Fractionation of phenolic compounds from lignin depolymerisation using polymeric aqueous biphasic systems with ionic surfactants as electrolytes

Lignin-based materials and chemicals represent a large class of potential added-value compounds for biorefineries; however, the difficulty in fractionating heterogenous phenolic compounds that result from lignin depolymerisation still remains a challenge. Herein, a set of polymer-based aqueous biphasic systems (ABS) comprising sodium polyacrylate (NaPA 8000) and polyethylene glycol (PEG 8000), in which ionic surfactants and ionic liquids are used as electrolytes at concentrations below 1 wt%, is investigated for this purpose. Binodal curves were determined for three electrolyte concentrations, namely, 0.01, 0.1 and 1.0 wt%, and an intermediate electrolyte concentration was selected to investigate the partition of five phenolic compounds, caffeic acid, vanillic acid, gallic acid, vanillin and syringaldehyde, on these systems. The results show that the ABS allow the manipulation of the partition of the five phenolic compounds, which culminates with their selective isolation, with vanillin selectivities of S-VN/VA = 23.75, S-VN/GA = 12.52 and S-VN/CA = 8.47. The electrolyte nature seems to play an important role in the fractionation of the phenolic compounds, due to the difference in their hydrophobic nature and speciation. This study demonstrates the ability of polymeric-based ABS, using ionic surfactants or ionic liquids as electrolytes, to efficiently separate and isolate five structurally similar phenolic compounds using a low-cost and very eco-friendly integrated process.