Um novo entendimento da segunda lei da termodinâmica para sistemas de destilação extrativa.

Abstract

The use of exergetic analysis in distillation columns is one of the bases for locating the sources of irreversibility of the process and thus making it more sustainable. The study of the Second Law is still challenging with regard to the interpretation of thermodynamic efficiencies of extractive distillation columns, being found in the literature values that cause discomfort, such as negative results. In this paper, this circumstance is investigated for the purpose of to clarify the possibility of obtaining negative values for efficiency according to the Second Law. Moreover, it was also evaluated the relationship of these efficiencies with the energy consumption of the reboilers. Finally, an in-depth investigation was carried out regarding the remixing effect vs. thermodynamic efficiency relationship. The extractive distillation process for the acetone/methanol chemical system was simulated using Aspen Plus, considering two different solvents, water and DMSO. Thermodynamic efficiency was investigated for changes in solvent content and azeotrope feed temperature. The results suggest that there is no correlation between Second Law efficiency and thermal load. On the other hand, the thermal load is directly related to the lost work, which is the appropriate parameter to be considered in thermodynamic evaluations. In quantitative terms, the remixing effect was not directly related to thermodynamic efficiency, in contrast, it showed a relationship with lost work, measurably, excluding cases with high solvent flows.