Galtier, Pierre

Lozano Blanco, Gisela

Marin, Guy

Surla, Karine

Thybaut, Joris

Ghent University Academic Bibliography

Microkinetic analysis of Fischer-Tropsch synthesis on Fe and Co catalystsGisela Lozano1, Joris W. Thybaut1, Karine Surla2, Pierre Galtier2, Guy B. Marin11LPT, Ghent University, Krijgslaan 281 – S5, B-9000 Ghent, Belgium2Institut Français du Pétrole, B.P. 3, 69390 Vernaison, FranceEUROPACAT-VIII26 - 31 August 2007, Turku, Finlandhttp://www.tw12.ugent.be/ 2Fischer-Tropsch synthesisnCO + 2nH2 → -(CH2)n- + nH2Ocoalbiomassnatural gasCommercially in operation inSouth Africa and MalaysiafuelsgaschemicalsGTL Bintulu (Malaysia)General scheme - ObjectiveThermochemistryMicrokineticmodel for Fe and CoReactionnetwork3ValidationSingle-Event MicroKinetics• Microkinetic model accounts for the rate of everyelementary step → detailed selectivities→ potentialtool to design more performing catalysts• Single-Event MicroKinetics (SEMK) consist of extracting the symmetry factors from the entropiccontribution• Unique single-event rate coefficient for eachreaction family=/,,globrglobσσ)exp()~exp( ,0,0 TRHRSThkk B =/=/ Δ−Δ=( )RTEAk a−= exp~~4General schemeThermochemistrySingle-Event MicroKineticmodelReactionnetwork5ValidationMMOMMMCMMMCOMMCOMCOMHMH+↔+↔+↔+32222MOHMHMOHMMOHMHMMO222 +↔++↔+MMCHMHMMCHMMMCHMHMMMCHMMMMCHMHMMMC22322+↔++↔++↔+Chain initiation6Reaction networkChemisorption/dissociationFormation building blocksFormation of waterChain growth and terminationM MMMMMMMMMCHMHMMCHMMMCHMHMMMCHMMMMCHMHMMMC22322+↔++↔++↔+Chain initiation7Reaction networkChemisorption/dissociationFormation building blocksFormation of waterMethylene insertion/de-insertionChain growth and terminationM MMMMMMMMMOMMMCMMMCOMMCOMCOMHMH+↔+↔+↔+32222MOHMHMOHMMOHMHMMO222 +↔++↔+MMCHMHMMCHMMMCHMHMMMCHMMMMCHMHMMMC22322+↔++↔++↔+Chain initiation8Reaction networkChemisorption/dissociationFormation building blocksFormation of waterReductive elimination/oxidative additionChain growth and terminationM MMMMMMMMMOMMMCMMMCOMMCOMCOMHMH+↔+↔+↔+32222MOHMHMOHMMOHMHMMO222 +↔++↔+MMCHMHMMCHMMMCHMHMMMCHMMMMCHMHMMMC22322+↔++↔++↔+Chain initiation9Reaction networkChemisorption/dissociationFormation building blocksFormation of waterβ-hydride elimination/additionChain growth and terminationM MMMMMMMMMOMMMCMMMCOMMCOMCOMHMH+↔+↔+↔+32222MOHMHMOHMMOHMHMMO222 +↔++↔+MMCHMHMMCHMMMCHMHMMMCHMMMMCHMHMMMC22322+↔++↔++↔+Chain initiation10Reaction networkChemisorption/dissociationFormation building blocksFormation of waterAlkene desorption/chemisorptionChain growth and terminationM MMMMMMMMMOMMMCMMMCOMMCOMCOMHMH+↔+↔+↔+32222MOHMHMOHMMOHMHMMO222 +↔++↔+• Numerical representation of molecules:– Boolean matrices– Standardized labels⎥⎥⎦⎤⎢⎢⎣⎡282828282828262825111233311373039010752810157194alkenes14752334208412922361318number elem. stepsalkanesalkylsMax. C atomM123456789 000010000C000001000C000100000C001010000C100101000C010010100C000001011C000000100C000000100M 987654321987654321Reaction network(chemical transformation)(storage)11General schemeThermochemistrySingle-Event MicroKineticmodelReactionnetwork12Validation• Probability of finding occupied/unoccupied neighbour surface atoms• Single-event kinetic coefficient:• Thermodynamic consistency