Highly efficient separation of adipic and glutaric acids from aqueous solutions by phosphonate-based deep eutectic solvents: Experimental and molecular insights

Adipic acid is used as a chemical feedstock to produce high-value products such as nylon, polyester, and plasticisers. However, the production process generates highly acidic wastewater containing adipic acid and its by-product, glutaric acid. Traditional treatment methods are often inefficient or environmentally harmful. In this study, four deep eutectic solvents (DES) were synthesized using tributyl phosphate (TBP) and trioctylphosphine oxide (TOPO) as the raw materials, combined with 1-octanol and DL-menthol. The extraction process was optimized through comprehensive experimentation and molecular simulation. TOPO/DL-menthol DES achieved 97 % recovery of adipic acid and 87 % recovery of glutaric acid within a single 5-min extraction step at 20 °C. This extractant demonstrated exceptional reusability, with structural stability confirmed through characterization. The extraction mechanisms were elucidated via thermodynamic studies, quantum chemical calculations, and molecular dynamics simulations. This study provides a green and recyclable solution for the recovery of carboxylic acids.