Insight into the rational design of reactive-extractive distillation for separating water/toluene/n-butanol via an improved sequential iterative optimisation

High-efficiency recovery of n-butanol (Bu) and toluene (Tol) from industrial wastewater plays a significant role in enabling sustainable chemical industry practices. In this work, we report a reactive-extractive distillation at reduced pressure and a solvent recovery column (RPRED) for separating a ternary azeotropic mixture of water/Tol/Bu via thermodynamic insights, which resulted in better technoeconomic and environmental performance than the conventional pressure swing distillation configuration. The work began by analysing the thermodynamic aspects of two azeotropic systems before and after EO hydration, the process feasibility, and the conceptual design of the RPRED process via ternary phase diagrams. The second part of the work focuses on a sequential iterative optimisation (SIO) approach with the verification of liquid holdup on trays in the iteration loop to perform rational optimisation, which considers the preoptimisation loop of determining the pressure boundary, the reflux ratio, and the distillate rate on the basis of the existing distillation boundary of Tol/Bu/ethylene glycol (EG) and the subsequent minimization of total annual cost to achieve a feasible solution at the refined optimisation loop. The third part of the work compares the SIO results with those of two genetic algorithm-based optimisation schemes, including the converged liquid holdup of the SIO approach and varying liquid holdup, which validates the reliability of our proposed SIO procedure. The fourth part of the work uses a conventional SIO optimised configuration consisting of the decantation and pressure swing distillation (DPSD) scheme, which was developed in our previous work, as a baseline of comparison against RPRED. Overall, the RPRED configuration resulted in superior economic, environmental, and thermodynamic efficiency performance relative to the DPSD configuration.