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  • Modeling Transient Adsorption/Desorption Behavior in a

    Gas Phase Photocatalytic Fiber Reactor

    Siegfried Denys, Jeroen van Walsem Siegfried.denys@uantwerpen.be

  • Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    2

    Photocatalysis: principle Catalyst: increases reaction rate without being consumed

    Photo-catalyst: catalyst activated by (UV-)light

    Most often titanium dioxide (TiO2)

    Po

    ten

    tia

    l (v

    s. S

    HE

    ) [V

    ]

    -1.0

    -0.5

    0.0

    0.5

    1.0

    1.5

    2.0

    2.5

    3.0Valence band

    Conduction band e- (-0.52)

    h+ (+2.53)

    hn Eg

    H2/H2O (-0.413)

    O2/H2O (+0.83)

    O2/O2- (-0.28)

    OH/H2O (+2.27)

    TiO2

    Red

    Red

    Ox

    Ox

    VOCs

    H2O, CO2

  • 3

    Photocatalysis: application fields

    Water purification/desinfection

    Self-cleaning materials

    Air purification

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

  • 4

    Gas phase photocatalytic fiber reactor

    TiO2

    Tubular photoreactor

    UV source

    Inlet: air acetaldehyde controlled C

    and Q Outlet: (to FTIR

    spectroscope)

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

  • To model the transient, dynamic adsorption/desorption of acetaldehyde as contaminated air flows through the reactor

    To estimate the adsorption/desorption rate constants

    5

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    Comsol model: goals

  • 6

    Comsol model: geometry

    Air outlet

    Air inlet

    FTIR cell (measurement)

    Fiber

    Fiber

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    Approx . 80,000 tetrahedral cells + refinement

  • 7

    Comsol model: Physics

    Laminar flow (Re < 800)

    Darcy equation (single-phase gas flow in a porous medium)

    stationary solver

    Species transport in porous media (incl. free flow)

    time dependent solver

    bulkAcalbulkAcal

    bulkAcal CCDt

    C,,

    ,

    u

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

  • 8

    Comsol results: no adsorption

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

  • 9

    Langmuir adsorption/desorption

    = ,(1 )

    =

    = (,)2

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    =,

  • Laminar flow (Re < 800)

    Darcy equation (single-phase gas flow in a porous medium)

    stationary solver

    Species transport in porous media (incl. free flow)

    Domain ODE

    time dependent solver + optimization solver (SNOPT)

    10

    Comsol physics incl. adsorption/desorption

    ttCFDoutAcaltxpeoutAcal

    aldoldesadsfilterAcal

    desadsbulkAcalbulkAcalbulkAcal

    CCObj

    rrrt

    C

    rrCCDt

    C

    2

    ,,,,,,

    ,

    ,,, u

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

  • 11

    Comsol results incl. adsorption/desorption

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    Parameters from analysis (exp) Parameters from Comsol optimization

    filter (mol kg-1

    ) K (m3

    mol-1

    ) filter (mol kg-1

    ) K (m3

    mol-1

    )

    Sample A 0.0126 255 0.0119 220

    Sample B 0.0425 222 0.0382 221

  • 12

    Conclusions

    Introduction Fiber reactor Comsol model Comsol model incl.

    adsorption/desorption Conclusions

    CFD/multiphysics is a versatile tool for parameter estimation:

    Time dependent solution

    Spatial distribution

    Implicit correction for air displacement

    Extension of Langmuir model

    1 vs several experiments

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