Novel Salting-Out-Assisted Liquid-Liquid Extraction for Efficient γ-Valerolactone Recovery from Aqueous Solutions

Different techniques were proposed to recover gamma-valerolactone (GVL) from aqueous solutions (e.g., supercritical CO2 and distillation), but high equipment and operational costs as well as the high-boiling polar nature of this organic solvent have limited its industrial usage. As an example, GVL has garnered attention as a sustainable solvent in lignocellulosic biomass pretreatment through organosolv, producing a cellulose-rich pulp, xylan-derived aqueous solution, and lignin-rich organic phase. The main drawback in this application is the elevated organic solvent consumption, which is responsible for the high cost and environmental impacts of the process. To address these issues, we proposed a novel, low-cost, high-efficiency, salting-out-assisted liquid-liquid extraction method to recover GVL from an organosolv-like solution. The solution containing glucose (0.19% w/w), xylose (1.03% w/w), H2SO4 (1.27% w/w), and GVL (55.54% w/w) was separated into organic and aqueous phases using NaCl and Na2SO4. In the organic phase, GVL concentrations of 84.9 +/- 0.2% with NaCl and 80.1 +/- 0.3% with Na2SO4 were achieved, while GVL recovery reached 92.0 +/- 0.3 and 99.0 +/- 0.6%, respectively. In the aqueous phase, glucose and xylose recoveries of 86.49 +/- 0.4 and 88.2 +/- 0.3% were, respectively, obtained with Na2SO4. To further enhance sustainability, approximately 30% of Na2SO4 dissolved in the aqueous phase was removed through refrigeration. Finally, a proper organosolv solution was tested to assess the efficacy of the proposed process. The proposed novel method, using Na2SO4, achieved similar or better recoveries compared to classical techniques such as supercritical CO2 and distillation. To conclude, this method could lower the cost barrier, making the use of the GVL aqueous solution economically sustainable.