|
|
Study of electrolyte influence on diaphragm discharge stability and efficiency
Němcová, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
This thesis is focused on so-called diaphragm discharge, which is one kind of electric discharges in liquid, which belongs among so-called AOP´s techniques, still more used for water cleaning in the present. One of effectiveness and stability indicators of diaphragm discharge is generation of hydrogen peroxide. In theoretical part, detail principle description of electric discharge in liquid is situated. Further, properties of electrolyte are introduced and general spectrophotometric method of obtained sample determination is described. In experimental part, a full procedure of experiment is introduced. Next part containing results and discussions introduces particular results of individual measurements and their reasons. Final chapter is the end, which forms total summary and evaluation of all results. By the application of all chosen electrolytes in solution at diaphragm discharge formation of hydrogen peroxide has appeared. Inorganic and organic electrolytes were used. As inorganic electrolytes following salts were selected – solutions of halogenides, next sodium nitrate as a representative of nitrates, potassium dihydrogenphosphate as a representative of phosphates, etc. Representative of organic electrolytes was citric acid. The value of initial conductivity of electrolytes had the main influence on hydrogen peroxide formation. Electrolytes potassium dihydrogenphosphate and sodium sulphate the great influence on effectiveness and stability of the diaphragm discharge. Their rate constants reached maximum value by the application of solution with initial conductivity of approximately 400 mikrosiemens, particularly 0.0492 mmol/l.min and 0.048 mmol/l.min. On the contrary, low values of rate constant were achieved in electrolyte ammonium chloride at around the same initial conductivity – 0.0269 mmol/l.min. During experiments stainless steel and platinum electrodes were used. It was found that kind of electrode material hadn’t influence on generation of hydrogen peroxide. Hydrogen peroxide was formed only in the cathode space.
|
|
|
Diagnostics of plasma generated in water solutions and its application
Holíková, Lenka ; Brablec, Antonín (referee) ; Kozáková, Zdenka (advisor)
This thesis deals with the study of parameters of diaphragm discharge in liquids. NaCl solution of different conductivity was used as a conductive medium. Conductivities were adjusted in the range from 220 to 1000 µS cm-1. Two diagnostic methods were used for the study of plasma parameters. The first one was employed in the laboratory of plasma chemistry at Faculty of Chemistry, Brno University of Technology, namely the optical emission spectroscopy. The second method used for plasma diagnostics was the time resolved ICCD camera at the Laboratoire de Physique des Plasmas at the École Polytechnique in Paris. The reactor for the diagnostics by optical emission spectroscopy had the volume of 4 l, and it was made of polycarbonate. PET diaphragm was placed in the barrier separating the cathode and the anode space. Electrodes were made of titanium coated with platinum. Electric power source supplied a constant DC voltage of maximum 5 kV and electric current up to 300 mA. Spectrometer Jobin Yvon TRIAX 550 with CCD detector was used during the experiments in order to measure overview spectra within the range from 200 to 900 nm as well as OH molecular spectra and Hß line spectra. All spectra were scanned in both discharge polarities, i.e. at the cathode and the anode part of reactor. The basic parameters of the discharge plasma were calculated from the spectra, that means rotational and electron temperature and electron density. Another part of experiment consisted of measurements by the ICCD camera iStar 734. Two types of reactors were used. The first one was the same as the reactor for the measurements by the optical emission spectroscopy. The second one was also made of polycarbonate, but the volume of conductive solution was 110 ml, only. HV electrodes made of stainless steel were placed in this reactor. Ceramic diaphragm (Shapal-MTM) was used in both reactors. Diaphragms had different thickness and diameter of holes. ICCD camera acquired photographs with details of processes of the bubbles generation and discharge operation (propagation of plasma channels), depending on solution conductivity, dimensions of the diaphragm, and with respect to the electrode part of the reactor.
