Isocratic 3-2-3 Mode SMBC

Simulated moving bed chromatography (SMBC) is a powerful approach to chromatographic fractionation (e.g., Andersson and Mattiasson, 2006). SMBC emulates counter-current separation where the mobile phase flows in the opposite direction of the solid phase (Perrin and Nicoud, 2001). The solid phase is represented by individual columns connected in series, and the mobile phase by inlet streams of Feed and Desorbent and outlet streams of Raffinate and Extract. Valves between the columns are systematically switched open or closed at timed intervals (switch time) to introduce the inlet streams and withdraw the outlet streams between the separation zones, simulating counter-current movement of the columns. Separation occurs due to the differential migration of the Feed mixture components through the column material. Components that interact more strongly with the column material are carried into the Extract, whereas weaker-interacting components move into the Raffinate. By adjusting the stream flow rates, the switch time, and the Desorbent composition, a cycle is established in which Feed and Desorbent are continuously added and highly purified products are continuously recovered.

Figure 1. Animation of 323 SMBC

Figure 1 shows an animation of an 8-column SMBC system in a “3-2-3” configuration, initially loading and then running at equilibrium. The 3-2-3 designation refers to the number of columns in each SMBC zone. The zones are defined as follows (Perrin and Nicoud, 2001):

• Zone 1: Between Desorbent inlet and Extract outlet; where the more retained component is desorbed
• Zone 2: Between Extract outlet and Feed inlet; where the less retained component is desorbed and the more retained component is enriched
• Zone 3: Between the Feed inlet and Raffinate outlet; where the more retained component is adsorbed and the less retained component is enriched and desorbed

A fourth zone consisting of columns between the Raffinate outlet and Desorbent inlet is commonly included in large scale SMBC systems (see Perrin and Nicoud, 2001 for review) and can be configured into the Semba Octave System. This zone serves as a buffer between Zones 1 and 3 to ensure that no Raffinate enters Zone 1. It is also used in some configurations as a point to recycle the Desorbent. Because the Semba Octave System can effectively prevent flow of Raffinate into Zone 1 simply by closing off the valve between Zone 3 and Zone 1, and because volumes of Desorbent are generally low enough to eliminate the need for recycling, Zone 4 is not necessary for most applications.

The isocratic mode is in contrast to Step mode operation, typically used for affinity binding purification methods.