Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...

Multiphase catalytic reactors: a perspective on current knowledge and future trends

The reaction kinetics and chemical equilibrium of the reversible esterification of methanol with acetic acid were investigated. This system is of major importance as a model reaction for reactive distillation. The reaction has been catalyzed both homogeneously by acetic acid itself and heterogeneously by an acidic ion-exchange resin (Amberlyst 15). The chemical equilibrium composition was measured for various temperatures and starting compositions of the reactants and products. Kinetic information was obtained at temperatures between 303.15 and 343.15 K at various starting compositions covering concentration ranges from the stoichiometric regime to the dilute regions. Both the esterification and the hydrolysis reaction were investigated to yield a model which is applicable for any starting composition. The homogeneous reaction has been described with a simple power-law model. The use of activities in the kinetic model instead of mole fractions results in a much smaller residual error. To compare pseudohom...

Reaction Kinetics and Chemical Equilibrium of Homogeneously and Heterogeneously Catalyzed Acetic Acid Esterification with Methanol and Methyl Acetate Hydrolysis

Kinetic theory based CFD simulation of turbulent fluidization of FCC particles in a riser

A novel calibration procedure for a fiber optic solids concentration probe

Compared with conventional fluidized beds, circulating fluidized beds have many advantages including better interfacial contacting and reduced backmixing (Lim et al, 1995) While there are many reports on the gas—solid circulating fluidized systems, liquid—solid and gas—liquid—solid circulating fluidized bed systems have been scantily studied However, extending current knowledge obtained in gas—solid systems to liquid—solids and gas—liquid—solid three-phase systems is shown to open new horizons for applications of circulating fluidized bed technology and expected to lead to the development of highly efficient liquid—solid and gas—liquid—solid reactors, especially for the ever growing field of biotechnology In order to fully appreciate the potential of those two types of liquid phase circulating fluidized beds, recent progress is reviewed in this article Their potential applications to biochemical processes are also discussed



Comparativement aux lits fluidises classiques, les lits fluidises circulants offrent de nombreux avantages, dont un meilleur contact interfacial et un retromelange reduit (Lim et al, 1995) Bien qu'un nombre important d'articles paraissent sur les systemes fluidises circulants gaz—solide, les systemes a lits fluidises circulants liquide—solide et gaz—liquide—solide ont fait l'objet de peu d'etudes On montre cependant que l'utilisation des connaissances actuelles sur les systemes gaz—solide pour les etendre aux systemes liquide—solides et aux systemes triphasiques gaz—liquide—solide ouvre de nouveaux horizons a l'application de la technologie du lit fluidise circulant et devrait permettre le developpement de reacteurs liquide—solide et gaz—liquide—solide hautement efficaces, en particulier pour le secteur de la biotechnologie toujours en croissance Afin d'apprecier pleinement le potentiel de ces deux types de lits fluidises circulants en phase liquide, les derniers progres en la matiere sont passes en revue dans cet article Leurs applications potentielles aux procedes biochimiques sont egalement examinees

(Gas-)liquid-solid circulating fluidized beds and their potential applications to bioreactor engineering

Depuis une dizaine d'annees, les reacteurs a lit fluidise circulant a cocourant descendant ont ete proposes pour faire concurrence aux reacteurs a lit fluidise circulant ascendant. Dans cet article, on resume les resultats publies des etudes sur les reacteurs de type descendant, et des directions sont recommandees pour la recherche. On a trouve que les reacteurs descendants offraient des avantages particuliers par rapport aux reacteurs a lit fluidise circulant ascendant et qu'ils etaient potentiellement interessants dans de nombreux procedes industriels, en raison principalement d'une structure d'ecoulement du gaz et des solides plus uniforme que dans le cas des reacteurs ascendants.

Cocurrent downflow circulating fluidized bed (downer) reactors — A state of the art review

Radial nonuniformity of flow structure in a liquid-solid circulating fluidized bed

Axial and lateral mixing of fine particles in a binary-solid riser have been investigated using a phosphor tracer method. The measured bimodal residence time distribution (RTD) demonstrated two types of axial dispersions of the fines: the dispersion of discrete particles and that of clusters. A proposed one-dimensional, bimodal dispersion model describes the bimodal RTDs very well. The axial Peclet number of the fines is not sensitive to the fraction of coarse particles, gas velocity and solids circulation rate. Lateral solids dispersion was determined by measuring the solids RTD at different radii using a point source tracer injection. A two-dimensional dispersion model describes the measured RTDs satisfactorily. Lateral solids mixing decreased as coarse particles were added into the riser. Correlations of the axial and lateral Peclet numbers obtained fit the experimental data well.



On a etudie le melange axial et lateeral de particules fines dans une colonne montante binaires-solides a l'aide d'une methode de tracage au phospore. La distribution du temps de sejour (DTS) bimodale mesuree illustre deux types de dispersions axiales des particules fines: la dispersion de particules discretes et la dispersion de grappes. On propose un modele de dispersion unidimensionnel bimodal qui decrit tres bien la DTS bimodale. Le nombre de Peclet axial des fins n'est pas sensible a la fraction des particules grossieres, a la vitesse du gaz et a la vitesse de circulation des solides. On a determine la dispersion laterale des solides en mesurant la DTS des solides a differents rayons a l'aide d'une injection de traceur ponctuelle. Un modele de dispersion bidimensionnel decrit les DTS de maniere satisfaisante. Le melange lateral des solides diminue avec l'ajout de particules grossieres dans la colonne. Des correlations obtenues pour les nombres de Peclet axial et lateral montrent un bon accord avec les donnees experimentales.

Axial and lateral dispersion of fine particles in a binary-solid riser

The hydrodynamics of a gas-liquid-solid circulating fluidized bed was investigated. A new regime, the three phase circulating fluidization regime, was discovered for the first time. The characteristics of this regime were compared with that of the conventional fluidization regime and the transport regime. The particle circulation rate and the gas and solids holdups in circulating fluidization regime were studied.



On a etudie l'hydrodynamique d'un lit fluidise circulant gaz-liquide-solide. Un nouveau regime, le regime de fluidisation circulant triphasique, a ete decouvert pour la premiere fois. Ses caracteristiques sont comparees a celles du regime de fluidisation classique et du regime de transport. On a etudie la vitesse de circulation des particules et les retentions de gaz et de solides en regime de fluidisation circulant.

Z.-Q. Yu

Papers

Cocurrent downflow circulating fluidized bed (downer) reactors — A state of the art review

Radial nonuniformity of flow structure in a liquid-solid circulating fluidized bed

Axial and lateral dispersion of fine particles in a binary-solid riser

Hydrodynamics of a gas‐liquid‐solid three phase circulating fluidized bed

Application of a fluidized reaction-distillation column for hydrolysis of methyl acetate