Evaluation of solvent effect on the amine-based CO2 absorbents by theory and experiment

Abstract

The three-dimensional reference interaction site model (3D-RISM) integral equation is applied to predict the hydration free-energies and solution enthalpies at infinite dilution for amines and alkanolamines. In particular, the closure equation for 3D-RISM is integrated with the bridge functions derived from minimizing the hard-sphere free-energy functional for different interactions. The density distributions of water molecules around different solute molecules are calculated to intuitively describe the solvent effects. The solution enthalpies and hydration free-energies are then determined by the density distributions. Meanwhile, the solution enthalpies for some alkanolamines with low volatility are measured, and the values at infinite dilution are thereby obtained through extrapolation. It is shown that the theoretical predictions are generally in agreement with the experimental results, suggesting that the current theoretical approach is reasonable to quantitatively evaluate the solvent effect of various amine-based CO2 absorbents.