The Direct Conversion of Cellulose into 5‐Hydroxymethylfurfural with CrCl₃ Composite Catalyst in Ionic Liquid under Mild Conditions

Abstract

Direct transformation of cellulose (PH101: DP∼200) into 5‐hydroxymethylfurfural (HMF) was investigated using the single CrCl3 or the combination of metal chlorides (CrCl3 with AlCl3, FeCl3, SnCl4, MnCl4, and CuCl2) in ionic liquid [Bmim]Cl under oil‐bath heating. As a result, a novel co‐catalysis CrCl3‐AlCl3 was determined to be the most efficient catalyst for the production of HMF. Compared with single CrCl3, the reaction time with CrCl3‐AlCl3 was reduced by nearly 1/3 when a similar HMF yield (58.3%) was obtained at 120 °C. Additionally, the catalytic mechanism of CrCl3‐AlCl3 was discussed. Furthermore, when celluloses with higher polymerization degree (filter paper: DP∼1500 and cotton: DP∼1950) were used, exceedingly higher yields of HMF (54.7% for filter paper and 59.5% for cotton) were obtained compared with previous work. This important result strongly indicates the general applicability of CrCl3‐AlCl3 for various kinds of natural cellulose with a huge range of DP.

Glucose Isomerizes to Fructose Catalyzed by the Eco‐Friendly and Biodegradable Ionic Liquids

“…It is well known that cellulose hydrolysis conducts readily at the acidic environment, and the conversion of fructose occurred even automatically without catalysts . Nevertheless, direct transformation of cellulose is still a big challenge . In addition, previous studies demonstrated that the isomerization of glucose to fructose has the highest activation energy in cellulose conversion, indicating that this process is the key and rate‐determining step in the consecutive processes of cellulosic biomass valorization.…”

Conversion of Glucose to 5-Hydroxymethylfurfural, Levulinic Acid, and Formic Acid in 1,3-Dibutyl-2-(2-butoxyphenyl)-4,5-diphenylimidazolium Iodide-Based Ionic Liquid

“…Current technologies use an additional isomerization step of glucose to fructose because dehydration of fructose to HMF occurs with better selectivity and higher rates [11,13]. The use of solid catalysts (hydrotalcite, zeolites, and different metal oxides), enzymes, or an aqueous base is renowned in the isomerization step of monosaccharide dehydration [2,6,8,13,14]. However, the high processing cost and the relatively low HMF yields (approximately 20.0-70.0%) are some of the disadvantages in those processes [2,6,8,13,14].…”

“…The use of solid catalysts (hydrotalcite, zeolites, and different metal oxides), enzymes, or an aqueous base is renowned in the isomerization step of monosaccharide dehydration [2,6,8,13,14]. However, the high processing cost and the relatively low HMF yields (approximately 20.0-70.0%) are some of the disadvantages in those processes [2,6,8,13,14].…”

“…IL is an organic or inorganic salt with a low melting point (under 100 • C), high thermal stability, chemical stability, low vapor pressure, and environmentally friendly as a solvent and catalyst [30][31][32][33]. Several notable applications of ILs include the use as a solvent or media in biomass conversion, as a catalyst for reaction, as corrosion inhibitors, and as a supporting material in membrane separation [3,14,[25][26][27]30]. IL can act as a green solvent, with a wide range of solubility, and as a catalyst to increase the HMF yield [3,[25][26][27]34].…”

“…Stahlberg et al [38] investigated IL's usage with lanthanide as catalysts in glucose conversion, obtaining an approximately 24.0% HMF yield [39]. The literature review results showed that IL acted as a more powerful solvent and Lewis acid catalyst in biomass conversion [3,6,14,23,25,27,28,40,41]. However, several ILs still have drawbacks in the hydrolysis process of biomass, glucose, and fructose due to the incompatible chemical structures of the ILs, resulting in a low HMF yield.…”