(87b) Cyclic Operation of Distillation Columns

Carsten Knösche, Jürgen Paschold, Steffen Bütehorn, BASF SE

Claudio Ribeiro, BASF Corporation

One of the earliest publications about the cyclic operation of distillation columns dates back to 1952 (Cannon, 1952). In the following decades numerous theoretical and experimental investigations were published. The scientific interest peaked in the mid 80-th. After that the number of publications decreased steadily presumably because of problems with the practical implementation of the cyclic operation modus. In 2011 Maleta et. al. (Maleta, 2011) published the design of a new cyclic separation tray which provides a promising way to put cyclic distillation into practice.

A theoretical analysis allows for predictions about the separation efficiency of cyclic distillation towers. Analytical solutions for binary mixtures and linear equilibrium lines are known (e. g. B. Horn, 1967). For arbitrary equilibria the corresponding set of describing equations can be solved numerically. It can be shown that depending on materials and operation conditions substantial improvements in separation efficiency are possible.

In the presentation a simple figurative explanation of the increase of separation efficiency in the cyclic mode of a distillation column is given. Theoretical predictions from numerical calculations are compared with experimental results obtained from cyclically operated columns. Moreover basic questions like minimum energy requirements and dimensioning of such columns are discussed.

Literature:

Cannon, M. R., Oil Gas J. 51, 1952

Maleta et. al., Chemical Engineering and Processing, 50, 2011

Horn, Ind. Eng. Chem. Process Des. Dev., 6, 1, 1967