Natural Gas Storage on Nanoporous Carbon Jacob Burress , Mikael - - PowerPoint PPT Presentation

Natural Gas Storage on Nanoporous Carbon

Jacob Burress, Mikael Wood, Sarah Barker, John Flavin, Cintia Lapilli, Parag Shah, Galen Suppes, Peter Pfeifer Alliance for Collaborative Research in Alternative Fuel Technology University of Missouri, Columbia, MO 65211

Overview Overview

• Powdered and monolithic

Powdered and monolithic activated carbons have been activated carbons have been made with corn cob as starting made with corn cob as starting material that have a large material that have a large methane storage capacity methane storage capacity

• Pore Space Structure

Pore Space Structure Analyzed: Analyzed:

• small angle x-ray scattering

small angle x-ray scattering (SAXS) (SAXS)

• computer simulations of pore

computer simulations of pore formation formation

• nitrogen adsorption isotherms

nitrogen adsorption isotherms

• scanning and transmission

scanning and transmission electron microscopy electron microscopy (SEM/TEM) (SEM/TEM)

• methane adsorption isotherms

methane adsorption isotherms

Why are Nanopores Important? Why are Nanopores Important?

• In narrow pores, van

der Waals potentials

• verlap; creating a

deep energy well

• Max. CH4 capacity in

pores of width 1.1 nm (simulations)

• van der Waals

potential of CH4 in pore

• f width 1.1 nm
• Energy loss more than

enough to compress CH4 into dense fluid; remaining energy heat

Binding energy: Binding energy: 17 17 kJ/mol kJ/mol

Nicholson (Carbon Vol. 36, 1998)

Why are Nanopores Important? Why are Nanopores Important?

~3.7 Å

Width Width ~6 Å ~6 Å Width Width ~11 Å ~11 Å Width Width ~22 Å ~22 Å

Definitions of Uptake Values Definitions of Uptake Values

( )

, , , ,

1

BulkGas Stored Chamber Sample Gas Chamber Gas Chamber Sample Chamber Piece

m m m m m

• =
• Stored Gas

Stored Gas Pore Pore Adsorbed Film Adsorbed Film Bulk (non-adsorbed) Gas Bulk (non-adsorbed) Gas Absolute Adsorbed Gas Absolute Adsorbed Gas

( )

, , , ,

1

absolute BulkGas adsorbed Chamber Sample Gas Chamber Gas Chamber Sample Chamber AdsorbedFilm BulkGas Skeletal

m m m m m V

• =
• +
• Gibb

Gibb’ ’s Excess Adsorbed s Excess Adsorbed Gas Gas

( )

, , , ,

1

Excess BulkGas Adsorbed Chamber Sample Gas Chamber Gas Chamber Sample Chamber Skeletal

m m m m m

• =

Methane Uptake Methane Uptake

N/A N/A 230-239 g/kg 230-239 g/kg M/M M/M 180 L/L 180 L/L 176-182 L/L 176-182 L/L V/V V/V 118 g/L 118 g/L 115-119 g/L 115-119 g/L M/V M/V ANG DOE ANG DOE Target Target ALL-CRAFT Best ALL-CRAFT Best Performance S- Performance S- 33/k 33/k

• Methane uptake measured

Methane uptake measured gravimetrically on powder gravimetrically on powder samples, monoliths measured samples, monoliths measured volumetrically as well. volumetrically as well.

• Values below reported as amount

Values below reported as amount

• f methane stored using a
• f methane stored using a “

“powder powder density density” ” of 0.5 g/ml

• f 0.5 g/ml

Summary of Storage Densities Summary of Storage Densities

119 g/L 118 g/L 24.9 g/L

Small Angle X-ray Scattering Small Angle X-ray Scattering

2r 2r L L

( )

2 2

• I q

r L =

Scattering from a cylinder, with finite Scattering from a cylinder, with finite thickness. thickness.

