Liquid–liquid extraction process of amino acids by a new amide-based functionalized ionic liquid

Abstract

The cost of separation and purification of amino acids accounts for more than 80% of their total production expenditure. Thus, investigation into new separation technology is of great importance. In this paper, a new hydrophobic amide-based functionalized ionic liquid ([EimCH₂CONHBu]NTf₂) was designed and synthesized for the extraction of amino acids. From the preliminary experiments we found that the ionic liquid has a special selectivity for tryptophan (Trp) when pH = 0.5, and that its partition coefficient (P_IL/W) can reach up to 10.02. Subsequently, important factors that affect the extraction process by [EimCH₂CONHBu]NTf₂ were studied systematically. It was found that the extraction equilibrium could be achieved in 30 min. It was found that pH influences the P_IL/W greatly; the smaller the pH value, the higher the P_IL/W. When pH > pK₂, the P_IL/W is close to zero. With the increase of the volume ratio of the ionic liquid, extraction efficiency increases, while the P_IL/W decreases. As for the effect of the initial concentration (C₀) of tryptophan, P_IL/W decreases with an increase of C₀ when [EimCH₂CONHBu]NTf₂ is used as the extractant. From the investigation of the effect of temperature if was found that the extraction process of amino acid by functionalized ionic liquids is exothermic. Experiments on the recycling and reuse of [EimCH₂CONHBu]NTf₂ were also performed, and it was found that the extraction efficiency of [EimCH₂CONHBu]NTf₂ does not change after four cycles. Finally, the mechanisms were probed and the results show that the hydrogen bond formed between the acetyl group of the ionic liquid and the NH₂ group of tryptophan accounts for the higher extraction efficiency.