1 / 42

Stages in Catalyst development

Preparation. Optimization. Optimization. Screening. Reaction. network. Kinetics. Increasing:. ·. time. Life tests. ·. money. ·. reality. Scale-up. Stages in Catalyst development. Trends: Parallel activities Subcontracting. MIXING. PLUG FLOW. DISPERSION. DIFFUSION.

treva
Download Presentation

Stages in Catalyst development

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Preparation Optimization Optimization Screening Reaction network Kinetics Increasing: · time Life tests · money · reality Scale-up Stages in Catalyst development Trends: Parallel activities Subcontracting

  2. MIXING PLUG FLOW DISPERSION DIFFUSION REACTION TRANSPORT PHENOMENA Transport Phenomena inPacked-bed Reactor

  3. Stability Mechanism Kinetics CATALYSIS ENGINEERING Reactor Transport Engineering Phenomena Catalyst Catalytic Reaction Engineering

  4. LABORATORY CATALYTIC REACTORS Steady state Transient Continuous flow Batch Semi-batch Discontinuous Plug flow Mixed flow Step Pulse Integral Differential Single pass Recycle Fluidization Internal External Riser reactor Berty reactor TAP Thermobalance Fluid bed Multitrack Packed bed Slurry Classification of Laboratory Reactors:Mode of Operation

  5. Classification of Laboratory Reactors:Contacting Mode PFR CSTR FBR Slurry/FBR with recycle Riser Riser FBR Slurry/FBR fluid recycle contn. cat feed fluid + cat. rec.

  6. Pep versus Rep

  7. Maximum allowable particle diameter versus (1 - x)n = 1, single phase, Pep = 0.5 dt = 50 mm dt = 5 mm dp (mm) dt = 1 mm 1 - x

  8. Catalyst size Practical catalyst: often: dp = 1 - 3 mm large reactor needed Option: dilution with inerts

  9. Catalyst wetting in trickle-flow reactors • Determined by friction and gravity • particle diameter • viscosity • linear velocity (from LHSV and Lb) • Example • LHSV = 2 m3 / (m3h)

  10. Catalyst wetting in trickle-flow reactors, Example LHSV = 2 m3/m3h l = 10-6 m2/s dp = 1 mm ul = LHSV.Lb = 2 Lb m/h Lb > 90 mm

  11. Maximum allowable particle diameter versus kinematic viscosity for complete wetting in trickle-flow reactors LHSV = 2 m3 / (m3h)

  12. Dilution with Inerts Hydrodynamics governed by small inert particles Kinetic performance governed by catalyst extrudates

  13. Maximum allowable particle diameter as a function of the catalyst fraction in a diluted bed

  14. Effect of Catalyst/Diluent Distribution in Decomposition of N2O

  15. Laboratory Reactors PFR: CSTR: FBR: TGA: Batch: • deactivation noted directly • small amounts of catalyst needed • simple • yields conversion data, not rates • larger amounts of catalyst and flows needed • deactivation not determined directly • direct rate data from conversions • non-ideal behaviour • continuous handling of solids possible • limited to weight changes • careful date interpretation needed • often mass-transfer limitations • catalyst deactivation hard to detect • yields conversion and selectivity data quickly over large range

  16. Mass and heat transport effectscatalyst particles • Mass and heat transport phenomena • Extraparticle transport • Intraparticle transport • Catalyst effectiveness • Generalizations • Catalyst shape, kinetics, volume change • Observable quantities • Criteria - transport disguises - experimental

  17. Gas film T s T T T b c c b c c s Bulk gas Exothermic Endothermic

  18. Gas film Ts Tb T T Cb Cs c c Bulk gas Exothermic Endothermic Gradients at Particle ScaleGas/solid Reactor

  19. Liquid film Gas film Bulk gas (bubble) T c Bulk liquid Exothermic Gradients at Particle ScaleGas/liquid/solid Slurry Reactor

  20. film layer cb cs Isothermal - External Mass Transport mass transfer reaction No transport limitations if: cs» cb When? How to determine cs?

  21. 10 -1 0.5 1 1 n = 2 0.1 0.01 0.001 0.01 0.1 1 Ca Isothermal - External Mass Transport Catalyst effectiveness: Observable quantity: rV = kVCn

  22. Nonisothermal - External Transport Mass: Heat: T and c coupled via b b: max. T-rise over film Catalyst effectiveness?

