Improved design of separation process for the recovery of cyclohexane and sec-butyl alcohol from wastewater

Abstract

Background: Economically recovering valuable cyclohexane and sec-butyl alcohol from wastewater is an important industrial problem worthy of research and investigation. The available separation flowsheet in open literature was a heat pump assisted four-column scheme combining heterogeneous azeotropic and extractive distillation. However, the above design achieves significant energy saving at the cost of huge capital investment and increased operational complexity involved in the compression system. The purpose of this paper is to develop an improved configuration for separating the ternary system without using the expensive compression system, and it can also significantly improve the economics.Methods: The core design concept of our proposed three separation flowsheets is to fully utilize the advantage of the heterogeneity of the ternary system by introducing the fresh feed into a decanter for natural liquid-liquid splitting and innovatively applying a direct-contact heat exchanger to preheat the fresh feed. Besides, the technologies of dividing-wall column, side-stream extractive distillation and heat integration are also integrated to the heterogeneous azeotropic and extractive distillation for further energy saving.Significant findings: In comparison with the existing design, our final proposed heat-integrated heterogeneous distillation process with two dividing-wall columns can significantly save energy consumption 24.5%, total annual cost 43.6% and CO2 emission 13.2%.