On the CO2 capture in water-free monoethanolamine solution: an ab initio molecular dynamics study

Monoethanolamine (MEA) based liquids are widely used materials for postcombustion CO2 capture. We report here an extensive ab initio molecular dynamic (AIMD) simulation study on CO2 sorption in water-free MEA liquid with a range of CO2 contents at 313 K. The simulation reveals the detailed CO2 capture mechanism that leads to the initial formation of a zwitterion species and the ultimate proton transfer from the zwitterion to a nearby MEA molecule. The ion pairs formed in the liquid result in strong electrostatic interactions among the molecules in the liquid. The variation of liquid density, volume, diffusion coefficient, power spectrum, and average heat of sorption at the selected CO2 loadings was systematically assessed. The results indicate that initially the volume of the MEA solution expands gradually and tops at 60% of CO2 loading. After that, the volume declines as a result of strong Coulomb interactions among the ion pairs at higher CO2 loadings. The calculated liquid densities and the average heats of sorption are in quantitative agreement with the available experimental values. The simulated power spectrum of the water-free liquid also resembles the infrared spectrum of 30% aqueous MEA solution. The characteristic features in the simulated power spectra are slightly blue-shifted upon CO2 uptake.