Define column hold-up

Answer 1

Sometimes: The amount of liquid phase required to fill the column with a liquid-vapor equilibrium.

Other Times:

The liquid that sticks to the column and makes it look "wet"

Answer 2

Column hold-up refers to the amount of liquid that accumulates in the column of a distillation apparatus during operation. It includes both the liquid that remains behind in the column and the liquid that is carried over with the vapor product. Proper management and control of column hold-up is essential for achieving efficient separation in distillation processes.