Nanofiltration of [MMIM][DMP]-Water-Mixtures - Influence of membrane properties on retention of the ionic liquid

Abstract:
In a nanofiltration process for (molten) salts two membrane properties are decisive whether an ionic liquid molecule passes through the membrane or not: The membrane density by means of molecular-weight-cut-off (MWCO) and the membrane charge. For nanofiltration membranes the MWCO can be determined by rejection-measurements with different polyethylene-glycols, which molecular weights vary between 100 and 1000 Dalton. The membrane charge can be deduced from Zeta-Potential-measurements on the surface of the membrane. With these two membrane parameters and several process parameters, which are recorded during experiments, the application of the Donnan-Steric-Pore-Model, a popular approach for modelling of common salt retention is possible. By comparison of model calculations and experimental results, it is possible to evaluate how these two membrane properties affect the retention of ionic-liquid-molecules. In general this model is only valid for low salt concentrations, but due to the high molecular weight of the ionic liquid molecules even small concentrations of IL in the mixture cover a broad range of mass fraction.

Keywords:
Ionic Liquid, Nanofiltration