Effect of relative volatility on the quantitative comparison of reactive distillation and conventional multi-unit systems

A previous paper presented a quantitative economic comparison of reactive distillation with a conventional multi-unit system for a wide range of chemical equilibrium constants. Assuming constant relative volatilities (α = 2), reactive distillation was shown to be less expensive than the conventional process. This paper extends this work to explore how the relative volatilities affect the design of these flowsheets in two ways: (1) relative volatilities between adjacent products and reactants are reduced, and (2) relative volatilities are temperature dependent. A fundamental difference between the two flowsheets is the ability in the conventional process to adjust the reactor temperature and distillation column temperatures completely independently, which is not possible in the reactive distillation process. Results show that 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.