For this question I am using Ethanol as an example. The following is the vapor-liquid equilibrium diagram for Ethanol under atmospheric pressures.

McCabe-Thiele Diagram Source: Wikipedia Ethanol (Data Page)

Under reduced pressures do the number of theoretical separations decrease for a given system? Ethanol for example needs approximately 14 separation "plates" to achieve the azeotrope.

From my understanding wouldn't this only break the azeotrope and allow separation to a higher purity? Ex. Vacuum operation doesn't increase the efficiency as far as theoretical required separations go. (Vacuum Operation Plates == Atmosphereic Operation Plate)

Note: For the purposes of this question efficiency is in reference to the number of theoretical plates, and not the total heat required to obtain the pure product.

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    $\begingroup$ The azeotrope is alway only reached for an infinite number of plates, so this question makes no sense in the way it is written. At different pressure, the two curves will look differently, making it easier or not to reach a certain composition. Without data at other pressures, that's hard to say. $\endgroup$ – Karl May 13 '18 at 21:29

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