Simulation of the Extractive Distillation Process of Ethanol-Water- Propylene Glycol System

Abstract

Anhydrous ethanol is of great importance in the chemical industry, due to its diversity of applications, fuel being the main one. Anhydrous ethanol is added to gasoline, in the proportion of 20 to 25%, in order to increase the octane, improve the performance and reduce the pollution rates. However, for that use, ethanol must be practically free of water, with at least 99.6% of alcohol content (% in volume). The challenge is that the ethanol-water mixture presents an azeotrope, which hinders the separation in conventional methods, such as simple distillation. For the anhydrous ethanol production, extractive and azeotropic distillation are the methods most used, consisting on the addition of a third substance in the distillation column capable of changing the liquid-vapor equilibrium behavior of the system, modifying the relative volatility of the compounds of the initial mixture and thereby obtaining complete separation of the components. As an alternative to the various processes used, this work proposes the extractive distillation process using propylene glycol as the solvent, being the third component for the separation of the ethanol-water system. The choice of solvent is based on the miscibility with water and the ability to absorb it, as it has a low vapor pressure and, since it has been seen that many of the solvents already in use are toxic and are pollutants, such as ethylene glycol. Therefore, the ethanol separation process using propylene glycol as the solvent was evaluated using ProSimPlus software. It was simulated on the short-cut column, with the S/F ratios equal to 0.5, 0.7 and 0.9. The molar fraction of ethanol obtained in the distillate was higher than 0.994, which accounts for approximately 99.9% volume, and could thus be qualified as anhydrous ethanol. The obtained results showed that the azeotrope was broken, the distillation process was technically possible, applying the propylene glycol.