A concept of limiting yield is proposed in light of the dependence ofbatch distillation yield on the number of theoretical plates. The number of theoretical plates corresponding to the limiting yield may be used as the criterion in designing a batch distillation column and evaluating an existing column. On the basis of limiting yield

the authors develope a new operation mode by controlling the column holdup in such a way that in a predetermined moment

some of the holdup is withdrawn from the column as an intermediate fraction in order to reduce the tailing effect and to increase the separating efficiency. Experimental work was carried out with success in confirming the proposed controlled holdup operation. Method of simulation is also reported and the theoretical computation agrees satisfactorily with the experimental result.