Robert Durand

Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites

Abstract Dehydration of fructose to 5-hydroxymethylfurfural was performed in a batch mode in the presence of a series of dealuminated H-form mordenites as catalysts, at 165°C, and in a solvent mixture consisting of water and methyl isobutyl ketone (1:5 by volume). Under the operating conditions used, the reaction was not controlled by external or internal diffusional limitations. Fructose conversion and selectivity to 5-hydroxymethylfurfural were found to depend on acidic and structural properties of the catalysts used as well as on the micropore vs. mesopore volume distribution of those catalysts. A maximum in the rate of conversion of fructose was observed for the H-mordenite with a Si/Al ratio of 11. A maximum in the selectivity to 5-hydroxymethylfurfural was observed only for H-mordenites with a low mesoporous volume. The high selectivity obtained (>90%) was correlated with the shape selectivity properties of H-mordenites (bidimensional structure), and particularly with the absence of cavities within the structure allowing further formation of secondary products. The influence of the microporosity vs. mesoporosity on the selectivity to 5-hydroxymethylfurfural was also studied, the formation of mesopores upon dealumination procedures being damaging to obtain a high selectivity. A significant increase in the selectivity (10%) was also obtained by simultaneous extraction of 5-hydroxymethylfurfural with methyl isobutyl ketone circulating in a countercurrent manner in a continuous catalytic heterogeneous pulsed column reactor. Finally, taking into account the most recent results reported in the literature and our own results, it is possible to revise the mechanism of the dehydration of fructose.

Selective preparation of furfural from xylose over microporous solid acid catalysts

Abstract Dehydration of xylose into furfural was performed in a batch mode in the presence of H-form faujasites and mordenites as catalysts, at 170°C and in a solvent mixture consisting of water and methylisobutylketone or toluene (1:3 by volume). In toluene used as the co-solvent, xylose conversion and selectivity to furfural were found to depend on both acidic and structural properties of the catalysts used. Under the operating conditions used, H-mordenite with a Si/Al ratio of 11 was found to be more selective for the formation of furfural from xylose than H-Y faujasite with a Si/Al of 15. As already shown in the case of the dehydration of fructose to 5-hydroxymethylfurfural, the better selectivity of H-mordenite, as compared to H-Y faujasite, results from the structural properties of these catalysts. The high selectivity obtained (90–95%) was correlated once again with the shape selective properties of H-mordenites and particularly with the absence of cavities within the structure allowing the further formation of secondary products. When methylisobutylketone is used as the co-solvent, lower selectivities to furfural are obtained, in spite of the better affinity of furfural for methylisobutylketone than for toluene. Nevertheless, the high selectivities obtained in a solvent mixture consisting of water and toluene then allow to consider a process of the kind previously described for the dehydration of fructose.

Silver-Platinum Bimetallic Catalysts for Oxygen Cathodes in Chlor-alkali Electrolysis: Comparison with Pure Platinum

New silver-platinum bimetallic oxygen reduction reaction (ORR) catalysts are investigated in alkaline media both for kinetics and stability aspects. Polycrystalline materials and carbon-supported nanoparticles (Pt/C and Ag-Pt/C) are compared. All catalyst active areas are evaluated by hydrogen adsorption voltammetry and transmission electron microscopy. ORR pathway, studied on a rotating ring-disk electrode, involves four electrons per oxygen molecule both on bimetallic and pure platinum catalysts in classical sodium hydroxide solution (1 M NaOH at 25°C). In industrial medium (11.1 M NaOH at 80°C), only three electrons are exchanged on bulk platinum resulting from partial peroxide formation; these peroxide ions are chemically decomposed in the active layer for carbon-supported catalysts leading to an apparent four-electron pathway. ORR is shown to be first order toward oxygen both in classical and industrial sodium hydroxide solutions. ORR kinetic parameters for silver-platinum bimetallic catalysts are comparable to platinum, even in industrial medium. Carbon-supported catalysts aging behaviors in industrial medium demonstrate the highly instable nature of Pt/C both in open-circuit and polarization, leading to particle growth and consequently to active area decrease. Conversely, Ag-Pt/C remains stable under the same aging conditions. Ag-Pt/C, stable and active, is therefore a suitable catalyst for the air cathode in the membrane chlor-alkali electrolysis process.

Development of a continuous catalytic heterogeneous column reactor with simultaneous extraction of an intermediate product by an organic solvent circulating in countercurrent manner with the aqueous phase

Abstract A new solid-liquid-liquid reactor has been developed in order to simultaneously benefit from the advantages of both the catalytic activity and molecular sieve properties of the zeolites, the superior performances of concentration gradient reactors for positive order consecutive chemical reactions and the extraction of an intermediate target product by a solvent with countercurrent flows. The first reaction experimented with, was the acido-catalyzed dehydration of the hexoses into 5-hydroxymethylfurfural. The study was divided in two parts: (1) laboratory tests in a 0.3-liter batch reactor where mordenites were found to be the most selective catalysts, (2) chemical engineering studies: first, hydrodynamic tests where the systems tested ([water·hexose·zeolite]-methylisobutylketone) enable large through-put capacities, second, chemical tests in a stainless steel pulsed column of 25 mm in diameter and 8220 mm in height. Simultaneously, some simulations have been executed on a software designed by CEA for liquid-liquid extractions and modified by introducing chemical reactions.

