Improved Design and Optimization for Separating Azeotropes with Heavy Component as Distillate through Energy-Saving Extractive Distillation by Varying Pressure

Abstract

With the aim of saving energy and capital cost, in this work we propose a novel extractive distillation strategy by varying pressure for the separation of pressure-sensitive azeotropic mixtures. Proceeding from the thermodynamic insight of ternary systems in extractive distillations, the considerable energy-saving potential by changing operating pressures is observed. The separation of acetone−methanol with a minimum boiling azeotrope using a heavy entrainer chlorobenzene is chosen as an illustrative case, and it belongs to a scarce classification 1.0-1a-m2 in which the component with higher boiling point is withdrawn as a product. Through the analysis of a ternary residue curve map and isovolatility curves, it could be observed that the minimal amounts of entrainer feed and extractive feasible regions in the ternary diagram are sensitive to pressures. A 3 atm pressure is preliminarily selected for the comparison with atmospheric pressure. The optimal pressure is found through sensitivity analysis. The results showed that 33.9% and 30.1% reductions in energy consumption and total annual cost, respectively, are achieved compared with that operated at atmospheric pressure. The discussion is then carried out by analyzing residue curve maps, relative volatility profile, and extractive efficiency indicators. Finally, heat integration was considered to further reduce costs. The methodology proposed in this work may provide some new theoretical guidance for the design and optimization of azeotrope separations through extractive distillation.

Review of extractive distillation. Process design, operation, optimization and control

“…3.1 indicates that low contents of impurities in the recycled stream is compulsory to guarantee high purity product. However, for (0.0-1)-H1 class, significant contents of impurities (3%) in the recycled entrainer was found helpful for reducing the process energy cost (You et al, 2017b). The reason could be explained because of arguments presented in Section 2: for class 1.0-1a, the achievable product is a RCM saddle while it is a RCM stable node for class 0.0-1.…”

Isobaric Vapor–Liquid Equilibria and Extractive Distillation Process Design for Separating Ethanol and Diethoxymethane

“…Thermodynamic analysis of the ternary diagram, containing residue curves and isovolatility curves, not only provides a criterion to estimate the feasibility of the entrainer but also is meaningful for the conceptual design of the extractive distillation process. − Based on the thermodynamic analysis, You et al studied the feasibility of separating acetone and methanol with water as the entrainer. Song et al determined the feasible region and separation sequence of ethanol + ethyl propionate + isobutyl acetate thernary systems.…”

Vapor–Liquid Equilibria and Conceptual Design of Extractive Distillation for Separating Ethanol and Ethyl Propionate

“…Thermodynamic analysis of ternary diagram, containing residue curves, isovolatility curves, and extractive composition profile, not only provides a criterion to estimate the feasibility of the entrainer but also is meaningful for the conceptual design of the extractive distillation process. − Based on the thermodynamic analysis, You et al studied the feasibility of separating acetone and methanol with water as the entrainer and the energy-saving potential with the increase in pressure. Gu et al explored the influences of entrainer and pressure on the isovolatility curves of entrainer + methanol + water ternary systems.…”