Liquid-liquid equilibria for applying solvent extraction of odoriferous compounds from bioglycerol

Due to a surplus of bioglycerol caused by the rapid increase in biodiesel production, its purification is relevant for adding value to this biodiesel coproduct. Usually, bioglycerol is purified by vacuum distillation, although it is a costly and energy-intensive process. Conversely, solvent extraction could be an interesting alternative for extracting compounds with similar solubility, such as the odoriferous present in crude bioglycerol. Considering that solvent extraction is subjected to the liquid-liquid equilibrium, this work reports phase equilibrium data of a model system comprising glycerol + H₂O 16% w/w as the diluent, propyl acetate as the solvent, and butyric acid as the solute, at temperature of 303.2 K and local atmospheric pressure of 94.5 kPa. The acid and water compositions of the equilibrium phases were quantified by acid–base titration and Karl Fischer titration, respectively. The solvent compositions were calculated using correlations based on solubility curves determined by the cloud point method. Subsequently, the mass fractions of glycerol were obtained by difference to unity. Propyl acetate proved suitable for this purpose, generating wide immiscibility region and strong tie-line inclination towards extract phase. The parameters of the molecular models NRTL and UNIQUAC were fitted to the experimental data, resulting in global deviations on a mass basis of no more than 0.36% for the calculation of equilibrium compositions. The group-contribution methods UNIFAC-LL and UNIFAC-Dortmund failed to predict the raffinate phase, revealing the relevance of experimental data. This is a fundamental study for applying solvent extraction in bioglycerol purification. Reducing the energy demand of this process adds value to the entire biodiesel production chain and contributes to the advancement of the bioeconomy, aiming at lower reliance on fossil fuels.