Chromatography true moving bed

If elution and frontal chromatography are still the main implementations used in preparative processes because of the simplicity of their development, processes like true moving bed (TMB) or simulated moving bed (SMB) have been used for about 40 years in large scale separations in petroleum or sugar industries [1,2]. In these processes, a countercurrent between solid and fluid phase is realized (or simulated) in order to improve process productivities and to decrease the eluent consumption. These implementations are now developed for laboratory and small productions and find a lot of applications in pharmaceutical and fine chemistry industries [3,4],... 

It can be shown that the performances of simulated moving beds are equivalent to those of true moving beds [11]. Also, SMB process has a lot of advantages compared to classical elution chromatography. With a continuous process, purified products are recovered at 100% with a low dilution and a low eluent consumption. Moreover, SMB process are not very sensitive to column efficiency and we can obtain very good product purities with even low column efficiencies [11],... 

Fig. 5.17 True moving bed (TMB) chromatography with internal concentration profile.

There are simple algebraic solutions for the linear ideal model of chromatography for the two main coimter-current continuous separation processes. Simulated Moving Bed (SMB) and True Moving Bed (TMB) chromatography. Exphcit algebraic expressions are obtained for the concentration profiles of the raffinate and the extract in the columns and for their concentration histories in the two system effluents. The transition of the SMB process toward steady state can be studied in detail with these equations. A constant concentration pattern can be reached very early for both components in colimm III. In contrast, a periodic steady state can be reached only in an asymptotic sense in colunms II and IV and in the effluents. The algebraic solution allows the exact calculation of these limits. This result can be used to estimate a measure of the distance from steady state rmder nonideal conditions. 

In general, a counter-current operation can achieve a more efficient separation than the cross-current operation considered above. In chromatography this is realized by the SMB technology. Chromatographic counter-current operation requires the mobile and stationary phases to move in opposite directions. Figure 5.14 illustrates the more or less hypothetical concept of an ideal counter-current system, denoted as true moving bed (TMB). This concept utilizes an actual circulation of the solid phase vfith a constant flow rate. 

An interesting realization of continuous chromatography is simulated moving-bed (SMB) chromatography. Here, a serial connection of several chromatographic columns leads to a continuous simulated countercurrent process. In order to further explain the attribute simulated , first the idea of the true moving bed (TMB) is shown. 

In a continuously operated production plant batchwise operation is a drawback. Principally speaking, the separation of a binary mixture with the components a and b can be carried out in a true moving bed (Seidel-Morgenstem et al. 2008). In Fig. 9.8-8 the principle of a countercurrent chromatography column is illustrated. The solid phase is moving downward whereas the mobile fluid phase is introduced at the bottom of the column. The feed of the components a and b is separated with the result that a raffinate containing a less adsorbable component a and an extract with the strong adsorbable component b are withdrawn as side streams. Therefore, the total column is subdivided into four zones ... 

Properties Annular chromatography True moving bed Simulated moving bed... 

SMB Simulated moving bed chromatography TCC true counter-current chromatography F SMB Feed stream R SMB raffinate product E SMB extract product... 

The first column based separations performed in a true industrial setting can be better demonstrated by the purification of petroleum on Fuller s earth in the 1920s. The 1950s marked the development of simulated moving bed (SMB) chromatography for the separation of sucrose and fructose in the sugar industry. However, these separations are limited low to medium pressure... 

The sorption applications include regeneration of porous beds, preparative scale supercritical chromatography, simulated moving beds, thermal swing schemes, and adsorption/desorption cycles. Although initial applications of supercritical fluids in this domain were on regeneration of porous beds, more recent emphasis on fractionation best reflects where the true potential of this technique lies. Typical examples are provided in Table 20.1.9. 

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