guaranteed by pple microscopic reversibilityModel equations( ) iiniCOi RFWddx =,0=iRGas-phase compoundsSurface intermediatesrek~oak~totalkylstotliMMMlalkanealkanesoarni MHMalkylMalkylsMrerlalkaneCCCpkzCCCkzR,,1,,~21~21≠=−−−≠−= ∑ →σσσσCH2MCH3MH CH3 CH3M M+( )RSAA rforrev 0~exp~~ Δ= 0,, rforareva HEE Δ−=( )RTEAk a−= exp~~13Pre-exponential factors• Entropy change associated to the chemisorption step proportionalto the loss of translational entropy• Single pre-exponential factors per reaction family• Fixed kinetic parameters in the model⎟⎟⎠⎞⎜⎜⎝⎛ Δ=≠RShTkA Bfor,0~exp~ ∑=≠ υ−=ΔnreactiiiTS SSS100,0 ~~~( )RSAA rforrev 0~exp~~ Δ= ∑∑==υ−υ=Δnreactjjjnprodiiir SSS10100 ~~~Benson GAV stable molecules and radicals00,/0/~~~chemgasTSiTSi SSS Δ+=14Thermochemistry• Calculated by phenomenological method (UBI/QEP)• Adjustable parameters: ∑∑==υ−υ+Δ=Δnprodjjjnreactiiigasrsurfr QQHH110,0,ABAAAB DQQQ += (“strong” chem. enthalpy)( ),..,, OHCA QQQQ =A (g)+B (g)BAQQ +A (s)+B (s)AB (g)enthalpyreaction coordinateABQAB (s)++ ABA B A BA B0,surfrHΔ0,gasrHΔ0,surfrHΔShustorovich et al., Surface Science Reports 31 (1998) 0,gasrHΔAQ BQ ABQGeneral schemeThermochemistrySingle-Event MicroKineticmodelValidationReactionnetwork16Validation on Fe and Co• Water-Gas Shift (iron oxide phase, formate mechanism, 6 additionalelementary reactions)• Range of experimental conditions:• Adjustable parameters:– QC,QH,QO on iron carbide phase (3)– QH on iron oxide phase (1)– Ea,for of kinetically relevant reactionfamilies (10)6-21ptot (bar)90Nobs2-6523-623H2/COT (K)Lox, Ph.D. Thesis, Ghent University (1987) 17Lozano-Blanco et al., OGST – Rev. IFP, Vol. 61 (2006), No. 4  • Primary-alcohols (CO insertion mechanism, 3 additional elementary reactions)• Range of experimental conditions:• Adjustable parameters:– QC,QH,QO on cobalt metallic phase (3)– Ea,for of kinetically relevant reaction families (12)20ptot (bar)22Nobs1.6-2493H2/COT (K)Fiore et al., Studies in Surf. Sci. and Cat. (2004)Iron CobaltCoFe243.3±3.2249.2±0.6-M – H553.7±6.0578.8±0.9-M – O611.2±2.7639.5±2.1-M – C91.6±24.386.2±0.62.4 1011107.0±6.6103.8±1.01.3 101271.9±3.161.9±0.52.3 101112.2±2.011.9±0.15.7 101174.3±10.377.7±0.78.8 101452.8±6.256.8±0.51.3 10130.00.02.2 1070.00.03.1 108(bar-1s-1 or s-1)Reaction family/elem. reactionMHMH 222 ↔+MMCOMCO ↔+ 2MMOMMMCMMMCO +↔+ 3MMMMCHMHMMMC +↔+MMMCHMHMMMCH 22 +↔+MMCHMHMMCH 232 +↔+MMOHMHMMO 2+↔+MOHMHMOH 22 +↔+forA~ (kJ/mol)  QE fora /,Parameter estimation18http://www.tw12.ugent.be/ 19CoFe--1.3 101386.1±1.496.3±0.51.1 1010103.6±2.0117.8±0.72.1 101043.5±2.044.8±0.48.9 109(bar-1s-1 or s-1)Reaction family/elem. reactionforA~ (kJ/mol)  QE fora /,Parameter estimationMHMCMMCHHMCnnnn2321212+↔++++MHCMHHMC nnnn 22212 +↔+ ++MHHMCMHMC nnnn +↔++ 212MHCHMC nnnn +↔ 22• Significant changes only in atomic chemisorption enthalpies andin elementary steps determining the product distribution (catalyst dependent parameters)T=553K;ptot=21bar;H2/CO=3■ H2 CO▲ H2OUCO2● CH4T=523K;ptot=21bar;H2/CO=3T=623K;ptot=21bar;H2/CO=3 T=573K;ptot=11bar;H2/CO=320Model validation on Fe00.40.81.21.60 20 40W/FCO ini (kgcat s/mol)yi (mol i/mol CO ini)00.40.81.20 20 40 60 80W/FCO ini (kgcat s/mol)yi (mol i/mol CO ini)00.20.40.60.810 20 40W/FCO ini (kgcat s/mol)yi (mol i/mol CO ini)00.20.40.60.80 20 40 60W/FCO ini (kgcat s/mol)yi (mol i/mol CO ini)http://www.tw12.ugent.be/ 21Model validation on Fe and CoT=573K;PT=11bar;H2/CO=3 T=523K;PT=21bar;H2/CO=3T=493K;PT=20bar;H2/CO=1.6;W/FCOini=48skg/molFeT=623K;PT=21bar;H2/CO=3Co0.0010.010.110 2 4 6 8Carbon numbery (mol i/mol HCs)0.00010.0110 2 4 6 8Carbon numbery (mol i/mol HCs)0.00010.0110 2 4 6 8Carbon numbery (mol i/mol HCs)0.00010.0110 2 4 6 8Carbon numbery (mol i/mol HCs)W/FCOini=24skg/mol W/FCOini=81skg/mol 0.0010.010.110 2 4 6 8Carbon numbery (mol i/mol HCs)0.0010.010.110 2 4 6 8Carbon numbery (mol i/mol HCs)W/FCOini=48skg/molalkanes alkanes alkanesalkenes alkenes alkenes0.00010.0010.010.10 2 4 6 8Carbon numbery (mol i/mol CO ini)0.00010.0010.010.10 2 4 6 8Carbon numbery (mol i/mol CO ini)0.000010.00010.0010.010.10 2 4 6 8Carbon numbery (mol i/mol CO ini)alkenesalkanes alcohols0.40.50.60.70.80.9500 550 600 650Temperature (K)yCH4 (mol/mol HCs)00.250.50.751500 550 600 650Temperature (K)α (n=5)• Chain growth probability:• At higher temperatures more hydrogenated products and lower molecular mass hydrocarbonsGeneral trends (Fe)H2/CO=3 H2/CO=6 ptot = 11 bar ; W/FCOini = 43-48 skg/molH2/CO=3 H2/CO=6 ntermnpropnpropn rrr,,,+=α22http://www.tw12.ugent.be/ 23Secondary reactions (Co) • Methanol addition– No effect on product distribution0.00010.0010.010.10 2 4 6 8Carbon numberYi (mol i/mol CO ini)0.00010.0010.010.10 2 4 6 8Carbon number1E-050.00010.0010.010.10 2 4 6 8Carbon numberalkanes alkenes alcoholsT=493K ; ptot=20bar ; H2/CO=2 ; W/FCOini=48skg/molhttp://www.tw12.ugent.be/ 24Secondary reactions (Co) • 1-octene addition– Increases selectivities towards n-octane and 1-nonanol0.00010.0010.010.10 2 4 6 8Carbon numberYi (mol i/mol CO ini)0.00010.0010.010.10 2 4 6 8Carbon number1E-050.00010.0010.010.10 2 4 6 8Carbon numberalkanes alkenes alcoholsT=493K ; ptot=20bar ; H2/CO=1.6 ; W/FCOini=48skg/molhttp://www.tw12.ugent.be/ 25Conclusions• A single model is able to describe product distributions onFe and Co catalysts with physically meaningful parameter values• Single-event concept (entropy differences) allows todescribe the typical deviations observed at lower carbon atoms• 3 activation energies show strong catalyst dependency• Relations between these activation energies and catalystproperties should be further investigatedhttp://www.tw12.ugent.be/ 26Acknowledgements• Financial support: Institut Français duPétrole (IFP) and IAP program funded by the Belgian Science Policy• PoliMi and EniTecnologieWater-Gas Shift• Formate mechanism Rethwisch and Dumesic, J. Catal., 101, 35-42 (1986) 27http://www.tw12.ugent.be/ 28Surface speciesFeCo00.20.40.60 20 40W/FCOini(skgcat/mol)θ (−)1.E-081.E-061.E-041.E-021.E+000 20 40W/FCOini(skgcat/mol)θ (−)00.20.40.60 20 40W/FCOini(skgcat/mol)θ (−)00.0020.0040.0060.0080.010 20 40W/FCOini(skgcat/mol)θ (−)θMOHθMMOθMHθM-alkylsθM θM-alkenesθMMCOθMMCH2θMMCOθMHθMθMMOθMOHθM-alkyls θM-alkenes

Microkinetic analysis of Fischer-Tropsch synthesis on Fe and Co catalysts

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Microkinetic analysis of Fischer-Tropsch synthesis on Fe and Co catalysts

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