Xinhua Qi

Catalytic dehydration of fructose into 5-hydroxymethylfurfural by ion-exchange resin in mixed-aqueous system by microwave heating

Catalytic dehydration of fructose into 5-hydroxymethylfurfural by microwave heating was studied in acetone-water mixtures in the presence of a cation exchange resin catalyst. The use of acetone–water reaction media resulted in yields of 5-HMF as high as 73.4% for 94% conversion at 150 °C. It was confirmed that there was no decrease of catalytic activity and selectivity for five reuses of the resin, which was in accordance with the elemental analysis results that showed that sulfonic acid groups attached on the resin were stable at the experimental conditions. A comparison between conventional sand bath heating and microwave heating revealed that the latter had a remarkable accelerating effect not only on fructose conversion, but also on 5-HMF yield. Under the conditions (5 ml of 2 wt% fructose solution, 0.1 g of resin, 150 °C and 10 min), fructose conversion and HMF yields by microwave heating (91.7% and 70.3%, respectively) were higher than those by sand bath heating (22.1% and 13.9% respectively). Therefore, the process that we developed in this study showed that high 5-HMF yields from fructose could be achieved under mild conditions.

Efficient process for conversion of fructose to 5-hydroxymethylfurfural with ionic liquids

An efficient process for the dehydration of fructose into 5-hydroxymethylfurfural (5-HMF) in ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) by using a sulfonic ion-exchange resin as catalyst was developed. A fructose conversion of 98.6% with a 5-HMF yield of 83.3% was achieved in 10 min reaction time at 80 °C. When the reaction temperature was increased to 120 °C, a 5-HMF yield of 82.2% was obtained in only 1 min for essentially 100% fructose conversion. No large decrease in 5-HMF selectivity occurred for initial fructose concentrations of up to 20 wt.%. Water content of up to 5% in the [BMIM][Cl] had no effect on the fructose conversion rate and 5-HMF yield, but water content higher than 5 wt.% led to lower conversions and yields. The ionic liquid and sulfonic ion-exchange resin could be recycled and exhibited constant activity for 7 successive trials. The proposed process of using an ionic liquid with ion-exchange resin catalyst greatly reduces the reaction time required over previous works for converting fructose to 5-HMF.

Fast Transformation of Glucose and Di-/Polysaccharides into 5-Hydroxymethylfurfural by Microwave Heating in an Ionic Liquid/Catalyst System

An efficient method for converting glucose into 5-hydroxymethylfurfural (5-HMF), in the presence of CrCl3 catalyst, is developed by using the ionic liquid 1-butyl-3-methyl imidazolium chloride as solvent. A 5-HMF yield of 71 % is achieved in 30 s for 96 % glucose conversion with microwave heating at 140 °C. The activation energy of glucose conversion is determined to be 114.6 kJ mol(-1), with a pre-exponential factor of 3.5 x 10(14) min(-1). Fructose, sucrose, cellobiose, and cellulose are studied and 5-HMF yields of 54 % are obtained for cellulose conversion at 150 °C during 10 min of reaction time. Recycling of the ionic liquid and CrCl3 is demonstrated with six cycles of use.

Acid‐Catalyzed Dehydration of Fructose into 5‐Hydroxymethylfurfural by Cellulose‐Derived Amorphous Carbon

Carbonaceous solid (CS) catalysts with --SO₃H, --COOH, and phenolic --OH groups were prepared by incomplete hydrothermal carbonization of cellulose followed by either sulfonation with H₂SO₄ to give carbonaceous sulfonated solid (CSS) material or by both chemical activation with KOH and sulfonation to give activated carbonaceous sulfonated solid (a-CSS) material. The obtained carbon products (CS, CSS, and a-CSS) were amorphous; the CSS material had a small surface area (<0.5 m² g⁻¹) and a high --SO₃H group concentration (0.953 mmol g⁻¹), whereas the a-CSS material had a large surface area (514 m²  g ⁻¹) and a low --SO₃H group concentration (0.172 mmol g⁻¹). The prepared materials were evaluated as catalysts for the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) in the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). Remarkably high 5-HMF yields (83 %) could be obtained efficiently (80 °C and 10 min reaction time). CSS and a-CSS catalysts had similar catalytic activities and efficiencies for the conversion of fructose to 5-HMF in [BMIM][Cl]; this could be explained by the trade-off between --SO₃H group concentration (high for CSS) and surface area (high for a-CSS). The cellulose-derived catalysts and ionic liquid exhibited constant activity for five successive recycles, and thus, the methods developed provide a renewable strategy for biomass conversion.

Hydrolysis of cellulose over functionalized glucose-derived carbon catalyst in ionic liquid

A sulfonated carbon material was prepared by incomplete hydrothermal carbonization of glucose followed by sulfonation. The carbon material contained -SO(3)H, -COOH, and phenolic -OH groups, and exhibited high catalytic performance for the hydrolysis of cellulose. A total reducing sugar (TRS) yield of 72.7% was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 110 °C in 240 min reaction time. The effect of water on the hydrolysis of cellulose in the catalytic system was studied. A water content of less than 2% in the ionic liquid promoted the formation of TRS, whereas a water content of greater than 2% lead to a decrease in TRS. The sulfonated carbon material catalyst was demonstrated to be stable for five cycles with minimal loss in catalytic activity. The use of an ionic liquid with functionalized carbon catalyst derived from glucose provides a green and efficient process for cellulose conversion.

