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 olutions LLC Pittsburgh, PA
Membrane/ S olvent Integrated Process Advantages • Tail-end technology which is Makeup easily used in retrofits Clean Flue Gas Air +CO 2 Solvent To • Combustor No steam extraction is Lean Solution Rich Solution required Expansion Valve • Heat pump is seamlessly Heat Pump Membrane Cycle integrated into the cooling and Unit Stripper Stripper Absorber heating of absorption/ stripping Flue Gas process Vapor Compressor • Operating pressure of the Vacuum stripper will be very flexible Pump Cross Heat Exchanger depending on the low quality Air CO 2 heat Lean Solution Rich Disadvantage Solution • Capital cost could be intensive 2
S ynthetic 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. S cience 2017;356:eaab0530
Membrane Terms • 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) 4
CO 2 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. – Selective removal of fast l permeating gases from slow permeating gases. N 2 – The solution-diffusion process can CO 2 + be approximated by Fick’s law: CO 2 ∆ P electivity - separation factor, α (typical selectivity for CO 2 / N 2 is 20-45) • S • 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 CO 2 / N 2 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 – S urface modification – Thermally – Phase separated polymer blends • Higher permeability and selectivity – Mixed-matrix membranes (MMMs) • Fundamental structure-property- • Inorganic membranes (superior in performance but are difficult to make processing relations needs to be large thin films) incorporated. – S upported 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 • S olutions: - Addition of interfacial agents - S urface modification of inorganic particles - Chemical modification of polymers - Use of flexible polymers 9
Insight Permeability Selectivity No MOF C10 O NH2 O HO J. Mat er. Chem. A , 2015 , 3 , 5014-5022 10 U.S . Pat ent Applicat ion 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 CO 2 N 2 5-10 nm • Use simple nanoparticle fillers • S urface modify the particles to tune optimal interactions with CO 2 and the polymer • Employ an advanced polymer with good compatibility and CO 2 transport properties • Create a membrane in which diffusion phenomena are determined by interactions with the particle and polymer surface 12
S urface 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 R 2 R 3 P N P N R 1 R 4 Ultra Flexible chains High chain mobility Improved gas solubility and diffusion Excellent chemical and thermal stability C-C =607 Δ Hf kJ/mol vs. P-N =617 Δ Hf kJ/mol 14
Polyphosphazenes R N P Organic-Inorganic Hybrid Polymeric System R n Living Cationic Polymerization Ring Opening Polymerization Cl Cl Cl Cl 250 o C PCl 5 P SiMe 3 N N P P N N Cl CH 2 Cl 2 , 25 o C n Cl Cl P P Cl Cl N Cl Cl Poly(dichlorophosphazene) Reactive Intermediate • Relatively Lower MW • High Molecular Weight (MW) • Well-controlled MW and PD • Relatively Large Scale Preparation • Room Temperature • Poor Molecular Weight Control • Small Scale Preparation • Broad Poly-disperity (PD) • End-chain Modifications • No End-chain Modifications 15
Polyphosphazenes Macromolecular Substitution NHR NR 2 or P N P N H N n n R 2 r o H 2 NHR NR 2 N R Library of Over 700 Cl NHR NR 2 Combination Different or P N P N P N Polyphosphazenes n n n NaOR Cl OR OR OR P N n OR • Synthetic Simplicity : Nucleophilic S ubstitutions • Synthetic Tunability : Homo-substitutions OR Mix-substitutions • Property Tunability : Glass Transition Temperature, S olubility, Degradability, Hydrophobicity 16
Polymer S creening O O O z HN z N P x N P x NH NH y y O O O z O O O O O O N P z z x N P N P x O x O O y=2% y y 250 Barrers 62 Selectivity O O O O O O z z N P x N P x NH NH y y 17 J. Mem. S ci. , 2001 , 186 , 249-256
Material Optimization Solution = Inter Penetrating Networks (IPN) Challenges • Not a film former • S ticky • Does not have required mechanical properties O O O z N P x O y=3% 18
Glass Transition S tudies Thermal Studies of Polyphosphazene IPN • Difference T g of uncrosslinked and ICE membranes Polyphoshazene vs. IPN is observed • Minor difference is observed between IPN vs. ICE membranes in Polyphosphazene T g studies. IPN membrane – Effect of extremely chain mobility ICE 40% -100 -50 0 50 100 150 200 • 30 compositions of ICE membranes Temperature (° C) have been evaluated for their R 2 R 3 thermal properties. P N P N – Long-term stability test are on going. 19 R 1 R 4
Membrane Casting Screening is done using films cast by hand Knife Polymer dope 20
10-12 microns 21
Polymer Membrane Results O Temperature Study O O z N P 560 x 50°C O 540 y=2% 250 Barrers 520 45°C CO 2 Permeability (Barrer) 62 Selectivity 40°C 500 480 35°C 460 30°C 440 R² = 0.9792 420 400 35 40 45 50 55 60 Selectivity CO 2 /N 2 22
Membrane Performance % wt. Loading of Nanoparticles Cast number Characterization Membrane results S electivity O Permeability O O z 30% unmodified particles LS -01-45A Turned into a gel N/ A N/ A N P x O with white y=2% precipitates (not useable) 10% surface modified 10 nm LIS -01-41 A S EM, TGA, DS C, 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- S EM, TGA, DS C, 1609 44 particles 43 membrane testing 60% loading 60% surface modified 10 nm LIS -01-51A* TGA, DS C, 250-400 25-30 particles Membrane 23 testing
Membrane Performance • Membrane of half a micron would yield permeance of 3200 1000 Literature data GPU with a selectivity of 44 for This work Robeson upper bound CO 2 / N 2 separation. CO 2 /N 2 selectivity 100 • Work is being performed to convert these materials properties into membranes ― 10 Open for collaborations • Module design― Open for 1 1 10 100 1,000 10,000 collaborations and j oint research. CO 2 permeability (Barrer) 24
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