In Fig. 3, if we change our observation point of the adsorption column movement in the moving-bed mode, we will see that it is equal to continuously moving the points of the adsorbent, feed mixture and component with drawal in the direction of the desorbent. As shown in Fig. 4, approximately the same quality of separation as in the moving-bed mode can be obtained by separating the adsorbent layers into several different columns while moving the introduction point of the feed mixture successively along in the direction of the flow of the desorbent. This is the principle behind the simulated moving-bed method. Next, let us consider the actual simulated moving-bed chromatographic separation device.
As shown in Fig. 4, the mouths of each column are connected to form a circular loop, with four openings for the feeding and drawing of fluids set in each column. While the fluids are circulating inside the column, assume that feed mixture F, desorbent D, component A, and component C are continuously allowed to enter or leave the column from each of the openings. Then, successively for the length of one full column at a time, the positions of the openings for F, D, A, C are changed in the direction of the circular flow at a regularly fixed point in time. Here the migration rate at each opening (Uv = column length/switching time) is set so that it will be smaller than component A's migration rate, Ua, and larger than component C's migration rate, Uc, i.e. (Ua>Uv>Uc). By operating the device under these conditions, it seems as if the adsorbent moved at a migration rate of Us ( = -Uv) in the opposite direction to the flow of the fluids. Therefore, components A and C move in the opposite direction from the feed mixture introduction point, F, and each component can be removed in a continuous manner from its respective with drawal point A and C.
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This is how the simulated moving-bed chromatographic separation system works. However, the weak point of the simulated moving-bed method is that it can only perform a separation resulting in two fractions. As can be seen in Fig. 4, with the simulated moving-bed device, there is always either components A or component C present in the area between the feed mixture introduction opening, F, and each opening for the arawal of components A and C respectively. Therefore, even if there existed in the feed mixture a component B, having a migration rate in between that of components A and C, and it collected in the vicinity of the feed mixture introduction point F, it would be impossible to extract this component B in a highly purified state, since it would only exist in a mixed form with either component A and C. Consequently, by a simulated moving-bed system, unless the position of elution of the component targeted for extraction was either the fastest or the slowest among the separated components it was impossible to extract the component by a single separation operation. In cases where a targeted component is eluted in a narrow position in between two impurities or other components, you either had to carry out the separation operation twice, or link two devices in series. Owing to this fundamental principle, the use of the simulated moving-bed system has been limited to 2 fractions. However, naturally there are many circumstances when the object of separation exists in a multiple component form. A system which could maintain the high efficiency of the simulated moving-bed mode and perform separations into three or more product divisions in a single step had long been awaited. It was here that through the organic combination of the strengths of the fixed-bed method adapted for the separation of multicomponent mixtures, and the simulated moving-bed mode which enables high purity, high concentration, and high recovery separation, a complete multicomponent separation system, the New JO Chromatographic Separation Device, was developed .