Generally, the selection of
an entrainer in extractive distillation depends on relative volatility,
but our previous research shows that relying on relative volatility
alone may not achieve the best economic and environmental benefits
in the process. In this work, the effects of different entrainers
on the separation process of ternary mixtures containing two minimum
boiling azeotropes by extractive distillation were studied using a
dichloromethane (DCM)/methanol (MeOH)/water system as an example.
Taking the gas emission and total annual cost as objectives, the separation
processes of eight entrainers in the DCM/MeOH/water system were optimized
and compared by a multiobjective optimization method. The optimization
results show that 1,3-propanediol had the best economic and environmental
benefits, although its relative volatility was not the best. The limitations
of screening entrainers by relying on relative volatility alone were
demonstrated. To achieve optimal economic and environmental benefits,
entrainer screening needs to consider the relative volatility, thermodynamic
properties of the entrainers, and possible thermal integration schemes.
This work provides a reference for the screening of entrainers and
process design in extractive distillation processes.