Batch Fractional Distillation Model Equations and Some Simple Algebraic Calculations

7 Batch Fractional Distillation Model Equations and Some Simple Algebraic Calculations 

Frequently, in the production of rare and valuable substances, the material flow is too small to make continuous distillation for the purpose of separation or purification practicable. The intermediate or raw product is then accumulated and held in storage before being fed to the fractionation column in intermittent batches. 

The distillation process, which is now unsteady, can be carried out in two modes. In the first mode, we allow distillation to proceed without outside intervention and at constant reflux until a prescribed fraction of the charge has been boiled off or the still contents have been concentrated to some desired value. In the course of the process, both the instantaneous and cumulative distillation composition and x, as well as the contents of the still, undergo a slow and continuous change. 

In the second mode of operahon, which is more common, the reflux ratio is continually and automatically adjusted so as to maintain a constant The boiler contents still change, as does the reflux ratio, but both the instantaneous and cumulative overhead compositions remain invariant with time. 

We now introduce two assumptions that allow us to draw on the principles and diagrams we previously established and used to describe continuous distillation. The first assumption presumes that the liquid content of the trays, or hold-up as it is termed, is negligible compared to the still contents. This allows us, in any material balance performed over the column, to ignore the 

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