Showing papers in "Canadian Journal of Chemical Engineering in 1985"

Hydrogen production by the catalytic steam reforming of methanol: Part 2: Kinetics of methanol decomposition using girdler G66B catalyst

Abstract: The rate of catalytic decomposition of methanol in the presence of steam has been studied using a commercial Girdler G66B CuO-ZnO low temperature shift catalyst from 150 to 250°C at atmospheric pressure. The mole ratio of steam to methanol was varied from 0 to 1.5, and the feed rates covered the range from 300 to 1400 kg s/mol. The data were successfully correlated using a simple reaction network involving CH3OH, H2O, CO and H2. A conventional reversible reaction rate equation was used which included a resistance term for site blockage by a CO surface complex. The methanol decomposition rate constants showed satisfactory Arrhenius behaviour with an activation energy of about 96 kJ/mole. On a etudie la vitesse de decomposition catalytique du methanol en presence de vapeur d'eau, en employant un catalyseur commercial de la reaction du gaz a l'eau a basse temperature (150 a 250°C a la pression atmospherique) Girdler G66B CuO-ZnO. On a fait varier le rapport molaire vapeur d'eau/methanol de 0 a 1,5 et les vitesses d'alimentation ont varie de 300 a 1400 kg s/mol. On a obtenu une bonne correlation des resultats obtenus, en employant une serie simple d'etapes reactionnelles impliquant CH3OH, H2O, CO et H2. On a employe une equation classique pour la vitesse des reactions reversibles qui inclut un terme de resistance pour le blocage des sites par un complexe de surface du CO. Les constantes de vitesse de decomposition du methanol suivent bien la loi d'Arrhenius avec une energie d'activation d'environ 96 kJ/mole

A turbulence closure model for dilute gas-particle flows

Abstract: A second order closure scheme is developed for the numerical prediction of isothermal, non-reacting, mono-dispersed, dilute gas-particle turbulent shear flows. The model is based on the two-equation (κ-ϵ) turbulence model developed for calculating the analogous gas-phase flows. Contrary to passive additives in a single phase flow, the particles will affect the turbulence structure of the continuous phase. Thus, the κ-ϵ model has been modified to account for the presence of the dispersed particles. In particular, the particles increase the dissipation rate because of the relative velocity fluctuations between the two phases. New proposals for these added effects based on particle size and loading are added to these equations. The resulting model is used to compute the axisymmetric jet in its developing region. The calculated jet spreading rate, centre-line velocity decay and entrainment rate are all in excellent agreement with published experimental data. Calculated turbulence quantities such as the kinetic energy and mean Reynolds shear stress are greatly reduced from their “clean jet” levels by the presence of the particles in good agreement with the available experimental data. On a mis au point un schema de fermeture de second ordre pour la prevision numerique d'ecoulements de cisaillement en regime turbulent de systemes dilues gaz-particules, isothermes, non reagissantes et mono-dispersees. Le modele est base sur le modele de turbulence κ-ϵ, a deux equations, developpe pour calculer les ecoulements analogues en phase gazeuse. Contrairement aux adjuvants passifs dans un ecoulement monophasique, les particules affectent la structure de la turbulence de la phase continue. Aussi, on a modifie le modele κ-ϵ. pour tenir compte de la presence des particules dispersees. Les particules augmentent particulierement la vitesse de dissipation a cause des fluctuations de la vitesse relative entre les deux phases. On a ajoute a ces equations des elements nouveaux bases sur les dimensions des particules et sur la charge pour tenir compte de ces effets additionnels. Le modele resultant est utilise pour calculer par ordinateur, un jet axisymetrique dans la zone de developpement. La vitesse de deploiement du jet calculee, la diminution de la vitesse sur l'axe et la vitesse d'entrainement se comparent toutes tres bien avec les resultats experimentaux publies dans la litterature. Les quantites calculees relatives a la turbulence, telles que l'energie cinetique et la contrainte de cisaillement de Reynolds moyenne, sont fortement reduites par rapport a leurs valeurs dans le cas de “jets propres” a cause de la presence des particules et ce, en accord avec les resultats experimentaux disponibles.

A new analysis of the turbulent flow of non‐newtonian fluids

Abstract: A new analysis has been developed for the turbulent flow of non-Newtonian fluids. Based on enhanced viscosity effects at the small time and length scales of the dissipative micro-eddies, the analysis predicts a thickening of the viscous sub-layer tending to increase throughput velocity and thus promoting drag reduction. The required flow parameters can be determined directly from rheograms, without employing correlations based on pipe-flow data. The results give good descriptions of flows of fluids with both power-law and Bingham behaviour and explain a number of peculiarities of such flows.

