Showing papers in "Canadian Journal of Chemical Engineering in 1982"

Correlations for prediction of molecular diffusivities in liquids

Abstract: New correlations have been developed for diffusivities in liquids at infinite dilution for normal paraffin solutions, for aqueous solutions, as well as generally for polar and non-polar solutions. The molar volume, parachor and radius of gyration for both solute and solvent were used as correlating parameters. The new correlations represent a significant improvement in accuracy for predicted diffusivities.

The flash pyrolysis of aspen-poplar wood

Abstract: A continuous fluidized bed bench scale flash pyrolysis unit operating at atmospheric pressure and feed rates of about 15 g/h has been successfully designed and operated. A unique solids feeder capable of delivering constant low rates of biomass has also been developed. Extensive pyrolysis tests with hybrid aspen-popular sawdust (105–250 μm) have been carried out to investigate the effects of temperature, particle size, pyrolysis atmosphere and wood pretreatment on yields of tar, organic liquids, gases and char. At optimum pyrolysis conditions high tar yields of up to 65% of the dry wood weight fed are possible at residence times of less than one second. On a concu et employe avec succes, a l'echelle du laboratoire, une unite de pyrolyse-eclair a lit fluidise continu; le dispositif fonctionnait a la pression atmospherique et a des debits d'alimentation d'environ 15 g/h. On a aussi mis au point un dispositif unique d'alimentation en matieres solides, capable d'assurer de faibles debits constants de biomasse. On a fait des experiences poussees de pyrolyse sur des sciures d'hybrides de peuplier-faux tremble (105—250 μm), dans le but d'etudier les effets de la temperature, de la granulometrie des particules, de l'atmosphere de la pyrolyse et d'un traitement prealable du bois sur les rendements en goudron, liquides organiques, gaz et matieres carbonisees. Il est possible, dans les conditions optimales de pyrolyse, d'obtenir des rendements eleves en goudron, qui peuvent atteindre 65% du bois sec d'alimentation en poids pour des temps de sejour de moins d'une seconde.

On the annular‐to‐wavy flow pattern transition during condensation inside horizontal tubes

Abstract: The annular to wavy and intermittent flow pattern transition during condensation inside horizontal tubes was investigated. Eight data sets corresponding to different tube diameters and different test fluids were used to test the predictions of several diabatic and adiabatic correlations. Deficiencies were found in these correlations which prevented consistent agreement with the data base. An improved correlation is proposed and shown to have a good deal of generality and accuracy in predicting this transition. On a etudie le passage du regime d'ecoulement annulaire au regime ondulatoire et intermittent, lors de la condensation a l'interieur des tubes horizontaux. On a employe huit series de donnees, qui correspondaient a differents diametres de tubes et divers fluides d'essai, pour verifier les previsions de diverses correlations diabatiques et adiabatiques. On a trouve des deficiences dans ces correlations, de sorte que l'on n'a pu obtenir un accord satisfaisant pour l'ensemble de ces donnees; on propose une meilleure correlation dont on montre qu'elle possede beaucoup de generalite et d'exactitude pour la prediction de cette transition.

Microscopic structure of athabasca oil sand

Abstract: A refined structural model for in situ oil sands is proposed in terms of the mutual arrangement of sand grains, fines, water and bitumen. In the Athabasca deposit, the sand grains consist mainly of quartz and their packing is such that the porosity is about 35%. In rich oil sand, 10–15% of the pore space is occupied by connate water whereas the remainder is occupied by bitumen. For lower grade oil sands, a direct correlation exists between the water content and the amount of fines (particles smaller than 44 μm) and an inverse correlation exists between the bitumen content and the amount of fines. These relationships are successfully explained in terms of the irreducible water saturation in a porous medium and the double layer interaction between sand and bitumen surfaces. On propose un modele detaille pour la structure des sables bitumineux in situ, decrivant la disposition relative des grains de sable, des particules fines, de l'eau et du bitume. Dans le gisement de l'Athabasca, les grains de sable consistent principalement de quartz, et leur tassement est tel que la porosite est d'environ 35%. Dans un sable riche en huile, 10–15% de l'espace des pores est occupe par de l'eau naturelle, tandis que le reste l'est par le bitume. Dans le cas des sables petroliferes de moindre qualite, une correlation directe existe entre la teneur en eau et la quantite de particules fines (<44 μm) et il y a une correlation inverse entre la teneur en bitume et la quantite de particules fines; on parvient a expliquer ces correlations en invoquant la saturation irreductible d'un milieu poreux par l'eau et l'interaction des couches doubles des surfaces du sable et du bitume.

