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C b M l l Si M bCarbon Molecular Sieve Membranes for Carbon Capture

Bee Ting, LOW and Tai-Shung, CHUNG

Department of Chemical and Biomolecular EngineeringNational University of Singapore

Email: [email protected]

21 June 2011

2nd ICEPE June 20-22, Frankfurt am Main, Germany

NUS Presentation Title 2006

Outline

● Introduction

Outline

Introduction

● Rationale of researchChallenges and proposed solutions

● Background and literature review

● Methodology

● Results and discussionEffect of pyrolysis temperatureEffect of azide content

● Conclusions

● Acknowledgements

2


I t d tiIntroduction

Industrialization and population growth

Higher fuel demand for power generation and transportation

Excessive usage of fossil fuel and greenhouse gas emissions

Global warming, rising sea level and climate changes

Solutions ?

3

NUS Presentation Title 2006Introduction

P t b ti C b C tPost-combustion Carbon Capture

● The deployment of renewable and clean energy sources is a long term solution for energy and environmental sustainability.

● Impossible to completely eliminate the use of fossil fuel in the short run.

● Reduction of carbon dioxide emission via capture and sequestration.

4

Source: http://www.co2captureproject.org/about_capture.html


Gas Purification Processes

Introduction

Gas Purification Processes ● Separation techniques for carbon capture

Ab ti d ti b ti d b t t● Absorption, adsorption, membrane gas separation and membrane contactors.

● Membrane separation is an emerging purification tool for CO2 removal.

Advantages of Membrane Technology

Low capital investmentEnvironmentally benign

Si l ti

Ease of process integration

S ll f t i t

High energy efficiency

Simple operationSmall footprint

5


Rationale of ResearchRationale of Research● Key challenges

● Low pressure of flue gas (i e CO /N● Low pressure of flue gas (i.e. CO2/N2separation is determined by the feed to permeate pressure ratio).Hi h l t i fl t f fl● High volumetric flow rate of flue gas.

● Proposed solutions● Membranes with high CO2 permeabilityMembranes with high CO2 permeability

to reduce the cost of carbon capture. ● A CO2/N2 selectivity of 20 to 40 is

sufficient.sufficient.● Carbon molecular sieve membrane

(CMSM) has high permeation flux.C C S f CO /

Source:

● Can CMSM be used for CO2/N2 separation?

6

T.C. Merkel, H. Lin, X. Wei, R. Baker, Power plant post-combustion carbon dioxide capture: An opportunity for membranes, J. Membr. Sci.359 (2010) 126–139.


Background● Carbon molecular sieve membranes (CMSMs)

● are inorganic membranes derived from the pyrolysis of polymeric precursors

Background

● are inorganic membranes derived from the pyrolysis of polymeric precursors.● consist of large pores (6-20 Å) connected by the smaller ultramicropores.

● CMSMs typically show good gas pair selectivity and permeability.yp y g g p y p y● Ultramicropores - good selectivity● Micropores - high gas permeability

7Source: M. Kiyonoa, P. J. Williams, W. J. Koros, Effect of pyrolysis atmosphere on separation performance of carbon

molecular sieve membranes, J. Membr. Sci. 359 (2010) 2-10.


Formation of CMSMs

Background

● The pyrolysis of polymeric precursors to form CMSMs is complex.

Formation of CMSMs

● Various parameters influence the resultant morphology of CMSMs.

• Polymer free volume & chain rigidity• Chemical functionalities

Properties of precursors

• Solvent for casting polymeric membranePre treatment g p y• Non-solvent pre-treatmentPre-treatment

• Carbonization temperature• Atmosphere (O2, N2, vacuum)• Soak time

Pyrolysis conditions

8

Soak time


Polymeric Precursors

Background

● Synthetic routes to design polymer precursors for making CMSMs● Molecular design of new polymers chemical modification polymer

Polymeric Precursors

● Molecular design of new polymers, chemical modification, polymer blending and organic-inorganic hybrids.

