Operation a) Azeotropes: If the mixture is azeotropic, then more advanced types of separation must be considered. b) Solids: If the material to be separated is high in solids, or contains tars or resins that could plug or foul a continuous unit, then a batch separation should be considered ( c) Optimum Pressure (i) Vacuum operation: Use of a vacuum should be considered for heat sensitive compounds or polymerizable materials. Vacuum is usually not used unless required 2 , then consider an alternative of using a refrigerant on the overhead and running the column at a lower pressure.