(442g) Liquid-Liquid Extraction of Alcohols From Aqueous Solutions Using Ionic Liquids

The production of alcohols and fuels via fermentation has been suggested as an alternative to the fossil-fuel based routes in recent years. Liquid-liquid extraction of organic compounds from dilute aqueous solutions using ionic liquids is a promising unit operation to replace energy- and cost-intensive separation techniques, e.g. distillation. The selection of appropriate ionic liquids (ILs) applied in chemical and separation processes requires reliable thermodynamic data. Therefore, systematic investigations of pure-component and mixture properties for systems containing ILs are essential. This work investigates the phase behavior of binary and ternary alcoholic solutions containing ILs as well as the extraction of 1-butanol from dilute aqueous solutions.

In a first step, physical and thermodynamic properties of pure IL and binary IL/alcohol mixtures of four ILs consisting of two different anions and two different cations were measured. The experimental investigations were carried out using vapor-pressure osmometry (VPO), gas-liquid chromatography (GLC), and a vibrating-tube densimeter at different temperatures and concentrations.

In a second step, pure-component IL model parameters for PC-SAFT were obtained from fitting to pure-IL densities and binary IL/alcohol data. The ILs were regarded as non-dissociated as well as non-aggregated. This approach allows for a quantitative modeling of densities and alcohol activity coefficients  over a broad concentration and temperature range.

Subsequently liquid-liquid equilibrium (LLE) phase diagrams for ternary water/alcohol/IL systems were determined experimentally. It was found that all considered ionic liquids seem to be promising agents for liquid-liquid extraction of the considered alcohols from dilute aqueous solutions. Using the IL model parameters based on only pure and binary component data, PC-SAFT was able to predict the experimental LLEs of these systems precisely.

Finally, with knowledge of the liquid-liquid phase behaviour a multistage liquid-liquid extraction is investigated. Therefore an equilibrium model was implemented to Aspen Custom Modeler^®. Important process parameters and the IL demand were identified by varying the number of theoretical stages, butanol fraction and phase ratio.