Stabilisation of emulsion droplets by fine powders

Abstract: Finely divided solids can stabilize emulsion droplets provided the solids are partially wetted by both the disperse liquid phase and the continuous liquid phase. The stabilisation of oil/water emulsions by finely divided solids in the presence of suitable organics has been related to the three phase (solid/oil/water) contact line. Schulman and Leja (1954a) and Taubman and Koretskii (1965) provide evidence that O/W emulsions are formed when the contact angle is less than 90° but inversion occurs to W/O emulsions when the contact angle exceeds 90°. We present a thermodynamic study of emulsion stabilization by finely divided solids, which is an extension of an earlier theory by Van der Minne (1928) who neglected interactions among the particles and droplets and also entropy effects due to Brownian motion. Only stable W/O emulsions are considered here. The starting point of the theory is an expression for the Helmholtz free energy associated with the oil/water interfaces stabilized by finely divided solids in the presence of surfactants. By minimising this free energy, it is shown that in a stable emulsion almost all the solid particles are adsorbed at the oil/water interface of the oil drops. This accounts for the experimental result that the average size of oil droplets decreases with increase in the concentration of solids. A particular example of emulsion stabilization by solids occurs in the hot water extraction process on the Athabasca oil sands. Both clay particles and anionic surfactants act as stabilizers of the bitumen droplets suspended in an aqueous alkaline environment.

Further aspects of powdered poplar wood liquefaction by aqueous pyrolysis

Abstract: The liquefaction of powdered poplar wood by rapid pyrolysis in water at 350°C has been studied further. It differs significantly from the liquefaction of wood chips in that oil yields are improved by pressurisation of the reactor. Oil yields (chloroform soluble) are about 45 per cent and are sensitive to water/wood mass ratios and residence time. Gas, measured in a new handling system, is produced in 5–12 per cent mass yields and contains 86–90 per cent carbon dioxide and 10–13 per cent carbon monoxide. The oil and aqueous phases contain carboxylic acids (particularly acetic), phenols, cyclohexanones, cyclopentanones, benzyl alcohols and furfural. On a poursuivi l'etude de la liquefaction du bois de peuplier en poudre par une pyrolyse rapide dans l'eau a 350°C celle-ci differe d'une maniere significative de la liquefaction des copeaux de bois par le fait que les rendements en huile augmentent avec la pression du reacteur. Les rendements en huile (soluble dans le chloroforme) sont d'environ 45% et dependent du rapport massique eau/bois et du temps de residence. La gaz, mesure dans un nouveau systeme de manutention, est produit avec un rendement massique de 5 a 12%; il contient 86 a 90% d'anhydride carbonique et 10 a 13% de monoxyde de carbone. Les phases huile et eau contiennent des acides carboxyliques (particulierement l'acide acetique), des phenols, des cyclohexanones, des cyclopentanones, des alcools benzyliques et du furfural.

Gravity settling in liquid/liquid dispersions

Abstract: An empirical expression for the prediction of dispersed phase hold-up and slip velocity in droplet dispersions settling under gravity is presented. Analysis of 998 published experimental results for 29 liquid/liquid systems from 14 different data sources shows that the slip velocity of the drop swarm is given in terms of drop diameter and physical properties of the system by: Good agreement between experimental and predicted values of slip velocity is obtained over a wide range of hold-up (0.01 to 0.76) and Reynolds number (0.16 to 3169).

Oil blob populations and mobilization of trapped oil in unconsolidated packs

Abstract: Residual oil was obtained by waterflooding, under water-wet conditions, in unconsolidated packs of glass spheres at low capillary numbers. Trapped oil blobs were mobilized in a sequence of decreasing size with subsequent increases in capillary number. The larger blobs, which extend over many adjacent pores, fission repeatedly upon mobilization and the smaller daughter blobs are restranded. There is negligible oil production until the blob population has been reduced to single pore blobs (singlets). Thus, the critical capillary number for mobilization of significant amounts of oil in unconsolidated bead packs is not related to the original blob size population, but rather to the conditions necessary for mobilization of singlets.

Screening and identification of extractive fermentation solvents using a database

Abstract: The ethanol fermentation has been studied as a model system for end product inhibition and extractive fermentation. Examination has been done on the basis of theoretical considerations, as well as experimental evaluation. For the latter case, a database has been developed in order to screen more than 1,500 solvents for their suitability as extractants in the system solvent-ethanol-water. Based on this screening, 62 solvents have been tested with yeast cultures to determine experimentally such important parameters as biocompatibility, distribution coefficients and phase stability. Fifteen of these solvents have proven to be completely biocompatible, while 26 were completely toxic, the remaining solvents showing different degrees of inhibition. In this paper, the theoretical and experimental procedures involved in the systematic screening of extractive fermentation solvents will be outlined. Also, some heuristic criteria will be presented that allow for an evaluation of solvent biocompatibility a priori. On a etudie la fermentation de l'ethanol comme systeme modele pour l'inhibition par un produit final et pour la fermentation extractive. Cette etude des basee sur des considerations theoriques ainsi que sur une evaluation experimentale. Dans ce dernier cas, on a etabli une base de donnees pour l'examen de plus de 1500 solvants relativement a leur utilite comme agents d'extraction dans le systeme solvant-ethanol-eau. A partir des resultats de cette etude, on a fait l'essai de 62 solvants en presence de cultures de levures, afin de determiner experimentalement differents parametres importants, tels que la biocompatibilite, les coefficients de distribution et la stabilite des phases; 15 de ces solvants se sont reve1es compleement biocompatibles, 26 se sont averes completement toxiques et les autres ont montre differents degres d'inhibition. On expose, dans le present travail, les procedures theoriques et experimentales employees pour la comparaison systematique des solvants pour la fermentation extractive. On presente aussi quelques criteres heuristiques qui permettent d'evaluer α priori la biocompatibilite des solvants.