Coupling of mixing and microbial kinetics for evaluating the performance of bioreactors

Abstract: The effect of the dynamics of the mixing process in mechanically stirred bioreactors upon their performance has been investigated by using a circulation-model for flow of fluid and a two-environment-model to account for the extent of micromixing in the vessel. With the help of an empirical kinetic model to depict the oxidative and the fermentative growth of bakers' yeast, experimentally observed effects of initial sugar concentrations upon critical dilution rates in continuous cultures of this system could be explained. Effect of different scales of operation upon productivities of fed-batch cultures of bakers' yeast could also be satisfactorily predicted. A discrete simulation procedure was found to be a convenient tool in coupling the two-environment circulation-model of mixing with kinetics of microbial reactions. On a etudie l'effet de la dynamique du processus de melange, dans les bioreacteurs agites mecaniquement, sur leurs performances; on a employe a cette fin un modele de circulation pour l'ecoulement du fluide et un modele comportant deux milieux pour representer le degre de micromelange dans le recipient. On a pu expliquer, grǎce a l'emploi d'un modele cinetique empirique de la croissance de la levure de boulangerie par oxydation et fermentation, les effets observes de la concentration initiale du sucre sur les vitesses de dilution critiques dans les cultures continues du systeme en question. On a pu aussi prevoir d'une maniere satisfaisante l'effet de l'operation a differentes echelles, sur les productivites des cultures de levure de boulangerie alimentees de maniere discontinue. On a trouve qu'une procedure de simulation discrete constituait un moyen approprie pour associer le modele de melange impliquant deux milieux, a la cinetique des reactions microbiennes.

Liquefaction of aspen poplar wood

Abstract: Dried and green aspen poplar wood suspended in water containing alkaline catalysts has been converted completely to an oil, water-soluble chemicals and gases if heated for one hour in the presence of carbon monoxide in a rocking batch reactor. Within the ranges of parameters studied: temperature (593—633 K), nominal reaction times (0—1 h), water-to-wood ratio (0.5:1—5:1), catalyst (Na2CO3, K2CO3, NaOH), amount of catalyst (7.0—12.5 wt %) and initial hydrogen to carbon monoxide ratios (2:1—0:1), the water-to-wood ratio was most important. Oil yields of ˜50% with a carbon plus hydrogen content of ˜80% and representing a carbon recovery of ˜66% were obtained. The higher heats of combustion ranged from 32.2 to 36.0 MJ/kg. Du bois de peuplier faux tremble (vert ou seche), en suspension dans l'eau contenant des catalyseurs alcalins est totalement converti en huile, en produits solubles dans l'eau et en gaz, lorsqu'on le chauffe pendant une heure en presence de monoxyde de carbone dans un reacteur discontinu a bascule. Sur les gammes des parametres etudiees: (a) temperature (593—633 K), (b) duree nominale de reaction (0—1 heure), (c) rapport eau/bois (0.5: 1—5: 1), (d) catalyseur (Na2CO3, K2CO3, NaOH), (e) quantite de catalyseur (7.0 a 12.5% en poids) et (f) rapport initial hydrogene/monoxyde de carbone (2: 1, 0: 1), la valeur du rapport eau/bois s'est averee tres importante. On a obtenu des rendements en huile de ˜50% avec des teneurs de ˜80% en carbone et hydrogene, ce qui represente une recuperation de carbone de ˜66%. Les chaleurs de combustion les plus elevees ont varie 32.2 et 36.0 MJ/kg.

Photocatalytic oxidation of various compounds over TiO2 and other semiconductor oxides; Mechanistic considerations

Abstract: A synthesis of studies on the photocatalytic oxidation of various compounds (isobutane, propene, alkyltoluenes, butanols, ammonia, halide ions in aqueous solution) is presented, TiO2 being the main photocatalyst. Comparisons are also made with other n-type semiconductors: ZrO2, V2O5, Sb2O4, ZnO, SnO2, CeO2, WO3. Information about the mechanism has been obtained by (i) an examination of the photocatalytic isotopic exchange of oxygen in competition with the oxidation of a hydrocarbon, (ii) kinetics and photoconductivity measurements, and (iii) oxidation of butanols by NO. The main conclusions are that these reactions proceed in an adsorbed phase and that dissociated oxygen species play an essential role. On presente une synthese d'etudes faites sur l'oxydation photocatalytique de divers composes (isobutane, propene, alkyltoluenes, butanols, ammoniac, ions halogenures en solution aqueuse), TiO2 etant le principal photocatalyseur. On fait aussi des comparaisons avec d'autres semi-conducteurs de type n, a savoir ZrO2, V2O5, Sb2O4, ZnO, SnO2, CeO2 et WO3. On a obtenu des informations sur le mecanisme en jeu (i) par l'examen de l'echange isotopique photocatalytique de l'oxygene en concurrence avec l'oxydation d'un hydrocarbure, (ii) par des mesures de la cinetique et de la photoconductivite et (iii) par l'oxydation des butanols par NO. On tire comme principales conclusions que les reactions precitees se font en phase adsorbee et qu'une espece d'oxygene dissocie joue un role essentiel.

