Selective extraction of benzene from benzene-cyclohexane mixture using 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid

Abstract

Separation of benzene and cyclohexane remains a challenging process in petrochemical industry due to their almost similar boiling temperatures. The present work validated the performance of a reportedly benzene-selective ionic liquid (IL), i.e. 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2Mim][BF4]) to extract benzene from its mixture with cyclohexane via liquid-liquid extraction. The ternary liquid-liquid equilibria of benzene+cyclohexane+[C2Mim][BF4] was investigated at 25 °C and under 1 atm with feed concentration of benzene ranging from 10 to 60 wt %. Good agreement was achieved between COSMO-RS prediction and the experimental data for the tie-lines obtained, whereby the root mean square deviation (RMSD) was 2.5%. The non-random two-liquid (NRTL) model was also successfully employed to correlate the experimental tie-lines, whereby the RMSD was 0.5%. The extractive performance of [C2Mim][BF4] was compared with other organic solvents in the literature and a few common ILs employed in our previous work. At equilibrium, IL was not present in the cyclohexane-rich layer, and the molar concentration of cyclohexane in the IL-rich layer was less than 0.01. The results indicated an efficient extraction process as the cross-contamination between the phases was minimal, and relatively less energy was required to recover the IL.