In my example, suppose we had a system of multiple components (benzaldehyde, benzyl alcohol, methyl benzoate) and wanted to separate the mixture using fractional distillation.

If we rule out any azeotrope formation, then the components should all be separable completely if the column is good enough right?

Also, suppose we collect a fraction in a vacuum distillation at 60 °C (bath temperature) with a head (thermometer) temperature of 33 °C. We collect some of it, but after time, it would stop and we have to increase the bath temperature (lets say 65 °C) to be able to continue to collect the 33 °C fraction (which stays at 33 °C). That’s because the boiling point of the initial mixture goes up and we distill the most volatile compound off.

But if the separation is good enough, we should be still able to get out the pure product out of this fraction because the head temperature hasn’t changed and it’s the same compound right?

  • $\begingroup$ Rather, good enough columns lead to pure enough products (individual ones or azeotropes). $\endgroup$
    – Poutnik
    Feb 16 at 3:52
  • $\begingroup$ But we have to increase the bath temperature continously to get all of the same fraction (33 °C) out right? As long as the head temperature remains constant it should be the same compound/azeotrope? $\endgroup$
    – Mäßige
    Feb 16 at 8:29
  • $\begingroup$ Mathematically, assuming matter continuity, the purity converges to 100% for infinite number of "column trays". Practically, good enough for good enough, as above. $\endgroup$
    – Poutnik
    Feb 17 at 10:09


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