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Adsorption Models for Coalbed Methane Production and CO2 ... · Adsorption Models for Coalbed Methane Production and CO 2 Sequestration K. A. M. Gasem ... properties and coal matrix

May 22, 2020

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  • November 12, 2004 1

    Oklahoma State University

    School of Chemical Engineering

    Adsorption Models for Coalbed Methane Production and CO2 Sequestration

    K. A. M. GasemR. L. Robinson, Jr.

    (Principal Investigators)

    Z. Pan J. E. Fitzgerald

    M. Sudibandryio

    Oklahoma State University

    Sponsored by theU.S. Department of Energy

  • November 12, 2004 2

    Oklahoma State University

    School of Chemical Engineering

    Equilibrium Adsorption Modeling

    § We seek simple, reliable adsorption equilibrium models that are suitable for generalized predictions and reservoir simulations.

    § Such models should:

    – Precisely represent pure and mixture isotherms

    – Facilitate accurate a priori predictions based on gas properties and coal matrix characterization

    Strategy: Use rigorous methodologies rooted in fundamentals to develop reliable methods of high industrial utility.

  • November 12, 2004 3

    Oklahoma State University

    School of Chemical Engineering

    Excess Ads. = Vads (ρads- ρgas)

    Pressure

    Exc

    ess

    Ad

    s.

    § At low pressures the isothermis nearly linear and ρads>>ρgas

    Local Density Near Surface

    Excess Adsorption: Near-Critical Behavior

  • November 12, 2004 4

    Oklahoma State University

    School of Chemical Engineering

    Pressure

    Exc

    ess

    Ads

    .

    § At higher pressures the isotherm has some curvature

    Local Density Near Surface

    Excess Ads. = Vads (ρads- ρgas)

    Excess Adsorption: Near-Critical Behavior

  • November 12, 2004 5

    Oklahoma State University

    School of Chemical Engineering

    Pressure

    Exc

    ess

    Ads

    .

    § At higher pressures the isotherm has some curvature and an excess adsorption maximum is reached.

    Local Density Near Surface

    Excess Ads. = Vads (ρads- ρgas)

    Excess Adsorption: Near-Critical Behavior

  • November 12, 2004 6

    Oklahoma State University

    School of Chemical Engineering

    Pressure

    Exc

    ess

    Ads

    .

    § The isotherm shape will eventually change concavity.

    Local Density Near Surface

    Excess Ads. = Vads (ρads- ρgas)

    Excess Adsorption: Near-Critical Behavior

  • November 12, 2004 7

    Oklahoma State University

    School of Chemical Engineering

    Pressure

    Exc

    ess

    Ads

    .

    § The excess adsorption will pass through zero at sufficiently high pressures.

    Local Density Near Surface

    Excess Adsorption: Near-Critical Behavior

    Excess Ads. = Vads (ρads- ρgas)Does this mean that coalbed reservoirs contain lessnatural gas at higher pressures?

  • November 12, 2004 8

    Oklahoma State University

    School of Chemical Engineering

    Excess and Absolute Adsorptionand Gas Capacity

    § Even though the excess adsorption, nE passes through a maximum and eventually through zero,the absolute adsorption, nA increases with pressure.

    Pressure

    Ads

    orpt

    ion

    Qua

    ntity

    § The gas capacity, nGCdenotes how much gas (both adsorbed and unadsorbed) is in the volumetric container of arbitrary Vvoid.

    nGC= nE+ρgasρhelium

    1φpack

    -1

    nA= nE+ Vads ρgas

    φpack =ρhelium

    ρapparent =Adsorbent volume

    Total volume§ The excess adsorption is

    sometimes called the Gibbs excess adsorption because it assumes two distinct phases, the adsorbed phase, and the unadsorbed phase.

  • November 12, 2004 9

    Oklahoma State University

    School of Chemical Engineering

    Comparison of Gibbs Excess, Absolute Adsorption and Gas-Capacity of Carbon Dioxide on Dry Activated

    Carbon at 45°C

    0

    5

    10

    15

    20

    25

    30

    0 2 4 6 8 10 12 14

    Pressure (MPa)

    Adso

    rptio

    n o

    r Am

    ount

    (mm

    ol/g

    )

    Gibbs Excess, SLD ModelAbsolute AdsorptionGas-In-Place

    0.529 g/cc Apparent Density

  • November 12, 2004 10

    Oklahoma State University

    School of Chemical Engineering

    Experimental Facility

    • Two experimental apparatuses are used in current studies.

