Sublimation as a separation technique

During a lecture, my professor said that sublimation at atmospheric pressure (1 atm), as a purification/separation technique, can be performed when the sublimating substance has a triple point falling at pressures above 100 mmHg. Why is this assumption made? Shouldn't sublimation at atmospheric pressure only occur when the atmospheric pressure (1 atm) falls below the triple point? In fact, only under this condition can be found a temperature at which the vapor pressure of the solid equals atmospheric pressure.


I don't understand why we consider 100 mmHg as the limit.
Furthermore, it has been said that the sublimation point of vanillin, at atmospheric pressure, falls at 48°C, so at these pressure and temperature values ​​we actually fall on the sublimation curve. Right?




Water triple point is $\pu{+0.01 ^\circ C}$ at about $\pu{610 Pa} \ll \pu{100 kPa}$ and water does sublime at freezing temperature. But slowly. I assume $\pu{100 mmHg}$ is a practical threshold for sublimation to have a possibly sufficient rate. There is no need to fit atmospheric pressure. Liquid evaporation occurs with vapor pressure below external pressure too.


Phase diagrams are about equilibrium.


At temperatures below their melting point, solids sublimate until the vapor pressure reaches the solid-gas line. Higher temperature means faster sublimation with higher vapor pressure. If the triple point has too low a pressure, we can use only a low maximum vapor pressure which may not be practical for larger quantities.


 4