Laminar flow past a permeable sphere

Abstract: Flow past an isolated permeable sphere has been studied. The complete Navier-Stokes equation governs the fluid motion outside the sphere, while Brinkman's extension of Darcy's Law is assumed to hold within the porous sphere. The Navier-Stokes equation is solved using a finite difference scheme. The flow within the porous sphere is solved in two different ways, each being efficient over a particular range of Reynolds number. Drag Coefficients are presented for dimensionless permeability, β, of 5, 10, 15, and 30 and for Reynolds numbers up to 50. The computed drag coefficients are within 10% of the experimental values observed by Masliyah and Polikar for 15 33, the range covered in their work. Separation was observed only for β > 10. The onset of separation is delayed considerably in porous spheres. On a etudie l'ecoulement au voisinage d'une sphere permeable et isolee. L'equation complete de Navier-Stokes regit le mouvement du fluide a l'exterieur de la sphere, tandis qu'on suppose que l'extension de Brinkman de la Loi de Darcy s'applique a l'interieur de la sphere poreuse. On resout l'equation de Navier-Stokes en employant un systeme de differences finies. On resout le probleme d'ecoulement a l'interieur de la sphere poreuse en procedant de deux manieres qui sont egalement efficaces sur une gamme particuliere de nombres de Reynolds. On presente les coefficients de traǐnee dans le cas d'une permeabilite adimensionnelle (β) de 5, 10, 15 et pour des nombres de Reynolds allant jusqu'a 50. Les valeurs des coefficients de traǐnee calcules se tiennent a 10% des valeurs experimentales observees par Masliyat et Polikar dans le cas de 15 10. Il se produit un retard considerable pour le debut de la separation dans le cas ou les spheres sont poreuses.

Stability of jets in liquid‐liquid systems

Abstract: Experiments were carried out to study the stability of jets in immiscible liquid systems under conditions where the jet velocity relative to continuous phase was zero. The laminar breakup lengths and the diameter of drops formed from laminar jets are in good agreement with the stability analysis for stationary column while breakup data for jets injected into quiescent liquids disagree with it. An approximate solution for theoretical drop size is presented. The experiment also showed that the hydrodynamic resistance of continuous phase increases the growth rate of disturbances but does not affect the wave length. On a etudie experimentalement la stabilite des jets dans les systemes de liquides immiscibles et dans des conditions ou la vitesse des jets, par rapport a la phase continue, etait nulle. Les longueurs de rupture laminaire et le diametre des gouttes formees a partir de jets laminaires concordent bien avec l'analyse de stabilite relative a une colonne stationnaire, tandis que les resultats relatifs a la brisure de jets injectes dans des liquides au repos sont en desaccord avec les resultats de cette analyse. On presente une solution approximative pour les dimensions theoriques des gouttes. L'experience a aussi indique que la resistance hydrodynamique de la phase continue augmente la vitesse de croissance des perturbations, mais n'affecte pas la longueur d'onde.

Characterization of zeolitic acidity I. The cracking of 2 mole % n-Butane over a fixed zeolite bed

Abstract: The use of a two mole percent n-butane in helium stream in a fixed bed mini-reactor at a temperature of 500°C over a zeolite bed (20 to 40 mesh and ≤ 5 grams in weight) was found to be a good tool for characterizing zeolitic acidity. In a broad spectrum of various kinds of zeolites tested, the test results are especially useful in differentiating the extremely active materials from the very active ones. Among the zeolites tested, the decreases in the order of HΩ > H-Zeolon > NH4-ZSM-5 > NH4Y (thermally modified) > NH4-erionite (thermally modified) > > HKL > NH4Y > NaY ˜ amorphous silica-alumina. The calculated first order rate constant covered a range from over 100 to 0.5 cm3/g•min. On a trouve qu'un bon moyen de caracteriser l'acidite zeolithique etait l'emploi d'un melange de butane normal a 2% molaire dans un courant d'helium dans un mini-reacteur, a une temperature de 500°C sur un lit fixe de zeolithe (20 a 40 mesh, ≤ 5-g). Les resultats des essais faits sur une grande variete de zeolithes de differentes natures, sont particulierement utiles pour differencier les zeolithes extrěmement actives des tres actives. Parmi les zeolithes soumises aux essais, l'ordre d'activite decroissante est le suivant: HΩ > H-Zeolon > NH4-ZSM-5 > NH4Y (modifiee thermiquement) > NH4-erionite (modifiee thermiquement) > > HKL > NH4Y > NaY ˜ silice-alumine amorphe. La constance de vitesse de premier ordre calculee a couvert une gamme s'etendant de 100 a 0.5 cm3/g min.

A Chemical equilibrium model for interfacial activity of crude oil in aqueous alkaline solution: The effects of pH, alkali and salt

Abstract: A chemical equilibrium model is proposed to describe the effects of acid content, pH and sodium ion concentration on the interfacial activity of crude oil in aqueous alkaline solutions. The model is based on an equilibrium among the dissociation of acids in the crude, the dissociation of the sodium salt containing the active species and the dissociation of water. It is shown that once the pH of the interface reaches the pKa of the acids, the interfacial tension (IFT) drops steeply and that further addition of sodium ions increases the IFT by shifting the equilibrium to form undissociated soap. On propose un modele d'equilibre chimique pour decrire les effets de la teneur en acide, du pH et de la concentration des ions sodium sur l'activite a l'interface d'un petrole brut dans les solutions alcalines. Le modele est base sur les equilibres pour la dissociation des acides dans le brut, la dissociation des sels de sodium contenant les especes actives et la dissociation de l'eau. On monre que des que le pH a l'interface atteint le pKa des acides, la tension interfaciale (IFT) chute brusquement et qu'une addition supplementaire d'ions sodium augmente l'IFT en deplacant l'equilibre dans le sens de la formation du compose saponifie non dissocie.

