A Comparative Study of the CO₂ Absorption in Some Solvent-Free Alkanolamines and in Aqueous Monoethanolamine (MEA)

The neat secondary amines 2-(methylamino)­ethanol, 2-(ethylamino)­ethanol, 2-(isopropylamino)­ethanol, 2-(benzylamino)­ethanol and 2-(butylamino)­ethanol react with CO₂ at 50–60 °C and room pressure yielding liquid carbonated species without their dilution with any additional solvent. These single-component absorbents have the theoretical CO₂ capture capacity of 0.50 (mol CO₂/mol amine) due to the formation of the corresponding amine carbamates and protonated amines that were identified by the ¹³C NMR analysis. These single-component absorbents were used for CO₂ capture (15% and 40% v/v in air) in two series of different procedures: (1) batch experiments aimed at investigating the efficiency and the rate of CO₂ capture; (2) continuous cycles of absorption–desorption carried out in packed columns with absorption temperatures brought at 50–60 °C and desorption temperatures at 100–120 °C at room pressure. A number of different amines and experimental setups gave CO₂ capture efficiency greater than 90%. For comparison purposes, 30 wt % aqueous MEA was used for CO₂ capture under the same operational conditions described for the solvent-free amines. The potential advantages of solvent-free alkanolamines over aqueous MEA in the CO₂ capture process were discussed.