was bubbled through a water bed. The volume flow of gases were measured with GIMONT (2000 ml/min) rotameters. The evaporation and dilution flows were ...
IAEA-SM-350/5
VOC REMOVAL BY SIMULTANEOUS ELECTRON BEAM AND BIOFILTER APPLICATION V. HONKONEN, J. RUUSKANEN, M. AATAMILA University of Kuopio
XA9847702
J. MAKELA University of Helsinki, Helsinki J. LEHTOMAKI Technical Research Centre of Finland, Helsinki B. SVARFVAR Abo Akademi University, Turku Finland A. CHMIELEWSKI, Z. ZIMEK, A. OSTAPCZUK Institute of Nuclear Chemistry and Technology, Warsaw, Poland Abstract During the recent years the stringent legislation and the public environmental knowledge has led to the situation in which many companies have to reduce their process and ventilation gas emissions consisting of volatile organic compounds (VOCs) and being noxious for environment. There are several different methods for VOC controls. In this research project we will focus to combine two novel and promising methods; electron beam treatment and biofiltration. Both of them are sufficient alone in many cases but with combination we hope to get more advantages. Now preliminary test series (phenol and styrene as test VOC matter) have been done to become certain that the radiation byproducts from electron beam irradiation are suitable for biofiltration and are not toxic to bio-organisms of a biofilter. Test series involved reference samples without irradiating and irradiated samples containing wet and dry air; dry air and VOC, and wet air and phenol. After e-beam irradiation with 13.5 kGy mean dose gas samples were collected to TENAXTA sampling tube and were later analyzed with gas chromatograph and mass selective detector combination. The results show that among the decomposition products in the gas there are mostly aldehydes and few esters, ketons and aromatic compounds which are known to be biodegradable.
87
1. INTRODUCTION
Volatile organic compounds (VOCs) include by definition all organic compounds that are capable of producing photochemical oxidants by reactions with nitrogen oxides in the presence of sunlight. Because VOCs are harmful for environment and human health there are nationals and international agreements and legislation to reduce VOC emissions, for example Geneve Protocol [ 1 ] and the forthcoming directive of European Union concerning the use of organic solvents in some industrial actions [2]. Now the stringent legislation and the public environmental knowledge have led to the situation where many companies have to reduce process and ventilation gas emissions which consist of VOCs. There are several methods for VOC controls, many kind of scrubbers, carbon adsorption, thermal and catalytic oxidation. In this research project we will focus to combine two novel and promising methods, i.e. electron beam treatment followed by biofiltration.
1.2. E-beam treatment of VOCs
Electron beam treatment of VOCs has been under the growing interest during the recent years. It has been found in the earlier investigations that electron beam can effectively clean different kind of dilute VOC contaminated gases [3-7]. In electron beam treatment the clean-up efficiency for VOCs depends on the organic compound to be treated and its concentration together with the total dose. Hirota et al. [5] found the removal efficiency at 10 kGy dose to be nearly 90% for xylene but only about 50 % for butylacetate. The curve of removal efficiency versus dose has typically the shape of (l-exp(-x*D))-function, where D is the dose and x is a constant depending from the compound to be treated and from its concentration (see Refs [3,5]). The electron beam treatment of VOCs is similar to the e-beam flue gas treatment process. Electrons are first accelerated to high energies under vacuum conditions in a vessel outside the intended reaction chamber. Then the fast electrons in the electron beam enter a reaction chamber, where they ionize VOCs and carrier gas molecules, creating a nonequilibrium plasma. This process creates a high amount of secondary electrons for every primary electron produced by the beam. The fast electrons and secondary electrons slow down quickly on the neutral species in the reaction chamber. These slow electrons then create reactive radicals through collisions with carrier gas and VOC molecules in the airstream. And these radicals are responsible to remove most of VOCs.