Wood liquefaction: Extended batch reactions using raney nickel catalyst

Abstract: Extended batch reactions, in which poplar is treated at 340°C in the presence of Raney nickel, water and hydrogen, give oil in yields of 36-41% with oxygen contents of 12-17%. Methane and carbon dioxide formation, hydrogen utilisation and cracking of the oil are favoured by fresh Raney nickel. There is some competition for methane and carbon dioxide production, higher hydrogen pressures favouring the former in the presence of fresh catalyst. Efficient mass transfer increases hydrogen utilisation and lowers the oil viscosity. It is concluded that Raney nickel has no significant advantage over other more convenient forms of nickel. Par un traitement prolonge en reacteur discontinu, du peuplier a 340°C en presence de nickel de Raney, d'eau et d'hydrogene on obtient des rendements en huiles de 36 a 41% avec des contenus en oxygene de 12 a 17%. La formation du methane et de dioxyde de carbone, l'utilisation de l'hydrogene et le craquage de l'huile sont favorises par la presence d'un catalyseur frai'chement prepare. II y a une certaine concurrence entre la production du methane et celle de l'anhydride carbonique et les pressions elevees d'hydrogene favorisent la formation du methane en presence d'un catalyseur frais. Un transfert de masse efficace augmente l'utilisation de l'hydrogene et diminue la viscosite de l'huile. On conclut que le nickel de Raney n'a aucun avantage important sur d'autres formes plus pratiques du nickel.

A study of agglomeration of coal-ash in fluidized beds

Abstract: Experimental data on agglomeration of coal-ash particles in a fluidized bed have been presented. It has been observed that above the “initial sintering temperature”, the ash particles are defluidized at velocities above their minimum fluidization velocity. The expression for minimum fluidization velocity has been modified by including a force-term due to the phenomenon of sintering in addition to those due to drag, gravity and kinetic energy. On presente des resultats experimentaux sur l'agglomeration de particules de cendres de charbon dans un lit fluidise. On a observe qu'au-dela de la “temperature initiale de frittage”, les particules de cendres etaient defluidisees a des vitesses superieures a leur vitesse minimale de fluidisation. On a modifie l'expression de la vitesse minimale de fluidisation en y incluant un terme de force du' au phenomene de frittage, et qui s'ajoute aux autres termes dus a la resistance au frottement, a la gravite et a l'energie cinetique.

Optimization of copper chloride based catalysts for ethylene oxyhydrochlorination

Abstract: In this work we have studied the effect of adding Li, Na or K chloride to CuCl2 supported on α-Al2O3, on its catalytic activity for the oxyhydrochlorination of ethylene to dichloroethane in a fixed bed reactor, at 573 K and atmospheric pressure Both NaCl and KCl show a strong promoting effect For the case of KCl, this effect has been further examined for a wide range of concentrations and a fixed amount of CuCl2 supported on either α-Al2O3, γ-Al2O3 or SiO2 gel The catalytic and thermogravimetric results obtained indicate that KCl is very effective on the overall rate, even at low concentrations, particularly because it increases considerably the rate of reoxidation of the reduced form of the catalyst In the case of the γ-Al2O3 series, the promoting effect is only moderate Ethylene oxyhydrochlorination data for a series of α-Al2O3 supported catalysts containing a constant K+/Cu2+ atomic ratio and increasing total amount of KCl + CuCl2 are shown The activity curve shows a maximum for about 18 wt % total active phase Finally, the influence of Ce, Nd and Pr chlorides on the activity of CuCl2 + KCl supported on α-Al2O3 is also shown In the case of Pr, the entire range of Pr3+/Cu2+ atomic ratios has been examined The results indicate that the rare earths, especially praseodymium, also have an additional positive effect on activity On a etudie l'effet d'additions de LiCl, NaCl ou KCl a CuCl2 supporte sur α — Al2O3 sur l'activite catalytique du chlorure cuivrique, dans l'oxyhydrochloration de l'ethylene en dichloroethane, dans un reacteur a lit fixe a 573 K et sous pression atmospherique NaCl et KCl ont tous deux produit un fort effet promoteur Dans le cas de KCl, on a examine cet effet, sur une large gamme de concentrations et une quantite fixe de CuCl2 sur un des supports suivants: α — Al2O3, γ — Al2O3 ou le gel de SiO2 Les resultats catalytiques et thermogravimetriques obtenus ont indique que KCl a exerce un effet marque sur la vitesse globale, měme en faible concentration, principalement en augmentant considerablement la vitesse de reoxydation de la forme reduite du catalyseur Dans le cas du support γ — Al2O3, l'effet promoteur n'est que modere On presente des resultats de l'oxyhydrochloration de l'ethylene effectues en presence de catalyseurs supportes sur α — Al2O3 comportant un rapport atomique (K+/Cu2+) constant, et une quantite de KCl + CuCl2 variable La courbe d'activite indique un sommet a environ 18% en poids total de la phase active Enfin, on presente aussi l'influence des chlorures de Ce, Nd et Pr sur l'activite du catalyseur CuCl2 + KCl supporte sur α — Al2O3 Dans le cas de Pr, on a etudie toute la gamme des rapports atomiques Pr3+/Cu2+ Les resultats indiquent que les terres rares et particulierement Pr, exercent un effet additionnel positif sur l'activite

