Experimental and theoretical examination of the chemical kinetics of a pollutant coating on porous particles [Elektronische Ressource] / von Radostin Gavrilov

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Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2009
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Universität Bayreuth
Forschungsstelle Atmosphärische Chemie





Experimental and theoretical examination of the chemical kinetics of a
pollutant coating on porous particles




Dissertationsschrift von
Diplom-Ingenieur Radostin Gavrilov




Vorgelegt der Fakultät für Biologie, Chemie und Geowissenschaften,
Universität Bayreuth


Content



1. INTRODUCTION ..............................................................................................................1
2. RELATION TO PREVIOUS WORK ON THE EXAMINATION OF DEGRADATION
KINETICS ................................................................................................................................4
2.1. Aim of the work...................................................................................................................4
3. MATERIALS AND METHODS .........................................................................................9
3.1. Aerosol smog chamber experiments...................................................................................9
3.2. Characterization of aerosol mass, size distribution and lifetime ..................................... 10
3.3. Sampling, solar simulator, Aerosil coating and aerosol feeding devices .............................14
3.3.1. Aerosil coating and aerosol production............................................................................ 14
3.3.2. Sampling device ................................................................................................................ 16
3.3.3. Solar simulator .................................................................................................................. 17
3.4. Measurement of the temperature gradients in the smog chamber......................................19
4. PRODUCTION OF OH-RADICALS IN THE SMOG CHAMBER....................................21
4.1. Precursors of OH radicals................................................................................................. 21
4.2. OH production..................................................................................................................24
4.3. Analytics the gas phase and characterization of the exposure atmosphere.....................26
5. ANALYSIS OF THE TEST COMPOUND AND THE PRODUCTS .................................33
6. TRANSPORT THROUGH POROUS AGGLOMERATES ..............................................36
6.1. General comments................................................................................................................36
6.2. Knudsen diffusion.................................................................................................................37
6.3. Surface diffusion ...................................................................................................................38
6.4. Calculation of effective diffusion coefficient ........................................................................39
6.5. Defining the mathematical model........................................................................................40
6.6. Fitting procedure of the parameter.......................................................................................47 Content



7. CALCULATION OF THE APPARENT RATE CONSTANT FROM THE DEGRADATION
CURVE OF THE TEST COMPOUND ....................................................................................49
8. EXPERIMENTAL RESULTS ..........................................................................................50
8.1. Measurement of the temperature gradient in the smog chamber........................................50
8.2. Analysis of the lost substance during the coating procedure...............................................57
8.3. Analysing the FEP foil at the bottom of the chamber..........................................................58
8.4. Ageing of the coated powder ................................................................................................59
8.5. Structure evaluation of the agglomerates .............................................................................59
8.6. Experiments with Aerosil in the smog chamber ..................................................................65
8.7. Analysis of the parameters and the gas-phase compounds..................................................67
8.8. Evaporation of Aldrin from the agglomerate surface at different temperatures..................67
8.9. Photolysis of Aldrin...............................................................................................................68
8.10. Degradation kinetics of Aldrin at different temperatures ....................................................70
8.11. Reaction products and their behavior ..................................................................................73
8.12. Verification of the rate constants of the reference hydrocarbons.........................................76
8.13. Calculation of the effective rate constant for the degradation of Aldrin ..............................79
9. RESULTS FROM THE FITTING PROCEDURE.............................................................83
10. REACTION WITH OZONE..........................................................................................91
11. ANALYSIS OF THE PRODUCTS FROM THE CHEMICAL REACTION....................93
11.1. Used material and facilities ..................................................................................................93
11.2. Carrying out the test..............................................................................................................93 Content



11.3. Photolysis of Aldrin...............................................................................................................94
11.4. Products formation and instability .......................................................................................95
12. DISCUSSION..............................................................................................................99
13. CONCLUSIONS........................................................................................................103
14. SUMMARY................................................................................................................104
15. ZUSAMMENFASSUNG ............................................................................................106
16. REFERENCES..........................................................................................................108
17. APPENDIX 1.............................................................................................................114

18. APPENDIX 2 ………………………………………..……………………..…………........118

DANKSAGUNG

ERKLÄRUNG






1 Introduction
1. Introduction
Pesticides are widely used in agriculture in order to improve the efficiency of food
production. About 5 million tons of pesticides are used world-wide annually (OECD, 2003).
A disadvantage of the large pesticide use is its potential impact on the environment by toxic
effects. Therefore, the interest in the distribution in the environment and the chemical
reactions increases constantly. The pesticides are semivolatile compounds. They are aerosol-
borne in the troposphere to a major portion. The variety of phase-transfer processes (such as
absorption and adsorption) has a big influence on chemical and biological transformation and
on the dispersion of the pesticides. Each process must be quantified individually in order to
understand the relevant processes for the degradation of a certain pesticide. The most
important degradation path of the pesticides is the chemical reaction with OH-radicals in the
atmosphere. Therefore, the reaction with OH-radicals is an important process with respect to
the regulations of the authorities on persistence in the environment.
There are various substances which are highly toxic and harmful for the human health and for
the environment, and 12 most harmful substances were included in the Stockholm convention
on persistent organic pollutants (POPs): Aldrin, Chlordane, dichlorodiphenyltrichloroethane
(DDT), Dieldrin, Endrin, Heptachlor, Mirex, Toxaphene, polychlorobiphenyls (PCBs),
hexachlorobenzene, dioxins and furans (EU, 2004). Aldrin was chosen for the experiments of
the present work. The degradation in the atmosphere and its products have been investigated
actively in the 70s of the past century. The aim of this work is to investigate Aldrin with a
novel experimental and mathematical approach.
It turned out in the present study that the smog chamber method for examining the kinetics of
the experiments needs to be interpreted in a new way. Agglomerated particles of fused silica
(Aerosil 380, DEGUSSA) served as model particles, were coated with the test substance,
exposed to OH radicals in the chamber and analyzed for the test substance. It now appears
that migration of the pesticides within the particles has to be taken into account after an
improved understanding of the transport processes in the porous particles.
This work attempts to explain the observations. The diffusion equation, coupled with
chemical reac