chabazite: a zeolite allowing selective adsorption of ... · i-sup 2008. molecular sieving: ......
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Vrije Universiteit BrusselDepartment of Chemical Engineering
Chabazite: A zeolite allowing selective adsorption of short chain alcohols
Lisa Devriese, Inge Daems, Ranjeet Singh*, Paul Webley*, Gino V. Baron, Joeri F.M. Denayer
(* Dept. Chem. Eng., Monash University, AU)
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Molecular sieving: Classical view
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Small pore openings • Large host-guest contact surface • Classical shape and size selectivity• Exclusion
• Slow diffusion• Larger molecules can not enter
Large pore openings
• Fast diffusion• All molecules can enter
• No classical shape and size selectivity
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Zeolitic pore systems
1D translation
Tubular pores
Spherical pores: Cage and Window zeolites
Hindered intra-cage diffusion
Chabazite
• Naturally occuring zeolite
• Elipsoidal cages connected
through 8 MR windows of 3.8 x 4.2 Å
• Separation of N2 and O2 from Ar
• Propane / propene separation
• Isostructural to SAPO-34: Methanol
to Olefins (MTO) catalysti-SUP 2008
5
Chabazite
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Double 6-ringconnecting 2
cages
Chabazite cage
8-ring window
10Å
6,7Å ± 4 Å
Elipsoidal cages with access through 8 MR 3.8 x 4.2 Å
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Molecular Assembling in Confined Spaces
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*Schenk M. et al, Journal of Catalysis, 214, 88-99, 2003
K’
Enthalpy∆∆HHEnergetic interactionEnergetic interaction
Entropy ∆SLoss of freedom in pore
RTH
eKK0
0
∆−
= '' *)'ln(0 RTKRTG cρ−=∆T
GHS 00
0∆−∆
=∆
Molecular packing:Optimisation enthalpy / entropyOptimisation enthalpy / entropy
7
Chain length exclusion in CHA zeolite
Linear hydrocarbon chainsn-alkanesalcoholsalkenes
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Chain molecules in CHA
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Linear hydrocarbon chains can diffuse through 10 MR
9
Synthetic CHA
M. Bourgogne, J.L. Guth, R. Wey, U.S. Patent 4503024, 1985
gel composition 0.17 Na2O : 2.0 K2O : 5.18 SiO2 : Al2 O3 : 224 H2O Si/Al ratio of 2.59
UC: Na0.8K9.5[Al10.3Si25.7O72] N2-porosimetry 0.17 ml/g (486 m2/g) , activated 350°C
Ranjeet Singh, Monash University, AU
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Ion exchanged CHA UC composition of exchanged Na-K-CHA K-CHA K10.7 [Al10.7Si25.3O72] 0.17 ml/g Na-CHA Na9.5K0.9 [Al10.4Si25.6O72] 0.23 ml/g Ca-Cha Ca4.7K0.8 [Al10.2Si25.8O72] 0.19 ml/g
10i-SUP 2008
11
Molecular Simulations Monte Carlo simulations: deviations when molecule length
approaches that of cage with small window
6
1David Dubbeldam et al., Understanding the window effect in zeolite catalysis,
Angew Chem Int Ed. 2003, 42, 3624-3626
K’
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n-alkane Henry constants
12
1.0E‐07
1.0E‐06
1.0E‐05
1.0E‐04
1.0E‐03
1 6 11 16
K' (m
ol/kg/Pa)
Nc
200 °C
215 °C
230 °C
250 °C
Very low degree of pore filling
Steric constraints: n-hexane: 10.1 Å - CHA cage: 10 Åi-SUP 2008
Adsorption thermodynamics
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15
19
23
27
31
35
39
0 50 100 150
‐ln(K0' (m
ol/kg/Pa))
‐∆H0 (kJ/mol)
C10
C11
C12
C9
C8C7
C6C5
C1
C2C3
C4
Ads
orpt
ion
entro
py
Adsorption enthalpy
Adsorption mechanism
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C1 to C5
Alkanes to C5 : stretched in cages
8,84 Å
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Adsorption thermodynamics
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15
19
23
27
31
35
39
0 50 100 150
‐ln(K0' (m
ol/kg/Pa))
‐∆H0 (kJ/mol)
C10
C11
C12
C9
C8C7
C6C5
C1
C2C3
C4
Adsorption mechanism
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C6 to C10
• C6 to C10 alkanes : coiled configuration
• Maximally 10 CH2 groups per cage
Adsorption thermodynamics
i-SUP 2008 17
15
19
23
27
31
35
39
0 50 100 150
‐ln(K0' (m
ol/kg/Pa))
‐∆H0 (kJ/mol)
C10
C11
C12
C9
C8C7
C6C5
C1
C2C3
C4
Adsorption mechanism
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C11 and larger
Alkanes > C11 : stretched over adjacent cages
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What happens in liquid phase, at high degree of pore filling ?
