Salting-out assisted acidic deep eutectic solvent Liquid-Liquid extraction of 2,3-Butanediol from aqueous Solutions: Green and sustainable approach

Biological fermentation is considered as a green and economically viable method to produce 2,3-Butanediol (BDO, potential alternative fuel). However, the downstream extraction of BDO is the challenging and cost determining factor in biological fermentation. Deep eutectic solvent (DSE) has been widely used in separation field for its simple preparation, cut-price, environment friendliness and recyclability. Nine acidic deep eutectic solvents (ADES) were prepared and used to construct a salting-out liquid-liquid extraction system to separate BDO from aqueous solution. The major experimental parameters influencing salting-out assisted liquid-liquid extraction (SALLE), including type and volume of ADES, salt type and concentration, BDO concentration, equilibrium time, equilibrium temperature, and solution pH, were investigated. Under optimal conditions when using TEAC/n-CA as extractant, the extraction efficiency, selectivity and distribution coefficient for 10% BDO were 92.3%, 281.0 and 121.1, respectively. Moreover, evaporation process was used to recover K3PO4, the recovery was more than 90%, and the extraction efficiency of BDO was still more than 92% after recycling 5 times. Meaningfully, the recovery and recycling of TEAC/n-CA were realized by adjusting hydrophobic capacity with pH-response characteristic of ADES, the recovery was more than 66%, and the extraction efficiency of BDO was still more than 91% after recycling 5 times. It demonstrated that salting-out agent and pH-responsive deep eutectic solvent could be repeatedly used. The novel processing offers a green and sustainable route for BDO extraction from aqueous solutions.