( ) ( )

( )

( )

( )

( ) ( ) ( )

2 2 / 2 1 4 2 2 2 2

sin cos * sin sin sin cos qL J qr I q d q L r

• =

Scattering in the limit L>>r Scattering in the limit L>>r

( ) ( ) ( ) ( ) ( )

1 1 1

sin 1 cos 1 . . , for

qL

u qL I q const du qL u qL I q const qL L q r

• =
• ( )

2 I q L

• ( )

1 I q qL

• ( )

6

2.3

Surface D

D I q q

Spanning Cluster Pore Space

Computer Modeling of Pore Computer Modeling of Pore Formation Formation

Two stage probabilistic

cellular automata (PCA) rule (two separate PCA’s in succession).

Pore space opened from inside out Pore space opened from

• utside in, creating a

spanning cluster

This models a two stage

activation process.

Qualitatively this model

fits well with observed data.

Carbon Non-Spanning Cluster Pore Space

SEM/TEM SEM/TEM

• Due to the small size of the

Due to the small size of the pores, ultra high resolution pores, ultra high resolution mode was used on the mode was used on the Hitachi S-4700 FESEM. Hitachi S-4700 FESEM. Beam energy was set to 5 kV Beam energy was set to 5 kV with a small working distance with a small working distance (3-4mm) (3-4mm)

• The beam energy was set to

The beam energy was set to 100 and 120 kV for the JEOL 100 and 120 kV for the JEOL 1200EX TEM 1200EX TEM

• Top image SEM on sample

Top image SEM on sample S-33/k, showing entrance to S-33/k, showing entrance to pore network pore network

• Bottom image TEM on

Bottom image TEM on sample S-56 showing ~1.5 sample S-56 showing ~1.5 nm wide pore nm wide pore

200 nm

200 nm 5.00 μm

S-33/k

Nitrogen Adsorption Isotherms Nitrogen Adsorption Isotherms

• Nitrogen isotherms show

Nitrogen isotherms show evidence of strong evidence of strong microporosity microporosity

• Plateau on linear isotherm

Plateau on linear isotherm

• BET surface area of ~2,200

BET surface area of ~2,200 m m2

2/g for sample S-33/k

/g for sample S-33/k

• Surface area of most recent

Surface area of most recent samples found to be ~3,000- samples found to be ~3,000- 3,500 m 3,500 m2

2/g

/g

• Gives total pore volume of

Gives total pore volume of 1.22 cc/g, porosity of 0.71 1.22 cc/g, porosity of 0.71

• Note: Surface area for

Note: Surface area for graphene graphene sheet (both sides) sheet (both sides) is 2,965 m is 2,965 m2

2/g (

/g (Chae Chae et. al.

• et. al.

Nature Nature Vol Vol 427 2004) 427 2004)

Pore Size Distribution from Pore Size Distribution from Nitrogen Isotherm Nitrogen Isotherm

• Done using non-local density functional theory (NLDFT) assuming

Done using non-local density functional theory (NLDFT) assuming slit-shaped pores slit-shaped pores

• Shows dominance of nanopores, especially pores width ~1.1nm

Shows dominance of nanopores, especially pores width ~1.1nm

S-33/k Peak at ~1.13 nm

Methane Adsorption Isotherms Methane Adsorption Isotherms

• Langmuir gives

Langmuir gives good fit of data good fit of data which is consistent which is consistent with the hypothesis with the hypothesis that surface is that surface is covered primarily covered primarily with a single with a single monolayer of monolayer of methane methane

• Langmuir

Langmuir parameter of parameter of b=0.814 MPa b=0.814 MPa-1

• 1
• Asymptotic value of 288.5 grams of adsorbed methane per

Asymptotic value of 288.5 grams of adsorbed methane per kilogram carbon kilogram carbon

• Langmuir fit gives a binding energy of ~22.7 kJ/mol, which

Langmuir fit gives a binding energy of ~22.7 kJ/mol, which is consistent with the high uptake values is consistent with the high uptake values

0.000 0.100 0.200 0.300 0.400 0.500 . 4

• .

