Report n° 06/324

This report should only be reproduced in its entirety

Degradation of a gas mixture at ppb level by a photocatalytic device

The performance of the photocatalytic device was assessed in an one cubic meter box byfollowing the removal of a gas mixture composed of acetaldehyde, propionaldehyde, heptane, toluene, o-xylene and styrene.

Also, the device as able to removed more than 99,99 % of the starting odour level.

Study for : Saint-Gobain Quartz S.A.S Attention of : Mr Molins Customer request nr : 00023858 Certech request nr: K371 Certech quotation nr : OP/06/104/CB

Emission date : 14-07-06

Scientific Approval, Quality Approval,

CERTECH asbl - CEntre de Ressources TEchnologiques en CHimie Rue Jules Bordet, Zone Industrielle C – B 7180 SENEFFE TVA BE 0470.677.454 ING 370-1128214-94 FORTIS 271-0204412-65 Tél : +32 (0)64 52 02 11 Fax : +32 (0)64 52 02 10 e-mail : info@certech.be

Degradation of a gas mixture at ppb level by a photocatalytic device

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1. Study objectives.

The aim of this study was to test a photocatalytic device (ref CERTECH 603Y002) received by Saint Gobain, for the degradation of a gas mixture at low concentration and the assessment of the odour removal.

2. Methodology The experiment was carried out in a 0,9 m³ box and the pollutants were analysed on line by means of GC-PID. The GC-PID is able to analyse gas concentration at ppb level without any pre-concentration. .

Figure 1 : photocatalytic device in the test chamber

It was proposed to work with the following mixture around 600 ppb for each compound :

• acetaldehyde

• propionaldehyde

• n-heptane

• toluene

• styrene

• o-xylene

Pollutants were introduced in the test chamber by using a micro-syringe.

Figure 2 shows the chromatogram of a GC-PID analysis of the mixture of acetaldehyde (peak 1), propionaldehyde (peak 2), heptane (peak 3), toluene (peak 4) , o-xylene (peak 5) and styrene (peak 6)

Degradation of a gas mixture at ppb level by a photocatalytic device

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Figure 2 : chromatogram profile of a gas mixture

Unfortunately, as shown in figure 3, there is an interference with acetaldehyde and an unknown peak in the blank. This interference had to be subtracted from the analysis.

Figure 3 : chromatogram profile of a blank.

Degradation of a gas mixture at ppb level by a photocatalytic device

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Air samplings on Airtoxics tubes were performed at different time.

Figure 4 : air sampling on Airtoxics tube.

This sampling concentrated molecules on the Airtoxics tubes. The sample was analysed by thermal desorption and gas chromatography coupled with a mass spectrometer detector. This allowed us to detect some by-products that could be formed during the experiment. The pumping flow was 100 ml/min and the pumping time varied from 5 to 60 minutes.

The evaluation of the odour removal was performed by sampling air at the start and at the end of the degradation test. These samples were analysed by dynamic olfactometry to quantify their odour concentration. Dynamic olfactometry was performed according to the standard EN13725 (results expressed in European odour unit per cubic meter) by using a panel of four pre-calibrated people. For this test, the concentration of the mixture was increased to have a strong starting odour.

The temperature and the relative humidity on the lab was recorded by a Dostmann electronic P570 humidity/temperature probe. The temperature and the humidity profile are shown in graph 1. The temperature rose from 23 to 25 during the tests and the humidity varied between 45 and 55 %.

Degradation of a gas mixture at ppb level by a photocatalytic device

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0

5

10

15

20

25

30

8:24:00 9:36:00 10:48:00 12:00:00 13:12:00 14:24:00 15:36:00

time

Tem

pera

ture

(°C

)

0

10

20

30

40

50

60

70

RH

(%)

temperature (°C) RH %

Graph 1 : temperature and humidity profiles

Degradation of a gas mixture at ppb level by a photocatalytic device

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3. Results. The results of the first test is reported on graph 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

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0 20 40 60 80 100 120 140times (min)

conc

entra

tion

(ppm

v)

toluene styrene propionaldehyde o-xylene heptane acetaldehyde

Device on

Graph 2 : mixture degradation profile.

The device was switched on position 3 after 64 min. As shown in graph 2, all chemical are quite rapidly removed from the gas phase. Heptane is removed slower than the others.

The chemical profile of the second test (at higher concentration) is shown at graph 3.

The device was switched on position 3 after 44 min. Removal profiles are similar for the two tests. Styrene and o-xylene are quickly removed followed by propionaldehyde, acetaldehyde, toluene and finally, heptane. The propionaldehyde and acetaldehyde have similar profile, the delay observed for acetaldehyde is due to its higher starting concentration.

