Catalysis and Catalysts - Catalyst Performance Testing 1 Stages in Catalyst development Preparation Screening Reaction network Kinetics Life tests Scale-up Increasing:  time  money  reality Optimization Trends:Parallel activities Subcontracting

Catalysis and Catalysts - Catalyst Performance Testing 2 Transport Phenomena in Packed-bed Reactor

Catalysis and Catalysts - Catalyst Performance Testing 3 Catalytic Reaction Engineering Kinetics Mechanism Stability Reactor Engineering Catalyst Transport Phenomena CATALYSIS ENGINEERING

Catalysis and Catalysts - Catalyst Performance Testing 4 Classification of Laboratory Reactors: Mode of Operation LABORATORY CATALYTIC REACTORS Steady stateTransient BatchSemi-batchDiscontinuousContinuous flow Plug flow IntegralDifferential Mixed flow Single passRecycleFluidization External Internal StepPulse Packed bed Riser reactor Thermobalance TAP Multitrack Berty reactor Fluid bed Slurry

Catalysis and Catalysts - Catalyst Performance Testing 5 Classification of Laboratory Reactors: Contacting Mode PFRCSTR FBR Slurry/FBR with recycle Riser Riser FBR Slurry/FBR fluid recycle contn. cat feed fluid + cat. rec.

Catalysis and Catalysts - Catalyst Performance Testing 6 Pe p versus Re p

Catalysis and Catalysts - Catalyst Performance Testing 7 Maximum allowable particle diameter versus (1 - x) n = 1, single phase, Pe p = x d p (mm) d t = 50 mm d t = 5 mm d t = 1 mm

Catalysis and Catalysts - Catalyst Performance Testing 8 Catalyst size Practical catalyst: often: d p = mm large reactor needed Option: dilution with inerts

Catalysis and Catalysts - Catalyst Performance Testing 9 n Determined by friction and gravity –particle diameter –viscosity –linear velocity (from LHSV and L b ) n Example –LHSV = 2 m 3 / (m 3 h) Catalyst wetting in trickle-flow reactors

Catalysis and Catalysts - Catalyst Performance Testing 10 Catalyst wetting in trickle-flow reactors, Example LHSV = 2 m 3 /m 3 h l = m 2 /s d p = 1 mm u l = LHSV.L b = 2 L b m/h L b > 90 mm

Catalysis and Catalysts - Catalyst Performance Testing 11 Maximum allowable particle diameter versus kinematic viscosity for complete wetting in trickle-flow reactors LHSV = 2 m 3 / (m 3 h)

Catalysis and Catalysts - Catalyst Performance Testing 12 Dilution with Inerts Hydrodynamics governed by small inert particles Kinetic performance governed by catalyst extrudates

Catalysis and Catalysts - Catalyst Performance Testing 13 Maximum allowable particle diameter as a function of the catalyst fraction in a diluted bed

Catalysis and Catalysts - Catalyst Performance Testing 14 Effect of Catalyst/Diluent Distribution in Decomposition of N 2 O

Catalysis and Catalysts - Catalyst Performance Testing 15 Laboratory Reactors –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 PFR: CSTR: FBR: TGA: Batch:

Catalysis and Catalysts - Catalyst Performance Testing 16 n Mass and heat transport phenomena –Extraparticle transport –Intraparticle transport n Catalyst effectiveness n Generalizations –Catalyst shape, kinetics, volume change n Observable quantities –Criteria - transport disguises - experimental Mass and heat transport effects catalyst particles

Catalysis and Catalysts - Catalyst Performance Testing 17 T c Exothermic T c Endothermic Gas film Bulk gas T s T b c s c b

Catalysis and Catalysts - Catalyst Performance Testing 18 Gradients at Particle Scale Gas/solid Reactor T c Exothermic T c Endothermic Gas film Bulk gas TsTs TbTb CsCs CbCb

Catalysis and Catalysts - Catalyst Performance Testing 19 T c Exothermic Liquid film Gas film Bulk liquid Bulk gas (bubble) Gradients at Particle Scale Gas/liquid/solid Slurry Reactor

Catalysis and Catalysts - Catalyst Performance Testing 20 Isothermal - External Mass Transport reactionmass transfer cscs cbcb film layer No transport limitations if: c s  c b When? How to determine c s ?

