Shi, Wei; Siefert, Nicholas S.; Morreale, Bryan D.
Molecular Simulations of CO2, H-2, H2O, and H2S Gas Absorption into Hydrophobic Poly(dimethylsiloxane) (PDMS) Solvent: Solubility and Surface Tension
JOURNAL OF PHYSICAL CHEMISTRY C, 119:19253-19265, AUG 20 2015

Henry's law constants were calculated for H2S, CO2, H2O, and H-2 gas absorption in the hydrophobic poly(dimethylsiloxane) (PDMS) solvent using an all-atom (AA) PDMS model. Calculations show that the relative gas solubility at 298 K decreases in the following order: H2S (147) > CO2 (19) approximate to H2O (15) > H-2 (1). Both quantum ab initio (AI) and classical force field (FF) gas-phase calculations show that these gases interact with the PDMS molecule in the order of H2S > CO2 > H-2; they decrease in the same order as gas solubility. The AA PDMS model gives CO2 solubility and PDMS surface tension values close to the experimental data, with differences of 14 and 8%, respectively. In addition, by using both the all-atom and united-atom PDMS models, our simulations suggest that it is challenging to develop a solvent which both has a significantly large surface tension and exhibits large CO2 solubility at high CO2 pressure. Finally, gas absorption effects on PDMS surface tension were investigated. CO2 absorption was simulated to decrease the solvent surface tension by 3 X 10(-3)-4 X 10(-3) N/m compared to the simulated neat PDMS solvent surface tension value of 21 x 10(-3) N/m; CO2 molecules exhibit the largest concentration in the gas-liquid interface region. In contrast, H2S absorption does not decrease PDMS surface tension, which is partially due to the strong H2S-PDMS interaction compared to the CO2-PDMS interaction.


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