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Molecular Simulations of the Thermophysical Properties of Polyethylene Glycol Siloxane (PEGS) Solvent for Precombustion CO2 Capture

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journal contribution
posted on 25.08.2016, 00:00 by Wei Shi, Nicholas S. Siefert, Hseen O. Baled, Janice A. Steckel, David P. Hopkinson
The thermophysical properties for neat polyethylene glycol siloxane solvent (PEGS) along with CO2, H2, H2O, and H2S gas absorption in PEGS at 298–373 K were investigated via molecular simulations. The predicted neat PEGS density, heat capacity, surface tension, and CO2 and H2 solubilities in PEGS solvent agree reasonably well with the experimental data, with typical differences of 0.8–20%, while the predicted PEGS solvent viscosity is 1.7–2.5 times larger than the experimental data. Gas solubility in PEGS at 298 K decreases in the following order, H2O (31000) > H2S (230) > CO2 (33) > H2 (1), which follows the same order as the gas–PEGS interaction. In contrast, gas diffusivity in PEGS at 298 K decreases in an opposite way, H2 (1) > CO2 (0.22) ≈ H2S (0.12) > H2O (0.018). The numbers in parentheses are the corresponding values relative to H2. Compared to the widely studied poly­(dimethylsiloxane) (PDMS) solvent, PEGS is more hydrophilic due to its stronger interaction with H2O and fewer branched −CH3 groups, which in turn leads to fewer hydrophobic pockets. The CO2/H2 solubility selectivity in PEGS is larger than that in PDMS due to a stronger interaction with CO2 in PEGS. Finally, it was found that CO2 absorption in PEGS could significantly improve the CO2–PEGS solution dynamics by 5–6 times, resulting in a decrease in solution viscosity and increase in diffusivity. These CO2 absorption effects are due to solution volume expansion upon CO2 absorption compared to the neat PEGS solvent volume and the possibility that CO2 acts as a “lubricant” to decrease the solvent–solvent interaction.