Kinetic parameters for gas phase photocatalysis: analytic versus multiphysics approach Siegfried Denys, Sammy Verbruggen & Silvia Lenaerts TiO2 gas phase Research goals photocatalysis Intrinic kinetic parameters Analytic model Comsol model Photocatalysis Catalyst: increases reaction rate without being consumed Photo-catalyst: catalyst activated by (UV-)light Most often titanium dioxide (TiO2) -1.0 TiO2 Conduction band P o te n tia l (vs. SH E ) [V ] -0.5 0.0 0.5 H2/H2O (-0.413) O2/O2-• (-0.28) Red VOC’s Ox hn ≥ Eg O2/H2O (+0.83) 1.0 1.5 Red 2.0 h+ (+2.53) 2.5 3.0 2 e- (-0.52) Valence band •OH/H O (+2.27) 2 Ox H2O, CO2 TiO2 gas phase photocatalysis Research goals Intrinic kinetic parameters Analytic model Comsol model Photocatalysis: application fields Water purification/desinfection Air purification Self-cleaning materials 3 TiO2 gas phase photocatalysis Research goals Intrinic kinetic parameters Analytic model Comsol model Research goals Main goal: development of suitable photoreactors for air purification Sub goal: determination and exploitation of the main catalyst characteristics driving photocatalytic activity in the gas phase 4 TiO2 gas phase photocatalysis Research goals Intrinic kinetic parameters Analytic model Comsol model Intrinsic kinetic parameters Slit covered by quartz plate UVA lamp Inlet Sealing rubber Outlet Flat bed photoreactor HVAC photoreactor Tubular photoreactor (glass fibre) 5 TiO2 gas phase photocatalysis Intrinic kinetic parameters Research goals Analytic model Comsol model Intrinsic kinetic parameters VOCbulk kads VOCs kdes Langmuir adsorption: fractional coverage of VOC on an illuminated TiO2 surface θ VOC K L C VOC 1 K L C VOC kLH Unimolecular LangmuirHinshelwood mechanism: r k LH θ VOC Intrinsic kinetic parameters 6 H2O, CO2 k LH K L C VOC 1 K L C VOC k app C VOC TiO2 gas phase Research goals photocatalysis Intrinic kinetic parameters Analytic model Comsol model Analytic model r k LH θ VOC 1 k app 1 K Lk k LH K L C VOC 1 K L C VOC 1 k k app C VOC C VOC Plot of kapp-1 ()and h () versus the average surface concentration CVOC for a) 1.1 mW cm-2, b) 1.8 mW cm-2 and c) 2.6 mW cm-2 incident UVA intensity 7 TiO2 gas phase Intrinic kinetic parameters Research goals photocatalysis Analytic model Comsol model Analytic model: mass transfer Mass conservation: Slit covered by quartz plate UVA lamp G C VOC , (x) x dx j ( x ) pdx Mass convection at the boundary: Inlet j( x ) Sealing rubber Outlet C VOC , (x) 1 h mass ( x ) 1 k app ( x ) Solution: Cout p L Cin x 8 dx C VOC Kt , , out C VOC , , in e 1 1 h mass 1 k app KtA G TiO2 gas phase Research goals photocatalysis Intrinic kinetic parameters Analytic model Comsol model Slit covered by quartz plate UVA lamp Inlet • • • • Sealing rubber Outlet b) inlet 250,000 cells Laminar flow catalyst surface Transport of diluted species outlet Surface reaction r 9 a) k LH K L C VOC 1 K L C VOC c) Comsol model TiO2 gas phase photocatalysis Research goals Intrinic kinetic parameters Analytic model Comsol model Comsol model: optimization • • • • • 10 Step 1: Stationary solver: laminar flow Step 2: transport of diluted species and optimization Nelder-mead Optimization variables: KL and kLH objective function: Obj C VOC , , out , e xp C VOC , , out ,CFD TiO2 gas phase photocatalysis Research goals Intrinic kinetic parameters Analytic model Comsol model Comsol model: results Acetaldehyde concentrations in steady state condition. The acetaldehyde inlet concentration was 43 ppmv (0.00179 mol m-3), at an effective total inlet gas flow rate of: a) 300 cm3 min-1, b) 375 cm3 min-1, c) 450 cm3 min-1, d) 525 cm3 min-1 and e) 600 cm3 min-1 11 TiO2 gas phase photocatalysis Intrinic kinetic parameters Research goals Analytic model Comsol model Comsol model: results Summary of the kinetic parameters calculated in accordance with the analytic mass transfer based method and the Comsol method after an optimization procedure -1 Intensity -2 [mW cm ] 12 -2 3 kLH [mol s m ] Mass transfer based (analytic) -1 KL [m mol ] Optimized numeric (CFD) Mass transfer based (analytic) 1.1 1.38 x 10 -6 (1.58 ± 0.13) x 10 -6 1.45 x 10 1.8 2.11 x 10 -6 (2.40 ± 0.20) x 10 -6 1.47 x 10 2.6 5.35 x 10 -6 (6.23 ± 0.47) x 10 -6 1.02 x 10 Optimized numeric (CFD) 4 (1.78 ± 0.15) x 10 4 4 (1.65 ± 0.11) x 10 4 4 (1.16 ± 0.08) x 10 4
© Copyright 2024 ExpyDoc
