A distillation column with an internal decanter is used to separate a mixture containing five some oxygenated and hydrocarbons and having at least three carbon atoms, and water. One of the species is partially miscible with water, as well as another organic species. Both binary pairs exhibit azeotropes above the minimum bubble-point temperature. The column is very sensitive to small disturbances which can lead to flooding, poor product quality, and migration of an embedded two-liquid phase region within the column. These disturbances can cause the column to move from one steady state to another for the same specifications. Multiple operating regimes are exhibited, with unusual transitions between them. Two regions involving multiple steady states are observed, one of which involves the partial-miscibility of two organic phases. The dynamics of moving interfaces between trays having one- and two-liquid phases, as well as controllers to insure that unwanted transitions do not occur, are examined.