|
|
|
Diaphragm discharge in organic dye solutions
Pajurková, Jana ; Možíšková, Petra (referee) ; Kozáková, Zdenka (advisor)
This Diploma thesis was focused on the degradation of dyes Saturn Red L4B (Direct Red 79) and Saturn Blue LB (Direct Blue 106) by DC diaphragm discharge (DC-DD). Supplied power was between 160 and 180 W. Conductivity and pH were changing at each electrode area during the DC diaphragm discharge, therefore the effect of pH and conductivity changes on the dye solution itself were examined. All samples were measured by UV-VIS spectrometer in the wavelength range of 300–800 nm. No significant dependence of dye absorption spectra on conductivity was observed, while pH significantly affected the absorption curves of dyes. Ageing of dye spectra showed significant changes of Saturn Red L4B. Next task was the comparison of dyes destruction efficiency by DC-DD, audiofrequency diaphragm discharge (AF-DD) and electrolysis. Dye decomposition by AF-DD was not observed at set conditions (voltage of 80–120 V, current of 2.2 A and frequency of 2 kHz). In the case of DC diaphragm discharge the electrolysis played an important role. Decomposition efficiency of the dyes by electrolysis was up to 15 %. The pumping effect in the DC diaphragm discharge was also investigated. Although the individual electrode areas were linked only by a small pinhole in a nonconductive barrier (the pinhole diameter of 0.3 mm), solutions of the anode and cathode compartment interacted with each other up to 10 %. Finally, the degradation products of Saturn Red L4B treated by DC-DD in two electrodes parts are also described. Decomposition products were determined by high performance liquid chromatography (HPLC) combined with the mass spectrometer.
|
|
|
Study of Plasma - Liquid Interactions
Němcová, Lucie ; Brablec, Antonín (referee) ; Obradovic, Bratislav (referee) ; Krčma, František (advisor)
Disertační práce se zabývá detailním studiem vlastností různých elektrických výbojů generovaných ve vodných roztocích. Tyto výboje se staly v posledním desetiletí velmi populárním tématem, a to zejména díky mnoha praktickým využitím jako například v biomedicíně, čištění odpadních vod, ekologii nebo nanoinženýrství. Studium je zaměřeno na generaci peroxidu vodíku, jakožto jednu z nejvýznamnějších částic generovaných právě elektrickými výboji v kapalinách. Pro první část této práce byla využita speciální výbojová komora zkonstruovaná na Fakultě chemické Vysokého Učení Technického v Brně. Komora byla rozdělena tenkou diafragmovou přepážkou na dvě poloviny, přičemž uvnitř přepážky se nacházela malá dírka. V každé části komory se nacházela jedna elektroda, a obě dvě části komory byly vyplněny kapalinou. Ze zdroje bylo do kapaliny aplikováno vysokofrekvenční napětí (1 a 2 kHz), které tak vlastně upravovalo roztok chloridu sodného (1.5 l). Bylo zjištěno, že tento druh napětí, v porovnání s DC, nezpůsobuje nežádoucí přehřívání roztoku (počáteční vodivost 100 - 800 S/cm) během jeho úpravy při zachování účinnosti produkce peroxidu. Experimentální aparatura pro druhou část práce byla sestavena na Gentské Univerzitě v Belgii. Stejnosměrný výboj byl generován v bublinách plynů (He, Ar, N2, vzduch) v prostředí vodných roztoků. Byla studována generace peroxidu vodíku a odbourávání organických barviv přítomných ve zkoumaném roztoku. Ke generaci peroxidu vodíku byl použit roztok NaH2PO4 . 2H2O (5 microS/cm, V= 750 ml), ke zkoumání rozkladu barviv byly použity roztoky organických barviv Direct Red 79 (20 mg/l) a Direct Blue 106 (20 mg/l, V= 750 ml). Minimální koncentrace peroxidu vodíku byla naměřena při aplikaci proudu 10 mA, zatímco maximální koncentrace peroxidu vodíku byla zaznamenána při použití proudu 30 mA. Rozklad organických barviv vykazoval stejné vlastnosti. Čím vyšší byla dodávaná energie, tím více barviva se odbouralo. Třetí část práce probíhala ve spolupráci s Queen's University of Belfast, Centrum for Plasma Physics, UK. K realizaci experimentů bylo využito vysokofrekvenčního plazmového skalpelu (Arthrocar). Bylo zjištěno, že hodnota koncentrace peroxidu vodíku dosahovala maxima v roztocích s nepatrným přídavkem alkoholu (0.25 %). Celkem byly