277522 Liquid-Liquid Extraction of Alcohols From Aqueous Solutions Using Ionic Liquids

Wednesday, October 31, 2012: 10:40 AM
306 (Convention Center )
Alexander Nann1, Christoph Held1, Martin Stoffers2, Andrzej Górak3 and Gabriele Sadowski1, (1)Department of Biochemical and Chemical Engineering, Laboratory of Thermodynamics, TU Dortmund University, D-44227 Dortmund, Germany, (2)Department of Biochemical and Chemical Engineering, Laboratory of Fluid Separations, TU Dortmund University, D-44227 Dortmund, Germany, (3)Department of Biochemical and Chemical Engineering, Laboratory of Fluid Separations, TU Dortmund University, Dortmund, Germany

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.

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