反应工程基础：Chap4-Isothermal Reactor Design2

1、Chapter 4 Isothermal Reactor DesignTying everything together Chaps. 1 and 2: Mole balance, reactor size Chap. 3: reactions Chap. 4: combine reactions and reactors, logical structure for the design of various types of reactors Reasoning, rather than memorizing numerous equations together with various

2、 restrictions and conditions under which each equation applies Attention: reactions that are operated isothermallyPart 2Mole balances written in terms of concentration and molar flow ratesOverview There are many instances when it is much more convenient to work in terms of the number of moles (NA, N

3、B) or molar flow rates (FA, FB, etc.) rather than conversion. Multiple reactions Membranes Unsteady stateDifference in algorithm1.Conversion algorithm mole balances on only one species2.Molar flow rate and concentration algorithmmole balance on each and every species4.9 Membrane reactors Increase co

4、nversion when the reaction is thermodynamically limited as well as to increase the selectivity when multiple reactions are occurring Provide a barrier to certain components while being permeable to others, Prevent certain components such as particulates from contacting the catalyst, Contain reactive

5、 sites and be a catalyst in itself (i.e., catalytic membrane) By having one of the products pass throughout the membrane, we drive the reaction toward completion.A3B + C612266C H3H + C HExampleMechanism of membrane reactorsFeedC6H12H2 permeateH2 permeateSweep gasSweep gasA3B + C612266C H3H + C HC6H6

6、C6H12H2AlgorithmChoose reactor volume rather than catalyst weight as independent variableAAdFrdVbWVMole balances on the chemical species that stay within the reactor, A and CCCdFrdVMole balances on B (H2) must be modified Balance on B in the catalytic bedInBy flowOutBy diffusionOutBy flowGenerationA

7、ccumulation-+=|VBF|VVBF-BRV+-BrV=0BBBdFrRdVRB: molar flow rate of B leaving through the sides the reactor per unit volume of reactor (mol/dm3s)The rate of transporting B out through the membrane:Molar flux of BBCBBSWkCCOverall mass transfer coefficient in m/sBBCBBSRW ak a CCMembrane surface area per

8、 unit volume of reactor2Area4Volume4DLaDDLBCBRk CCCkk a0BSCkC: s-1B (CB)B (CBS)Use of membrane reactors to enhance selectivityAB C + DFeedAB, FB0FA0B, FB0BBBdFrRdV(Chapter 6)l燃烧尾气为高浓度的CO2，便于捕获和后续处理；l采用透氧膜高温原位供氧，降低纯氧燃烧的成本；l燃烧温度相对较低，易与其它能源动力过程结合。中国科技大学，陈初升 教授1000C4.10 Unsteady-state operation of stirr

9、ed reactors Startup of a CSTRto determine the time necessary to reach steady-state operation Semibatch reactors Predict the concentration and conversion as a function of time Analytical solutions vs. numerical solutionsTwo basic types of semibatch operationsABCDB is slowly fed to a reactor containin

10、g AGenerally used when unwanted side reactions occur at high concentrations of Bor when the reaction is highly exothermicAmmonolysis, chlorination, hydrolysisType I:Type II: reactive distillationA and B are charged simultaneously, one of the products is vaporized and withdrawn continuously.Removal o

11、f one of the products in this manner shifts the equilibrium toward the right, increasing the final conversion.Removal of one of the products further concentrates the reactant, thereby producing an increased rate of reaction and decreased processing time. Acetylation reaction, esterification reaction

12、s in which water is removed4.10.1 Startup of a CSTR0AAAAdNFFr Vdt0AAAAdCCCrdtConversion is meaningless during startup; Use Concentration as variable1st order reaction01AAACdCkCdt01 exp11AACtCkk00,AAtCCts: the time necessary to reach 99% of the steady-state concentration, CAS01AASCCk4.61StkSlow react

13、ion with small k4.6St Rapid reactions with large k4.6StkGeneral mole balance equationAArkC0.99AASCC4.10.2 Semibatch reactorsMotivation: to enhance selectivity in liquid-phase reactions. ABDABU2DDABrk C C2UUABrk C CInstantaneous selectivity 22DDABDAD UUUABUBrk C Ck CSrk C Ck CThe way to achieve more

14、D: B slowly fed to pure AABCConstant molar feed, 0, CB0 00AAdNr V tdtMole balance on species A yieldsReaction:RateoutRate ofgenerationRate ofaccumulationRatein-+=4.10.3 Writing the semibatch reactor equations in terms of concentrationsAAAAd C VVdCdVr VCdtdtdtRate ofaccumulationRateRateRate ofinoutge

15、neration0000dVdt Overall mass balanceof all speciesFor a constant-density system0dVdt0Semibatch reactor volume as a function of time00VVt0AAAVdCCVrdtBalance on A: 0AAAdCrCdtVBalance on B: 0BBBdNr VFdtIn - Out + Generation = Accumulation0BF0Br VBdNdt0BBBBBdVCVdCdVCr VFdtdtdtBalance on B: 00BBBBCCdCrd

