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SAFT-VR Mie is extended to quadrupolar molecules and their mixtures by incorporating an explicit Helmholtz contribution for quadrupole–quadrupole interactions. Two quadrupolar terms are considered:...

This work expands the scope of the SAFT-VR Mie framework by considering its application and that of its polar variant (SAFT-VR Mie-GV) to real phase behavior in alcohol/n-alkane and alcohol/water systems. This requires supplementing existing parameters for alcohols with parameter sets for all primary and secondary alcohols in the C1–C5 range. Parameter degeneracy is overcome using a novel variation of the discretized regression approach, by considering the average absolute deviations (AADs) for the mixture VLE resulting from each regressed parameter set in the discretized eAB/k–np space. The resulting parameter sets exhibit excellent predictions for the alcohol/n-alkane and alcohol/water systems. The comparable results of the polar and nonpolar variants suggest that an explicit polar term is not necessary to describe the phase behavior of alcohols in the considered mixtures. The choice of association scheme is more significant, with the 2C scheme yielding excellent predictions for alcohols in mixtures wit...

The Cubic Plus Association (CPA) equation of state (EoS) is extended with the theory for quadrupolar molecules of Gross, yielding the CPA-G model. CPA-G is compared to the recently developed qCPA, which uses the polar theory of Larsen and coworkers. Each model requires an additional adjustable parameter for quadrupolar molecules. The models are evaluated by means of their ability to model the phase equilibria of binary mixtures of CO2 or benzene with n-alkanes and 1-alkanols, as well as binary mixtures of quadrupolar molecules. A refined technique of accounting for cross-association in the CO2 + 1-alkanol systems is proposed, allowing an improved description of these systems without the use of a binary interaction parameter. Accounting for cross-association in the benzene + 1-alkanol systems investigated in this work did not lead to improved results. Both CPA-G and qCPA provide significant improvements over nonpolar CPA in both n-alkane and 1-alkanol mixtures, with excellent results obtained in the subcritical region without the use of binary interaction parameters. qCPA continues to provide excellent predictions in the supercritical region, while CPA-G overestimates the solubility pressures in the supercritical region. Both quadrupolar models can qualitatively predict the existence of three-phase equilibrium in the CO2 + n-alkane and CO2 + 1-alkanol systems. The simple combining rules used for cross-quadrupolar interactions in both CPA-G and qCPA do not take molecular orientation into account and are unable to truly capture the phase behaviour in the CO2 + benzene system.

The phase behaviour of three (1-decanol + n-dodecane)-mixtures in the presence of supercritical CO2 was investigated. Phase equilibrium measurements were conducted at temperatures ranging between 308 K and 348 K, with solute mass fractions ranging between 0.017 and 0.621. The experimental data emphasize the dominant influence of n-dodecane in the solute mixture. It has been proposed that the presence of n-dodecane interrupts the formation of alcohol multimers and thus significantly improves the solubility of 1-decanol in supercritical CO2. The ternary system also displays a slight cosolvency effect. The experimental data was used to determine solute–solute binary interaction parameters for the RK-Aspen model in Aspen Plus®. Addition of these interaction parameters improved the correlative capability of the equation of state allowing for future improved process modelling of systems involving these components.