    • The mass balance approach is employed in both.

    • Expected uncertainty in the measurements is estimated at:– 2% for the pure fluids – 6% for the mixtures

  • November 12, 2004 11

    Oklahoma State University

    School of Chemical Engineering

    Vacuum Pump

    Pressure Temp.

    Heat Exchanger

    Air Temperature BathRuska Pump

    Vent

    Water Heaterand Pump

    Pressure

    Equ

    ilibr

    ium

    Cel

    l

    Mag

    netic

    Pum

    p

    Temp.

    Vent

    Air Temperature Bath

    Motor

    SamplingValve

    Gas ChromotagraphHe CH4 CO2 N2 C2 He

    Experimental DesignThe experimental method employs a mass balance principle, based on careful volumetric measurements.

  • November 12, 2004 12

    Oklahoma State University

    School of Chemical Engineering

    § Volumetric measurements§ Moisture content § PVT density predictions § Adsorbed phase density estimates

    Factors Affecting Equilibrium CBM Adsorption Measurements

  • November 12, 2004 13

    Oklahoma State University

    School of Chemical Engineering

    CO2 and Ethane Adsorption on Activated Carbon (OSU)

    0

    2

    4

    6

    8

    10

    0 2 4 6 8 10 12 14

    Pressure (MPa)

    Adso

    rptio

    n (m

    mol/g

    )

    Carbon Dioxide, Gibbs

    Carbon Dioxide, Absolute

    Ethane, Gibbs

    Ethane, Absolute

  • November 12, 2004 14

    Oklahoma State University

    School of Chemical Engineering

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    0 500 1000 1500 2000

    Pressure, psia

    Ads

    orpt

    ion,

    mm

    ol/g

    Absolute Adsorption on Fruitland Coal at 115°F

    CO2

    Nitrogen

    Methane

  • November 12, 2004 15

    Oklahoma State University

    School of Chemical Engineering

    Mixture Adsorption on Illinois-6 Coal at 115°F

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    0 200 400 600 800 1000 1200 1400 1600 1800

    Pressure (psia)

    Abs

    olut

    e A

    dsor

    ptio

    n (m

    mol

    /g c

    oal) Pure CO2

    Mixture Total

    Pure CH4

    CO2 in Mixture

    CH4 in Mixture

    LRC

    Mixture is 60/40 CH4/CO2

  • November 12, 2004 16

    Oklahoma State University

    School of Chemical Engineering

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    1.6

    0.0 0.1 0.2 0.3 0.4 0.5

    Normalized Slit Width

    Loca

    l Den

    sity

    , g/c

    cStrategy: Use rigorous methodologies rooted in fundamentals to develop reliable models…

    Bulk Gas

    Adsorbate

    Mean Field Approximation

  • November 12, 2004 17

    Oklahoma State University

    School of Chemical Engineering

    Molecular Interactions

    Gas Molecule

    z L - z

    Coal Surface

    ( ) ( ) ( )zLzz 2fs1fsfs −µ+µ=µ

    ff

    fs1 fs2

    ρwall = 1 / b

    Local Density

    Area / 2

  • November 12, 2004 18

    Oklahoma State University

    School of Chemical Engineering

    Modeling Approach

    § Articulate the physics of the adsorption phenomenon.

    § Rely on VLE and PVT data to provide required model inputs for fluid-fluid (εff , σff ) interactions.

    § Generate fluid-solid (εfs, σfs ) interactions applicable to all models; e.g.,– εfs is estimated from theory or regressed– L is obtained from matrix pore distribution or regressed– A is regressed or obtained from accessible characterization

    § For matrix characterization, seek the ability to utilize limited adsorption data involving only one fluid.

