Improved design of separation system for the recovery of benzene and isopropanol from wastewater

In order to recover valuable benzene and isopropanol from wastewater, development of energy-efficient design flowsheet of this separation system is a relevant design problem in industry and worthy of investigation. The available separation methods in open literature were to either use a triple-column pressure swing distillation or by combining heterogeneous azeotropic distillation and pressure-swing distillation. Although the above two separation methods having the favorable feature of not introducing any foreign component into the system, the economics and energy consumption of the above separation design flowsheets can still be significantly improved. The purpose of this paper is to develop an improved design flowsheet for this separation task, not ever seen in open literature, making use of natural liquid-liquid splitting in a decanter and arranging the distillation sequence so that one of the preceding column to be designed as a stripper to preserve latent heat of this column's top vapor stream. Further energy-saving schemes of this separation system were also thoroughly investigated. It is found that the economics of our proposed heat-integrated separation system can significantly cut 75.1% and 66.2% in total operating cost and total annual cost, respectively, as compared to that of the best separation system recently proposed in open literature.