fundamental understanding of heterogeneously catalyzed ... › publication › 8537895 › file ›...
TRANSCRIPT
Laboratory for Chemical Technology, Ghent University
http://www.lct.UGent.be
Fundamental understanding of heterogeneously catalyzed reactions:
from hydrocarbon oxidation to bio-alcohol dehydration
K. Alexopoulos
1
UCCS visit, Lille, February 7, 2017
Heterogeneous Catalysis: a Multiscale process
2
UCCS visit, Lille, February 7, 2017
Reactive intermediates
in reaction mechanism
Spectroscopic
studies
Ultra high vacuum
0.01-1 kPa
Temporal Analysis
of Products
Sub millisecond time
resolution experiments for
insight into reaction
mechanism
Bench scale
micro-reactors Pilot plants Industrial reactor
Low-moderate pressure
5-30 kPa
Moderate-high pressure
500-3000 kPa
Reaction kinetics study for
obtaining reaction rate
coefficients
Demonstration
Commercial
scale production
In situ/Ab initio Techniques
3
UCCS visit, Lille, February 7, 2017
Ab initio operando or in situ
Metal-Support Interaction
Reaction mechanism
on site
during reactionQuantum Chemistry
Outline
• Hydrocarbon oxidation on metal oxides
• Bio-alcohol dehydration in zeolites
4
UCCS visit, Lille, February 7, 2017
Hydrocarbon oxidation
5
UCCS visit, Lille, February 7, 2017
CH3
CH3
+ 3O2
3H2O
C
O
C
O
O
+
Environmental application:
elimination of exhaust gases
Industrial application:
production of important chemicals
Total oxidation
Selective oxidation
CxHy + (x+y/4)O2 xCO2 + (y/2)H2O
Reaction mechanism on metal oxides
6
UCCS visit, Lille, February 7, 2017
After Haber and Witko, J. Catal., 216 (2003) 416
Hydrocarbon Oxygen Oxygen vacancy Metal
Mars-van Krevelen
RH + 2O2- ROOH + 4e
O2 + 4e 2O2-
catalyst reduction catalyst reoxidation
extracted from catalyst
injected in catalyst
Supported metal oxides
7
UCCS visit, Lille, February 7, 2017
Total oxidation Selective oxidation
Vanadium Titanium Oxygen Copper Cerium
V2O5/TiO2 CuO/CeO2
J.C. Conesa, Nanospain Conference, 2009 Alexopoulos et al., J. Phys. Chem. C, 2010
Operando measurements
8
UCCS visit, Lille, February 7, 2017
I0 I
sam
ple
x
Structure of the active
phase (e.g. coordination,
oxidation state)
H2O C3H8
CO2
O2
Conversion, selectivity
XANES at Cu K edge •-------• Mass spectrometry
𝐶3𝐻8+ 5𝑂2
𝐶𝑢𝑂−𝐶𝑒𝑂2/𝐴𝑙2𝑂3 3𝐶𝑂2+ 4𝐻2𝑂
< 1s
Experimental setup
9
UCCS visit, Lille, February 7, 2017
BEAM
Oven
Capillary made out of quartz
(ID = 0.9 mm, OD = 1.0 mm)
ID24 (in transmission)
ESRF
Cat. quartz quartz
10 mm
