Microkinetic Modeling of Bioalcohol Dehydration in H-FAU, H-MOR, H-ZSM-5 and H-ZSM-22
Zeolites
Methusalem, Advisory Board Meeting, June 24, 2013
1http://www.lct.ugent.be
LaboratoryLaboratoryLaboratoryLaboratory forforforfor
Chemical Chemical Chemical Chemical TechnologyTechnologyTechnologyTechnology
C.M. Nguyen, K. Alexopoulos, M.-F. Reyniers, G.B. Marin
Methusalem, Advisory Board Meeting, June 24, 2013
2
Overview
• Introduction
• Alcohol adsorption
• Alcohol dehydration
• Conclusions
Methusalem, Advisory Board Meeting, June 24, 2013
3
Bioalcohols to hydrocarbons as a green route
van der Borght et al.,i–SUP, Bruges, Belgium, May 6, 2012.
Methusalem, Advisory Board Meeting, June 24, 2013
4
Different temperatures = different product distributions
Ethanol
dehydration
Taarning et al.,Energy Environ. Sci., 4 (2011) 793
H-ZSM-5
Methusalem, Advisory Board Meeting, June 24, 2013
5
Different zeolites = different product distributions
H-SAPO-34
MTO
H-ZSM-5
MTG
H-FER
Olefins
Gasoline
Haw et al., Acc. Chem. Res. 36 (2003) 317
Methusalem, Advisory Board Meeting, June 24, 2013
6
Zeolite Models: 1 acid site per unit cell
12-MR
12-MR
H-F
AU
H-M
OR
H-Z
SM
-22
H-Z
SM
-5
10-MR 10-MR
Si/Al = 47 Si/Al = 95
Si/Al = 95 Si/Al = 35
Methusalem, Advisory Board Meeting, June 24, 2013
7
Process optimization utilizes microkinetic modeling
Marin and Yablonsky, Kinetics of Chemical Reactions: Decoding Complexity, Wiley-VCH, 2011
Methusalem, Advisory Board Meeting, June 24, 2013
8
C1-C4 alcohol adsorption thermodynamics
Nguyen et al., Europacat X, Glasgow, August 28, 2011
Methusalem, Advisory Board Meeting, June 24, 2013
9
Nature of ROH-ZeOH complexes
PHYSISORPTION PHYSISORPTIONCHEMISORPTION
�Nature of ROH-ZeOH has remained unclear fromexp. data [1&2].�Molecular dynamics (MD) simulations for CH3OH-Zeolite [3]:
�Hzeolite strongly fluctuates midway between BAS and CH3OH.�Chemisorbed fraction increases with decreasing zeolite pore size.
[1] Mirth et al. J. Chem. Soc. Faraday Trans. 86, 3039 (1990). [2]Zamaraev andThomas, Advanced inCatalysis 41, 335 (1996). [3]Payneet al.J. Am. Chem. Soc. 121, 3292 (1999).
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250 300
Ra
dia
l d
istr
ibu
tio
n
fun
ctio
n,
g(r
)
distance, r (pm)
O-H1
O-H2
Methusalem, Advisory Board Meeting, June 24, 2013
10
Ab initio MD simulation: NVT, 500K
H1H2O
50
100
150
200
250
1 2 3 4 5 6
O-H
dis
tan
ce (
pm
)
time (ps)
O-H1
O-H2
0.5
1
1.5
2
2.5
2000 2500 3000 3500
ab
sorb
an
ce (
a.u
.)
frequency (cm-1)
Methusalem, Advisory Board Meeting, June 24, 2013
11
IR spectrum
Chem.
Phys.
ν(O-H) / ZeOH
ν(C-H)
ν(O-H)
Bonn et al. Chem. Phys. Letts. 278 (1997) 213 Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481
-0.1
-0.05
0
0.05
0.1
3100 3300 3500 3700
ΔA
bso
rba
nce
(a
.u.)
