Phosphotungstic Acid Encapsulated in Metal-Organic Framework as Catalysts for Carbohydrate Dehydration to 5-Hydroxymethylfurfural

MIL-101, a chromium-based metal-organic framework, is known for its very large pore size, large surface area and good stability. However, applications of this material in catalysis are still limited. 5-Hydroxymethylfurfural (HMF) has been considered a renewable chemical platform for the production of liquid fuels and fine chemicals. Phosphotungstic acid, H3PW12O40 (PTA), encapsulated in MIL-101 is evaluated as a potential catalyst for the selective dehydration of fructose and glucose to 5-hydroxymethylfurfural. The results demonstrate that PTA/MIL-101 is effective for HMF production from fructose in DMSO and can be reused. This is the first example of the application of a metal-organic framework in carbohydrate dehydration.

On the Mechanism of Lewis Acid Catalyzed Glucose Transformations in Ionic Liquids

A complementary computational and experimental study of the reactivity of Lewis acidic CrCl2, CuCl2 and FeCl2 catalysts towards glucose activation in dialkylimidazolium chloride ionic liquids is performed. The selective dehydration of glucose to 5-hydroxymethylfurfural (HMF) proceeds through the intermediate formation of fructose. Although chromium(II) and copper(II) chlorides are able to dehydrate fructose with high HMF selectivity, reasonable HMF yields from glucose are only obtained with CrCl2 as the catalyst. Glucose conversion by CuCl2 is not selective, while FeCl2 catalyst does not activate sugar molecules. These differences in reactivity are rationalized on the basis of in situ X-ray absorption spectroscopy measurements and the results of density functional theory calculations. The reactivity in glucose dehydration and HMF selectivity are determined by the behavior of the ionic liquid-mediated Lewis acid catalysts towards the initial activation of the sugar molecules. The formation of a coordination complex between the Lewis acidic Cr2+ center and glucose directs glucose transformation into fructose. For Cu2+ the direct coordination of sugar to the copper(II) chloride complex is unfavorable. Glucose deprotonation by a mobile Cl- ligand in the CuCl42- complex initiates the nonselective conversion. In the course of the reaction the Cu2+ ions are reduced to Cu+. Both paths are prohibited for the FeCl2 catalyst.

Fermentable sugars recovery from lignocellulosic waste-newspaper by catalytic hydrolysis

The urgent need for alternative renewable energies to supplement petroleum-based fuels and the reduction of landfill sites for disposal of solid wastes makes it increasingly attractive to produce inexpensive biofuels from the organic fraction of the municipal solid waste. Therefore, municipal waste in the form of newspaper was investigated as a potential feedstock for fermentable sugars production. Hydrolysis of newspaper by dilute phosphoric acid was carried out in autoclave Parr reactor, where reactor temperature and acid concentration were examined. Xylose concentration reached a maximum value of 14 g/100 g dry mass corresponding to a yield of 94% at the best identified conditions of 2.5 wt% HPO, 135°C, 120 min reaction time, and at 2.5 wt% HPO, 150°C, and 60 min reaction time. For glucose, an average yield of 26% was obtained at 2.5 wt% HPO, 200°C, and 30 min. Furfural and 5-hydroxymethylfurfural (HMF) formation was clearly affected by reaction temperature, where the higher the temperature the higher the formation rate. The maximum furfural formed was an average of 3 g/100 g dry mass, corresponding to a yield of 28%. The kinetic study of the acid hydrolysis was also carried out using the Saeman and the two-fraction models. It was found for both models that the kinetic constants (K) depend on the acid concentration and temperature. The degradation of HMF to levulinic acid is faster than the degradation of furfural to formic acid. Also, the degradation rate is higher than the formation rate for both inhibitors when degradation is observed.

Development of a heterogeneous catalyst for lignocellulosic biomass conversion:Glucose dehydration by metal chlorides in a silica-supported ionic liquid layer

An attempt is made to immobilize the homogeneous metal chloride/EMIMCl catalyst for glucose dehydration to 5-hydroxymethylfurfural. To this end, ionic liquid fragments were grafted to the surface of SBA-15 to generate a heterogenized mimick of the homogeneous reaction medium. Despite a decrease in the surface area, the ordered mesoporous structure of SBA-15 was largely retained. Metal chlorides dispersed in such ionic liquid film are able to convert glucose to HMF with much higher yields as is possible in the aqueous phase. The reactivity order CrCl > AlCl > CuCl > FeCl is similar to the order in the ionic liquid solvent, yet the selectivity are lower. The HMF yield of the most promising CrCl-Im-SBA-15 can be improved by using a HO:DMSO mixture as the reaction medium and a 2-butanol/MIBK extraction layer. Different attempts to decrease metal chloride leaching by using different solvents are described. © 2013 American Institute of Chemical Engineers Environ Prog.