Comparison of different extractive distillation processes for chloroform/n‐hexane separation: design and control

Abstract

Background When extracting total glycosides from Panax notoginseng, a waste liquid containing chloroform and n‐hexane will be produced. These waste liquids are not separated and recycled in time, which will not only waste resources but also cause environmental pollution. Chloroform and n‐hexane form an azeotrope which cannot be separated by ordinary distillation methods. This study proposes three extractive distillation processes to separate the chloroform/n‐hexane azeotrope: conventional extractive distillation (ED), side‐stream extractive distillation (SSED) and extractive dividing wall column (EDWC). The total annual cost (TAC) and carbon dioxide (CO2) emissions of the three options were compared, and the optimal process was selected. Furthermore, this research developed dynamic control of the optimal process. Results Compared with ED, from the perspective of economic indicators, the SSED process showed 18.9% reduction in TAC yet the EDWC process showed 33.2% reduction in TAC. In terms of CO2 emission indicators, the EDWC process also is more advantageous. Three control structures thus were developed for EDWC: applying ±5% or ±10% feed flow disturbance, and feed composition disturbance. The results show that CS3 with temperature composition cascade control structure can perfectly control all disturbances. Conclusion This paper designs an economical, environmentally friendly and controllable chloroform/n‐hexane azeotropic separation process, which can provide a reference for the industrial application of chloroform/n‐hexane separation. © 2022 Society of Chemical Industry (SCI).

Control structure selection of increased‐pressure extractive distillation process for DMC‐MeOH azeotropic mixture

“…Thus, there are several studies in the literature which proposed alternative temperature control structures for the extractive distillation of different binary azeotropic systems, such as acetone-methanol, [33] isopropyl alcohol (IPA)-water, [34] ethanol-water, [35] tetrahydrofuran (THF)-water, [36] benzene-cyclohexene, [37] benzene-acetonitrile, [38] ethyl acetate-ethanol, [39] dichloromethane-methanol, [40] and chloroform-n-hexane. [41] Nevertheless, there are only two process control studies for extractive distillation of DMC-methanol azeotropic mixture [22,24] where both extractive and recovery columns operate at atmospheric pressures.…”