The mechanism of catalytic cracking of n‐alkenes on ZSM‐5 zeolite

Abstract: The catalytic cracking of n-alkenes on ZSM-5 zeolite at 405°C can occur both by a monomolecular mechanism and a bimolecular process. In the latter, cracking is preceeded by dimerization. We show that pentenes are cracked exclusively by the bimolecular process. The dominant cracking mechanism for n-hexenes also requires initial dimerization, although a small proportion (<19%) of the total cracking may proceed by a monomolecular process. Cracking of n-heptenes is predominantly monomolecular, with only 13% of the total occurring via an initial dimer formation. The cracking of n-octenes and n-nonenes can be interpreted by assuming a monomolecular mechanism only. Thus it appears that at 405°C olefins smaller than C6 are stable with respect to direct cracking and must dimerize before a species is formed which is unstable enough to crack. No molecular hydrogen was produced in any of the cracking reactions reported here in the range of conversions studied.

Kinetic studies of wheat straw hydrolysis using sulphuric acid

Abstract: The kinetics of cellulose and hemicellulose hydrolysis of wheat straw were studied using both isothermal and non-isothermal techniques in a batch reactor. Reactions were carried out between 100 and 210°C and product sugars were analyzed using a Bio-Rad HPX-87P liquid chromatographic column. A simple first order series reaction model was used for both cellulose and hemicellulose hydrolysis reactions and kinetic parameters were obtained for the Arrhenius rate equations for three different sulphuric acid concentrations (0.5, 1.0 and 1.5%). Activation energies remained constant with acid concentration but the pre-exponential factors showed an increase with acid concentration. To minimize the amount of experimental data required and to achieve a unique solution to the kinetic parameters, the technique of combining isothermal and non-isothermal reaction data was studied.

Multistage continuous cultivation of blue-green alga spirulina maxima in the flat tank photobioreactors with recycle

Abstract: Spirulina maxima was continuously cultivated in four 64-liter flat tank photobioreactors in cascade, under continuous 30 klx fluorescent light and nonaseptic condition, in an industrial grade synthetic medium which bubbled with atmospheric air. The increase in the number of stages resulted in the higher biomass concentration and allowed operation with a dilution rate D higher than the alga specific growth rate μ. However, multistage operation does not permit a significant increase in productivity. The recycling of the all culture medium with biomass increased the net productivity of the first two stages of the multistage system. The flat tank design offered great advantages over other geometrical configurations by occupying less space for indoor cultivation, minimizing the water loss by evaporation, and permitting a greater flexibility in construction, installation, and operation. This system was operating continuously for two years in our laboratory for indoor mass production of S. maxima biomass. The flat tank configuration gave the highest areal productivity Pa = 60.5 g/m2·d and highest volumetric productivity Pv = 1.17 g/L·d when operated as a single stage continuous cultivation with high solid recycle. These values are the highest ever reported for any indoor or outdoor mass production system for S. maxima. On a cultive en continu la micro-algue Spirulina maxima, dans quatre photobior%eacteurs a cuves plates de 64 L disposes en cascade sous I'eclairage continu d'une lampe fluorescente de 30 klx et dans des conditions non aseptiques dans un milieu synthetique de type industriel avec barbotage d'air atmospherique. L'accroissement du nombre d'etages a comme resultat une plus grande concentration de la biomasse et permet de fonctionner a une vitesse de dilution D plus elevee que la vitesse de croissance sp%ecifique de I'algue u. Toutefois, le fonctionnement multi-etage ne permet pas d'obtenir un accroissement significatif de la productivite. Le recyclage, avec la biomasse, de tout le milieu de culture augmente la productivite nette des deux premieres Ctapes du systeme. Le concept des cuves plates presente de grands avantages sur d'autres formes geometriques en exigeant moins d'espace pour la culture interieure, en minimisant la perte d'eau par evaporation et en permettant une plus grande flexibilite dans la construction, I'installation et le fonctionnement. On a employe ce systeme au laboratoire continuellement pendant deux ans, pour la production interieure massive de biomasse, en employant la micro-algue Spirulina maxima. La forme des cuves plates a permis I'obtention de la productivite la plus elevee par unite de surface, soit Pa = 60, 5 g/m2 d et de la productivite la plus elevee par unite de volume a savoir Pv = I. 17 g/L.d, pour un fonctionnement en culture continue a un seuletage et avec un recyclage important de solides. Ces valeurs sont les plus elevees qui aient jamais ete rapportees pour un systkme de production massive, a I'interieur ou I'exterieur, impliquant la micro-algue Spirulina maxima.

