Sustainable Recovery of High Added-Value Vanilla Compounds from Wastewater Using Green Solvents

The growing demand for high added-value products, such as vanilla-derived compounds, and increasing environmental regulations make evident the need to find new sustainable solvents for extraction processes, which meet both legislative requirements and expected yields. Vanilla-derived compounds are known for their antioxidant and beneficial properties for human health. These compounds can be recovered from effluent streams, promoting decontamination and revaluation of wastewater. The potential of using neoteric solvents, i.e., biobased solvents and hydrophobic eutectic solvents, as an alternative to conventional volatile organic solvents, such as ethyl acetate, for sustainable recovery of vanilla-derived compounds through liquid-liquid extraction from aqueous environments was investigated. Three biobased solvents (2-methyltetrahydrofuran, cyclopentyl methyl ether, and D-limonene) and three hydrophobic eutectic solvents constituted by menthol and organic acids (1:1 DLmenthol:octanoic acid, 1:1 DL-menthol:decanoic acid, and 2:1 DL-menthol:dodecanoic acid) were evaluated. The extraction process was optimized in terms of the stirring time and solvent:feed volume ratio. The effect of the initial solute concentration was also analyzed. The extraction efficiency of solvents was determined by UV-visible spectrophotometry and high-performance liquid chromatography with diode-array detection. The experimental results indicated that 2-methyltetrahydrofuran yielded the highest extraction efficiency from a vanilla bean extract solution for both vanillin (95.37%) and vanillic acid (91.96%) with good repeatability (RSD < 0.40%). Regarding the rest of the neoteric solvents, cyclopentyl methyl ether and hydrophobic eutectic solvents provided extraction values between 31.6 and 95.4% for both vanilla-derived compounds, while D-limonene was significantly less effective. Finally, a solvent recycling and reuse study was successfully carried out, showing that 2-methyltetrahydrofuran stands out as a promising biobased extraction solvent for sustainable recovery of valuable vanilla constituents.