Studies Of Pyrolysis And Cold Plasma Of C₂～C₄ Alcohol Fuels

In this dissertation, the pyrolysis and cold plasma discharges of biomass fuels, including C₂, C₃ and C₄ alcohols, have been investigated by the tunable synchrotron vacuum ultraviolet (VUV) photoionization combined with molecular-beam mass spectrometry (MBMS).In the first chapter, the importance and necessity of pyrolysis studies of biomass fuels are described. Some basic concepts related to pyrolysis are briefly introduced. The development of the experimental methods on pyrolysis diagnostic technology is reviewed and evaluated. The advantages of tunable synchrotron VUV photoionization combined with molecular beam mass spectrometry offer significant improvements over previous methods, which are superior signal-to-noise, soft ionization, and tunability of photon energy for isomeric identification of complex pyrolysis products.In Chapter 2, the experiment setup of pyrolysis is introduced in detail. Firstly, the advantages of synchrotron radiation light source, the parameters of storage ring of National Synchrotron Radiation Laboratory (NSRL) and the structures of U10 and U14C beamlines are presented. Secondly, the operation principle of the endstation and the experimental procedures are described. Finally, the theoretical methods used in this thesis are briefly introduced.In Chapter 3, the pyrolysis study of ethanol at low pressure is presented in detail. Products Observed from ethanol pyrolysis, including H₂,CH₃,CH₄,H₂O,C₂H₂,C₂H₄,CO,H₂CO,C₃H₄,C₂H₂O,C₂H₄O,C₂H₄O,C₄H₆ and C₄H₈, are identified unambiguously by measurements of photoionization efficiency spectra. Mole fraction profiles of these pyrolysis species are measured at the selective photon energies near ionization thresholds. The dissociation channels and consumption reactions of ethanol are calculated by ab initio Gaussian-3 (G3) procedure. The experimental results are in good agreement with theoretical predictionsPyrolysis of C₃ alcohols (1-propanol and 2-propanol) has been studied in Chapter 4. The formation pathways of pyrolysis species are investigated with the help of G3B3 method. In general, the decomposition of the two precursors occurs primarily by the dehydration reaction at low temperature, and the production of radicals becomes dominant and the decomposition reaction is controlled by chain processes at high temperature. Different types of H₂- and CH₄-molecular elimination processes are involved in radical reactions. The pyrolysis species in the two systems are strongly affected by the structures of their precursors, especially the position of OH in 1-/2-propanol.Pyrolysis studies of C₄ alcohols including 1-butanol, 2-butanol, i-butanol and t-butanol at low pressure have been reported in Chapter 5. The identification of reaction species, the measurements of mole fraction and the theoretical calculations of decomposition pathways are discussed in detail. The species produced by primary reactions have a strong relationship with the structures of pyrolysis precursors, while the species generated by the secondary reactions are independent of the butanol structures. The dissociation mechanisms of the butanols include complex fission, simple fission and H-atom abstraction, which are in roughly good agreement with previous results.In the last chapter, low-pressure cold plasma discharges, which are used to simulate some hot core environments in the star-forming region, have been investigated by employing single-photon vacuum ultraviolet photoionization mass spectrometry. Enols with two to four carbon atoms are detected in plasma discharges of alcohols, indicating that enols can result from alcohol destructions induced by ultraviolet and cosmic radiation and accelerated electrons that are abundant in the interstellar medium. This observation, together with the detection of ethenol toward Sgr B2, suggests that larger enols, such as propenols and butenols, could be in the search list of potential molecular species to be identified in interstellar space. The laboratorial effort presented here shows that VUV photoionization sampling of plasma discharges is a potential method for understanding new interstellar molecules and their formation mechanisms.