Prediction of the Basicity of Aqueous Amine Solutions and the Species Distribution in the Amine−H₂O−CO₂ System Using the COSMO-RS Method

Abstract

A conductor-like screening model for real solvents (COSMO-RS) was applied to the study of the amine−H2O−CO2 system. pK a values for 25 amines including a variety of alkanolamines and some cyclic or aromatic amines were calculated by the COSMO-RS method coupled with the density functional theory (DFT). The predictions of pK a values were compared using different DFT levels for geometry optimization and also with those based on another solvation model (SM5.4/A). The DFT-COSMO calculation at the BP/TZVP level has shown a relatively good correlation with experimental values for the 25 amines (R 2 ≅ 0.8) at a low computational cost. With this method, we have developed a calculation model to predict the equilibrium ratio between carbamate and bicarbonate anions in a CO2-loaded aqueous amine solution and have confirmed the validity of the prediction model by 13C NMR spectroscopy.

Experimental study into carbon dioxide solubility and species distribution in aqueous alkanolamine solutions

“…It is well known that bicarbonate formation occurs at a lower rate than carbamate formation while bicarbonate formation results in a large CO 2 absorption capacity [3]. However, we found that some 'moderately' hindered amines have combined desirable characteristics such as high rate and large capacity for CO 2 absorption [4,5].…”

“…For the sterically hindered primary amine, 2-amino-2-methyl-1-propanol (AMP), it has been confirmed by previous 13 C NMR studies that CO 2 absorption in aqueous AMP solutions predominantly gives the bicarbonate anion at equilibrium [3,11]. Ciftja et al [11] performed speciation on 30 wt% aqueous solutions of AMP with different amounts of CO 2 at 25ºC where the carbamate yield was at most 0.03 in the loading range from 0.12 to 0.62.…”

“…(2) occurs faster than the reaction in eqn. (3). Bicarbonate formation stoichiometrically requires 1 mol of amine per mole of CO 2 and allows for a large CO 2 capacity whereas carbamate formation requires 2 mol of amine per mole of CO 2 .…”

“…Amine scrubbing is the most promising and currently applicable technology used in an industrial scale for the capture of CO 2 from a gas stream [1]. To maximise the capture efficiency and to reduce energy costs we previously developed CO 2 capture systems and high performance CO 2 absorbents [2][3][4][5]. Recently, we demonstrated that hindered amino alcohols for the promotion of CO 2 capture can be developed by rational molecular design and by the placement of functional groups [4,5].…”

Aqueous piperazine derivatives for CO2 capture: Accurate screening by a wetted wall column

“…The ethanol group next to the amino group on piperi- dine ring introduces steric hindrance and reduces stability of carbamate. 13 C NMR experiments carried out by Paul et al (2009) and Yamada et al (2010), both show that there is no carbamate formed in CO 2 -loaded 2-PE solution. The reaction proceeds through the formation of bicarbonate and 2-PE exhibits a higher P CO 2 * than PZ below the critical loading.…”