A rotating annular chromatograph for continuous separations

Abstract

Preparative, multicomponent liquid chromatographic separations have been achieved by using a slowly rotating annular sorbent bed with fixed multiple feed points and fixed product withdrawal locations. The cation exchange separation of copper, nickel, and two cobalt complexes has been extensively used to study the effects of rotation rate, eluent rate, bed loading, and column size on separation performance. Experimental results have been compared with three theoretical models: plate theory, an analytical solution which incorporates multicomponent Langmuir isotherms, and an extension of the analytical solution to include dispersion effects. SCOPEWith its versatility, high resolution capabilities, and nearuniversal potential applicability, chromatography lacks only throughput capacity to make it an ultimate separation technique. Typical chromatographic separations are made in fixed columns and, as such, are inherently batch in nature. Various attempts have been made to increase the capacity of chromatographic devices either through cyclic operation of large-diameter columns or through continuous feeding of a mixture and continuous removal of the components in moving-bed systems. Several reviews of methods which attempt to achieve continuous chromatographic separations have appeared in the literature, e.g., Rendell (1975), Sussman and Rathore (1975), and Sussman (1976). These include counterflow, moving-bed systems, crossflow moving-bed systems, and simulated moving-bed systems.The objective of this work was to describe the performance results obtained by using a rotating annular sorbent bed, which has been successfully used to achieve continuous separations. The effects of feed rate, eluent velocity, bed loading, and rotation rate on the separation performance of such a device are discussed. Also discussed is the application of plate theory and an extension of the analytical solution describing a rotating annular sorbent bed. With such information, engineers should be able to make large-scale continuous chromatographic separations possible. CONCLUSIONS AND SIGNIFICANCEThis study was made to obtain experimental data showing the effects of feed rate, feed concentration, rotation rate, and eluent velocity on the separation performance of a rotating annular sorbent bed. This bed receives a constant flow of a feed mixture and continuously separates the mixture into its respective solutes.Both plate theory and an extension to the analytical solution of Rhee et al. (1970) to include dispersion effects were applied to the rotating bed. While plate theory is simpler to apply, the extended model is particularly useful when a nonlinear adsorption isotherm must be considered. Agreement between the extended model and experimental concentration profiles was excellent. When a conventional column was used to obtain the necessary adsorption and dispersion parameters of a desired separation, both models adequately predicted the experimental effects of varying the rotation rate and eluent velocity. The extended model, however, with i...

Continuous Separation of Fructooligosaccharides Using an Annular Chromatograph

“…This system is the opposite of the device of Begovich et al (3). This system has the following advantages.…”

Preparative continuous annular chromatography (P-CAC), a review

“…Many of the theoretical developments have been discussed in previous papers reviewed by Begovich and Sisson [15] and Howard et al [16]. The steady-state material balance for a conventional chromatograph may be written as follows:…”

“…The effects of the rotation rate, the feed flow rate, the feed concentration dependence, the feed bandwidth, the eluent flow rate, and the annulus width on parameters such as resolution or feed exit bandwidth were investigated by several authors [14,15,16,22,23,24,25].…”

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Modeling and Applications of Downstream Processing

“…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).…”