Combustion of low heating value fuels and wastes in the spouted bed

Abstract: In a spouted bed burner, the flow-maintained vortex of particles operates as a heat exchanger, preheating the incoming mixture without diluting it. This makes it a combustor especially attractive for incinerating low heating value fuels and wastes. Bench-scale experimental studies were carried out to assess the ability of the spouted bed to burn efficiently poor fuels and waste materials in various aggregative states. The paper reports results of two series of experiments with gaseous and liquid fuel-containing streams. High levels of hydrocarbon conversion and combustion efficiency were attained for mixtures that would not be combustible by other methods without an auxiliary fuel. Dans un brǔleur en lit “spouted”, le vortex des particules maintenu par l'ecoulement agit comme un echangeur de chaleur, en prechauffant le melange alimente sans le diluer; cette caracteristique en fait un dispositif de combustion particulierement interessant pour l'incineration des combustibles et des dechets de faibles valeurs calorifiques. On a procede a des etudes experimentales, a l'echelle du laboratoire, pour evaluer l'aptitude du lit “spouted” a brǔler de facon efficace des combusbibles et des dechets de faibles valeurs calorifiques dans divers etats d'agglomeration. On presente les resultats de deux series d'experiences sur des combustibles gazeux et liquides; on a obtenu des niveaux eleves de conversion en hydrocarbures et d'efficacite de combustion dans le cas de melanges qui ne pourraient brǔler par d'autres methodes sans l'addition d'un combustible auxiliaire.

Some characteristics of concentration fluctuations in free turbulent jets

Abstract: Becker, Hottel and Williams have employed marker nephelometry to determine many characteristics of the nozzle fluid concentration field of the round turbulent free jet: the mean concentration, concentration fluctuations, intermittency factor, spectrum and correlation functions, and integral scales. In the present work a much larger jet nozzle was employed, 7.14 cm throat diameter compared to 0.635 cm in the reference, and the Reynolds number was correspondingly greater, around 270,000 compared to 54,000. The results support Becker et al's findings and extend the range of the data. In particular, the spectrum of the concentration fluctuations has been measured into the viscous convective subrange where a (-1) power mode dependency on wave number is indicated, as expected for the slow diffusing smoke marker. Other new measurements include the skewness, kurtosis, and probability density function of the concentration fluctuations. Becker, Hottel et Williams ont employe la nephelometrie pour determiner plusieurs caracteristiques du champ de concentration du fluide a l'ajutage d'un jet libre turbulent et circulaire: (a) la concentration moyenne; (b) les fluctuations de la contration; (c) le facteur d'intermittence; (d) le spectre et les fonctions de correlation; (e) les echelles integrales. On a employe, dans le present travail, un ajutage de jet bien plus grand (7.14 cm a l'ouverture) que dans le cas de leur travail (0.635 cm); le nombre de Reynolds a ete proportionnellement plus eleve (environ 270,000) comparativement a 54,000. Les resultats obtenus corroborent ceux de Becker et collaborateurs, et en etendent le domaine des donnees. On a particulierement mesure le spectre des fluctuations de la concentration a l'interieur du domaine convectif visqueux, ou la dependance avec la puissance (-1) du nombre d'onde est apparue, comme on s'y attendait, dans le cas ou le marqueur etait une fumee a diffusion lente. D'autres mesures comprennent celles de l'ecart entre le mode et la moyenne, du curtosis et de la fonction de densite de probabilite des fluctuations de la concentration.

A chromatographic study of diffusion of single components and binary mixtures of gases in 4A and 5A zeolites

Abstract: Results of a chromatographic study of diffusion of light hydrocarbons and other permanent gases in 4A and 5A zeolites are reported. The data for CF4 and iC4Hm, on 4A sieve (no penetration of the zeolite lattice) suggest that micropore diffusion occurs primarily by a Knudsen mechanism. The majority of the measurements were made with small particles of crushed commercial pelleted zeolites under conditions of intracrystalline diffusion control. The dominance of intracrystalline resistance is shown by the similarity in the time constants obtained with different sizes of particle and the results are generally consistent with earlier gravimetric data. The data for the binary systems containing two adsorbed species are consistent with the simple hypothesis that each species in the mixture diffuses independently with the same intrinsic mobility as for single component diffusion at the same temperature. However, the actual diffusivity of a species in the binary mixture may differ from the pure component diffusivity due to differences in the form of the quilibrium isotherms. On presente les resultats d'une etude chromatographique de la diffusion d'hydrocarbures legers et d'autres gaz permanents dans des zeolithes 4A et 5A. Les resultats, dans le cas du CF4 et de l'iCH4Hm, sur le tamis moleculaire 4A (absence de penetration du reseau de la zeolithe), suggerent que la diffusion dans les micropores se fait essentiellement par un mecanisme de Knudsen. On a fait la majeure partie des mesures en employant des petites particules de zeolithes commerciales, pelletisees et broyees dans des conditions impliquant le controle par la diffusion intracristalline. La predominance de la resistance intracristalline est indiquee par la similitude des constantes de temps obtenues avec des particules de differentes dimensions et par le fait que les resultats correspondent de maniere generale avec des donnees gravimetriques obtenues anterieurement. Les donnees relatives aux systemes binaires contenant deux composants adsorbes sont conformes a l'hypothese simple selon laquelle chaque composant du melange diffuse independamment avec la měme mobilite intrinseque que lorsqu'il s'agit de la diffusion d'un simple composant a la měme temperature. Toutefois, la diffusivite effective d'un composant dans le melange binaire peut differer de la diffusivite du composant pur, par suite de differences dans la forme des isothermes d'equilibre.