88
1.2 Biofiltration of VOCs
Together with the e-beam treatment a new environment and user friendly alternative for VOC control is biofiltration. Although different biofilter realisations have great differences the basic idea is same for all of them. Biofiltration is the use of microorganism growing in the media (solid or liquid) through which the gas to be treated is forced [8,9]. A schematic line drawing from a popular trickling filter system can be seen in Fig. 1. While moving through the filter the VOCs in the air transfer from gas phase to water phase where the bioorganisms can destroy (metabolize) the contaminants. The end products of this VOC destruction process are carbon dioxide, water and different metabolism residues. The microorganisms are maintained by nutrients provided by medium or carried by water, oxygen and different components absorbed from the air stream to be treated. Biofiltration has notable advantages compared to other VOC control techniques. It has moderate capital costs and low operating costs. The process has no hazardous by-products. Biofilters can be use to control various odours and dilute VOCs. The clean-up efficiency is in many case over 90 %. Biofiltration is a "natural" way to remove VOCs. The water need of biofiltration is small and wastewater flow from the biofilter is fairly clean. Disadvantages of biofiltration are its relatively large space requirement and that it is not possible to handle effectively sources where the concentration fluctuate highly. The large space requirement is to provide adequate residence time for VOC adsorption and destruction. In some cases VOCs with high concentration are
Liquid «—I Distribution (System
FIG. 1. Schematic presentation of a tricling filter system. 89
poisonous also for decomposing microorganisms. Therefore the actual filters might be supported by dilution chambers to confirm the filter operation. In addition, biofilter is not an on/off filter, it must have some time to adapt a certain gas stream. 1.3. Advantages of joint filtration
The aim of our study is to solve the biofiltration problems described above by our joint filtration technique. By joining electron beam treatment and biofiltration we can combine the properties of two good choice. With low emission rate the biofilter can purify the air stream alone and we have the minimum energy consumption, i.e. minimum operating costs. With higher emission rates the electron beam treatment is a powerful prefilter which change VOC concentrations to optimal levels applied to the biofilter. Because of the typical dependence of electron beam removal efficiency from dose is something like (l-exp(-x*D))-function, in the most cases only moderate doses should be needed to drop the concentration to the optimal level used in the biofilter. In many industrial processes the sudden leakage spikes as a result from system temporary malfunction are quite common. In that situation a biofilter doesn't have enough time to adapt to the change of the concentration. But if we would have a continuous on-line monitoring of VOC concetration before the filtration unit we could cut the spikes away with electron beam treatment.
2. MATERIAL AND METHODS The gas samples used in the preliminary tests were prepared as shown in the Fig. 2. Pressurised air was flowing through a VDO pressure control valve to a glass bottle which was fulfilled with CaCl2*2 H2O (Riedel-deHaer). After this drying bottle the flow was devided to two VOC source Compressed air Airflow devider
Sample
FIG. 2. Preparation of the gas samples. 90
GASMET
parts. One part was used to evaporate VOC (in this case phenol or styrene) and the other part was used for dilution the gas mixture. When the wet samples were done the dilution part from air flow was bubbled through a water bed. The volume flow of gases were measured with GIMONT (2000 ml/min) rotameters. The evaporation and dilution flows were fed through a 3 way valves to the sample boxes (40*100*25 mm, stainless steel with 0.025 mm 99.6 % titanium window) made for the irradiation tests. The concentrations of VOCs and the humidity of the samples were measured by GASMET™ FT-IR multicomponent gas analyser to secure that the concentrations were between the desired limits. In dry samples the amount of water was 0.1% (equal to 4 % relativ humidity) and in the wet phenol samples the amount of water was between 2.6 % (equal to 98% relativ humidity). The gas samples were prepared in the University of Kuopio from where they were transported to Abo Akademi University to be irradiated. During the transportation and storage over a night the samples were kept at 0 °C temperature. The samples were irradiated with 175 kV ESI Electroncurtain accelerator with 13.5 kGy mean dose. The mean of absorbed doses was detected by two film dosimeters the placed just under the window and at the bottom of the sample box. The irradiated samples and 100 ml nitrogen which flowed through a sample box were pumped through glass pipes containing about 130 mg Chrompack Tenax-TA 60-80 MESH. These Tenax tubes were transported back to Kuopio (stored at temperature 0 °C) and analysed with Chrompact TCT, Hewlett-Packard 5890A gas chromatograph with J & W Scientific colone (length 30 m, ID0.25 mm, film thickness 0.25 fim) and Hewlett-Packard 5970 series mass selective detector.
3. RESULTS
Chromatograms of the irradiated air and VOC samples with the lists of identified compounds with their retention times are shown in Figs. 3-6. From the chromatograms of irradiated VOC samples the background of irradiated air and non-irradiated samples with VOCs were substracted. The compounds which were probable irradiation products of phenol in dry air were found to be phenol, 2-nitro; pentanal; acetic acid, phenylmethyl ester; aceticacid, phenyl ester and butanal. In the case of phenol in wet air the compounds were heptanal; hexanal; acetic acid, phenylmethyl ester; butanal and pentanal. In the chromatogram of irradiated styrene in dry air was very high peak of benzaldehyde (see Fig. 6). Other plausible compounds of styrene degradation process were toluene; pentanal; methyl ethyl ketone; heptanal; hexanal; methanamine, N-methyl-N-nitro; butanal; acetophenone and benzene.
