Extraction of 1,3-Propanediol from Fermentation Broth Using Ionic Liquids

The separation of 1,3-propanediol from fermentation broth is a challenging and energy demanding step using the conventional applied distillation. Therefore, an alternative separation process must be developed. Thus far, extraction has not been used because of the low solubility of 1,3-propanediol in organic solvents due to its high polarity. Application of ionic liquids could overcome this limitation. Hence, the application of ionic liquids for the extraction of 1,3-propanediol was evaluated in this work. There are two possibilities for the use of ionic liquids in extraction systems with a feed stream that consists primarily of water: hydrophobic ionic liquids can be used as a second immiscible phase or hydrophilic ionic liquids can be applied in aqueous two-phase systems. These two possibilities were investigated using different ionic liquids and evaluating the determined 1,3-propanediol distribution coefficients. Five representative ionic liquids were chosen and the distribution coefficients of the main fermentation by-products, acetic and butyric acid, were additionally determined. The ionic liquid-based aqueous two-phase system containing the ionic liquid 1-butyl-3-methylimidazolium trifluoromethansulfonate (Im4,1 CF3SO3) and a phosphate salt as second phase forming component turned out to be most suitable. Hence, this system was further investigated. Therefore, the influence of the temperature, pH and mass fraction of Im4,1 CF3SO3, the phosphate salt and 1,3-propanediol as well as of the metabolites acetic acid and butyric acid on the distribution coefficient of 1,3-propanediol was determined. The results served as a basis for the development of a multi-stage extraction model validated through multi-stage mixer-settler experiments. This model is important to determine relevant process parameters and to evaluate the suitability of the extraction as alternative for the separation of 1,3-propanediol in the context of the whole process. The process parameters of the extraction were investigated in the last step, these parameter include the number of stages, the phase ratio, the pH and the mass fraction of the involved components.