Comparative Study of Liquid–Liquid Phase Equilibria of the Type II Systems Water + Carboxylic Acids (C₅ and C₆) + Acetate Esters: Measurement and Correlation

Abstract

A study on the type 2 liquid–liquid equilibrium (LLE) behavior of the water + valeric or caproic acids + acetate esters (n-propyl, isopropyl, n-amyl, and n-hexyl acetates) ternary systems was performed at T = 298.2 K and p = 101.3 kPa. Solubility and tie-line data were experimentally determined using cloud point and HPLC methods, respectively. The results were validated through acid–base and Karl Fischer titration methods. For these systems, the thermodynamic models of NRTL and UNIQUAC were successfully applied to fit the experimental tie-lines and the values of the binary interaction parameters were obtained. Evaluation of the capacity of each solvent was performed using the calculation of distribution coefficients and separation factors. The influence of extraction temperature and the type of the esteric solvent on the immiscibility region was found to be minor. As a result, all the chosen acetate esters have relatively high separation factors and are suitable separating agents for aqueous valeric or caproic acid mixtures.

Comparative Evaluation of the Liquid–Liquid Equilibria of the Extraction of Valeric or Caproic Acids from Water by Esters

“…Table lists the equilibrium compositions (in mass fraction) on the solubility curve for the mixtures {water–VA or CA–cyclic and aromatic esters (CHA, BA, and BB)}. The experimental equilibrium data for the similar ternary systems containing water, acids, and some acetate esters have been previously reported by the authors . The solubility ternary phase diagrams for the studied mixtures at 298.2 are shown in Figure a,b.…”

“… a Standard uncertainties u are u ( T ) = 0.1 K u ( n ) = 0.0005, u ( p ) = 1 kPa, and u ( w ) = 0.006. b The experimental LLE compositions for the (water + VA or CA) binary mixtures have previously been reported by the authors …”

“…Table summarizes the experimental refractive index and density values along with the literature data for the used solvents. − The experimental data for water and the acids (VA and CA) have been previously reported by the authors . Thus, the experimental and literature − data of refractive index and density of water and the acids have not been shown in Table .…”

“…As a continuation of our studies on these systems, the three nonaliphatic esters (two aryl and one cyclic ester) were examined as extracting solvents for aqueous mixtures of VA and CA. Moreover, the obtained LLE result can be compared with that of previous study …”

“…These fatty acids are partially water-miscible and can be extracted from water using different solvents with relatively high efficiency. Among many organic solvents, which have been used as extractants in various LLE systems, − esters are appeared to be suitable solvents for the efficient extraction of the organic acids from aqueous solution. This group of solvents has various advantages of low toxicity, low solubilities in water, high distribution constants and selectivities, and others.…”