~5 mg cat. (particle size: 75-100 μm)
Fixed bed reactor
Gas flow
Oven with reactor
MFCs
Valves MS
Types of experiments
10
UCCS visit, Lille, February 7, 2017
Isothermal step response experiments on CuO-CeO2/Al2O3
Catalyst reduction and oxidation cycles:
He | 2%C3H8/He He | 10%O2/He
constant flow rate = 1.5 10-5 mol/s
Total oxidation reaction experiments:
He | (1%C3H8+ 5%O2)/He
space times = 38.3-127.7 kg s / mol
Catalyst reduction: Cu K XANES
11
UCCS visit, Lille, February 7, 2017
Catalyst reduction: a two step process is found
Time:
T = 723 K
Catalyst reduction: XANES & MS
12
UCCS visit, Lille, February 7, 2017
Mechanism of catalyst
reduction:
Cu2+ Cu1+ Cu0
No CO2 when the
catalyst is fully reduced
The analysis of XANES
agrees with the MS results
0
0.5
1
1.5
2
0 100 200 300 400 500 600 700
gas p
hase c
om
po
sit
ion
(%
)
time (sec)
C3H8
CO2
0
10
20
30
40
50
60
70
80
90
100
so
lid
ph
ase c
om
po
sit
ion
(%
)
Cu(0)
Cu(+1)
Cu(+2)
T = 723 K
Catalyst reoxidation: Cu K XANES
13
UCCS visit, Lille, February 7, 2017
Catalyst reduction is reversible with reoxidation
Time: T = 723 K
Catalyst redox cycles: effect of T
14
UCCS visit, Lille, February 7, 2017
T (K) 573 623 673 723
τred (s) 431 149 44 22
τox (s) 1.1 1.0 0.5 0.4
red
t
CueX
12ox
t
CueX
10
re-oxidation of catalyst occurs faster than its reduction at all T
both processes speed up with T
Catalyst reduction Catalyst re-oxidation
Catalyst redox cycles: effect of T
15
UCCS visit, Lille, February 7, 2017
Ea = 70.0 kJ/mol
Ea = 24.0 kJ/mol
Catalyst reduction Catalyst re-oxidation
Propane total oxidation: MS
16
UCCS visit, Lille, February 7, 2017
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0 25 50 75 100 125 150
pro
pa
ne
co
nve
rsio
n (
mo
l/m
ol)
space time (kg s/mol)
573 K
623 K
673 K
-8
-7
-6
-5
-4
1.4 1.5 1.6 1.7 1.8
ln(-
r C3
H8
,o)
1000/T (1/K)
Ea = 70.4 ± 11.8 kJ/mol
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0 25 50 75 100 125 150
pro
pa
ne
co
nve
rsio
n (
mo
l/m
ol)
space time (kg s/mol)
573 K
623 K
673 K
-8
-7
-6
-5
-4
1.4 1.5 1.6 1.7 1.8
ln(-
r C3
H8
,o)
1000/T (1/K)
Ea = 70.4 ± 11.8 kJ/molEa = 70.4 kJ/mol
Apparent activation energy
from MS analysis agrees with
the apparent activation
energy from the XANES
analysis for catalyst reduction
Steady state conditions:
• γ = yO2(0) / yC3H8(0) = 5
• CO2: main product
• CO: not observed
• C3H6: very small traces (ca. 100
ppm) within experimental error
,08H3Ccat
83
F
HC 1WB
eAX
Propane total oxidation: Cu K XANES
