Comparison of heterogeneous azeotropic distillation and extractive distillation methods for ternary azeotrope ethanol/toluene/water separation

Ethanol and toluene are important organic solvents in chemical industry. Ethanol, toluene and water present a ternary minimum-boiling azeotrope and three binary azeotropes. In this article, two methods are studied to separate the ternary azeotrope: heterogeneous azeotropic distillation using the toluene, which is in the system itself, as entrainer and extractive distillation with glycerol as the only one solvent. In the heterogeneous azeotropic distillation, the pressures of the three columns are changed respectively to achieve heat integration. In the extractive distillation, only one solvent and two columns are used to separate the ternary mixture. Experiment shows that the partially heat-integrated heterogeneous azeotropic distillation reduces the energy cost and total annual cost by 27.7% and 13.4% respectively compared with the conventional heterogeneous azeotropic distillation. Unexpectedly, the extractive distillation can save 18.8% and 39.3% in the energy cost and total annual cost respectively compared with the partially heat-integrated heterogeneous azeotropic distillation.