Experimental Setup and Simulation Flow Sheet

Section 6.2 presents various models capable to describe front propagation phenomena in chromatographic columns. It has to be kept in mind that these models account only for effects occurring within the packed bed. A HPLC plant, however, consists of several additional equipment and fittings besides the column. Therefore, the effect of this extra column equipment has to be accounted for to obtain reasonable agreement between experimental results and process simulation. Peripheral equipment (e.g., pipes, injection system, pumps, and detectors) causes dead times and mixing. Thus, it can contribute considerably to the band broadening measured by the detector. 

So-called plant dispersion or extra column effects have to be taken into account by additional mathematical models rather than including them indirectly in the model parameters of the column, for example, by altering the dispersion coefficient. The combination of peripheral and column models can be implemented in a modular simulation approach. In a flow-sheeting approach the boundary conditions of different models are connected by streams (node balances) and all material balances are solved simultaneously. 

As mentioned in Chapters 2 and 4, peak distortion is caused by nonideal equipment not only outside the column but also inside the column. Although sophisticated measurements such as NMR (Tallarek, Bayer, and Guiochon, 1998) allow the investigation of the packed bed only, from a practical viewpoint the observable performance of a column always includes the effects of walls, internal distributors, and filters. Using the method described in this chapter, these are always contained in certain model parameters (e.g., in The column manufacturers have to ensure a proper bed packing and flow distribution (Chapter 4) and, thus, negative influence of imperfections on column performance, for example, on Dax, can be 

---