Definição de sequências de separação utilizando curvas residuais: colunas convencionais versus colunas com retirada lateral.

Abstract

The great importance of the distillation process is due to the effectiveness in the separation of the most different mixtures. However, the operation of distillation columns demands great amount of energy, what has been motivating researches in the sense of reducing this energy consumption. The economy, in investment terms and operational costs, in distillation processes can be gotten through the substitution of conventional columns (twoproducts column) for columns with lateral retreat (side-stream column). Intuitively, the lateral current should contain mainly the intermediary component. Besides, the literature suggests that this lateral current is in the vapor phase if the retreat happens below the feeding and in the liquid phase if above feed, according the indication of Tedder and Rudd (1978). In this point, the residual curves become of fundamental importance for choice of systems where we can substitute conventional columns for columns with lateral retreat. Using the approach of the residual curves, this work shows a new processe and new distillation sequences for old processes. The studies were accomplished for mixtures azeotropics, so that the lateral current could be a binary azeotropic or a pure component. The obtained results show that the advantage of the columns with lateral retreat depends on the location of the initial feeding in the composition triangle. Another interesting conclusion is that the lateral retreat can happen in the liquid phase, even the retreat being located below the feeding. However, the use of the residual curves as approach for definition of separation sequence should be careful, because, in some cases this approach affirms to be impossible a separation when, in fact, the separation is extremely easy. An example of this situation is the dehydration of aqueous mixtures of etanol using ethylene glycol as solvent.