Destabilization of fluidized beds due to agglomeration part I: Theoretical model

Abstract: This is the first part of a series of two papers to study the agglomeration phenomenon which causes destabilization of certain low and high temperature fluidized beds. A theoretical model is proposed to determine the conditions under which defluidization occurs in fluidized beds in which cohesion forces between granules arise due to the presence of sticky fluids and/or high temperatures. Such bonding mechanisms between particles as solid—liquid bridges, visco-elastic flattening and high temperature sintering are considered. The theoretical model predicts breakup of aggregates in the bed due to forces generated by bubble motion. The theoretical results are compared with experimental measurements in Part II of the paper. Ceci est la premiere partie d'une serie de deux articles dans lesquels on etudie le phenomene d'agglomeration qui produit la destabilisation de certains lits fluidises a basse et a haute temperature. On propose un modele theorique afin de determiner les conditions dans lesquelles la defluidisation survient dans des lits fluidises, les forces de cohesion entre les granules apparaissent du fait de la presence de fluides adhesifs et/ou de temperatures elevees. On considere divers mecanismes de liaison entre les particules, tels que pontages solide—liquid, aplatissement viscoelastique et frittage a temperature elevee. Le modele theorique prevoit la rupture des agregats dans le lit, du fait des forces generees par le mouvement des bulles. Les resultats theoriques et les mesures experimentales seront comparees dans la seconde partie du travail.

A model for liquid‐liquid extraction column performance — The influence of drop size distribution on extraction efficiency

Abstract: A precise model for predicting liquid-liquid extraction column efficiency based upon assumed hydrodynamic, axial mixing and mass transfer behaviour has been formulated and solved numerically. The complex nature of the dispersed phase can be better described by drop-size-dependent residence time distribution (RTD). Both the variation of axial velocities due to drops of different sizes, i.e. forward mixing, and the axial dispersion for the drops of the same size have been considered in this model. The computed results reveal that the effects of both varying velocities and dispersion of drops on extraction efficiency are appreciable and cannot be neglected, and the efficiency may be overestimated if only a forward mixing model is adopted. The comparison of the experimental values of NODP with those predicted shows that the mass transfer data obtained in RDC agree well with the values predicted by the present model for the case of solute transfer in cd direction, and are slightly higher than the predicted ones for the transfer in dc direction. On a formule et resolu numeriquement un modele precis pour prevoir l'efficacite d'une colonne d'extraction liquide-liquide base sur un comportement hydrodynamique hypothetique, le melange axial et le transfert de masse ayant ete formules et resolus numeriquement. On peut mieux decrire la nature complexe de la phase dispersee par une distribution de temps de sejour qui depend de la dimension des gouttes. On a considere, dans ce modele, a la fois la variation des vitesses axiales avec la dimension des gouttes (melange devance) et la dispersion axiale pour les gouttes de memes dimensions. Les resultats calcules revelent que l'effet de la variation des vitesses et celui de la dispersion des gouttes sur l'efficacite d'extraction sont appreciables et ne peuvent etre negliges; l'efficacite peut etre surestimee si seul un modele de melange devance est adopte. La comparaison des valeurs experimentales de Nodp avec les valeurs predites indique que les donnees de transfert de matiere obtenues dans RDC concordent bien avec les valeurs prevues par ce modele dans le cas du transfert du solute dans la direction c d; les valeurs experimentales sont legerement plus elevees que les valeurs prevues dans le cas du transfert dans la direction d c.

An experimental investigation of minimum fluidization velocity at elevated temperatures and pressures

Abstract: Minimum fluidization data at elevated temperatures and pressures are relatively scarce in the literature. This study was undertaken to provide some new data under these conditions. Minimum fluidization velocities at temperatures up to 800°K and pressures up to 5 MPa were measured for uniformly-sized glass beads with diameters between 0.2 mm and 4 mm in beds ranging in diameter from 30 mm to 50 mm. The experimental results are compared with a number of empirical correlations from the literature to determine the validity of the correlations under these elevated temperature and pressure conditions. On ne trouve, dans la litterature, que relativement peu d'information sure les seuils de fluidisation a temperatures et pressions elevees. eette etude a ete entreprise dans le but d'obtenir des donnees nuvelles dans ces conditions. On a mesure les vitesses minimales de fluidisation a des temperatures s'elevant jusqu' a 800 k et des pressions allant jusqu'a 5MPa. pour des billes de verre de dimensions uniformes de diametres compris entre 0,2 et 4 mm, et des lits de diametres compris entre 30 et 50 mm. On a compare les resultats obtenus avec un certain nombre de correlations empriques existant dans la litterature, dans le but de determiner la validite de ces correlations dans les conditions de temperature et de pression elevees.

