Liquid holdup in batch distillation column affects the transfer of mass and heat and thus the whole dynamic response of the system.The role of column holdup on the performance of batch distillation has been studied by researchers in the past

but it is still the focus of debate because none of the studies is systematical.In this paper

the degree of difficulty of separation is proposed to correlate different parameters in batch distillation and the constant holdup model is built.The effect of holdup on batch distillation was studied systematically.It was found that condenser and reflux drum holdup was detrimental to the separation

but increasing column holdup might improve the performance in some cases.Further studies on the dynamic role of column holdup showed that the ratio of column holdup to initial charge acted as a factor.So an optimum initial charge existed for a column when the degree of difficulty of separation q＜0.7

which was checked and proved by experiments with toluene-ethyl benzene system.