Mass transfer kinetics during the extraction of m-cresol from model coal tar using betaine/glycerol deep eutectic solvents

Abstract

Betaine/glycerol, a common deep eutectic solvent (DES), is an effective extractant used for separating phenolic compounds from model coal tar. Its mass transfer kinetics during extraction is the basis of industrial applications. The physical properties of the model oil and the DES were measured in this study. Then, the modified Lewis cell was used to determine the mass transfer coefficients and extraction rates of the mass transfer kinetics. The effects of the process parameters, including temperature, stirring rate, specific interfacial area, and water quantity of the DES on the kinetics were investigated. In addition, the mechanism of mass transfer kinetics was studied using simulation and experimental studies. The results demonstrate that the physical properties of DES vary greatly with temperature and water quantity, while the physical characteristics of model oil show less variations. The mass transfer coefficient increases and the extraction rate accelerates with increased stirring rate, temperature, and water quantity in the DES. The DES phase functions as the mass transfer resistance area during extraction. An increase in the specific interfacial area did not result in an obvious variation in the mass transfer coefficient, although the extraction rate increased. Finally, results of the simulation and experimental studies showed that the mass transfer kinetics of extraction are controlled by diffusion. Phenolic compounds diffuse from the oil phase into the DES phase and react with DES by forming hydrogen bonds, resulting in the separation of phenolic compounds.