ISBN 9783843916608

978-3-8439-1660-8, Reihe Verfahrenstechnik

Martin Stoffers
Liquid-Liquid Extraction of n-Butanol from Aqueous Solutions Using Ionic Liquids

173 Seiten, Dissertation Technische Universität Dortmund (2014), Softcover, A5

Zusammenfassung / Abstract

The separation of n-butanol from fermentation broth using distillation is energy- and cost-intensive. Liquid-liquid extraction is a promising alternative to distillation due to mild operating conditions. In this thesis ionic liquids were used as extraction solvent since they enable simple solvent regeneration.

From the multitude of available ionic liquids two were selected with regard to their extraction ability for n-butanol from aqueous feeds, namely 1-hexyl-3-methylimidazolium tetracyanoborate (Im6,1 tcb) and 1-decyl-3-methylimidazolium tetracyanoborate (Im10,1 tcb). First pure component properties, properties of binary mixtures from water/ionic liquid and the liquid-liquid equilibrium of the system synthetic medium/ionic liquid were investigated. The highest distribution coefficients were found for n-butanol, followed by butyric acid > acetone > acetic acid > ethanol. The feasibility of a continuously operated multi-stage extraction was demonstrated with Im6,1 tcb. Pilot scale experiments confirmed the successful scale-up from laboratory scale to a mixer-settler unit. It was shown that thermodynamic equilibrium is reached in one physical stage of the mixer-settler unit. Hence, the use of an equilibrium approach for modelling was enabled.

The multi-stage extraction model in AspenPlus® was successfully applied to simulate the mixer-settler experiments. The liquid-liquid equilibrium data were described by the NRTL gE-model. Using the experimental pilot scale data the model was validated. It was extended to an integrated extraction-distillation process for the purification of n-butanol and regeneration of ionic liquid in order to compare this process to a distillation-based benchmark process in a computer-aided process analysis. The purification costs were highly dependent on the solubility of ionic liquid in water and the uncertain solvent price. Although showing a lower n-butanol distribution coefficient compared to Im6,1 tcb, Im10,1 tcb caused less costs due to the poor solubility in water. The integrated extraction-distillation process was cheaper than the benchmark process which was highly sensitive to the price for thermal energy.