Beyond dividing wall columns: Improved process intensification through liquid-only transfer and heat integration

Many chemical companies aim to achieve climate neutrality by 2050, requiring raw material changes and significant reductions in process energy. Since distillation accounts for a large share of energy use, it is a key target for process improvements. One promising approach is thermal coupling between columns, which is already industrially implemented, especially in dividing wall columns. However, such configurations often suffer from limited operational flexibility due to the fixed vapor split between parallel sections, which is largely fixed during design and difficult to adjust during operation. This limitation can be overcome by replacing each bidirectional vapor-and-liquid connection with a liquid-only transfer side stream. This concept allows each column to operate at an individual pressure and enables new options for heat integration. The present study introduces a structured approach for assessing and optimizing such systems with one or two liquid-only transfer side streams, particularly when combined with direct heat integration. Promising configurations are first identified through an efficient shortcut screening and can further be optimized using superstructure optimization. A case study on separating benzene, toluene, and para-xylene demonstrates that liquid-only transfer configurations with direct heat integration can significantly reduce energy and costs, and in many cases outperform conventional thermally coupled systems.