An ionic liquid–organics–water ternary biphasic system enhances the 5-hydroxymethylfurfural yield in catalytic conversion of glucose at high concentrations

Abstract

Increasing glucose loading in the 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ionic liquid containing dissolved CrCl 3 catalyst system led to excessive formation of humins and serious decrease in 5-hydroxymethylfurfural (5-HMF) yield. A biphasic system containing glycol dimethyl ether (GDE) as 10 the extraction phase, and [BMIM]Cl/CrCl 3 /glucose in combination with a partitioned amount of GDE and an appropriate amount of water as the reaction phase was found highly efficient for the reaction; CrCl 3 catalyzed the formation of 5-HMF in 64.5 mol% yield from a very high glucose concentration (80 wt% with respect to the ionic liquid) at 108°C. This 5-HMF yield in the [BMIM]Cl-GDE-H 2 O ternary biphasic system nearly doubled that obtained in the single [BMIM]Cl/CrCl 3 /glucose reaction phase. Importantly, 15 the GDE phase contained about 56% of the generated 5-HMF without detectable contamination by the ionic liquid or carbohydrates. GDE served multiple functions: as a hydrogen-bond acceptor, it exhibited excellent extraction performance for 5-HMF; due to its low boiling point and suitable solubility saturation point in the ionic liquid, a sustained GDE bubbling phenomenon in the ionic liquid phase was observed that promoted the rate of inter-phase mass-transfer of 5-HMF under reaction; and GDE mediated the 20 [BMIM]Cl phase to a reduced viscosity. In addition, an appropriate amount of water in the ternary system promoted the extraction efficiency of 5-HMF and also lowered the viscosity of [BMIM]Cl/glucose. The ionic liquid-organics-water ternary biphasic system has been demonstrated for high 5-HMF productivity and separation efficiency.

Mechanistic understanding of humin formation in the conversion of glucose and fructose to 5-hydroxymethylfurfural in [BMIM]Cl ionic liquid

“…It should be noted that a high weight ratio of 1 : 2 for sugar : [BMIM]Cl solvent was used to intensify humins formation, as high glucose concentration always leads to a poor 5-HMF selectivity due to dominant humins. 24 A temperature as high as 130 C was also used for the same purpose. The effect of reaction temperatures on solid humins formation was explored (entries 1-4, Table 1).…”

“…Cr(II, III) salts were reported as catalysts for isomerization/dehydration of glucose to 5-HMF in ionic liquids, such as 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). [24][25][26][27][28] Ionic liquids are also applied in 5-HMF synthesis from fructose or even cellulose. 29 For hexoses conversion in [BMIM]Cl with CrCl 2 or CrCl 3 as catalysts, typical 5-HMF selectivity is about 70% and 90% with glucose and fructose as feedstock, respectively.…”

“…[24][25][26][27][28] Signicant efforts have been made to reduce the humins formation such as adopting proper ligands for CrCl 3 , introducing an organic phase for in situ 5-HMF extraction, and reducing sugar feed concentration. 24 A biphasic system consisting of [BMIM]Cl and glycol dimethyl ether (GDE) signicantly increased the 5-HMF yield by minimizing the residence time of 5-HMF in the IL reaction media. 24 However, the humins byproducts remained substantial even under optimized conditions.…”

“…24 A biphasic system consisting of [BMIM]Cl and glycol dimethyl ether (GDE) signicantly increased the 5-HMF yield by minimizing the residence time of 5-HMF in the IL reaction media. 24 However, the humins byproducts remained substantial even under optimized conditions. 5-HMF alone was also found stable in certain IL phases but reactive for humins formation in aqueous media.…”

An overview of the biphasic dehydration of sugars to 5-hydroxymethylfurfural and furfural: a rational selection of solvents using COSMO-RS and selection guides

“…In all cases CrCl 3 was the catalyst employed and the performance was similar reaching quantitative conversions of glucose and yields ranging from 64 to 50% for the mentioned solvents. 82 Fructose as substrate for 5-hydroxymethylfurfural in biphasic systems. A compilation of works starting from fructose as substrate is presented in Table 2.…”