Air sampling for the odour characterisation were taken before switching the device and after 150 min. A blank sample was also taken before introducing the mixture in the test chamber.

Results are shown in table 1

Degradation of a gas mixture at ppb level by a photocatalytic device

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0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120 140 160time (min)

conc

entra

tion

(ppm

v)

toluene styrene propionaldehyde o-xylene heptane acetaldehyde

Device onOdour air sampling, start

Odour air sampling, end

Graph 3 : second test at higher concentration.

Table 1 : Odour characterisation results

Odour level (OUE/m³)

Blank 23

Mixture level 6600

After test 17

% removal > 99,99 %

The photocatalytic device is able to remove more than 99,99% of the odour. The odour level after the degradation test is similar to the blank.

The graphs 4 and 5 show the chromatograms of the air sampling on Airtoxics sampler tubes. The Airtoxics sampler was used to trap lighter chemical that could be present in the air.

No significant by-products are observed on the sampling as it can see in graph 6. Beside the mixture components, acetic acid is detected in the first test after 30 minutes and some unknown chemical are observed in the second test on the sample taken after 55 minutes.

The “step” observed between 2 and 4 minutes on the chromatograms is due to the presence of water adsorbed on the Airtoxics.

Degradation of a gas mixture at ppb level by a photocatalytic device

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0

10000000

20000000

30000000

40000000

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60000000

0 5 10 15 20 25 30 35 40 45

time (min)

resp

onse

(u.a

)

Before test (sampling time 5 min) 30 min test (sampling time 10 min) 60 min (sampling time 10 min)

acetaldehdyepropionaldehdye

heptane

toluene

0

10000000

20000000

30000000

40000000

50000000

60000000

15 15.2 15.4 15.6 15.8 16

time (min)

resp

onse

(u.a

)

styreneo-xylene

Graph 4 : chromatogram of the air samples on Airtoxics tubes for the first test.

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0 5 10 15 20 25 30 35 40 45

time (min)

resp

onse

(u.a

.)

Before test (sampling time (5 min) after 55 min (sampling time 20 min) after 150 min (sampling time 60 min)

acetalehyde

propionaldehyde

heptane

toluene

0100000002000000030000000400000005000000060000000700000008000000090000000

15 15.2 15.4 15.6 15.8 16

time (min)

resp

onse

(u.a

)

styrene

o-xylene

Graph 5: chromatogram of the air samples on Airtoxics tube for the second test.

The estimation of the heptane, toluene, o-xylene and styrene concentration are reported on table 2. For this purpose, the PID value just before starting the device was used to estimate the concentration of the other samples. The results are reported on table 2. The PID value when the compound is detected is also indicated.

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Table 2 : Concentration estimation of heptane, toluene, styrene and o-xylene in the gas phase from the air sample on Airtoxics tube

Cartouche/PID (ppmv)

Cartouche (ppmv)

Cartouche (ppmv)

PID (ppmv) PID (ppmv)

Test 1 0 min 30 min 60 min 30 min 60 min

Heptane 0.59 0.0853 0.00142 0.03 nd

Toluene 0.67 0.0089 0.00009 nd nd

Styrene 0.676 0.0204 0.000492 nd nd

o-xylene 0.478 0.0253 0.00144 nd nd

Test 2 0 min 55min 150 min 55 min 150 min

Heptane 2.07 0.056 0.000174 0.099 nd

Toluene 1.91 0.0176 0.000038 nd nd

Styrene 0.39 0.0084 0.000079 nd nd

o-xylene 1.13 0.0222 0.000246 nd nd

The concentration estimated of heptane, toluene, styrene and o-xylene from the air sampling indicates that detected by-product are well below the ppbv level.

0

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0 5 10 15 20 25 30 35

time (min)

resp

onse

(u.a

.)

test 1 after 30 min (sampling time 10 min) test 2 after 55 min (sampling time 20 min)

acetic acid

heptane

toluene

styrène/o-xylene

unknow

Graph 6 : air sampling results of the first test after 30 min and the second test after 55 min.

Degradation of a gas mixture at ppb level by a photocatalytic device

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4. Conclusions.

The performance of the photocatalytic device was assessed in an one cubic meter box by following the removal of a gas mixture composed of acetaldehyde, propionaldehyde, heptane, toluene, o-xylene and styrene. Heptane needs more time than the other chemicals to be removed.

The device is able to remove more than 99,99 % of the starting odour level.

Some by products, acetic acid and unidentified chemicals, are produced at concentration well below the ppbv level.