Enhancing aqueous systems fermentability using hydrophobic eutectic solvents as extractans of inhibitory compounds

Biomass can be transformed into energy, high value chemicals or bioethanol. Nevertheless, the production of the latter is limited by the presence of inhibitory compounds that hinder the sugar fermentation process. This paper proposes menthol-based Hydrophobic Eutectic Solvents (HESs) as green solvents in the liquid extraction of phenolic compounds from diluted aqueous solutions. In particular, the main goal of the work is to analyse the capacity of the HESs to extract phenolic compounds (phenol, guaiacol and syringol) and glucose (as model sugar), since both types of compounds are present in the aqueous phase generated after washing with water the oil obtained in the fast pyrolysis of the biomass. As this is a preliminary study, two model mixtures constituted by solute (phenolic compound or glucose) and deionized water were used. Once HESs were prepared using menthol and three organic acids (octanoic acid, decanoic acid and dodecanoic acid), liquid–liquid extractions were performed in order to test the ability of these solvents to extract the abovementioned compounds from water. Firstly, stirring and centrifuging times were optimized and the effect of varying the solvent/feed ratio and the initial concentration of the solution {phenolic compound + water} were studied. Afterwards, since the goal of this work is to remove phenols from water to enhance sugars fermentability, the liquid extraction of glucose from water using the same HESs were also experimentally carried out at the optimized conditions. The obtained results are very promising, as HESs can easily extract phenols but not glucose, which would improve the subsequent sugar fermentation process.