Preferential heating of aqueous amine solutions using infrared radiation at selected vibrational frequencies: A molecular dynamics study

A recent CO2 capture experiment suggests microwaves might be beneficial for regeneration of aqueous amine solutions due to both thermal and non-thermal effects (S.J. McGurk et al., Appl. Energ. 192, 126 (2017)). We investigate this issue here with large-scale classical molecular dynamics (MD) simulations. Specifically, we simulate the heating selectivity in aqueous amine solutions using electromagnetic radiation with different frequencies in both microwave and infrared regions. An atomistic sample containing 13,880 water molecules and 4,096 monoethanolamine (MEA) molecules, corresponding to 50 wt. % amine aqueous solution, was heated under electric fields with frequencies ranging from 0.01 to 107.83 THz. The infrared frequencies were selected based on the computed partial vibrational density of states of water and MEA. Unlike the microwave case, we found that preferential heating of water or amine can be achieved using their relevant vibrational frequencies in the infrared region, suggesting that microwave heating is not an optimal choice for aqueous amine regeneration. Interestingly, only flexible water models augmented with an anharmonic O-H bond stretching potential were able to quantitatively predict the expected differential heating profiles of systems involving water.