Catalysis and Catalysts - Catalyst Performance Testing 21 Isothermal - External Mass Transport Catalyst effectiveness: Observable quantity: r V = k V C n

Catalysis and Catalysts - Catalyst Performance Testing 22 Nonisothermal - External Transport Mass: Heat: T and c coupled via   max. T-rise over film Catalyst effectiveness?

Catalysis and Catalysts - Catalyst Performance Testing 23 Nonisothermal - External Transport Series expansion: General kinetics: Ca small

Catalysis and Catalysts - Catalyst Performance Testing 24 Isothermal - Internal Mass Transport Slab Mass balance, steady state diffusion & reaction 1st order irreversible: Boundary conditions: xx+dx 0L x* c* 

Catalysis and Catalysts - Catalyst Performance Testing 25 Catalyst Effectiveness Slab: Limits: 1 st order  

Catalysis and Catalysts - Catalyst Performance Testing 26 Kinetics unknown effectiveness cannot be calculated Wheeler-Weisz: (n th order) Weisz-Prater Criterion: Diffusion Control?

Catalysis and Catalysts - Catalyst Performance Testing 27 ExothermalEndothermal c T TsTs cscs TsTs cscs c T Typical values: (exothermal) similar profiles c and T determined by Prater number Nonisothermal - Internal Transport

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

Catalysis and Catalysts - Catalyst Performance Testing 29 Nonisothermal - Internal Transport Internal effectiveness factor:  s = 10  i varied Criterion:

Catalysis and Catalysts - Catalyst Performance Testing 30 Criterion bed T-gradient Analogous to particle T-gradient: Compare with:

Catalysis and Catalysts - Catalyst Performance Testing 31 Criterion:  = 1 ± 0.05 External transfer: Internal transfer: Also: while Bi m >~10 s=1,2,3 (geometry) while Bi m >~10 s=1,2,3 (geometry) Weisz-Prater more severe than Carberry criterion Mass Transport Limitations? Internal / External

Catalysis and Catalysts - Catalyst Performance Testing 32 Criterion:  = 1  0.05 External transfer: Internal transfer: Series expansion of  expression around 1 for slab, first order irreversible reaction results in: strongest influence External gradient criterion more severe than internal gradient criterion Heat Transport Limitations? Internal / External

Catalysis and Catalysts - Catalyst Performance Testing 33 Heat Transport Limitations? Largest T-gradient ? Internal: External: For x=0 c=0 largest T-gradient gas-solid liquid-solid external gradient negligible Industrial: internal gradient largest Laboratory: external gradient largest Internal / External

Catalysis and Catalysts - Catalyst Performance Testing 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

Catalysis and Catalysts - Catalyst Performance Testing External mass transfer: 2. Internal mass transfer: depends on: 1/L, (n+1)/2 reaction order, E a app = ½E a true depends on: L, flow rate, 1 st reaction order, E a app = 0 How to check whether limitations are present? Observed reaction rate: Summary Dependence r v,obs 1. Kinetics: does not depend on L, n reaction order, E a app = E a true

Catalysis and Catalysts - Catalyst Performance Testing 36 Observed Temperature Behaviour Catalysed steam gasification of carbon (coke) on Ni catalyst C + H 2 O CO + H 2 Ni p(H 2 O)=26 kPa thermobalance coked catalyst: Ni/Al 2 O /T r(obs) E a (kJ/mol) order n

Catalysis and Catalysts - Catalyst Performance Testing 37 Apparent Rate Behaviour

Catalysis and Catalysts - Catalyst Performance Testing Particle size variation 2. Flow rate variation at constant space time! particle size observed rate egg-shell catalysts? Diagnostic Tests - Mass-Transport Limitations x A,3 W3W3 x A,2 W2W2 x A,1 W1W1 x

Catalysis and Catalysts - Catalyst Performance Testing 39 What’s observed? intraparticle limitation particle size dependent reaction order (n+1)/2 activation energy: E a (true)/ d p /mm /T kvkv wide pore silica effect d p Limiting case: ‘Falsified kinetics’

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

Catalysis and Catalysts - Catalyst Performance Testing 41 Consecutive irreversible first order reaction A  R  S Concentration 0 / i FW C A C S C R Same C R

Catalysis and Catalysts - Catalyst Performance Testing 42 More Efficient Catalyst Testing PC-controlled microreactor set-up Parallel reactors in one oven: Sixflow reactor set-up Experimental design