I t i i P l Ch t i tiIntrinsic Polymer Characteristics

Free volume and rigidity Chemical groups

Structural Morphology of CMSMs

Pore size Pore connectivity

Gas Transport Properties of CMSMS

P bilit S l ti it9

Permeability Selectivity


Current State of the Art

Literature Review

● Comparison of the CO2/N2 separation performance of polymeric b d CMSM ith th R b b d

Current State of the Art

membranes and CMSMs with the Robeson upper bound. 1000

100

1

10CO2/N2selectivity

0,1

1

0,1 1 10 100 1000 10000

CO2 permeability (Barrer)

Figure 1. CO2/N2 separation performance of polymeric membranes

Figure 2. CO2/N2 separation performance of carbon molecular sieve membranes (CMSMs)

10Reference: L. M. Robeson, The upper bound revisited, J. Membr. Sci. 320 (2008) 390–400

polymeric membranes carbon molecular sieve membranes (CMSMs)


MethodologyMethodology● The incorporation of azide monomers within a high free volume polyimide in

the form of pseudo-interpenetrating polymer network (IPN) fine tunes the free

CC CO O CH3H3C

CF3O CH3

p p g p y ( )volume distribution.

0.206FDA-TMPDA/azide (70-30)

NC C

N

O O CH2H3C

CF3

NHO NH

CH3

NH H

O

HN

0.15

func

tion

6FDA-TMPDA 6FDA-TMPDA/Azide (90-10)

6FDA-TMPDA

O CH2 HN

HN NHCH2

H HNH3C

HN

O

CH3

Chemical crosslinks 0.05

0.10

babi

lity

dens

ity ( )

6FDA-TMPDA/Azide (70-30)

6FDA-TMPDA/azide (90-10)

CCN

C CN

CO

O

O

O

CH2

CH3H3C

H3C

CF3

CF3NH

NH

O

CH3

CN

C

O

O

0.00

Pro

b

O O CH3H3C O1.0 1.5 2.0 2.5 3.0 3.5

o-Ps lifetime (ns)

Figure 3. Pore size distribution of 6FDA-TMPDA and 6FDA-TMPDA/Azide IPN

Figure 4. 6FDA-TMPDA/Azide crosslinked pseudo IPN

11Reference: B. T. Low et al., Tuning the free volume cavities of polyimide membranes via the construction of pseudo-

interpenetrating networks for enhanced gas separation performance, Macromolecules 42 (2009) 7042–7054.


Polyimide/azide CMSMs

Methodology

Polyimide/azide CMSMs

● As a proof of concept, 6FDA-TMPDA with high intrinsic free volume was selected for investigation.

● To study the effect of (1) heat treatment/carbonization temperature and (2) azide loading on the CO /N separation performance(2) azide loading on the CO2/N2 separation performance.

● The polyimide and polyimide/azide IPN dense membranes were prepared by solvent casting.p p y g

● Heat treatment/carbonization of the isotropic films were conducted in a vacuum furnace to produce free-standing CMSMs

O(b)

CC CO O CH3H3CCF3

(a)

N3 N3CH3

NC C

N

O O CH3H3C

CF3

Figure 5. (a) 6FDA-TMPDA polyimide and (b) 2,6-Bis(4-azidobenzyldiene)-4-methylcyclohexanone (Azide)12

NUS Presentation Title 2006Results and Discussion

Eff t f H t T t t T tEffect of Heat Treatment Temperature

imide

CF3N-H

Figure 6. Thermal degradation profiles of 6FDA-TMPDA/azide pseudo-IPNs 13


Gas Transport Properties

Results and Discussion

Gas Transport Properties● 250 ºC to Tg → glassy to rubbery polymer → ↑ Permeability, ↓ Selectivity ● Tg to 550 ºC → intermediate → ↑ Permeability, ↑ Selectivity

CO /CH(b)

g ↑ y, ↑ y● 550 to 800 ºC → carbon → ↓ Permeability, ↑ Selectivity

H2

CO2/CH4(a) (b)

Tg TgIntermediateIntermediate CarbonCarbon

CO2H2/N2

N2

CH4

CO2/N2

Figure 7. (a) Permeability and (b) permselectivity as a function of heat treatment temperatures14


Hypothesis


Hypothesis

Polymer Intermediate Carbon

Transition from glassy to rubbery state

Degradation of thermally liable groups

Degradation of remaining heteroatomy

Polymer chains become more flexible

y g p

Pore evolution dominates

g

Rearrangement and densificationmore flexible

Permeability increases, selectivity

dominates

Permeability and l ti it i

densification

Permeability decreases, selectivityincreases, selectivity

decreases selectivity increase decreases, selectivity increases

15Increasing temperature


Effect of Azide Content


Effect of Azide Content● At 550 ºC, the addition of 10 wt% azide increases the d-space. The d-space

decreases as the azide content increases to 30 wt%.● The broad peak at 10 º < 2θ < 20 º accounts for the high permeability of CMSMs

that were pyrolyzed at 550 ºC.● At 800 ºC the d space decreases with higher azide content

550 ºC 800 ºC(b) (a)

● At 800 ºC, the d-space decreases with higher azide content.

