PROCESS

Method of operating a heavy ends column in an acetic acid production unit having a reaction section, a light ends recovery section including a light ends distillation column, and a heavy ends column. A stream containing acetic acid and propionic acid obtained from the light ends recovery section is fed to the heavy ends column through a feed inlet positioned at an intermediate point in the heavy ends column. A product stream containing acetic acid is withdrawn from the heavy ends column through a sidedraw product outlet position above the feed inlet, and a product stream containing the propionic acid is withdrawn from the heavy ends column through a heavy product outlet positioned below the feed inlet. The pressure in the heavy ends column above the feed inlet is lower than the pressure of the stream containing acetic acid and propionic acid that is fed to the heavy ends column.