Investigation of a phosphate/1-butyl-3-methylimidazolium trifluoromethanesulfonate/water system for the extraction of 1,3-propanediol from fermentation broth

Abstract

The recovery of 1,3-propanediol from fermentation broth is challenging because of its high polarity and high boiling point. Extraction is an attractive alternative to the commonly used distillation process, which is very energy intensive and thus costly. Due to the low solubility of 1,3-propanediol in organic solvents, extraction has not yet been considered. Ionic liquid-based aqueous two-phase systems could constitute an alternative extraction system for the purification of 1,3-propanediol and are therefore investigated in this study. The distribution coefficient of 1,3-propanediol and the selectivity for it over the by-products of the fermentation, i.e., acetic acid and butyric acid, are determined in different ionic liquid-based aqueous two-phase systems. Based on these results, the ionic liquid-based aqueous two-phase system, phosphate/1-butyl-3-methylimidazolium trifluoromethanesulfonate (Im_4,1 CF₃SO₃), is chosen for further investigation. The effects of the temperature, pH and Im_4,1 CF₃SO₃, phosphate and 1,3-propanediol mass fractions on the phase diagram are examined. Furthermore, the influence of the fermentation by-products on the liquid–liquid equilibrium is determined. All experiments were performed using synthetic media to identify the effects of the process parameters independently from non-ideality incorporated through the use of real fermentation broth. To verify that this approach leads to correct results, results obtained with fermentation broth were compared to those obtained with synthetic media prior to these experiments. The recovery and potential re-use of the ionic liquid, Im_4,1 CF₃SO₃, is finally analysed by repeating some of the experiments with recovered ionic liquid.