  • November 12, 2004 19

    Oklahoma State University

    School of Chemical Engineering

    Selected Theories for Modeling High-Pressure Adsorption

    § Simplified Local Density Model(Rangarajan et al., 1995; Fitzgerald et al., 2003)

    § Ono-Kondo Lattice Model(Aranovich et al., 1996; Sudibandriyo, 2003)

    § Two-Dimensional Equation of State Model(DeGance, 1992; Zhou et al., 1994; Pan et al, 2003)

  • November 12, 2004 20

    Oklahoma State University

    School of Chemical Engineering

    SLD-EOS AdsorptionModeling: An Example

  • November 12, 2004 21

    Oklahoma State University

    School of Chemical Engineering

    The SLD model:

    § Provides a consistent theory which accounts for adsorbate-adsorbate (fluid-fluid) and adsorbate-adsorbent (fluid-solid) molecular interactions

    § Delineates the adsorbent structural properties based on assumed physical geometries of the adsorbent

    § Predicts the adsorbed-phase density, which facilitates prediction of absolute gas adsorption

    Why the SLD Model?

  • November 12, 2004 22

    Oklahoma State University

    School of Chemical Engineering

    The Simplified Local Density (SLD) Model

    z L-z -

    AdsorbentSurface

    Adsorbed Phase

    Bulk Phase[ ]bayPTf ibulki ,,,,ˆ

    r

    [ ]bzazxzPTf iadsi ),(),(),(,,ˆr

    ρ

    [ ]zfsiΨ

    ( )( )

    ( ) ( )0

    ˆ)(),(ˆ

    ln =−Ψ+Ψ

    +

    kT

    zLz

    yf

    zzxf fsifs

    ibulk

    i

    adsi

    r

    r ρEquilibrium Relationship:

  • November 12, 2004 23

    Oklahoma State University

    School of Chemical Engineering

    Fluid- Fluid Interactions within Slit

    Fluid-Fluid Interactions

    The fugacity near the surface is a function of position:

    ( )( )

    −+

    ++

    +

    −−

    =

    ∑∑

    21)(1

    21)(1ln

    )(

    )()(2)(2

    22

    )(

    )(ln1

    )(

    )(2

    )(

    )(ˆln

    bz

    bz

    za

    zazx

    b

    bbzx

    RTb

    za

    RT

    Pb

    RTz

    P

    RTz

    P

    b

    bbzx

    Pzx

    zf

    jijj

    jijj

    jijj

    i

    adsi

    ρ

    ρ

    ρρ

    Bulk- Phase Interactions[ ][ ]bbRT

    Ta

    bRT

    P

    ρρ

    ρ

    ρρ )21(1)21(1

    )(

    1

    1

    ++−+−

    −=PR-EOS:

  • November 12, 2004 24

    Oklahoma State University

    School of Chemical Engineering

    Fluid-Solid Interactions

    ρwall = 1 / b

    σff / 20.142 nmσ

    ss = 0.335 nm

    Slit Length L

    Local Density

    Area / 2

    z

    Depiction of a SlitWe use Lee’s partiallyintegrated (10-4) potentialmodel todescribe thefluid-solid interactions.

    ( ) ( ) ( )( )

    ( )( )[ ]

    σ−+′

    σ−

    σσεπρ=Ψ

    =

    4

    1 4

    4

    10

    102

    12

    1

    54)(

    iss

    ifsifs

    ifsifsatomsfs

    iizz

    z

  • November 12, 2004 25

    Oklahoma State University

    School of Chemical Engineering

    Extending SLD to Mixtures

    § We set Cij and Dij to zero for all component interactions in the gas phase

    § We regress Cij (Dij=0) in the adsorbed phase

    ∑∑=i j

    ijji axxa ∑∑=i j

    ijji bxxb

    ( ) 2/)C1(aaa ijjiij −+= ( ) 2/)D1(bbb ijjiij ++=

  • November 12, 2004 26

    Oklahoma State University

    School of Chemical Engineering

    Database Used§ We have assembled the OSU Adsorption Database

    which contains pure, binary, and ternary mixture adsorption measurements conducted at Oklahoma State University on eight different matrices.

