5-Hydroxymethylfurfural (HMF) is a crucial biobased compound for synthesizing chemicals and biofuels, but the direct conversion of glucose to HMF suffers low yield and purification problems. In this paper, a cheap and efficient deep eutectic solvent (DES) of choline chloride−chromium chloride (ChCl−CrCl 3 • 6H 2 O) was developed to convert glucose and other carbohydrates to HMF. High HMF yields of 70.2, 78.6, 72.6, and 71.7% were achieved from glucose, fructose, high fructose corn syrup, and sucrose, respectively. The DES ChCl−CrCl 3 •6H 2 O could be reused nine times without a significant loss of catalytic activity. In addition, a method was developed to regenerate humins-polluted DES. Combined with ultraviolet and visible spectrum data and density functional theory calculation, [Cr(H 2 O) 2 Cl 3 Ch] + was identified as the active species in DES ChCl−CrCl 3 •6H 2 O. This paper proposed a new effective system to convert carbohydrates to HMF. The discovery of active species provides a base for future studies on dehydration mechanisms.

This work presents experimental and kinetic modeling studies on fructose dehydration to 5-hydroxymethylfurfural (HMF) in the solution of mixed acetone and water, catalyzed by hydrochloric acid (HCl). A reaction scheme that added an intermediate was proposed. A corresponding kinetic model that considered the parameters, including temperature (383−423 K), initial substrate concentration (10−100 g/L), and catalyst concentration (5−60 mmol/L), was established, and the influence of solvent ratio (3−19) was also studied. The maximum yield was 91% in the ideal plug flow reactor under the optimized condition (T = 383 K, C F0 = 10 g/L, C HCl = 10 mmol/L). The model can well support the delicate reactor design since an industrially accessible HMF production process was proposed in this work.

Converting carbohydrates to 5-hydroxymethylfurfural (HMF) is an important goal for biorefinery. Although various deep eutectic solvents (DESs) have been reported for HMF production, the field lacks systematic research on the effect of cations and anions and an effective catalytic system for converting concentrated carbohydrates. Here, 12 kinds of DESs containing four cations and six anions were systematically evaluated and tetraethylammonium bromide (TEAB) was confirmed as the most effective DES, which provided HMF yields of 90 and 76% from fructose and glucose, respectively. The stable bromide-substituted intermediate may explain the positive effect of bromide based on the results of density functional theory calculation. A high concentration substrate has an adverse impact on the selectivity of HMF due to the HMF concentration caused by glucose, CrCl3·6H2O, and concentrated HMF. To inhibit the condensation, a biphasic system of TEAB/THF is developed to convert a highly concentrated glucose of 62.5 wt % (83.3 wt % with respect to TEAB), providing an excellent HMF yield of 72%. This study has revealed the impact of cations and anions of DESs on HMF production, which will serve as a base for designing task-specific DESs. Moreover, an efficient catalytic system to produce HMF from concentrated glucose was also provided.

5-Hydroxymethylfurfural (HMF) is a high-value biomass-derived platform chemical derived from renewable biomass, which is a great alternative to petroleum-based chemicals; however, it cannot be produced on a large scale at present because of the limitation of a low HMF yield and costly production. In this work, an experimental study of one-pot production of HMF from glucose in an acetone−water solvent was conducted. The effects of inorganic salts (in specific, NaCl) on miscible solvents were studied because inorganic salts could affect the phase structure of solvents. We also study the influence of the ratio between Lewis acid and Brønsted acid (L/B) on the dehydration reaction. After parameter optimization experiments, up to 64.5% HMF yield was obtained at the condition of C 0 = 1.25 w/v %, C AlCl 3 = 1.25 w/v %, C HCl = 10 mmol•L −1 , T = 160 °C, and o/a = 80/20, and the optimized L/B was 1.25 kg•mol −1 . Finally, an economic and efficient HMF production process including HMF purification and catalyst recycling was proposed; the HMF product could be produced and separated with high recovery (∼88%) and purity (∼85%) in the process. Our findings and analysis would provide support for the choice of the reaction system and bifunctional catalyst synthesis in the subsequent industrial demonstration development.