frequency (cm-1)
Methusalem, Advisory Board Meeting, June 24, 2013
12
Rotation along O…H bond
ν(O-H)
ν(O-H)
Bonn et al. Chem. Phys. Letts. 1997 (278) 213
Methusalem, Advisory Board Meeting, June 24, 2013
13
Eads: theory vs experiment
experimenttheory
H-ZSM-5
Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481 Lee et al. J. Phys. Chem. B 101 (1997) 381
Methusalem, Advisory Board Meeting, June 24, 2013
14
Influence of carbon number
Nguyen et al. Phys. Chem. Chem. Phys. 12, 9481 (2010)
∆H0ads = αNC + β
α = -12 kJ mol-1 per C
-160
-140
-120
-100
1 2 3 4
∆E
ads
/ kJ
mol
-1
Carbon number
β = -100 kJ mol-1 per C
Phys. (H-ZSM-5, Straight)
Chem. (H-ZSM-5, Straight)
Methusalem, Advisory Board Meeting, June 24, 2013
15
Influence of zeolite topology
-180
-155
-130
-105
-80
1 2 3 4
ΔH
0a
ds/
kJ
mo
l-1
Carbon number
H-FAU
H-MOR (12-MR)
H-ZSM-5 (Straight)
H-ZSM-5 (Zigzag)
H-ZSM-22
Methusalem, Advisory Board Meeting, June 24, 2013
16
Influence of branching level
Nguyenet al. J. Phys. Chem. C 115 (2011) 8658.
1-BuOH i-BuOH
2-BuOH t-BuOH
Methusalem, Advisory Board Meeting, June 24, 2013
17
Zeolite-catalyzed alcohol conversion to fuels and chemicals
Alcohols
Ethers
Olefins
Aromatics
ValidationGoal: Simulate the influence
of reaction conditions and zeolite framework on product distribution
H-FAU H-ZSM-5
H-MOR H-ZSM-22
Method:
T, P, W/F, %H2OReactor
simulation
Reaction network
Thermo-dynamics
Methusalem, Advisory Board Meeting, June 24, 2013
18
Ab-initio based microkinetic modeling
Validation
Reactor simulation
Reaction network
Thermo-dynamics
Methusalem, Advisory Board Meeting, June 24, 2013
19
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
Methusalem, Advisory Board Meeting, June 24, 2013
20
Desorption profile of adsorbed ethanol in H-MOR
Kondo et al. J. Phys. Chem. C 114 (2010) 20107
H-MORStatic IR cell reactorNo DEE is observed
Methusalem, Advisory Board Meeting, June 24, 2013
21
Ethanol dehydration in a flow reactor at 368 – 398 K
[1] Chiang & Bhan, J. Catal. 271(2010) 251
12-MR
Turn
over
freq
uenc
yDifferential flow reactor
0.05 bar ethanol
Ethene is observed only in 8-MR side pocket of H-MOR [1].8-MR side pockets prevent formation of bulky ethanol dimers [1].
M 1
AlO O
H
AlO O
HO
H
M 2
AlO O
H
OH
AlO O
CH2H
AlO O
H
AlO O
H
OAl
O
H
OH5C2 H
O
H
C2H5
OAl
O
H
OH
O
H
C2H5
D1 D2
OAl
O
H5C2 O
H
C2H5
DEE*
Ethene*
(1)
(3)
(7)
(4)
(2)(5)
(6)
(8)
(9)
Ethoxide
+ H2O(g)
- H2O(g)
+ H2O(g)
- H2O(g)
+ C2H4(g)- C2H4(g)
+ DEE(g) - DEE(g)
+ C2H5OH(g)
- C2H5OH(g)
- C2H5OH(g)+ C2H5OH(g)
+ C2H4(g)
- C2H4(g)
OAl
O
H
O
H
C2H5
- C2
H 5OH (g
)
+ C 2
H 5O
H (g)
(11)
(12)
(10)
C1
Methusalem, Advisory Board Meeting, June 24, 2013
22
Reaction network of ethanol dehydration
Methusalem, Advisory Board Meeting, June 24, 2013
23
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
Methusalem, Advisory Board Meeting, June 24, 2013
24
Dispersion – corrected pbc[DFT-D]
( )∑ ∑=∈
−−
−=L Lji
ijD
ij
ji
D LrfLr
ccsE
0,6
666
2
DDFTDDFT EEE +=−
� VASP 4.6
� Plane wave basis set & Projector Augmented Wave method
� GGA PBE-D2 implementation for zeolites [1,2].
� Brillouin zone sampling restricted to the Γ point.
