Contributions au génie des réactions polyphasiques (Contributions to multiphase reaction engineering)

This HDR presents researches developed on the characterization and modelling of multiphase catalytic reactors (in particular three-phase fixed bed), on the investigation of biphasic catalysis systems (using ionic liquids or amphiphilic core-shell polymers), and on the development of non-conventional (hybrid) processes for the environment, in the areas of waste & water treatment and CO2 mitigation

Selective hydrogenation in trickle-bed reactor. Experimental and modelling including partial wetting.

A steady state model of a trickle bed reactor is developed for the consecutive hydrogenation of 1,5,9-cyclododecatriene on a Pd/Al2O3 catalyst. Various experiments have shown that the selectivity of this reaction towards the product of interest is much lower in co-current down-flow (trickle-bed) than in up-flow. This is due to uneven liquid distribution and to partial wetting of the catalyst surface at low liquid flow rates. The non-isothermal heterogeneous model proposed here takes into account the partial wetting of the catalyst, as well as the resistances to heat and mass transfer at the gas-liquid, liquid-solid and solid-gas interfaces. It assumes that the catalyst particles can be divided into two distinct concentration zones corresponding to the wetted and dry catalyst surfaces; mass transfer between these two zones is described by a simplified diffusion mechanism. Compared to previous models assuming a uniform concentration of liquid-phase components inside the catalyst particles, this model improves the prediction of the outlet concentrations of hydrogenation products

Theoretical analysis of tracer method for the measurement of wetting efficiency

This work investigates the tracer technique for the measurement of catalyst wetting efficiency, f, in trickle-bed reactor. The model of Ramachandran et al. (1986), based on a 2D description of the tracer diffusion, is applied for the full range of wetting efficiency. It is also extended to account for the effects of axial dispersion, liquidsolid mass transfer, pattern of the wetted zone on the pellet, and distribution of the partial wetting along the reactor. The numerical method for parameter optimisation implies a frequency domain least-squares procedure. A sensitivity analysis has been performed proving the wetting efficiency may be derived with convenient accuracy in usual trickle-bed conditions: high Peclet and Biot numbers. For f>0.3, it is shown that wetting efficiency can be accurately calculated from apparent particle diffusivities derived in liquid-full conditions (Deapp,LF) and in partial wetting regime (Deapp,TB), using the following relation: f=sqrt(Deapp,TB)/(Deapp,LF)

AD–OX: A sequential oxidative process for water treatment— Adsorption and batch CWAO regeneration of activated carbon

A sequential process for water treatment involving usual adsorption on activated carbon (AC) followed by wet air catalytic oxidation of the adsorbed pollutants has been carried out in a fixed bed reactor with a mixture of two model pollutants. The first step achieves water purification while the second one reduces the organic pollution but also, more importantly, performs some AC in situ regeneration. The experimental work has been done with AC yet extensively used and stabilized by long range continuous oxidation. The two steps have been analyzed successively showing very important drop of adsorption capacity with respect to fresh AC but efficient oxidative partial regeneration. As expected with used AC no more evolution occurs in between two consecutive runs. The first step of competitive adsorption has been simulated by a model leading to higher diffusivities than estimations based on correlations. The main features of the complex second step, involving simultaneous non-isothermal desorption and three phase catalytic reaction, are qualitatively explained

Carboscories : carbonatation minérale en Nouvelle-Calédonie : rapport bibliographique. Tome Nickel et technologie (rapport scientifique 2015)

La carbonatation minérale ex-situ, accélérant un processus naturel thermodynamiquement favorable, est considérée comme une voie possible pour le piégeage du CO2 émis par les installations industrielles. La situation insulaire de la Nouvelle-Calédonie, avec une proximité des flux de CO2 émis et des ressources carbonatables, est favorable au développement d’une filière. La carbonatation des résidus de pyrométallurgie, largement étudiée dans le monde au stade du laboratoire (notamment par plusieurs équipes d’universités américaines prestigieuses), n’a pas encore pu être menée à un stade pilote/pré-industriel, du fait notamment de verrous liés au procédé (faibles rendements de carbonatation liés à la passivation des surfaces réactives ; conditions opératoires contraignantes). Le projet CARBOSCORIES s’inscrit dans la continuité du projet ANR/CARMEX (2009-2012) qui a permis des avancées significatives sur la carbonatation minérale ex-situ, avec notamment le développement, au Laboratoire de Génie Chimique de Toulouse (LGC), d’un procédé en mode « batch » couplant attrition et réaction de carbonatation (thèse B. Bonfils, 2012). L’objectif de CARBOSCORIES concerne le transfert des acquis du nouveau procédé CARMEX aux scories de la SLN déjà caractérisées chimiquement et minéralogiquement dans le projet CARMEX et l’évaluation des potentialités de carbonatation des scories de KNS, seconde source de résidus industriels potentiellement carbonatables. En effet, il existe une différence majeure entre les scories issues des deux procédés. Les scories SLN sont finement fractionnées (<5 mm) grâce à un passage de la scorie en fusion à la sortie du four devant un rideau d’eau de mer (trempe), alors que les scories KNS sont grossièrement concassées après refroidissement (plus lent) à la sortie du four. Les processus de cristallisation s’en trouvent modifiés, ce qui peut influer sur les potentialités de carbonatation. Il est donc proposé dans le cadre du projet CARBOSCORIES de : - de tester la démarche ‘CARMEX’ de carbonatation, valider la bonne réactivité des scories vis-à-vis du CO2 et d’étudier en détail les sousproduits de réaction, finement divisés ; - de réaliser des calculs bilanciels massiques et énergétiques de l’intégration du procédé aux installations industrielles à partir des paramètres opératoires principaux des sites, afin de quantifier l’efficacité de l’unité de carbonatation dans les deux environnements industriels ; - de proposer aux industriels des perspectives opérationnelles en fonction du comportement à la carbonatation des deux types de scories. Des recommandations de préparation industrielle seront proposées le cas échéan

