| dc.description.abstract | The PC-SAFT equation of state (EOS) is widely used for estimating the thermodynamic properties of pure substances, drug solubility, and predicting phase equilibrium in mixed solutions. In the PC-SAFT EOS, the number of pure substance parameters required to describe these molecules varies according to the type of substance. For non-associating molecules, three parameters are needed: the segment diameter (σ), the number of segments (m), and the interaction energy parameter between the chain molecules (ϵ). For associating molecules, two additional parameters are required to describe the intermolecular associating forces: the association volume (κAB) and the association energy parameter (ϵAB). Furthermore, a specific association scheme is necessary to describe the manner of molecular association. When applying the PC-SAFT EOS to phase equilibrium in mixed solutions, binary interaction parameters (k_ij) are used to enhance the model′s accuracy. These k_ij parameters are typically obtained by regressing phase equilibrium experimental data of mixed solutions. In this study, we attempt to estimate the k_ij parameters required for the PC-SAFT EOS using the COSMO-SAC model. Specifically, we adjust the k_ij values so that the PC-SAFT EOS can provide an excess Gibbs free energy (▁Gex) that matches the COSMO-SAC model under given system conditions, thereby obtaining the required k_ij parameters. We hope that this method will enable the PC-SAFT EOS to accurately predict fluid phase behavior in systems where the pure substance parameters and molecular structures are known, thereby avoiding reliance on experimental data for mixed fluids.
In this study, we investigated the vapor-liquid equilibrium (VLE) of 273 binary mixture systems composed of 92 substances, including 179 systems consisting of non-associating molecules and 94 systems containing associating molecules. The results show that the method developed in this study performs excellently in VLE prediction. For non-associating molecule systems, the average absolute relative deviation in pressure (AARD-P) is 4.13%, and the average absolute deviation in vapor phase mole fraction (AAD-y) is 1.48%. For systems containing associating molecules, the AARD-P and AAD-y are 7.76% and 3.44%, respectively. In contrast, when the PC-SAFT EOS predicts phase equilibrium without considering k_ij parameters, the AARD-P and AAD-y are 8.92% and 3.27% for non-associating molecule systems and 19.14% and 5.03% for systems containing associating molecules, respectively. The above results indicate that in the absence of experimental data to regress and obtain the necessary k_ij parameters for the PC-SAFT EOS, the method proposed in this study can provide more accurate and reliable phase equilibrium predictions compared to the PC-SAFT EOS without k_ij parameters. The advantage of the proposed method compared to COSMO-SAC lies in its ability to accurately predict VLE under high-pressure conditions, especially when system conditions exceed the critical point of one component in the mixture. On the other hand, COSMO-SAC model requires experimental vapor pressure values for VLE calculations, whereas the PC-SAFT can estimate vapor pressures of pure substances with known pure substance parameters. This advantage allows for VLE prediction even in the absence of experimental vapor pressure data. Furthermore, the proposed method maintains high predictive accuracy across a temperature range of 100 K in high-pressure systems. This capability is particularly important in chemical engineering and industrial applications, as it effectively handles various operating conditions from low to high temperatures and pressures. To verify the effectiveness of the k_ij parameters obtained by the proposed method, we compared the k_ij parameters obtained from this work with those optimized through experimental VLE data to confirm the consistent temperature-dependence of k_ij parameters from these two methods. | en_US |