Low-Temperature Production of 5-Hydroxymethylfurfural from Fructose Using Choline Chloride–Ethylene Glycol–Maleic Acid Ternary Deep Eutectic Solvents

Low-temperature production of 5-hydroxymethylfurfural (HMF) from fructose in ternary deep eutectic solvents (TerDESs) of choline chloride (ChCl), ethylene glycol (EG), and maleic acid (MalA) is proposed. A fructose conversion of 99.9% and an HMF yield of 87.3% are achieved in TerDES with ChCl/EG/MalA = 3:1:1 at 70 °C in 30 min. The ChCl can effectively activate the hydroxy groups of fructose by lengthening the C–O bonds. The EG can both improve the formation of ChCl–MalA DES with wide ranges of component ratios and reduce the viscosity of the DES. A reaction mechanism considering the synergistic effect of the components in TerDES is suggested to explain the enhanced dehydration of fructose under mild conditions. The recycling results of the TerDES show stable yields of HMF within five recycle runs. This work offers an efficient solution to a green and sustainable process for a high yield of HMF production.