The separation of ternary azeotropic mixture : thermodynamic insight and improved multi-objective optimization

Abstract

Acetonitrile (ACN) and Ethanol (EtOH) are important organic solvents and they are frequently used as mobile phase in high performance liquid chromatography resulting in the production of waste ternary mixture ACN/EtOH/water. The separation of such ternary systems is a key to recovery valuable solvents in waste liquid from views on economic and environmental benefits. Thus, we proposed an effective separation strategy of triple-column extractive distillation (TCED) to separate such ternary mixture with three binary azeotropes and a single ternary azeotrope for the first time. The suitable entrainer and the separation sequence were determined by thermodynamic insights (i.e., residue curve maps, isovolatility line, univolatility line and material balance lines). In addition, an improved multi-objective genetic algorithm optimization embedding the weak mutation and detection/deduplication of overlapping solutions was employed to optimize the proposed process with plenty of continuous and discrete decision variables. Finally, DMSO was determined as the most appropriate entrainer to separate such complex ternary mixture. The separation sequence of TCED process was determined as the ACN first, then EtOH and water as the last product. The optimal TCED process with the trade-off benefits between fixed capital investment and annual operating costs was obtained.