![]() This means that you don't have any extra major factors to make the two compounds want to separate from each other. The boiling points are significantly different (-1☌ butane vs -43☌ propane), and this allows for an ok separation with the first stage - The chemical composition is very similar (both alkanes, only 1 CH2 different), and so the activity coefficient is close to 1, meaning close to ideal mixture behavior. 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. These nomograms have two vertical coordinates, one for pressure, and another for temperature. DePriester in an article in Chemical Engineering Progress in 1953. Defining effectively as getting above 90% purity (though in practice you will want upwards of 95%, even 99% or above), one stage is insufficient. DePriester Charts provide an efficient method to find the vapor-liquid equilibrium ratios for different substances at different conditions of pressure and temperature.
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