Thermodynamic properties and vapor–liquid equilibria of associating fluids, Peng–Robinson equation of state coupled with shield-sticky model

Combining Peng–Robinson (PR) equation of state (EOS) with Liu et al.’s association contribution derived from shield-sticky model (SSM), a new cubic-plus-association (CPA) EOS is proposed to describe the thermodynamic properties of pure associating fluids and their mixtures. The CPA-SSM EOS contains five molecular parameters (a0, c1, b, ω and δɛ/k) for the pure associating fluids, while for non-associating fluids it reduces to PR EOS with three molecular parameters (a0, c1, b). The molecular parameters are obtained by fitting the saturated pressures and/or liquid molar volumes at wide temperature ranges. The overall average absolute deviations (AADs) of 58 pure associating fluids and 20 non-associating fluids are 0.74% and 0.54% for saturated vapor pressure, 2.00% and 1.85% for liquid molar volumes respectively. The enthalpies of vaporization for 13 pure associating fluids are well predicted by using these molecular parameters. The molecular parameter b for homologous substances shows a good linear relationship with respect to their corresponding molecular weights. Using one temperature-independent binary adjustable parameter kij, satisfactory results of vapor–liquid equilibria (VLE) for both self- and cross-associating systems are obtained. The overall AADs of the equilibrium temperatures, pressures and vapor phase mole fractions are 1.46 K, 1.26 kPa and 0.0197 respectively for 25 self-associating systems, and 0.75 K, 0.50 kPa and 0.0155 respectively for 29 cross-associating systems. Other caloric properties such as the excess molar enthalpies of mixing are also successfully computed. The CPA-SSM EOS proposed has been proved to have comparable accuracy as other models but with much simpler form.