GB655364A - Improvements relating to fractional distillation - Google Patents

Abstract

In fractional distillation using a thermally-insulated, non-packed column, the input of heat to the still is regulated so that the average velocity of the vapour in the column lies between 2D/a and 20D/a, where D is the diffusion constant of the vapour and a is half the minimum internal cross-sectional dimension of the column. Air should preferably be excluded from the upper part of the column where the return-flow of condensate begins. This method utilizes very low-vapour-velocities which increase the number of theoretical plates obtainable from a given column. The column may be a jacketed cylindrical tube with or without a cylindrical core, or a bubble-cap column. In the latter case a is half the diameter of the funnels inside the caps. The jacket of the column may be evacuated or may contain a boiling liquid. A mathematical formula for the calculation of D for a binary mixture, is given in the Specification. In an example, a mixture of benzol and carbon tetrachloride was fractionated at atmospheric pressure using a tube 30 cm. long and 0.3 cm. radius, the "heads" being withdrawn through a heated tube leading to a condensate trap having a cooled surface maintained only a little below the boiling temperature of the mixture. The supply of heat was adjusted to 9 X 10-3 cal./sec. giving an average vapour-velocity of 0.13 cm./sec. The number of theoretical plates obtained was 100.