RD (Reactive Distillation) is especially attractive in systems where certain chemical and phase equilibrium conditions co-exist. The reaction and distillation take place in the same zone of a distillation column, the reactants being converted with the simultaneous separation of the products and recycle of unused reactants. As the products must be separated from reactants by distillation, this implies that the products should be lighter and/or heavier than the reactants. The ideal case is when one product is the lightest and the other product is the heaviest, with the reactants being the intermediate boiling components. Moreover, as both operations occur simultaneously in the same unit, there must be a proper match between the temperatures and pressures required for reaction and separation.
If there is no significant overlap of the operating conditions of reaction and separation, then the combination of reaction and distillation is not possible (e.g., a high pressure reaction cannot be combined with a vacuum distillation).