catalytic 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 ANALYSISI.IntroductionA.Why study reactors?B.Definition and classification of reactorsC.Reactor/process design perspective: from the laboratory to the full-scale plantD.Selection of reactors in the laboratory and plantII.Laboratory and Bench Scale ReactorsA.Kinds B.Criteria for selection of lab/bench scale reactors; applicationsIII.Plant ReactorsA.Common typesB.Fixed catalyst bed reactors: characteristics, advantages, limitationsC.Fluidized beds: characteristics, advantages, limitationsD.Criteria for selectionIV.Collecting, Analyzing and Reporting Data from Laboratory ReactorsA.General approach and guidelinesB.Criteria for choosing catalyst form and pretreatment, reaction conditionsC. Choosing mode of reactor operation; differential and integral reactors D.Analyzing and reporting data from laboratory reactors1. Analysis of rate data: objectives and approach2. Integral analysis3. Differential analysisV.Examples

  • New HDS Unit, ARCO Carson, CA Refinery

  • 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 reactorsOur 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 ReactorsWhat 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 ReactorsSizeMethods of charging/discharging: batch or steady-state flow Motion of particles with respect to each otherFluid flow type: tubular or mixed-fluid

  • Table 12.1 Classification of Catalytic ReactorsBasis for ClassificationClassesExamplesSizeLaboratoryBench scalePilot scalePlant scale0.5 cm diam. tubular microreactor (0.1-1 g catalyst)2.5 cm diam. x 30-50 cm long tubular reactor (50-200 g catalyst)7.5 cm diam x 6-10 m long tubular reactor (20-100 kg catalyst)1-6 m diam x 20-50 m long tubular reactor (20-100 metric tons cat.)Methods of charging and dischargingBatchFlow, steady stateStirred liquid and solidsa. tubular, fixed catalyst bedb. slurry, mixed fluid, mixed solidsMotion of catalyst particles relative to each otherFixedRelative motionTubular fixed solids (fixed bed)a.fluidized bedb.slurry bubble columnFluid flowTubular, plug flowMixed fluid flowTurbulent gas in tubular fixed bed Slurry reactor with mechanical stirring

  • Reactor/process design perspectiveFig. 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 plantReactors are used for many different purposes: to study the mechanisms and kinetics of chemical reactions to provide data for validation of process simulationsto investigate process performance over a range of process variables to obtain design datato 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 typerate of deactivationeconomicsother process requirements

  • II. Common Lab and Bench Scale Reactorsfixed bed tubularstirred gas, fixed bed stirred liquid/gas, stirred catalystfluid bedfixed bed, transient gas flow

    Laboratory and bench-scale reactors vary greatly in size, complexity, cost, and application.

  • Table 12.2 Laboratory and Bench-Scale Catalytic ReactorsClassesClass ExamplesFeaturesFixed bed tubularLaboratory differential/integralBench-scale integral0.5 cm diam tubular microreactor (0.1-1 g catalyst, solid catalyst, gas fluid; glass or metal2.5 cm diam. x 30-50 cm long tubular reactor (50-200 g catalyst); solid catalyst, gas or liquid fluid; metalStirred gas, fixed bedStirred batchBatch recycleBertyCarberrymicroreactor, 1 g catalyst, glass or met. microreactor, 1 g catalyst, glass or met.bench-scale, 2-200 g cat., 10-100 atm, stainless steel, circulating gasbench-scale, 2-200 g cat., 10-100 atm, stainless steel, spinning catalyst basketStirred liquid/gas, stirred catalystStirred batchBubble slurrybench-scale, 2-50 g cat., 1-200 atm, glass or metal heterogeneous or homogeneous catalystFluid bedLaboratoryBench-scale transportRecirculating transportmicroreactor, 1-5 g cat, 1 atm, glass bench-scale, 50-200 g catal, 1-10 atm, metal

    Fixed bed, transient gas flowPulse flowTPD/TPSRRadio tracer exchange MS/Transient responseFrequency responsemicroreactor, 0.1-1 g catalyst, glass or metal, 1 atm

  • Fig. 12.2 Features of representative laboratory reactors [Levenspiel, 1979].

  • Figure 12.3 Laboratory Pyrex FBR reactor (courtesy of the BYU Catalysis Laboratory).

  • Figure 12.4 Berty internal recycle reactor.

  • Gas-Liquid CSTR (UCSB)Batch Reactor (UCSB)

  • Bench scale reactor (courtesy of Shell Corp.)

