Catalysis : an Integrated Approach to Homogeneous ...

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7 -CATALYTIC REACTION ENGINEERING 279 7.3.2 Homogeneous Catalysis Several important homogeneously catalysed reactions involve more than one phase. Examples are found in carbonylations, hydroformylations, hydrogena- tions, hydrocyanation, oxidations and polymerisations. Typically reactant(s) such as oxygen, hydrogen and/or carbon monoxide have to be transferred from the gas phase to the liquid phase, where reaction occurs. The liquid phase contains the homogenous catalyst together with a liquid reactant and often a solvent. The transport from one phase to the other again requires a driving force in the form of concentration or temperature gradients. The latter can usually be neglected. Figure 7.12 shows the concentration profiles which are established in a direction perpendicular to the gas-liquid interface. I gas liquid Fig. 7.12. Concentration profile of a reactant in the neighbourhood of a gas-liquid interface with a homogeneously catalysed reaction in the liquid phase. 1. 2. 3. 4. Several steps can be distinguished: transport of A from the bulk of the gas phase to the gas-liquid interface. transfer of A at the interface from the gas to the liquid phase. transport of A towards the bulk of the liquid. reaction of A in the liquid. Steps 1 and 2 are strictly physical and consecutive to each other. In most cases the resistances corresponding to steps 1 and 2 can be neglected when compared to these corres onding to steps 3 and 4. This means that the liquid phase concentration of A, P CA~, can be calculated from: (7.129)
280 7 -CATALYTIC REACTION ENGINEERING where HA = the Henry coefficient of A, Pa ml mol-l, and PA = partial pressure of A in the bulk of the gas phase, Pa. Steps 3 and 4 cannot, in general, be separated from each other: the transport away from the interface occurs simultaneously with the chemical reaction. In the next section this will be analyzed quantitatively in a way analogous to Section 7.3.1. 7.3.2.1 Transport simultaneous with reaction Utilization factor For positive partial reaction orders with respect to the reactant which has to be transferred, the existence of a concentration profile leads to a reaction rate per unit reaction volume, i.e. liquid volume, which is lower than the volumetric rate that would be obtained in the absence of concentration gradients. The extent of this slowing down of the reaction can be expressed by the effectiveness factor, also called liquid utilization factor in this context, defined for a single reaction as: reaction rate with transport limitations (7.130) TIL = reaction rate at the conditions prevailingat the liquid side of the interface It follows from the above definition that for an irreversible first-order reaction, the utilization factor is given by: (7.131) where the superscript, 1, has been omitted for convenience of notation, and with k, = the volumetric first-order rate coefficient, s-l, and a, = AL /VL the volumetric interface surface area, mi! mi3. The calculation of the molar flux of A at the interface, NA I y=~, follows from the film theory. Film theory In the film theory the complete resistance to mass transfer from the interface to the bulk of the liquid is confined to a fictitious film along the interface. The bulk of the fluid is considered to be perfectly mixed in the direction perpendicular to the interface, i.e. the concentration of A is uniform beyond the film. Figure 7.13 shows the concentration profile of A according to the film theory. Furthermore, the only transport mechanism considered in the film is that of molecular diffusion perpendicular to the interface. The diffusion of A in the fictitious liquid film obeys Fick’s law: (7.132)
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Studies in Surface Science and Cata
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Studies in Surface Science and Cata
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Preface Catalysis is a fascinating
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industrial context of the features
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Contents Preface ..................
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4.3.4 P-Elimination and Deinsertion
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7.4.1 Scope .......................
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12.3 Adsorption Isotherms .........