studovány čtyři 0.15 M roztoky BaCl2, Na2CO3, KCl a NaCl (V= 20 ml), jejichž počáteční vodivost se pohybovala kolem 13 mS/cm. Z výsledků bylo patrné, že největší rozdíl hodnot pH byl zaznamenán u roztoků s přídavkem ethanolu. V optických emisních spektrech byly identifikovány především radikály OH, které jsou prekurzory peroxidu vodíku. Výsledky ukázaly, že plazma v takovémto roztoku je stále tvořeno, což může být považováno za první krok generace plazmatu v organických sloučeninách. Poslední část práce byla zaměřena na tzv. mikroplazmatický jet v přímém kontaktu s kapalnou fází. Tato experimentální práce byla realizována na pracovišti Nanotechnology & Integrated Bio-Engineering Centre (NIBEC), University of Ulster, UK během studijní stáže. Jako vodivé médium byl použit roztok trihydrátu kyseliny chlorozlatité s různou počáteční vodivostí. Zajímavým zjištěním je fakt, že při tomto druhu měření bylo generováno stabilní plazma i při velmi malém výbojovém proudu (0.05 a 0.2 mA), a tedy i peroxid vodíku vznikal při velmi malé vstupní energii, což může být považováno za velmi dobrý výsledek.
|
|
|
Diagnostics of diaphragm discharge in liquids
Dřímalková, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The main goal of this thesis is the diagnostics of the diaphragm discharge generated in liquids. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. Using two kinds of inorganic salt solutions the work studied the influence of conductivity and electrolyte kind on the diaphragm discharge and its static current-voltage characteristics. The last task of the work investigated the emission spectra produced by the discharge. The theoretical part of the work presents mechanisms of the discharge generation in gases including the description of particular kinds of known discharges. The base theories of the discharge ignition in liquids are mentioned as well. Experiments were carried out in the reactor divided by the dielectric barrier (diaphragm) with a central pin-hole into two electrode spaces. Diaphragm was made of PET and the pin-hole initial diameter was 0.4 mm. Stainless steel electrodes were installed in the same distance of 2 cm from the barrier and symmetrically with respect to the diaphragm. Time resolved characteristics of current and voltage were recorded using two-channel oscilloscope which detected their output values. Parameters were measured by the constantly increasing DC voltage with a step of 50 V. When the regular discharge was ignited voltage had been gradually decreased. Used solutions contained sodium sulphate or sodium phosphate electrolyte at six different conductivities. Radiation emitted by the discharge was recorded by the spectrometer Jobin Yvon TRIAX 550. Emission spectra were investigated for one electrolyte at two different conductivities. The part with results presents all dependencies that were achieved during the measurements and all obtained data are compared. Recorded time resolved characteristics determine breakdown moment and describe current and voltage in particular parts within the static current-voltage curve. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement the measured curve moves towards lower voltage which means that the breakdown voltage is decreased. Changing the inorganic salt the change of voltage related to the creation of bubbles in the diaphragm surroundings is observed. However, the change of electrolyte does not induce any significant change of the breakdown voltage. The last part of the work was focused on the optical emission spectroscopy of the discharge. Typical line system of OH radicals was identified in measured spectra which intensity was not dependent on the salt concentration. The work show particular processes taking place in the diaphragm surroundings when DC voltage is applied on the electrodes in electrolyte up to the diaphragm discharge ignition. Further, results describing the influence of conductivity and electrolyte changes on the processes are presented. The breakdown moment of the discharge and its dependence on the solution conductivity was determined. Optical emission spectroscopy revealed the contents of radiation emitted by the discharge.
