FACULTY OF ENGINEERING ANDARCHITECTURE

Ethylene Oligomerization on Bifunctional Heterogeneous Catalysts:Model Development and Catalyst Optimization

ARCHITECTURE

Model Development and Catalyst OptimizationK. Toch, J.W. Thybaut and G.B. Marin E-mail: Kenneth.Toch@UGent.beK. Toch, J.W. Thybaut and G.B. Marin

Universiteit Gent, Laboratory for Chemical Technology Krijgslaan 281 (S5), 9000 Ghent, Belgium - http://www.lct.UGent.be

E-mail: Kenneth.Toch@UGent.be

Introduction and Objective Experimental Study Modelling Approach: SEMK

� Valorization of natural gas and biogas by Oxidative

Coupling of Methane, followed by Oligomerization to

Introduction and Objective Experimental Study Modelling Approach: SEMK

1.8wt% Ni-SiO2-Al2O3absence of acid catalysis

Single-Event MicroKinetics:� classification of elementary steps into reaction families Coupling of Methane, followed by Oligomerization to

Liquids (OCMOL)[1]

� Detailed mechanistic

absence of acid catalysis

→ determination of metal-ion kinetics

� classification of elementary steps into reaction families

(energetic/enthalpic considerations)

� accounting for symmetry effects (entropic consideration)� Detailed mechanistic

insights lead to an ‘in-

silico’ optimization of

both the catalyst and

4.89wt% Ni-Beta

both metal-ion as acid catalysis

� accounting for symmetry effects (entropic consideration)

� pre-exponential factors calculated based on statistical

thermodynamicsboth the catalyst and

process conditions

applied (Model Based

both metal-ion as acid catalysis

→ determination of acid kinetics

Operating conditions:

� activation energies/reaction enthalpies: determined by

regression

� catalyst descriptors: catalyst propertiesapplied (Model Based

Catalyst Design)[2] Operating conditions:

T: 443 – 523 K | p0C2: 1.0 – 3.5 Mpa | Wcat/F0: 4.0 – 15.0

intrinsic kinetics regime (absence of transport limitations)

� catalyst descriptors: catalyst properties

� kinetic descriptors: reaction family propertiesintrinsic kinetics regime (absence of transport limitations)

Metal-ion kinetics determination Acid kinetics determination

� 1.8wt% Ni-SiO2-Al2O3 is highly selective

towards dimerization (83-86%)

→mainly production butenesC2H4

C HC2H4C2H4 C4H8C2H4

met

al-io

n ac

tivity

�4.89wt% Ni-Beta is highly selective towards

dimerization (>80%)

→mainly production butenes→mainly production butenes

→ maximum up to C8 detected→ no odd carbon numbered components

Ni+

Ni+ Ni

+

Ni+

C2H4C2H4

C2H4C2H4C4H8

Ni+

C4H8

...

C2H4

met

al-io

n ac

tivity

insertion

chemisorptionchemisorptioninitiation

→mainly production butenes

→ maximum up to C8 detected→ lower activity (≈60%) than 1.8wt% Ni-→ no odd carbon numbered components

� Product selectivities independent of operating

conditions18

Ni NiC2H4 C2H4

met

al-io

n ac

tivity

termination

→ lower activity (≈60%) than 1.8wt% Ni-SiO2-Al2O3

but:

→ formation of odd carbon numbered

12

14

16

18

C4H8C4H8

C4H8C8H16 H

+

C8H16

acid

act

ivity

→ formation of odd carbon numbered components (C3 and C5)

� Alkylation of C4 to C8, with consecutive

6

8

10

12

Yie

ld (

%)

Butene

Hexene

H+

H+

C4H8

H+

C8H16 H

alkylation, isomerization ...

acid

act

ivity

alkylation / beta-scission

(de-)protonation

(de-)protonation� Alkylation of C4 to C8, with consecutive

cracking to C3 and C5 components

→ selectivity towards C3 and C5: 0.5–2.0%

18

20

22

0

2

4

6

14

16

2

2.5

10

12

14

16

18

Co

nv

ers

ion

(%

)

0

0 5 10 15 20 25

Conversion (%)10

12

calc

ula

ted

(%

)

1.5

2

calc

ula

ted

(%

)

4

6

8

10

Co

nv

ers

ion

(%

)

� Insertion/termination mechanism inspired by

homogeneous polymerization kinetics6

8

XC

2-

calc

ula

ted

(%

)

0.5

1S

cr-

calc

ula

ted

(%

)

0

2

0 5 10 15

W/F° (kgcat s molC2-1)

� Parameters estimates by regression to 51 exp.

data points

→ significant parameter estimates

4

6

4 6 8 10 12 14 16

XC2 - experimental (%)

