This is your most reliable way of knowing for sure if they will separate. Reasoning: - If you look at the Txy diagram at a given pressure and choose a temperature, the maximum separation you can get would separate the two by about 0.3-0.4 in mole fraction (AKA 0.3 x1 vs 0.7 x2 kind of thing). You can get significant separation in one stage, but it would be insufficient for most purifying purposes. Defining effectively as getting above 90% purity (though in practice you will want upwards of 95%, even 99% or above), one stage is insufficient.
