Towards water-insensitive CO2-binding organic liquids for CO2 absorption: Effect of amines as promoter

Abstract

Abstract CO2-binding organic liquids (CO2-BOLs) or reversible ionic liquids (RILs), are non-aqueous CO2-triggered switchable polarity solvents which can be used for energy efficient CO2 capture. In this study, the novel three-component CO2-BOLs are introduced. They are comprised of 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU) as an organic superbase and an alkanol in conjunction with an amine as a promoter. Screening experiments were performed to find the best combination of CO2-BOL components based on CO2 loading and absorption rate. The variables were: the type of alcohol (methanol, n-butanol, sec-butanol, tert-butanol and 1-hexanol) and the type of amine (EEA, MEA, AMP, DEA, AEEA, PZ, TETA and DETA) using the DBU superbase. Statistical mixture design approach using Minitab 18 software was implemented for the design of experiments, modeling and optimization of CO2 loading at the fixed temperature of 35 °C and the initial CO2 pressure of 25 bar. It was found that DBU/MeOH/MEA system with the molar ratio of 0.3/0.17/0.53 has the maximum equilibrium absorption (αeq) and CO2 uptake within 30 min (αR) of 0.444 and 0.267 mol CO2/mol solvent, respectively. Amine additives promoted absorption efficiency and inhibited formation of solid precipitates (bicarbonate salt) in the presence of water impurity. Characterization of ionic species and explaining the water-inhibitory effect of MEA were obtained from FTIR, 1H NMR and 13C NMR spectroscopic analysis. Equilibrium CO2 solubility data in DBU/MeOH (1/2) and DBU/MeOH/MEA (0.3/0.6/0.1) CO2-BOLs were also obtained at temperatures of 308.2 and 318.2 K and pressure range of 0–33 bar. The results of present study can be used to effectively utilize CO2-BOLs in the wet conditions with higher absorption efficiency and lower regeneration energy.