17
UCCS visit, Lille, February 7, 2017
no changes in the spectra
catalyst remains oxidized
under total oxidation reaction
conditions
Time: T = 723 K
Theoretical considerations
18
UCCS visit, Lille, February 7, 2017
Theoretical considerations
19
UCCS visit, Lille, February 7, 2017
E
Atom with neighbors
E
Isolated atom
Fine structure due to
photoelectron scattering
on neighbor atoms
- Green formalism
- Muffin-tin potential
- Cluster size of 830 pm
Local structure around Cu
20
UCCS visit, Lille, February 7, 2017
0
0.2
0.4
0.6
0.8
1
1.2
1.4
8970 8980 8990 9000 9010 9020 9030
Energy [eV]
No
rma
lis
ed
μ(E
)
Reduced Catalyst
Theoretical fit
Oxidized Catalyst
Theoretical fit
Structure Bond XANES fit values (pm)
fcc Cu Cu-Cu Cu reference foil: 264
Reduced catalyst: 264
monoclinic
CuO Cu-O
CuO reference: 201-202
Oxidized catalyst: 210-211
Propane total oxidation: Conclusion
21
UCCS visit, Lille, February 7, 2017
Alexopoulos et al., Appl. Catal. B, 2010
pm 202201pm 211210
ref
OCu
cat
OCu dd
Eact = 70 kJ/mol Eact = 24 kJ/mol
Enhanced activity due to weaker Cu-O bonds
Outline
• Hydrocarbon oxidation on metal oxides
• Bio-alcohol dehydration in zeolites
22
UCCS visit, Lille, February 7, 2017
Bioalcohols to hydrocarbons as a green route
23
UCCS visit, Lille, February 7, 2017
Crude oil
Chemicals
Hydrocarbon
Motorfuel
Ethylene
Propylene
C4 stream
Benzene
Toluene
Xylenes
Chemicals
Hydrocarbon
Motorfuel
Ethylene
Propylene
C4 stream
Benzene
Toluene
Xylenes
Sugar
Starch
Lignocellulosics
Bioethanol
/Biobutanol
Platform molecule
Bioalcohols-to-hydrocarbons
(BTH)
Zeolite-catalyzed bio-alcohol conversion
24
UCCS visit, Lille, February 7, 2017
Validation
Reactor model
Reaction mechanism
Thermo-dynamics
higher HC alkenes ROH
Ethanol conversion to higher HC
25
C2H5OH
C2H5OH
C2H5OC2H5
C2H4
H2OC2H5OH
H2O C2H4
C4H8
Path A Path D
UCCS visit, Lille, February 7, 2017
H-ZSM-5, T = 573 K, pEtOH,0 = 30 kPa
Alexopoulos et al., Angew. Chem. Int. Ed., 2016
Ethanol adsorption in H-ZSM-5
-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)-70
-60
-50
-40
-30
-20
-10
0
10
ΔΕ
(kJ/
mo
l)
Nudged Elastic Band
calculation with
PBE-D2 functional
H-b
on
din
g
protonation
UCCS visit, Lille, February 7, 2017
26
Adsorbed ethanol monomer in H-ZSM-5
27
UCCS visit, Lille, February 7, 2017
Oα Oβ Hα Hβ O
Oz
Si
O
Al
O
O+e
H
H
-
+
Oe
H
Oz
Si
O
Al
O
H
+
-
0 1 2 3 4
R (Å)
0
0.1
0.2
0.3
0 1 2 3
700 K
g (
R)
R (Å)
0
0.1
0.2
0.3
500 K
g (
R)
0
0.1
0.2
0.3
400 K
g (
R)
0
0.1
