Experimental screening of ionic liquids as mass agents in the n-hexane/1-hexene extractive distillation

Abstract

n-Hexane and 1-hexene are highly valued compounds within the petrochemical industry because of their wide range of applications. These compounds are generally found together in the same stream. Their separation is difficult to accomplish by conventional distillation due to their close boiling points. Technologies currently used to separate n-hexane and 1-hexene at industrial scale range from membrane processes to extractive distillation and liquid-liquid extraction with organic solvents. However, these processes present several technical and environmental drawbacks. A promising alternative is extractive distillation with ionic liquids as entrainers. In this work, a screening of ten ionic liquids was made to check their potential in the extractive distillation of n-hexane and 1-hexene mixtures. Firstly, the ionic liquids’ extractive properties were determined to establish which ionic liquids are suitable for the n-hexane/1-hexene extractive distillation. Five ionic liquids, namely [4bmpy][TCM], [4bmpy][Tf2N], [bmim]2[Co(SCN)4], [P66614][TCM] and [P66614][DCA] were selected. Secondly, vapor-liquid equilibrium experiments for the binary systems {n-hexane or 1-hexene + ionic liquid} were conducted at 343.2, 363.2 and 383.2 K to select the minimum solvent-to-feed ratio that guarantees homogenous ternary systems {n-hexane + 1-hexene + ionic liquid}. Then, the vapor-liquid equilibria for the ternary systems {n-hexane + 1-hexene + ionic liquid} were determined at the same three temperatures with a solvent-to-feed ratio on a mass basis of 10. Besides, solvent-to-feed ratios of 7.5 and 5 were also used for those systems containing [P66614]-based ionic liquids. n-Hexane/1-hexene relative volatilities up to 2.3 were obtained, overcoming those provided by other ionic liquids and organic solvents. Finally, the NRTL model was used to adjust the ternary data accuracy.