A new metric for the evaluation and selection of energy-intensified extractive distillation sequences

Extractive distillation is a widely-used but energy-intensive method for separating homogeneous azeotropic mixtures into pure components. Numerous design alternatives have been proposed for reducing energy consumption in such processes, including alternatives with side-streams, column stacking and thermally coupled sequences. However, there is very little guidance in the literature about which alternative is likely to work the best in a given situation.To address this deficiency, in this work, seventeen industrially-relevant chemical systems comprising two species that form a minimum boiling azeotrope and a heavy entrainer are selected for study. Two ordinary and six energy-saving flowsheet alternatives for extractive distillation processes were also selected. Each of the eight flowsheet alternatives was optimized for each of the 17 chemical systems. A novel metric RCB (the ratio of the entrainer flow rate to the heavy key flow rate) is proposed to facilitate interpretation of the results. General trends in the relative attractiveness of the three energy-saving strategies (side streams, thermal coupling, column stacking heat integration) were found as RCB changes. An understanding of these trends can help engineers to understand the conditions for which various energy-savings strategies are most likely to be effective.