CO2 Separations Using Room

Temperature Ionic Liquids and

Membranes

Richard D. NobleAlfred T. & Betty E. Look

Professor

of Chemical Engineering

Douglas L. GinChemistry/ChBE Dept.

Ionic Liquids

Imidazolium-based

Room Temperature Ionic Liquids (RTILs)

• Organic salts

• Become liquid at or below 100 C

• Non-flammable

• Negligible vapor pressure

• Thermally stable above 200oC

• Polymerizable versions

• High CO2 solubility

– Good CO2/N2

solubility selectivity

[emim]

[Tf2N-]

Henry’s Constants (H) of CO2,

CH4, and N2 at 40 C

RTILs CO2 CH4 N2

[emim][dca] 95 2000 4800

[emim][Tf2N] 46 550 1160

[emim][CF3SO3] 71 1200 2700

[hmim][Tf2N] 40 352 940

α = 25

ILs Work by Solubility Selectivity

Amine Functionalized RTILs & RTILs

with Free Amines

Amine Functionalized RTIL/RTIL

Mixture

N N

NH2

Tf2N

NN

Tf2N

hmim Tf2N

NH2(CH2)3 mmim Tf2N

65.5 mole % [hmmim] [Tf2N]/34.5 mole%

[NH2(CH2)3mmim][Tf2N]

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000 2500 3000

Hap

p (

atm

)

Time (min)

α = 250

CO2 Unloaded vs Loaded for a 50/50 mole %

Mixture of MEA/[hmim][Tf2N]

RTIL-Amine TechnologyExchange 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

1.0

10.0

100.0

1 10 100 1000 10000 100000

CO2 Permeability (Barrers)

CO

2 / N

2 P

erm

sele

cti

vit

yRobeson Plot for CO2/N2

Region Attractive to

Industrial Use

Polymer membranes

“Flux selectivity trade-off”

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

L

10 Barrer/0.1 micron = 100 GPU

First-Generation Poly(RTIL)

Gas Separation Membranes

• Synthesize RTIL monomers of the following types in two or three simple steps:

• Polymerize into (lightly crosslinked) films

NNR1

Tf2N

NNR2

Tf2N

O

O

R1 = Me, Bu, Hx R2 = Me, Bu

Neat polymerized RTIL – no free

RTIL

N NO

OO

N N

TfN

Tf TfN

Tf

- Gemini vinylimidzolium

- PES support

Region Attractive to

Industrial UseSILMs

1.0

10.0

100.0

1 10 100 1000 10000 100000

CO2 Permeability (Barrers)

CO

2 / N

2 P

erm

sele

cti

vit

yRobeson Plot for CO2/N2

Polymer membranes

“Flux selectivity trade-off”

First generation

poly(RTIL)

membranes

Styrene-based

Acrylate-basedSILMs

Poly(RTILs) w/ Pendant Groups

N N

Tf2N

OON N

Tf2N

O

N N

Tf2N

N N

Tf2N

NN

Poly(RTILs) Above Upper Bound

Polymer membranes

Region Attractive to

Industrial UseSILMs

1.0

10.0

100.0

1 10 100 1000 10000 100000

CO2 Permeability (Barrers)

CO

2 / N

2 P

erm

sele

cti

vit

y

“Flux selectivity trade-off”

SILMs

PEG-Poly(RTILs)

Nitrile-Poly(RTILs)

Poly (RTILs)

Polymer – RTIL Composites

• While poly(RTILs) have good CO2 separation

properties, they have low P (D).

• Combine polymerizable imidazolium salts w/

non-polymerizable RTILs to improve

diffusion?

N N

Tf2N

N N

Tf2N

80% 20%

Polymerizable RTIL + free

RTILN N

OO

ON N

TfN

Tf TfN

Tf

N N

TfN

Tf

+

33 wt% 67 wt%

On PES support

No support

Improved Permeability

Polymer membranes

Region Attractive to

Industrial UseSILMs

1.0

10.0

100.0

1 10 100 1000 10000 100000

CO2 Permeability (Barrers)

CO

2 / N

2 P

erm

sele

cti

vit

y

“Flux selectivity trade-off”

SILMs

PEG-Poly(RTILs)

Nitrile-Poly(RTILs)

Polymer – RTIL

Composite

Gels: Solid Networks

Physical Gel

physically bonded network

hydrogen bonding, van der

Waals interactions, and

π-π bond stacking

sol-gel thermal transition

Polymer membranes

Region Attractive

to Industrial UseSILMs

SILMs

Hmim/Tf2N Supor supported

Hmim/Tf2N gel Supor supported

Poly(RTILs)Hmim/Tf2N gel bulk

Hmim/Tf2N bulk

1.0

10.0

100.0

1 10 100 1000 10000 100000

CO2 Permeability (Barrers)

CO

2/N

2P

erm

sele

cti

vit

yGel Membranes: Liquid-Like Permeability

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 CO2/N2

selectivity on the cost of capturing 90% ofthe CO2 in flue gas for membranes with aCO2 permeance of 1000, 2000, and 4000gpu at a fixed pressure ratio of 5.54

Opportunities

Ionic Liquid Design

Different Morphologies

Facilitated Transport

Specific CO2 Separations

•CO2/N2 post combustion (low P)

•CO2/H2 precombustion (high T)

•CO2/CH4 natural gas (high P)

Looking Ahead

Fabrication of SAPO – 34 – Poly(IL)

Composite Membranes

29

100 nm

UV light

crosslinker

NN

Tf2N

poly(IL)

NN

Tf2N

[emim][Tf2N]

SAPO-34

10 wt% of SAPO-34 &(80-20)wt% of styrene poly(IL) and

[emim][Tf2N] composite membrane

Hudiono, Y.C., et.al., J. Membr. Sci. 2010(in press)

100 nm

10

100

1 10 100 1000

P(C

O2)/

P(C

H4)

P(CO2) (Barrers)

10

100

1 10 100 1000

P(C

O2)/

P(N

2)

P(CO2) (Barrers)

CO2/CH4 & CO2/N2 Using 3-

component Mixed Matrix Membranes

(100-0)

(80-20)

(60-40) (40-60)

Increasing SAPO-34 loadings

(100-0)(80-20)

(60-40)

(40-60)

Imidazolium-Based Cationic Polymer

Architectures

(Ohno, Kato)

Rare or unprecedented poly(imidazolium) architecturesPreviously synthesized

poly(imidazolium) architectures

(Radosz)

(Bara, Noble, Gin)

(only 3 prior examples)

Ionene Membranes

Ionene: main-chain polycation

Imidazolium-based ionenes:

N N R1 N N X R2 XN N R1 N N R2

X X n

+

X = halide

OO

R1, R2 =

Composites with Nanostructure

• Liquid crystals based on imidazolium

salts can form ordered materials with

nanometer scale pores filled with RTILs

or other non-organic solvents

NN C12NNC12

BF4 BF4

O

NN

BF4

10 wt%

3

2 (degrees)

3 + 30 wt %(1/√6)

(1/√8)

RTILType I Q230 (Ia3d)

Type I Q224 (Pn3m)

Phase Behavior of Other Imidazolium Gemini LLCs

3 + 10 wt % RTIL

4

• Preferred LLC phase depends on

choice of anion, bridge, and tail type (Jason Bara)

RTIL

RTIL

N

N

Br

N

N

BF4

N

N N

N

Br Br4

N

N

BF4

ON

N

BF4

• 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 CO2 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

The University of Colorado