0.2
0.3
300 K
g (
R)
0
0.1
0.2
0.3
0.4100 K
g (
R)
Hα Hβ
T↗
Oz
Si
O
Al
O
O+e
H
H
-
+
Oe
H
Oz
Si
O
Al
O
H
+
-
0 1 2 3 4
R (Å)
0
0.1
0.2
0.3
0 1 2 3
700 K
g (
R)
R (Å)
0
0.1
0.2
0.3
500 K
g (
R)
0
0.1
0.2
0.3
400 K
g (
R)
0
0.1
0.2
0.3
300 K
g (
R)
0
0.1
0.2
0.3
0.4
100 K
g (
R)
Hα Hβ
T↗
Alexopoulos et al., J. Phys. Chem. C, 2016
NVT, 300 K
Adsorbed ethanol dimer in H-ZSM-5
28
UCCS visit, Lille, February 7, 2017
Oα Oβ Hα Hγ O Hβ
-
+O
e1
H5C2
H
Oe2
C2H5
H
H
Oz
Si
O
Al
O
0 1 2 3
R (Å)
0 1 2 3 4
R (Å)
0
0.1
0.2
0.3
0 1 2 3
50
0 K
g (
R)
R (Å)
0
0.1
0.2
0.3
40
0 K
g (
R)
0
0.1
0.2
0.3
0.4
30
0 K
g (
R)
Hβ Hα Hγ
T = 300 – 500 K
NVT, 300 K
Alexopoulos et al., J. Phys. Chem. C, 2016
Ethanol adsorption isotherms in H-ZSM-5
29
UCCS visit, Lille, February 7, 2017
0
400
800
1200
1600
0 0.05 0.1 0.15 0.2 0.25
CEt
OH
(mm
ol/
kg)
pEtOH (mbar)
total
dimer
monomer
2
211
2
211
1
2
EtOHEtOH
EtOHEtOH
BASEtOHpKKpK
pKKpKCC
C2H5OH
C2D5OH
T = 313 K
Alexopoulos et al., J. Phys. Chem. C, 2016
EtOH(g) + 𝐾
1 monomerads
EtOH(g) + monomerads 𝐾
2
dimerads
Projected vibrational DOS at 300K
30
UCCS visit, Lille, February 7, 2017
Oe
C2D5
H
Oz
Si
O
Al
O
H
Oe1
D5C2
H
Oe2
C2D5
H
H
Oz
Si
O
Al
O
Oe
C2H5
H
Oz
Si
O
Al
O
D
Oe1
H5C2
D
Oe2
C2H5
D
H
Oz
Si
O
Al
O
Oe
C2H5
H
Oz
Si
O
Al
O
H
Oe1
H5C2
H
Oe2
C2H5
H
H
Oz
Si
O
Al
O
Inte
nsit
y
Alexopoulos et al., J. Phys. Chem. C, 2016
Experimental IR difference spectra at 300K
31
UCCS visit, Lille, February 7, 2017
ΔIR = IRads - IRzeo
Alexopoulos et al., J. Phys. Chem. C, 2016
Reaction scheme for ethanol dehydration
32
C2H5OH
C2H5OH
C2H5OC2H5
C2H4
H2OC2H5OH
H2O C2H4
C4H8
Path A Path D
• Path A: ethanol to ethene via 5 mechanisms
• Path B: ethanol to diethyl ether (DEE) via 2 mechanisms
• Path C: diethyl ether (DEE) to ethene via 1 mechanism
• In total: 21 elementary steps
UCCS visit, Lille, February 7, 2017
Ethanol to Ethene (path A): monomolecular
EtOH(g) C2H4(g) + H2O(g)
ZeOH
AlO O
H
AlO O
HO
+
H
H
-
OAl
O
H
O
H
H C3
W
H2O(g) C2H4(g)
TS16
C2H4(g)
H2O(g)
OAl
O
H
OH H
O
H
H
-
+
OAl
O
H
OH H
O
H
C2H5
-
+
2W C2
TS19
H2O(g) C2H4(g) EtOH(g)
H2O(g)
C2H4(g) EtOH(g)
C2H4(g)
AlO O
H
C2H4(g)
AlO O
H
O+
H
-
M2 Ethoxy TS3
Ethene* TS4
H2O(g)
AlO O
CH2H
AlO O
H C2H4(g)
H2O(g)
AlO O
HO
+
H
-
AlO O
HO
+
H
H
-
EtOH(g)
W
TS15
H2O(g)
EtOH(g)
C2H4(g)
H2O(g)
M1
UCCS visit, Lille, February 7, 2017
33
AlO O
HO
+
H
-
Ethanol to Ethene (path A): bimolecular
M1
OAl
O
H
OH H
O
H
C2H5
-
+
C2
TS13 C2H4(g)
C2H4(g)
-OAl
O
H
O+
HO
H
C2H5
D2
