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

i-SUP 2008 33

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

i-SUP 2008 26

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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28

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

i-SUP 2008 46

Gas phase:

• Low degree of pore filling• Unrestricted motion from cage to cage• No “packing” or “assembly”problems

i-SUP 2008 47i-SUP 2008 47

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