Establishment And Applications Of Associating Square-well Chain Fluid Thermodynamic Model With Variable Well-width Range

In this paper, the associating square-well chain fluid equation of state with variable well-width range (ASWCF-VR EoS) was developed by coupling the SWCF-VR EoS with an association model for dimerization. The EoS was used to reproduce the thermodynamic properties of associating fluids such as pVT behavior, phase equilibria, enthalpy changes. In addition, the relationships between the molecular parameters and molar masses of some homologues were investigated. Subsequently, an EoS-based surface tension model was established with the combination of the ASWCF-VR EoS and Butler model.The molecular parameters of78pure associating fluids were obtained by correlating the saturated vapor pressures and liquid molar volumes. The overall average absolute deviations (AADs) between correlated and experimental data are0.76%for vapor pressures and0.75%for molar volumes. The optimized molecular parameters were employed to predict the vaporization enthalpies with an overall AAD of3.84%. The results substantiate the reliability of the ASWCF-VR EoS for pure associating fluids. It is observed that there are the functional relationships between the molecular parameters and molar masses of some homologues, especially the high linear relationships between non-associating parameters and molar masses validated by the high squares(R2>0.98) of their correlation coefficients. Through the relationships, the pVT properties of other homologue members of the homologues were satisfactorily predicted, which laid a solid foundation to develop the group-contribution ASWCF-VR EoS. With the introduction of the standard Lorentz-Berthelot rule and adjustable binary interaction parameters, the ASWCF-VR EoS was applied to fluid mixtures. The vapor-liquid equilibria of binary associating mixtures under both reduced and elevated pressures were successfully correlated with the temperature-independent binary parameters. By use of the binary parameters, the ASWCF-VR EoS can well predict the vapor-liquid equiliria of multicomponent mixtures. Due to the wide temperature ranges and complicated phase coexistence curves, the temperature dependency of the binary interaction parameters are required in calculating the gas-liquid equilibria of CO2+methanol and CO2+ethanol and liquid-liquid equilibria of conventional associating systems.In the ASWCF-VR EoS, ionic liquids (ILs) were treated as the square-well chain fluids with hydrogen-bonding. Their associating parameters were presented according to those of alkanols. while the non-associating parameters were obtained by fitting their experimental densities to the EoS. It is found that the overall AAD for44ILs is only0.06%. Moreover, the non-associating parameters of [Cnmim][NTf2] family vary with molar masses linearly and squares (R2) of the correlation coefficients are greater than0.985. With these expressions, the densities of other members can reliably be predicted over a wide temperature and pressure range. The saturated vapor pressures of several [Cnmim][NTf2] members estimated by ASWCF-VR EoS have the same order of magnitudes with experimental ones and their predicted vaporization of enthalpies are also close to experimental ones. By using the above molecular parameters and temperature-independent adjustable binary parameters, the ASWCF-VR EoS was successfully extended to binary systems containing ILs with an overall bubble pressure AAD of6.89%. The temperature-dependent parameters were employed to describe the solubilities of CO2in ILs and the liquid-liquid equilibria of binary systems containing ILs more accurately. The treatment can lead to the excellent representation of the abrupt slope changes of pressure-composition curves for CO2+IL systems. However, the big deviations between correlated and experimental results for an aqueous IL solution were obseved as a result of the ignorance of the electrostatic interaction.A surface tension model for liquid mixtures was proposed by integrating the ASWCF-VR EoS into the Butler model and applied to various liquid mixtures such as conventional liquid mixtures, aqueous alcohol-amine solution, binary IL-containing systems, binary polymer-containing systems and liquid alloys. In this model, the effect of mixing on molar surface areas were taken into account and the temperature-dependency of binary interaction parameters was neglected. Both the predictions and correlations of binary liquid mixtures were given for comparison and the correlated results were achieved with both composition-independent and composition-dependent binary parameters. The results show that the composition-independent binary parameters caused good agreement between correlated and experimental data for the most of conventional liquid mixtures and the systems with similar components, while the composition-dependency of binary parameters need to be considered for the successful description of the surface properties of the strongly polar systems and the liquid mixtures with distinct components. With the optimized adjustable parameters, the ASWCF-VR EoS satisfactorily captured the surface tensions of multicomponent systems.