Avaliação econômica e termodinâmica do processo de destilação extrativa.

Abstract

Extractive distillation sequences have received special attention from researchers due to the high energy consumption and the low thermodynamic efficiency associated to this process. The thermodynamic efficiency has been simplified in the literature, but in this work it was approached intrinsically, thus the physical meaning of the terms related to efficiency like minimum work, work equivalent, lost work and entropy production were discussed from a physical and mathematical point of view. Process intensification alternatives have been highlighted in the reduction of energy consumption and costs in the distillation processes. Likewise, thermal integration is an alternative to reduce the energy consumption of distillation processes. The conventional extractive distillation sequences with and without thermal integration were approached in this work. They were analyzed from the economic, thermodynamic and energy optimum points of view and the main parameter of analysis was the solvent content. In addition to the high energy consumption and low thermodynamic efficiency, the extractive distillation also include a irreversibility that is reported as responsible for the low thermodynamic efficiency of this process, and this was another point of analysis on the flowcharts studied. The study cases were the azeotropic mixtures formed from ethanol-water and acetone-methanol using ethylene glycol and water as solvents, respectively. The sequences with and without thermal integration were studied considering the proposed procedure and the whole system was analyzed for the economic and thermodynamic terms, also each column (extractive and recovery columns) was separately analyzed for thermodynamic terms, besides the evaluation of the remixing effect. The results show that the configuration with thermal integration is thermodynamically more efficient when compared to the non-integration configuration, moreover the configuration with thermal integration presented lower values of TAC and energy consumption, even when negative values for thermodynamic efficiency are found, and that the thermodynamic terms must be compared to cases involving the separation of the same mixture.