Search

Dimethyl ether is an environmentally friendly alternative to diesel fuel. This fuel can be produced directly from synthesis gas in a slurry bubble column reactor. We predicted the performance of the slurry bubble column reactor for dimethyl ether synthesis using a recirculation model and comparison with axial dispersion results. The differential equations of recirculation and axial dispersion models for the dimethyl ether synthesis are solved for a similar kinetic equation. A comparison of the results with experimental data from the literature confirms that the recirculation model better represents the reactor behavior. Finally, the effects of operating variables are studied using a simulation framework.

Catalytic hydrodechlorination reactions of p-chloro-m-cresol (PCMC) and p-chloroaniline (PCA) were investigated in a slurry reactor using a Ru/TiO2 catalyst. The organic reaction intermediates, m-cresol and aniline, were further converted into methylcyclohexanol and cyclohexylamine respectively. Kinetics of PCMC hydrogenation was studied over the ranges in temperature, 323–373 K, H2 partial pressure, 0.34–1.38 MPa, PCMC concentration, 3.5–14 mM and catalyst loading, 0.1–2 kg/m3. The reaction orders with respect to PCMC and H2 were evaluated as 0.5 and 0.8 respectively. It was found that aniline hydrogenation is the rate-determining step in the hydrotreatment of PCA. Kinetics of aniline hydrogenation was studied at 343 and 363 K over the ranges in H2 partial pressure, 0.34–1.38 MPa, aniline concentration, 5.4–21.5 mM and catalyst loading, 0.1–0.6 kg/m3. The reaction orders with respect to aniline and H2 were found to be 1.3 and 1.0 respectively. © 2012 Canadian Society for Chemical Engineering

The gas–liquid volumetric mass transfer coefficient was determined by the dynamic oxygen absorption technique using a polarographic dissolved oxygen probe and the gas–liquid interfacial area was measured using dual-tip conductivity probes in a bubble column slurry reactor at ambient temperature and normal pressure. The solid particles used were ultrafine hollow glass microspheres with a mean diameter of 8.624 µm. The effects of various axial locations (height–diameter ratio = 1–12), superficial gas velocity (uG = 0.011–0.085 m/s) and solid concentration (eS = 0–30 wt.%) on the gas–liquid volumetric mass transfer coefficient kLaL and liquid-side mass transfer coefficient kL were discussed in detail in the range of operating variables investigated. Empirical correlations by dimensional analysis were obtained and feed-forward back propagation neural network models were employed to predict the gas–liquid volumetric mass transfer coefficient and liquid-side mass transfer coefficient for an air–water–hollow glass microspheres system in a commercial-scale bubble column slurry reactor. © 2012 Canadian Society for Chemical Engineering

Considerable attention has been given to the dynamic behaviour of polymerisation processes. Distinct non-linear phenomena have been predicted (multiple steady states, periodic, and non-periodic oscillations), but experimental confirmation of such responses has been usually confined to free-radical polymerisations systems. Particularly, olefin polymerisation reactors are expected to exhibit complex oscillatory dynamics, but this sort of dynamic behaviour has not been reported experimentally. In this work, real industrial data obtained in a full-scale polyethylene slurry reactor confirm the existence of complex oscillatory behaviour that can lead to process runaway, validating model predictions about the existence of complex dynamics in similar processes. On a porte une attention toute particuliere au comportement dynamique des procedes de polymerisation. Des phenomenes distincts non lineaires ont ete predits (regimes permanents multiples, oscillations periodiques et non periodiques), mais la confirmation experimentale de ces reactions etait habituellement reservee aux systemes de polymerisation radicalaire. Les reacteurs de polymerisation des olefines sont censes avoir des dynamiques oscillatoires complexes, mais ce type de comportement dynamique n'a pas ete demontre sur le plan experimental. Dans la presente etude, de veritables donnees industrielles relevees sur un reacteur a combustible en suspension en polyethylene a grande echelle ont confirme l'existence d'un comportement oscillatoire complexe qui peut provoquer un emballement du processus. Ces resultats valident les predictions du modele relatives a l'existence de dynamiques complexes dans des processus similaires. © 2010 Canadian Society for Chemical Engineering

