哈尔滨工业大学

Kinetic Analysis of the Photocatalytic Kinetic Analysis of the Photocatalytic

Degradation of GasDegradation of Gas--phase phase

Formaldehyde for Different Formaldehyde for Different

Concentration Range with PackedConcentration Range with Packed--bed bed

Reactor Reactor

Yu-Hua Li, Kun Wang , Qing-Liang Zhao

Chung-Shin Yuan (Taiwan)

Introduction

Objectives

Experimental Methods

Results and Discussions

Conclusions

CONTENT

INTRODUCTION

Formaldehyde is ubiquitous in indoor

environment and could exist for a long time.

Formaldehyde is harmful to human health.

The removal of formaldehyde has been a

major issue and continuing emphasis in the

past decade.

INTRODUCTION

(CONT.)

Many investigations on the removal of

formaldehyde has been conducted.

Although the formaldehyde of high

concentration has been successfully

decomposed with photocatalytic reactor, it is

still unsure the relatively low concentration

can be decomposed effectively.

INTRODUCTION

(CONT.)

The significant mass transfer resistance

resulting from relatively low concentration

The insufficient areal UV light intensity

OBJECTIVES

To look into the difference of formaldehyde

photodegradation between high and low

concentration

To investigate into the kinetic mechanism of

the photodegradation of formaldehyde

EXPERIMENTAL METHODS

Experimental apparatus and procedure

Analytical methods

1- nitrogen cylinder, 2- oxygen cylinder, 3-dynacalibrator, 4-mass flow

controller, 5-needle valve, 6-one-way valve, 7-humidifier, 8-hygrometer,

9-15-watt black lamp, 10-photocatalytic reactor, 11-temperature

controller, 12-heating tape

1

1

2

3

4

4

4

5

5

5

5

6

6

6

4 6

8

9

7

712

10

11

Analytical Methods

Standard procedure promulgated in the

Chinese Air Quality-Spectrophotometric

Determination of Formaldehyde, Method

Acetylacetone (GB/T 15516-1995).

UV-visible spectrophotometer(Shimadzu

Corporation, UV 160-A)

RESULTS AND DISCUSSION

Effect of influent formaldehyde

concentration on the reaction rate

Kinetic model for photodegradaton of

formaldehyde on the TiO2

Effect of influent formaldehyde concentration

on the reaction rate

4 6 8 10 12 14 16 18 20 22

0.5

1.0

1.5

2.0

2.5

Oxygen content=21%

Amount of photocatalyst=0.095 g

Water vapor concentration=853 ppmv

Form

aldeh

yd

e re

acti

on r

ate/

mg

⋅g-1

⋅hr-1

Formaldehyde concentration/mg⋅m-3

70 oC 85

oC 100

oC

115 oC 130

oC

Effect of influent formaldehyde

concentration on the reaction rate(cont.)

0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0

0.1

0.2

0.3

0.4

0.5

0.6F

orm

ald

ehyd

e re

acti

o r

ate/

mg

⋅g-1

hr-1

Formaldehyde concentration/mg⋅m-3

70 oC 85

oC 100

oC

115 oC 130

oC

Oxygen content=21%

Amount of photocatalyst=0.032 g

Water vapor concentration=853 ppmv

Kinetic model for photodegradaton of

formaldehyde on the TiO2

Langmuir-Hinshelwood model

KC

kKCr

+

=

1

kkKCkKC

KC

r

1111+=

+=

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

0.00 0.05 0.10 0.15 0.20 0.250.0

0.5

1.0

1.5

2.0

2.51/r

1/C

70 oC

The formaldehyde concentration

range was 5~20 mg⋅m-3

85 oC 100

oC

115 oC 130

oC

系数 70 oC 85 oC 100 oC 115 oC 130 oC

k 9.470 8.583 6.293 5.685 4.666

K 0.0128 0.0120 0.0115 0.0105 0.0098

R2 0.97 0.97 0.97 0.97 0.98

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

0.50 0.75 1.00 1.25 1.50 1.75 2.000

1

2

3

4

5

6

7

0.50 0.75 1.00 1.25 1.50 1.75 2.000

1

2

3

4

5

6

7

0.50 0.75 1.00 1.25 1.50 1.75 2.000

1

2

3

4

5

6

7

0.50 0.75 1.00 1.25 1.50 1.75 2.000

1

2

3

4

5

6

7

0.50 0.75 1.00 1.25 1.50 1.75 2.000

1

2

3

4

5

6

7

The formaldehyde concentration

range was 0.6~1.2 mg⋅m-3

1/r

1/C

70 oC 85

oC

100 oC

115 oC 130

oC

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

Power-rate Law Equation

nkC

dt

dCr ==

)ln()ln()ln( Cnkr +=

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

1.0 1.5 2.0 2.5 3.0 3.5-1.0

-0.5

0.0

0.5

1.0ln

(r)

ln(C)

70 oC

The formaldehyde concentration

range was 5~20 mg⋅m-3

85 oC 100

oC

115 oC 130

oC

系数 70 oC 85 oC 100 oC 115 oC 130 oC

k 0.110 0.105 0.104 0.097 0.095

n 0.906 0.937 0.942 0.977 0.988

R2 0.96 0.96 0.96 0.97 0.97

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

The formaldehyde concentration

range was 0.6~1.2mg⋅m-3

ln(r

)

ln(C)

70 oC 85

oC 100

oC

115 oC 130

oC

Kinetic model for photodegradaton of

formaldehyde on the TiO2(cont.)

系数 70 oC 85 oC 100 oC 115 oC 130 oC

k 0.452 0.434 0.396 0.360 0.317

n 1.082 1.109 1.148 1.190 1.370

R2 0.99 0.99 0.99 0.99 0.99

CONCLUSIONS

the decomposition of formaldehyde was

apparently affected by influent

formaldehyde concentration.

The reaction rate of influent

formaldehyde concentration of 5~20

mg/m3 can be accounted for by using the

rate expression of L-H model.

Power-rate model was feasible for

describing the photocatalytic oxidation for

influent formaldehyde concentration of

0.6~1.2 mg/m3

The concentration variation process for

high and low influent formaldehyde

concentration was different.

CONCLUSIONS

(CONT.)

The photodegradation conclusion obtained

from high influent formaldehyde

concentration didn’t suit low influent

formaldehyde concentraiton.

CONCLUSIONS

(CONT.)