CbbC
sqq
+=
1 CbCKq
+=
1'
CompetitiveAdsorption isotherm
K’ adsorption constantqs saturation capacity
and
Langmuir equation
Batch isotherms
20
n-alkanes on CHA in liquid phase
0123456789101112
0123456789
10
C-a
tom
s/ca
ge
mol
ecul
es/c
age
Ca-CHA299K
Cut-off between C2 and C3
Complete cage filling
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1-alcohols on CHA in liquid phase
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0123456789101112
0123456789
10
C-a
tom
s/ca
ge
mol
ecul
es/c
age
Ca-CHA299K
Cut-off between C2 and C3
2nd cut-off between C4 and C5
22
1-alcohols on CHA in liquid phase
02468
1012141618202224
methanol
ethanol
1-propanol
1-butanol
1-pentanol1-hexa
nol1-heptanol
q (m
olec
/ SC
)
02468101214161820222426
q (C
-at /
SC
)
Na CHA (2007)Na CHA (2007)Na-CHA
299K
⇒ No clear cut-off⇒ Cations affect adsorption mechanism
Decreasing capacity
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Cation effect
23
1-alcohols on CHA in liquid phase
02468
1012141618202224
methanol
ethanol
1-propan
ol1-butan
ol1-pen
tanol1-hexa
nol1-hep
tanol
q (m
olec
/ SC
)
02468101214161820
q (C
-at /
SC
)
K CHA (2007)K CHA (2007)
K-CHA299K
Cut-off between C4 and C5
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Cation effect
CBMC modelling
24
With cations!
R. Krishna, J.M. van Baten,, Sep. Purif. Technol. (2007), doi:10.1016/j.seppur.2007.09.008
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Gas phase versus Liquid phase
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1.0E‐07
1.0E‐06
1.0E‐05
1.0E‐04
1.0E‐03
1 6 11 16
K' (m
ol/kg/Pa)
Nc
200 °C
215 °C
230 °C
250 °C
n-C70123456789101112
0123456789
10
C-a
tom
s/ca
ge
mol
ecul
es/c
age
Gas phase Liquid phase
n-C3Gas phase:
• Low degree of pore filling• Unrestricted motion from cage to cage• No “packing” or “assembly”problemsLiquid phase:
• High degree of pore filling• Restricted motion from cage to cage• Molecular packing becomes critical• Small molecules pack better: configurational entropy advantage
1 pentanol molecule / cage
4 ethanol molecules / cage
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Liquid phase, mixtures?
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
150 200 250 300 350 400 450time (min)
Cou
t / C
in
C15C16
Column separation experiments
Ethanol / propanol mixture adsorption
27
0
2
4
6
8
10
12
14
0.0 0.2 0.4 0.6 0.8 1.0
externe molfractie 1-propanol
q (m
olec
/ SC
)
C2olC3oltotaal
0
2
4
6
8
10
12
0.0 0.2 0.4 0.6 0.8 1.0
externe molfractie 1-propanol
q (m
olec
/ SC
)
C2olC3oltotaal
Na-CHACa-CHA
Mole fraction 1-propanol Mole fraction 1-propanol
Mole fraction 1-propanolMole fraction 1-propanol
Propanol Propanol
Ethanol Ethanol
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Breakthrough curves Ca-CHAethanol/1-propanol
⇒ preferential adsorption of the shortest molecule ethanol
0.00.20.40.60.81.01.2
0 2 4 6 8 10 12 14 16 18 20 22 24 26Geëlueerd volume (ml)
Rel
atie
ve c
once
ntra
tie C2ol / C2ol(blanco) C3ol / C3ol(blanco)
rela
tive
conc
entr
atio
n
ethanol
1-propanol
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Ethanol – Hexanol binary equilibrium
29
0
1
2
3
0.0 0.2 0.4 0.6 0.8 1.0
Xi
q (m
mol
/g C
HA
)
ethanolhexanol
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0
Yi
Mole fraction C6-ol
Mole fraction C6-ol
Mole fraction C6-ol
ethanol
hexanol
q (mmol /g)
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0.00.20.40.60.81.01.2
0 4 8 12 16 20 24 28 32Geëlueerd volume (ml)
Rel
atie
ve c
once
ntra
tie C2ol / C2ol(blanco) C6ol / C6ol(blanco)
rela
tive
conc
entr
atio
n
30
Breakthrough curves Ca-CHAethanol/1-hexanol
ethanol
1-hexanol
⇒ preferential adsorption of ethanol⇒ exclusion of 1-hexanol
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CO2 / CH4 separation
32
0.0E+00
1.0E‐06
2.0E‐06
3.0E‐06
4.0E‐06
5.0E‐06
6.0E‐06
7.0E‐06
8.0E‐06
9.0E‐06
0 200 400 600 800 1000 1200 1400 1600 1800
C
Time (s)
CH4
CO2
CH4 CO2
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33
Conclusions
• CHA operates in the opposite way to most zeolites
and excludes longer chains from adsorption.
