Transcript Document

CARE
Cabin Air Reformative Environment
Performance of Thermal-catalytic
Oxidization Technology for
Formaldehyde Removal at Typical
Indoor Environment
Xu Han
Tianjin University
2013-05-14
Sample characterization
• Characterization: SEM/BET
Materials:
•Impregnated carbon
•Metal oxidation
•pore diameter distribution
SEM
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Selection of materials
• PERFORMANCE:
• CuO/MnO2 shows best performance;
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CuO/C(1.5)
Al2O3/KMnO4(3.0)
CuO/MnO2(1.3)
Concentration [ppm]
0.9
0.8
Testing condition [1]:
Temperature:24.5±1℃, RH:50±3 %，Flow rate：
10.59 L/min，Concentration：1.0±0.1ppm，
Residence time：0.01s
Ag Cu Cr/C(1.5)
CuO/MnO2(3.0)
0.7
0.6
Media
CuO/C
Ag/Cu/Cr
/C
CuO/
MnO2
Al2O3/
K2MnO4
Pellet size
1.5 mm
sphere
1.5 mm
sphere
3.0 mm
sphere
3.0 mm
sphere
Bed density[2] (kg/m3)
538.1
550.3
477.3
733.4
BET surface
area[3](m2/g)
824
743
120.4
-
Average pore
diameter[3] (Å)
20.7
20.1
11.8
-
Total pore volume [3]
(cm3/g)
0.427
0.373
0.355
-
0.5
0.4
0.3
0.2
0.1
0
0.0
5.0
10.0
15.0
20.0
Time [h]
Figure 1. Formaldehyde outlet concentration for cases with
different media
[1] ANSI/ASHRAE STANDARD 145.1-2008:Laboratory Test3Method for Assessing the Performance of Gas-Phase Air-Cleaning
System: Loose Granular Media [2] ANSI/ASHRAE STANDARD 2854, [3] V-Sorb 2800P
Effect of GHSV
• GHSV: gas hourly space velocity, h-1
• Affection: residence time, conversion rate, stabilization time, mass
transfer coefficient of external diffusion (through affect face velocity).
100
500,000 h-1
1,000,000 h-1
80
Conversion (%)
2,000,000 h-1
60
40
20
0
0
50
100
150
200
250
300
Time (min)
Figure 1. Formaldehyde conversion at different GHSV
(equivalent to residence times of 0.0072, 0.0036 and 0.0018 s)
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Objectives: make reaction
reach stabilization ASAP,
meanwhile, own proper
conversion rate and bed depth.
Note: testing condition: temperature 25±1 ℃; relative humidity 50±1% RH; inlet formaldehyde concentration
Effect of Diffusion
• Method: keep operation condition and GHSV constant, change face
velocity in the reactor;
0.5
0.4
0.98
-3
Reaction rate r (10 ppb.m/s)
1.00
0.3
0.96
0.94
0.2
fm
0.92
r
0.1
0.0
0.4
0.8
1.2
1.6
Mass transfer effectiveness factor fm
r
0.90
2.0
(Cin  Cout )  G
ABET
fm 
hm  As
hm  As  k  ABET
C wp 
- r' R 2 
Cs De
?= 1
?<< 1
Mass diffusion was eliminated
when Vface≥ 1.2m/s
Face velocity (m/s)
Figure 1. Reaction rates at different face velocities in the reactor
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Note: testing condition: 850±30 ppb inlet concentration, 25±1 ℃, 50±1% RH and GHSV 1,000,000 h-1
Effect of Temperature and
Concentration
• Method: tests of various inlet concentration (180 to 1300 ppb) were
performed at four temperatures;
100
Conversion (%)
80
60
180℃
120℃
60℃
25℃
40
20
The formaldehyde onethrough conversion
decreases as the inlet
concentration increases
especially when the
temperature is low.
0
200
400
600
800
1000
1200
1400
Inlet concentration (ppb)
Figure 1. Formaldehyde conversion at different inlet concentrations in
the range of 180-1300 ppb at different temperatures
Note: testing condition: water vapor concentration 615,000 ppm, equivalent to 50±1% RH at 25±1 ℃; GHSV
1,000,000 h-1.
Effect of Relative Humidity
• Method: formaldehyde one-through conversions was tested with the
same inlet concentration at three different relative humidity levels;
100
The results showed
significant influence of
relative humidity on the
performance of
CuO/MnO2 catalyst for
formaldehyde conversion
Conversion (%)
80
60
5 ± 0.5% RH
50 ± 1.0% RH
65 ± 2.0% RH
40
20
0
0
50
100
150
200
250
Time (min)
Figure 1. Formaldehyde conversion at different relative humidities
Note: testing condition: reaction temperature 25±1
7 ℃, inlet formaldehyde concentration 320±15 ppb, GHSV
-1
1,000,000 h
Kinetic Model and Reaction
Mechanism
Table 1. Kinetic Fitting Results Utilizing Different Models
Model
Reaction Mechanism
Rate Expression
First
ordera
Gaseous reaciton
L-Hb
Two absorded reactants reaction
with competitive adsorption
r
kKCs
(1+ KCs ) 2
E-Rb
Adsorbed formaldehyde reacts with
gaseous O2
r
kKCs
(1 + KCs )
MVKb
Electronic balance between
formaldehyde and O2
r
k' C s
(1 + k' ACs )
r  k'Cs
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a(Zhang,
Y.P. et al. 2003).
b(Hurtado,
P. et al. 2004 and Liotta, L.F. 2010)
Temp.
(℃)
R2
25
-2.56
60
-1.34
120
180
25
60
120
180
25
60
120
180
25
60
120
180
0.69
0.99
0.54
0.92
0.99
0.99
0.28
0.82
0.99
0.99
0.28
0.82
0.99
0.99
Kinetic Model and Reaction
Mechanism
• Method: applying and L-H model Arrhenius law to experimental data
in the catalytic oxidation of formaldehyde by CuO/MnO2.;
6x10-3
4x10-3
180℃
120℃
60℃
25℃
Nonlinear regression by
bimolecular L-H model
Reaction rate, Experimental (ppb.m/s)
Reaction rate (ppb.m/s)
5x10-3
10-2
3x10-3
2x10-3
10-3
400
600
800
1000
Surface concentration (ppb)
Figure 1. Reaction rate at different surface formaldehyde
concentration under different temperatures
10-3
R2=0.96
10-4
10-4
0
200
180℃
120℃
60℃
25℃
Linear regression
by y=x
10-3
10-2
Reaction rate, Predicted (ppb.m/s)
Figure 2. Parity plot comparing experimentally measured reaction rate
with the predicted reaction rate of the L-H model.
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Conclusions
• The performance of catalytic oxidation of formaldehyde by
CuO/MnO2 at typical indoor environmental condition and
concentration level (30-75% conversion).
• The humidity shows significant influence on the catalytic oxidition of
formaldehyde by CuO/MnO2 at room temperature.
• The efficiency increased with increased temperature and decreased
challenge concentration, and became independent of concentration
when the temperature was increased to 180 ℃.
• The catalytic oxidation of formaldehyde by CuO/MnO2 follows the LH model best.
• Further study was ongoing to study the mechanism of humidity
effect and long term performance.
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Thank you!
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