CO 2 Separations Using Room Temperature Ionic Liquids and Membranes Richard D. oble Alfred T. & Betty E. Look Professor of Chemical Engineering Douglas L. Gin Chemistry/ChBE Dept.
Ionic Liquids
Imidazolium-based Room Temperature Ionic Liquids (RTILs) Organic salts Become liquid at or below 100 C on-flammable egligible vapor pressure Thermally stable above 200 o C Polymerizable versions [emim] High CO 2 solubility Good CO 2 / 2 solubility selectivity [Tf 2 - ]
Henry s Constants (H) of CO 2, CH 4, and 2 at 40 C α = 25 RTILs CO 2 CH 4 2 [emim][dca] 95 2000 4800 [emim][tf 2 ] 46 550 1160 [emim][cf 3 SO 3 ] 71 1200 2700 [hmim][tf 2 ] 40 352 940 ILs Work by Solubility Selectivity
Amine Functionalized RTILs & RTILs with Free Amines
Amine Functionalized RTIL/RTIL Mixture H 2 Tf 2 H 2 (CH 2 ) 3 mmim Tf 2 Tf 2 hmim Tf 2
Happ (atm) 65.5 mole % [hmmim] [Tf2]/34.5 mole% [H 2 (CH 2 ) 3 mmim][tf 2 ] 20 18 16 14 12 10 8 6 4 2 0 0 500 1000 1500 2000 2500 3000 Time (min) α = 250
CO 2 Unloaded vs Loaded for a 50/50 mole % Mixture of MEA/[hmim][Tf 2 ]
RTIL-Amine Technology Exchange the water-amine solution with a RTIL-amine solution Reduces energy needed to heat solution by 1/3 to 1/2 Eliminates the energy lost to water evaporation RTILs do not evaporate Protects amine against oxidation/vapor press. loss
Membranes/Morphologies
CO 2 / 2 Permselectivity 100.0 Robeson Plot for CO 2 / 2 Region Attractive to Industrial Use 10.0 Flux selectivity trade-off Polymer membranes 1.0 1 10 100 1000 10000 100000 CO 2 Permeability (Barrers)
Membrane Terminology Flux = moles/(surface area time) = J J = (D S) ΔP L Permeability = (D S) Permeance = (D S) = Material Prop L Thickness
Membrane Terminology Permeability = (D S) Barrer Permeance = (D S) GPU 10 Barrer/0.1 micron = 100 GPU L
First-Generation Poly(RTIL) Gas Separation Membranes Synthesize RTIL monomers of the following types in two or three simple steps: O R 1 R 2 O Tf 2 R 1 = Me, Bu, Hx Tf 2 R 2 = Me, Bu Polymerize into (lightly crosslinked) films
eat polymerized RTIL no free RTIL O O O Tf Tf Tf Tf - Gemini vinylimidzolium - PES support
CO 2 / 2 Permselectivity Robeson Plot for CO 2 / 2 First generation 100.0 poly(rtil) membranes SILMs Region Attractive to Industrial Use 10.0 1.0 Styrene-based Acrylate-based Flux selectivity trade-off 1 10 100 1000 10000 100000 CO 2 Permeability (Barrers) Polymer membranes SILMs
Poly(RTILs) w/ Pendant Groups Tf 2 Tf 2 O O O Tf 2 Tf 2
CO 2 / 2 Permselectivity Poly(RTILs) Above Upper Bound 100.0 SILMs Region Attractive to Industrial Use 10.0 1.0 Poly (RTILs) PEG-Poly(RTILs) itrile-poly(rtils) Flux selectivity trade-off Polymer membranes SILMs 1 10 100 1000 10000 100000 CO 2 Permeability (Barrers)
Polymer RTIL Composites While poly(rtils) have good CO 2 separation properties, they have low P (D). Combine polymerizable imidazolium salts w/ non-polymerizable RTILs to improve diffusion? Tf 2 80% 20% Tf 2
Polymerizable RTIL + free RTIL O O O + Tf Tf 33 wt% Tf Tf Tf Tf 67 wt% o support On PES support