6 . 6

• 1

. 1 .

• 1

. 5 1 . 5

• 2

. 2 .

• 4

. 4 .

• 6

. 6 .

• 1

. 1

• 1

5 1 5

• 2

2

• 5

> 5 Pore Width Range [nm] Pore Volume [cc/g]

Pore Size Distribution from Pore Size Distribution from Methane Isotherm Methane Isotherm

• Shows dominance

Shows dominance

• f nanopores,
• f nanopores,

especially in pores especially in pores

• f width 6-15 Å
• f width 6-15 Å
• Gives total pore

Gives total pore volume of 1.513 volume of 1.513 cc/g, porosity of cc/g, porosity of 0.752 0.752

• Determined via

Determined via method from method from Sosin Sosin and Quinn, and Quinn, Carbon 34 1335 Carbon 34 1335 (1996) (1996)

S-33/k

Comparison of Methods Comparison of Methods

0.000 0.100 0.200 0.300 0.400 0.500 0.4 - 0.6 0.6 - 1.0 1.0 - 1.5 1.5 - 2.0 2.0 - 4.0 4.0 - 6.0 6.0 - 10.0 10 - 15 15 - 20 20 - 50 >50 Pore Width Range [nm] Pore Volume [cc/g]

Methane Nitrogen

~15 ~15 ~4 ~4 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A SAXS SAXS N/A N/A ~11 ~11 0.021 0.021 0.094 0.094 1.107 1.107 1.222 1.222 0.710 0.710 Nitrogen Nitrogen N/A N/A ~11 ~11 0.062 0.062 0.254 0.254 1.197 1.197 1.513 1.513 0.752 0.752 Methane Methane Average Average Nanopore Nanopore Length [Å] Length [Å] Average Average Nanopore Nanopore Width [Å] Width [Å] Macropore Macropore (>50 nm) (>50 nm) Volume Volume [cc/g] [cc/g] Mesopore Mesopore (2 (2– –50 nm) 50 nm) Volume Volume [cc/g] [cc/g] Micropore Micropore (pore diameter (pore diameter 0.5 0.5– –2 nm) 2 nm) Volume [cc/g] Volume [cc/g] Total Pore Total Pore Volume Volume [cc/g] [cc/g] Porosity Porosity

TEM TEM

Conclusions and Future Conclusions and Future

• Activated Carbon made from Missouri corn cob

Activated Carbon made from Missouri corn cob has proven to be an excellent candidate for has proven to be an excellent candidate for alternative fuel storage at a low cost. alternative fuel storage at a low cost.

• Department of energy target of 118 g/L has been

Department of energy target of 118 g/L has been met. met.

• Carbon has been analyzed with a variety of

Carbon has been analyzed with a variety of methods which give consistent results. methods which give consistent results.

• Carbon is still being optimized.

Carbon is still being optimized.

• Still getting results from the test fixture on the

Still getting results from the test fixture on the pickup. pickup.

• Shows promise for hydrogen storage as well

Shows promise for hydrogen storage as well (Mikael Wood et. al. 1:51 PM today in room (Mikael Wood et. al. 1:51 PM today in room 502). 502).

200 nm

5.00 μm 5.00 μm 100 nm

Density Functional Theory Pore Density Functional Theory Pore Volume Distribution Volume Distribution

• Non-Local Density Functional Theory (NLDFT)

Non-Local Density Functional Theory (NLDFT) for slit-shaped pores was used. for slit-shaped pores was used.

• Relationship between this theory and the

Relationship between this theory and the experimental data is given by the generalized experimental data is given by the generalized adsorption isotherm (GAI) adsorption isotherm (GAI) where N(P/P0) is the experimental adsorption where N(P/P0) is the experimental adsorption isotherm data, W is the pore width, N(P/P0,W) is isotherm data, W is the pore width, N(P/P0,W) is the isotherm on a single pore of width W, and the isotherm on a single pore of width W, and f(W) is the pore size distribution function. f(W) is the pore size distribution function.

