Energy-saving improvement of heat integration for separating dilute azeotropic components in extractive distillation

Three-column extractive distillation is often used to separate dilute azeotropic components. Although heat integration is not new, there are many new findings for it in the three-column extractive distillation process. For the first time, three kinds of multi-effect heat integration and five kinds of solvent sensible-heat recovery are compared. It is first found that the pre-concentrator distillate composition and the solvent feed temperature that are always ignored have unexpected effects on heat integration. It is first found that different forms of heat integration can all be fully thermally integrated by adjusting parameters especially the above two. Moreover, it is first found that splitting the fresh feed into two streams, one for the pre-concentrator and the other for the extractive column can improve some heat-integrated processes. Four improvement methods are proposed based on these findings. Separating dilute aqueous isopropanol is used to study these specific effects. Two other examples are used to illustrate the feasibility of the improvement methods. The results show that heat integration can be improved to be more energy efficient than the original heat integration, and even than some new methods.