Effect of reboiler placement on energy and cost in intensified reactive-extractive distillation

• Placement of reboiler in thermally coupled distillation affect the energy • Reboiler in reactive extractive column increased energy and cost • Reboiler in entrainer recovery column yielded energy and cost savings • Comprehensive analysis on internal vapor flowrate Double-column reactive extractive distillation (DCRED) is widely used for separating water-containing azeotropic mixtures, and numerous studies have explored process intensification to enhance its energy and economic performance. Thermally coupled (TC) configurations are an established intensification strategy in distillation systems; however, when applied to DCRED (TC-DCRED), energy and cost reductions are not consistently achieved, and the underlying causes remain unclear. This study investigates the effect of reboiler placement in TC-DCRED using the tetrahydrofuran (THF)/methanol (MeOH)/water system as a case study. Two configurations are examined: TC-DCRED-FCR, where the reboiler is located in the reactive–extractive distillation column, and TC-DCRED-SCR, where the reboiler is placed in the conventional distillation column. The TC-DCRED-FCR configuration leads to a 44.75% increase in reboiler duty and a 100.82% increase in total annual cost (TAC) relative to conventional DCRED. In contrast, TC-DCRED-SCR achieves 10.41% energy savings and a 2.38% reduction in TAC. These differences arise from interactions among side-draw flow, internal vapor flow, operating pressure, and bottom-product composition, which significantly affect reflux ratio, boil-up rate, and column geometry. Overall, TC-DCRED-SCR demonstrates energy and economic advantages, particularly for the THF/MeOH/water system.