Kinetic modeling of lignin catalytic hydroconversion in a semi-batch reactor

International audienceA kinetic modeling for lignin catalytic hydroconversion over a supported CoMoS catalyst in a semi-batch reactor has been constructed based on analysis results from Gel Permeation Chromatography (GPC) and two-dimensional Gas Chromatography (GC × GC). The model includes 15 pseudo-component lumped products classified by their states and functional groups. Hydrogen consumption, liquid-gas mass transfer resistance and vapor-liquid equilibrium are accounted for. Physical and chemical parameters were estimated from experiments carried out at 350 °C and 80 bar. The resulting model is able to fit the experimental data well. From estimated parameters, it is deduced that the bottlenecks of lignin catalytic hydroconversion are the deeper conversion of the soluble oligomeric fractions and the relatively slow hydrodeoxygenation rate

Mass transfer studies through biological membranes. A chemical engineering approach

International audienceThis contribution describes the classical way that the process of drug diffusion through skin is studied experimentally. One use the Franz cell in association with a linear model based on Fick diffusion model, linear equilibrium relations and the assumption that the skin can be assumed to be a dense membrane. It appears that the way the Franz cell is used is related to the existence of an analytical solution of the model that is available in classical textbooks [1]. Due to numerical methods, improvements in the description of the process of drug transfer can be proposed. Firstly, the highly complex multiphase/multilayer structure of the skin can be taken into account. Such models have been proposed in the literature devoted to mass transfer through skin [2]. They are more or less complex depending on the properties of the studied layer. In the Stratum Corneum, the pure diffusion model is always assumed due to its avascular nature. However, some papers propose to take into account its structural properties by 2D or 3D "biphasic brick-and-mortar" models with simple partition coefficients between the two phases but diffusion coefficients variable in space [3]. Some improvements were further made adding porosity and tortuosity in the model. In the viable epidermis (VE), some authors have added a convection term to model the transport into blood and lymphatic capillary partition. But the transport has also been modelled using a dispersion term, which includes diffusion and convection at the same time. As far as we know, all these models remain generally based on a linear description of thermodynamic equilibrium and diffusion in order to get, if possible, analytical solutions [4]. Compartment models are also commonly used within this framework [2]. Secondly, modern diffusion theory (Irreversible thermodynamics approach, Maxwell-Stefan approach [5,6]) as well as network model approach could be used provided that more sophisticated thermodynamic models of the skin and knowledge on skin structure to be available

Liquid Organic Hydrogen Carriers or Organic Liquid Hydrides: 40 Years of History

International audienceThe term LOHC stands for Liquid Organic Hydrogen Carriers. The term has been so well accepted by the scientific community that the studies published before the existence of this name are not very visible. In this mini-review, we have tried to rehabilitate various studies that deserve to be put back in the spotlight in the present context. Studies indeed began in the early 1980s and many publications have compared the use of various organic carriers, various catalysts and reactors. Recent reviews also include the economic aspects of this concept

Kinetics of toluene hydrogenation—integrating a dynamic approach regarding catalyst activity

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Kinetic Modeling for the Gas-Phase Hydrogenation of the LOHC γ-Butyrolactone–1,4-Butanediol on a Copper-Zinc Catalyst

International audienceLiquid organic hydrogen carriers (LOHCs) are an interesting alternative for hydrogen storage as the method is based on the reversibility of hydrogenation and dehydrogenation reactions to produce liquid and safe components at room temperature. As hydrogen storage involves a large amount of hydrogen and pure compounds, the design of a three-phase reactor requires the study of gas and liquid-phase kinetics. The gas-phase hydrogenation kinetics of LOHC γ-butyrolactone/1,4-butanediol on a copper-zinc catalyst are investigated here. The experiments were performed with data, taken from the literature, in the temperature and pressure ranges 200–240 °C and 25–35 bar, respectively, for a H2/γ-butyrolactone molar ratio at the reactor inlet of about 90. The best kinetic law takes into account the thermodynamic chemical equilibrium, is based on the associative hydrogen adsorption and is able to simulate temperature and pressure effects. For this model, the confidence intervals are at most 28% for the pre-exponential factors and 4% for the activation energies. Finally, this model will be included in a larger reactor model in order to evaluate the selectivity of the reactions, which may differ depending on whether the reaction takes place in the liquid or gas phase

Détermination de constantes cinétiques du craquage catalytique par la modélisation du test de microactivité (MAT)

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Conception réalisation et évaluation d'un réacteur à plaques milli-structurées pour le couplage autotherme de la déshydrogénation du méthylcyclohexane et de la combustion du toluène

International audienceHeat exchanger reactor (HER) conception consists on separately studying the two involved reactions with opposite thermicity to define volumes and characteristics of each reactor and doing spatially tally powers to improve HER energetic efficiency. To produce 5mg.s-1 hydrogen at about 370°C, a HER coupling methylcyclohexane dehydrogenation and toluene combustion was designed, built and evaluated. Methylcyclohexane dehydrogenation being slow, first order kinetic law but highly endothermic, the reactor consisted in 2 granular beds containing 9,22g of 0,5%Pt/Al2O3 catalyst, with 4,5mm*3mm of section and 440mm of length. Toluene combustion being rapid and limited by transfer at the wall, the reactor consisted in 6 plates structured with self-supplied 2mm*3mm ducts, coated each with 400mg of 2%Pt/Al2O3. The thermal efficiency was about 90% and exchanged heat flows were about 20 kW.m-2.La conception d'un réacteur-échangeur (HER) consiste à étudier séparément les deux réactions de thermicité opposée mises en jeu pour définir les volumes et caractéristiques de chaque réacteur et ensuite à faire concorder spatialement les puissances mises en jeu pour augmenter l'efficacité énergétique du HER. Pour produire 5mg.s-1 d'hydrogène à 370°C, un HER couplant la déshydrogénation du méthylcyclohexane et la combustion du toluène a été conçu, fabriqué et testé. La déshydrogénation du méthylcyclohexane étant lente, d'ordre 1 mais fortement endothermique, le réacteur obtenu est constitué de 2 lits granulaires contenant 9,22g de 0,5%Pt/Al2O3 de section 4,5mm*3mm et de longueur 440mm. Pour la combustion du toluène rapide et limitée par le transfert externe, le réacteur est constitué de 6 plaques structurées par des canaux de 2mm*3mm, enduites chacune d'environ 400mg de 2%Pt/Al2O3 et auto-distributrice. L'efficacité thermique est de l'ordre de 90% et les flux échangés sont de 20 kW.m-2

Port Hamiltonian representation of heat exchanger

International audienceIn this contribution we present an irreversible port Hamiltonian representation of a heatexchanger. The approach is based on a compartment representation of the heat exchanger

Correlation between deactivation and Pt-carbonyl formation during toluene hydrogenation using a H-2/CO2 mixture

International audienceH-2/CO2 mixtures derived from biomass degradation may be regarded as a renewable source of hydrogen that could be used for hydrogenation reactions. The practicality of directly using a CO2-containing H-2 feed was evaluated during the hydrogenation of toluene to methylcyclohexane at 75 degrees C and ambient pressure. An operando DRIFTS study was carried out to unravel some of the mechanistic features of this reaction over a 0.88% Pt/Al2O3 catalyst, in particular to rationalize the loss of activity observed in the presence of CO2. We report, for the first time, a quantitative link between the loss of activity for hydrogenation and the formation of carbonyls adsorbed on the platinum, while the deactivation could not be correlated to the species formed onto the alumina, e.g. carbonates, hydrogenocarbonates and formates. (C) 2010 Elsevier Inc. All rights reserved