91
TIC:DA1.D 04
3e+07 10.47
2 5e*07 J 2e*07 ]
13.74
1.5e*07 J i 1e*07 -
5.42
5000000 J 2.41
4.61 4 00
6.00
8.00
10!00
1,7 23
13
5181D
19.98
12.00 14.00 16.00 18!oo 20.00
21.84 22.00
28SH7 24.00
26.00
28.00
Time->
Compound
# Ret Time
4.606 4.974 5.416 7.273 7.66
# Ret Time
Compound
Butanal, 3-methyl-
13.475
BenzakJehyde
Octane
13.738
Octanal
Toluene
14.343
Octane, 1-chloro-
Hexanal
17.043
Nonanal
Decane
17.229
Acetophenone
8.262
Benzene, 1,2-dimethyl
17.791
Phenol
9.428
Styrene
18.123
Benzenemethanol,.alpha...alpha.-dimethyl-
10.471
Heptanal
10.797
Decane
21.836
Benzothiazole
11.004
1H-Pyrrole, 2-methyl-
22.816
Tetradecane
12.335
2-Heptanone, 6-methyl-
19.98
Decanal
FIG. 3. Chromatogram of sample of dry air.
TIC OF1.0
5**07
1
4«*07 . 3Se*O7 3e*07 2 5e*07 -
i.Se*07 14.35 '
-
'
•
5 42
iOOOOOO •
3.00
1
0 4 00
# Ret Time
7 27
iLJi. tttW
8.60
10 41
. L. . 10.00
12.00
Compound
MX 1 1.37 ha 70 14!00
1ft!0Q
« Ret Time
% ft f
M 00
2o!00
29.28 22.00
24!o6
26]O0
Compound
2.446
Isopropyl Alcohol
10.578 Cyclotetrasilioxane, octametyl-
3.005
Butanal
10.808 Decane
3.143 Azetidine, 1-nitroso4.656
Pentanal
4.969
Hehane,2,4-dimethyl-
5.421
Toluene
2e!oO
11.077 Decane, 4-methyl11.21 Decane. 4-methyl13.623 Ethanone, 1 -cyclopenthyl13.72 Octanal
5.672 Cydotrisilioxane, hexametyl
14.353 Octane, 1-chloro-
5.742 Methyl Isobutyl Ketone
17.097 Dodecane
6.258 2,4-DimethyM -heptene
17.392 Acetic acid, phenyl ester
7.271
Hexanal
18.115 Phenol
7.673
Nonane
18.367 2,4,6-Cydoheptatrien-1-one, 2-amino-
9.447
Styrene
19.259 Phenol, 2-nitro-
Heptanal
19.696 Acetic add, phenylmethyl ester
10.426
FIG. 4. Chromatogram of sample with phenol in dry air. 92
'
TIC WF1 D 1( 00 3 Se«07 10 61 3^07 2 5e+O7
553
740
t
2e*O7
1 Se»07
17
13.86
ie+07 -
°6
14.47 473
soooooo 3.04 0 -r,
,
*•
h
6 00
X)
# Ret Time 2.454
800
-Mf-
. .V , . , , . - . 1
1000
14 00
12OT
Compound Isopropyl Alcohol
16'00
18 00
# Ret Time 10.611 10.93
20'00
22!0O
24^00
\ 2600
Compound Heptanal Decane
3.044
Butanal
3.247
Chloroform
13.619
BenzaWehyde
4.731
Pentanal
13.862
Octanal
5.532
Toluene
14.47
5.817
Toluene
17.083
7.395
Hexanal
17.217
Dodecane
7.787
Nonane
17.317
Acetophenone
Benzene, 1,3-dimefhyl-
18.002 19.779
Acetic acid, phenylmethyl ester
8.39 9.561
Styrene
.,'-}.