Cellulose-derived superparamagnetic carbonaceous solid acid catalyst for cellulose hydrolysis in an ionic liquid or aqueous reaction system

A cellulose-derived carbonaceous solid acid catalyst that has superparamagnetism was synthesized by incomplete hydrothermal carbonization of cellulose followed by Fe3O4 grafting and –SO3H group functionalization. The as-prepared superparamagnetic carbon catalyst contained –SO3H, –COOH, and phenolic –OH groups and exhibited good catalytic activity for the hydrolysis of cellulose in either an ionic liquid phase or aqueous phase. A total reducing sugar (TRS) yield of 68.9% was obtained with ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) at 130 °C for a 3 h reaction time. A TRS yield of 51% was obtained with water at 180 °C for a 9 h reaction time. The catalyst was applied to rice straw for which a TRS yield of 35.5%, based on the total mass of loaded rice straw, was obtained in [BMIM][Cl] at 150 °C in 2 h. The superparamagnetic carbonaceous solid acid catalyst was easily separated from the reaction products with an external magnetic field and used for subsequent recycling experiments. The activity of the recycled catalyst decreased with a recycle number that is attributed to some loss of the catalyst and adsorption of humin products on the active catalyst sites.

Synergistic conversion of glucose into 5-hydroxymethylfurfural in ionic liquid-water mixtures.

A method for converting glucose into 5-hydroxymethylfurfural (5-HMF) without using chromium-containing catalysts was developed. The method uses ionic liquid-water mixtures with a ZrO(2) catalyst. Addition of a certain amount of water (10-50 wt.%) into the 1,3-dialkylimidazolium chloride ionic liquid promoted the formation of 5-HMF from glucose compared with that in either pure water or in the pure ionic liquid. A 5-HMF yield of 53% was obtained within 10 min at 200 °C in a 50:50 w/w% 1-hexyl-3-methyl imidazolium chloride-water mixture in the presence of ZrO(2). The 1,3-dialkylimidazolium ionic liquids having Cl(-) or HSO(4)(-) anions were effective for promoting 5-HMF formation. Addition of protic solvents such as methanol and ethanol to the ionic liquid had a similar synergistic effect as water and promoted fructose and 5-HMF formation. The results reported in this work can be extended to other fields, where the ratio of ionic liquid and protic solvent can be adjusted to promote the desired reactions.

Adsorption of 1‑Butyl-3-Methylimidazolium Chloride Ionic Liquid by Functional Carbon Microspheres from Hydrothermal Carbonization of Cellulose

Functional carbonaceous material (FCM) loaded with carboxylic groups was prepared by hydrothermal carbonization of cellulose in the presence of acrylic acid. The resulting FCM was used as adsorbent for recovery of a water-soluble ionic liquid, 1-butyl-3-methyl-imidazolium chloride ([BMIM][Cl]). The FCM consisted of microspheres (100-150 nm) and had a low surface area (ca. 20 m(2)/g), but exhibited adsorption capacity comparable to that of commercial activated carbon which can be attributed to the presence of high content of polar oxygenated groups (-OH, -C═O, -COOH) as revealed by spectral analyses. Sorption of [BMIM][Cl] onto FCM adsorbent could be well-described by pseudo-second-order kinetics. Thermodynamic and adsorption isothermal analyses revealed that the adsorption process was spontaneous, exothermic, and could be described by the Freundlich adsorption model. The FCM adsorbent could be regenerated effectively and recycled for at least three times without loss of adsorption capacity. The results of this work provide a facile method for production of functional carbonaceous materials from renewable resources that can be used for treatment of aqueous streams containing small concentrations of ionic liquid, [BMIM][Cl].

Efficient one-pot production of 5-hydroxymethylfurfural from inulin in ionic liquids

An efficient one pot, two-step process was developed for the preparation of 5-hydroxymethylfurfural (5-HMF) from inulin in ionic liquids under mild conditions. In the first step, the ionic liquid 1-butyl-3-methyl imidazolium hydrogen sulfate ([BMIM][HSO4]) was used as both solvent and catalyst for the rapid hydrolysis of inulin into fructose with 84% fructose yield in 5 min reaction time. In the second step, 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) and a strong acidic cation exchange resin were added to the mixture to selectively convert fructose into 5-HMF, giving a 5-HMF yield of 82% in 65 min at 80 °C, which is the highest 5-HMF yield reported by thus far for an inulin feedstock.

Production of Biofuels and Chemicals with Ionic Liquids

Ionic liquids (ILs) are composed of cations and anions that exist as liquids at relatively low temperatures (<100 C). They have many attractive properties, such as chemical and thermal stability, low flammability, and immeasurably low vapor pressures. This review provides a summary of the fundamental structural features of ionic liquids, the physical properties, and their applications as solvents for biomass.