This paper analyzes and compares optimization results for simulated diabatic columns Co theoretically derived optimization results from the isoforce method for the same system. The separation of ethanol and water is used to illustrate the two methods and bring out their common and special features. The results, which are presented in McCabe-Thiele diagrams, show partial compatibility between the methods. The isoforce method is found to require total reflux ratios close to the azeotrope, and a reformulation of the method is suggested. It is also shown that the separation work obtained in an adiabatic stripping column can not be achieved in a diabatic column without adding a (distributed) condenser in the upper section of the column, or more plates.