The local hydrodynamic behaviours in an external loop airlift slurry reactor, including the gas holdup, bubble rise velocity, bubble size, were measured with a fibre optic probe. The liquid circulation velocity was measured with an ultrasound Doppler velocimetry. Two-dimensional simulations were carried out in the framework of Two-Fluid formulation coupled with a k-ϵ turbulence model. The lateral forces and interphase turbulence were taken into account and good agreement between the experimental and simulation results was obtained. The simulations show that the lateral forces and interphase turbulence have noticeable influence and should be included in the CFD model. On a mesure a l'aide d'une sonde a fibres optiques les comportements hydrodynamiques locaux dans un reacteur a suspensions a air ascendant et a boucle externe, incluant la retention de gaz, la vitesse de montee des bulles et la taille des bulles. La vitesse de circulation du liquide a ete mesuree avec un velocimetre Doppler a ultrasons. Des simulations bidimensionnelles ont ete effectuees dans le cadre d'une formulation a deux fluides couplee a un modele de turbulence k-ϵ. On a tenu compte des forces laterales et de la turbulence interphasique et de bons accords ont ete trouves entre les resultats experimentaux et des simulations. Les simulations montrent que les forces laterales et la turbulence interphasique ont une influence notable et devraient etre incluses dans le modele CFD.

Propylene partial oxidation over hydrophobic catalysts was studied in a slurry reactor. Due to the hydrophobicity of the catalyst, a direct reaction mechanism between the gas phase reactants and the catalyst was proposed for the reaction. The experimental results and the predictions based on this model are consistent, indicating that the proposed mechanism is reasonable for propylene oxidation over the hydrophobic catalyst. Also, due to the hydrophobicity and the low density of the catalyst, it is observed that there is non-uniform catalyst particle distribution in the reactor. The effect of the catalyst particle non-uniformity on the reaction is discussed and predictions are made based on the model. The effect of different operating conditions for the slurry reactor on propylene conversion, selectivity to CO2, and acrylic acid yield have been studied. A comparison between results obtained using the hydrophobic and hydrophilic catalysts shows the advantage of using the hydrophobic rather than hydrophilic catalysts for propylene partial oxidation in the slurry reactor, which is attributable to the direct reaction mechanism over the hydrophobic catalysts.

Enhancement in the reaction rate of hydrogenation of p-nitrotoluene on Raney nickel in a three-phase slurry reactor due to the presence of water in the reaction mixture has been observed. The promoting action was found to be dependent on the initial concentration of water, the reaction rate passed through a maximum when the initial water concentration varied from 0.0 to 10.85 (mmol cm-3). A two to three fold increase in the reaction rate dependent on the temperature has been observed at the optimum water concentration. However, at very high concentrations (above 8.0 mmol cm-3) water inhibited the hydrogenation. The reaction is not influenced significantly by the presence of p-toluidine.

Photocatalytic disinfection using TiO2 particles suspended in a reactor involves two major problems; the exponential decrease of light availability due to the scattering of UV light by particles themselves and the difficulty of recycling particles. To resolve these problems, scratched optical-fibres, inserted in glass tubes were used to diffuse UV light uniformly in a reactor. Comparative disinfection studies using these optical-fibres were done in both cases of suspended and immobilised photocatalysts. Disinfection capability with the immobilised photocatalysts at 4.9 µE s−1 dm−3 was twice that of the slurry reactor. Survival ratios of less than 0.2 were obtained with a residence time of 50 min and an initial cell concentration of 10000 cfu cm−3 in the 6 dm3 plug-flow type reactor. © 2000 Society of Chemical Industry

On a utilise un plan d'experience statistique afin d'etudier les effets de la pression, de la temperature, du chargement de catalyseur et de la vitesse de melange sur les solubilites (C * ) et les coefficients de transfert de matiere volumetriques gaz/liquide (k L a) pour H 2 , N 2 , CO, CH 4 et C 2 H 4 dans un melange liquide d'hexanes contenant un catalyseur a l'oxyde de fer dans un reservoir agite de 4 litres. Des correlations statistiques ont ete etablies pour les valeurs de k L a pour les gaz utilises. C'est la vitesse de melange et la concentration de solides qui agissent le plus sur k L a. A de faibles concentrations de catalyseur, on a observe un maximum dans k L a et a des concentrations >37% massique, k L a diminue de plus d'un ordre de grandeur.

An ultrasonic transmission technique is under development to determine the concentration of solids in a three-phase slurry reactor by measuring the velocity of ultrasound in slurries. Preliminary measurements have been made on slurries consisting of water, glass beads, and air bubbles. The data show that both the sound speed and attenuation are well-defined functions of both the solid and gas concentrations in the slurries. A simple model is proposed to correlate the concentration of solids with the measured ultrasonic signals.

