Crema, Claudia (2012) Studio della decomposizione di tetracloroetilene e metanolo attivata da plasma non termico in aria. [Magistrali biennali]
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The Thesis is about the decomposition of VOCs (Volatile Organic Compounds) using non-thermal plasma techniques. To study the decomposition process, tetrachloroethylene and methanol were chosen as model VOCs. Initially, these two compounds were studied independently, in both dry and humid air (RH=40%) and, subsequently, together. The plasma was produced by a corona discharge in direct current in both positive (DC+) and negative (DC-) polarity and the byproducts of both VOCs were identified using FT-IR (Fourier Transform-Infrared Spectroscopy) and GC/MS (Gas Chromatography/Mass Spectrometry) analysis. For tetrachloroethylene it was found that its decomposition is more efficient at higher initial concentrations (750 ppm > 500 ppm > 250 ppm > 100 ppm) in DC- and that there is no effect of the initial concentration in DC+, in contrast to previous studies of the research group and studies found in literature. For methanol instead, the trend of the decomposition is the same as for other VOCs: the decomposition is more efficient at lower initial concentrations. The study of the decomposition in humid air is very useful for industrial applications as well as to understand the role of the hydroxyl radical (produced by the plasma in the presence of water) in the degradation of VOCs. It was found that, for tetrachloroethylene, the presence of hydroxyl radical does not affect the decomposition both in DC+ and DC-, thereby suggesting that there is no reaction between the two species. The hydroxyl radical was also studied by Optical Emission Spectroscopy (OES), in order to achieve more information. The results are in agreement with that of the decomposition. For methanol, the efficiency of the decomposition in humid air is higher in DC- and lower in DC+. In fact, In DC- there is a great production of hydroxyl radicals, which can react with methanol. In DC+, instead, the efficiency is lower because in the presence of humidity ions form hydrate complexes, which are less reactive. The study of the two compounds together showed an increase of the efficiency of the decomposition of methanol and a decrease of the efficiency of the decomposition of tetrachloroethylene for both DC+ and DC-. This result can be attributed to the presence of •Cl. Methanol in fact competes with tetrachloroethylene for the reaction with •Cl and this competition explains the increase in the efficiency of the decomposition of methanol and the decrease in the efficiency of the decomposition of tetrachloroethylene.
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