Switchable (pH driven) aqueous two-phase systems formed by deep eutectic solvents as integrated platforms for production-separation 5-HMF

Abstract The function to induce dynamic-phase shifts between mono/biphasic systems is crucial to separation processes. Switchable (pH driven) ATPS composed of DESs and salts are here disclosed to act as integrated platforms for the production-separation processes. The catalytic carbohydrate conversion to 5-hydroxymethylfurfural (5HMF) was conducted in a homogeneous acidic aqueous-DES medium. Then, the formation of the biphasic region was induced by tailoring the pH of the aqueous homogeneous medium, leading to the complete separation of 5-HMF from the carbohydrate. Herein, the effects of the phase-forming DES species (composed of ethanol/n-propanol and [N4444]Cl), the K3C6H5O7 concentration and pH on the distribution of 5-HMF and fructose in DES-ATPSs were investigated. The optimal composition of the DES-ATPS system was 30 wt% [N4444]Cl:ethanol (1:2) or [N4444]Cl:n-propanol (1:2) and 35 and 40 wt% K3C6H5O7, respectively. The results showed that the integrated platforms have good catalytic effect, and the conversion rate of fructose reached 87.21%, with a 5-HMF yield of 46.76% and 0.1 g of apple peel produced 15.43 mg 5-HMF. The extraction efficiency of the DES-ATPS composed of [N4444]Cl:ethanol (1:2) and [N4444]Cl:n-propanol (1:2) were the highest within 20 min (5-HMF extraction efficiency 98.53% and 98.59%, respectively), which has economic benefits and comprehensiveness.