Investiga??es na qu?mica de combust?es usando modelos da cin?tica qu?mica te?rica e simula??es num?ricas

• Ano de defesa: 2020
• Autor(a) principal: Machado, Gladson de Souza
• Orientador(a): Bauerfeldt, Glauco Favilla
• Banca de defesa: Bauerfeldt, Glauco Favilla , Silva, Clarissa Oliveira da , Sant'Anna, Carlos Mauricio Rabello de , Klachquin, Graciela Arbilla de , Faria, Roberto de Barros
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal Rural do Rio de Janeiro
• Programa de Pós-Graduação: Programa de P?s-Gradua??o em Qu?mica
• Departamento: Instituto de Qu?mica
• País: Brasil
• Palavras-chave em Português: Combust?o; Formalde?do; ?cido f?rmico; Acetona; Butanol
• Palavras-chave em Inglês: Combustion; Formaldehyde; Formic Acid; Acetone; Butanol
• Área do conhecimento CNPq: Qu?mica
• Link de acesso: https://tede.ufrrj.br/jspui/handle/jspui/6176

This work aims to investigate the action of theoretical chemical kinetics models for the treatment of combustion chemistry related problems. Four different cases were studied. In the first case, the hydrogen abstraction reaction channel in the formaldehyde + hydroxyl radicals reaction mechanism was investigated at the CCSD(T)/CBS level, with a pre-barrier complex and a saddle point stabilized by 3.31 and 1.35 kcal mol-1 with respect to the reactants, respectively. However, Gibbs free energy profile suggests that the formation of the pre-barrier complex at temperatures above 550 K is an endergonic process. Therefore, above this temperature value the reaction can be considered elementary, and the calculation of the rate coefficients is suggested by the canonical variational transition state theory method. In the second case study, the kinetic investigation of the decomposition of formic acid was carried out. Although the two main pathways, decarboxylation and dehydration, presented very similar barrier values, 65.40 and 65.03 kcal mol-1, respectively, at the CCSD(T)/CBS level, the prevalence of the dehydration pathway can be explained by the isomerization reaction between the Z and E conformers. The rate coefficient for the formation of the Z-conformer is always higher than that for the other conformer. Furthermore, through RRKM calculations and subsequent solution of the master equation, it was found that the transition from the second order regime to the falloff regime occurs at 0.5 atm at 1400 K. In the third case study, five initiation steps in acetone combustion mechanism were investigated: four unimolecular reactions and one bimolecular reaction, the latter being the abstraction of hydrogen by molecular oxygen. These reactions were analyzed at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level. Rate coefficients were calculated using the RRKM theory with subsequent solution of the master equation, for the unimolecular reactions and for the bimolecular reaction the canonical transition state theory was applied. The dissociation reaction, breaking of the C-C bond, proved to be the main route among the unimolecular steps. The combustion mechanism proposed by Sarathy was optimized by the insertion of the calculated kinetic parameters calculated for acetone, and the error in the prediction of ignition time was reduced from 81% to 24%. Finally, in the fourth case study, 0D simulations of an ideal Otto cycle were performed with the following fuels: acetone, butanol, ethanol, butanol/ethanol and acetone/butanol/ethanol. A spark model was proposed through the dissociation of 5% of oxygen and fuels. In the integration of the combustion mechanism, the analysis of reaction rates demonstrated that all fuels are mainly initiated by the reaction of oxygen atoms with methyl radicals, generating formaldehyde and hydrogen atoms. These atoms pass through some stages until the formation of hydroxyl radicals, which react with the fuels through hydrogen abstraction reactions. After analyzing the case studies, it is concluded that the choice of the quantum mechanical method combined with thermodynamics, the appropriate kinetic model and numerical analyzes generated satisfactory results, capable of proposing solutions for open discussions in the literature, new rate coefficients and interpretations from a combustion mechanism