elementary step based assessment of ethylene ......faculty of engineering and architecture...
TRANSCRIPT
-
FACULTY OF ENGINEERING ANDARCHITECTURE
Elementary Step Based Assessment of Ethylene Oligomerization Kinetics and Corresponding Catalyst Optimization
ARCHITECTURE
and Corresponding Catalyst OptimizationK. Toch, J.W. Thybaut and G.B. MarinK. Toch, J.W. Thybaut and G.B. Marin
Universiteit Gent, Laboratory for Chemical TechnologyKrijgslaan 281 (S5), 9000 Ghent, Belgium
Single-Event MicroKinetic (SEMK) ModellingIntroduction and Objective
http://www.lct.UGent.be E-mail: [email protected] 281 (S5), 9000 Ghent, Belgium
Valorization of natural gas by SEMK-concept:
Single-Event MicroKinetic (SEMK) ModellingIntroduction and Objective
Valorization of natural gas by
Oxidative Coupling of Methane
followed by Oligomerization of
SEMK-concept:
� classification of elementary steps into reaction families
(energetic/enthalpic considerations)followed by Oligomerization of
Liquids[1] (OCMOL FP7 Integrated
Project)
(energetic/enthalpic considerations)
� accounting for symmetry effects (entropic consideration)
Project)
Model Based Catalyst Design[2] for
ethylene oligomerization (thisethylene oligomerization (this
PhD project)number of single-events ne activation energy for a single-event reaction familyExperimental Study number of single-events ne
≈> symmetry effectpre-exponential factor
≈> entropic losses during transition state formation
activation energy for a single-event reaction familyExperimental Study
16
181.8 wt% Ni-SiO2-Al2O3
10
12
14
16
Co
nv
ers
ion
(%
)
443 K
463 K
493 K
503 K
1.8 wt% Ni-SiO2-Al2O3� weak acidity (absence of
acid catalyzed reactions) k
k
4
6
8
10
Co
nv
ers
ion
(%
)
503 Kacid catalyzed reactions)
� ASF behavior on Ni
Operating conditions:
kINS(C4) Ni
+ Ni
+
Ni+
kINS(C6) Ni+
0
2
4
0 2 4 6 8 10 12
Co
nv
ers
ion
(%
)
Operating conditions:
T (K) 443 – 503
p (MPa) 1.5 – 3.5
esINS
esCINS kk =)( 4
esINS
esCINS kk 3)( 6 =
Model parameters:18
0 2 4 6 8 10 12
Space time (kgcat s molC2-1)
p (MPa) 1.5 – 3.5
τ (kgcat s moleth-1) 4.0 – 12.0
x 0 (mol mol-1) 0.1 – 0.3
INSCINS kk =)( 4 INSCINS kk 3)( 6 =
Model parameters:
� pre-exponential factors calculated based on statistical thermodynamics
� activation energies/reaction enthalpies: determined by regression1214
16
18
Co
nv
ers
ion
(%
)
1.5 MPa
2.5 MPa
xeth0 (mol mol-1) 0.1 – 0.3
� activation energies/reaction enthalpies: determined by regression
� catalyst descriptors: catalyst properties via e.g. physisorption and
chemisorption enthalpies, metal-ion site concentration …68
10
12
Co
nv
ers
ion
(%
)
3.5 MPa
chemisorption enthalpies, metal-ion site concentration …
� kinetic descriptors: reaction family properties via e.g. pre-
exponential factors and activation energies0
2
4
6
Co
nv
ers
ion
(%
)
18
Reaction network:
initiation (INI), chemisorption of ethylene (CHEM), insertion (INS) and
0
0 2 4 6 8 10 12
Space time (kgcat s molC2-1)
12
14
16
18� initiation (INI), chemisorption of ethylene (CHEM), insertion (INS) and
termination (TER) and (de-)protonation
� limited up to C olefins (experimentally validated)
6
8
10
12
Yie
ld (
%)
Butene
Hexene
� limited up to C8 olefins (experimentally validated)
� considerations:
1. quasi-equilibrated initiation and (de-)protonation
0
2
4
6
Yie
ld (
%)
1. quasi-equilibrated initiation and (de-)protonation
2. chemisorbed olefins on Ni-sites are in pseudo-stationary state
3. irreversible insertion of ethylene in a Ni-alkene complex and 00 5 10 15 20 25
Conversion (%)
3. irreversible insertion of ethylene in a Ni-alkene complex and
termination
Parameter Estimation and Model Performance
kINS(C4) Ni
+ Ni
+ Ni
+ Ni
+ Ni
+
KINI KCHEM,C2 KCHEM,C2
Estimated parameters Values (kJ mol-1)
ΔHPHYS(C2) -8.9 ± 0.2
kTER(C4)
kINS(C6) 120
140
ΔHPHYS(C2) -8.9 ± 0.2
ΔΔHPHYS(2C) -12.3 ± 0.4
ΔHCHEM,C2 -49.5 ± 0.7
kINS(C6)
… KCHEM,C2
80
100
120
-6m
ol s-
1)
ΔHCHEM,C2 -49.5 ± 0.7
Ea,INS 89.2 ± 0.5
E 83.2 ± 0.5
Ni+
… KCHEM,C2
20
40
60
F C2
,sim
(10
-
Conclusions and Future Work
Ea,TER 83.2 ± 0.5
F-value (significancy): 1.0 105 (Ftab: 3.20)
F-value (adequacy): 0.79 (F : 2.55)
0
20
0 20 40 60 80 100 120 140
8
0.8
1� Ni-SiO2-Al2O3 allowed to investigate metal-ion oligomerization kinetics in
detail
F-value (adequacy): 0.79 (Ftab: 2.55) FC2,exp ( 10-6 mol s-1)
4
6
(10
-6m
ol s-
1)
0.6
0.8
(10
-6m
ol s-
1)
detail
� typical ASF product distribution was obtained, indicated by the
operating conditions independency of product selectivities
2
4
FC
4,s
im(1
0
0.2
0.4
FC
6,s
im(1
0 operating conditions independency of product selectivities
� metal-ion oligomerization kinetic described using SEMK
� tuning of catalyst behavior will be possible through the acid catalysis on0
0 2 4 6 8
F ( 10-6 mol s-1)
0
0 0.2 0.4 0.6 0.8 1
F ( 10-6 mol s-1)
� tuning of catalyst behavior will be possible through the acid catalysis on
a dedicated support
FC4,exp ( 10-6 mol s-1) FC6,exp ( 10
-6 mol s-1)
� linear relationship between product yields and ethylene conversion
� product selectivities independent of operating conditions
[1] http://www.ocmol.eu
[2] J.W. Thybaut, I.R. Choudhury, J.F. Denayer, G.V. Baron, P.A. Jacobs, J.A. Martens and G.B. Marin, Top.
Catal. (52) 1251 - 1260
This presentation reports work undertaken in the context of the project “OCMOL, Oxidative Coupling of Methane followed by Oligomerization to Liquids”. OCMOL is a Large Scale Collaborative Project supported
� product selectivities independent of operating conditions Catal. (52) 1251 - 1260
This presentation reports work undertaken in the context of the project “OCMOL, Oxidative Coupling of Methane followed by Oligomerization to Liquids”. OCMOL is a Large Scale Collaborative Project supported
by the European Commission in the 7th Framework Programme (GA n°228953). For further information about OCMOL see: http://www.ocmol.eu or http://www.ocmol.com.