An Equation of State Based on PC-SAFT for Physical Solvents Composed of Polyethylene Glycol Dimethylethers

Abstract

A technical equation of state (EoS), according to the perturbed chain statistical associating fluid theory (PC-SAFT), is developed for solvent blends composed of polyethylene glycol dimethylethers (PEGDMEs/glymes), that is, CH3O[CH2CH2O]nCH3 with n = 3, ..., 9. These solvent blends are employed in industry under the commercial names Selexol or Genosorb, primarily for the physical absorption of H2S and CO2 from acid gases. The molecular parameters for the EoSs of the pure fluids comprising the solvent, notably for the n = 3 and 4 members of the homologous series, are obtained by fitting the PC-SAFT EoS to published vapor pressure and liquid density data. Because of the limited availability of experimental data for the glymes with n ≥ 5, PC-SAFT is used as a predictive tool to determine the molecular parameters for the n = 5, ..., 9 members of the homologous series. To exploit the extrapolative capabilities of PC-SAFT, the n = 1 and 2 members of the homologous series are included in this study. The mixture of glymes is modeled using the van der Waals one-fluid mixing rules with the Lorentz–Berthelot combining rules, whereby the binary interaction parameters kij among the members of the homologous series are all set to zero. The performance of the mixture EoS is assessed by a comparison of predicted properties with experimental data. The thermodynamic model is also briefly applied to describe the vapor–liquid equilibrium behavior of glymes and their blends with CO2. The comparison with available experimental data shows that the resulting model provides a description of the thermodynamic behavior of this system suitable for engineering purposes.