Comparison of Complete Extractive and Azeotropic Distillation Processes for Anhydrous Ethanol Production Using Aspen Plus™ Simulator

Abstract

Performance of the extractive and azeotropic distillation processes using ethylene glycol and cyclohexane as solvents, respectively, for anhydrous ethanol production, were investigated using 02 RadFrac columns each and solvent recycling streams via simulation in Aspen Plus™ Simulator. Both operate at 1 atm, and feed flow rate equals to 100 kmol.h-1 (ethanol – 0.896 and water – 0.104 in mole fractions at the azeotropic point). The NRTL-RK was the model used for extractive and azeotropic distillations. The anhydrous ethanol purity from top of the 1st column of the extractive distillation (22 stages) was 99.50 % (on a mole basis) and water with 99.20 % of purity at the top of the 2nd column. On the other hand, in the azeotropic distillation, the 1st column (30 stages) had a bottom product of anhydrous ethanol purity of 99.99 % and water with 99.99 % of purity in the 2nd column, also at the bottom. Both processes produced anhydrous ethanol with a high-grade purity required by the standard norms ASTM D4806, EN 15376, and ANP 36. However, the extractive distillation spent 1,928.2 kW in the reboilers against 4,680.3 kW in the azeotropic distillation, demonstrating extractive distillation is the most economical option. Consequently, the energy consumption is an essential analysis for choosing the type of distillation, when an azeotropic mixture needs a good separation task. Finally, the extractive distillation demonstrated to be much more competitive than azeotropic distillation for this type of mixture although azeotropic distillation obtained a higher purity of anhydrous ethanol.