Annular chromatography

Multiport Switching Valve Chromatography (ISEP/CSEP) 

The introduction of this valve and the fact that the stationary phase is packed into fixed beds offers a great variety of possible column interconnections. Besides 

The number of columns in certain sections and their intercormection can be chosen according to the process needs. To ensure continuous operation of the system the number of columns has to be adjusted to the time needed for the operation of each individual step. Many systems are known, for example, for the purification of amino acids and sugars on ion exchange resins. 

As mentioned before, the complete parallel interconnection of the columns is similar to annular chromatography. The second border case is to connect all beds 

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The idea of annular chromatography was first mentioned by A.J.P. Martin [4] in 1949 where he summarized a discussion with his colleagues Prof. Tiselius and Dr. Synge. In his summary Martin writes ... 

Martin further mentioned that the scheme he described has already been tried out by Dr. Wadman of the University of Bristol. Wadman, however, never published any results of his very first work on annular chromatography. Martin and Synge won a joint Nobel price in chemistry for their work in partition chromatography, Tiselius won a Nobel price in chemistry for his work in electrophoreses. 

Compared to the continuous annular chromatography systems sold by Isopro International and used throughout the ORNL studies, the P-CAC units developed by Prior Separation Technology feature several design modifications which will be presented hereafter. As can be seen from Fig. 3, the P-CAC system consist of three major parts the P-CAC head, the annular column, and the drive including the control panel. Figure 3 represents a schema of the laboratory sized P-CAC used as a Research and Development tool. 

Continuity and rate equations can also be written in a cylindrical coordinate system for the two-dimensional annular chromatography. Assuming steady state and neglecting velocity and concentration variations in the radial direction, the above-mentioned equations may then be written as... 

An analytical solution of these mass-transfer equations for linear equilibrium was found by Thomas [36] for fixed bed operations. The Thomas solution can be further simplified if one assumes an infinitely small feed pulse (or feed arc in case of annular chromatography), and if the number of transfer units (n = k0azlu) is greater then five. The resulting approximate expression (Sherwood et al. [37]) is... 

Recently, the simultaneous chromatographic inter-separation of the PGMs (platinum group metals) and base metals by continuous annular chromatography has been demonstrated [46]. The basic configuration of the P-CAC is used to separate the PGMs from base metals and to inter-separate them in the same apparatus is shown in Fig. 9. 

Compared to the SMB system the annular chromatography allows the continuous separation of a multicomponent mixture as it is most often the case in biopharmaceutical separations. 

Several examples of these applications were summarized previously [1], and more recently the use of annular chromatography for the synthesis of triacetin has been reported [10]. 

For more complex feed mixtures other approaches for continuous operation of the chromatographic separation have to be considered. One example is annular chromatography with a rotating stationary phase. This concept was developed in the 1950s as a continuous method for paper chromatography by Solms (1955). In annular chromatography the stationary phase is packed between two concentric cylinders and rotates around a central axis (Fig. 5.14). 

As mentioned before, the complete parallel interconnection of the columns is similar to annular chromatography. The second border case is to connect all beds in series. With an appropriate choice of inlet and outlet streams as well as internal flow rates, this set-up is better known as Simulated Moving Bed (SMB) chromatography. 

To find a suitable process concept the final differentiation is given by the number of fractions to be collected. Notably, one fraction can contain either one single component (e.g. one target product) or a group of numerous components (e.g. several impurities). Some process concepts, such as SMB, SSRC and CLRC, can only separate a feed mixture into two fractions. In contrast, batch elution chromatography, annular chromatography, ISEP, etc. separate feed streams into three or more fractions. 

Schmidt, S., Wu, P., Konstantinov, K., Kaiser, K., Kauling, J., Henzler, H.-J., Vogel, J. H. Konti-nuierliche Isolierung von Pharmawirlcstoffen mittels annularer Chromatographie, Chem. Ing. Tech., 2003, 75, 3, 302-305. 

Continuous annular chromatography (CAC) has been the subject of several recent experimental studies (120, 121), models (122, 123) and a brief review (124). The equipment is very similar to the CRAE (Figure 7). Feed, eluent, and regeneration solutions (if necessary) are fed to fixed points or arcs at the top of an annular packed bed which rotates slowly about its axis. As the chromatogram develops, the components separate... 

Finke B, Stahl B, Pritschet M, Facius D, Wolfgang J, Boehm G. Preparative continuous annular chromatography (P-CAC) enables the large-scale fractionation of fructans. J Agric Food Chem 2002 50 4743 748. 

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