0

0 0.5 1 1.5 2 2.5

Scr - experimental (%)W/F° (kgcat s molC2 )

p0C2 = 3.5 MPa | �: 443 K, �: 473 K, �: 493 K

→ significant parameter estimates→ adequate model predictions

Catalyst descriptors ΔHphys(C2) ΔΔHphys(2C) ΔHchem(C2) Kinetic descriptors Ea,ins Ea,ter Catalyst descriptors ΔHphys(C2) ΔΔHphys(2C) ΔHchem(C2) ΔHpr Kinetic descriptors Ea,alk

XC2 - experimental (%) Scr - experimental (%)

Catalyst descriptors ΔHphys(C2) ΔΔHphys(2C) ΔHchem(C2) Kinetic descriptors Ea,ins Ea,ter

Est. value (kJ mol-1) -7.2 ± 0.2 -12.3 ± 0.4 -49.9 ± 0.6 Est. value (kJ mol-1) 76.3 ± 0.6 67.8 ± 0.6

Catalyst descriptors ΔHphys(C2) ΔΔHphys(2C) ΔHchem(C2) ΔHpr Kinetic descriptors Ea,alk

Est. value (kJ mol-1) -4.9 ± 1.7 -9.9 ± 2.6 -39.3 ± 0.7 -46.6 ± 18.9 Est. value (kJ mol-1) 65.1 ± 22.5

phys: physisorption, chem: chemisorption, ins: insertion, ter: termination phys: physisorption, chem: chemisorptio, pr: protonation, alk: alkylation

‘In Silico’ Catalyst Development‘In Silico’ Catalyst Development

� The SEMK model for ethylene oligomerization, including the kinetic 2.5

5.00

� The SEMK model for ethylene oligomerization, including the kinetic

descriptors, as ‘engine’ of the catalyst development tool

�Adjustable parameters:

→ catalyst descriptors, c.q., catalyst properties

2

Se

lect

ivit

y (

%)

Gasoline

Propylene3.00

4.00

Se

lect

ivit

y (

%)

Gasoline

Propylene

→ catalyst descriptors, c.q., catalyst properties→ reaction conditions

�Objective function defined on economic relevant base1

1.5

Se

lect

ivit

y (

%)

2.00

3.00

Se

lect

ivit

y (

%)

�Objective function defined on economic relevant base

e.g., maximization of the yield of gasoline or propylene0.5

1

Se

lect

ivit

y (

%)

1.00

Se

lect

ivit

y (

%)

0

423 473 523 573 623 673 723 773

Temperature (K)

0.00

10 30 50 70 90

ΔHpr (kJ mol-1)

�Low temperature: only metal-ion catalyzed reactions

Temperature (K)

Ni-Beta studied, p0C2 = 3.5 MPa, Wcat/F0 = 1.0 kgcat s molC2

-1

pr

modified Ni-Beta, T = 573 K, p0C2 = 3.5 MPa, Wcat/F0 = 1.0 kgcat s molC2

-1

however:

� Simultaneous determination of catalyst properties and

Future WorkConclusions

�Low temperature: only metal-ion catalyzed reactions

� High temperature: increasing importance of cracking

� Simultaneous determination of catalyst properties and

reaction conditions is a difficult optimization problem

� Expand the experimental dataset on the Ni-Beta

Future WorkConclusions

� Ni-SiO2-Al2O3 and Ni-Beta allowed to investigate resp. the metal-ion and acid catalyzed � Expand the experimental dataset on the Ni-Beta

→ increased insight in the effect of the reaction conditions on the catalyst’s activity→ input for the kinetic model

� Ni-SiO2-Al2O3 and Ni-Beta allowed to investigate resp. the metal-ion and acid catalyzed

oligomerization kinetics in detail

� Ni-SiO2-Al2O3 studied is more active than Ni-Beta

� Expand and refine the kinetic model

→ more significant determination of catalyst and kinetic descriptors

� Use the refined kinetic model as ‘engine’ for the catalyst development tool

� Ni-SiO2-Al2O3 studied is more active than Ni-Beta

→ lower chemisorption enthalpy of ethylene → lower physisorption enthalpies of the olefins

� Catalyst descriptors were determined significant

[1] http://www.ocmol.eu

� Use the refined kinetic model as ‘engine’ for the catalyst development tool

→ determine a full set of optimal catalyst properties and reaction conditions for different, economic relevant, objective functions, e.g., maximized gasoline yield

� Catalyst descriptors were determined significant

� Optimal reaction conditions and catalyst properties determination using the tool is possible

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

[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

different, economic relevant, objective functions, e.g., maximized gasoline yield

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.