Comparisons of the yields and properties of the oil products from direct thermochemical biomass liquefaction processes

Abstract: Several different direct thermochemical biomass conversion processes are compared based on the results of an experimental program using standard wood and peat feedstocks. The program was part of the International Energy Agency, Biomass Liquefaction Test Facility project. The operating conditions of the processes compared differed greatly. General correlations of the properties of the oils produced from these processes are made based on the severity of the operating conditions. Important parameters in considering process severity are temperature, pressure, time at reaction conditions and added reactants or catalysts. On a compare plusieurs procedes directs differents de transformation thermochimique de la biomasse, en se basant sur les resultats d'un programme experimental ou I'ou employait des alimentations de bois et de tourbe. Le programme faisait partie du projet d'installation d'essais de liquefaction de la biomasse de I'Agence internationale d'Energie. Les conditions operatoires des procedes compares etaient tres differentes. Les proprietes des huiles produites par ces divers procedes ont ete correlees avec la severite des conditions operatoires. Celle-ci a pour parametres importants, la temperature, la pression, le temps dc sejour dans les conditions de la reaction et les reactifs ou les catalyseurs ajoutes.

Destabilization of fluidized beds due to agglomeration part II: Experimental verification

Abstract: The limiting fluidization-defluidization condition for fluidized beds of sticky particles has been studied experimentally in both low temperature beds in which defluidization occurs due to the presence of sticky fluids and in high temperature beds where agglomeration occurs due to sintering of the granules. The experimental results described herein as well as others taken from the literature are compared to the predictions of the theoretical model developed in Part I of this paper. On a etudie experimentalement la condition limite fluidisation-defluidisation dans le cas des lits fluidises de particules collantes dans les deux cas suivants: dans les lits a basse temperature dans lesquels la defluidisation se produit par suite de la presence de fluides adhesifs, et dans des lits a temperature elevee o-l'agglomeration est due du frittage des granules. On compare les resultats experimentaux decrits dans le present travail ainsi que ceux d'autres rapportes dans la litterature avec les previsions du modele theorique etabli dans la premiere partie de cet article.

Carbon number distribution of fischer — Tropsch CO-hydrogenation products from precipitated iron catalysts

Abstract: It is shown that in a series of precipitated iron catalysts, some show a break in the Anderson-Schulz-Flory (ASF) plot of the distribution of linear products and others do not. It is also shown that the above break is due solely to the change in slope of the linear paraffins and that no such break occurs in the distributions of α or β-olefins. Our conclusion is that the paraffins and olefins are all primary products and that each has a characteristic rate of termination, but all have a common rate of propagation. A growth scheme which explains our observations is presented. On a constate que, dans un serie de catalyseurs au fer precipite, certains presentent une discontinuitye dans la representation graphique de la distribution d' Anderson, Schulz et Flory des produits lineaires, alors que d'autres n'en presentent pas. On a aussi note que cette discontinuee n'est due qu'au changement de pente des paraffines lineaires et qu'aucune discontinuitye de ce type ne se produit dans les distributions des α- ou des β-olefines. Notre conclusion est que les paraffines et les olefines sont toutes de produits primaires et que chacune a une vitesse caracteristique de terminaison, alors que toutes ont la meme vitesse de propagation. On presente un schema pour la croissance qui explique ces observations.

Peat adsorption of herbicide 2,4-D from wastewaters

Abstract: The possibility of utilizing peat as adsorbent for removal of the pesticide 2,4-D from contaminated wastewaters has been evaluated in this investigation. Batch tests were conducted at different conditions of initial solute concentration, pH, particle size of adsorbent, temperature and ratios of weight of adsorbent to solution volume, in order to determine the optimum range of these variables for the adsorption operation. Removal ratios for the 2,4-D of the order of 90% were obtained under optimum conditions. The adsorption of 2,4-D in peat is described adequately by the Freundlich isotherm. Continuous tests, utilizing adsorption columns, were then conducted in order to determine the design parameters for a proposed treatment plant. The column tests were adequately correlated by the Bohart-Adams equation. La possibilite d'utilisation de la tourbe comme adsorbant pour l'elimination du pesticide 2,4-D des eaux residuaires contaminees a ete evaluee dans cette investigation. Des essais discontinus ont ete effectues pour differentes conditions de concentration initiale du solute, pH, granulo-metrie de la tourbe utilisee, temperature, et du rapport poids d'adsorbant par volume de solution avec pour objectif de determiner la plage optimale de ces variables pour une operation d'adsorption. Dans des conditions optimales l'efficacite de reduction de la concentration de 2,4-D est de l'ordre de 90%. L'adsorption du 2,4-D par la tourbe est bien representee par l'isotherme de Freundlich. Des essais d'adsorption continue avec des colonnes d'adsorption ont ete effectues pour determiner les parametres d'une unite de traitement industrielle. Les tests continus ont ete representes adequatement par l'equation de Bohart-Adams.

Characterization of hydrodynamic parameters in rotating disc and oldshue-rushton columns. Hydrodynamic modelling, drop size, hold-up and flooding

Abstract: Flooding rates, dispersed phase hold-up, hold-up profile and drop-size distribution were investigated in rotating disc and Oldshue Rushton 0.10 m diameter, 18 compartment columns with toluene-water as the liquid-liquid system. The axial dispersed phase hold-up and the mean drop size in both contactors varied significantly with column height. The hold-up profiles were correlated by semi-theoretical models. On a etudie les vitesses d'engorgement, la retention de la phase dispersee, le profil de retention et la distribution des dimensions des gouttes dans des colonnes a disques rotatifs et des colonnes de Oldshue et Rushton a 18 compartiments et de 0.10 m de diametre, le systeme liquide-liquide elange toluene-eau. La Retention axiale de la phase dispersee et la dimension moyenne des gouttes dans les deux contacteurs ont varie d'une maniere significative avec la hauteur de la colonne. On a etabli, au moyen de modeles semi-theoriques, des correlations pour les profils de retention.

