Design and optimization for the separation of xylene isomers with a novel double extractants-based extractive distillation

Xene is a crucial chemical raw material, serving as a synthetic monomer and solvent extensively employed in coating, medicine, rubber and other industries. It contains of three isomers: o-xylene (OX), m-xylene (MX), and p-xylene (PX), their separation is considered a worldwide challenge due to their extremely close boiling points. A novel extractive distillation based on double extractants is first proposed to separate these isomers in this paper, while it was considered impractical to separate these isomers by distillation technology alone in the past. Through the analysis of residual curve and extractant screening, two potential solvents, i.e., N-Methylpyrrolidone (NMP) and Tetramethylene sulfone (Sul) were used as extractants, and then the separation sequences were designed and optimized. The extractive distillation processes were optimized by sequential iterative method according to the minimum total annual cost (TAC), and the best separation sequence and process parameters were determined. For comparison, it was found that the optimized double extractant-based extractive distillation (DEED) process has the best economic performance with TAC of 5.72*106$, and the energy consumption was greatly reduced by 41.2% compared to the single extractant-based extractive distillation (SEED). This article provides a new perspective on energy-efficient distillation technology for industrial xylene separation and purification production.