Computational Screening of Physical Solvents for CO Pre-combustion Capture.

A computational scheme was used to screen physical solvents for CO pre-combustion capture by integrating the commercial NIST database, an in-house computational database, chem-informatics, and molecular modeling. A commercially available screened hydrophobic solvent, diethyl sebacate, was identified from the screening with favorable physical properties and promising absorption performance. The promising performance to use diethyl sebacate in CO pre-combustion capture has also been confirmed from experiments. Water loading in diethyl sebacate is very low, and therefore, water is kept with H in the gas stream. The favorable CO interaction with diethyl sebacate and the intermediate solvent free volume fraction leads to both high CO solubility and high CO/H solubility selectivity in diethyl sebacate. An in-house NETL computational database was built to characterize CO, H, N, and HO interactions with 202 different chemical functional groups. It was found that 13% of the functional groups belong to the strong interaction category with the CO interaction energy between -15 and -21 kJ/mol; 62% of the functional groups interact intermediately with CO (-8 to -15 kJ/mol). The remaining 25% of functional groups interact weakly with CO (below -8 kJ/mol). In addition, calculations show that CO interactions with the functional groups are stronger than N and H interactions but are weaker than HO interactions. The CO and HO interactions with the same functional groups exhibit a very strong linear positive correlation coefficient of 0.92. The relationship between CO and H gas solubilities and solvent fractional free volume (FFV) has been systematically studied for seven solvents at 298.2 K. A skewed bell-shaped relation was obtained between CO solubility and solvent FFV. When an organic compound has a density approximately 10% lower than its density at 298.2 K and 1 bar, it exhibits the highest CO loading at that specific solvent density and FFV. Note that the solvent densities were varied using simulations, which are difficult to be obtained from the experiment. In contrast, H solubility results exhibit an almost perfect positive linear correlation with the solvent FFV. The theoretical maximum and minimum physical CO solubilities in any organic compound at 298.2 K were estimated to be 11 and 0.4 mol/MPa L, respectively. An examination of 182 experimental CO physical solubility data and 29 simulated CO physical solubilities shows that all the CO physical solubility data are within the maximum and minimum with only a few exceptions. Finally, simulations suggest that in order to develop physical solvents with both high CO solubility and high CO/H solubility selectivity, the solvents should contain functional groups which are available to interact strongly with CO while minimizing FFV.