The solubility of H2S and CO2 in a diethanolamine solution at low partial pressures

Abstract: The solubility of H2S, CO2 and their mixtures in a 2.0 kmol m−3 aqueous solution of diethanolamine has been determined at 40°C and 100°C at partial pressures of the acid gases between 0.003 and 6.5 kPa. The results have been compared with values calculated by a method of prediction. On a determine, aux temperatures de 40° et 100°C, la solubilite de l'anhydride carbonique, de l'hydrogene sulfure et leurs melanges dans une solution aqueuse de diethanolamine (2, O kmol m−3 DEA). On a fait varier les pressions partielles entre 0,003 et 6,5 kPa. On a compare les resultats avec ceux obtenus par une methode de prevision.

Mass transfer in a reciprocating plate extraction column — effects of mass transfer direction and plate material

Abstract: The mass transfer performance of 5 cm diameter reciprocating plate column has been measured with the system n-butyric acid/kerosene (dispersed)/water (continuous). In most of the tests, the reciprocating plate stack was made of stainless steel which was preferentially wet by the continuous phase. During the mass transfer process the holdup and in some cases the Sauter mean droplet diameter were measured. The mass transfer effectiveness, expressed as the height of a transfer unit (Hax) corrected for axial mixing, depended on the phase flow rates, the agitation rate and the direction of mass transfer. For continuous to dispersed phase mass transfer (c d), the mass transfer was more effective, i.e. Hax was lower than for d c mass transfer under the same external conditions. Qualitative and quantitative observations indicated much larger drop sizes in the d c case due to enhanced coalescence. Although mass transfer was less effective under d c conditions, the column capacity was increased. The same effects were also observed when the plate stack was modified by inserting some Teflon plates which were partly wet by the dispersed phase. On a mesure la performance au transfert de masse d'une colonne de 5 cm de diametre a plateaux alternants pour le systeme acide butyrique normal/kerosene (disperse)/eau (phase continue). Dans la plupart des essais, les plateaux alternants etaient faits d'acier inoxydable, qui est mouille de facon preferentielle par la phase continue. On a mesure, durant le procede de transfert de masse, la retention et, dans certains cas, le diamktre moyen de Sauter des gouttelettes. L'efficacite du transfert de masse, exprimee par la hauteur d'unite de transfert (Hox) corrigee pour le melange axial, depend des debits des phases, de la vitesse d'agitation et de la direction du transfert de masse. Dans le cas du transfert de masse a la phase continue a la phase dispersee ( cd), le transfert de rnasse s'est avere plus efficace, c'est-&hdire que Hox etait plus faible que dans le cas du transfert de masse de la phase dispersee & la phase continue (d c) dans les memes conditions externes. Des observations qualitatives et quantitatives ont indique la presence de gouttes de plus grandes dimensions dans le cas d c, par suite d'une augmentation de la coalescence. Bien que le transfert de masse ait ete moins efficace dans les conditions d c, la capacitC de la colonne s'est accrue. On a aussi observe les memes effets lorsqu'on a modifii le materiau des plateaux en y introduisant quelques plateaux de Teflon qui sont mouillks partiellernent par la phase dispersee.

An axisymmetric model of flow in the annulus of a spouted bed of coarse particles. Model, experimental verification and residence time distribution

Abstract: An axisymmetric model of flow in the annulus of a spouted bed of coarse particles which takes into account non-Darcy flow and utilizes a new and general axial pressure boundary condition at the spout-annulus interface is presented. The pressure boundary condition and the annulus pressure distribution are experimentally verified and the model used to calculate the residence time distribution and the flowrate at the top of the annulus. In addition, the average axial velocity profile in the annulus is calculated and compared with predictions of several one-dimensional flow models. On presente un modele axisymetrique d'ecoulement dans l'espace annulaire d'un lit “spoute” de grosses particules, qui suppose un ecoulement n'obeissant pas a la loi de Darcy et qui utilise une condition-limite de pression axiale generale a l'interface “spout'-anneau. On a verifie experimentalement la condition limite sur la pression et la distribution de la pression dans l'espace annulaire et le modele a ete employe pour calculer la distribution du temps de sejour et le debit lu sommet de l'anneau. On a aussi calcule le profil moyen de vitesse axiale dans l'espace annulaire et on l'a compare avec les predictions de plusieurs modeles d'ecoulement a une dimension.