28l00
Octane, 1-chloroNonanal
Phenol
FIG. 5. Chromatogram of sample with phenol in wet air. Abundance
TIC:DS1.D 1394
10.09
5.5e+07 j 5e+07 4 4.5e+07 J
552
3.5e+07 3e+07 2.5e+07 2e+07
17.08
7.31
1 5e+07 1e+075000000 0
0.64
4.6£
444
12.15
3.16
T
8.07 6 bo'
tit- 10:00
13 4h
16.! 17.82
J 12:00 UlOO 16.00 18.00 20.00 22.00 24.00 26.00 28.00
Time~>
# Ret Time 2.447
Compound Isopropyl Alcohol
# Ret Time 11.096
Compound 1 H-Pynole, 2-methyl-
3.001
Butanal
12.152
2-Butanone
3.157
Chloroform
13.413
Methanamine, N-methyl-N-nitro-
3.38
Benzene
13.94
4.686
Pentanal
14.089
Undecane
Benzaldehyde
5.298
Acetic acid
14.444
Octane, 1-chloro-
5.516
Toluene
16.212
Benzaldehyde, 2-hydroxy-
5.635
Toluene
16.51
7.312
Hexanal
16.652
Benzeneacetaldehyde
7.699
Nonane
17.083
Nonanal
Benzene.(epoxyethyl)-,(R)0-
8.071
Ethylbenzene
17.147
Dodecane
8.305
Benzene, 1,3-dimethyl-
17.278
Acetophenone
Styrene
17.817
Phenol
10.087 10.64
Heptanal
19.14
10.924
Decane
20.013
Phenol, 2-nitroDecanal
FIG. 6. Chromatogram of sample with styrene in dry air. 93
4. DISCUSSION
In the earlier research it has been shown that a big part of the irradiation products of VOC treatment will be in the solid (aerosol) phase. In these preliminary test we made a sensible conclusion to investigate only gas phase compounds of the samples. When we will have a joint filtration unit which will have a trickling filter as a biofilter then we can be sure that all (at least most) of the solid particles will be washed away from the air stream with the water trickling through the filter unit. Now we wanted to become certain that the irradiation of phenol or styrene samples does not produce any substances which would be more harmful to the environment or to the biofilter than what phenol and styrene are by themselves. The compounds found in the irradiated samples were mostly aldehydes and few esters, ketons and aromatic compounds which are known to be biodegradable. Earlier Anderson et al. (1997) studied oxidation of styrene using a silent discharge plasma. They noticed many same products (acetophenone, benzaldehyde, phenol and benzene) which were presents also in our samples [10]. Unfortunately degradation products of used TENAX resin in the background seemed to be similar as compounds we were observing from samples. That's why we were not able to be absolutely sure if some of those products were coming from irradiation of VOCs or from TENAX resin. Our results partly show that TENAX resin cause a quite high background level in the analyse. Further investigation are needed to select suitable absorbents for collecting byproducts after irradiation of VOCs. In this preliminary test the removal efficiencies of styrene and phenol in dry air were 38 % and 32 %, respectively. One reason to this low efficiency might be the irregular dose distribution in the sample box.
ACKNOWLEDGEMENTS This work was partly supported
by
Savo Foundation
for
Advanced
Technology.
Acknowledgements also to the Centre for International Mobility CIMO for the grant to A. Ostapczuk to make possible the research visit in Finland and to the University of Kuopio for the travel grant to V. Honkonen to IAEA Symposium.
REFERENCES [1] UNITED NATIONS, Draft protocol to the 1979 convention on long-range transboundary air pollution concerning the control of emissions of volatile organic compounds or their transboundary fluxes, Economic Commission for Europe, Geneva (1991). [2] EUROPEAN COMMISSION, COM(96) 538 final (1996). 94
[3] PAUR, H.-R., MÄTZING, H., WOLETZ, K., Removal of volatile organic compounds from industrial offgas by irradiation induced aerosol formation, J. Aerosol Sei. 22 Suppl. 1 (1991) S509-S512. [4] MÄKELÄ, J. M., HIROTA, K., NAMBA, H., TOKUNAGA, O., REISCHL, G. P., Aerosol particle formation by irradiation of benzene-N2, Toluene-N2 and TCE-N2 mixtures, Proc. 10th Symp. on Aerosol Sei. and Techn., Muroran, Japan, (1993) 105-107. [5] HIROTA, K., WOLETZ, K., PAUR, H.-R., MÄTZING, H., Removal of butylacetate and xylene from air by electron beam, a product study, Radiât. Phys. Chem. 46 4-6 (1995) 10931097. [6] VITALE, S. A., BROMBERG, L., HADIDI, K., FALKOS, P., COHN, D. R., Decomposing VOCs with an electron-beam plasma reactor, Chemtech , 26 4 (1996) 58-63. [7] PENETRANTE, B. M., HSIAO, M. C , BAYLESS, J. R., Electron beam and pulsed corona processing of volatile organic compounds in gas streams, Pure & App. Chem. 68 5 (1996) 1083-1088. [8] DIKS, R. M. M., OTTENGRAF, S. P. P., "Technology of trickling filters", Biologische Abgasreinigung, Kommission Reinhaltung der Luft im VDI und DIN, VDI-Berichte 1104 (1994) 19-37. [9] HARTIKAINEN, T., MARTIKAINEN, P., RUUSKANEN, J., MUTKA, K.,NYRÖNEN, T., KÄLLSTRÖM, M., VANHATALO, M, A method and facilities for cleaning effluent gases. Finnish Patent 94316 (1995). [10] ANDERSON, G., SNYDER, H., COOGAN, J., CANAVAN, H., "Oxidation of styrene using silent discharge plasma", Presented in ICOP'97, San Diego, California,USA, 1997.
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