Sustainable recovery of benzene and tert-butanol from wastewater using energy-efficient heterogeneous azeotropic pressure-swing distillation with multi-objective optimization

The wastewater generated in the production process of tert-butanol usually contains benzene and tert-butanol, but benzene, tert-butanol and water can form a mixture which exhibits one ternary azeotrope and three binary azeotropes. This system is pressure-sensitive, and its ternary phase diagram features a heterogeneous region. Accordingly, changing the operating pressure or using a decanter for natural liquid-liquid separation are proposed for separating the mixture. The NSGA-II algorithm is utilized for multi-objective optimization of these separation processes to identify the optimal scheme. In comparison to the pressure-swing distillation (PSD) and heterogeneous azeotropic distillation (HAD), the heterogeneous azeotropic pressure-swing distillation (HAPSD) process demonstrates superior performance. Compared to the PSD-2 process, the total annual cost (TAC), exergy destruction, the total energy consumption (TEC) and CO₂ emissions of the HAD process are reduced by 41.00 %, 41.68 %, 19.79 % and 40.55 %, respectively, while those of the HAPSD process are reduced by 64.55 %, 67.73 %, 45.30 % and 68.10 %, respectively. Additionally, the HAPSD process incorporates heat pump technology and heat integration technology to minimize energy demand. The results reveal that the HAPSD process combined with heat integration and heat pumps outperforms the PSD process and HAD process. Specifically, compared with the PSD process, it achieves significant reductions in various indicators: 75.47 % in TAC, 88.94 % in TEC, 88.10 % in gas emissions, and 87.87 % in exergy destruction, respectively.