Studies on Batch Distillation

Abstract

Total reflux distillation was studied as a method of batch distillation. Fig.1 is an explanation diagram of total reflux distillation. The distillation system consists of a column and a total condenser as usual: in addition, it has a large-sized, volume-adjustable overflow vessel which is set up in reflux-return passage between the outlet of total condenser and the column top.In the course of total reflux distillation method, a large volume of liquid holdup of constant composition in the overflow vessel is taken out as distillate, after the distillation system has attained to the equilibrium state, due to the constant reflux ratio of total reflux.The total reflux distillation is operated at the reflux ratio of the total reflux; therefore, unlike in ordinary distillation, it is not necessary in this case to select reflux ratio for operating variable. But, in order to obtain distllate of desired composition, volume of the overflow vessel should be controlled so that the liquid holdup will be in a definite condition.The fundamental equations for total reflux distillation are obtained from material balance in reference to the distillation system: Eqs.1 & 8 are general equations for a plate tower and a packed colum with binary mixtures, respectively. Eqs.5 and 12 are special cases in which vapor holdup in the column and vapor-liquid in vapor line and total condenser are negligible, and liquid holdups of any plate are equal. Eqs.7 and 14 are applicable to mixtures which obey Raoult's law.Fig.6 (right) shows the experimental results of total reflux distillation in a packed column, Fig.6 (left) the results calculated by means of Eq.12, and Fig.7 over-all comparison. According to these figures, the experimental and calculated results approximately agree with each other.