Extraction of volatile fatty acids from aqueous solution by in situ formed deep eutectic solvent with methyltrioctylammonium chloride

Volatile fatty acids (VFAs) such as acetic acid have a wide range of applications with high demand. Since acetic acid is well soluble in water, treating its wastewater presents a technical challenge. In this work, new hydrophobic deep eutectic solvents (DESs) were synthesized by using methyltrioctylammonium chloride (TOMAC) as hydrogen bond acceptor (HBA) and acetic acid as hydrogen bond donor (HBD). The properties of DESs were characterized by DSC, TG, and FT-IR. As HBA, TOMAC was used for in situ generation of DES to extract acetic acid from aqueous solution. The extraction efficiency reached 65.28% when TOMAC/acetic acid was 7:3 (molar ratio), which is better than that of the traditional acetic acid extractants, such as tributyl phosphate (60.46%). When metal ions such as Ca2+, Mg2+, and Fe3+ coexist in solution, the salt precipitation effect not only prevents the emulsification phenomenon but also improves the acetic acid extraction effect. For volatile fatty acids such as propionic acid, butyric acid, and valeric acid, the extraction efficiency of TOMAC was good, reaching 84.96%, 92.04%, and 95.81%, respectively. The method of using TOMAC to extract acetic acid from aqueous solutions by forming DES in situ provides a new way for the treatment of VFAs wastewater.