• In zeolites with cages connected by narrow windows,
molecules are preferably confined in the cage, not in
the windows.
• Purification processes: remove traces of small
molecules from mixtures of heavier components.
• Use in membrane processes?
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34
Acknowledgements
Ir. Els Leemans
IAP, IWT
FWO Vlaanderen
I. Daems, et.al, Chem. Comm. (2007) 13, 1316–1318
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36
Very difficult, slow desorption
Ca CHA: Desorption with octane
0.00.20.40.60.81.0
0 5 10 15 20 25 30 35 40 45 50 55 60 65Geëlueerd volume (ml)
Abs
olut
e co
ncen
trat
ie(g
ewic
hts%
)
C2olC6ol
0.000.020.04
0.060.080.10
0 5 10 15 20 25 30 35 40 45 50 55 60
D~2.10-17m²/s
0,01 ml/g CHA
ethanol
conc
entr
atio
n(w
t %)
CBMC pure component prediction
R. Krishna, J.M. van Baten, Separating n-alkane mixtures by exploiting differences in the adsorption capacity within cages of CHA, AFX and ERI zeolites, Sep. Purif. Technol. (2007), doi:10.1016/j.seppur.2007.09.008
AIChE Annual Meeting 2007 –Salt Lake City 37
Alkane conformations in CHA
AIChE Annual Meeting 2007 –Salt Lake City 38
39
Vapor phase isotherms Ca-CHA 70°C
higher capacity for methanol
0
0.04
0.08
0.12
0.16
0 0.02 0.04 0.06 0.08 0.1Pvap/Psat
q (g
/g)
methanol 1-butanol Langmuir fit 1-butanol
40
Liquid phase in iso-C8 on Ca-CHA
02468
1012141618202224
methanol
ethanol
1-propan
ol1-butan
ol1-pen
tanol1-hexa
nol1-hep
tanol
q (m
olec
/ SC
)
02468101214161820
q (C
-at /
SC
)
Ca CHA tweede staal (2007)Ca CHA eerste staal (2004)Ca CHA tweede staal (2007)Ca CHA eerste staal (2004)
Equimolar mixture simulations
41
AIChE Annual Meeting 2007 –Salt Lake City 42
Window effect - Commensurate diffusion
Dubbeldam and Smit, J. Phys. Chem. B, Vol. 107, No. 44, 2003
Erionite
AIChE Annual Meeting 2007 –Salt Lake City 43
Low coverage – Henry constants
4 6 8 10 12Carbon number
K' (
mol
/kg/
Pa)
BetaMordeniteYSilicaliteCBV760ZSM-22Montmorillonite
1 10-7
1 10-2
1 10-3
1 10-4
1 10-5
1 10-6
1 10-1
Exponential increase of K’ with CN
44
0 200 400 600 800
t (s)
n-hexane
n-heptane
n-octane
n-nonanen-decane
NaY (325 °C)
Retention n-alkanes in vapor phase
→ longer chains more strongly adsorbed
45
Molecular assembling Molecular assembling is the arrangement of
adsorbed molecules inside confined pore systems, hereby optimizing the balance between energetic (∆∆HH) and steric (∆∆SS)contributions.
∆G=∆∆HH-T∆∆SS
Enthalpy = ΦR+ΦD +ΦP+Φµ+Φq +ΦS
Entropy
adsorbate-adsorbate
van der Waals electrostatic
∆H
∆S
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Gas phase:
• Low degree of pore filling• Unrestricted motion from cage to cage• No “packing” or “assembly”problems
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Liquid phase:
• High degree of pore filling• Restricted motion from cage to cage• Molecular packing becomes critical• Small molecules pack better: configurational entropy advantage
1 pentanol molecule / cage
4 ethanol molecules / cage
48
Chabazite and adsorbed molecules
Smaller molecules pack better: Configurational entropy advantage
10 Å
6,7Å
2 propane molecules
1 pentane molecule
Adsorption kinetics
49
0.00
0.05
0.10
0.15
0.20
0 50 100 150 200 250
q (m
l/g z
eolit
e)
Time (h)
methanolc5C8
Diffusion limitations for C5 – Possibly also for longer chains
Ca-CHA299K
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Access blocking by coiled molecules
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CHA crystal
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Molecular Assembling in Confined Spaces
High Adsorption Potential ⇒ High Energetic Interaction
Limited space ⇒ Large entropy losses / Steric effects⇒ Molecular packing critical