increasing MEA concentrations. The highest K_Gɑ was obtained in this work (11.7 kmol m^-3∙kPa^-1∙h^-1) is around one order of magnitude higher than most other literature studies. Having more MEA molecules on the surface of the droplets led to higher K_Gɑ. In addition, it was shown that absorption efficiency was largely determined by inlet CO₂ to MEA molar ratio. ¹³C-NMR spectra results revealed that similar levels of carbamate was formed for MEA concentrations up to 70 wt.%. A simplified analysis on regeneration heat duty showed that decreasing water amount can lead to 3-10 fold decrease in reboiler energy duty.