Figure 8. XRD spectra of 6FDA-TMPDA/azide pseudo-IPNs carbonized at (a) 550 0C and (b) 800 0C 16





Table 1. Pure gas data for 6FDA-TMPDA/Azide CMSMs pyrolyzed at 550 ºC

Sample PCO2 (Barrer) α (CO2/N2) α (CO2/CH4)

6FDA-TMPDA 6810 25 60

g y y

6FDA-TMPDA/Azide (90-10) 9290 26 40

6FDA-TMPDA/Azide (70-30) 3640 24 66

Table 2. Pure gas data for 6FDA-TMPDA/Azide CMSMs pyrolyzed at 800 ºC

Sample PCO2 (Barrer) α (CO2/N2) α (CO2/CH4)

6FDA-TMPDA 1460 31 62

6FDA TMPDA/Azide (90 10) 850 33 1106FDA-TMPDA/Azide (90-10) 850 33 110

6FDA-TMPDA/Azide (70-30) 280 32 164

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HypothesisResults and Discussion

Hypothesis● The transition for 6FDA-TMPDA/Azide (70-30) is broad which indicates the

presence of multiple nano-domains with varying compositions.p p y g p● polyimide-rich and azide-rich domains

● 6FDA-TMPDA/Azide (90-10) is more h d th fhomogenous and the process of pore evolution during pyrolysis creates CMSM with better pore connectivity.

● For 6FDA-TMPDA/Azide (70-30), the pores are trapped within the denser azide-rich domains (i.e. poor pore connectivity).

Azide-richPolyimide

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Post combustion Carbon Capture?Post-combustion Carbon Capture?● A low pyrolysis temperature of 550 ºC produces CMSMs with high CO2 flux.

100

● The CO2/N2 selectivity is not a strong function of the carbonization temperature.● Good CO2/N2 separation performance but practicability issues need to be solved.

100

ctiv

ity

Robeson’s upper bound for polymeric materials

perm

sele

c

6FDA-TMPDA (800 0C)

6FDA TMPDA/azide (90 10)

6FDA-TMPDA/azide (70-30) (800 0C)

6FDA-TMPDA (550 0C)


CO

2/N2

p 6FDA-TMPDA/azide (90-10) (800 0C)

(550 C)


10100 1000 10000

CO permeability (Barrer)

Figure 9. A comparison of the CO2/N2 separation performance of CMSMs with the upper bound

CO2 permeability (Barrer)

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ConclusionsConclusions

● The incorporation of azide within the polyimide matrixThe incorporation of azide within the polyimide matrix ● alters the free volume of the polymeric precursors and ● generates parallel change in the structure of the corresponding CMSMs.

● Different heat treatment temperatures create distinct states of the membrane● Polymer, intermediate and carbon.

● Two competing processes of (1) pore evolution and (2) structural rearrangement/Two competing processes of (1) pore evolution and (2) structural rearrangement/ densification exists for the formation of intermediate and carbon membranes.

● Increasing the azide content generally reduces the permeability of the CMSMs. An exception was observed for 6FDA-TMPDA/Azide (90-10) at a pyrolysisAn exception was observed for 6FDA TMPDA/Azide (90 10) at a pyrolysis temperature of 550 ºC.

● 6FDA-TMPDA/Azide (90-10) that was pyrolyzed at 550 ºC shows a high CO2permeabilit of 9290 Barrer and a CO /N selecti it of 26permeability of 9290 Barrer and a CO2/N2 selectivity of 26.

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AcknowledgementsAcknowledgements

National University of Singapore

Agency for Science, Technology and Research (A*star), Singapore

PublicationB. T. Low, T. S. Chung, Carbon molecularsieve membranes derived from pseudo-interpenetrating polymer networks for gasinterpenetrating polymer networks for gasseparation and carbon capture, Carbon 49(2011) 2104-2112.

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