elementary step based assessment of ethylene ......faculty of engineering and architecture...

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: Kenneth.Toch@UGent.beKrijgslaan 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.