A statistical approach was developed to investigate the effects of pressure, temperature, mixing speed and solid concentration on kLa for gaseous hydrogen, ethylene, and propylene in liquid n-hexane containing solid polypropylene powder in a 4-litre agitated reactor. The solubilities of the gases appeared to follow Henry's Law. Statistical correlations to predict kLa were proposed and response surfaces were constructed. kLa values appeared to reach a maximum around 15 mass% and sharply decrease above 30 mass%. The effects of pressure and temperature on kLa were found to depend on the gas-liquid system and operating conditions used. On a mis au point une methode statistique pour etudier les effets de la pression, de la temperature, de la vitesse de melange et de la concentration de solides sur kLa pour de l'hydrogene, de l'ethylene et du propylene gazeux dans du n-hexane contenant de la poudre de polypropylene solide dans un reacteur agite de 4 litres. Il semble que les solubilites des gaz suivent la loi d'Henry. On propose des correlations statistiques afin de predire kLa, et des surfaces de reponse sont construites. Les valeurs de kLa semblent atteindre un maximum autour de 15% en masse et diminuent considerablement autour de 30% en masse. On a trouve que les effets de la pression et de la temperature sur kLa dependaient du systeme gaz-liquide et des conditions de fonctionnement utilisees.

The behavior of a vibrating column of liquid as a slurry reactor and the dependence of the mass transfer resistances on the frequency of oscillation and liquid temperature were studied. The hydrogenation of liquid acetone over Raney nickel was chosen as the model reaction. The tortuosity factor of the catalyst was determined from measurements with two different particle sizes.

Fischer-Tropsch synthesis (FTS) on K promoted Fe catalyst was studied in three bubble column slurry reactors (BCSR) of 2.5, 5, and 10 cm diameter. The objective was to check data reproducibility under conditions of arbitrary alterations of various parameters. First order rate constants evaluated on the basis of appropriate slurry reactor models were chosen as an approximate measure to characterize data reproducibility and catalyst activity. It was found that rate constants and hence reproducibility may differ by a factor of two if different batches and precipitations of catalyst are considered. Within the parameter ranges covered in this study this rule of thumb is valid irrespective of reactor diameter, type of sparger, catalyst concentration, temperature, pressure, and gas flow rate. The rate constants compare well with literature data. On a etudie la synthese Fischer-Tropsch sur un catalyseur au Fe activee par le K dans trois reacteurs a colonnes a bulles et suspension dont les diametres etaient respectivement 2.5, 5 et 10 cm. L'objectif du travail etait de verifier la reproductibilite des resultats dans des conditions de perturbations arbitraires de divers parametres. On a choisi, comme mesure approximative servant a caracteriser la reproductibilite des donnees et l'activite du catalyseur, des constantes de vitesse de premier ordre evaluees a l'aide de modeles de reacteurs a suspension appropries. On a constate que les constantes de vitesse done la reproductibilite peuvent differer d'un facteur 2, si l'on considere differents lots du catalyseur. Dans les limites des gammes des parametres couvertes dans la presente etude, cette regie empirique est valable, independamment du diametre du reacteur, du type de barboteur, de la concentration du catalyseur, de la temperature, de la pression et du debit de gaz. Les constantes de vitesse se comparent bien avec celles donnees dans la litterature.

The analysis of the overall effectiveness factor for the reaction system involving heterogeneous-homogeneous chain reactions at low concentration of one species is studied. A more general theoretical analysis for estimating the overall effectiveness factor of reaction systems which can be a heterogeneous-homogeneous chain reaction system at low concentration of one species in a slurry reactor is presented, incorporating all the transport parameters. The concepts of overall effectiveness factors for reactions have been extended from the traditional heterogeneous reaction system to the heterogeneous-homogeneous chain reaction system. The effects of reaction mechanism and kinetic models on the overall effectiveness factor are also proposed. Comparisons of the overall effectiveness factor for a slurry reactor with or without considering the reaction mechanism are also obtained.

