Salting-out extraction of acetoin from fermentation broth using ethyl acetate and K2HPO4

As one of the hydrophilic platform chemicals, acetoin could be produced by microbial fermentation. Although it could be separated from fermentation broth at high recovery by salting-out extraction (SOE) using hydrophilic solvent and inorganic salt, some of impurities in fermentation broth were also distributed to the top phase, which was not favorable for the following distillation process. In this work, a system based on ethyl acetate and K2HPO4 was selected to improve this technique by adding ethanol as cosolvent in the single SOE process or using two-stage countercurrent extraction. The separation conditions such as ethanol and K2HPO4 concentration, stirring and standing time were explored and the reuse of recovered solvent and phosphate were tried. The acetoin recovery of 95.3% was obtained through a single SOE process using a mixed solvent containing 20% ethanol, or 91.3% via a two-stage countercurrent SOE process using ethyl acetate only under the condition of K2HPO4 concentration 50% (m/v) in fermentation broth and volume ratio 1:1 for fermentation broth to solvent. Organic acids, residual glucose and coloring matters were not detected in the top phase, and acetoin loss during solvent removal was greatly reduced. The results indicate that the methods are very prospective in industrial application.