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In this work, bromelain was recovered from ground pineapple stem and rind by means of precipitation with alcohol at low temperature. Bromelain is the name of a group of powerful protein-digesting, or proteolytic, enzymes that are particularly useful for reducing muscle and tissue inflammation and as a digestive aid. Temperature control is crucial to avoid irreversible protein denaturation and consequently to improve the quality of the enzyme recovered. The process was carried out alternatively in two fed-batch pilot tanks: a glass tank and a stainless steel tank. Aliquots containing 100 mL of pineapple aqueous extract were fed into the tank. Inside the jacketed tank, the protein was exposed to unsteady operating conditions during the addition of the precipitating agent (ethanol 99.5%) because the dilution ratio "aqueous extract to ethanol" and heat transfer area changed. The coolant flow rate was manipulated through a variable speed pump. Fine tuned conventional and adaptive PID controllers were on-line implemented using a fieldbus digital control system. The processing performance efficiency was enhanced and so was the quality (enzyme activity) of the product. No presente trabalho, a enzima bromelina foi obtida a partir da casca e do talo do abacaxi, através de precipitação com álcool, com controle de temperatura. Bromelina é o nome de um grupo de enzimas proteolíticas com propriedades anti-inflamatórias e digestivas. O controle de temperatura é fundamental para evitar a desnaturação irreversível da proteína e, consequentemente, aumentar a qualidade da enzima recuperada. O processo foi realizado em duas plantas-piloto: um tanque de vidro e outro de aço-inox. Foram utilizadas alíquotas contendo 100 mL de caldo de abacaxi nos tanques. Dentro do tanque encamisado, a proteína foi exposta a condições operacionais instáveis durante a adição do agente precipitante (etanol 99,5%), porque a razão de diluição "caldo de abacaxi: etanol" e a área de transferência de calor eram alteradas. A vazão do fluido refrigerante foi manipulada através de uma bomba de deslocamento positivo. Os controladores convencional e PID adaptativo sintonizados foram implementados online, utilizando um sistema de controle digital Fieldbus. Observou-se uma melhoria no desempenho do processo, assim como na qualidade (atividade enzimática) do produto.

Gaseous ethanol may be recovered from the effluent gas mixture of the sugar cane fermentation process using a staged absorption column. In the present work, the development of a nonlinear controller, based on a neural network inverse model (ANN controller), was proposed and tested to manipulate the absorbent flow rate in order to control the residual ethanol concentration in the effluent gas phase. Simulation studies were carried out, in which a noise was applied to the ethanol concentration signals from the rigorous model. The ANN controller outperformed the dynamic matrix control (DMC) when step disturbances were imposed to the gas mixture composition. A security device, based on a conventional feedback algorithm, and a digital filter were added to the proposed strategy to improve the system robustness when unforeseen operating and environmental conditions occured. The results demonstrated that ANN controller was a robust and reliable tool to control the absorption column.