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Catalytic Reactors

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Information about Catalytic Reactors
Education

Published on January 11, 2008

Author: Margherita

Source: authorstream.com

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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:  "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 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 A. Kinds 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 V. Examples Slide2:  New HDS Unit, ARCO Carson, CA Refinery I. Introduction :  I. Introduction Why study reactors? The design of catalyst and reactor are closely interrelated. Design of catalytic processes requires a knowledge reactor design, operation optimization and selection Progress in improving our standard of living depends on our ability to design reactors Our personal existence depends on controlling cellular reactions in our body while that of the human race hangs on the outcome of enormous global reactions. B. Definition and Classification of Reactors:  B. Definition and Classification of Reactors What is a Reactor? A device that encloses the reaction space, and which houses the catalyst and reacting media. A container to which reactants are fed and products removed, that provides for the control of reaction conditions. Classification of Reactors Size Methods of charging/discharging: batch or steady-state flow Motion of particles with respect to each other Fluid flow type: tubular or mixed-fluid Reactor/process design perspective:  Reactor/process design perspective Fig. 12.1 Structure of Catalytic Process Development [adapted from J. M. Smith, Chem. Eng. Prog., 64, 78 (1968)]. D. Choosing reactors in the lab and plant:  D. Choosing reactors in the lab and plant Reactors are used for many different purposes: to study the mechanisms and kinetics of chemical reactions to provide data for validation of process simulations to investigate process performance over a range of process variables to obtain design data to produce energy, materials and products. Choosing the right reactor is critical to the engineering process and is dictated by many different variables such as reaction type rate of deactivation economics other process requirements II. Common Lab and Bench Scale Reactors:  II. Common Lab and Bench Scale Reactors fixed bed tubular stirred gas, fixed bed stirred liquid/gas, stirred catalyst fluid bed fixed bed, transient gas flow Laboratory and bench-scale reactors vary greatly in size, complexity, cost, and application. Slide11:  Fig. 12.2 Features of representative laboratory reactors [Levenspiel, 1979]. Slide12:  Figure 12.3 Laboratory Pyrex FBR reactor (courtesy of the BYU Catalysis Laboratory). Slide13:  Figure 12.4 Berty internal recycle reactor. Slide14:  Gas-Liquid CSTR (UCSB) Batch Reactor (UCSB) Slide15:  Bench scale reactor (courtesy of Shell Corp.) II. Laboratory and Bench Scale Reactors:  II. Laboratory and Bench Scale Reactors Criteria for selection of lab and bench-scale reactors; applications Satisfying intended application Avoiding deactivation Avoiding inter- and intra- particle heat and mass transport limitations Minimizing temperature and concentration gradients Maintaining ideal flow patterns Maximizing the accuracy of concentration and temperature measurements Minimizing construction and operating costs Common Types of Catalytic Plant Reactors:  Common Types of Catalytic Plant Reactors Fixed-bed Reactors Packed beds of pellet or monoliths Multi-tubular reactors with cooling Slow-moving pellet beds Three-phase trickle bed reactors Fluid-bed and Slurry Reactors “Stationary” gas-phase Gas-phase Liquid-phase Slurry Bubble Column Ebulating bed B. Fixed-bed reactors: characteristics, advantages, limitations :  B. Fixed-bed reactors: characteristics, advantages, limitations Advantages: Flexible- large variation in operating conditions and contact times is possible Efficient- long residence time enables a near complete reaction Generally low-cost, low-maintenance reactors Disadvantages: Poor heat transfer with attendant poor temperature control Difficulty in regenerating or replacing spent catalyst Slide22:  Fig. 12.6 Commercial 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. Figure 12.5 Commercial fixed-bed, adiabatic catalytic reactor. Slide23:  Table 12.6 Characteristics of Plant-Scale Fluidized and Slurry Bed Reactors Slide24:  Figure 12.7 Liquid-phase slurry reactors: (a) forced-circulation, slurry-bed reactor, (b) bubble-column, slurry-bed reactor. Slide25:  Figure 12.8 Batch-slurry reactor for hydrogenation of specialty chemicals. Slide26:  Fig. 12.9 Design of typical FCC transfer-line (riser) reactor with fluidized-bed regenerator. Slide27:  Figure 12.10 Commercial FCC riser reaction designs (a) Exxon, (b) UOP. Slide28:  Fluid Cat Cracker (Chevron) Stacked Fluid Cat Cracker (UOP) Slide29:  Shell Cat-Cracker All-riser Cracking FCC Unit Criteria for Selection of Plant Reactors:  Criteria for Selection of Plant Reactors General Criteria. deactivation rate and regeneration policy reaction conditions catalyst strength and attrition resistance process economics Role of Cp/(-DHr) 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. Slide31:  Optimal Temperature Progression Figure 12.12 Optimum temperature progression (and locus of maximum rates) of (a) reversible endothermic reaction and (b) reversible exothermic reactions. Slide32:  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 staged adiabatic fixed-bed reactors with interstage furnace heating for a strongly endothermic reaction such as reforming of methane. Collecting, Analyzing and Reporting Data from Laboratory Reactors :  Collecting, Analyzing and Reporting Data from Laboratory Reactors Different purposes: activity/selectivity and life data for catalyst selection chemical reaction mechanistic and kinetic data for understanding the reaction at a fundamental level, modeling the reaction process, and/or designing reactors process variable data over a wide range of conditions for purposes of designing large-scale reactors, experimentally validating models and optimizing the catalytic process. Data collection typically involves three major steps (Fig. 12.14): selection of a reaction and catalyst selection of a reactor type analysis of the data Slide34:  Figure 12.14 Process of obtaining rate and kinetic data; note that statistical methods are used in Steps 2 and 3 and in the recycle process. Slide35:  Table 12.7 Proposed Guidelines for Choosing Catalyst Form, Pretreatment, and Reaction Conditions and for Reporting of Data [Ribiero et al., 1996]. 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. Table 12.7 Continued:  Table 12.7 Continued 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. Analyzing and reporting data from laboratory reactors:  Analyzing and reporting data from laboratory reactors Analysis of rate data: objectives finding a rate equation determining catalyst activity, selectivity and activity stability determining the effects of important process variables such as temperature, pressure, reactant concentrations, and space velocity on activity, selectivity and stability Extracting rate constants and concentration dependencies Integral analysis Differential analysis Slide38:  Figure 12.15 Test for integral analysis of rate data involving plot of W/FAo versus integrated reciprocal rate. Integral Analysis of Rate Data Slide39:  Differential Analysis of Rate Data Fig. 12.16 (a) Differential analysis to obtain reaction rates. (b) Plot to obtain reaction orders. References:  References 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.

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