Towards a new oxidation process using ozone to regenerate coked catalysts

This work focuses on the regeneration of a zeolite catalyst from industry deactivated by fouling with coke. To replace high temperature combustion, a common and energy intensive process, an oxidation process under milder conditions (50°C-200°C) has been investigated using ozone. Coked zeolite has been oxidized by an ozone stream in a fixed bed reactor, and regeneration kinetics was followed by analyzing carbon content of the particles and ozone concentration at the outlet. The effects of temperature, time on stream and ozone inlet concentration on carbon removal efficiency were studied. Moreover, elemental analysis showed that a maximum of 74.3% of carbon could be removed from the coked catalyst after 6.5 h. Moreover, the total specific surface area, the pore size distribution and the total pore volume (mainly mesopores) have been evaluated on coked and regenerated samples

Dynamics of internal diffusion during the hydrogenation of 1,5,9-cyclododecatriene on Pd/Al2O3

Dynamic and pseudo-steady state diffusion–reaction models were simulated for the three-phase consecutive hydrogenation of 1,5,9-cyclododecatriene on a shell Pd/Al2O3 catalyst in order to examine the time evolution of concentration profiles inside the catalyst pellet: a model accounting only for the dynamics of the active layer and a model taking also into account the inert part of the catalyst were compared. In the conditions of the semibatch experiments (T=433 K, pH2=1.2 MPa), all the models lead to the same bulk concentration–time curves, but the hydrocarbon concentration profiles in the pores are dependent on the model. The influence of the diffusion in the inert part of the catalyst on the bulk concentrations becomes nonnegligible only when the external liquid volume (out of the catalyst) is reduced. The transient evolution of the concentration profiles in the pores show that hydrogen concentration reaches its steady state within a few seconds, while the evolution of the organic concentration profiles is slower. Furthermore, the reaction rate has been found to be only affected by the hydrogen diffusion. The diffusion of organics can control the reaction rate only for low values of organic concentration and higher pressure in hydrogen

Effet d'une phase solide finement dispersée sur le transfert gaz-liquide en réacteur autoclave et en colonnes à bulles

On a cherché à quantifier et comprendre l’effet de particules microniques sur le transfert de matière gaz-liquide. Les mesures ont été réalisées à la fois en colonne à bulles et en réacteur agité par une turbine à induction de gaz pour des suspensions de nature (charbons, silices hydrophiles et hydrophobisées), de taille (de 4 à 32 μm) et de concentrations variées. En colonne à bulles, la vitesse de transfert entre l’air et l’eau est essentiellement liée à l’hydrodynamique, et aucun des solides étudiés n’a permis d’améliorer ni la rétention gazeuse, ni le coefficient de transfert. Au contraire, à partir de 5 g/l, l’ajout des plus fines particules de silice hydrophile a eu un effet négatif. En réacteur agité, la nature du gaz a également été étudiée, mais là encore le transfert gaz-liquide n’est que peu modifié, avec le plus souvent des variations inférieures à 15% par rapport au cas diphasique, mais jusqu’à +50% pour les silices hydrophobisées aux plus fortes vitesses d’agitation

Ultrasonic sludge pretreatment under pressure

The objective of this work was to optimize the ultraso und (US) pretreatment of sludge. Three types of sew-age sludge were examined: mixed, secondary and secondary after partial methanisation ("digested" sludge). Thereby, several main process parameters were varied separately or simultaneously: stirrer speed, total solid content of sludge (TS), thermal operating conditions (adiabatic vs. isothermal), ultra-sonic power input (PUS), specific energy input (ES), and for the first time external pressure. This parametric study was mainly performed for the mixed sludge. Five different TS concentrations of sludge (12-36 g/L) were tested for different values of ES (7000-75,000kJ/kg TS) and 28 g/L was found as the optimum value according to the solubilized chemical oxygen demand in the liquid phase (SCOD). PUS of 75-150 W was investigated under controlled temperature and the "high power input - short duration" procedure was the most effective at agiven ES. The temperature increase in adiabatic US application significantly improved SCOD compared to isothermal conditions. With PUS of 150 W, the effect of external pressure was investigated in the range of 1-16 bar under isothermal and adiabatic conditions for two types of sludge: an optimum pressure of about 2 bar was found regardless of temperature conditions and ES values. Under isothermal conditions, the resulting improvement of sludge disintegration efficacy as compared to atmospheric pressure was by 22-67% and 26-37% for mixed and secondary sludge, respectively. Besides, mean particle diameter (D[4,3]) of the three sludge types decreased respectively from 408, 117, and 110 μm to about 94-97, 37-42, and 36-40 μm regardless of sonication conditions, and the size reduction process was much faster than COD extraction

Effect of partial wetting on liquid/solid mass transfer in trickle bed reactors

The wetting efficiency of liquid trickle flow over a fixed bed reactor has been measured for a wide range of parameters including operating conditions, bed structure and physico-chemistry of liquid/solid phases. This data bank has been used to develop a new correlation for averaged wetting efficiency based on five different non-dimensional numbers. Finally liquid/solid mass transfer has been determined in partial wetting conditions to analyse what are the respective effects of wetting and liquid/gas flow turbulence. These effects appear to be separated: wetting being acting on liquid/solid interfacial area while the liquid/solid mass transfer coefficient is mainly connected to flow turbulence through the interstitial liquid velocity. A correlation has been proposed for liquid/solid mass transfer coefficient at very low liquid flow rate