Fundamental understanding of heterogeneously catalyzed ... › publication › 8537895 › file › 8537897.pdf · heterogeneously catalyzed reactions: from hydrocarbon oxidation

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


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


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


Hydrocarbon oxidation

5


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


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


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


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


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


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


Catalyst reduction: a two step process is found

Time:

T = 723 K

Catalyst reduction: XANES & MS

12


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


Catalyst reduction is reversible with reoxidation

Time: T = 723 K

Catalyst redox cycles: effect of T

14


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


Ea = 70.0 kJ/mol

Ea = 24.0 kJ/mol

Catalyst reduction Catalyst re-oxidation

Propane total oxidation: MS

16


(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


no changes in the spectra

catalyst remains oxidized

under total oxidation reaction

conditions

Time: T = 723 K

Theoretical considerations

18


Theoretical considerations

19


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


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


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


Bioalcohols to hydrocarbons as a green route

23


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


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


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


26

Adsorbed ethanol monomer in H-ZSM-5

27


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


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


Ethanol adsorption isotherms in H-ZSM-5

29


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


EtOH(g) + 𝐾

1 monomerads

EtOH(g) + monomerads 𝐾

2

dimerads

Projected vibrational DOS at 300K

30


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


Experimental IR difference spectra at 300K

31


ΔIR = IRads - IRzeo


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


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


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)


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*


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)


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)


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


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)


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)


mechanism 6

mechanism 7

Rate analysis: path B in H-ZSM-5

40


X = 10%, T = 500K T = 500K, X = 10%, pEtOH,0 = 10kPa


1.E-03

1.E-02

1.E-01

1.E+00

0.1 1 10 100

TOF

( m

ol /

mo

l H+

/ s)


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)


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



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


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


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

//upload.wikimedia.org/wikipedia/commons/b/b0/Ethanol-3D-balls.png

http://www.google.be/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=blHJ6qoybURhzM&tbnid=uHqSKZLxnxAmsM:&ved=0CAUQjRw&url=http://en.wikipedia.org/wiki/Polar_bond&ei=IKC7U4X5MY6d0wWakICADQ&bvm=bv.70138588,d.ZGU&psig=AFQjCNEfP6vEOLKgq64jdIjJrSJybKbizw&ust=1404891533689441

http://www.google.be/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=blHJ6qoybURhzM&tbnid=uHqSKZLxnxAmsM:&ved=0CAUQjRw&url=http://en.wikipedia.org/wiki/Polar_bond&ei=IKC7U4X5MY6d0wWakICADQ&bvm=bv.70138588,d.ZGU&psig=AFQjCNEfP6vEOLKgq64jdIjJrSJybKbizw&ust=1404891533689441

Bio-ethanol dehydration: industrial scale

44


45


Bio-ethanol dehydration: Conclusion

Molecular scale

Lab scale

Industrial scale

Acknowledgments

46


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


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


• 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


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


• rj turnover frequency of elementary step j


• 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


-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

:


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:


58

C1

OAl

O

H

O

H

C2H5

DEE*

- OAl

O

O+

H

C2H5

H

:

Glossary

59


• 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

)

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Fundamental understanding of heterogeneously catalyzed ... › publication › 8537895 › file › 8537897.pdf · heterogeneously catalyzed reactions: from hydrocarbon oxidation