Liquid–Liquid Equilibrium and Interfacial Tension of Hexane Isomers–Methanol Systems

Abstract

Liquid–liquid equilibrium (LLE) and therefore interfacial tension are highly dependent on molecular architecture. In processes, where branched molecules are involved, these properties often cannot be measured; therefore, there is a need for thermodynamic modeling to make these properties accessible. A methodology, which allows for the prediction of liquid–liquid equilibria of systems containing branched molecules, was developed recently, where the lattice cluster theory is combined with the chemical association lattice model. In this contribution, it was proved whether the methodology can consider small changes in molecular architecture. Therefore, binary LLE of methanol and four hexane isomers were estimated and predicted. All predicted LLE showed a very good agreement with the experimental data. Additionally, the interfacial tension and interfacial concentration profiles were estimated for the investigated systems and calculated by the density gradient theory. For that, its influence parameter was adjusted to a single data point.

Calculation of Droplet Coalescence in Binary Liquid–Liquid Systems: An Incompressible Cahn–Hilliard/Navier–Stokes Approach Using the Non-Random Two-Liquid Model

“…For this parameter, droplet shape was investigated in order to determine the effect of κ on interfacial stability and thickness, as well as physical parameters such as interfacial tension. However, typical values of the influence parameter, as reported in the literature, , are in the order of magnitude from 10 –6 to 10 –7 . Since these values require very fine grids or restrict the study to sub-microscale simulations, we preliminarily chose higher values of 10 –4 (case a), 5 × 10 –5 (case b), and 10 –5 (case c), respectively, to obtain feasible simulation times for technically relevant scales.…”

Modeling Interfacial Properties with Spot-DGT-ePC-SAFT for Binary Mixtures Including Ionic Liquid-Based Systems

“…Several theoretical models have been developed to study the microscopic structure of the interfacial phase. Among them, density gradient theory (DGT) has been widely accepted as a promising model to describe the interfacial properties of fluids, due to its accuracy and simplicity in the calculation. − DGT with the influence parameters of pure substances adjusted from their surface tensions can be used to predict other interfacial properties (density profile, interfacial adsorption, and interfacial thickness) for pure system and the interfacial properties of their mixtures. − However, the work on the IL-containing mixtures is still limited, and the only work was conducted by Oliveira et al, where the soft-statistical associating fluid theory (SAFT) was combined with DGT. Furthermore, IL–CO 2 is an important system for developing an IL-based technology for CO 2 separation, while the theoretical model based on DGT for such a system has not been available.…”

“…Principally, DGT (i.e., full DGT) can be extended to the mixtures for common substances. − ,− However, for the IL-based systems, the extension can be a challenge due to the characterization of ILs with negligible vapor pressures. For example, in ePC-SAFT, the ionic term was used to describe the long-range electrostatic force between the cation and anion with a significant contribution, even at a very low density, leading to that the equilibrium vapor phase of ILs cannot be found at the packing fraction higher than 10 –12 and the mole fraction of IL greater than 10 –10 . , This is reasonable considering the negligible vapor pressure of ILs, and numerically, for a pure IL, this is not a serious problem in solving DGT. , While for IL-based mixtures, if the equilibrium composition cannot be solved, a serious numerical problem will be generated when calculating the density profile of vapor–liquid interphase because the local chemical potential does not equal the bulk chemical potential when approaching to the vapor phase.…”

Liquid‐Liquid Equilibrium and Interfacial Properties of the System Water + Hexylacetate + 1‐Hexanol

“…Such a theoretical framework, which permits the calculation of the interfacial tension related to the LLE was established twenty years ago [7]. The basic idea of this approach is the applica-tion of the density gradient theory, originally developed by Van der Waals [8] and rediscovered by Cahn-Hilliard [9], to incompressible fluids, where the Helmholtz energy can be replaced by the Gibbs energy and consequently the thermodynamic properties can be modelled with a g E model rather than an equation of state [10,11] The method was used for different binary [12][13][14][15][16][17][18][19][20][21], ternary [14,21,[22][23][24][25][26] and quaternary mixtures [21,[27][28][29]. Recently, also the time-dependency of the interfacial tension caused by diffusion [14,16,24,27] or caused by a chemical reactions [21,29] were studied.…”