Thermodynamic Insights and Multiobjective Optimization for Toluene/Acetonitrile/Hexane Ternary System under Varying Feed Compositions

Abstract This work explores the separation processes for toluene/acetonitrile/hexane (Serafimov class 2.0–2b-B) in the full concentration range. While previous studies on class 2.0–2b-B systems primarily examined fixed feed compositions or relied on single conventional configurations, different heterogeneous azeotropic separation processes of toluene/acetonitrile/hexane mixtures under different feed compositions are studied in this work. The feed region is divided into two blocks by a line connecting the unstable node with the lowest temperature and the stable node with the highest temperature. Consequently, with the feed located to the right of line AC, the heterogeneous azeotropic distillation with direct separation process (HAD-DS) is proposed. In contrast, with the feed located to the left, conventional heterogeneous azeotropic distillation process (HAD-CON), HAD process with partial HEX reflux (HAD-PHR), and HAD process with partial OH reflux (HAD–OHR) are proposed. Subsequently, a multiobjective optimization algorithm and TOPSIS method are employed to minimize TAC, CO2 emissions, and exergy loss. When the feed composition is situated to the right side of the AC line and the feed composition is 0.4 HEX/0.4 TL/0.2 ACN, the TAC of the optimized HAD-DS process is 4.59 × 105 \$/y, exergy loss is 343.80 kW, and CO2 emission is 457.96 kg/h. When the feed composition is situated to left and the feed composition is 0.3 HEX/0.4 TL/0.3 ACN. Compared with HAD-CON, HAD–OHR process reduces TAC, CO2 emissions and exergy loss by 34.51%, 39.53% and 41.56%, respectively.