Abstract
Complex plasma chemical reactions of carbon dioxide (CO2) and water vapor (H2O) activated in low-temperature non-catalytic atmospheric pressure plasma jet were investigated in this thesis. By collisions of plasma electrons with the CO2 and H2O molecules, a major fraction of the kinetic energy is transferred into molecular vibrational energy, which can then be accumulated to the level of crossing the bonding barriers, commencing the plasma chemical reactions. In this fashion, heating the whole reaction tank to close to 1000oC, as necessarily done in the conventional CO2 conversion reactions, can be done without and high efficiency reactions between CO2 and H2O molecules are activated at the ambient condition. The production of the radicals of CO, C2, OH, O, H, and CH, as a result from the plasma reactions between CO2 and H2O molecules, were evident from the observation of the characteristic peaks of the optical emission spectroscopy (OES) spectra. By assuming the existence of a constant average efficiency factor i for each OES radical peak during the plasma reactions, the species concentrations could be acquired from the characteristic peak intensities of the OES spectrum (Ii) via a simple relation of Ci = Ii ×alphai. We then varied the plasma reaction parameters, such as the plasma power, water vapor concentration, and flow rate, to obtain a series of OES spectra, from which a series of simultaneous equations of i, Ci, and Ii were established based on mass conservation. Finally, we used a computational method to solve the alphai‘s from these equations. With that, we are able to unveil the activation of CO2 and H2O in the plasma and the proceeding of the myriad intermediates reactions as influenced by the experimental parameters. As a check, we also used an alcohol vapor detector to measure the concentration of one of the key end products of the plasma reactions. The results show that when the power increases to elevate the electron temperature, carbon dioxide and water dissociate further to generate more radicals which then interact to form organic compounds like alcohols, ketones, aldehydes, and hydrocarbon. On the other hand, as the water concentration increases, more hydrogen is generated to react with the various intermediate species to form ethanol, acetone, and ethane. Finally, when the flow rate of the carbon dioxide and water vapor is reduced, the molecules of water and carbon dioxide have shorter residence times in the plasma reactor so that smaller amounts of radicals are produced to generate the organic compounds.