16、tVODE solver.example4.10.4 Writing the semibatch reactor equations in terms of conversionReaction: ABC + DB is fed to a vat containing only A initially.Reaction: 1st order in A and 1st order in BThe limiting reactantis the one in the vat.00AAANNNXFor species B: 000tBBiBANNF dtNXInitialAdded to the v

17、atReacted up to t00BBANF tNXIf no B initially0AAAdNdXr VNdtdt Mole balance on A0CCiANNNXAs for C or DCDAABCC Crk C CKRate law:00000000000001AAAACBiBABBADNXNCVVtNXCVtNF tNXVCVVtNXCVtConcentrations of A, B, C,D as a function of conversion and time2000001/BiBAACkXNF tNXNXKdXdtVt(Numerical solution: con

18、version as a function of time)Equilibrium conversion (shift towards right continually) CeDeCeDeCAeBeAeBeCeDeAeBeNNC CVVKNNC CVVN NNN0000020001 1AeAeCAeBAeAeeBAeNXNXKNXF tNXNXXF tNX2001AeCeCBeNXtK XK FX2000000114121BBBCCCCAAAeCF tF ttFKKKKNNNXKor:ClosureMole balanceRate lawStoichiometryCombineEvaluat

19、eThe heart of chemical reaction engineering for isothermal reactorsFor any reactors: batch reactor, CSTR, PFR, PBR, membrane reactor, semibatch reactor4.8 Microreactors Emerging technology in CRE High surface area-to-volume ratios Typical channel width: 100 m, length 2 cm High surface area-to-volume

20、 ratio, ca. 10,000 m2/m3 High heat, mass transfer Surface-catalyzed reactions can be greatly facilitated Hot spots in highly exothermic reactions can be carried out isothermally To study intrinsic kinetics of reactions Production of toxic or explosive intermediates (e.g., microexplosion) Shorter res

21、idence times, narrower residence time distributionsApplications: specialty chemicals, combinatorial chemical screening, lab-on-a-chip, chemical sensorsPlug flow:AAdFrdVExample: MicroreactorBASF：微反应器技术成功的工业应用T型混合器混合界面周期摆动Re 200涡的出现 Re1500MicroLIF：刘喆：刘喆Droplet based micro-reactorTice, J. D.; Song, H.;

22、 Lyon, A. D.; Ismagilov, R. F. Langmuir 2003Mixing vs. DispersionSotowa, K. I.; Irie, K.; Fukumori, T.; Kusakabe, K.; Sugiyama, S. Chem. Eng. Technol. 2007Nanoparticle preparationMixing Intensification by Chaotic Advection inside Droplets for Controlled Nanoparticle Preparation（博士生：刘喆）Higher liquid

23、flow rateCase N1(poor mixing)Case N2(poor mixing)Case N3Case N4Case N5Case N6Case A1Case A2Case A3Case A4Case A5Case A6IMRET-10: 10th International Conference on Microreaction TechnologyApril 6-10, 2008New Orleans, LA Fine Chemicals and Pharmaceuticals Synthesis and ProductionCatalyzed and Enzymatic

24、al ProcessesMixing, Mass Transfer and Heat Exchange Characterization and SimulationProgress in the Commercialization of Micro Process Technology - Panel Discussion Energy Generation and Fuel Processing Novel Process Windows Unusual Ways of Processing Polyreactions / Fine Chemicals and Pharmaceutical

25、s Synthesis and Production Sensing and Process Analytics Multiphase Reactions, Dispersions and Foams Particles and Functional Materials .Propane conversion at ambient temperatureOxidative conversion of propane with catalystCatalytic oxi-cracking of hexane for olefinsDirect CH4 conversion to liquid o

26、xygenatesCatalyst activation for CNF synthesisAerosol reactor1. Mole balance on monomers2. Rate lawsA. Nucleation Kinetics B. Growth Kinetics 3. Flocculation (Collision) Kinetics 4. Balance Equations AEROSOL NANOPARTICLE PLUG FLOW REACTORS To produce fine particles of controlled size Particle sizes

27、typically be in the range from 10 to 500 nm Applications for examples:SnO2 for carbon monoxide gas sensorsTiO2 for fiber optics SiO2 for fumed silica and optical fibers C for carbon black fillers in tires Fe for recording materials Ni for batteries Nanostructured composite silica-carbon particles at

28、 high production rates (up to 700 g/h) are synthesized by oxidation of hexamethyldisiloxane in our pilot-scale air-hydrogen burner The manufacture of nanostructured titania particles made by titanium tetraisopropoxide oxidation in a premixed methane-oxygen aerosol reactor is precisely controlled with the electric field across the flame created by the two plate electrodes 高温气相合成纳米TiO2热态小试