EtOH(g) C2H4(g) + H2O(g)
ZeOH
EtOH(g)
AlO O
H
EtOH(g)
D1
OAl
O
H
OH5C2 H
O
H
C2H5
-
+ EtOH(g)
EtOH(g)
H2O(g) H2O(g)
UCCS visit, Lille, February 7, 2017
34
AlOO
H
OAl
O
H5C2O
+
H
C2H5
-
AlO O
H
O+
H
-
-OAl
O
H
O+
HO
H
C2H5
AlO O
HO
+
H
-
Ethanol to Diethyl ether (path B)
2EtOH(g) DEE(g) + H2O(g)
ZeOH M1
EtOH(g)
AlO O
H
ZeOH
DEE(g)
M2 Ethoxy
TS3 H2O(g)
AlO O
CH2H
TS12
D1 D2
TS8
EtOH(g) H2O(g)
EtOH(g)
OAl
O
H
OH5C2 H
O
H
C2H5
-
+
H2O(g)
EtOH(g)
DEE(g)
H2O(g) EtOH(g)
EtOH(g) DEE*
UCCS visit, Lille, February 7, 2017
35
Diethyl ether to Ethene (path C)
DEE(g) EtOH(g) + C2H4(g)
OAl
O
H5C2O
+
H
C2H5
- OAl
O
H
O
H
C2H5
ZeOH
DEE(g)
AlO O
H
DEE* C1
TS10
Ethene*
AlO O
H
EtOH(g)
AlO O
H
ZeOH
C2H4(g)
DEE(g)
C2H4(g)
EtOH(g)
UCCS visit, Lille, February 7, 2017
36
Overview full reaction network
37
AlO O
HO
+
H
-
AlOO
H
OAl
O
H5C2O
+
H
C2H5
-
-OAl
O
H
O+
HO
H
C2H5
OAl
O
H
OH5C2 H
O
H
C2H5
-
+
OAl
O
H
OH H
O
H
C2H5
-
+
OAl
O
H
OH H
O
H
H
-
+
AlO O
HO
+
H
H
-
AlO O
H
O+
H
-
AlO O
H
AlO O
H
AlO O
CH2H
AlO O
H
OAl
O
H
O
H
C2H5
W
M1
M2
D1
D2
DEE*
C1
C2
Ethoxy
Ethene*+
H2O
(g)
-H2O
(g)
(0)
OAl
O
H
O
H
HC3
2W
- EtOH(g)
+ EtOH(g)
- C2H4(g)
+ C2H4(g)
(19)
(18)
UCCS visit, Lille, February 7, 2017
Alexopoulos et al., J. Catal., 2016
Path # A B C
Mechanism # 1 2 3 4 5 6 7 8
(0) W ↔ H2O(g) + * 1 0 1 0 0 0 0 0
(1) EtOH(g) + * ↔ M1 1 1 1 0 0 1 1 0
(2) M1 ↔ M2 0 1 1 0 0 1 0 0
(3) M2 ↔ Ethoxy + H2O(g) 0 1 0 0 0 1 0 0
(4) Ethoxy ↔ Ethene* 0 1 0 0 0 0 0 0
(5) Ethene* ↔ C2H4(g) + * 0 1 0 0 0 0 0 1
(6) M1 + EtOH(g) ↔ D1 0 0 0 0 1 0 1 0
(7) D1 ↔ D2 0 0 0 0 1 0 1 0
(8) D2 ↔ DEE* + H2O(g) 0 0 0 0 0 0 1 0
(9) DEE* ↔ DEE(g) + * 0 0 0 0 0 1 1 -1
(10) DEE* ↔ C1 0 0 0 0 0 0 0 1
(11) C1 ↔ Ethene* + EtOH(g) 0 0 0 0 0 0 0 1
(12) Ethoxy + EtOH(g) ↔ DEE* 0 0 0 0 0 1 0 0
(13) D2 ↔ C2 + C2H4(g) 0 0 0 0 1 0 0 0
(14) C2 ↔ M1 + H2O(g) 0 0 0 0 1 0 0 0
(15) M1 ↔ W + C2H4(g) 1 0 0 0 0 0 0 0
(16) M2 ↔ C3 0 0 1 0 0 0 0 0
(17) C3 ↔ W + C2H4(g) 0 0 1 0 0 0 0 0
(18) W + EtOH(g) ↔ C2 0 0 0 1 0 0 0 0
(19) C2 ↔ 2W + C2H4(g) 0 0 0 1 0 0 0 0
(20) 2W ↔ W + H2O(g) 0 0 0 1 0 0 0 0
Path A (mechanism # 1-5) EtOH(g) ↔ C2H4(g) + H2O(g)
Path B (mechanism # 6-7) EtOH(g) + EtOH(g) ↔ DEE(g) + H2O(g)
Path C (mechanism # 8) DEE(g) ↔ C2H4(g) + EtOH(g)
with e.g.:
TOFpathB =
TOFm6 + TOFm7
where:
TOFm6 = TOFrxn12
TOFm7 = TOFrxn8
1.E-09
1.E-07
1.E-05
1.E-03
1.E-01
0 20 40 60 80 100
TOF
( m
ol /
mo
l H+
/ s)
EtOH Conversion (%)
mechanism 1
mechanism 2mechanism 3
mechanism 4
mechanism 5
