Enhancement of conventional distillation configurations for ternary mixtures separation

Rigorous simulations at steady-state are conducted for the separation of two different ternary mixtures by conventional distillation with direct and indirect separation sequence. The studied chemical systems are (ethanol/n-propanol/n-butanol) and (benzene/toluene/m-xylene) with 99 mol% products purity at different feed compositions: (45/10/45), (33.3/33.3/33.3), and (10/80/10). In order to reduce the remixing effects in the first column a sidedraw stream is introduced at peak point composition of middle component as transfer stream to the second column. Economic optimization is carried out for the conventional and improved configurations based on energy consumption and total annual cost (TAC) as the objective function. The results indicate that improvements of thermodynamic performance of both columns are achievable and the maximum TAC saving is 29% in case of indirect sequence and 19% for direct sequence at low concentration of middle component. Improved conventional distillation sequences show a significant reduction of flue gas emissions (CO₂, SO_x, and NO_x) whish is generated by the combustion process of the utility systems.