Alain Perrard

Kinetics of glucose hydrogenation in a trickle-bed reactor

Abstract The kinetics of the catalytic hydrogenation of aqueous solutions of d -glucose to produce sorbitol was studied in a high pressure trickle-bed reactor with cocurrent downflow mode. The hydrogenation reactions were performed on a supported nickel catalyst in the temperature range 343 to 403 K and in the pressure range 4 to 12 MPa. Reaction rates were measured on the catalyst extrudates as such or after crushing and sieving them. The kinetic data obtained from measurements of the initial reaction rates as a function of temperature, pressure and mass of catalyst were interpreted with a Langmuir-Hinshelwood rate law where the reaction between adsorbed glucose and hydrogen is the rate-determining step.

Behavior of silica aerogel networks as highly porous solid solvent media for lipases in a model transesterification reaction.

Highly porous silica aerogels with differing balances of hydrophobic and hydrophilic functionalities were studied as a new immobilization medium for enzymes. Two types of lipases from Candida rugosa and Burkholderia cepacia were homogeneously dispersed in wet gel precursors before gelation. The materials obtained were compared in a simple model reaction: transesterification of vinyl laurate by 1‐octanol. To allow a better comparison of the hydrophobic/hydrophilic action of the solid, very open aerogel networks with traditional organic hydrophobic/hydrophilic liquid solvents, this reaction was studied in mixtures containing different proportions of 2‐methyl‐2‐butanol, isooctane, and water. The results are discussed in relation to the porous and hydrophobic nature of aerogels, characterized by nitrogen adsorption. It was found that silica aerogels can be considered as “solid” solvents for the enzymes, able to provide hydrophobic/hydrophilic characteristics different from those prevailing in the liquid surrounding the aerogels. A simple mechanism of action for these aerogel networks is proposed.

Catalytic hydrogenation of arabinonic acid and arabinonolactones

Abstract Aqueous solutions of arabinonic acid in equilibrium with the corresponding γ-lactone and δ-lactone were hydrogenated to arabitol in a batch reactor in the presence of an active-carbon-supported, ruthenium catalyst. Total conversion was achieved at 100 °C under 10 MPa H2 pressure. Depending upon the impurities present in solutions, the selectivities to arabitol were in the range 93.6–97.9% and the initial reaction rates in the range 73–460 mmol h −1 g Ru −1 . Introduction of small amounts of sodium anthraquinone-2-sulfonate in pure solution decreased the reaction rate, but increased the selectivity from 93.6% to 97.9%. The presence of these molecules, which remain adsorbed on the catalyst surface even after successive recycling of catalyst, decreased markedly the rate of dehydroxylation reactions leading to unwanted deoxy-products. The promoter molecules probably act as modifier of the metal surface because of their basic and/or oxido-reduction properties.

Hydrogenation of gluconolactones in equilibrium with gluconic acid on ruthenium catalyst

Water solutions of glucono-δ-lactone and glucono-γ-lactone in equilibrium with gluconic acid were hydrogenated with molecular hydrogen in the presence of a commercial carbon-supported ruthenium catalyst (5% Ru/C, Engelhard Escat 40). Reactions were conducted batchwise on 20 wt% solutions under 100 bar pressure in the temperature range 80–140°C. Reaction rates were unexpectedly high at moderate temperatures (e.g., 0.58 mol h-1 gRu-1 at 100°C) because lactones were probably the reactive species. The selectivity to sorbitol at total conversion was larger than 99% at temperatures lower than 100°C. Kinetic study was done at different temperatures, pressures and concentrations. Modelling of the reaction kinetics showed that the reaction followed a rate law corresponding either to the Langmuir–Hinshelwood mechanism without H2 dissociation, or to the Horiuti–Polanyi mechanism.

Oxygen adsorbed on metallic oxides and the redox mechanism

Abstract Reactions of propene and methanol with the labile oxygen of Sb4SnFe0.25Ox, Cr2O3 and V-Mo-O catalysts have been studied by isotherm and temperature programmed techniques. It is shown that the labile oxygen of the tin antimony oxide catalyst is involved in the redox mechanism of selective propene oxidation and that weakly bound labile oxygen of chromia participates in the conversion of methanol to formaldehyde. In some cases, however, the labile oxygen is only a part of the molybdenum oxide: lattice oxygen diffuses readily to the surface to react with methanol or propene at 300°–400°C.

Oxidative dehydrogenation of rosalva to costenal on supported silver catalysts

Abstract The synthesis of costenal (dec-9-enal) was achieved by oxidative dehydrogenation of rosalva (dec-9-en-1-ol) on silicon carbide supported silver catalysts (4.5% Ag/SiC) at 450°C in a flow reactor. The substrate was vapourized in a stream of oxygen diluted with 25 volumes of nitrogen (flow rate 140–650 l h −1 ). The optimum oxygen to substrate ratio was ca. 1.5. The highest costenal yield (51%) was obtained at 70% conversion as the contact time of the gas flow with the catalyst was the shortest (0.028 s). The activity was stable for a period of 96 h on stream.