Evaluation of the potential of a combination of batch and continuous countercurrent operation in preparative chromatography

Preparative chromatoraphy is increasingly applied for the separation or purification of value-added products from mixtures. For the isolation of a certain target component out of complex multi-component mixture, it is typically necessary to apply conventional batch chromatography. A disadvantage of batch chromatography is the limited productivity due to the low loading factors applicable. In this respect, the continuous simulated moving bed technology is an alternative method due to the advantages of high throughputs and low eluent consumptions. However, the conventional SMB-technology is only suitable for the separation of binary mixtures. In the contribution a combination of batch chromatography and subsequent continuous countercurrent chromatography is investigated theoretically. The procedure considered can be divided into two steps. At first, an optimized amount of sample is injected on a batch column. Applying appropriate collecting strategies, fractions can be taken in which the target component is located in the first or last position of the elution order. Subsequently, the fractions obtained using batch chromatography are fed to a continuous countercurrent unit (SMB) for isolating the target component in one of the two effluent streams. Using this concept it is not necessary to obtain the pure target component already in the first step (batch column). Thus, higher loading factors could be applied. The separation process in the batch column is theoretically analysed using a well-established model for a ternary mixture (the equilibrium dispersive model). Both linear and nonlinear isotherms are considered in extensive simulations. The design of the combined process is discussed based on the example of investigating the separation of an intermediate component in the mixture. Several optimization algorithms (e. g. a random search method) are applied to determine optimal operating points based on different objective functions (e. g. productivity, eluent consumption). The convergence behaviour and the results obtained by different algorithms are compared. It is shown that the studied combined technique has under certain conditions the potential of increasing productivity and reducing eluent consumption in practical separations compared to batch chromatography alone