Simplified Conceptual Design Methodology for Double-Feed Extractive Distillation Processes

Abstract

Shortcut methods have an important role in the conceptual design of distillation processes because they rapidly provide constraints for important design parameters such as minimum reflux ratio, number of stages, process feasibility, possible splits, and, specifically for extractive distillation, minimum solvent feed ratio and maximum reflux ratio. In this work, a simplified method using reversible distillation models has been applied to the conceptual design of double feed extractive distillation columns. This work uses continuation methods for calculating the curves that determine the feasibility region and all of the resulting design parameters. Combining continuation methods with the column equations yields a simple method for calculating the pinch curves that border the feasibility region. As previously found by other authors, we observed that these extractive distillation pinch curves, in addition to determining the feasibility region, are also useful for calculating an approximate minimum entrainer feed ratio independent of other parameters, as well as accurately pinpointing the minimum and maximum reflux ratios. Applications to example extractive distillation systems allow us to conclude that the method is reliable, fast, and much easier to implement than other methods presented previously in the literature. The systems acetone–methanol–water and ethanol–water–ethylene glycol were employed as case studies, allowing a graphical assessment of the method; however, it can be used in the analysis of systems with more than three components.