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

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

Viscosity Measurements of Two Potential Deepwater Viscosity Standard Reference Fluids at High Temperature and High Pressure

This paper reports high-pressure viscosity measurements for Krytox GPL 102 lot K2391 and tris­(2-ethylhexyl) trimellitate (TOTM). These two viscous liquids have recently been suggested as potential deepwater viscosity standard (DVS) reference fluids for high temperature, high pressure viscosity studies associated with oil production from ultradeep formations beneath the deepwaters of the Gulf of Mexico. The measurements are performed using a windowed, variable-volume, rolling-ball viscometer at pressures between 7 and 242 MPa and temperatures between 314 and 527 K with an expanded uncertainty of 3% at a 95% confidence level. The viscosity results are correlated using an empirical temperature/pressure-dependent function and a modified Vogel–Fulcher–Tammann (VFT) Equation. The present viscosity data for TOTM and Krytox GPL 102 lot K2391 are in good agreement with the available reported data in the literature at lower temperatures and pressures. The viscosity values of TOTM and Krytox GPL 102 lot K2391 are 9.5 mPa·s and 25 mPa·s, respectively, at 473 K and 200 MPa, whereas the desired DVS viscosity value at this condition is 20 mPa·s. Although the viscosity of Krytox GPL 102 lot K2391 is closer to the targeted value, a comparison of the present viscosity results with data obtained for lot K1537 indicates a very large lot-to-lot variation of the viscosity for this polydisperse perfluoropolyether oil, which represents a significant deficiency for a DVS

High-Temperature, High-Pressure Volumetric Properties of Propane, Squalane, and Their Mixtures: Measurement and PC-SAFT Modeling

This study reports the high-temperature, high-pressure density data for propane, squalane, and their binary mixtures for five compositions at temperatures to 520 K and pressures to 260 MPa. The density measurements are obtained with a floating-piston, variable-volume, high-pressure view cell. From the density data, the isothermal and isobaric excess molar volumes upon mixing are computed. For the mixture compositions studied here, the excess volume is mostly negative, showing a minimum at 0.6550 mole fraction of propane and becomes less negative as the propane concentration increases. The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) provides good representation for the experimental data. A mean absolute percent deviation (δ) of 1.4% is obtained with the PC-SAFT EoS when using propane and squalane pure component parameters fit to density data at high-temperature, high-pressure conditions