    § Included in the database are details regarding:- Adsorbates, adsorbent, temperature, pressure,

    composition, and moisture content

    - Gibbs and absolute adsorption in both SI and English engineering units

    - The expected experimental uncertainty for each adsorption measurement

  • November 12, 2004 27

    Oklahoma State University

    School of Chemical Engineering

    OSU Adsorption Database

    0.7 – 13.7328.2CH4, CO2, N2, C2H6Dry Illinois #6, Beulah Zap, Wyodak, Upper Freeport, Pocahontas

    Coal

    77-81

    0.7 – 13.7319.3CH4, CO2, N2Wet LB Fruitland Coal74-76

    0.7 – 12.4328.2CH4, CO2, N2 MixturesWet Tiffany Coal70-73

    0.7 – 13.7328.2CH4, CO2, N2Wet Tiffany Coal67-69

    0.7 – 12.4319.3CH4, CO2, N2 MixturesWet Illinois #6 Coal64-66

    0.7 – 12.4319.3CH4, CO2, N2Wet Illinois #6 Coal61-63

    0.7 – 12.4319.3CH4, CO2, N2 MixturesWet Fruitland Coal58-60

    0.7 – 12.4319.3CH4, CO2, N2Wet Fruitland Coal55-57

    0.7 – 12.4318.2CH4, CO2, N2 MixturesDry AC – F 40051-54

    0.7 – 13.7318.2CH4, CO2, N2, C2H6Dry AC – F 40047-50

    Pressure Range (MPa)

    Temp (K)

    AdsorbateAdsorbentSys. No.

  • November 12, 2004 28

    Oklahoma State University

    School of Chemical Engineering

    Literature Database

    0.44 – 9.19178 - 298N2AC, Coconut shell 20

    0.05 – 0.8 294 - 351CH4, CO2AC, Norit RB118-19

    0.02 – 20.2303 - 318CO2AC, Calgon F-40017

    0.09 – 9.40233 - 333CH4AC, Coconut shell 16

    0.008 – 6.0 298CH4, CO2, N2AC, Norit R1 Extra 13-15

    0.05 – 3.35278 - 328CO2AC, F30/470 12

    0.11 – 6.69296 - 480CH4, CO2AC, PCB-Calgon Corp. 10-11

    0.003 – 3.84213 - 301CH4, C2H4, C2H6, CO2AC, BPL 6-9

    0.0 – 13.5283 - 333CH4, C3H8Charcoal4-5

    0.026 – 1.50311 - 422N2, CH4, C2H6AC, Columbia Grade L 1-3

    Pressure Range (MPa)

    Temp (K)

    AdsorbateAdsorbentSys. No.

  • November 12, 2004 29

    Oklahoma State University

    School of Chemical Engineering

    Literature Database – 2

    0.03 – 6.00 298CH4, CO2, N2 mixturesAC, Norit R1 Extra 43-46

    0.12 – 2.97301CH4,C2H4,C2H6mixtures

    AC, BPL39-42

    0.14 – 15.02298CH4, C2H6Zeolite, 13 X 37-38

    0.056 – 1.15283 - 303CH4, C2H4, C2H6Zeolite, G5 34-36

    2x10-5 – 0.21283 - 368CO2, H2S, C3H8H-Modernite 31-33

    0.03 – 17.61298 - 348CH4, CO2, N2, C2H6Zeolite, Linde 5A 27-30

    0.35 – 8.23298 - 348N2Zeolite, Linde 13 X 26

    0.03 – 14.56 298N2, CO2AC, Norit R1 24-25

    0.05 – 9.5303 - 383N2, CH4, C3H8AC, F30/470 21-23

    Pressure Range (MPa)

    Temp (K)

    AdsorbateAdsorbentSys. No.

    CBM Adsorbates: CH4, CO2, N2, C2H4, C2H6, C3H8, H2S

  • November 12, 2004 30

    Oklahoma State University

    School of Chemical Engineering

    Why Activated Carbon?

    § Modeling of adsorption behavior on coals is complicated by: - The difficulty in characterizing the coal matrix

    adequately

    - Assessing the effect of water on the adsorption behavior

    § Dry activated carbon provides a simpler reference matrix for modeling adsorption.

    § Desired models for adsorption on wet coals should apply readily for adsorption on dry activated carbon.

