Experimental and modeling study of the autoignition of 1-hexene/iso-octane mixtures at low temperatures

Autoignition delay times have been measured in a rapid compression machine at Lille at temperatures after compression from 630 to 840 K, pressures from 8 to 14 bar, \Phi = 1 and for a iso octane/1 hexene mixture containing 82% iso-octane and 18% 1 hexene. Results have shown that this mixture is strongly more reactive than pure iso-octane, but less reactive than pure 1 hexene. It exhibits a classical low temperature behaviour, with the appearance of cool flame and a negative temperature coefficient region. The composition of the reactive mixture obtained after the cool flame has also been determined. A detailed kinetic model has been obtained by using the system EXGAS, developed in Nancy for the automatic generation of kinetic mechanisms, and an acceptable agreement with the experimental results has been obtained both for autoignition delay times and for the distribution of products. A flow rate analysis reveals that the crossed reactions between species coming from both reactants (like H-abstractions or combinations) are negligible in the main flow consumption of the studied hydrocarbons. The ways of formation of the main primary products observed and the most sensitive rate constants have been identified

Molecular and macromolecular structure changes in polyamide 11 during thermal oxidation

The present article reports a study of thermal oxidation of unstabilized polyamide 11 films at several temperatures (90–165 °C) under atmospheric pressure and under various oxygen pressures (up to 1.6 MPa) at 110 °C. The chemical structure changes are monitored by IR spectroscopy (carbonyl groups) and UV–visible spectrophotometry (yellowing). Molar mass changes are determined by size exclusion chromatography (SEC). By investigating the influence of oxygen pressure it is clearly shown that reactions involving P° radicals other than O2 addition cannot be neglected under atmospheric pressure. Under the conditions of this study limited to relatively low oxidation levels, IR and UV measurements indicate that carbonyl groups and chromophores responsible for yellowing have the same relative yield whatever the temperature and oxygen pressure. SEC measurements highlight the significant predominance of random chain scissions over crosslinking events. Crosslinking only appears after an induction time, presumably because it involves reactions between primary oxidation products. The ratio of carbonyl groups over chain scissions is about 7.5 at low conversion and about 2.5 at high conversion, showing that α amino alkoxy radicals are mainly transformed into imides without chain scission

Thermooxidative aging of polydicyclopentadiene in glassy state

Thermal aging of thin films of unstabilized polydicyclopentadiene (pDCPD) at several temperatures ranging from 120 to 30 C was investigated by means of carbonyl build up by FTIR with ammonia derivatization, double bond titration, mass uptake measurement, hydroperoxides titration by iodometry and DSC coupled with sulfur dioxide treatment. In the temperature range under investigation, pDCPD is in glassy state and it oxidizes faster than common polymers oxidized at rubbery state (e.g. polydienic elastomers). Using the kinetic analysis, these results were ascribed to increased initiation rate due to catalyst residues, some possible intramolecular processes favoring propagation, or a very low termination rate of oxidation radical chains because of the control of termination reactions by macroradical diffusion

Estratégias para a redução da concentração de catalisadores na polimerização radicalar por transferência de átomo : uma abordagem de estudo cinético por modelagem matemática e simulação

Orientador: Liliane Maria Ferrareso LonaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: No contexto da Polimerização Radicalar por Desativação Reversível (RDRP), a associação do mecanismo de Regeneração de Ativador por Transferência de Elétrons (ARGET) à Polimerização Radicalar por Transferência de Átomos (ATRP) tem atraído atenção em termos de pesquisa, principalmente por ser um método de polimerização ambientalmente e economicamente mais favorável se comparada a ATRP convencional, devido à redução da concentração de catalisador verificada no processo. Pela escassez de registros em literatura, este trabalho tem como objetivo principal prover ferramentas matemáticas para simular a síntese de polímeros obtidos via ARGET ATRP, com a originalidade de contribuição voltada para a compreensão da cinética de reação de agentes redutores. Através de dados experimentais encontrados na literatura, dois modelos matemáticos propostos aplicados aos processos de homopolimerização e copolimerização aleatória via ARGET ATRP foram validados. A modelagem matemática desenvolvida é baseada no Método dos Momentos, sendo aplicado o Método Pseudocinético para o caso equivalente a copolimerização aleatória. No processo de validação realizado, constantes cinéticas, dentre aquelas que não se tem registros na literatura, foram ajustadas aos modelos através de algoritmo de otimização. Resultados fornecidos pela modelagem indicam que quanto maiores as concentrações iniciais de tanto do desativador quanto do agente redutor, maior a conversão de monômero, maior o peso molecular médio e menor a dispersividade. Simulações feitas também confirmam que a concentração inicial de desativador é um parâmetro crítico com maior sensibilidade do que a de agente redutor no processo ARGET ATRP em soluçãoAbstract: In the context of Reversible Deactivation Radical Polymerization (RDRP), the association of Activators Regenerated by Electron Transfer (ARGET) mechanism with the Atom Transfer Radical Polymerization (ATRP) has attracted attention in terms of research, mainly because it is an environmentally and economically more favorable polymerization method if compared to conventional ATRP, due to the catalyst concentration reduction verified in the process. By the scarcity of records in literature, this work has as main objective to provide mathematical tools to simulate the synthesis of polymers obtained by ARGET ATRP, with the originality of contribution focused on the comprehension of the reaction kinetics for the reducing agents. Through the experimental data found in the literature, two proposed mathematical models applied to the homopolymerization and random copolymerization processes via ARGET ATRP were validated. The mathematical modeling developed is based on the method of moments, being applied the method of pseudo-kinetic constants for the case equivalent to the random copolymerization process. In the model validation, kinetic constants, among those that have no records in the literature, were obtained by optimization algorithm. Results provided by the modeling indicate that the higher the initial concentrations of both deactivator and reducing agent, the monomer conversion, the higher the number-average molecular weight and the lower the dispersity. Simulations done also confirm that the initial concentration of deactivator is a critical parameter with higher sensitivity than the reducing agent in solution ARGET ATRP processMestradoEngenharia QuímicaMestre em Engenharia Química1725186CAPE