Ionic liquid-based salting-out extraction of bio-chemicals

Abstract

Ionic liquids (ILs) are known as green solvents, and have been widely used in the dissolution and transformation of biopolymers, the extraction of bioactive compounds and metal ions, and the capture of SO2 or CO2. However, less attention was given to the separation of bio-based chemicals, such as diols and organic acids. Bio-based chemicals can be efficiently separated by organic solvent-based salting-out extraction (SOE) from fermentation broths, while organic solvents are normally unfriendly to environment and process safety in commercialized production due to their toxicity or/and flammability. In recent years, the IL-based SOE system has been explored in the separation of bio-based chemicals as an alternative of organic solvent-based SOE system. In this review, the progress of IL-based SOE of bio-based chemicals has been summarized, including the effect of ILs structure on the formation of aqueous two phases, and the influences of ILs structure and concentration, temperature and pH on the partition behaviors of target products and ILs as well as removal of impurities. Most of bio-based chemicals could be distributed into the IL-rich phase with high recovery, while the partition behaviors of bio-based chemicals are sometimes different from that in organic solvent-based SOE systems. Although the results of IL-based SOE are promising, further studies are still required in the increased selectivity of target products over by-products, recovery and recycling of ILs, and the separation between ILs and bio-based chemicals. Additionally, three kinds of integrated bioprocesses would be developed on basis of utilization of ILs as extractant for SOE, catalyst for condensation reaction and solvent for pretreatment of lignocellulose.