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A phenomenological model was developed to describe the dynamic evolution of the batch suspension polymerization of methyl methacrylate in terms of reactor temperature, pressure, concentrations and molecular properties of the final polymer. Then, the phenomenological model was used as a process constraint in dynamic data reconciliation procedures, which allowed for the successful monitoring of reaction variables in real-time and on-line. The obtained results indicate that heat transfer coefficients change significantly during the reaction time and from batch to batch, exerting a tremendous impact on the process operation. Obtained results also indicate that it can be difficult to attain thermodynamic equilibrium conditions in this system, because of the continuous condensation of evaporated monomer and the large mass transfer resistance offered by the viscous suspended droplets.

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Resumo O ácido polilático (PLA), o mais conhecido bioplástico com potencial para ser o substituto dos polímeros derivados do petróleo, é produzido pela polimerização do ácido lático. A aplicação do ácido lático para a produção de ácido polilático tem levado a um aumento substancial no seu consumo. Entretanto, o custo da matéria-prima representa um grande obstáculo na produção econômica de ácido lático para essa finalidade. Assim, vários materiais têm sido considerados como substratos alternativos, incluindo subprodutos de indústrias agrícolas, indústrias de alimentos e biomassas naturais. O presente trabalho avaliou o uso de resíduos da indústria de alimentos como suplemento nutricional do soro de leite para produção de ácido lático por cultura mista imobilizada de bactérias láticas (Lactobacillus acidophilus LA-5, Bifidobacterium BB-12 e Streptococcus thermophilus). Foram testadas três condições de pH (6,0; 6,5 e 7,0) e três condições de temperatura (30 °C, 35 °C e 40 °C) de fermentação. Também foram testados três níveis de suplementação do soro de leite com cada um dos resíduos: água de maceração de milho – AMM (0%, 5% e 10%); vinhaça (0%, 5% e 10%) e extrato de levedura (0%, 3% e 6%). Ao final da fermentação, observou-se que os tratamentos com temperatura de 40 °C e o pH inicial de 7,0 apresentaram teor de ácido lático 10% superior aos demais. Todos os resíduos foram efetivos em aumentar a produção de ácido lático quando suplementados no soro de leite. O extrato de levedura apresentou a maior concentração de ácido lático, com 0,0307 mol.L-1, resultado 20% superior ao da água de maceração de milho e vinhaça.

Os autores declararam que não há conflito de interesse. Financiamento: Os autores declararam que não receberam financiamento para o desenvolvimento da pesquisa

There are few studies with mathematical models representative of the effect of agitation on the poultry carcass cooling. Thus, the Computational Fluid Dynamics (CFD) technique was applied in the modeling and simulation of this process. Two process conditions were studied: (a) without agitation (NA) by recirculation (0 m 3 hr −1 ) and (b) with agitation (WA) by recirculation (8 m 3 hr −1 ). The simulation was performed in the software ANSYS 18.2 in a steady-state step, for the fluid flow, followed by a transient step (60 min), for the heat transfer. In NA condition R 2 is equal to 0.9959 and NRMSE (%) of 6.32%. WA condition obtained R 2 equal to 0.9923 and NRMSE (%) of 6.39%. The final temperatures were 7.11 and 5.31 C, for recirculation flows of 0 and 8 m 3 hr −1 , respectively. Increases in the volumetric flow of recirculation have a positive effect on reducing the time required for reaching the final temperature of the carcass. Practical Applications:We demonstrate that the CFD model was able to adequately predict the temperature drop profile inside the carcass, overcoming the capacity of traditional empirical models. The CFD model was sensitive to the effects of the cooling water turbulence. It was possible to numerically demonstrate that the turbulence generated by the agitation of the cooling water by recirculation causes a positive effect on the cooling rate of the carcasses. The results point to the possibility of using CFD modeling to optimize the equipment and the precooling process of poultry carcasses. Such optimization can represent a reduction in energy consumption for cold water production or even a reduction in precooling time, which contributes to the environmental sustainability and microbiological safety of poultry meat. | INTRODUCTIONThe precooling of carcasses is the last stage of the poultry slaughtering process and it aims at the quick reduction of the temperature in order to prevent the proliferation of microorganisms deteriorators and pathogens and minimizes the appearance of negative technological effects, for example, the PSE condition (James, Vincent, de Andrade Lima, & James, 2006). The precooling process can be performed by passing through a cooling tunnel with forced air, or by immersing the carcass in cold water, in tanks called chillers (Carciofi & Laurindo, 2007;Huezo, Smith, Northcutt, & Fletcher, 2007). Precooling in chillers can be performed in two or more stages. Whatever the configuration, it is required that the water temperature in the last stage is not higher than 4 C and the temperature in the first stage should not exceed 16 C (BRASIL, 1998).Immediately after slaughter, the poultry has an average temperature, measured at the center of the breast, of 42 C. In the feather removal stage, the slaughtered poultry is immersed in water heated up to 70 C, contributing to the maintenance of the carcass at high temperatures. When entering the precooling section, the carcass has

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