Tabela 3. Teores de monômero finais após aplicação das estratégias para sua redução.T -temperatura; NaPS -persulfato de sódio; TBH -terc-butil-hidroperóxido; MBS -metabissulfito de sódio.
AGRADECIMENTOS Agradeço ao Prof. Reinaldo Giudici pela oportunidade, apoio, paciência e pela valiosa orientação durante esses três anos de trabalho em conjunto. Agradeço a Prof. Cláudia Sayer pela co-orientação e pela sua participação em mais esta etapa da minha formação. Agradeço aos professores Darci Odloak e Galo A. Carrillo Le Roux pela participação em minha qualificação e pelas sugestões e devidas correções. Agradeço ao Departamento de Engenharia Química da Escola Politécnica da Universidade de São Paulo pelo apoio e pelas oportunidades proporcionadas. Agradeço à Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) pela concessão da bolsa e pelo suporte financeiro a este projeto. A BASF pelo fornecimento dos monômeros.
ABSTRACTThe increasing demand for the production of polymers with more tight properties has placed great emphasis on the development of accurate and robust online monitoring techniques of polymerization reactions.Unfortunately, most of the main characteristics are not measurable online from analytical methodologies currently available and, therefore, in practice, the final properties of polymer latexes are obtained through off line characterization of discrete samples collected from the process, resulting in measurement delay which is undesirable for real-time control. On the other hand, since most of the polymerization reactions are highly exothermic, it is possible to quantify continuously the heat release rate based on temperature measurements and energy balance equations that, in turn, can be used to infer valuable information about the state of process.However, this approach requires up-dating the value of the global heat exchange coefficient through reaction, once this parameter is subject to significant time variations.Therefore, this work aims to examine the feasibility of joint implementation of the concepts of reaction calorimetry and nonlinear state observers for estimation of the states of a chemical process. In order to do that, two distinct chemical reactions will be considered: a) a hydrolysis of acetic anhydride reaction, b) an emulsion copolymerization reaction.The results showed that this approach shows a strong dependence of the tuning parameters, preventing its use for online monitoring of a chemical process. On the other hand, applying the heat balance it is possible to infer continuously the heat release rate and the states of polymerization reactions. Keywords: nonlinear state observer, reaction calorimetry, hydrolysis of acetic anhydride, emulsion polymerization. = J J J J J J J p n
The decrease of initiation efficiency (radical entry efficiency) during seeded emulsion copolymerizations of styrene and butyl acrylate with different residual monomer reduction strategies was evaluated. Experiments were carried out using 50 and 99wt.% of styrene in monomer feed stream. Simulations were performed with a detailed mathematical model of the process that takes into account the diffusion control of initiation, propagation and termination. Results showed that the radical entry into polymer particles is strongly influenced by the aqueous phase kinetics and by the monomer solubility in aqueous phase. Simulation results were compared to experimental results of residual monomer and showed that the residual monomer content can be reduced by a temperature increase at the end of the polymerization. However, an additional feeding of more initiator, even when combined with such an increase of temperature, did not lead to a smaller residual monomer content due, mainly, the kinetic of termination in aqueous phase and radical anchoring. A model that accounts for the reduction of initiator efficiency (free radical entry efficiency) was successfully used to explain the behavior of the experimental observations and was able to correctly predict the qualitative trends of the effectiveness of different residual monomer reduction strategies.
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