CO 2 / 2 Permselectivity Improved Permeability 100.0 SILMs Region Attractive to Industrial Use 10.0 1.0 Polymer RTIL Composite PEG-Poly(RTILs) itrile-poly(rtils) Flux selectivity trade-off Polymer membranes SILMs 1 10 100 1000 10000 100000 CO 2 Permeability (Barrers)
Gels: Solid etworks Physical Gel physically bonded network hydrogen bonding, van der Waals interactions, and π-π bond stacking sol-gel thermal transition
CO 2 / 2 Permselectivity Gel Membranes: Liquid-Like Permeability 100.0 SILMs Region Attractive to Industrial Use 10.0 1.0 Hmim/Tf 2 bulk Hmim/Tf 2 gel bulk Hmim/Tf 2 Supor supported Hmim/Tf2 gel Supor supported Poly(RTILs) Polymer membranes SILMs 1 10 100 1000 10000 100000 CO 2 Permeability (Barrers)
Membrane Terminology Permeability = (D S) Barrer Permeance = (D S) GPU L 10 Barrer/0.1 micron = 100 GPU (commercial polymer membrane) 1000 Barrer/0.1 micron = 10,000 GPU (gel membrane)
Figure 1: Effect of membrane CO 2 / 2 selectivity on the cost of capturing 90% of the CO 2 in flue gas for membranes with a CO 2 permeance of 1000, 2000, and 4000 gpu at a fixed pressure ratio of 5.5 4
Opportunities Ionic Liquid Design Different Morphologies Facilitated Transport Specific CO 2 Separations CO 2 / 2 post combustion (low P) CO 2 /H 2 precombustion (high T) CO 2 /CH 4 natural gas (high P)
Looking Ahead
Fabrication of SAPO 34 Poly(IL) Composite Membranes SAPO-34 100 nm UV light crosslinker Tf 2 poly(il) Tf 2 [emim][tf 2 ] 100 nm 10 wt% of SAPO-34 & (80-20)wt% of styrene poly(il) and [emim][tf 2 ] composite membrane Hudiono, Y.C., et.al., J. Membr. Sci. 2010(in pr 29
P(CO 2 )/P(CH 4 ) P(CO 2 )/P( 2 ) CO 2 /CH 4 & CO 2 / 2 Using 3- component Mixed Matrix Membranes 100 Increasing SAPO-34 loadings 100 (100-0) (60-40) (80-20) (60-40) (40-60) (100-0) (80-20) (40-60) 10 1 10 100 1000 P(CO 2 ) (Barrers) 10 1 10 100 1000 P(CO 2 ) (Barrers)
Imidazolium-Based Cationic Polymer Architectures Previously synthesized poly(imidazolium) architectures Rare or unprecedented poly(imidazolium) architectures (Radosz) (only 3 prior examples) (Bara, oble, Gin) (Ohno, Kato)
Ionene Membranes Ionene: main-chain polycation Imidazolium-based ionenes: R 1 + X R 2 X R 1 R 2 X X X = halide n R 1, R 2 = O O
Composites with anostructure Liquid crystals based on imidazolium salts can form ordered materials with nanometer scale pores filled with RTILs or other non-organic solvents C 12 BF 4 BF 4 O C 12 10 wt% BF 4
Phase Behavior of Other Imidazolium Gemini LLCs Br Br 4 (1/ 6) 3 + 30 wt % Br 3 Type I Q 230 (Ia3d) RTIL (1/ 8) RTIL Type I Q 224 (Pn3m) 2 (degrees) BF 4 O BF 4 3 + 10 wt % RTIL BF 4 4 RTIL (Jason Bara) Preferred LLC phase depends on choice of anion, bridge, and tail type
Composite Ionic Liquid Structures Will Provide High Selectivity Liquids High Permeabiltiy & Selectivity Membranes Huge Range of Materials Issues: Coating (Thickness) Mechanical Properties
SUMMARY Amine addition provides an order of magnitude increase in CO 2 loading and selectivity. Polymers synthesized that exceed the upper bound on Robeson plot. Composite structures provide enhanced P and maintain α. Gel membranes provide liquid-like P and maintain α.
Finish
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