From Model Component Behaviour to Industrial Reactor Simulation:

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From Model Component Behaviour to Industrial
Reactor Simulation

• Aromatic Hydrogenation in Hydrocracking

J. W. Thybaut and G. B. Marin Laboratorium voor
Petrochemische Techniek, Ghent University
Eurokin Workshop, Dow Terneuzen, November 25, 2002
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(hydro)cracking as refinery process
end products
gasses
LPG
LPG
reforming
gasoline
naphtha
kerosine
kerosine
diesel
diesel
LPG/gasoline
alkylation
medium gasoil
kerosine diesel
cracking
heavy gasoil
residu
coking
industrial fuel
bitumen
destillation tower

• hydrocracking
• catalytic cracking

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detailed refinery scheme
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(No Transcript)
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catalytic versus hydrocracking

• catalytic cracking
• carbon rejection
• riser-regenerator-configuration
• LPG/gasoline
• product rich in unsaturated components

• hydrocracking
• hydrogen addition
• downflow packed bed
• kerosine/diesel
• few aromatics, low S- en N-content in product

choice is nuanciated and depends on local
conditions
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hydrocracking reaction mechanism
fluidum phase
acid sites
physisorption
zeolite

(de)-protonation
alkyl-shift
(de)-hydrogenation
PCP-branching
metal sites



ß-scission


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overview

• single-event model
• carbon number and acid strength effects in
  hydrocracking
• toluene hydrogenation in the vapor phase
• toluene hydrogenation in the liquid phase
• simulation of an industrial reactor

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single event

• alkyl-shift, PCP-branching, b-scission
• rate coefficient depends on reaction type and
  type of the carbenium ions involved (s,t)
• forward and backward reaction are one elemenatry
  step
• forward step consists of 2x more single events
  than the backward step

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building blocks rate equation
alkyl-shift PCP-branching ?-scission
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detailed rate equation
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net rates of formation

• summation over all elementary steps
• number of terms increases with carbon number
• ?relumping fast fundamental

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overview

• single-event model
• carbon number and acid strength effects in
  hydrocracking
• toluene hydrogenation in the vapor phase
• toluene hydrogenation in the liquid phase
• simulation of an industrial reactor

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carbon number effect

• (i) physisorption effects, (ii) extent reaction
  network, (iii) carbenium ion stability

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carbenium ion stability
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standard protonation enthalpy

• same effect on reacting carbenium ion and
  activated complex

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quantitative

• important for lower carbon numbers
• levelling out for higher carbon numbers

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catalyst effect

• (i) physisorption, (ii) number of sites,
• (iii) acid strength

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standard protonation enthalpy




zeolite I
zeolite II

• same effect of acid strength on stability of
  reacting carbenium ion and activated complex

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quantitative

• Y-zeolite weakest acid sites
• intermediate dealumination degree ? strongest
  acid sites

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overview

• single-event model
• carbon number and acid strength effects in
  hydrocracking
• toluene hydrogenation in the vapor phase
• toluene hydrogenation in the liquid phase
• simulation of an industrial reactor

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model construction
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experimental

• inlet partial pressure effects
• negative for toluene
• m ? -0.2
• positive for hydrogen
• n ? 0.6 tot 1.8

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quantumchemistry literature
gas phase
catalyst surface
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model assumptions

• Competitive H2 and toluene chemisorption (E)
• 1st 2nd H-addition not rate determining (Q)
• 5th 6th H-addition quasi equilibrated (L)
• reactant chemisorption quasi equilibrated
• product desorption fast and irreversible

equal rate coefficients 1st to 4th H-addition
(no rate-determining step)
3rd of 4th H-addition rate determining
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reaction scheme
surface reactions
chemisorption
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rate equation

• equal rate coefficients
• rate-determining step
• i3,4

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calculation preexponential factors

• 10-12 immobile surface species
• 10-10 mobile surface species
• 1015 mobility in transition state
• 10-2 2 reactants ? 1 product

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estimation enthalpies/energies

• chemisorption enthalpies
• toluene -70 kJ mol-1 hydrogen -42 kJ mol-1
• activation energies
• similar behaviour of no RDS and 4H RDS
• ? no RDS because of its more general character

no RDS 3H RDS 4H RDS Eact (kJ mol-1) 38 80
35 F-value 104 5 102 104
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agreement model - experiments

• surface concentrations
• toluene high (60)
• hydrogen low (20)
• free sites low (20)

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overview

• single-event model
• carbon number and acid strength effects in
  hydrocracking
• toluene hydrogenation in the vapor phase
• toluene hydrogenation in the liquid phase
• simulation of an industrial reactor

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gas versus liquid

• industrial
• 3-phase reactor (gas/liquid/solid)

• laboratory
• gas phase reactor (Berty) reaction mechanism
• 3-phase reactor (Robinson-Mahoney) liquid phase
  effects

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model construction

• kinetic scheme identical
• thermodynamic ideality
• gas phase ideal (fugacities gt 0.95, even gt0.99)
• liquid non ideal
• chemisorbed state ideal mixture
• liquid
• deviation from ideality with respect to ideal gas
  state (comparison with gas phase results)
• chemisorbed state
• only interaction with catalyst surface,
  independent from surface concentrations ? ideal
  mixture

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rate equation

• liquid phase
• gas phase

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simulation regression

• simulation results in too high toluene
  conversions ? adjust via regression

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regression results
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overview

• single-event model
• carbon number and acid strength effects in
  hydrocracking
• toluene hydrogenation in the vapor phase
• toluene hydrogenation in the liquid phase
• simulation of an industrial reactor

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simulation model

• reactor model
• mass, energy and momentum balance
• geometry
• reaction model (kinetics)
• relumped single-event model for isomerization and
  cracking of (cyclo)-alkanes
• microkinetic model for the hydrogenation of
  aromatic components

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reactor equations

• geometry
• cocurrent downflow packed bed reactor
• mass heat transfer limitations
• gas liquid interface mass heat
• liquid solid interface none
• internal mass

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geometry operating conditions
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temperature profiles
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aromatic profile
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hydrogen profiles
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aromatic content - temperature profile
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aromatic content - aromatic profile
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aromatic content - hydrogen profile
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conclusions

• standard protonation enthalpy in hydrocracking
• describes the carbon number dependence
• describes acid strength effects
• hydrogenation of aromatics
• effect aromatic resonance stabilization
  disappears upon chemisorption on Pt-surface
• equal rate coefficients for first 4 H-additions

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conclusions

• liquid phase
• fugacities adequately describe liquid phase
  effects in chemisorption
• surface reaction steps are affected by the
  aggregation state of the reactants
• simulation of an industrial reactor
• hydrogenation of aromatics leads to hot spot
• mass transfer limitations between gas and liquid
  phase for high aromatic content in the feed

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acknowledgement

• IAP-PAI programme funded by the Belgian
  Government, financial support
• Mark Saeys, quantumchemical calculations

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thanks!