Zeitschrift für Membranwissenschaft und -technologie

Abstrakt

Recovery of Ionic Liquids from Wastewater by Nanofiltration

Jose F. Fernandez, Robert Bartel, Ulrike Bottin-Weber, Stefan Stolte and Jorg Thoming

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.