Switchable solvents used in green process engineering

The increasing demand for sustainable chemical processes has intensified research into green alternatives to conventional organic solvents. Switchable solvents (SS) are a promising class of environmentally friendly solvents whose polarity and miscibility can be reversibly tuned by external triggers such as CO₂, base or acid addition, or a mild temperature shift. This dynamic property allows the same solvent to act in multiple roles—extraction, separation, and regeneration—while enabling recyclability and reducing environmental impact. In this study, SS were investigated for their applicability in green process engineering, with a focus on lignocellulosic biomass fractionation and solvent recyclability. Vineyard pruning residues (VPR), a widely available lignocellulosic waste, were subjected to pretreatment with different solvent systems, in their native and switched states. Pretreatment efficiency was evaluated through lignin solubilization, solid recovery, and structural characterization by UV–Vis spectroscopy, thermogravimetry and FTIR. Complementary thermochemical methods were also applied, both to broaden lignin valorization and to assess whether lignin-derived phenolics could serve as candidates for a new class of switchable solvents. Additionally, microbial biomass (Paracoccus carotinifaciens, Panaferd® AX) was employed as a model to demonstrate solvent switching and reuse. Fatty acid–based SS were cycled through base-induced switching, enabling solvent regeneration across multiple extractions. Overall, the findings demonstrate that switchable solvents provide a versatile and recyclable platform for green process engineering, supporting both biomass valorization and the development of sustainable, circular solvent systems.