1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
1.E+00
425 450 475 500 525
TOF
( m
ol /
mo
l H+
/ s)
Temperature (K)
mechanism 1
mechanism 2
mechanism 3
mechanism 4
mechanism 5
1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Ethanol pressure (kPa)
mechanism 1
mechanism 2
mechanism 3
mechanism 4
mechanism 5
1.E-08
1.E-06
1.E-04
1.E-02
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Water pressure (kPa)
mechanism 1
mechanism 2
mechanism 3
mechanism 4
mechanism 5
Rate analysis: path A in H-ZSM-5
39
T = 500K, pEtOH,0 = 10kPa X = 10%, pEtOH,0 = 10kPa
X = 10%, T = 500K T = 500K, X = 10%, pEtOH,0 = 10kPa
UCCS visit, Lille, February 7, 2017
1.E-03
1.E-02
1.E-01
1.E+00
0 20 40 60 80 100
TOF
( m
ol /
mo
l H+
/ s)
EtOH Conversion (%)
mechanism 6
mechanism 7
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
425 450 475 500 525
TOF
( m
ol /
mo
l H+
/ s)
Temperature (K)
mechanism 6
mechanism 7
1.E-03
1.E-02
1.E-01
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Ethanol pressure (kPa)
mechanism 6
mechanism 7
1.E-03
1.E-02
1.E-01
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Water pressure (kPa)
mechanism 6
mechanism 7
Rate analysis: path B in H-ZSM-5
40
T = 500K, pEtOH,0 = 10kPa X = 10%, pEtOH,0 = 10kPa
X = 10%, T = 500K T = 500K, X = 10%, pEtOH,0 = 10kPa
UCCS visit, Lille, February 7, 2017
1.E-03
1.E-02
1.E-01
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Water pressure (kPa)
Path A
Path B
Path C
1.E-03
1.E-02
1.E-01
1.E+00
0.1 1 10 100
TOF
( m
ol /
mo
l H+
/ s)
Ethanol pressure (kPa)
Path APath B
Path C
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
425 450 475 500 525
TOF
( m
ol /
mo
l H+
/ s)
Temperature (K)
Path A
Path B
Path C
1.E-03
1.E-02
1.E-01
1.E+00
0 20 40 60 80 100
TOF
( m
ol /
mo
l H+
/ s)
EtOH Conversion (%)
Path A
Path B
Path C
Reaction path analysis in H-ZSM-5
41
UCCS visit, Lille, February 7, 2017
T = 500K, pEtOH,0 = 10kPa X = 10%, pEtOH,0 = 10kPa
X = 10%, T = 500K T = 500K, X = 10%, pEtOH,0 = 10kPa
0
20
40
60
80
100
0 4 8 12 16
Co
nv
ers
ion
/Se
lec
tivit
y
pH20,0 (kPa)
X
C2H4
DEE
X (%)
S-C2H4 (%)S-DEE (%)
Wcat/FEtOH,0 = 6.5 kg s / mol
PEtOH,0 = 24 kPa
Kinetic model: experimental validation
42
UCCS visit, Lille, February 7, 2017
Alexopoulos et al., J. Catal., 2016
Wcat/FEtOH,0 = 8.3 kg s / mol
PEtOH,0 = 29 kPa
T = 503 K
Industrial dehydration reactor
43
UCCS visit, Lille, February 7, 2017
adiabatic
reactor
bio-ethanol (aqueous ethanol solution)
adiabatic
reactor
ethylene
