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Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Reaction Engineering in Heterogeneous Catalysis - Reaction and mass transport in porous.

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Presentation on theme: "Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Reaction Engineering in Heterogeneous Catalysis - Reaction and mass transport in porous."— Presentation transcript:

1 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Reaction Engineering in Heterogeneous Catalysis - Reaction and mass transport in porous catalysts - Up-Scaling of Reactors Reinhard Schomäcker Institut für Chemie der Technischen Universität Berlin

2 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis

3 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis

4 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis

5 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis

6 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis

7 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Schematic presentation of a chemical process Reactant- purification Reaction Product- isolation Main product solvent, reactants, catalyst BP Heat Procedure for reactor design 1. Stoichiometry und Thermodynamics 2. Apparatus and Conditions 3. Calculation of Conversion and Reactor Size 4. Calculation of Material Flow

8 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Steps of Heterogeneous Reaction 1.Diffusion of reactant to catalyst 2.Transport of reactant within catalyst pores 3.Adsorption of reactant on catalyst surface 4.Reaction 5.Desorption of products from catalyst surface 6.Transport of products out of catalyst pores 7.Diffusion of products away from catalyst

9 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Langmuir Hinshelwood Mechanism A B

10 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Mass Transport and Heterogeneous Catalysis Principles Surface layer catalyst Concentration profile fluid phase Influence of mass transport on the temperature dependance of het. catalysis Mass transport influence

11 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Description of pore diffusion A Average free path length Average molecular velocity D g ~ T 1,5 und D g ~ 1/p 1. Fick`s Law

12 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis a) Diffusion in pores d p >> b) Knudsen – Diffusion d p = D K ~ T 0.5 c) Intermediate range N 2, X N 2, X =? N2N2 Wicke-Kallenbach-Experiment porous material

13 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Description of simultaneous reaction and pore diffusion temporal change changes of materialchanges caused of materials within= amount by transport + by reactions volume element dV one dimensional Spherical geometry

14 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Mass balance of sperical particle in steady state Solution of mass balance and description of average reaction rate with r= kc n and =-1 renormalized parameter = Thiele-Modulus radial concentration profil within sperical pellet

15 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis r = r het Reaction without mass transport limitation Effectiveness factor effectiveness factor

16 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Influence of pore diffusion on effective rate constant

17 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Film diffusion und Reaction

18 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Discussion of a first order reaction with r s =k s c w ß(c 0 -c w ) = k s c w Border cases: k s << ß c w =c 0 ( no layer formation) c0c0 cwcw k s >> ß c w 0 c0c0 cwcw

19 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Calculation of eff. volume related rate constant d sphere d d Particle volume a Particle surface

20 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Temperature dependance:

21 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis L G G L Packed Bubble Column Column Gas-Liquid-ReactorsGas-Solid-Reactors Three-Phase-Reactors Fixed Bed Reactor Katalysator G L LG G Trickle Bed Reactor G Tube Reactor G K+L Tank Reactor

22 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Universal mass balance VRVR jAjA r Akk. Transp. Reaction Residence time

23 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis [-] Damköhler Number reactor reaction Solution of general mass balance with boundary conditions for Different reactions and reactor results in X = f(Da, reactor)

24 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Ideal Tube Reactor (PFTR) 0 L z q nAnA. - steady state ( X/ t=0) - no back mixing (plug flow) - Volume of feed is constant - no radial concentration gradient (one dimensional system) - characteristic time is definied by: =V R /V.

25 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis 0 L z q nAnA. (4-17)

26 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Separation of variables: Integration Z: 0 L X: 0 X e

27 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis 0. Order reaction: r 0 =k (X)=1 2. Order reaction: r 0 =kc A0 c B0 (X)=(1-X) 2 1. Order reaction: r 0 =kc A0 (X)=1-X

28 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis 2. Order reaction: r 0 =kc A0 c B0 (X)=(1-X)(1- X) Conversion as function of Damköhler number

29 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Design of a reactor: Demands: X e, n P (X); X e Da Residence time: Reactor capacity :Reactor volume: Produced product

30 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Fluidized bed reactor (CSTR) M CSTR VRVR 1. Order reation: (X)=1-X coordinate z inletoutlet cAcA

31 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis 2. Order reaction: (X)=(1-X)(1- X) Simple procedure for solution of mass balance: X/Da = (X) Reactor design: X (X) 1 1 X/Da XeXe (X) ; X e Da ; L P V R =V.

32 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Comparison of ideal reactors CSTR and PFTR Dependence of Conversion on Damköhler number for 1. order raction

33 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Heat balance of chemical reactors universal heat balance VRVR jAjA r q. [J/m 2 s] universal mass balance universal heat balance integral heat balance

34 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis d 1 2 T TkTk The cooled CSTR

35 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis (4-46) (4-47) (4-48) Coupling Equation

36 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Separation for T: Design of cooling follows solution of MB:. L P V R =V Calculation of T a or T k from T 0

37 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Safty Scenario Stability analysis a)F W high,T-T K low:right b)F W low,T-T K high :wrong Quantitative calculation MB HB

38 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Example: 1. Order reaction X DaT T e e mitDakMass balance E RT E A () () ()() 1 1 ()()()1 1 0 StTTT Dae e Coupling eqn. ad E RT E

39 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis Qualitative Description of other reactors BR und PFTR Adiabatic reactors BR: PFTR: cooled reactors BR: PFTR:

40 Institut für Chemie Ringvorlesung Methods in Heterogeneous Catalysis r TKTK Radial temperature profile with tube reactor r tube < r crit. r tube > r crit.


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