|
|
|
Diaphragm discharge in organic dye solutions with focus on electrolytic decomposition
Davidová, Jaroslava ; Brablec, Antonín (referee) ; Kozáková, Zdenka (advisor)
This Diploma thesis is focused on physical and chemical effects which contribute to the decomposition of organic dyes by diaphragm discharge generated in water solutions. Due to the application of DC high voltage source in continuous regime, there is an effect of electrolysis contributing to the dye decomposition by diaphragm discharge. The aim of this work was to find out when the electrolysis is running (or when is the moment of discharge breakdown) and which factors influence the breakdown. The other goal was decomposition of selected textile and food organic dyes by electrolysis itself. In the theoretical part, theory about creation of electrical discharges in aqueous solutions is noted and various types of underwater discharges are described. Background researches about underwater electrical discharges used in the world are mentioned as well as the use of diaphragm discharges and various ways how to remove organic dyes from wastewater. Finally, theories of electrolysis, UV-VIS spectroscopy and basis of other analytical methods useful for detection of organic molecules are described. Experimental part is oriented to experiment procedure which was carried out in a reactor with separated electrode areas. Separation was made by dielectric diaphragm with a pinhole in the centre. Its initial diameter was 0.4 mm. Used chemicals and course of experiments are described in this part, too. First, the breakdown moment in the reactor was investigated (i. e. determination, when only electrolysis was operating) by formation of hydrogen peroxide and measurement of dynamic (time resolved) electrical characteristics. Next, decomposition of selected dyes by electrolysis was carried out. As the decomposition was related to decolorization of the solution, UV-VIS spectroscopy in the range of 350–700 nm was used for determination of dye concentration. Next part focused on results presents various factors which had an effect on breakdown of diaphragm discharge. These factors are kind of used electrolyte, initial conductivity of solution, kind of dye, temperature of solution and type of reactor (or solution volume). From the result, the most important factor is initial solution conductivity. After the determination of the breakdown moment, the electrolysis of organic dyes was performed. The applied current was 10 mA, initial conductivity was 500 µS/cm and used electrolyte was NaCl. Moreover comparison of dye decomposition in dependence on the different applied power was realized. From this comparison one can assume, there is no significant contribution of electrolysis (the efficiency is approximately 15 %) to the diaphragm discharge in aqueous solution.
|
|
|
Analysis of humic acids solutions after their decomposition by diaphragm discharge
Totová, Ivana ; Švejdová, Dana (referee) ; Kozáková, Zdenka (advisor)
Preliminary results of research focused on the applications of DC diaphragm discharge in water solutions containing humic substances are presented in this diploma thesis. Electrical discharges in water produce various reactive species such as radicals (•OH, •O, •H), ions and molecules (H2O2, O3). These species have high oxidation potential and thus they easily react with order species and molecules. Such reactions could lead, for example, to destruction of organic pollutants dissolved in water. This work studies this effect on humic matters that can be contained in water coming from floods. Diaphragm discharge investigated by this work was created in the reactor using konstant DC high voltage up to 2 kV that gave the total input power from 100 to 200 W. Breakdown and discharge ignition started in the pin-hole in the dielectric barrier separating two electrode spaces (anode and cathode space). Presented work investigates decomposition of humic substances by the electric discharge in the dependence of solution properties and discharge conditions. Parameters such as initial solution conductivity, electrolyte kind or input power have been investigated. Moreover, substantial effect of pH on humic acid decomposition has been observed. Refraktometry and absorption spectroscopy in UV-VIS region together with fluorescence spectroscopy has been used for the detection of changes in humic solutions.
