Evolution Of Pinch Point Zone And Batch Distillation Process With A Side Withdrawal

The pinch point zone is one of the basic theoretical problems for distillation process, and it is very useful for the operation and design of the distillation column. A lot of researches focus on pinch point zone in a continous distillation column, however, no research is carried out in this area in a batch distillation column. In this paper, the pinch point zone in a multicomponent batch distillation process is studied, furthermore, the batch distillation process with a side withdrawal is developed based on the pinch point zone research.The effect of reflux ratio, relative volatility and composition of feed to the pinch point zone in batch distillation column for multicomponent ideal system was studied by simulation, based on a constant molar hold-up batch distillation model. Evolution of the pinch point zone in a multicomponent batch distillation column was obtained.In order to study the batch distillation process with a side withdrawal, a constant volume hold-up batch distillation model with a side withdrawal was established and solved by Gear method. The characteristics of batch distillation process with a side withdrawal were investigated by simulation. The simulation results show that: The distillation time of the batch rectification with a side withdrawal for purification of intermediate component from the light and heavy impurities is greatly reduced and its capacity factor is increased comparing with the conventional batch rectification. Furthermore, the effects of operation parameters such as the position of side withdrawal, the top reflux ratio and side reflux ratio were studied by the orthogonal array design method. The result shows that: The position of the side withdrawal, the side reflux ratio and top reflux ratio are important parameters for batch rectification with side withdrawal, and they have optimal values in such a process.The batch distillation experiments for separating benzene, toluene and p-xylene were carried out to verify the constant volume hold-up batch distillation model with a side withdrawal. The results show that the simulation results agree well with those of experiments. The experimental results prove that the batch rectification with a side withdrawal can save distillation time and energy comparing with the conventional batch rectification.