Preparation of 5-hydroxymethylfurfural from fructose and precursors over H-form zeolites

Abstract Dehydration of fructose into 5-hydroxymethylfurfural was performed in a batch mode in the presence of H-form zeolites as catalysts, at 165°C and in a solvent mixture consisting of water and methylisobutylketone (1:5 by volume). Fructose conversion and selectivity to 5-hydroxymethylfurfural were found to depend on both acidic and structural properties of the catalysts used. A maximum in the rate of conversion of fructose was observed for Si/Al ratios of 15 and 11 for HY faujasites and H-mordenites, respectively. A maximum in the selectivity to 5-hydroxymethylfurfural was only observed for H-mordenites. The high selectivity obtained (>90–95%) was correlated with the shape-selective properties of H-mordenites, and particularly with the absence of cavities within the structure allowing the further formation of secondary products. Fructose precursors such as sucrose, Jerusalem artichoke and inulin were also found to be selectively transformed into 5-hydroxymethylfurfural under the same operating conditions.

Catalyst gradient for cathode active layer of proton exchange membrane fuel cell

The experimental use of catalyst gradients within the active layer of a PEMFC cathode allows studying the influence of the location effect of Pt nanoparticles on cathode performances. The catalyst gradient effect quantitatively and qualitatively depends on porosity: it is stronger for non-porous active layers than for porous ones. The origin of the catalyst gradient effect is not the same according to porosity: oxygen diffusion is a rate limiting step for non-porous active layers, while ionic-ohmic drop is limiting for porous ones. Thus, the catalyst utilisation efficiency increases with the preferential location of Pt nanoparticles close to the gas diffusion layer side in non-porous active layers and close to the proton exchange membrane side in porous active layers. In the latter case, better performances are observed. Therefore, the optimisation of catalyst utilisation is obtained with thin porous active layers and with preferential location of Pt nanoparticles close to the proton exchange membrane side. These experimental results are confirmed by modelling both diffusion and ionic ohmic drop within active layers with catalyst gradients.

Selective oxidation of 5-hydroxymethylfurfural to 2,5-furan-dicarboxaldehyde in the presence of titania supported vanadia catalysts

Oxidation of 5-hydroxymethylfurfural to 2,5-furan-dicarboxaldehyde was performed in a batch reactor at 363 K in the presence of supported V 2 O 5 /TiO 2 catalysts with different vanadium loadings, and in toluene and methyl isobutyl ketone as the solvents. An air pressure of 1.6 MPa allowed the fast in situ regeneration of the catalyst and the complete transformation of the starting reactant. It appears that a multilayered V 2 O 5 /TiO 2 catalyst with a structure close to that of bulk V 2 O 5 is preferred since involving more V=O species responsible for the oxidation of alcohols. In addition, a higher turnover frequency is obtained in the presence of methyl isobutyl ketone as the solvent. This is particularly suitable for a further development of the reaction on a pilot scale as far as 5-hydroxymethylfurfural is extracted with that solvent in the preceding chemical step and thus may be directly used in the oxidation step.

Hydrolysis of sucrose in the presence of H-form zeolites.

Abstract Hydrolysis of sucrose was performed in aqueous medium in the presence of various H-form dealuminated zeolites (H-BEA, H-MFI, H-MOR, H-Y-FAU). For all catalysts, hydrolysis takes place with a high selectivity whatever the conversion is. The important feature to be noted is the capacity for those catalysts to act as specific adsorbents of colored by-products formed during the course of the reaction, 5-hydroxymethylfurfural (HMF) in particular. The amount of this by-product can be reduced to less than 100 ppm, thus offering an alternative route for the production of colorless invert sugars. In this way, H-Y FAU (Si/Al=15) was found to have the better balance between activity, selectivity and by-product amount.

Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy

The carbon-13 chemical shifts for a number of relatively rigid ketoximes are presented. It is shown that the chemical shift difference, A6 (sj~rr-onri), for the carbons a to the oxime carbon depends on the dihedral angle between the C=N and C.-H bonds. This stereochernical dependence is then used to determine the preferred conforn~ation of substituted cyclohexanone oximes.

Hydrolysis of Fructose and Glucose Precursors in the Presence of H-form Zeolites 1

We have recently reported on the advantages of the use of microporous catalysis like zeolites compared to macroporous catalytic systems, like ion-exchange resin, to achieve the selective transformation of fructrose or fructose precursors sucrose or inulin into 5-hydroxymethylfurfural in water as the solvent.2-4 However, specific properties of the catalyst (controlled acidity, crystallinity, micropore volume) were required for the reaction to take place with a high selectivity. 1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 21-26,1996.