|
|
|
Electric characteristics of the diaphragm discharge in electrolyte solutions
Dřímalková, Lucie ; Slavíček, Pavel (referee) ; Kozáková, Zdenka (advisor)
The main object of this thesis is the diagnostics of the diaphragm discharge generated in water solutions containing supporting electrolytes (mostly NaCl), and description of particular processes before and after discharge breakdown by DC non-pulsed voltage up to 2 kV. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work is focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. The theoretical part of the work presents proposed mechanisms of the discharge generation in water solutions including the description of particular kinds of known discharges. Diaphragm discharge is one of many possible configurations of electrical discharges in liquids. In fact, electrical discharge in water forms non-thermal plasma, which is generated by high voltage, and many physical and chemical processes are started in plasma channels (so-called streamers). Among physical processes, high electrical field, shock waves and last but not least emission of electromagnetic radiation in visible and ultra-violet radiation belongs. The most important chemical processes are generation of various active species as hydrogen peroxide, and OH radical. Three batch plasma reactors using a diaphragm configuration with different total volume (4 l, 100 ml and 50 ml) are employed in the presented work. The discharge is created in an orifice (a pin-hole) in the dielectric barrier separating two electrode parts of the reactor. DC non-pulsed high voltage up to 4 kV is used for the discharge generation. Electrodes are made of stainless steel or platinum, and they are installed in parallel to the diaphragm in a variable distance from the dielectric barrier in each reactor part. The dielectric barrier is made of PET or Shapal-MTM ceramics with the variable thickness (0.2?2 mm). One pin hole st the diaphragm center with diameter of 0.2?1.5 mm are used in contemporary experiments. Time resolved characteristics of current and voltage are recorded using four-channel oscilloscope which detected their output values. Parameters are measured by the constantly increasing DC voltage with a step of 100 V. The solutions containing sodium chloride electrolyte are used at five different conductivities. Recorded time resolved characteristics determine breakdown moment, and describe current and voltage in particular parts within the static current-voltage curve. The breakdown appeared at lower applied voltage when the electrode distance is enhanced. However, the electrode distances higher than 4 cm does not induce any significant change of the breakdown voltage. The influence of pin-hole diameter is less obvious in the studied range, but a slight enhancement of breakdown voltage is observed with the increasing pin-hole diameter. Current-voltage characteristic curve moves towards lower voltage with the diaphragm thickness enhancement. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement, the measured current-voltage curve moves towards lower voltage which means that the breakdown voltage is decreased. Sizes of the reactors do not have any effect on the processes before and after discharge breakdown.
|
|
|
Alkaloid decomposition by electric discharges in liquids
Jonisová, Lenka ; Kozáková, Zdenka (referee) ; Krčma, František (advisor)
Plasmachemical processes are one of the methods used for wastewater treatment. Sewage and household wastewaters include a variety of organic substances that must be removed to reuse water in industry or households. The aim of this diploma thesisisthe observation of alkaloids decomposition by plasma chemical process. The theoretical part is focused on plasma generation in liquids and characterization of selected alkaloids. The decomposition of caffeine and quinine in direct current electrical discharge in liquid with diaphragm configuration is investigated in this work. The experiments were carried out in a batch reactor divided into two parts by a diaphragm made from ceramic material ShapalTM-M (thickness 3.0 mm, pin-hole diameter 1.0 mm). The stainless steel electrodes of 5×12 cm size were used. The mean electric power was set to 135 W for an operation time of 60 minutes in each experiment. Caffeine solutions (total volume of 4 L) were prepared in concentrations of 10, 25 and 50 ppm, quinine solutions in concentrations of 5, 10 and 15 ppm. The initial conductivity was adjusted by sodium chloride at three different values – 400, 750 or 1000 µS•cm-1. The experimental part consisted also of using analytical methods necessary for compound quantification. Hydrogen peroxide formation during the electrical discharge was determined by colorimetric method based on generation of yellow complex with titanium(IV) sulfate reagent. The caffeine concentration was measured by UV spectrometric method at wavelength 273 nmand thenHPLC/MS analysis was performed. Quinine degradation was monitored by UV-VIS spectrometry and fluorescent measurements. The plasma generation in water solutions induces formation of hydroxyl radical, hydrogen peroxide, oxygen, hydrogen and other reactive species. Hydrogen peroxide is produced and then utilized in degradation of organic compounds and thus lower concentration of H2O2was measured in solution with caffeine and quinine than in solution without alkaloids. However, the situation is different between cathode chamber and anode chamber. There is only negligible amount of H2O2used on degradation in cathode chamber. In contrary, the considerable degradation of caffeine and quinine and diminished concentration of H2O2 was observed in anode chamber.
|
|
| |
guest ::
