Polyphosphazene-based gas separation membranes: Pushing the - - PowerPoint PPT Presentation

Polyphosphazene-based gas separation membranes: Pushing the boundaries

254th ACS National Meeting in Washington, DC, August 20-24, 2017

• Dr. Hunaid Nulwala

CEO Liquid Ion S

• lutions LLC

Pittsburgh, PA

Membrane/ S

• lvent Integrated Process

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Membrane Unit

CO2 Vacuum Pump

Stripper

Clean Flue Gas Air +CO2 Cross Heat Exchanger Rich Solution Lean Solution Lean Solution Rich Solution

Absorber

Makeup Solvent Flue Gas Expansion Valve Vapor Compressor Heat Pump Cycle Air

Stripper

To Combustor

Advantages

• Tail-end technology which is

easily used in retrofits

• No steam extraction is

required

• Heat pump is seamlessly

integrated into the cooling and heating of absorption/ stripping process

• Operating pressure of the

stripper will be very flexible depending on the low quality heat Disadvantage

• Capital cost could be intensive

• Used in variety of industrial,

medical, and environmental applications. – desalination, dialysis, sterile filtration, food processing, dehydration

• Low energy requirements
• Compact design
• No moving parts and modular

S ynthetic Membranes

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Permeability/Selectivity Material Property Accessing thin membranes Material Processing Ho Bum Park et al. S cience 2017;356:eaab0530 Stages

Membrane Terms

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• Permeability is a mat erial property: describes rate of permeation of a solute through a material,

normalized by its thickness and the pressure driving force

• Permeance is a membrane property: calculated as solute flux through the membrane normalized by

the pressure driving force (but not thickness)

• Ideal selectivity describes the ratio of the permeabilities (or permeances) of two different

permeating species through a membrane, and is a mat erial property

• High membrane permeance is achieved by both material selection (high permeability) and

membrane design (low thickness)

CO2 S eparation Using Membranes

• Mechanism of separation: diffusion through a non-porous membrane
• A pressure driven process - the driving force is the partial pressure difference of each gas in the

feed and permeate.

• S

electivity - separation factor, α (typical selectivity for CO2/ N2 is 20-45)

• Permeability = solubility (k) x diffusivity (D) (normalized over thickness)
• Either high selectivity or high permeability – Trade-off.

– Selective removal of fast permeating gases from slow permeating gases. – The solution-diffusion process can be approximated by Fick’s law:

N2 + CO2 CO2

∆P

l

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Permeance Vs. Permeability

• Current state-of-the-art fully

commercialized membrane materials for CO2/ N2 separations: 250 permeability with selectivity of 35-50.

• These are cast @

100nm thickness, giving permeance of 2500 GPU.

The scale bar is in microns to illustrate permeability and permeance for a membrane material which as permeability of 1000 Barrers.

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Mechanical Properties, Film Forming Ability

Needs

• More stable and robust membranes

– Mechanically – Chemically – Thermally

• Higher permeability and selectivity
• Fundamental structure-property-

processing relations needs to be incorporated.

• Various approaches to exceed the

upper bound and access better performing membranes.

– S urface modification – Phase separated polymer blends – Mixed-matrix membranes (MMMs)

• Inorganic membranes (superior in

performance but are difficult to make large thin films)

– S upported ionic liquids – Facilitated transport

Membrane Material Advances

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Mixed Matrix Membranes

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• Poor compatibility of the polymer and inorganic particles that leads to poor adhesion at

the organic-inorganic interface.

• General trade-off between selectivity and permeability

The Trouble with Mixed Matrix Membranes

• S
• lutions:
• Addition of interfacial

agents

• S

urface modification of inorganic particles

• Chemical modification of

polymers

• Use of flexible polymers

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Insight

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Permeability Selectivity

• J. Mat er. Chem. A, 2015, 3, 5014-5022

U.S . Pat ent Applicat ion number: 14/ 519,743

O HO O C10

NH2

No MOF

Interface

If you can’t beat ‘em, join ‘em!

• Makes use of envelopment effects which have plagued mixed matrix membranes
• Diffusion phenomena determined by interactions with the particle and polymer

surface

• Possibility of using simple nanoparticle fillers
• Advanced polymers allow an excellent starting point

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Interfacially-Controlled Envelope (ICE) Membranes

Plan of Attack for Mixed Matrix Membranes

• Use simple nanoparticle fillers
• S

urface modify the particles to tune optimal interactions with CO2 and the polymer

• Employ an advanced polymer with good compatibility and CO2

transport properties

• Create a membrane in which diffusion phenomena are determined

by interactions with the particle and polymer surface

CO2 N2

5-10 nm

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• Careful and detailed screening of

the surface modifier was carried

• ut.
• Nanoparticles have been

synthesized @ 200g levels for 3 different loadings

S urface Functionalized Nanoparticles

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Polymer particle interface

Ultra Flexible chains High chain mobility Improved gas solubility and diffusion P N P N R1 R2 R3 R4