The moment method has been used extensively to evaluate parameters of chemical reactions, adsorption or reactor design, but only for linear systems. Moment analysis of nonlinear systems is studied in the present work. A general complicated reaction system involving nonlinear terms in a batch slurry reactor is chosen to demonstrate the method. The first and second improved solutions in Laplace domain and moment expressions are obtained. The improved solution can converge to the exact solution if the iterative procedures are repeated several times. La methode des moments est largement utilisee pour evaluer les parametres de reactions chimiques, d'adsorption et de conception de reacteur pour des systemes lineaires. On a effectue dans ce travail l'analyse des moments de systemes non lineaires. Cette methode est illustree a l'aide d'un systeme complexe general de reactions faisant intervenir des termes non lineaires dans un reacteur discontinu a combustibles en suspension. On a obtenu des solutions ameliorees dans le domaine de Laplace ainsi que l'expression des premier et deuxieme moment. Il est possible de faire converger la solution amelioree vers la solution exacte si la procedure iterative est repetee a plusieurs reprises.

Experimental leaching runs were carried out in a continuous concurrent laboratory size bubble column 5.2 cm in internal diameter and 2.90 m tall. The system studied was the dissolution of a synthetic covellite (CuS) in ammoniacal solution in the presence of pure oxygen. Behaviour of the column with respect to gas holdup and solids concentration profiles was measured without reaction by using nitrogen in place of oxygen. Gas holdup values were in agreement with literature results. However, solids concentration profiles for the mixed particle size solid used were of a more complex nature than those obtained for uniformly sized solids. Conversions obtained at various temperatures and gas and liquid velocities were analyzed in terms of the estimated rates of the individual rate processes occurring. From these results, gas absorption rate was clearly the controlling mechanism at high temperatures, and surface chemical reaction rate was controlling at low temperatures. Hence, the rate controlling steps can be identified in bubble column reactors from currently available literature correlations, together with independent kinetic measurements. On a fait des experiences de lixiviation dans une colonne a bulles de laboratoire a alimentation continue et a co-courant, dont les dimensions correspondaient a un diametre interieur de 5.2 cm et a une hauteur de 2.90 m. L'etude a porte sur la dissolution d'une covellite (CuS) synthetique dans une solution ammoniacale en presence d'oxygene pur. On a determine le comportement de la colonne en ce qui a trait aux profils de retention de gaz et de concentration des matieres solides, en l'absence de reaction, en substituant l'azote a l'oxygene. Les valeurs de la retention du gaz sont en accord avec celles qui existent dans la litterature; toutefois, les profils de concentration en matieres solides, dans le cas du solide a particules mixtes employe, se sont averes plus complexes que ceux qu'on a obtenus avec des matieres solides de dimensions uniformes. On a analyse les conversions obtenues a differentes temperatures et differentes vitesses du gaz et du liquide, en termes de vitesses estimees pour chacun des processus isole. On deduit de ces resultats que l'absorption du gaz etait clairement le mecanisme limitant aux temperatures elevees, tandis que la reaction chimique de surface etait l'etape limitante aux basses temperatures. Il s'ensuit qu'on peut identifier, dans les reacteurs a colonnes a bulles, les etapes qui contrǒlent la vitesse a partir des correlations disponibles dans la litterature et de mesures cinetiques independantes.

The optimum operating temperature and pH have been determined for a catalyst prepared by the insolubilization of a hepatic microsomal mixed-function oxidase on glass beads. Temperature is a more significant variable than pH in determining potential catalyst yield (total product/unit catalyst). An operating range of about 25–28°C is optimal with respect to catalyst life at pH 7.6. Like the purified soluble oxidase, the glass bead-mounted enzyme catalyzes the NADPH- and oxygen-dependent oxidation of a variety of amines, hydrazines, and thioureylenes. The catalyst has been used in a simple slurry reactor to prepare mg quantities of N-oxide metabolites of prochlorperazine, guanethidine, and ethylmorphine.

Solids concentration profile was measured for the basic babble column slurry reactor configuration: steady flow with respect to gas and batch with respect to solid and liquid. The result confirmed the exponential profile predicted by a diffusion model. An application is discussed. On a mesure le profil de concentration de solides dans le cas d'une configuration de base d'un reacteur pour suspensions epaisses muni d'une colonne a bulles: il s'agissait d'un ecoulement stable par rapport au gaz et discontinu par rapport au solide et au liquide. Les resultats obtenus ont confirme le profil exponentiel qu'un modele de diffusion avait predit. On y discute une application.

Methode quantitative de determination de l'influence de la distribution des temps de sejour, en fonction des parametres pertinents