An overview of discrete stochastic controllers: Generalized PID algorithms with dead-time compensation

Abstract: Digital computer control systems have enabled use of a wide variety of different algorithms compared with the classical analog proportional-integral-derivative controllers. Design techniques have been presented for many of these in diverse areas of the literature. Some algorithms are designed to give minimum time responses, or to give specified closed loop responses, or to satisfy classical guidelines for stability. By contrast, the design of discrete optimal stochastic controllers is not based on considerations such as stability, frequency response, or dead-time compensation properties, but rather on optimizing some criterion of performance such as the output error variance. Therefore, it is of interest to investigate how these controllers behave with respect to some of the more traditional ways of evaluating or designing controllers. In this paper, both intuitive and theoretical arguments are presented to illustrate the very desirable properties of these controllers and their relationship to many other algorithms. In particular, they are shown to contain proportional-integral-derivative terms and to be related to other well-known controllers, to have optimal compensation for process dead-time and optimal filtering properties, and to have very desirable stability and frequency response characteristics. In this sense, the paper provides a unifying overview of univariate stochastic controllers. Les systemes de contrǒle avec calculateurs numeriques permettent d'employer une grande variete d'algorithmes, comparativement aux contrǒleurs analogiques classiques a actions proportionnelles, integrales et derivees. On trouve, dans divers secteurs de la litterature technique, des donnees pertinentes aux methodes de conception d'un grand nombre de contrǒleurs. Certains algorithmes sont concus pour fournir des reponses en un temps minimal, ou pour donner des reponses specifiques en boucle fermee, ou encore pour repondre a des problemes classiques de stabilite. Au contraire, la conception des contrǒleurs stochastiques optimaux, discrets, ne repose pas sur des considerations telles que la stabilite, la reponse en frequence ou la compensation de temps mort, mais plutǒt sur l'optimisation d'un critere de performance tel que la variance de l'erreur de sortie. Il est par consequent d'un interět certain d'etudier le comportement de ces contrǒleurs en termes des criteres plus traditionnels d'evaluation. On presente des arguments intuitifs et des arguments theoriques pour illustrer les proprietes les plus souhaitables de ces contrǒleurs, et leurs relations avec de nombreux autres algorithmes. En particulier on montre qu'ils comportent des termes d'actions proportionnelles, integrales et derivees et qu'ils sont egalement relies a d'autres types bien connus de contrǒleurs, qu'ils ont une compensation optimale de temps mort, des proprietes de filtrage optimal et des caracteristiques de stabilite et de reponse en frequences tres souhaitables. En ce sens, l'article constitue une presentation generale unifiee des contrǒleurs stochastiques a variable unique.

Catalytic hydrogenation and asphaltene conversion of athabasca bitumen

Abstract: Bitumen from the Athabasca Oil Sand deposits was hydrogenated using three MoO3-CoO catalysts having markedly different median pore diameters. The results were interpreted in terms of the reaction rates being controlled by the rate of pore diffusion of asphaltene micelles. Catalysts with larger pore diameters produced higher conversions per unit surface area. However, the accessible catalyst surface area per unit volume of reactor decreased as the catalyst pore diameter increased. The decreasing surface area was responsible for the general decrease in conversion with increasing pore diameter. Higher conversions are obtained with higher surface area catalysts having smaller pores, even though pore diffusion controls the rate of reaction.

Reactions and residence time distributions in motionless mixers

Abstract: Motionless mixers are modeled as open, circular tubes with parabolic velocity distributions except at a few isolated planes where radial mixing occurs via an instantaneous coordinate transformation. Possible transformations are constrained by continuity of volumetric flow. Complete flow inversion appears the theoretically optimal transformation, being superior to complete mixing. A model consisting of intermediate planes of complete mixing approximates existing experimental data on the Kenics Static Mixer when four Kenics elements are made equivalent to a single plane of complete mixing. This model preserves the essential nature of a laminar flow residence time distribution while providing a relatively simple means of estimating mixer performance.