( )

0 ,

MAX MIN

W W

P P N N W f W dW P P

• =

Brunauer-Emmett-Teller Surface Brunauer-Emmett-Teller Surface Area Area

• Most widely used method for determination of surface

Most widely used method for determination of surface area of solids area of solids

• BET Formula given by:

BET Formula given by:

• where m is the mass of gas adsorbed at a relative pressure

where m is the mass of gas adsorbed at a relative pressure (P/P (P/P0

0) (P

) (P0

0 taken as the saturation pressure of adsorptive gas),

taken as the saturation pressure of adsorptive gas), m mmono

mono

is the mass of adsorbate constituting a monolayer of is the mass of adsorbate constituting a monolayer of surface coverage, and C is the BET constant. surface coverage, and C is the BET constant.

( )

1 1 1

mono

P C P m m P P C P P =

• +

BET Theory Cont. BET Theory Cont.

• BET equation in linear form:

BET equation in linear form:

• N

NA

A is Avogadro

is Avogadro’ ’s number, s number, A ACrossSection

CrossSection is the cross-sectional area of

is the cross-sectional area of the gas molecule, and M is the molecular mass of the gas. the gas molecule, and M is the molecular mass of the gas.

• A

ACrossSection

CrossSection for Nitrogen is 16.2 Å

for Nitrogen is 16.2 Å2

2/molecule

/molecule

1 1 1

mono mono

P P C P P Cm Cm P m P

• =

+

• 1

mono

C slope Cm

• =

1

mono

intercept Cm =

1

mono

m slope intercept

• =

+

mono A CrossSection Total

m N A Total Surface Area S M = =

Methane Binding Energy Methane Binding Energy

1 ( )

q RT

T b T Langmuir parameter e p T

• =

=

• 1

293 152.4 ln 0.814 K J q MPa p g T

• =
• ln

T q specific heat of adsorption RT bp T

• =

=

• (

)

, 293 0.52 p T are the reference pressure and temperature T is the Absolute temperature room temperature K Universal Gas Constant R is the Specific Gas Constant Molar Mass J R for methane g K = =

Methane Binding Energy Methane Binding Energy

00 /(

) 3 3

1 8

U kT x y z

kT b e m

• =

Localized Adsorption Localized Adsorption

( , ) min ( , , )

z

U x y U x y z

< <

• 1

00 2 (

)

x y z

U h

• +

+ +

• 1

12 1 A

0.814 MPa 3.00 10 s (0.0160 kg/mol) / 293 K

z

b m N T

• =

=

• =

=

x y z

assume

• =

=

NA = 22.7 kJ/mol

T.L. Hill, An Introduction to Statistical Thermodynamics (Dover, 1986).

• G. Bomchil et al., “Structure and dynamics of methane

adsorbed on graphite.” Phil. Trans. Roy.

• Soc. Lond. B 290, 537-552 (1980).

Why are Nanopores Important? Why are Nanopores Important?

3.7 Å ~11 Å 1.9 Å ~4 Å ~22 Å

Small Angle X-ray Scattering Small Angle X-ray Scattering

Scattering in the limit L>>r Scattering in the limit L>>r

( )

1 I q qL

• ( )

2 I q L

• ( )

2 2

• I q

r L =

2r 2r L L

( ) ( ) ( ) ( ) ( )

1 1 1

sin 1 cos 1 . . , for

qL

u qL I q const du qL u qL I q const qL L q r

• =
• Scattering from a cylinder, with finite

Scattering from a cylinder, with finite thickness. thickness.

( ) ( )

( )

( )

( )

( ) ( ) ( )

2 2 / 2 1 4 2 2 2 2

sin cos * sin sin sin cos qL J qr I q d q L r

• =

2.3

Surface

D