Systems Design, Modeling, and Thermoeconomic Analysis of Azeotropic Distillation Processes for Organic Waste Treatment and Recovery in Nylon Plants

Nylon-6 and nylon-6,6 processes produce considerable amount of organic waste (known as light oil) consisting of n-pentanol, cyclohexanone, and cyclohexene oxide, which are difficult to separate and recover. This Article proposes six novel process designs to separate the light oil into three value-added products based on azeotropic distillation using water as an entrainer. These azeotropic distillation process designs take into account direct sequence, indirect sequence, thermal coupled column, and three types of dividing wall columns (dividing wall at the top, bottom, and middle of columns, respectively) for entrainer recovery. A conventional distillation process design for separation of the same light oil is also modeled and analyzed for comparison. High-fidelity process simulations are performed for each of the seven process designs in Aspen Plus. We further conduct exergy analyses and technoeconomic analyses to evaluate and compare the exergy efficiencies and economic performances of these seven process designs. The results indicate that the proposed azeotropic distillation process design with dividing wall at the middle of the column has the best performance in terms of both exergy efficiency and total annual cost.