Design specifications1
T0 (K) 673
P0 (kPa) 590
Ethylene production (kT y-1) 220
Ethanol content (wt.%) 26
Catalyst mass (ton) 6
C2H5OH C2H4 + H2O H = 46 kJ/molEtOH
2 C2H5OH (C2H5)2O + H2O H = 12 kJ/molEtOH
(C2H5)2O C2H4 + C2H5OH H = 70 kJ/molEtOH
1 US Patent 2013/0090510 A1 assigned to IFP Energies Nouvelles and Total
Research & Technology
Bio-ethanol dehydration: industrial scale
44
UCCS visit, Lille, February 7, 2017
45
UCCS visit, Lille, February 7, 2017
Bio-ethanol dehydration: Conclusion
Molecular scale
Lab scale
Industrial scale
Acknowledgments
46
UCCS visit, Lille, February 7, 2017
THEORY
• M.-F. Reyniers, G.B. Marin (UGent):
– Long Term Structural Methusalem Funding by the Flemish Government – grant number BOF09/01M00409
– Stevin Supercomputer Infrastructure
• M.-S. Lee, V.-A. Glezakou, R. Rousseau (PNNL):
– US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences
– Environmental Molecular Science Laboratory (EMSL)
– National Energy Research Scientific Computing Center (NERSC)
EXPERIMENT
• S. Cristol (ULille), M. Newton (ESRF)
• Y. Liu, Y. Zhi, J.A. Lercher (TUM)
• K. Van der Borght, V. Galvita (UGent)
Reactor equations: lab scale
47
UCCS visit, Lille, February 7, 2017
Reactor continuity equations for each gas-phase component i
with PSSA for the surface species k:
Fi =Fi,0 at W=0
• Fi molar flow rate of component i (mol s-1)
• W catalyst mass (kg)
• Ct acid site concentration (mol H+ kg-1)
• Ri net production frequency of component i
(molecules site-1 s-1 = mol molH+-1 s-1)
• rj turnover frequency of elementary step j
(molecules site-1 s-1 = mol molH+-1 s-1)
• kj rate coefficient of elementary step j
• 𝜃 coverage of surface species k
• pi partial pressure of gas phase component i
• νji stoichiometric coefficient of component i
in the elementary step j
𝑑𝐹𝑖𝑑𝑊= 𝐶𝑡𝑅𝑖 = 𝐶𝑡 𝑣𝑗𝑖𝑟𝑗
𝑗
𝑅𝑘 = 𝑣𝑗𝑘𝑟𝑗𝑗
= 0
𝜃𝐻+ + 𝜃𝑘𝑘
= 1
with 𝑒. 𝑔. 𝑟𝑗 = 𝑘𝑗𝜃𝑘𝑝𝑖
Reactor equations: industrial scale
48
UCCS visit, Lille, February 7, 2017
Fi =Fi,0 at W=0
• Fi molar flow rate of component i (mol s-1)
• W catalyst mass (kg)
• Ct acid site concentration (mol H+ kg-1)
• Ri net production frequency of component i
(molecules site-1 s-1 = mol molH+-1 s-1)
• rj turnover frequency of elementary step j
(molecules site-1 s-1 = mol molH+-1 s-1)
• kj rate constant of elementary step j
• 𝜃𝑘 coverage of surface species k
• pi partial pressure of gas phase component i
• νjk stoichiometric coefficient of component k
in the elementary step j
• T temperature (K)