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List of contributors E.B.M. Doesbur
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Introductory section
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Chapter 1 History of catalysis 1.1
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1 -HISTORY OF CATALYSIS 5 One of th
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1 - HISTORY OF CATALYSIS 7 was disc
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1 -HISTORY OF CATALYSIS exlenaed em
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1 -HISTORY OF CATALYSIS 11 aromatiz
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1 -HISTORY OF CATALYSIS 13 had a gr
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1 - HISTORY OF CATALYSIS 15 The new
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1 -HISTORY OF CATALYSIS 17 1960 law
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1 - HISTORY OF CATALYSIS TABLE 1.2
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1 -HISTORY OF CATALYSIS 21 1900 195
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Chapter 2 Catalytic processes in in
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2 - CATALYTIC PROCESSES IN INDUSTRY
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2 - CATALYTIC PROCESSES IN INDUSTRY
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flue gaa t c t air Vacuum gas ol 2
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2 -CATALYTIC PROCESSES IN INDUSTRY
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2 -CATALYTIC PROCESSES JN INDUSTRY
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Chapter 3 Chemical kinetics of cata
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3 - CHEMICAL KINETICS OF CATALYSED
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3 -CHEMICAL KINETICS OF CATALYSED R
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Fundamental catalysis
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Chapter 4 Bonding and elementary st
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4 -BONDING AND ELEMENTARY STEPS IN
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Chapter 5 Heterogeneous catalysis 5
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5 -HETEROGENEOUS CATALYSIS 161 a. _
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5 -HETEROGENEOUS CATALYSIS 163 appr
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5 -HETEROGENEOUS CATALYSIS 165 In r
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5 - HETEROGENEOUS CATALYSIS 167 lit
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5 - HETEROGENEOUS CATALYSIS 169 An
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5 -HETEROGENEOUS CATALYSIS 171 A ma
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5 - HETEROGENEOUS CATALYSIS 173 2 L
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5 - HETEROGENEOUS CATALYSIS 175 (3)
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5 -HETEROGENEOUS CATALYSIS 177 20 '
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5 -HETEROGENEOUS CATALYSIS 179 with
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5 - HETEROGENEOUS CATALYSIS 181 In
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5 -HETEROGENEOUS CATALYSIS 183 Info
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5 -HETEROGENEOUS CATALYSIS 185 0 20
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5 - HETEROGENEOUS CATALYSIS 187 TAB
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5 -HETEROGENEOUS CATALYSIS 189 i)U
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5 -HETEROGENEOUS CATALYSIS 600 560
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5 -HETEROGENEOUS CATALYSIS 193 b H
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Chapter 6 Homogeneous catalysis wit
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6 -HOMOGENEOUS CATALYSIS WlTH TRANS
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6 - HOMOGENEOUS CATALYSIS WlTH TRAN
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6 -HOMOGENEOUS CATALYSIS WITH TRANS
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6 - HOMOGENEOUS CATALYSIS WlTH TRAN
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6 - HOMOGENEOUS CATALYSIS WITH TRAN
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6 -HOMOGENEOUS CATALYSIS WlTH TRANS
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Page 268 and 269: Applied catalysis
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8 - PREPARATION OF CATALYST SUPPORT
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8 -PREPARATION OF CATALYST SUPPORTS
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8 - PREPARATION OF CATALYST SUPPORT
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Chapter 9 Preparation of supported
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PREPARATION OF SUPPORTED CATALYSTS
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Catalyst characterization
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Chapter 10 Ca ta I yst characteriza
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10 -CATALYST CHARACTERIZATION WITH
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10 - CATALYST CHARACTERIZATION WITH
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I0 -CATALYST CHARACTERJZATION WITH
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Chapter 11 Temperature programmed r
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11 -TEMPERATURE PROGRAMMED REDUCTIO
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11 -TETEMPERATURE PROGRAMMED REDUCT
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Chapter 12 The use of adsorption me
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12 -ADSORPTION METHODS 421 pairs of
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12 -ADSORPTION METHODS 423 of multi
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12 -ADSORPTION METHODS 425 son of t
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12 - ADSORPnON METHODS 427 equation
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12 - ADSOWON METHODS / Fig. 12.4. T
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12 - ADSOFSTION METHODS 431 - a i-
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12 -ADSORPTION METHODS 433 uptake o
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12 - ADSOlU'TION METHODS 435 gives
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12 - ADSOFSTION METHODS 437 condens
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Future trends
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Chapter 13 Future trends The large
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13 - FUTURE TRENDS 443 control of t
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13 -FUTURE TRENDS 445 the conversio
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Subject Index x-Acceptor Iigands, 2
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SUBJECT INDEX 449 - see also Extend
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SUBJECr INDEX 451 Ethane, 143 Ethen
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SUBJECT INDEX 453 Hydrogen peroxide
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SDJJTT INDEX 455 Octane number, 24,
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SUBJECT INDEX 457 RBS, 383 Reaction
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SUBJECT INDEX 459 - see also Ruther
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STUDIES IN SURFACE SCIENCE AND CATA
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Volume 35 Volume 36 Volume 37 Volum
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Volume 70 Volume 71 Volume 72 Volum
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