Banca de DEFESA: CRISTIANO DE SOUZA ALMEIDA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : CRISTIANO DE SOUZA ALMEIDA
DATE: 15/09/2020
TIME: 10:00
LOCAL: Plataforma RNP
TITLE:

Kinetic Study of the Unimolecular Reactions in the Dimethoxymethane Pyrolysis and Combustion Mechanisms

KEY WORDS:

dimethoxymethane, combustion, unimolecular, polyoxymethylene dimethyl ethers.

 

PAGES: 65
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Cinética Química e Catálise
SUMMARY:

Currently, the search for renewable and clean energy resources, important and strongly interconnected characteristics, is gaining increasing prominence in scientific research. Within this focus, great interest has been dedicated to the energy efficiency of a category of oxygenated fuels: polyoxymethylene dimethyl ethers (POMDME). Dimethoxymethane (DMM, CH₃OCH₂OCH₃) is found in this group, offering cleaner combustion, free from soot and polluting oxides such as SOx. This study aims at proposing a sub mechanism of initiation steps for the DMM combustion and pyrolysis kinetic models. Specifically, the kinetics and thermodynamics of DMM unimolecular reactions are discussed. Calculations were performed at the M06-2X/aug-cc-pVTZ level including geometry optimizations, vibrational frequencies and reaction paths calculations. Results suggest that the dissociation reaction pathway, forming CH₃ + OCH₂OCH₃, is the main reaction channel, with the lowest dissociation limit, 82.40 kcal.mol^-1. The reaction channels that lead to H₂COCHOCH₃ + H₂, CH₃O + CH₂OCH₃ and HCOCH₂OCH₃ + H₂ are competitive, with reaction barriers of 85.90, 87.38 and 87.95 kcal.mol^-1, respectively. Hydrogen atom dissociation pathways, with a dissociation limit of 94.56 and 95.86 kcal.mol^-1, and the decomposition reaction that leads to H₂ + CH₂OCH₂ + H₂CO are unfavorable, both from the kinetic and thermodynamic points of view.Changing the focus of the study to the decomposition reactions of the primary radicals, the pathways that lead to HCO + CH₂OCH₃, H₂CO + HCOCH₃, H₂COCHO + CH₃ are highlighted because they are the most favorable, with reaction energies in the respective values 15.87, 9.97 and -1.76 kcal.mol^-1, the latter having an exothermic profile. Results for the dissociation reactions agree with the literature data. The kinetics of decomposition reactions, on the other hand, represent a new contribution to this work. Kinetic parameters, calculated with the canonical variant transition state method, for the most important reaction channels, contributed to the inclusion of these steps in the combustion model for dimethyl ether, as well as the composition of the combustion model for DMM. Finally, the thermodynamic and kinetic information on the unimolecular processes related to the combustion of DMM obtained in this work have shown to be an important contribution to the understanding of the combustion of alternative POMDME fuels.

BANKING MEMBERS:
Presidente - 1716351 - GLAUCO FAVILLA BAUERFELDT
Externo ao Programa - 1808284 - MARCIO SOARES PEREIRA
Externo à Instituição - LEONARDO BAPTISTA - UERJ