Study of Chemical Processes in Electrical Discharges in Liquids

kniha odborná

angličtina

The main goal of the presented Ph.D. thesis is an attempt of a complex description of the electrical discharge generated in liquids from the viewpoint of its electrical, physical and chemical characteristics, as well as from the viewpoint of various, especially chemical, processes initiated by the discharge in water. Particularly, the diaphragm discharge created using the DC non-pulsed high voltage of about 2 kV only is investigated. Various chemical active species such as radicals, ions and molecules are produced by the discharge in water. These species can react together to form other molecules or they can attack another molecules of compounds dissolved in water and cause their subsequent decomposition. Such property of the electrical discharge generated in water can be utilised in the field of water treatment to remove undesirable or even harmful compounds from water environment. Taking into account these considerations, the study of chemical processes is oriented both on the production of reactive species and the degradation of mainly organic compounds by the discharge in water solution is carried out. All experiments are carried out in the specially constructed batch discharge reactor. The device uses the dielectric diaphragm that divides the reactor into two chambers with one high voltage electrode in each part. As the DC non-pulsed voltage is applied to create the discharge, two different plasma channels with the opposite polarity propagate towards each electrode, and thus it is possible to study the selected processes in both polarities simultaneously. A very important parameter that must be properly adjusted for the stable discharge operation is conductivity of the solution. However, the overall input power supplied into the reactor does not depend on its magnitude. For the conductivity adjustment, various electrolytes are dissolved in water. Generation of hydroxyl radicals and hydrogen peroxide by the discharge in various water solutions, as well as the influence of the discharge conditions on the process are investigated by this work. Determination of OH radicals is carried out by the optical emission spectroscopy, the concentration of produced hydrogen peroxide is determined by the colorimetric method using the specific titanium reagent. Especially the magnitude of the applied voltage influences the generation process for both species and their production is significantly enhanced by the increasing high voltage. The formation of hydrogen peroxide strongly depends on the voltage polarity, too, the process is much effective in the positive discharge. Also the influence of other parameters such as conductivity of the solution, used electrolyte, properties of the dielectric diaphragm and electrodes are studied and discussed in details. The utilisation of the optical emission spectroscopy in the connection with the diaphragm discharge as an alternative light source for the detection of various elements (especially alkaline metals) in water solutions is proposed by the work. Degradation processes in the diaphragm discharge are studied firstly in water solutions of various organic dyes. The decomposition of these compounds is related to their discoloration thus the absorption spectroscopy can be simply used for the determination of the dye concentration. The destruction of the dye molecule by the discharge was confirmed and two possible mechanisms of the degradation process are assumed: the attack of OH radicals to the dye molecule and the electrochemical oxidation caused by the electrolysis. The dye degradation initiated by UV radiation produced by the discharge could also occur in the solution, however, the influence of this effect is not studied within this work. The influence of various discharge conditions, for example, applied voltage (magnitude and polarity), conductivity and pH of the solution, used electrolyte, chemical structure of the dye molecule, presence of iron, etc., on this process is discussed. In short,

Electrical discharges in liquids, diaphragm discharge, generation of hydrogen peroxide, decomposition of organic dyes, humic matters solutions, solutions of electrolytes

STARÁ, Z.

2006

1. 8. 2006

Vutium

Brno

80-214-3224-1

Study of Chemical Processes in Electrical Discharges in Liquids

PhD Thesis

384

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