Polymer of Choice

Excellent chemical and thermal stability C-C =607ΔHf kJ/mol vs. P-N =617 ΔHf kJ/mol Macromolecular substitution

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P N P N P N Cl Cl Cl Cl Cl Cl

250oC

P N Cl Cl

n

PCl5

CH2Cl2, 25oC

P N Cl Cl Cl SiMe3

Polyphosphazenes

N P R R n

Ring Opening Polymerization Living Cationic Polymerization

Poly(dichlorophosphazene) Reactive Intermediate

• High Molecular Weight (MW)
• Relatively Large Scale Preparation
• Poor Molecular Weight Control
• Broad Poly-disperity (PD)
• No End-chain Modifications
• Relatively Lower MW
• Well-controlled MW and PD
• Room Temperature
• Small Scale Preparation
• End-chain Modifications

Organic-Inorganic Hybrid Polymeric System

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Macromolecular Substitution

• Synthetic Simplicity: Nucleophilic S

ubstitutions

• Synthetic Tunability: Homo-substitutions OR Mix-substitutions
• Property Tunability: Glass Transition Temperature, S
• lubility,

Degradability, Hydrophobicity Library of Over 700 Different Polyphosphazenes

P N OR OR n P N NHR NHR n

• r

P N NR2 NR2 n P N NHR OR n

• r

P N NR2 OR n NaOR Combination R N H2 R2 N H

• r

P N Cl Cl n

Polyphosphazenes

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Polymer S creening

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N P NH HN O x y z N P NH O O x y z O O O O O P N O x z y O O P N NH x z y O O P N NH x z y O O O P N O x z y O O O P N O x z y=2%

• J. Mem. S

ci., 2001, 186, 249-256 250 Barrers 62 Selectivity

Challenges

• Not a film former
• S

ticky

• Does not have required

mechanical properties

Material Optimization

O O O P N O x z y=3%

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Solution = Inter Penetrating Networks (IPN)

• Difference Tg of uncrosslinked

Polyphoshazene vs. IPN is observed

• Minor difference is observed

between IPN vs. ICE membranes in Tg studies.

– Effect of extremely chain mobility

• 30 compositions of ICE membranes

have been evaluated for their thermal properties.

– Long-term stability test are on going.

Glass Transition S tudies

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• 100
• 50

50 100 150 200 Temperature (° C)

Thermal Studies of Polyphosphazene IPN and ICE membranes

Polyphosphazene IPN membrane ICE 40%

P N P N R1 R2 R3 R4

Membrane Casting

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Polymer dope Knife Screening is done using films cast by hand

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10-12 microns

Polymer Membrane Results

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R² = 0.9792

400 420 440 460 480 500 520 540 560 35 40 45 50 55 60

CO2 Permeability (Barrer) Selectivity CO2/N2

Temperature Study

50°C 45°C 40°C 35°C 30°C

O O O P N O x z y=2%

250 Barrers 62 Selectivity

Membrane Performance

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O O O P N O x z y=2%

%

• wt. Loading of Nanoparticles

Cast number Characterization Membrane results Permeability S electivity 30% unmodified particles LS

• 01-45A

Turned into a gel with white precipitates (not useable) N/ A N/ A 10% surface modified 10 nm particles LIS

• 01-41 A

S EM, TGA, DS C, Membrane testing 659 41 20% surface modified 10 nm particles LS

• 01-51 B*

Membrane testing 675-1025 20-33 40% surface modified 10 nm particles LIS

• 01-41 B, LIS
• 01-

43 S EM, TGA, DS C, membrane testing 1609 44 60% surface modified 10 nm particles LIS

• 01-51A*

TGA, DS C, Membrane testing 250-400 25-30

60% loading

1 10 100 1000

1 10 100 1,000 10,000

CO2/N2 selectivity CO2 permeability (Barrer)

Literature data This work Robeson upper bound

• Membrane of half a micron

would yield permeance of 3200 GPU with a selectivity of 44 for CO2/ N2 separation.

• Work is being performed to

convert these materials

properties into membranes ―

Open for collaborations

• Module design― Open for

collaborations and j oint research.

Membrane Performance

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• Further optimization of membrane

composition Design of Experiments – Optimized surface modification of the nanoparticles – Optimized concentration of nanoparticles – Optimized level of crosslinking

• 30 composition done
• DS

C studies complete – Minor differences in Tg – S tructure-property relationship is being carried out

• Performance testing in Progress.

Design of Experiments Matrix

Using statistical analytical tools to

• ptimize membrane composition

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Liquid Ion S

• lutions, Carbon Capture

S cientific and Penn S tate University gratefully acknowledge the support

• f the United S

tates Department of Energy’ s National Energy Technology Laboratory under agreementDE- FE0026464, which is responsible for funding the work presented.

• Dr. S

cott Chen

• Dr. Zij iang Pan
• Dr. Zhiwei Li
• Prof. Harry Allcock
• Dr. Zhongj ing Li
• Dr. Yi Ren
• Dr. David Luebke
• Krystal Koe
• Dr. Xu Zhou

Acknowledgement

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