Christophe Calais

Reactivity of ethanol over hydroxyapatite-based Ca-enriched catalysts with various carbonate contents

The Guerbet reaction of ethanol to produce heavier products was performed over a series of extensively characterized carbonate-containing hydroxyapatites (HAPs) with different Ca/P ratios and thus different densities, strengths and natures of acid and basic sites. These properties were correlated with the reactivity of the solids and an optimal ratio between the amount of acid and basic sites was evidenced (ca. 5). The best performance was accordingly obtained over the Hap-CO3 catalyst, which gave a yield of 30% of heavier alcohols at 40% ethanol conversion.

Comparative Studies of Chlorine Dioxide Reactions with Muconic Acid Derivatives and Lignin Model Compounds

Abstract The reaction of chlorine dioxide with different types of lignin model compounds was investigated in order to compare the kinetics and to evaluate the amount of oxidant consumed by the different substrates. Complete reaction of lignin model compounds was observed at ClO2‐to‐substrate molar ratios of 0.9–1.2, which corresponds to an electron transfer varying between 5–6 equivalents per mole of substrate. Muconic acid derivatives also fully reacted, at a ClO2‐to‐substrate molar ratio of 1.2, with the oxidant consumption being about 4 equivalents per mole of substrate. The reaction of mixtures of phenolic, non‐phenolic, and muconic acid type substrates showed that the reaction rates of non‐phenolic and muconic acid type substrates were rather similar. This study suggests that further reaction between ClO2 and the primary lignin oxidation products, such as muconic acid type structures could be the cause of overconsumption of oxidant in a D stage.

Titration of free phenolic groups in pulps 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract The ClO2 titration method for in situ measurement of free phenolic groups in pulp has been improved to minimize interferences from other groups susceptible to react with ClO2. The method is based upon the reaction between free phenolic groups and chlorine dioxide at a temperature of 0°C, in the presence of dimethyl sulfoxide. Theoretically, one free phenolic group consumes two molecules of ClO2. The pH of the ClO2 treatment was advantageously fixed at 6.7 using a phosphate buffer, and a new protocol was proposed to avoid any possible interference of quinone groups (either present in pulp or formed during the procedure) on the residual ClO2 titration step. The results obtained on isolated lignin samples were compared to those measured by 31P NMR spectroscopy. The ClO2 method gave substantially higher values, for reasons which deserve further investigation.

Selective reduction ofpara-substituted diphenyldisulfides catalysed by a sulfided NiMo supported on alumina catalyst

Abstract The reactivity of a series of para -substituted diphenyldisulfides (X-DPDS, X = OH, NH 2 , CH 3 , NO 2 , CH 3 ) have been determined in a G/L/S reactor in the presence of a sulfided nickel molybdenum sulfide catalyst. Except for the case of the para -nitro derivative, the reaction is highly selective towards S-S bond hydrogenolysis since thiols were the only products formed. Molecular mechanics calculations evidenced that all the X-DPDS adopted the same conformation. These results may account for a high accessibility of the S-S bond to a plane surface explaining the high selectivity observed. Among the substituted DPDS, the dinitro compound was found to be poorly reactive and under more severe experimental conditions, hydrogen attacks preferentially the N-O bond. Theoretical considerations may explain this behaviour. The presence of the other substituents i.e. Cl, NH 2 , CH 3 , OH, in a para position induces a diminution of the reaction rate whatever their nature. This behaviour is different from the one observed in homogeneous media using nucleophilic reagents to perform the same reaction. To interpret this discrepancy between the results of the heterogeneous reaction and those obtained in homogenous media, it is assumed that in the first case the reaction does not imply an important electron transfer from the catalytic site to the adsorbed molecules.