  • November 12, 2004 31

    Oklahoma State University

    School of Chemical Engineering

    We have developed:

    § State-of-the-art SLD, OK and 2-D EOS models and mixing rules to represent CBM adsorption equilibrium of pure fluids and mixtures within their experimental uncertainties.

    § Generalized and matrix-calibrated models to provide accurate predictions within one to three times the experimental uncertainties.

    § Improved computational capabilities, including robust algorithms for solving adsorption equilibrium for a variety of models.

    Model Development

  • November 12, 2004 32

    Oklahoma State University

    School of Chemical Engineering

    § Despite their different theoretical bases, in general, 2-D EOS, SLD, and OK models give comparable results in their correlative and predictive abilities based on the gas properties and the accessible characterization of the adsorbent.

    § Specifically the models:

    1. Correlate pure component adsorption within the experimental uncertainties (4% AAD).

    2. Predict all pure component adsorption within 10% AAD.

    Model Development - 2

  • November 12, 2004 33

    Oklahoma State University

    School of Chemical Engineering

    4. Correlate the total and individual component adsorption in the binary systems within the expected experimental uncertainties.

    5. Predict total adsorption for the binary and ternary systems studied within the expected experimental uncertainties.

    6. Predict the individual component adsorption in the binaryand ternary systems within twice the expected experimental uncertainties.

    7. Matrix-calibrated models provide reasonable predictions for high-pressure adsorption, typically within twice the expected experimental uncertainties

    Model Development - 3

  • November 12, 2004 34

    Oklahoma State University

    School of Chemical Engineering

    Sample Results

  • November 12, 2004 35

    Oklahoma State University

    School of Chemical Engineering

    SLD-PR Model Representation of Methane Adsorption on Various Wet Coals

    0.0

    0.2

    0.4

    0.6

    0.8

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0Pressure (MPa)

    Gib

    bs

    Ad

    sorp

    tio

    n (

    mm

    ol/g

    ) .

    Fruitland #2 at 319 KIllinois #6 at 319 KTiffany at 328 KLower Basin Fruitland at 319 K

  • November 12, 2004 36

    Oklahoma State University

    School of Chemical Engineering

    SLD Component Nitrogen Adsorption inMethane/Nitrogen Mixtures on Dry AC

    0

    1

    2

    3

    4

    0 500 1000 1500 2000Pressure (psia)

    Nitr

    og

    en E

    xces

    s A

    dso

    rptio

    n (m

    mo

    l/g)

    Methane/Nitrogen 80/20Methane/Nitrogen 60/40Methane/Nitrogen 40/60Methane/Nitrogen 20/80Pure NitrogenRepresentationPredictions

  • November 12, 2004 37

    Oklahoma State University

    School of Chemical Engineering

    Summary of Pure-Gas Adsorption Using 2-D Peng-Robinson (PR) EOS

    Regressing A and εfs for each system

    Generalized predictions

    0.60.0504.7432Coals

    --0.6178.61922Activated Carbons

    --0.1992.41922Activated Carbons

    Regressing σm,0, δ and εfs for each system

    0.60.0674.9432Coals

    --0.1081.4 1922Activated Carbons

    Regressing a, b, and k for each isotherm

    WAAERMSE%AADNPTSAdsorbents

  • November 12, 2004 38

    Oklahoma State University

    School of Chemical Engineering

    Deviation Plot of the Two-ParameterOK Model Results

    -40.0

    -30.0

    -20.0

    -10.0

    0.0

    10.0

    20.0

    30.0

    40.0

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0

    Pressure, MPa

    % D

    evia

    tio

    n

    Overall AAD = 3.6 %

  • November 12, 2004 39

    Oklahoma State University

    School of Chemical Engineering

    0.0

    2.0

    4.0

    6.0

    0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

    Pressure, MPa

    Gib

    bs

    Ad

    sorp

    tio

    n, m

    mo

    l/g A

    C

    303 K323 K343 K362 K 383 K Two-Parameter OK ModelGeneralized OK Model

    OK Model Predictions of Methane Adsorptions onDry Activated Carbon at Various Temperatures

