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Modeling Transient Adsorption/Desorption Behavior in a
Gas Phase Photocatalytic Fiber Reactor
Siegfried Denys, Jeroen van Walsem [email protected]
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
VOC’s
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
𝑟𝑎𝑑𝑠 = 𝒌𝒂𝒅𝒔𝐶𝐴𝑐𝑎𝑙,𝑏𝑢𝑙𝑘(1 − 𝜃𝐴𝑐𝑎𝑙)
𝑟𝑑𝑒𝑠 = 𝒌𝒅𝒆𝒔𝜃𝐴𝑐𝑎𝑙
𝑟𝑎𝑙𝑑𝑜𝑙 = 𝒌𝒂𝒍𝒅𝒐𝒍(𝐶𝐴𝑐𝑎𝑙,𝑓𝑖𝑙𝑡𝑒𝑟)2
Introduction Fiber reactor Comsol model Comsol model incl.
adsorption/desorption Conclusions
𝜃𝐴𝑐𝑎𝑙 =𝐶𝐴𝑐𝑎𝑙,𝑓𝑖𝑙𝑡𝑒𝑟
𝛤𝑓𝑖𝑙𝑡𝑒𝑟
• 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