Bypass chromatography--design and analysis of an improved strategy for operating batch chromatography processes.

The possibility to improve the performance of batch chromatographic separations by using so-called bypass method is analyzed for the first time. In bypass chromatography, only a part of the feed is introduced into the column and purified to purity larger than the desired value. The resulting fractions are then blended with fresh feed to match the given purity constraints. A general approach is presented for designing bypass batch chromatography. Analytical design equations, based on equilibrium theory of chromatography, are presented for the case of binary systems with linear or competitive Langmuir adsorption isotherms under ideal conditions. The approach allows direct calculation of optimal loading and amount of bypass so that arbitrary purity requirements are satisfied without waste streams. It is shown that the bypass strategy enhances productivity of batch chromatography without an increase in the eluent consumption. In the case of a Langmuir isotherm, maximum productivity and minimum eluent consumption are always obtained when the less retained component is collected from the column at 100% purity. In contrast, the optimal purity of the second fraction from the column is typically less than 100% and depends on the purity constraint of the more retained component. In the case of linear isotherms, operation with touching bands is preferred.