Effect of entrainers with different boiling point sequences on the design and performance for side-stream extractive distillation processes.

• A thermal coupled SSED sequence with intermediate and heavy entrainers is investigated. • The SSED is adopted to separate the binary mixture of acetone + n- heptane. • The SSED sequence with p -xylene can offer reduction of TAC and CO 2 emissions. An azeotropic mixture of acetone and n -heptane is commonly found in many pharmaceutical wastewaters. In this work, the separation of acetone / n -heptane was studied using intermediate- and high-boiling-point entrainers (benzene and p -xylene, respectively). To maximize the economic benefits and mitigate the economic and environmental impact of the separation process, traditional extractive distillation and side-stream extractive distillation processes were developed for different entrainers. The sequential iteration method was employed to optimize the extractive distillation process, with the total annual cost as the constraint objective. The results show that p -xylene can facilitate the separation of acetone / n- heptane, with high efficiency and low energy consumption, when using a double distillation column. Among the four separation processes developed, the p -xylene side-stream extractive distillation process delivers the best economic and environmental performance, with a total annual cost of 6.04 × 10⁵ $/y and CO 2 emissions of 1114.66 kg/y. Compared to the case of traditional p -xylene extractive distillation and benzene side-stream extractive distillation processes, the total annual cost of the p -xylene side-stream extractive distillation process was reduced by 9.56% and 49.22%, respectively, while the corresponding CO 2 emissions were reduced by 15.71% and 48.85%. [Display omitted] [ABSTRACT FROM AUTHOR]