Catalytic cracking and skeletal isomerization of n-Hexene on ZSM-5 Zeolite

Abstract: The catalytic cracking and skeletal isomerization of n-hexenes on 80/100 mesh HY zeolite has been studied in the temperature range 350–405°C, and compared with results previously obtained on ZSM-5 zeolites. Species with less than three carbon atoms were not observed as primary cracking products, with traces of ethylene formed only as a secondary product. Although propylene and propane may be formed partially by monomolecular cracking of n-hexenes, the dominant cracking process is bimolecular. Dimerization, followed by disproportionation gives stable C3, C4 and C5 species, in addition to C9, C8 and C7 fragments. The probability of these larger fragments undergoing further cracking before desorption increases with temperature, but is significantly less than found on ZSM-5 zeolites. The main products of skeletal isomerization were monomethylpentenes, with those isomers which can originate from tertiary carbonium ions dominant. Dimethylbutenes were formed mainly as secondary products. The rate of the dimerization-cracking process in which two n-hexene species participate is ⋍ six times slower than the reaction involving a monomethylpentene species and a linear hexene. The increase in the rate of the latter process with respect to the former is reduced on ZSM-5, and this can be attributed to the narrower pore size within this zeolite. In contrast to ZSM-5, there is significant formation of alicyclics, paraffins and aromatic species. The residual coke was found to be considerably poorer in hydrogen content than comparable material formed on ZSM-5. On a etudie le craquage catalytique et l'isomerisation des hexenes normaux sur une zeolithe HY de 80/100 mesh, sur une gamme de temperature de 350–405°C et on a compare les resultats avec ceux obtenus anterieurement sur les zeolithes ZSM-5. On n'a pas observe de composes a moins de trois atomes de carbone dans les produits primaires du craquage, et seulement des traces d'ethylene dans les produits secondaires. Bien que le propylene et le propane puissent etre formes en partie par le craquage mono-moleculaire des n-hexenes, le procede de craquage dominant est bimoleculaire. La dimerisation, suivie de la disproportionation, produit des composes en C3, C4 et C5 stables, en plus de fragments en C9, C8 et C7. La probabilite que ces plus gros fragments subissent un craquage supplementaire avant la desorption, augmente avec la temperature, mais elle est de maniere significative plus faible que celle observee sur les zeolithes ZSM-5. Les principaux produits de l'isomerisation ont ete les monomethylpentenes, les isomeres susceptibles de provenir des ions carbonium tertiaires etant predominants. Les dimethylbutenes ont ete formes surtout comme produits secondaires. La vitesse du processus de dimerisation-craquage dans lequel participent deux n-hexenes, est environ six fois plus faible que la reaction impliquant une espece monomethylpentene et un hexene lineaire. L'augmentation de la vitesse de ce dernier processus, par rapport au precedent, est plus faible sur ZSM-5, et ceci peut etre attribue aux dimensions plus petites des pores de cette zeolithe. Contrairement au cas de ZSM-5, il y a une formation importante de composes alicycliques, paraffiniques et aromatiques. On a trouve que le coke residuel etait bien plus pauvre en hydrogene que le produit comparable forme sur la ZSM-5.

Comparison of the sulfation rates of calcium, magnesium and zinc oxides with SO2 and SO3

Abstract: The sulfation rates of reagent grade calcium and zinc oxides and technical grade magnesium oxide with sulfur trioxide and sulfur dioxide - oxygen mixtures have been measured thermogravimetrically. Experiments have been conducted to determine the rate of reaction for various particle radii (0.071-0.151 mm), temperatures (450-1100 K.) and concentrations of sulfur dioxide, sulfur trioxide (0.075-0.62 moles/m3), oxygen (0-1.5 moles/m3). Experimental results are presented which compare the sulfation rates of each basic oxide with sulfur dioxide and sulfur trioxide at different temperatures. The rate of sulfation of different oxides are compared under the same experimental conditions. On a mesure par thermogravimetrie, les vitesses de sulfatation des oxydes de calcium et de zinc de qualite certifiee et de l'oxyde de magnesium de qualite technique par l'anhydride sulfurique ou par des melanges, d'anhydride sulfureux et d'oxygane. On a fait des experiences pour determiner la vitesse de reaction, pour differents rayons de particules (0.071 a 0.151 mm), differentes temperatures (450 a 1100K) et differentes concentrations de SO2, SO3 (0.075 a 0.062 mole/m3) et de O2 (0 a 1.5 mole/m3). On presente des resultats experimentaux qui permettent de comparer les vitesses de sulfatation de chacun des oxydes basiques avec SO2 et avec SO3, a differentes temperatures. On compare la vitesse de sulfatation des differents oxydes dans les mimes conditions experimentales.

A study of the separation efficiency in horizontal thermal diffusion columns with external refluxes

Abstract: The separation theory of horizontal thermal diffusion columns with external refluxes, which was developed by Halle and Jury, has been derived by use of an orthogonal expansion technique. Considerable improvement is obtained when the refluxes and feed position are carefully chosen. The present formulation can be extended to other conjugated Graetz problems in continuous-contact countercurrent separation processes with refluxes at both ends. La theorie de la separation dans des colonnes a diffusion thermique horizontales avec reflux exterieurs, due a Halle et Jury, a ete developpee en utilisant une technique d'expansion orthogonale. On obtient une amelioration considerable lorsqu'on choisit soigneusement la position de l'alimentation et des reflux. On peut etendre cette formulation a d'autres problemes conjugues de Graetz, dans les procedes de separation a contre-courant et contact continu, comportant des reflux aux deux extremites.

