Effect of Water on Phenol Separation from Model Oil with Ionic Liquids Based on COSMO-RS Calculation and Experimental Study.

Ionic liquids (ILs) are widely used in the extraction of phenolic compounds from low-temperature coal tar (LTCT). However, both ILs and LTCT contain a certain amount of water. The existence of water may have a remarkable impact on the phenol separation performance of ILs with different structures. In this work, the capacity and selectivity for -cresol, as well as the solubility of cumene and dodecane in different IL-HO mixtures, were firstly calculated by the conductor-like screening model for real solvents (COSMO-RS) at infinite dilution. The calculation covers ILs with different anionic and anionic structures and different water contents. To explore the effect of water in IL on separation performance, 1-ethyl-3-methyl imidazolium acetate ([Cmim][Ac]) was selected as the representative IL, and then the molecular interactions between the [Cmim][Ac]-HO mixture solvent and solute (including -cresol, cumene, and dodecane) were analyzed by COSMO-RS. The results indicated that both water and -cresol could form hydrogen bonds with [Cmim][Ac]. The competition between them leads to decreasing separation performance for -cresol of the [Cmim][Ac]-HO mixture with increasing water content. Moreover, through analyses of -cresol extraction efficiency, distribution coefficient, selectivity, and entrainment of cumene and dodecane, the experimental results confirmed that the presence of water in [Cmim][Ac] had a negative effect on the separation of -cresol. The viscosity and UV-vis spectra of the [Cmim][Ac]-HO mixture were also measured. Water in ILs should be removed as much as possible to ensure a better dephenolization effect and avoid phenol containing wastewater.