Ionic liquids as bulk liquid membranes on levulinic acid removal: A design study

Ionic liquids are considered as green solvents because of their remarkable properties. In view of this, imidazolium-based ionic liquids were used as a bulk liquid membrane (BILM) for levulinic acid removal. Four different hydrophobic ionic liquids, 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf2N], 1-Butyl-3-methylimidazolium hexafluoro phosphate [BMIM][PF6], 1-Hexy1-3-methylimidazolium bis (trifluoromethylsulfonyl)imide [HMIM][Tf2N], 1-Hexyl-3-methylimidazolium hexafluorophosphate [HMIM] [PF6], were used in the membrane phase. Tributyl phosphate was used as a carrier (0-2 mol/L) in the membrane, and NaOH solutions (0-4 N) were used as stripping phase respectively. Various parameters such as initial levulinic acid concentration in the feed, carrier concentration and ionic liquid type in the membrane, and NaOH concentration in the stripping phase were examined by using D-optimal design. D-optimal design based on the Response Surface Methodology (RSM) is a design method that provides the relationship between independent and dependent factors with a minimum number of experiments. Levulinic acid was successfully transported through BILM using imidazolium-based ionic liquids. Extraction and stripping removal efficiencies were selected as dependent variables and calculated from the experimental results. The experimental results were analyzed by analysis of variance (ANOVA). According to ANOVA, the second order model equations were obtained for dependent variables and have been the good fit with the experimental results. The optimal conditions for BILM process were performed to obtain the higher removal efficiencies. The highest extraction and stripping efficiencies have obtained in case of higher concentration values of TBP and NaOH. Additionally, the molar fluxes at extraction and stripping interfaces were calculated from experimental data. As a result, this design study showed that ionic liquids as bulk liquid membranes can be used on levulinic acid removal. (C) 2018 Elsevier B.V. All rights reserved.