Batch Extractive Distillation With Two Reboilers

Batch extractive distillation (BED) is used to separate azeotrope or the mixture of which the relative volatility is close to 1.0. For it has both advantages of batch distillation and extractive distillation, batch extractive distillation is becoming increasingly important to the production of small scale and high value products like fine chemicals and pharmaceuticals. There are some researches about the regular batch extractive distillation, most of which are based on laboratory-scale. This paper has scaled up the regular batch extractive distillation and investigated influences of some operating parameters such as reflux ratio,flow rate of solvent feeding,temperature of solvent on the product purity,production rate,consumption of solvent etc. Furthermore there are some disadvantages of the regular batch extractive distillation. This paper proposed a new mode of batch extractive distillation which has two reboilers to overcome the disadvantages existing in the regular batch extractive distillation such as volume limitation of reboiler,less flexible and so on. In the mode with two reboilers, there is an additional reboiler as the solvent reboiler while the other is kept as the feed reboiler. During the process, the solvent introduced at the top of the column is separated from the liquid flow downwards by equilibrium distillation in the solvent reboiler and the feed reboiler contains only feed mixture of which boiling point is much lower than that of the solvent. The experiments for separation of ethanol-water using ethylene glycol as the solvent were carried out. The results proved the advantages of the new mode over the regular BED such as the stable reboiler temperature,easier control,saving of operating time,and higher recovery of product. This paper also established the rigorous equilibrium-stage mathematical models of bath extractive distillation with constant molar liquid holdup. The mathematical model is a group of still equations and is resolved by revised two point implicit method. The results were compared with the experiments and influences of reflux ratio,flow rate of solvent and solvent feeding stage location were researched.