Intermolecular interactions of phenolic mixtures studied to aid implementation of bio-based phenol use in the polycarbonate industry

Renewable phenol can be obtained from pyrolytic bio-oil, which contains not only phenol, but also other phenolic compounds, oxygenates and carboxylic acids. For applications of renewable phenol in production of polycarbonates, it is required to upgrade and separate intermediate products and phenol. To support separation and purification approaches for bio-based phenol, interactions related to separation and purification of phenol and phenolics have been studied together with extraction results, focusing on phenol separation from low concentration aqueous streams by liquid-liquid extraction. The effect of the presence of other components and the effect of the substitution of the phenols were studied at 293 < T/K < 333. High phenol distribution ratios were obtained, the presence of especially polar impurities decreased the distribution ratios for phenol. Increasing the ratio of phenol to extractant weakened the primary hydrogen bond as a result of homoconjugate competition of phenol. Analysis with isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy showed that interaction with phenol is based on hydrogen bonding, not proton transfer. Thus extractants with a high hydrogen bond basicity have a high potential. This explains that, although 2-nitrophenol and thiophenol have a lower pKa value than phenol, their interaction with the phosphine oxide extractant is weaker. (C) 2021 The Author(s). Published by Elsevier Ltd.