A Quantitative Comparison of Steady- State Designs for Reactive Distillation and Conventional Reactor/column/recycle System

Reactive distillation is an excellent example of recent advances in process intensification. It combines reaction and separation operations in one piece of equipment. This paper studies the steady-state economic optimum design of a chemical process with a generic exothermic reversible reaction A+B↔C+D for two different process flowsheets: a conventional multi-unit reactor/separator/recycle structure and a reactive distillation column. Each system is optimized in terms of total annual cost (energy and capital). The effects of two parameters on the design of each flowsheet are studied: (1) the chemical equilibrium constants and (2) the temperature dependency of relative volatilities. The most fundamental difference between the two flowsheets is the ability in the conventional process to adjust reactor temperature and distillation column temperatures completely independently. This is not possible in the reactive distillation process. Results show that reactive distillation is significantly less expensive than the conventional process for all values of the chemical equilibrium constant when relative volatilities are constant. However, when relative volatilities are temperature dependent and decrease significantly as temperatures approach those required for reasonable reaction rates, the reactive distillation column becomes more expensive than the conventional flowsheet.