  23. Nonisothermal - External Transport Ca small General kinetics: Series expansion:

  24. L 0 Isothermal - Internal Mass Transport Slab Mass balance, steady state diffusion & reaction 1st order irreversible: Boundary conditions: 1.0 f 0.1 x+dx x 0.8 c* 0.6 1.0 0.4 2.0 0.2 10.0 0.0 1.0 0.8 0.6 0.4 0.2 0.0 x*

  25. Slab: 1st order 1 hi 0.1 0.1 1 10 f Catalyst Effectiveness Limits:

  26. Diffusion Control? Kinetics unknown effectiveness cannot be calculated Wheeler-Weisz: (nth order) Weisz-Prater Criterion:

  27. T T Ts Ts cs cs c c Exothermal Endothermal Nonisothermal - Internal Transport similar profiles c and T determined by Prater number Typical values: 0-0.3 (exothermal)

  28. L 0 Nonisothermal - Internal Transport Slab Heat and mass balance, steady state Effective conductivity 0.1-0.5 J/m.K.s Boundary conditions: x+dx x Prater number temperature and concentration profile similar (scaling)

  29. Nonisothermal - Internal Transport Internal effectiveness factor: g s= 10 bi varied Criterion:

  30. Criterion bed T-gradient Analogous to particle T-gradient: Compare with:

  31. Mass Transport Limitations? Internal / External Criterion:  = 1 ± 0.05 Internal transfer: External transfer: Also: while Bim>~10 s=1,2,3 (geometry) Weisz-Prater more severe than Carberry criterion

  32. Heat Transport Limitations? Internal / External Criterion: h = 1 ± 0.05 Series expansion of h expression around 1 for slab, first order irreversible reaction results in: External transfer: strongest influence Internal transfer: External gradient criterion more severe than internal gradient criterion

  33. Heat Transport Limitations? Internal / External Largest T-gradient ? Internal: External: For x=0 c=0 largest T-gradient Industrial: internal gradient largest Laboratory: external gradient largest 10-104 gas-solid 10-4-0.1 liquid-solid external gradient negligible

  34. Heat Transport Limitations? External / Bed Comparison of external and bed gradient (neglecting wall contribution and bed dilution): > 100 > 1 ~ 1 Bed gradient criterion more severe than external gradient criterion

  35. Summary Dependence rv,obs Observed reaction rate: 1. Kinetics: does not depend on L, n reaction order, Eaapp= Eatrue 2. Internal mass transfer: depends on: 1/L, (n+1)/2 reaction order, Eaapp= ½Eatrue 3. External mass transfer: depends on: L, flow rate, 1st reaction order, Eaapp= 0 How to check whether limitations are present?

  36. Ni C + H2O CO + H2 5 Ea(kJ/mol) 0 61 1 1 0.75 164 r(obs) 0.1 0.6 order n 0.01 0.9 1.0 1.1 1.2 1.3 1.4 1000/T Observed Temperature Behaviour Catalysed steam gasification of carbon (coke) on Ni catalyst • p(H2O)=26 kPa • thermobalance • coked catalyst: Ni/Al2O3

  37. Apparent Rate Behaviour

  38. xA,1 xA,2 xA,3 x W1 W2 W3 Diagnostic Tests - Mass-Transport Limitations 1. Particle size variation egg-shell catalysts? observed rate particle size 2. Flow rate variation at constant space time!

  39. 0.1 dp/mm kv 0.38 0.01 1.4 2.4 0.001 1.90 1.95 2.00 2.05 2.10 1000/T What’s observed? intraparticle limitation Limiting case: ‘Falsified kinetics’ activation energy: Ea(true)/2 reaction order (n+1)/2 wide pore silica effect dp particle size dependent

  40. Proper Catalyst Testing • Adhere to criteria • Ideal reactor behaviour: PFR or CSTR • Isothermal bed • Absence of limitations: observables, diagnostic tests • Compare catalysts at low conversion; For high conversions use feed/product mixtures • Compare selectivities at same conversion level

  41. W / F 0 i Consecutive irreversible first order reaction A  R  S 1 C C A S 0.8 0.6 Concentration 0.4 Same CR C R 0.2 0 0 20 40 60 80 100

  42. More Efficient Catalyst Testing • PC-controlled microreactor set-up • Parallel reactors in one oven: Sixflow reactor set-up • Experimental design

More Related