Validation of the CO2/N2O Analogy Using Molecular Simulation

Abstract

CO2 readily reacts in aqueous amine solutions. The properties of free CO2 in amine solutions are therefore difficult to obtain directly and are often predicted from the nonreacting molecule N2O due to the similarities in mass and structure. This often-used empirical “CO2/N2O analogy” is verified in this work using molecular simulation. Continuous fractional component Monte Carlo (CFCMC) simulations in the osmotic ensemble were used to compute the Henry coefficients of CO2 and N2O in the solvents water, ethanol, n-heptane, and a 30% aqueous MEA solution at a temperature of 303 K. Molecular dynamics (MD) simulations were performed to compute the self-diffusivities of CO2 and N2O in the aforementioned solvents at 303 K. Different force fields for CO2 and water were used. The computed Henry coefficients and self-diffusivities of CO2 and N2O in the solvents are in good agreement with available experimental data. The simulation results indicate that the CO2/N2O analogy is valid for aqueous MEA solution at 303 K. The Henry coefficient and self-diffusivity ratios of CO2 to N2O in water and 30% MEA solution are approximately 0.77 and 1.1, respectively. Additional simulations where all the amines have reacted with CO2 confirm that reactions have little impact on the physical absorption and diffusion properties of CO2.