Fractionnement de deux bois tropicaux (eucalyptus et wapa) par traitement thermomécanique en phase aqueuse. Partie II: Caractéristiques chimiques des résidus et considérations cinétiques sur la solubilisation des hémicelluloses

We have characterized the residual solids derived from the aqueous phase liquefaction of two tropical wood species. The liquefaction process comprises the following steps: preparation of an aqueous suspension of milled wood, preheating at 135°C, sudden decompression through an orifice (ΔP = 17.2 MPa), reaction at 80–230°C and rapid quenching. The residues have been analyzed by two methods: acid hydrolysis and elemental analysis. The quantification of the monosaccharides present in the residues allows us to follow the solubilization profiles of both hemicelluloses and cellulose. The elemental composition of the residues is related to the severity of the process and it becomes a solubilization index for the hemicelluloses and the lignin. The chromatographic analysis of the gaseous phase after liquefaction has resulted in the determination of CO₂ as the only gas produced up to 230°C. Kinetic first order models represent well the solubilization of the hemicelluloses and the CO₂ formation.     

Détermination électrochimique du nombre de sherwood minimum pour un milieu macro‐poreux (fritté — lit fixe de grains)

In this work, an electrochemical method used for the determination of solid‐liquid mass transfer coefficients has been applied to the measurement of the Sherwood number for the stationary diffusional mass transfer between a porous material and a stationary liquid in the pores. Such a minimum Sherwood number was determined for sintered metals and for fixed beds of spherical grains. The theoretical aspects are based on the analogy of the problem with competition between molecular diffusion and heterogeneous chemical reaction in a porous catalyst.     

Augmentation,par régénération électrochimique du substrat,de la production d'une biomasse (thiobacillus ferrooxidans DSM 583) pour un procédé biologique de récupération de métaux

A bioelectrochemical reactor regenerates the substrate of the acidophilic bacterium Thiobacillus ferrooxidans DSM 583 (ferrous ions). This reactor uses a through-flow porous fixed bed or carbon as cathode. A linearizing non-linear regulator insures an efficient control of the intensity imposed to the electrochemical reactor. The protein concentration, correlated to the biomass concentration, is 6.4 fold increased for a 55 h growth, including a 20 h electrolysis. The metal tolerance and the metal fixation capacity of a T. ferrooxidans biomass are presented both for solutions including one or two metallic ions and an industrial waste. A bioelectrochemical process based on these characteristics is proposed for removing metal ions from wastes.     

Etude de l'élimination des ions Cu (II) de la solution aqueuse par sorption sur la zéolithe a study of the removal of Cu (II) from aqueous solution by sorption on Zeolite A

The objective of this study is to present the results of removal of copper by the method of sorption on zeolite A. The batch experiments were conducted for both the kinetics for the sorption isotherms. The experimental variables studied were pH, contact time at different initial concentrations, the amount of sorbent, temperature and stirring speed. The sorption capacity depends on the pH and mass of sorbent, but the temperature and stirring rate showed no influence. Several mechanisms of retention of copper on the zeolite could be competitive (ion exchange, complexation or precipitation and sorption). The modeling of experimental data on kinetics showed that the model of pseudo‐second order describes satisfactorily the sorption on the zeolite, and that the limiting step of the speed distribution intraparticle. Statistical analysis of the constants for Langmuir‐Freundlich equation has shown that this model seems most appropriate to describe this phenomenon of sorption, which indicates the heterogeneity of the surface sorption of the zeolite. Copyright © 2011 Canadian Society for Chemical Engineering