Liquid–liquid extraction of levulinic acid from aqueous solutions using hydrophobic tri-n-octylamine/alcohol-based deep eutectic solvent

Abstract

Levulinic acid (LA) is one of the top-12 most promising biomass-based platform chemicals, which has a wide range of applications in a variety of fields. However, separation and purification of LA from aqueous solution or actual hydrolysate continues to be a challenge. Among various downstream separation technologies, liquid–liquid extraction is a low-cost, effective, and simple process to separate LA. The key breakthrough lies in the development of extractants with high extraction efficiency, good hydrophobicity, and low cost. In this work, three hydrophobic deep eutectic solvents (DESs) based on tri- n -octylamine (TOA) as hydrogen bond acceptor (HBA) and alcohols (butanol, 2-octanol, and menthol) as hydrogen bond donors (HBDs) were developed to extract LA from aqueous solution. The molar ratios of HBD and HBA, extraction temperature, contact time, solution pH, and initial LA concentration, DES/water volume ratios were systematically investigated. Compared with 2-octanol–TOA and menthol–TOA DES, the butanol–TOA DES exhibited the superior extraction performance for LA, with a maximum extraction efficiency of 95.79±1.4%. Moreover, the solution pH had a great impact on the LA extraction efficiency of butanol–TOA (molar ratio=3:1). It is worth noting that the extraction equilibrium time was less than 0.5 h. More importantly, the butanol–TOA (3:1) DES possesses good extraction abilities for low, medium, and high concentrations of LA