Polar soft-SAFT: theory and comparison with molecular simulations and experimental data of pure polar fluids

Abstract

The consideration of polar interactions is of vital importance for the development of predictive and accurate thermodynamic models for polar fluids, as they govern most of their thermodynamic properties, making them highly non-ideal fluids.

Quantifying the effect of polarity on the behavior of mixtures of n‐alkanes with dipolar solvents using polar soft‐statistical associating fluid theory (Polar soft‐SAFT)

“…Polar soft-SAFT EoS 34 expresses the residual Helmholtz free energy density (a res ) of a fluid as the sum of the different microscopic contributions to its total free Helmholtz energy attributed to different molecular effects, written for pure fluids as:…”

“…Additional details on the expressions of soft-SAFT along with its extension and application to pure polar fluids, polar soft-SAFT, can be found in the original works. 34,43,44 Extending the computations of polar soft-SAFT to mixtures is straightforward for the chain, association, and polar terms as they are explicitly written for mixtures. The reference term is applied to multicomponent mixtures by using the generalized Lorentz-Berthelot (LB) combining rules, used to calculate the crossed size, σ ij , and energy, ε ij :…”

“…[21][22][23] A number of polar versions of SAFT-based EoSs have been developed in recent years, explicitly taken into account the polar nature of substances, including PC-SAFT, 9,[24][25][26][27][28][29][30] GC-SAFT, 31 SAFT-VR, 12,32,33 and more recently, soft-SAFT. 34 Nonetheless, a major hurdle in the application of most of these models to polar systems is associated with difficulties in converging to a unique set of pure polar fluid molecular parameters, when four or more parameters are regressed simultaneously. 24,27,35,36 This degeneracy of the parameter search space and appearance of many possible sets that can accurately represent the pure fluid is faced for both nonpolar and polar SAFT models.…”

“…Recently, we have extended the soft-SAFT EoS 43,44 to the explicit modeling of polar fluids, namely, polar soft-SAFT EoS. 34 Moreover, we have established a consistent and simplified procedure for the regression of molecular parameters of pure polar fluids, through fixing not only the dipole/quadrupole moment to the experimental value as seen in previous works, 12,24,26,[28][29][30]35,37,40 but also fixing a priori the fraction of polar segments within the molecule (socalled x p parameter). In this manner, the robustness of the model is preserved as only fitting the three nonassociating parameters (m, σ, ε/k B ) is required, similar to the case of nonassociating polar fluids such as polar aprotic solvents.…”

“…The dipolar fluids examined in this work include 1-hexene, chloroform, dichloromethane, tetrahydrofuran, acetone, dimethylformamide (DMF), and N-methyl pyrrolidone (NMP). These fluids have been chosen for practical reasons given their wide industrial applications, being almost industry standards for a wide range of applications 2,3,7,45 as well as more fundamental reasons, as they present a variable range of dipole moment from low to high (0.3 < μ < 4.0 D) that allows to effectively test the limits of our simplified modeling approach for polar fluids, 34 and the variety in their polar strength leads to varying phase equilibria behavior, VLE and LLE, when extended to binary mixtures with n-alkanes. Overall, it is intended to assess the validity of our simplified modeling approach and to test the predictive capability and robustness of polar soft-SAFT for these challenging mixtures.…”