Research Article
Jose F. Fernandez, Robert Bart
Abstract
this study, the possibility to recover ionic liquids from their respective wastewater by nanofiltration was tested in two case studies. The experiments were performed using a commercial dead-end stirred cell and/or a cross-flow cell especially developed for this purpose. Hydrophilic ionic liquids are being presently used for the dissolution of cellulose and its further regeneration by water addition. Wastewater containing a mixture of 1-butyl-3-methylimidazolium chloride (IM14 Cl) and 1-butyl-3-methylimidazolium acetate (IM14 1COO) was treated by nanofiltration and the ionic liquids were recovered as an aqueous solution which is also almost free of undesired by-products. On the contrary, hydrophobic ionic liquids are commonly used in biphasic systems to perform either enzymatic or whole-cell biotransformations. Wastewater containing hydrophobic ionic liquids derived from the conversion of 2-octanone to 2-octanol was also tested, and the ionic liquids used can be recovered as a separate phase by concentrating them beyond the solubility limit. The effect of other wastewater components on the recovery was also investigated with the ionic liquid 1-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) amide, IM16 (CF3SO2)2N. Furthermore, using model solutions of 1-hexyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) amide, Pyr16 (CF3SO2)2N, it could be evidenced that the formation of a new phase of ionic liquid during the concentration process follows a nucleation-growth mechanism. In this case, up to 69% of the ionic liquid originally present in the feed was separated. Additionally, the effective recovery rate was duplicated up to 33% by using a coalescence filter. Some suggestions to increase both theoretical and effective recovery rates are also discussed.