  • November 12, 2004 40

    Oklahoma State University

    School of Chemical Engineering

    CH4 Absolute Adsorption for CH4 / CO2 onWet Fruitland Coal

    0

    0.1

    0.2

    0.3

    0.4

    0.5

    0.6

    0.7

    0.8

    0.9

    1

    0 200 400 600 800 1000 1200 1400 1600 1800 2000

    Pressure (psia)

    CH

    4 A

    bsol

    ute

    Ads

    orpt

    ion

    (mm

    ol/g

    )

    Pure CH4

    80% CH4

    60% CH4

    40% CH4

    20% CH4

    Wong-Sandler - Case 2

    One-fluid - Case 1

  • November 12, 2004 41

    Oklahoma State University

    School of Chemical Engineering

    0.0

    0.1

    0.2

    0.3

    0.4

    0.5

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

    Pressure (MPa)

    Gib

    bs A

    dsor

    ptio

    n (m

    mol

    /g)

    Pure CH4Total CH4 in Mixture

    Pure N2N2 in MixtureTwo-BIP OK ModelOK Predictions

    Gibbs Adsorption of a 50/50 Mole % CH4 / N2 Feed Mixture on Wet Tiffany Coal at 327.6 K

  • November 12, 2004 42

    Oklahoma State University

    School of Chemical Engineering

    -0.2

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

    Pressure (MPa)

    Gib

    bs A

    dsor

    ptio

    n (m

    mol

    /g)

    TotalCO2CH4N2OK from PureOK form Pure & Binary

    Total and Individual Gibbs Adsorption of a 10/40/50 Mole % CH4 / N2/CO2 Feed Mixture on Wet Tiffany Coal at 327.6 K

  • November 12, 2004 43

    Oklahoma State University

    School of Chemical Engineering

    0.0

    1.0

    2.0

    3.0

    4.0

    5.0

    6.0

    7.0

    8.0

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

    Pressure, MPa

    Gib

    bs

    Ad

    sorp

    tio

    n, m

    mo

    l/g A

    C

    CO2CH4N2C2H6OK ModelOK Predictions

    Matrix-Calibrated OK Model Predictions of Pure-Gas Adsorption on Dry Activated Carbon at 318.2 K

  • November 12, 2004 44

    Oklahoma State University

    School of Chemical Engineering

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    1.6

    1.8

    2.0

    0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

    Pressure (MPa)

    Gib

    bs

    Ad

    sorp

    tio

    n (

    mm

    ol/g

    Co

    al)

    WyodakBeulah ZapIllinois-6PocahontasUpper FreeportTwo-Parameter OK ModelOK Predictions

    Matrix-Calibrated OK Model Predictions of CO2 Adsorptions on Dry Coals at 328.2 K

  • November 12, 2004 45

    Oklahoma State University

    School of Chemical Engineering

    Pressure (MPa)

    0

    5

    10

    15

    20

    25

    0.0 2.0 4.0 6.0 8.0 10.0

    CH

    4A

    bso

    lute

    Ad

    sorp

    tio

    n (

    mm

    ol/g

    )

    Surface area and fluid-solid Interactionregressed based on 12 Data points 233 K

    293 K

    273 K

    253 K

    313 K

    333 K

    Matrix-Calibrated 2-D PR EOS Model Predictions of Methane Absolute Adsorption on Dry Activated Carbon

  • November 12, 2004 46

    Oklahoma State University

    School of Chemical Engineering

    Closure§ The SLD-EOS, OK, and 2D EOS, frameworks are

    effective for modeling high-pressure mixture adsorption.

    § The use of matrix-calibrated models will minimize the experimental effort required to obtain accurate adsorption predictions for a specific CBM site.

    § A potential exists for developing a priori predictive models using fully-generalized parameters determined by accessible adsorbate and adsorbent characterizations.

  • November 12, 2004 47

    Oklahoma State University

    School of Chemical Engineering

    However! To fully exploit the potential of the models in CBM recovery and CO2 sequestration processes, we need to:

    § Develop a more rigorous approach to account for the effect of water on CBM adsorption systems.

    § Develop an accurate equation of state, which exhibits accurate hard-sphere limiting behavior, to improve modeling of high-pressure gas adsorption.

    § Systematically-selected measurements should be conducted to expand our database on mixtures adsorption and delineate the effects of moisture content and competitive adsorption.

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