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Author: Schmidt, Michael ×

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    How activated carbon improves the performance of non-thermal plasma removing methyl ethyl ketone from a gas stream
    ([Amsterdam] : Elsevier B.V., 2021) Schmidt, Michael; Kettlitz, Manfred; Kolb, Juergen F.
    The combination of non-thermal plasma (NTP), operated at room temperature and at atmospheric pressure in air and in combination with activated carbon filters offers a more efficient removal of VOCs from gas streams than each individual method alone. Efficiencies, synergies and mechanisms of this combination were investigated by means of comprehensive quantitative Fourier transform infrared spectroscopy analysis. Therefore, dry and wet synthetic air containing about 90 ppm of methyl ethyl ketone (MEK) were treated with non-thermal plasma (NTP) and an intentionally undersized activated carbon (AC) filter, separately and in combination. As a result, removal of about 50 % was achieved for NTP or AC alone but a removal close to 95 % was found for the combination. Ozone, generated by the NTP, was reduced by 55 % with the AC-filter. For the operation of the NTP with humid air, a decomposition of the pollutant on AC was observed even after the plasma was switched off.
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    About the Development and Dynamics of Microdischarges in Toluene-Containing Air
    (Dordrecht : Springer Science + Business Media B.V., 2019) Brandenburg, Ronny; Jahanbakhsh, Sina; Schiorlin, Milko; Schmidt, Michael
    The development of microdischarges and the inception dynamics of subsequent microdischarges in an electrode arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode, operated in air with a small toluene admixture, is studied. The discharge is operated with sinusoidal high voltage. A gated ICCD camera and a current probe enable the recording of images and current pulses of the single microdischarges, respectively, while the spatio-temporally resolved development is measured with a multi-dimensional time-correlated single photon counting technique. The overall discharge dynamics changes significantly if a concentration of 35 ppm toluene is added to dry air. A lower high voltage amplitude than in dry air is needed for stable discharge operation. This can be explained by the lower ionization energy of toluene compared to molecular oxygen and nitrogen. The microdischarge development is the same with or without admixture, i.e. a positive (cathode directed) streamer mechanism is observed. Lower mean power is dissipated into the discharge when toluene is admixed. The main effect caused by toluene admixture is the suppression of high-energy microdischarges in case of the cathodic pin half-cycle of the sinusoidal high voltage. The influence on the inception voltage by additional ionization mechanisms and volume memory effects, the consumption of energetic electrons for toluene decomposition reactions, and the modification of the surface by plasma treatment are discussed as possible reasons.
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    Plasma-activation of larger liquid volumes by an inductively-limited discharge for antimicrobial purposes
    (Basel : MDPI, 2019) Schmidt, Michael; Hahn, Veronika; Altrock, Beke; Gerling, Torsten; Gerber, Ioana Cristina; Weltmann, Klaus-Dieter; von Woedtke, Thomas
    A new configuration of a discharge chamber and power source for the treatment of up to 1 L of liquid is presented. A leakage transformer, energizing two metal electrodes positioned above the liquid, limits the discharge current inductively by utilizing the weak magnetic coupling between the primary and secondary coils. No additional means to avoid arcing (electric short-circuiting), e.g., dielectric barriers or resistors, are needed. By using this technique, exceeding the breakdown voltage leads to the formation of transient spark discharges, producing non-thermal plasma (NTP). These discharges effected significant changes in the properties of the treated liquids (distilled water, physiological saline solution, and tap water). Considerable concentrations of nitrite and nitrate were detected after the plasma treatment. Furthermore, all tested liquids gained strong antibacterial efficacy which was shown by inactivating suspended Escherichia coli and Staphylococcus aureus. Plasma-treated tap water had the strongest effect, which is shown for the first time. Additionally, the pH-value of tap water did not decrease during the plasma treatment, and its conductivity increased less than for the other tested liquids. © 2019 by the authors.
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    Studies on the Electrical Behaviour and Removal of Toluene with a Dielectric Barrier Discharge
    (Berlin : de Gruyter, 2014) Schmidt, Michael; Schiorlin, Milko; Brandenburg, Ronny
    This contribution attempts to establish an easy-to-apply non-thermal plasma reactor for efficient toluene removal. Derived from the already established knowledge of the so called Dielectric Barrier Discharge (DBD) Stack Reactor a new model reactor was used in this work. The DBD Stack Reactor is a multi-elements reactor but in this work only one stack element was used to investigate the efficiency and efficacy of toluene removal. In case of reliable results the scalability process for industrial application is already well known. Therefore, laboratory experiments were conducted in dry and wet synthetic air with an admixture of 50 ppm toluene. Along with the toluene removal process the electrical behaviour of the discharge configuration was investigated. It was found that the electrical capacitance of the dielectric barrier changes with variations of the operating voltage. This could be due to the changes in the area of the dielectric barrier which is covered with plasma. Additionally, it was found that the power input into the plasma, at a fixed operating voltage, is proportional to the frequency, which is in agreement with the literature.Regarding the decomposition process, the total removal of toluene was achieved at specific input energy densities of 55 J L-1 under dry conditions and 110 J L-1 under wet conditions. The toluene removal was accompanied by the production of nitric acid (dry conditions) and formic acid (wet conditions). The latter suggested a combination of the plasma reactor with a water scrubber as an approach for total removal of pollutant molecules.