• cp specific heat capacity (J kg-1 K-1)
• G mass flow rate (kg s-1)
• ∆𝐻𝑓,𝑖 enthalpy of formation of component i (J mol-1)
• De,i effective diffusion coefficient (m² s-1)
• Ci concentration inside the catalyst pellet (mol m-3)
• 𝜉 position coordinate within catalyst pellet
• 𝑅𝑖 net production rate
in case of diffusion limitations (mol molH+-1 s-1)
• ρf density of the fluid (kg m-3)
• ρs density of the pellet (kg m-3)
• ρb density of the bed (kg m-3)
• dp pellet diameter (m)
T =T0 at W=0 𝑑𝑇
𝑑𝑊=1
𝐺𝑐𝑝 ∆𝐻𝑓,𝑖𝑖=1
𝑅𝑖𝐶𝑡
𝑑𝐹𝑖𝑑𝑊= 𝐶𝑡𝑅𝑖
𝑅𝑘 = 𝑣𝑗𝑘𝑟𝑗𝑗
= 0
with 𝑒. 𝑔. 𝑟𝑗 = 𝑘𝑗𝜃𝑘𝑝𝑖
𝜃𝐻+ + 𝜃𝑘𝑘
= 1 NA
NO
M
AC
RO
M
ICR
O
𝑑𝑝𝑡𝑑𝑊= −𝑓
𝐺2
𝜌𝑏𝜌𝑓𝐴𝑟3𝑑𝑝
p =p0 at W=0
0 = 𝐶𝑡𝑅𝑖𝜌𝑠 −4
𝑑𝑝2
2
𝜉𝐷𝑒,𝑖𝑑𝐶𝑖𝑑𝜉+𝑑𝐷𝑒,𝑖𝑑𝜉
𝑑𝐶𝑖𝑑𝜉+ 𝐷𝑒,𝑖
𝑑2𝐶𝑖
𝑑𝜉²
𝐶𝑖= 𝐶𝑖𝑠 𝜉 = 1
𝑑𝐶𝑖𝑑𝜉= 0 𝜉 = 0
at W ≠ 0
Importance of diffusion limitations
49
UCCS visit, Lille, February 7, 2017
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
log
De,i (m
² s
-1)
log d (m)
(𝑛 + 1)
2
𝑑2𝜌𝑅𝑖𝑜𝑏𝑠
6𝐷𝑒,𝑖𝐶𝑖𝑠 < 0.08
Weisz-Prater criterion:
𝐷𝑒,𝑖 =휀𝑝𝐷𝑖𝜏𝑝
1
𝐷𝑖=1
𝐷𝑖,𝑚+1
𝐷𝑖,𝐾
𝐷𝑖,𝐾 =2
3
𝑑𝑝𝑜𝑟𝑒
2
8𝑅𝑇
𝜋𝑀𝑖
Knudsen diffusion coefficient: Molecular diffusion coefficient:
𝐷𝑖,𝑗 = 1 × 10−7
𝑇1.75
𝑃𝑡𝑜𝑡( Σ𝑣 𝑖1/3+ Σ𝑣 𝑗
1/3)2
1
𝑀𝑖+1
𝑀𝑗
1/2
Bosanquet equation:
T=673 K
Diffusion limitations
𝑑𝑐
𝑑𝑝
E1 like TS15
50
M1
AlO O
HO
+
H
H
-
W
AlO O
HO
+
H
H
-
SN2 TS3
51
H2O(g)
M2
AlO O-
H
O+
H
:
Ethoxy
AlOO
Syn elimination TS16
52
C3
OAl
O
H
O
H
H
M2
- Al
OO
H
O+
H
H
:
Syn elimination TS19
53
C2H4(g)
C2
-
H
O
H
OAl
O
HO+
HH
:
:
2W
-
+ O
H H
AlO O
O
H
H
H
TS4
54
Ethoxy
AlOO
H
:
Ethene*
:
AlOO
H
SN2 TS12
55
DEE*
- OAl
O
H5C2
O+
H
C2H5
Ethoxy
:
AlOO
O
H
C2H5
DEE*
SN2 TS8
56
H2O(g)
OAl
O
H5C2O
+
H
C2H5
-
D2
- OAl
O
O
H
C2H5
H
O+
H :
Ethanol-assisted syn-elimination TS13
57
C2H4(g) C2
OAl
O
H
OH H
O
H
C2H5
-
+
D2
- OAl
O
HO+
H
O
H
C2H5H:
Syn elimination TS10
58
C1
OAl
O
H
O
H
C2H5
DEE*
- OAl
O
O+
H
C2H5
H
:
Glossary
59
UCCS visit, Lille, February 7, 2017
• Molecular Dynamics (MD): a technique by which one
generates the atomic trajectories of a system of N
particles by numerical integration of Newton’s equation
of motion, for a specific interatomic potential, with certain
initial and boundary conditions.
• Radial Distribution Function (RDF): a pair correlation
function, which describes how, on average, the atoms in
a system are radially packed around each other.
• Vibrational Density Of States (VDOS): the Fourier
transform of the velocity-velocity time-correlation function
𝐷 𝜔 = 𝑒−𝑖𝜔𝑡 𝒗 𝜏 ∙ 𝒗 𝜏 + 𝑡 𝑑𝑡∞
0
𝑔𝛼𝛽 𝑟 = 1
𝑁𝛼𝜌𝛽 𝛿(𝑟 − |𝑹𝐽 − 𝑹𝐼|
𝐼𝜖𝛼,𝐽𝜖𝛽
)