� Convergence criteria: Ecutoff = 600 eV, ∆ESCF = 10-6 eV,Max force = 0.02 eV/Å
� CI-NEB for transition state location [3]
� Statistical thermodynamics & PHVA – MBH [4][1] Grimme J. Comput. Chem. 27 (2006) 1787 [2] Kresse et al. J. Phys. Rev. B 48 (1993) 13115[3] Henkelman et al. J. Chem. Phys. 13 (2000) 9978 [4] De Moor et al. J. Chem. Theory Comput. 7 (2011) 1090
Methusalem, Advisory Board Meeting, June 24, 2013
25
Monomolecular pathway (300 K)
Methusalem, Advisory Board Meeting, June 24, 2013
26
Bimolecular pathway (300 K)
Methusalem, Advisory Board Meeting, June 24, 2013
27
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
(1) C2H5OH(g) + * ↔ M1
(2) M1 ↔ M2
(3) M2 ↔ Ethoxy + H2O(g)
(4) Ethoxy ↔ Ethene*
(5) Ethene* ↔ Ethene(g) + *
(6) M1 + C2H5OH(g) ↔ D1
(7) D1 ↔ D2
(8) D2 ↔ DEE* + H2O(g)
(9) DEE* ↔ DEE(g) + *
(10) DEE* ↔ C1
(11) C1 ↔ M1 + Ethene(g)
(12) C1 ↔ Ethene*+ C2H5OH(g)
Methusalem, Advisory Board Meeting, June 24, 2013
28
Reactor simulation
vib
B
B
B
B
qqwhere
Tk
E
q
q
h
Tk
Tk
G
h
Tkk
=
∆−=
∆−=
expexp‡0
‡‡
immobile surface species
where, F molar flow (mol/s),
W catalyst weight (kg) , Ct acid site concentration (mol H+/kg),
R turnover frequency, r reaction rate (molecules/site/s = mol/mol H+/s),
νji the stoichiometric coefficient of component i in the elementary step j
��∗ �����∗��
� 0
Plug flow reactor equations for each gas-phase
component i with QSSA for the surface species i*:
�� �� � ���� � �������
�
TST for reaction rate coefficients:
(apart from Ethene* where a 2D translation
and 1D rotation is assumed)
Methusalem, Advisory Board Meeting, June 24, 2013
29
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
Methusalem, Advisory Board Meeting, June 24, 2013
30
Experimental validation
0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X (%) S-DEE (%) S-C2H4 (%)
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Good agreement between theory (full lines) and experiment (points)
H-MOR
0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X (%) S-DEE (%) S-C2H4 (%)
Methusalem, Advisory Board Meeting, June 24, 2013
31
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Better agreement between theory (full lines) and experiment (points),
if the activation energy for ethoxy formation is slightly increased (+2 kJ/mol)
H-MOR
(3) M2 ↔ Ethoxy + H2O(g)
Methusalem, Advisory Board Meeting, June 24, 2013
32
Influence of reaction conditionsC2H4 yield (%)
450 460 470 480 490 500Temperature (K)
10
15
20
25
30
35
40
45
Eth
anol
pre
ssur
e (k
Pa)
0
2
4
6
8
10
12
14H-ZSM-5
More ethene at higher T and lower pEtOH
Methusalem, Advisory Board Meeting, June 24, 2013
33
Is DEE a primary product?
T= 495 K, H-ZSM-5
YES
0
5
10
15
20
25
30
0 1 2 3 4
Co
nv
ers
ion
(%
)
site time (mol H+ s / mol EtOH0 )
H-ZSM-22
H-ZSM-5
H-MOR
H-FAU
Methusalem, Advisory Board Meeting, June 24, 2013
34
Influence of zeolite topology
10-MR zeolites more reactive than 12-MR zeolites
10 kPa EtOH,
T= 473 K
Methusalem, Advisory Board Meeting, June 24, 2013
35
Factors governing zeolite reactivity
Ea,D1 AD1 kD1/368 KH–FAU 154 5.1 1013 6.3 10–9 H–MOR (12–MR) 161 1.2 1015 1.6 10–8 H–ZSM–5 136 6.2 1013 3.1 10–6 H–ZSM–22 122 1.1 1014 5.2 10–4
Ea,D1
D1
DEE*
TSII
Methusalem, Advisory Board Meeting, June 24, 2013
36
TS stabilization: Hydrogen bonds
Methusalem, Advisory Board Meeting, June 24, 2013
37
TS stabilization: Electrostatic interactions
H-FAU H-MOR
H-ZSM-5 H-ZSM-22
Ele
ctro
stat
ic p
oten
tial /
eV
Electrostatic: H-FAU < H-MOR < H-ZSM-5 < H-ZSM-22
Methusalem, Advisory Board Meeting, June 24, 2013
38
Stabilization factor, α
ΔΔΔΔEEEETSIITSIITSIITSII
TSII (H-FAU)
TSII (ZeOH)
D1 (H-FAU)
D1 (ZeOH)
ΔΔΔΔ((((ΔΔΔΔEEEEads,D1ads,D1ads,D1ads,D1))))
)( 1,Dads
TSII
E
E
∆∆∆=ααααα
H-FAU 0.0
H-MOR 0.4
H-ZSM-5 1.9
H-ZSM-22 3.1
E
H-FAU is the reference
Methusalem, Advisory Board Meeting, June 24, 2013
39
Conclusions
• First principles microkinetic modeling provides predictive
guidance for the influence of catalyst’s characteristics and reaction
conditions on reactivity and product selectivity.