The kinetics of absorption of so3 in calcium and magnesium oxides

Abstract: Results of an experimental study of the absorption of SO3 by CaO and MgO particles are reported Uptake rates are shown to be controlled by intragranular diffusion and are essentially independent of gross particle size in the range 006-033 mm The data can be correlated by the swelling grain model of Georgakis et al(12) The uptake rate in MgO is considerably faster than in CaO but this difference is shown to be attributable mainly to differences in grain size and porosity Activation energies for diffusion of SO3 through the product layer are about 40 kJ/mol for both absorbents and diffusivities at 800 K are about 10−8 cm2 S−1 The results are discussed in relation to the development of an efficient dry scrubbing flue gas desulphurization process On rapporte les resultats d'une etude experimentale de l'absorption de SO3 par des particules CaO et MgO On montre que les vitesses d'absorption sont contro'lees par la diffusion intragranulaire et sont essentiellement independantes des dimensions brutes des particules comprises entre 006 et 033 mm On peut etablir une correlation de ces donnees au moyen du modele a grains gonflants de Georgakis et al(12) La vitesse d'absorption, dans le cas de MgO, est bien plus elevee que dans celui de CaO, mais on indique que cette discordance est surtout attribuable a des differences dans la dimension des grains et la porosite Les energies d'activation, pour la diffusion de SO3 dans la couche du produit, sont a peu pres de 40 kJ/mole pour les deux absorbants, et les diffusivites a 800 K sont d'environ 10−8 cm2 s−1 On discute les resultats en relation avec la mise au point d'un procede efficace de desulfuration des gaz de fumee par epuration par voie seche

Rheology and tensile properties of polypropylene reinforced with glycerol-treated mica†

Abstract: Mica platelets were left untreated or coated with glycerol at 1%. 5% or 10% by mass, and extruded in carboxyl-modified polypropylene at volume fractions up to 20%, and at temperatures between 468 and 528 K. At a shear rate of 10 s and at 500 K, the Einstein coefficient decreased from 2.1 when glycerol was added. The flow behavior index, ranging between 0.57 and 0.45, decreased when the shear rate or amount of mica or of glycerol was increased, while the opposite occurred when the temperature was raised. In the solid state, the tensile modulus increased, but the tensile strength was degraded. Des plaquettes de mica laissees comme telles ou imbibees de glycerine a 1%, 5% ou 10% en masse ont ete extrudees dans du carboxy-polypropylene a des fractions volumiqucs allant jusqu'a 20%, et a des temperatures comprises entre 468 et 528 K. A un taux de cisaillement de 10 s et a 500 K, le coefficient d'Einstein a diminue de 2.1 apres adjonction de glycerine. L'indice du comportement d'ecoulement, compris entre 0.57 et 0.45. decroǐt lorsqu'on augmente le taux de cisaillement, la quantite de mica ou de glycerine, alors que c'est l'inverse qui se produit lorsque l'on fait croǐtre la temperature. Dans l'etat solide, le module elastique croǐt, mais la force elastique etait degradee.

Species grouping in multicomponent adsorption calculations

Abstract: The validity of the assumption of species grouping, which combines several adsorbable species into a fewer number of pseudo-species in adsorption calculations, was examined by comparing the equilibrium concentrations obtained from exact calculations with those obtained with the use of the assumption. It was found that if the adsorption affinities of the individual species exhibited by their single-species isotherms are of the same order of magnitude, the use of the species grouping assumption yields acceptable results. This procedure applies to three situations, including those in which (a) all the species are grouped into a single pseudo-species; (b) the various species are combined into several (but fewer) pseudo-species; and (c) only some of the species are grouped, while the others remain individual species. On a etudie la validite dans les calculs d'adsorption, de l'hypothese selon laquelle plusieurs especes adsorbables se combinent pour former un petit nombre de pseudo-especes; cette etude a consiste a comparer les concentrations d'equilibre obtenues, a partir de calculs exacts, avec celles que l'on peut calculer en employant l'hypothese en question. On a constate que, si les affinites d'adsorption des especes individuelles deduites des isothermes de chaque espece etaient du me'me ordre de grandeur, l'emploi de l'hypothese du regroupement des especes fournit des resultats acceptables. La methode mentionnee s'applique a trois situations dans lesquelles (a) toutes les especes sont groupees en une seule pseudo-espece; (b) les diverses especes sont combinees en plusieurs pseudo-especes; (c) quelques especes seulement sont groupees, tandis que les autres demeurent des especes individuelles.

A fundamental study on recovery of copper with a cation exchange membrane: Part 2 — Transfer rate of copper and hydrogen ion through a cation exchange membrane

Abstract: Transfer rates of copper and hydrogen ion through a cation exchange membrane were measured experimentally for the systems of Cu/H-SO4 and Cu/H-NO3. Transfer rates of anions in the membrane were also measured, and they were negligible compared to those of the cations. Cupric ion and hydrogen ion transfer in a ratio of 1:2 and in opposite directions. The self-diffusion coefficient of cupric ion in the membrane is obtained from the transfer rate of copper in high concentrations of sulfuric or nitric acid solutions using the equilibria data obtained in our previous work. The coefficient of the hydrogen ion is similarly obtained.

Interfacial tensions of oil, water, chemical dispersant systems

Abstract: Oil-water interfacial tension measurements are reported for systems of crude oils, distilled and salt water, and chemical dispersants, using the spinning drop technique. By varying the amount of dispersant and the volumetric ratio of water to oil it is possible to deduce an effective oil-water partition coefficient for the interfacial tension reducing species and to suggest a relationship between the extent of interfacial tension reduction and dispersant concentration. The implications of the results in assessing the mechanism and effectiveness of the chemical dispersion process are discussed.

