Modeling study on the neopentyl+ O2 reaction system and experimental and modeling study on MTBE pyrolysis and oxidation

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Wei, Ru
Electric filters.; Methyl groups--Oxidation.; Pyrolysis.; Environmental Sciences
thesis / dissertation description
A modeling study on neopentyl radical + O2 reaction system is conducted in this study. Thermodynamic parameters on all species and important transition states are calculated. A thermochemical kinetic analysis is performed. Thermodynamic parameters are estimated using group additivity with HBI groups. Transition state energies are evaluated from experimental and theoretical data in the literature, combined with elementary reaction modeling to account for temperature effects. Transition state structures, vibration frequencies and entropies are determined from semi-empirical calculations, MOPAC PM3. Kinetics are analyzed with quantum RRK theory for k(E) coupled with modified strong collision analysis of Gilbert et al for fall-off. An elementary reaction mechanism is constructed to model experimental data in the literature focusing on this neopentyl + O2 reaction system. Experimental and modeling studies are conducted for methyl tert-butyl ether (MTBE) pyrolysis and oxidation. Experimental data are presented in argon diluent in a high pressure, flow reactor over a wide temperature range and at three pressures of 4, 7, 10 atm. Three equivalence ratios were selected for the study of oxidation of MTBE. On-line GC-FLD was used to analyze reacted mixture from flow reactor. Iso-butene and methanol are observed as major products from both oxidation and pyrolysis of MTBE experiments. Acetone, formaldehyde, propene and methane are additional important products. A detailed, pressure and temperature dependent, kinetic model is developed for the pyrolysis and oxidation of MTBE. The mechanism includes oxidation and thermal decomposition of the major products and other important intermediates. Thermodynamic parameters, transition states and kinetics are estimated, evaluated and analyzed as in the neopentyl modeling work. Chebyshev polynomials (7 x 3) incorporate the pressure and temperature dependence into rate constant expressions. A modified Chemkin Interpreter is used to incorporate the combined pressure and temperature dependent rate expressions into the Chemkin integrators. A specific reaction series: one of β -scission of C.CR'COOH, hydroperoxy alkyl radical to form an olefin plus a hydroperoxy methyl radical RC.OOH. This RC.OOH rapidly decompose to lower energy products: RCHO + OH. Little or no evidence is observed for formation of the final products in the transition state of the first β-scission step.