Energy-Saving Separation of the Ethanol-tert-Butanol-Water Azeotrope System Based on an Ionic Liquid

The separation requirements of the ethanol-tert-butanol-water system are difficult to meet due to the formation of azeotropes under normal pressure. After screening the four most important ionic liquids, i.e., [BMIM][BF4], [EMIM][Cl], [HMIM][Cl], and [EMIM][AC], ionic liquid [EMIM][AC] was selected as extractant, and quantum chemical calculations based on COSMO-SAC theory were carried out to analyze the mechanism of the separation process. An ethanol-tert-butanol-water extractive distillation process was designed, optimized with the goal of the lowest total annual economic cost, and the cost of carbon dioxide emissions was calculated. To further save energy, a heat pump distillation process was designed and compared with the conventional ionic liquid process. The annual total cost of the heat pump distillation process is reduced by 10.11 %, and carbon dioxide emission costs are reduced by 61.9 %. Comparison with the conventional extractive distillation process and its modified process revealed economic advantages for the ionic liquid extractive distillation process and its heat pump version.