Stabilization and destabilization of mineral fines-bitumen-water dispersions in tailings from oil sand extraction plants that use the hot water process

Abstract: Effects of acid and polyvalent cations on flocculation and settling of tailings dispersions from an oil sand extraction plant are used to develop a model for previously puzzling pH dependent aspects of the hot water process. The model features calcium-bicarbonate surface complexes that reduce mineral fines-bitumen interactions, destabilize bitumen-water emulsions and enhance attachment of air bubbles to bituminous surfaces. Protonation of bicarbonate allows agglomeration through formation of calcium-carboxylate bridging complexes at mineral-bitumen interfaces. On a utilise les effets des acides et des cations polyvalents sur la floculation et la sedimentation de dispersions de residus provenant d'une usine d'extraction de sables bitumineux, pour developper un modele permettant de simuler certains effets bizarres du pH dans le procede d'extraction a l'eau chaude. Ce modele fait intervenir des complexes superficiels du bicarbonate de calcium qui diminuent les interactions entre les fines particules minerales et le bitume, destabilisent les emulsions bitume-eau et facilitent la fixation de bulles d'air sur les surfaces de bitume. La protonation du bicarbonate permet l'agglomeration par suite de la formation de ponts de complexes calcium-carboxylate aux interfaces des particules minerales et du bitume.

A mass transfer study of a new electrochemical reactor stirred by gases evolved at the counter electrode

Abstract: Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a horizontal cylinder cathode stirred by oxygen evolved at a horizontal lead anode placed below the cylinder. Variables studied were: oxygen discharge rate, electrolyte concentration and cylinder diameter. Oxygen discharge was found to increase the rate of mass transfer by a factor ranging from 1.5 to 5 over the natural convection value depending on the rate of oxygen discharge at the lead anode. The data were correlated by the equation: J = 25.0 Re−0.53 Mass transfer coefficients measured at an array of horizontal cylinders agreed with the results for single cylinders. A new electrochemical reactor built of a set of parallel arrays of horizontal cylinders and stirred by the counter electrode gases is proposed as offering an efficient way of stirring with no external stirring power requirement. On a mesure les coefficients de transfert de masse dans le cas de la formation d'un depo't de cuivre a partir d'une solution acidifiee de sulfate de cuivre, sur une cathode cylindrique horizontale, agitee par de l'oxygene emis a une anode de plomb horizontale placee sous le cylindre. On a etudie les variables suivantes: la vitesse de degagement de l'oxygene, la concentration de l'electrolyte et le diametre du cylindre. On a constate que le degagement de l'oxygene augmentait la vitesse du transfert de masse d'un facteur de 1.5 a 5 par rapport a la valeur correspondant a la convection naturelle, selon la vitesse de degagement de l'oxygene a l'anode de plomb. On a correler les resultats au moyen de l'equation: J = 25.0 Re−0.53 Les resultats des mesures des coefficients de transfert de masse pour un ensemble de cylindres horizontaux sont en bon accord avec ceux obtenus avec des cylindres individuels. On propose un nouveau reacteur electrochimique construit a partir d'une serie d'ensembles de cylindres horizontaux, agites par les gaz de contre-electrode; ce reacteur presenterait un moyen efficace d'agitation, sans qu'on ait besoin de fournir de puissance d'agitation externe.

Studies of molybdena‐alumina catalysts. X. temperature programmed desorption of H2S and thiophene

Abstract: Temperature programmed desorption (TPD) and reduction (TPR) studies were carried out on H2S and thiophene adsorbed on Mo/Al2O3 and CoMo/Al2O3 catalysts. Freshly sulfided and pyridine poisoned catalysts were run. For sulfided catalysts, the major products of desorption of thiophene were thiophene and butene, leaving a carbonaceous residue. Subsequent TPR in H2 effected complete removal of the residue with formation of H2S, thiophene and butene. The residue appeared to consist of an easily reactive thiophene polymer and a less-reactive, sulfur-containing coke. Runs on poisoned catalysts showed less adsorption but product profiles were similar, showing that the adsorption characteristics of the remaining sites were not significantly altered. On a etudie H2S et le thiophene adsorbes sur les catalyseurs Mo/Al2O3 et CoMo/Al2O3, par desorption a temperature programmee (TPD) et par reduction a temperature programmee (TPR). Les essais ont ete effectues avec des catalyseurs fraǐchement sulfures et avec des catalyseurs empoisonnes par la pyridine. Pour les catalyseurs sulfures les produits principaux de la desorption du thiophene ont ete le thiophene et le butene, laissant un residu carbone. Une TPR subsequente dans l'hydrogene a permis de supprimer le residu avec formation de H2S, de thiophene et de butene. Le residu semble comporter un polymere du thiophene reactif, et un coke contenant du soufre et moins reactif. Les essais sur les catalyseurs empoisonnes ont conduit a une adsorption moindre, mais des profils de produits similaires, ce qui montre que les caracteristiques de l'adsorption sur les sites restants ne sont pas modifiees de facon significative.