(161d) Evaluation of Amine-Free Switchable Solvents for Biomass Extractions

This work evaluates novel switchable solvents for their properties and potential for product recovery. Switchable solvents are a class of chemicals that can reversibly transition between two distinct forms in response to an external trigger. A well-known example is dimethylcyclohexylamine (DMCHA), which shifts from a hydrophobic to a hydrophilic state upon exposure to water and carbon dioxide. The amine can be switched back to its hydrophobic state by removing CO₂. This switchability potentially enables non-distillation based product recovery and solvent recycling.

While amine-based switchable solvents show promise for extractions, their inherent toxicity and corrosiveness present significant challenges. To address these concerns, this work explores a new class of greener, amine-free switchable hydrophilicity solvents (SHS), using carboxylic acids. These carboxylic acids are hydrophobic in their pure form. Upon the addition of an aqueous base, the acid undergoes deprotonation, forming a hydrophilic mixture. This process is reversible, as introducing CO₂ restores the mixture to its hydrophobic state.

Potential amine-free candidates were screened for switchability, optimizing key parameters such as the acid-to-base ratio, water-to-acid ratio, and base type. Selected candidates, along with their optimized parameters, were then tested for their efficacy in extracting valuable components from biomass. A key separation explored in this study is the extraction of the bio-monomer betulin from birch bark. Betulin, which is hydrophobic in nature, is extracted from birch bark in the hydrophobic SHS. Addition of aqueous NaOH allows for the solvent to be switched to its hydrophilic state and the recovery of a betulin-rich phase. The optimized efficiency of this extraction is quantified via product recovery, selectivity, and solvent recyclability.