• Alcohol adsorption strength increases with decreasing zeolite pore
size (indicative of primary driving vdW forces).
• Entropy-enthalpy compensation governs the shape-selectivity
effect of H-ZSM-5 on adsorption of butanol isomers.
• 10-MR zeolites are more reactive than 12-MR zeolites (more effectively stabilized TS by HB/Electrostatic interactions)
Methusalem, Advisory Board Meeting, June 24, 2013
40
• Long Term Structural Methusalem Funding by the
Flemish Government – grant number BOF09/01M00409
• European Community’s Sixth Framework Programme
(contract nr 011730)
• Fund for Scientific Research (FWO) – Flanders
• Stevin Supercomputer Infrastructure of Ghent University
• Experimental data (H-MOR): Kristof Van der Borght
• Ab initio MD: Roger Rousseau, Mal-Soon Lee
Acknowledgements
Methusalem, Advisory Board Meeting, June 24, 2013
41
Glossary
• Alcohol chemisorption: Upon chemisorption over the Brønsted acid site, the acid proton is completely transferred to the alcohol, leading to formation of a positively charged oxonium ion.
• Alcohol physisorption: An alcohol is physisorbed over the Brønsted acid site and is stabilized by strong hydrogen bonds with the zeolite. The acid proton is still attached to the zeolite.
• Electrostatic potential: evaluated from the interaction between a negative unit charge and the local charge density. This factor is critical in stabilizing positively charged adsorbed complexes and especially transition states in the zeolite.
Methusalem, Advisory Board Meeting, June 24, 2013
42
Zeolites are promising catalysts for biorefinery processes
Fluidic Catalytic Cracking & Hydrocracking are based on Zeolites
Huber andCorma, Angew. Chem. Int. Ed. 46 (2007) 7184.Taarning et al., Energy Environ. Scie. 4 (2011) 793.
Methusalem, Advisory Board Meeting, June 24, 2013
43
Influence of temperature
10 kPa EtOH, H-MOR
More ethene formation at higher T
0
5
10
15
20
0 2 4 6 8
Co
nv
ers
ion
(%
)
space time ( kg s / mol )
503 K
495 K
473 K
453 K0
20
40
60
80
100
0 2 4 6 8
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll li
ne
s) s
ele
ctiv
ity
(%
)
space time ( kg s / mol )
0
2
4
6
8
10
12
0 2 4 6 8 10 12
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll l
ine
s)
yie
ld (
%)
Conversion (%)
10 kPa EtOH 50 kPa EtOH
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll l
ine
s)
sele
ctiv
ity
(%
)
Conversion (%)
10 kPa EtOH 50 kPa EtOH
Methusalem, Advisory Board Meeting, June 24, 2013
44
Is DEE a primary product?
T= 495 K, H-MOR
YES
0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X-sim (%)
S-DEE-sim (%)
S-E-sim (%)
X-exp (%)
S-DEE-exp (%)
S-E-exp (%)
Methusalem, Advisory Board Meeting, June 24, 2013
45
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Good agreement between theoretical (full lines) and experimental
(points) conversion
H-ZSM-5
0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X-sim (%)
S-DEE-sim (%)
S-E-sim (%)
X-exp (%)
S-DEE-exp (%)
S-E-exp (%)
Methusalem, Advisory Board Meeting, June 24, 2013
46
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Better agreement between theory (full lines) and experiment (points)
by modifying the kinetics of reaction 10, i.e. k10-mod=10 k10, K10-mod=K10
H-ZSM-5
(10) DEE* ↔ C1
Methusalem, Advisory Board Meeting, June 24, 2013
47
Experimental results
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / molH-ZSM-5
Kristof van der Borght , personal communication
Methusalem, Advisory Board Meeting, June 24, 2013
48
Experimental results
Kristof van der Borght , personal communication
Ethanol
DEEEthylene
Higher hydrocarbons
Eff
lue
nt
com
po
siti
on
(%)