Liquid–Liquid Equilibria for (Water + Propionic Acid or Butyric Acid + 2-Octanol) at 298.2, 308.2, and 318.2 K

Solubility and tie-line compositions were determined for the aqueous mixtures of propionic and butyric acids with 2-octanol at T = (298.2, 308.2, and 318.2) K and 101 kPa. The ternary mixtures display type-1 liquid–liquid phase diagrams. To correlate the experimental tie-line data, the thermodynamic models of NRTL and UNIQUAC were used. The calculated binary interaction parameters in the NRTL model were reliable with the experimental liquid–liquid equilibrium (LLE) data through the model of Marcilla et al. The capacity of 2-octanol as a solvent was evaluated through the determination of solute distribution coefficient and selectivity. The effect of temperature on the biphasic area was found to be small. The selected solvent has a reasonably high extraction capacity and may serve as a suitable separating agent for aqueous propionic or butyric acid mixtures. However, butyric acid is more hydrophobic in nature, exhibits larger solute distribution coefficients and selectivities than propionic acid, and may be better extracted by the solvent.