“Simulations were carried out for starting compositions of alkanolamine/water solvent ratios of 30/70 w/w MEA/W and 22.5/77.5 w/w DEAB/W which are typical for the absorption process2,4 and at a typical process temperature of 313 K.22,40 The mole fractions of species in mixed solutions at various CO2 loadings were obtained from NMR spectroscopic studies.41,42 The absolute compositions for each system are given in the ESI† (Tables S1 and S2). A comparison with experimental43,44 data such as densities and viscosities is given in Fig. 2. There is a very good agreement for liquid densities over the entire range of CO2 loading (deviations are below 1% for MEA and 2.5% for DEAB). The calculated viscosities are also in good agreement with experiment and correctly reproduce the trend of increasing viscosities with increasing loading. According to our findings, the TIP4P/2005 water model45 performs slightly better for solvent viscosities of DEAB, but less so for the diffusion coefficients of complex mixed aqueous alkanolamine solutions.14 The large changes in density and viscosity with CO2 loading for MEA with respect to DEAB can be rationalized by the fact that the number of absorbed CO2 molecules in MEA at 0.5 loading is about 2 times larger than that in DEAB even at 0.815 loading.
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| Fig. 2 Comparison of liquid state properties with experiments at T = 313 K. Panel (A) shows the densities of the five- and six-component mixed solvents, panels (B) and (C) display the viscosities of the MEA/MEAH+/MEACOO−/W/CO2 and DEAB/DEABH+/W/CO2/HCO3−/CO32− systems as a function of CO2-loading. | ||
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