This investigation focuses on the distillation mole fraction curves that have been used in the design and synthesis of reactive and non-reactive separation processes. Based on deriving new expressions to calculate the non-equilibrium residue composition maps for reactive separation processes it incorporates mass transfer effects and design aspects. It also discusses the chosen strategy to solve the differential algebraic equation (DAE) system in order to find the non-equilibrium reactive mole fraction curves. It is shown that in the MTBE synthesis problem, the stationary reactive points calculated by equilibrium and non-equilibrium approaches do not coincide for reactive saddle-point azeotrope.