Acetic acid is, among carboxylic acids, the one present in the highest concentration in the atmosphere and it is largely responsible of the problematic phenomenon of the acid rains. The major sources of acetic acid emission in atmosphere are vehicle exhaust gases and biomass combustion. Acetic acid, given its quantitative presence in biomass pyrolysis liquid, is used as reference species in biofuels design and, consequently, an accurate knowledge of its reactivity is mandatory in order to develop new and competitive alternative fuels. In the first part of this thesis, studies of the acetic acid reactivity have been deepened investigating the possible reactive pathways that the radical CH2COOH, obtained through dehydrogenation of the methyl group, can pursue with OH and CH3 radicals, which, usually, are present in high concentration in combustion and pyrolysis processes. All the reactions have been studied from a strictly theoretical point of view using the EStokTP code. Reactants, products and transition states properties, such as geometry, vibrational frequencies and energy, have been obtained with ab initio electronic structure calculations, while the rate constants with transition state theory solving the master equation. At the end, the kinetic parameters for the modified Arrhenius expression have been obtained, for each reaction studied, through nonlinear regression. In the second part, all the kinetic data obtained, have been added to the kinetic mechanism of Politecnico di Milano POLIMI which describe combustion, pyrolysis and partial oxidation of hydrocarbons and oxygenated compounds, such as acetic acid. Using the OpenSMOKE++ program, simulations of acetic acid combustion and pyrolysis have been performed in different reactors and conditions. The data coming from each simulation have been collected, post-processed and compared with the experimental ones and the ones obtained with the mechanism POLIMI without the addition of the new reactions.
L’acido acetico è, tra gli acidi carbossilici, quello presente in più alte concentrazioni in atmosfera ed è, in buona parte, responsabile del problematico fenomeno delle piogge acide. Le maggiori fonti di emissione in atmosfera di acido acetico sono i gas di scarico dei veicoli e la combustone delle biomasse. L’acido acetico, vista la sua presenza quantitativa nel liquido proveniente dalla pirolisi di biomasse, viene utilizzato come specie di riferimento nel design di biocombustibili e di conseguenza un’accurata conoscenza della sua reattività è d’obbligo per poter sviluppare combustibili alternativi competitivi. Nella prima parte di questa tesi, gli studi sulla reattività dell’acido acetico sono stati approfonditi andando ad investigare i possibili cammini reattivi che il radicale CH2COOH, ottenuto per deidrogenazione del gruppo metilico, può intraprendere con i radicali OH e CH3, i quali, solitamente, sono presenti in alte concentrazioni nei processi di combustione e pirolisi. Tutte le reazioni sono state studiate da un punto di vista strettamente teorico utilizzando il codice EStokTP. Le proprietà di reagenti, prodotti e stati di transizioni, quali geometrie, frequenze d vibrazioni ed energie, sono ottenute tramite calcoli ab initio di strutture elettroniche, mentre le costanti cinetiche di reazione tramite l’impiego della teoria dello stato di transizione e la risoluzione della master equation. Tramite regressioni lineari sono stati infine determinati i parametri cinetici dell’espressione di Arrhenius modificata per ogni reazione oggetto di studio. Nella seconda parte, i dati cinetici delle reazioni studiate sono stati aggiunti al modello cinetico del Politecnico di Milano POLIMI per la combustione, pirolisi e ossidazione parziale di idrocarburi e composti ossigenati, tra cui l’acido acetico. Con l’aiuto del programma OpenSMOKE++, simulazioni riguardo la combustione e la pirolisi dell’acido acetico sono state performate in diversi reattori e condizioni. I dati così ottenuti sono stati raccolti, post-processati e confrontati con quelli sperimentali e con quelli ottenuti con il meccanismo POLIMI senza l’aggiunta delle nuove reazioni.
Reactivity of resonance stabilized radicals produced in biofuel combustion : the CH2COOH radical
SANTORO, MATTEO
2018/2019
Abstract
Acetic acid is, among carboxylic acids, the one present in the highest concentration in the atmosphere and it is largely responsible of the problematic phenomenon of the acid rains. The major sources of acetic acid emission in atmosphere are vehicle exhaust gases and biomass combustion. Acetic acid, given its quantitative presence in biomass pyrolysis liquid, is used as reference species in biofuels design and, consequently, an accurate knowledge of its reactivity is mandatory in order to develop new and competitive alternative fuels. In the first part of this thesis, studies of the acetic acid reactivity have been deepened investigating the possible reactive pathways that the radical CH2COOH, obtained through dehydrogenation of the methyl group, can pursue with OH and CH3 radicals, which, usually, are present in high concentration in combustion and pyrolysis processes. All the reactions have been studied from a strictly theoretical point of view using the EStokTP code. Reactants, products and transition states properties, such as geometry, vibrational frequencies and energy, have been obtained with ab initio electronic structure calculations, while the rate constants with transition state theory solving the master equation. At the end, the kinetic parameters for the modified Arrhenius expression have been obtained, for each reaction studied, through nonlinear regression. In the second part, all the kinetic data obtained, have been added to the kinetic mechanism of Politecnico di Milano POLIMI which describe combustion, pyrolysis and partial oxidation of hydrocarbons and oxygenated compounds, such as acetic acid. Using the OpenSMOKE++ program, simulations of acetic acid combustion and pyrolysis have been performed in different reactors and conditions. The data coming from each simulation have been collected, post-processed and compared with the experimental ones and the ones obtained with the mechanism POLIMI without the addition of the new reactions.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150160