  • II. Laboratory and Bench Scale ReactorsCriteria for selection of lab and bench-scale reactors; applications Satisfying intended applicationAvoiding deactivationAvoiding inter- and intra- particle heat and mass transport limitationsMinimizing temperature and concentration gradientsMaintaining ideal flow patternsMaximizing the accuracy of concentration and temperature measurementsMinimizing construction and operating costs

  • Table 12.3 Seven Criteria for Selection of Laboratory and Bench-Scale Catalytic ReactorsCriterionIssues Involved/Measures of/Methods to Meet Criterion1. Satisfy purpose of measurement (i.e., application)Measure: (1) intrinsic activity/selectivity, (2) kinetics of reaction and deactivationObtain mechanistic understandingSimulate process 2. Avoid catalyst deactivation where possible; where not, decide if fast or slowSee Chap. 5 (B&F) on avoiding different kinds of catalyst deactivationFast decay causes activity and selectivity disguises and requires use of transient or transport reactorSlow decay best studied using CSTR or differential reactor3. Avoid inter- and intra-particle heat and mass transport limitationsThiele modulus less than 0.5; small particles or thin catalyst layerMinimize film thickness with high flow rates, turbulenceOperate at low conversionsUse CSTR or differential reactor4. Minimize temperature and concentration gradientsGradients cause activity and selectivity disguisesMaximize mixing in batch reactor and CSTR; use inerts Use CSTR or differential reactor where possible5.Maintain ideal flow patternsMinimize mixing and laminar flow in tubular reactors;Maximize mixing and minimize gradients in CSTRAvoid gas or liquid holdup in multi-phase reaction systems6. Maximize accuracy of concentration and temperature measurementsSensitive analytical methods and well-placed, sensitive probesSufficiently high product concentrations7. Minimize construction and operating costsSelect the least expensive reactor that will satisfy the other criteriaConsider ways of minimizing size of catalyst and volume of reactant gas

  • Table 12.4 Applications of Lab/Bench Test ReactorsReactor Type Catalyst Selection Activity/SelectivityReactor/DesignFundamental MechanismProcess SimulationLifeKineticsIntegral AdiabaticX (overall avg. conv.)XX IsothermalX (overall conv. at T)XXDifferential Single PassX (intrinsic)X (intrinsic)X (eliminate) RecycleX (intrinsic)X (intrinsic)X (eliminate) Stirred gasX (intrinsic)X (kinetics)X (intrinsic)X (eliminate)X (model)Fluid bed/ TransportX (fast deact.)X (fast deact.)X (fast deact.)XMicro-pulseX (comparative, initial)XTransientX (elem. steps)XX (model)

  • Common Types of Catalytic Plant Reactors

    Fixed-bed ReactorsPacked beds of pellet or monolithsMulti-tubular reactors with coolingSlow-moving pellet bedsThree-phase trickle bed reactors

    Fluid-bed and Slurry ReactorsStationary gas-phaseGas-phaseLiquid-phaseSlurryBubble ColumnEbulating bed

  • Table 12.5 Characteristics of Plant-Scale Fixed Bed Reactors Advantages1.Ideal plug (or mixed) flow2.Simple analysis3.Low cost, low maintenance4.Little loss or attrition5. Greater variation in operating conditions and contact times is possible6.Usually a high ratio of catalyst to reactantslong residence time complete reaction7Little wear on catalyst and equipment8.Only practical, economical reactor at very high pressuresDisadvantages1. Poor heat transfer in a large fixed bed. a. Temp. control and measurement difficult b. Thermal catalyst degradation c. Non uniform rates.2. Non uniform flow patterns e.g. channeling3. Swelling of the catalyst; deformation of the reactor4. Regeneration or replacement of the catalyst is difficult - shut down is required.5. Plugging, high pressure drop for small beads or pellets - P is very expensive.6. Pore diffusional problems intrude in large pelletsOvercoming the Disadvantages1.Monolithic supports overcome disadvantages 2, 5 & 62.Temperature control problems are overcome with: a. Recycle b. Internal and external heat exchanges c. Staged reactors d. Cold shot cooling e. Multiple tray reactor - fluid redistributed & cooled between stages. Catalyst is easily removed - varied from tray to tray.f. Use of diluentsg. Temperature self regulation with competing reactions, one endo and one exothermic.h. Temp control by selectivity and temporarily poisoning the catalyst

  • B. Fixed-bed reactors: characteristics, advantages, limitations

    Advantages:Flexible- large v


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