Cabin Air Reformative Environment

C A R E

Performance of Thermal-catalytic Oxidization Technology for

Formaldehyde Removal at Typical Indoor Environment

Xu HanTianjin University

2013-05-14

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Sample characterization• Characterization: SEM/BET

SEM • pore diameter distribution

Materials:• Impregnated carbon• Metal oxidation

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• PERFORMANCE:• CuO/MnO2 shows best performance;

Selection of materials

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.0 5.0 10.0 15.0 20.0

CuO/C(1.5) Ag Cu Cr/C(1.5)Al2O3/KMnO4(3.0) CuO/MnO2(3.0)CuO/MnO2(1.3)

Con

cent

ratio

n[p

pm]

Time [h]

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

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 -

[1] ANSI/ASHRAE STANDARD 145.1-2008:Laboratory Test Method for Assessing the Performance of Gas-Phase Air-Cleaning System: Loose Granular Media [2] ANSI/ASHRAE STANDARD 2854, [3] V-Sorb 2800P

Figure 1. Formaldehyde outlet concentration for cases with different media

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• GHSV: gas hourly space velocity, h-1

• Affection: residence time, conversion rate, stabilization time, mass transfer coefficient of external diffusion (through affect face velocity).

Effect of GHSV

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 320±15 ppb.

Time (min)

0 50 100 150 200 250 300

Conversion (%

)

0

20

40

60

80

100

500,000 h-1

1,000,000 h-1

2,000,000 h-1

Figure 1. Formaldehyde conversion at different GHSV (equivalent to residence times of 0.0072, 0.0036 and 0.0018 s)

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Effect of Diffusion• Method: keep operation condition and GHSV constant, change face

velocity in the reactor;

Note: testing condition: 850±30 ppb inlet concentration, 25±1 , 50±1% RH and GHSV 1,000,000 h℃ -1

Face velocity (m/s)

0.0 0.4 0.8 1.2 1.6 2.0

Mass transfer effectiveness factor f

m

0.90

0.92

0.94

0.96

0.98

1.00

Reaction rate r (10

-3ppb

.m/s)

0.1

0.2

0.3

0.4

0.5

fmr

Figure 1. Reaction rates at different face velocities in the reactor

BET

)(A

GCCr outin

BETsm

smm AkAh

Ahf

eswp DC

Rr 2'-C

Mass diffusion was eliminated when Vface≥ 1.2m/s

?= 1

?<< 1

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Effect of Temperature and Concentration

• Method: tests of various inlet concentration (180 to 1300 ppb) were performed at four temperatures;

Note: testing condition: water vapor concentration 15,000 ppm, equivalent to 50±1% RH at 25±1 ; GHSV ℃1,000,000 h-1.

Figure 1. Formaldehyde conversion at different inlet concentrations in the range of 180-1300 ppb at different temperatures

The formaldehyde one-through conversion decreases as the inlet concentration increases especially when the temperature is low.

Inlet concentration (ppb)

200 400 600 800 1000 1200 1400

Conversion (%

)

0

20

40

60

80

100

180℃120℃ 60℃ 25℃

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Effect of Relative Humidity• Method: formaldehyde one-through conversions was tested with the

same inlet concentration at three different relative humidity levels;

Note: testing condition: reaction temperature 25±1 , inlet formaldehyde concentration 320±15 ppb, GHSV ℃1,000,000 h-1

Figure 1. Formaldehyde conversion at different relative humidities

The results showed significant influence of relative humidity on the performance of CuO/MnO2 catalyst for formaldehyde conversion

Time (min)

0 50 100 150 200 250

Conversion (%

)

0

20

40

60

80

100

5 ± 0.5% RH50 ± 1.0% RH65 ± 2.0% RH

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Kinetic Model and Reaction Mechanism

Table 1. Kinetic Fitting Results Utilizing Different Models

a(Zhang, Y.P. et al. 2003). b(Hurtado, P. et al. 2004 and Liotta, L.F. 2010)

Model Reaction Mechanism Rate Expression Temp.(℃) R2

First ordera Gaseous reaciton

25 -2.5660 -1.34120 0.69180 0.99

L-HbTwo absorded reactants

reaction with competitive adsorption

25 0.5460 0.92120 0.99180 0.99

E-Rb Adsorbed formaldehyde reacts with gaseous O2

25 0.2860 0.82120 0.99180 0.99

MVKbElectronic balance

betweenformaldehyde and O2

25 0.2860 0.82120 0.99180 0.99

sCk'r

2s

s

)KC+(1kKC

r

)KC+(1kKC

s

sr

)ACk'+(1Ck'

s

sr

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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.;

Surface concentration (ppb)

200 400 600 800 1000

Reaction rate (ppb

. m/s)

0

10-3

2x10-3

3x10-3

4x10-3

5x10-3

6x10-3

180℃120℃60℃25℃Nonlinear regression bybimolecular L-H model

Reaction rate, Predicted (ppb.m/s)

10-4 10-3 10-2

Reaction rate, E

xperimental (ppb

. m/s)

10-4

10-3

10-2

180℃120℃60℃25℃Linear regressionby y=x

R2=0.96

Figure 1. Reaction rate at different surface formaldehyde concentration under different temperatures

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 L-H model best.

• Further study was ongoing to study the mechanism of humidity effect and long term performance.

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Thank you!