Screening of Double Solvents Based on Multi-Index Evaluation Method for the Selective Separation m-Cresol from Model Oil

Ionic liquid (IL) as an extractant is an effective method for separating oil- phenol mixtures. However, relatively high neutral oil entrainment can lead to oil loss and a remarkable reduction in phenol purity. To reduce the entrainment of neutral oil in the extraction process, a double-solvent extraction system composed of IL 1-ethyl-3-methyl imidazolium acetate ([C(2)mim][Ac]) and an organic solvent was investigated. The multi-index evaluation method was used to screen the conventional organic solvent. The double-solvent extraction experiments were employed to verify the accuracy of the COSMO-RS prediction. Eighteen organic solvents, the interaction energy with m-cresol and cumene (neutral oil), their extraction ability, and mutual solubility with [C(2)mim][Ac], were calculated by COSMO-RS. Alkane and cycloalkane were screened due to their strong interaction and low distribution coefficient with cumene, as well as the low mutual solubility with [C2mim][Ac]. The experimental results were in good agreement with the COSMO-RS prediction, and cyclopentane as an organic solvent had the lowest distribution coefficient and entrainment of cumene because of its strong nonpolarity and hydrogen-bond repulsive interaction, which was explained by the sigma-profile and sigma-potential analysis. When the cyclopentane-to-[C(2)mim][Ac] mass ratio increased from 0.0 to 3.0, the entrainment of cumene was evidently declined from 39.5 to 5.8% and the selectivity to m-cresol was improved from 378.0 to 1058.5.