Separation of butyric acid from aqueous media using menthol-based hydrophobic deep eutectic solvent and modeling by response surface methodology

In the last decade, research on deep eutectic solvents used in many fields with different roles in chemistry has attracted great interest. Literature reviewing shows that one of these solvents' most common usage areas is extraction applications as green extraction media, especially to recover biomass conversion products. In this work, hydrophobic deep eutectic solvents (HDES) with different hydrogen bond donors (HBD) and hydrogen bond acceptor (HBA) were mixed and used as a solvent to separate butyric acid from aqueous solutions. Menthol (M)-based HDESs were prepared using three long-chain carboxylic acids (nonanoic acid (NA), decanoic acid (DA), and dodecanoic acid (DDA)) and trioctylphosphine oxide (TOPO) in different molar ratios of binary combinations. Density and refractive index values of HDES were determined. To assess the obtained results, extraction efficiency (E%) and distribution coefficient (D) values were calculated. It was observed that HDES containing menthol and TOPO were extracted more than 90% of butyric acid from the water phase. The transition of butyric acid from the aqueous to the organic phase was demonstrated by FTIR analysis. The Box-Behnken method based on response surface methodology (RSM) was used to explore the impacts of the experimental conditions on reactive extraction yield and to obtain a model equation for the separation of butyric acid from its aqueous solution using M:TOPO hydrophobic deep eutectic solvent.