Otimização e controlabilidade do processo de destilação extrativa de alta pureza.

Abstract

Distillation is one of the oldest and most important separation processes used in chemical and petrochemical industries. On the other hand, it is a process whose thermodynamic efficiency is very low, responding for the highest percentage the overall energy consumption of the plant. In this sense the distillation is the most targeted distillation processes with regard to energy consumption and that's how this work came. In case of mixtures where one observes the presence of azeotropes the conventional distillation i f shows unable to promote the desired separation. The separation of these mixtures is not possible through conventional distillation and usually they are separated using azeotropic distillation: homogeneous (extractive) or heterogeneous (azeotropic). In both processes, a third component is added to enable the separation. The behavior the column in study in this work presents characteristics of a column of extractive distillation and the question that draws the most attention on this type of distillation is the effect of solvent over the separation; more specifically, the effect of amount of solvent and, several articles evaluate this effect by sensitivity analysis. However, little attention is given on the controllability of the process. The present study aims to evaluate the sensitivity of the process at steady state before operational changes and to verify the possibility of multiple steady states in the extractive distillation process, and to evaluate the effect of solvent concentration and the number of stages on the controllability of the extractive distillation process. Due to its industrial importance, dehydration of aqueous mixtures of ethanol using as solvent ethylene glycol was the system chosen as case study. According to the results, the increase in extraction section of an extractive distillation column is favorable to any separation that occurs in this type of column. It was possible to demonstrate the possibility of maintaining the energy consumption of this type of column, despite the increase in size, with the manipulation of the variables: the ratio of reflux, flow of solvent and distillated, and solvent and azeotropic mixture feed stage. Finally, it was determined that a better controllability of "small" columns was obtained in a low concentration of the solvent, while a high level of solvent concentration is better in the "large" columns.