Upgrading of aspen poplar wood oil over HZSM-5 zeolite catalyst

Abstract: Thermally fractionated components of an oil prepared by the liquefaction of aspen poplar wood have been upgraded using a HZSM-5 zeolite catalyst to yield products rich in benzene, toluene, xylenes and higher molecular weight aromatics. The effect of reactor temperatures on the relative abundance of these products has been studied. On a procede a la valorsiation de composes obtenus par fractionnement thermique d'une huile produite par liquefaction du bois de peuplier faux-tremble, en employant pour catalyseur la zeolithe HZSM-5; on a obtenu des produits riches en benzene, toluene, xylenes et des produits aromatiques de poids moleculaire plus eleve. On a etudie l'effet de la temperature des reacteurs sur l'abondance relative de ces produits.

Intraparticle mass transfer in bidispersed porous ion exchanger part II: Mutual ion exchange

Abstract: Intraparticle mass transfer of mutual ion exchange in MR-type resin was analyzed based on the assumption of parallel diffusion of counter ions in the solid phase and the macropore. Local equilibrium was also assumed between the concentration of counter ions in the solid phase and in the macropore, and the mass action law was applied. The Nernst-Planck equation was applied to the fluxes of ions diffusing through the solid phase and the macropore. The derived equations were solved numerically by using macropore and solid phase diffusivities obtained earlier by isotopic ion exchange. The theoretical lines agreed fairly well with the experimental uptake curves of R-H-NaCl, R-Na-HCl, R-Na-Zn(NO3)2, R-Zn-NaNO3 and R-H-ZnCl2 systems. The lower the concentration of bulk solution Co is, the smaller the effect of Co on the ion exchange rate becomes. The experimental uptake curves of Co ≤ 0.01 (mmole/cm3) were not affected by Co but agreed fairly well with the theoretical line for solid phase diffusion control. An approximate estimation method for obtaining the uptake curve was also proposed. This method gave fairly good approximation for equal valence ion exchange and for R-Na-Zn(NO3)2 systems. On a analyse le transfert de masse intraparticulaire dans l'echange d'ions dans une resine de type MR; dans l'hypothese d'une diffusion parallele des contre-ions dans la phase solide et dans les macropores. On a aussi suppose l'equilibre local entre la concentration des contre-ions dans la phase solide et dans les macropores, et on a applique la loi d'action de masse. On a aussi applique l'equation de Nernst-Planck aux flux des ions diffusant par la phase solide et par les macropores. On a resolu numeriquement les equations etablies, en employant les diffusivites en phase solide et dans les macropores obtenues anterieurement par echange isotopique d'ions. Les courbes theoriques ont assez bien concorde avec les courbes d'adsorption experimentale pour les systemes de R-H-NaCl, R-Na-HCl, R-Na-Zn(NO3)2, R-Zn-NaNO3 et R-H-ZnCl2. Plus la concentration globale de la solution Co etait faible, et plus l'effet de Co sur la vitesse de l'echange d'ions est faible. Les courbes d'absorption experimentale a Co s 0,01 mmole/cm3 ne sont pas affectees par Co, mais elles sont en assez bon accord avec la courbe theorique pour un phenomene controle par la diffusion en phase solide. On propose aussi une methode approchee d'evaluation pour obtenir la courbe d'absorption; cette methode fournit une assez bonne approximation, dans le cas des systemes d'echange d'ions de meme valence et pour R-Na-Zn(NO3)2.

Equilibria of H2S and CO2 in triethanolamine solutions

Abstract: The equilibrium solubility of H2S and CO2 has been measured in 2.0, 3.5 and 5.0 mol/L triethanolamine solutions. Data were obtained at temperatures of 25°, 50°, 75°, 100° and 125°C at partial pressures of the acid gases ranging from 0.01 to 6360 kPa. Enthalpies of solution were calculated from the solubility data. On a determine, aux temperatures de 25°, 50°, 75°, 100° et 125°C, la solubilite respective de l'anhydride carbonique et de l'hydrogene sulfure dans des solutions aquenses 2,0, 3, 5, et 5,0 molaire de triethanolamine. Les prssions partielles de l'anhydride carbonique et de l'hydrogene sulfure out varie de 0,01 a 6360 kPa. On a utilise les resultats obtenus pour calculer les enthalpies des solutions.

Liquid diffusion measurement by holographic interferometry

Abstract: The use of classic interferometry to study liquid diffusion has been well known since the 1940's. Much more recently holographic interfereometry was introduced in this field of study. In this paper a description of the general characteristics of holographic interferometry is presented. The evolution as well as the improvements of the technique are describged. L'emploie de l'interferometrie classique pour etudier la diffusion dans les liquides est bien connu depuis les annees 1940; ce n'est que plus recemment que l'interferometrie holographique a ete introduite dans ce domaine. On presente une description des caractaristiques generales de l'interferometrie holographique. On discute l'evolution etles ameliorations de cette technique.