Gradient SMB Chromatography

Improved performance is achieved with a more complex operation and layout of the process, which requires precise process design and control - especially when a recycling of the section IV outlet is applied. An open-loop operation without eluent recycling between sections I and IV is more robust and allows for more pronounced gradients, which is particularly attractive when regeneration of the adsorbent is difficult. 

Manipulating adsorption strength is most readily achieved by variation of solvent composition (or column pressure in the case of SFC-SMB, see Section 5.2.6.2). However, there exist further options for implementing gradients. In particular, the use of salt and pH gradients is attractive in the context of bioseparations (see some of the 

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Gradient elution chromatography is a separation method that exploits the effect of the fluid phase composition on the retention behavior of the feed components. It is widely used, especially for analytical separations in the areas of the life sciences, in biochemistry, and in the biotechnologies e.g., separation of complex mixtures of proteins or peptides), hi its conventional implementations, SMB units are operated under isocratic conditions. The composition of the fluid phase, e.g., the organic modifier concentration, the pH, or the buffer concentration remain constant in all the sections of the SMB unit. However, it has recently been shown that SMB units can also be operated under solvent gradient mode (SG-SMB). Then, the feed and desorbent streams introduced have a different composition. The fluid phase composition is different in each section. It is chosen independently, in order to... 

The gradient concept can be applied also in SMB chromatography. This approach was first suggested for separations using supercritical fluids (Clavier, Nicoud, and Perrut, 1996). It is capable of increasing productivity and product concentrations, as well as of reducing eluent consumption. Theoretical and experimental studies... 

The development of preparative chromatographic processes in fine chemistry and in pharmaceutical industries is a very important field of research. This new process called SF-SMB (Supercritical Fluid Simulated Moving Bed) is a attempt to optimize preparative chromatography by three ways the choice of a supercritical C02 as eluent, the implementation of the simulated moving bed, and the use of an elution strength modulation in the process, performing a pressure gradient. 

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