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"An ounce of careful plant design is worth ten pounds of reconstruction." LECTURE 12: LABORATORY AND INDUSTRIAL CATALYTIC REACTORS: SELECTION, APPLICATIONS, AND DATA ANALYSIS. I. Introduction A. Why study reactors? B. Definition and classification of reactors
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"An ounce of careful plant design is worth ten pounds of reconstruction."LECTURE 12: LABORATORY AND INDUSTRIAL CATALYTIC REACTORS: SELECTION, APPLICATIONS, AND DATA ANALYSIS
A. Why study reactors?
B. Definition and classification of reactors
C. Reactor/process design perspective: from the laboratory to the full-scale plant
D. Selection of reactors in the laboratory and plant
II. Laboratory and Bench Scale Reactors
B. Criteria for selection of lab/bench scale reactors; applications
III. Plant Reactors
A. Common types
B. Fixed catalyst bed reactors: characteristics, advantages, limitations
C. Fluidized beds: characteristics, advantages, limitations
D. Criteria for selection
IV. Collecting, Analyzing and Reporting Data from Laboratory Reactors
A. General approach and guidelines
B. Criteria for choosing catalyst form and pretreatment, reaction conditions
C. Choosing mode of reactor operation; differential and integral reactors
D. Analyzing and reporting data from laboratory reactors
1. Analysis of rate data: objectives and approach
2. Integral analysis
3. Differential analysis
Fig. 12.1Structure of Catalytic Process Development [adapted from J. M. Smith, Chem. Eng. Prog., 64, 78 (1968)].
Reactors are used for many different purposes:
Choosing the right reactor is critical to the engineering process and is dictated by many different variables such as
Laboratory and bench-scale reactors vary greatly in size, complexity, cost, and application.
Fig. 12.2Features of representative laboratory reactors [Levenspiel, 1979].
Figure 12.3Laboratory Pyrex FBR reactor (courtesy of the BYUCatalysis Laboratory).
Batch Reactor (UCSB)
Fig. 12.6Commercial fixed-bed reactor designs for controlling temperature: (a) multi-tubular heat-exchange reactor, (b) series of fixed-bed, adiabatic reactors with interstage heating or cooling.
Characteristics of Plant-Scale Fluidized and Slurry Bed Reactors
Figure 12.7Liquid-phase slurry reactors: (a) forced-circulation, slurry-bed reactor, (b) bubble-column, slurry-bed reactor.
Figure 12.8Batch-slurry reactor for hydrogenation of specialty chemicals.
Fig. 12.9Design of typical FCC transfer-line (riser) reactor with fluidized-bed regenerator.
Stacked Fluid Cat Cracker (UOP)
All-riser Cracking FCC Unit
Fig. 12.11(a) Operating line for a highly exothermic reaction in an ideal tubular reactor with pure reactant and (b) corresponding reciprocal rate versus conversion curve and area V/FAo for a CSTR. (c) Operating line for a highly exothermic reaction in an ideal tubular reactor with dilute reactant and (d) corresponding reciprocal rate versus conversion curve and area V/FAo for a PFR.
Figure 12.12Optimum temperature progression (and locus of maximum rates) of (a) reversibleendothermic reaction and (b) reversible exothermic reactions.
Fig. 12.13(a) Use of staged adiabatic tubular fixed-bed reactors with interstage cooling to achieve optimum temperature progression in the cases of exothermic reversible, exothermic irreversible and endothermic reactions. (b) Design schematic for stagedadiabatic fixed-bed reactors with interstage furnace heating for a strongly endothermic reaction such as reforming of methane.
Data collection typically involves three major steps (Fig. 12.14):
Figure 12.14Process of obtaining rate and kinetic data; note that statistical methods are used in Steps 2 and 3 and in the recycle process.
1. Catalyst Properties and Characterization
a.Catalysts/surfaces should be carefully prepared and pretreated so as to be free of solid contaminants such as sulfur, chlorides, and carbon that might affect activity.
b. Support effects should be avoided by studying reactions on single crystals of the active catalytic phase, e.g., metal, metal films, and/or relatively highly-concentrated, poorly-dispersed supported metals. Preparation methods should be used which minimize decoration of the metal surface, e.g., decomposition of metal carbonyls on supports. Supported base metal catalysts need to be well-reduced to avoid complications due to unreduced metal oxides.
c. In the case of structure-sensitive reactions, effects of surface structure and/or dispersion need to be taken into account.
d. Metal dispersion/surface area should be measured using proven and/or standard (ASTM) methods, e.g., hydrogen chemisorption or titration rather than CO chemisorption for metals.
e. Methods of preparation and characterization should be reported in detail. Methods for calculating surface area and dispersion should also be carefully reported. Reporting these methods and the surface area or dispersion of catalyst samples should be a requirement for publication of specific activity data.
2. Reaction Conditions
a. TOF and kinetic data must be measured in the absence of pore diffusional restrictions, film mass transfer limitations, and heat transfer limitations (generally at low temperature and low conversion). Experimental evidence and calculations based on well-known criteria (e.g., the Thiele modulus for pore diffusional resistance) should be provided in publications to demonstrate that the data were obtained in the absence of these effects.
b. TOF and kinetic data must be measured in the absence of deactivation effects, e.g., poisoning, coking, and sintering. The burden of proof that such effects are absent should be on the authors of a publication.
c. TOF data should be collected over wide ranges of temperature and reactant concentrations to facilitate valid comparison with data from other laboratories and to provide meaningful data for determining temperature and concentration dependencies.
d. TOF data should be reported at specified conditions of temperature, reactant concentrations, and conversion. These specifications should be used by reviewers and editors as a minimum reporting requirement for publication in a journal.
Test for integral analysis of rate data involving plot of W/FAo versus integrated reciprocal rate.
Integral Analysis of Rate Data
(a) Differential analysis to obtain reaction rates. (b) Plot to obtain reaction orders.
Differential Analysis of Rate Data
1.O. Levenspiel, Chemical Reaction Engineering, 2nd and 3rd Eds., John Wiley and Sons, 1972, 1999.
2. O. Levenspiel, The Chemical Reactor Minibook, OSU Bookstores, 1979.
3. J.M. Smith, Chemical Engineering Kinetics, 3rd Ed., McGraw Hill, 1981.
4. "Reactor Technology," Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 19, 3rd Ed, John Wiley, 1982, pp. 880-914.
5. G.F. Froment and K.B. Bischoff, Chemical Reactor Analysis and Design, John Wiley, 1990.
6. O. Levenspiel, The Chemical Reactor Omnibook, 1993, OSU Bookstores, 1993.
7. C. H. Bartholomew and R. J. Farrauto, Fundamentals of Industrial Catalytic Processes, Chapman and Hall, 2005, Chap. 4.