Batch Distillation With A Side Withdrawal For Purification Of Heat Sensitive Material

A batch distillation process with a side withdrawal for purification of heat sensitive material in batch stripper was proposed in this paper. A mathematic model for batch distillation with a side withdrawal for purification of heat sensitive material was established, the model was solved by the Gear integration method and optimized by a simulated annealing algorithm.The effects of temperature of the top storage vessel, reaction rate, liquid holdup in reboiler and location of side withdrawal to batch distillation process were investigated by the optimization results. When the feedstock in the top storage vessel is kept in bubble point, the thermal reaction in the top storage is large, but when the temperature in the top storage is kept in a cold state, thermal losses can be greatly reduced, and the recovery is greatly improved. Generally, the smaller reaction rate is, the higher the recovery of heat sensitive material is; The lower liquid holdup of bottom reboiler is, the higher the recovery of heat sensitive material is, because low liquid holdup can greatly reduce the residence time of heat sensitive material in the reboiler and reduce the thermal loss. In the batch stripper with a side withdrawal , there is an optimal side withdrawal stage related to relative volatility. Moreover, if the feedstock in the top storage vessel in a batch stripper is kept in cold state, the batch stripper with a side withdrawal is superior to the batch rectifier with a side withdrawal for the purification of heat sensitive material, whether the light or heavy inpurities produced by the heat sensitive compound.The experiments of batch distillation with a side withdrawal in a batch stripper for separation of benzene, toluene and ortho-xylene were carried out, and experiment results were agreed well with simulation results. Furthermore, a batch distillation process with direct-contact heat transfer reboiler and a side withdrawal in a batch stripper is investigated, due to the residence time in the reboiler is short, this process is more suitable to purify heat sensitive material.