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 Solutions LLC Pittsburgh, PA Membrane/Solvent Integrated Process
Advantages • Tail-end technology which is Makeup easily used in retrofits Clean Flue Gas Solvent Air +CO2 To Combustor • No steam extraction is Lean Solution Rich Solution
required Expansion Valve Heat pump is seamlessly Heat • Membrane Pump
Cycle Stripper Stripper
integrated into the cooling and Unit Absorber
heating of absorption/stripping Flue Gas process Vapor Compressor
• Operating pressure of the Vacuum Pump Cross Heat stripper will be very flexible Exchanger
depending on the low quality Air CO2 heat Lean Solution Rich Disadvantage Solution • Capital cost could be intensive
2 Synthetic Membranes
Permeability/Selectivity Material Property Material Processing • 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
Accessing thin membranes Stages 3 Ho Bum Park et al. Science 2017;356:eaab0530 Membrane Terms
• Permeability is a material 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 material property
• High membrane permeance is achieved by both material selection (high permeability) and membrane design (low thickness)
4 CO2 Separation 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.
– Selective removal of fast l permeating gases from slow permeating gases. N 2 – The solution-diffusion process can CO2 + be approximated by Fick’s law: CO2
∆P
• Selectivity - 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. 5 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.
Mechanical Properties, Film Forming Ability 6 Membrane Material Advances
Needs • Various approaches to exceed the • More stable and robust membranes upper bound and access better – Mechanically performing membranes. – Chemically – Surface modification – Thermally – Phase separated polymer blends • Higher permeability and selectivity – Mixed-matrix membranes (MMMs) • Fundamental structure-property- • Inorganic membranes (superior in processing relations needs to be performance but are difficult to make large thin films) incorporated. – Supported ionic liquids – Facilitated transport
7 Mixed Matrix Membranes
8 The Trouble with Mixed Matrix Membranes
• 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
• Solutions: - Addition of interfacial agents - Surface modification of inorganic particles - Chemical modification of polymers
- Use of flexible polymers 9 Insight
Permeability
Selectivity
No MOF C10 NH2 O HO O
J. Mater. Chem. A, 2015, 3, 5014-5022 10 U.S. Patent Application number: 14/519,743 Interface
If you can’t beat ‘em, join ‘em!
Interfacially-Controlled Envelope (ICE) Membranes
• 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 11 • Advanced polymers allow an excellent starting point Plan of Attack for Mixed Matrix Membranes
CO2 N2
5-10 nm • Use simple nanoparticle fillers
• Surface 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
12 Surface Functionalized Nanoparticles
• Careful and detailed screening of the surface modifier was carried out.
• Nanoparticles have been synthesized @ 200g levels for 3 different loadings
Polymer particle interface 13 Polymer of Choice
Macromolecular substitution
R2 R3
P N P N
Ultra Flexible chains R1 R4 High chain mobility Improved gas solubility and diffusion Excellent chemical and thermal stability C-C =607ΔHf kJ/mol vs. P-N =617 ΔHf kJ/mol
14 Polyphosphazenes
R N P Organic-Inorganic Hybrid Polymeric System R n
Ring Opening Polymerization Living Cationic Polymerization Cl Cl o Cl Cl P 250 C PCl 5 e N N P N Cl P N SiM 3 Cl Cl n , o P P Cl CH2Cl2 25 C Cl Cl N Cl Poly(dichlorophosphazene) Reactive Intermediate
• High Molecular Weight (MW) • Relatively Lower MW • Relatively Large Scale Preparation • Well-controlled MW and PD • Poor Molecular Weight Control • Room Temperature • Broad Poly-disperity (PD) • Small Scale Preparation • End-chain Modifications • No End-chain Modifications 15 Polyphosphazenes
Macromolecular Substitution
NHR NR2 P N or P N H n n r R2N o NHR RNH2 NR2 Library of Over 700 Cl NHR NR Combination 2 Different P N P N or P N n n n Polyphosphazenes Na Cl OR OR OR OR P N n OR
• Synthetic Simplicity: Nucleophilic Substitutions • Synthetic Tunability: Homo-substitutions OR Mix-substitutions • Property Tunability: Glass Transition Temperature, Solubility, Degradability, Hydrophobicity 16 Polymer Screening
O O O HN z z N P N P x x
NH NH
y y
O O O z O O O O O O N P z x z N P N P x O x O O y=2%
y y 250 Barrers
O 62 Selectivity O O O O O z z N P N P x x NH NH y y 17 J. Mem. Sci., 2001, 186, 249-256 Material Optimization
Solution = Inter Penetrating Networks (IPN) Challenges • Not a film former • Sticky • Does not have required mechanical properties
O O O z N P x
O
y=3%
18 Glass Transition Studies
Thermal Studies of Polyphosphazene IPN and ICE membranes • Difference Tg of uncrosslinked Polyphoshazene vs. IPN is observed
• Minor difference is observed Polyphosphazene between IPN vs. ICE membranes in
IPN membrane Tg studies. – Effect of extremely chain mobility ICE 40%
-100 -50 0 50 100 150 200 Temperature (°C) • 30 compositions of ICE membranes have been evaluated for their R2 R3 thermal properties. P N P N – Long-term stability test are on going. R1 R4 19 Membrane Casting
Screening is done using films cast by hand
Knife
Polymer dope
20 10-12 microns
21 Polymer Membrane Results
O O O z Temperature Study N P x 560 50°C O
y=2% 540
250 Barrers 520 62 Selectivity 45°C 40°C 500
480 35°C
Permeability (Barrer) 460
2 30°C CO 440 R² = 0.9792
420
400 35 40 45 50 55 60
Selectivity CO2/N2 22 Membrane Performance
%wt. Loading of Nanoparticles Cast number Characterization Membrane results
Selectivity O Permeability O O z N P 30% unmodified particles LS-01-45A Turned into a gel N/A N/A x with white O precipitates (not y=2% useable) 10% surface modified 10 nm LIS-01-41 A SEM, TGA, DSC, 659 41 particles Membrane testing 20% surface modified 10 nm LS-01-51 B* Membrane 675-1025 20-33 particles testing 40% surface modified 10 nm LIS-01-41 B, LIS-01- SEM, TGA, DSC, 1609 44 particles 43 membrane testing 60% loading 60% surface modified 10 nm LIS-01-51A* TGA, DSC, 250-400 25-30 particles Membrane 23 testing Membrane Performance
• Membrane of half a micron 1000 Literature data would yield permeance of 3200 This work GPU with a selectivity of 44 for Robeson upper bound CO2/N2 separation. 100 • Work is being performed to convert these materials selectivity
2 10 properties into membranes ― /N 2 Open for collaborations CO 1 • Module design― Open for 1 10 100 1,000 10,000 collaborations and joint CO2 permeability (Barrer) research. 24 Design of Experiments Matrix
• 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 • DSC studies complete
– Minor differences in Tg – Structure-property relationship is being carried out Using statistical analytical tools to • Performance testing in Progress. optimize membrane composition
25 Acknowledgement
Liquid Ion Solutions, Carbon Capture • Dr. Scott Chen Scientific and Penn State University • Dr. Zijiang Pan gratefully acknowledge the support of the United States Department of • Dr. Zhiwei Li Energy’s National Energy Technology Laboratory under agreementDE- FE0026464, which is responsible for • Prof. Harry Allcock funding the work presented. • Dr. Zhongjing Li • Dr. Yi Ren
• Dr. David Luebke • Krystal Koe • Dr. Xu Zhou
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