Solvent Selection for the Extraction of 2-Phenylethanol from Aqueous Phases: Density and Viscosity Studies

Abstract

An interesting alternative to the chemically produced 2-phenylethanol is its biotechnological synthesis. However, one of the drawbacks of this process is that the synthesized solute is typically toxic (nonbiocompatible) to the producing microorganism in the aqueous phase. Thus, an in situ product removal technique is recommended for separating the product, for instance, by liquid–liquid extraction using a hydrophobic and biocompatible solvent. First, the liquid–liquid equilibrium between 2-phenylethanol + water was measured between 293.15 K and 323.15 K at 101.3 kPa, and modeled with PC-SAFT. Then, life cycle analysis using CHEM21 methodology, experimental data, and the perturbed-chain statistical associating fluid theory (PC-SAFT) were used to evaluate the applicability of potential solvents for 2-phenylethanol recovery from water by calculating the partition coefficient of the solute in the solvent + water biphasic system. The solvents selected were methyl isobutyl ketone, 2-methyl-3-buten-2-ol, 2-octanone, and dibutyl phthalate. Thus, density and viscosity were measured for pure 2-phenylethanol, all the selected solvents, and the binary mixtures of 2-phenylethanol and each solvent. The temperature range for all the measurements was from 293.15 K to 333.15 K at 101.3 kPa. Excess volumes were calculated from the density of mixtures, obtaining negative deviations from ideality for 2-phenylethanol + 2-methyl-3-buten-2-ol, 2-phenylethanol + methyl isobutyl ketone, and 2-phenylethanol + 2-octanone and positive deviations for 2-phenylethanol + dibutyl phthalate. The density was modeled with PC-SAFT and the viscosity with PC-SAFT + entropy scaling. The information on the molecular interactions between 2-phenylethanol and the extracting solvents, provided by the models fed from the performed experiments, allows reducing the further experimental load when designing the in situ extraction process from a fermentation broth.