Batch chromatographs

Chromatography is primarily a separation technique. If it is applied for the collection of pure material then it is called preparative chromatography, and if one fractionates with the aid of a pump on fine-particle columns, it is called modern preparative liquid chromatography. The aim is to extract as much material in as pure a state as possible. 

In order to satisfy this aim, two chromatographic variants have to be taken into consideration  

In batch chromatography, one phase moves (the mobile phase) and the other remains stationary. 

In continuous chromatography the conventional stationary phase is moved countercurrent in a moving bed against the mobile phase. By adjusting the flow-rate of the bed and the mobile phase, one can enrich and separate a component or even a group of components in one direction or the other. 

Manufacturers of preparative instruments see Appendix) supply both types of apparatus. 

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Fig. 3. Schematic presentation of the operating principle of a batch chromatographic reactor. A pulse of compound A is injected into the reactor. As the substance travels through the reactor it is converted into compounds B and C, which are continuously separated. (Reprinted with permission from [134])...

Fig. 5. Complex behavior of a batch chromatographic reactor system. After an inlet step, three steady states were detected at the reactor outlet. Experimental data for acetic acid (filled circle), ethanol (x), water (+) and ethyl acetate (open circle) were successfully fitted by a mathematical model (solid and dashed lines). (Reprinted with permission from [159])... 

The dynamics of the system were studied using a batch chromatographic reactor. The reactor was saturated with hexane prior to feeding with the mixture of 1 mol/1 isoamyl alcohol and propionic acid dissolved in hexane. The concentration profiles recorded at the column outlet are shown in Fig. 12. 

Fig. 12. Outlet concentration profiles from a batch chromatographic bioreactor for enzyme catalyzed esterification. Water, which when in the liquid phase irreversibly inhibits the reaction, is adsorbed. The profiles of water (open circle), propionic acid (filled square), isoamyl alcohol (filled triangle) and isoamyl propionate (open square) at the reactor outlet are presented. (Reprinted with permission from [178])...

The amount of component i in the outlet stream can be calculated for a batch chromatographic process using Eq. 7.3, whereby h and t2ji are the beginning and the end, respectively, of the fraction collection for pure component i. 

Design and Optimization Strategy for Batch Chromatographic Column... 

The main idea behind the design and optimization strategy for batch chromatographic columns is the equality of concentration profiles if their dimensionless parameters (i.e. number of stages and loading factor) are identical. As mentioned... 

Figure 7.7 Design and optimization strategy for batch chromatographic column.

Chromatographic batch reactors are employed to prepare instable reagents on the laboratory scale (Coca et al., 1993) and for the production of fine chemicals. These applications include the racemic resolution of amino acid esters (Kalbe et al., 1989), acid-catalyzed sucrose inversion (Lauer, 1980), production of dextran (Zafar and Barker, 1988) and saccharification of starch to maltose (Sarmidi and Barker, 1993a). Sardin et al. (1993) employed batch chromatographic reactors for different esterification reactions such as the esterification of acetic acid with ethanol and the transesterification of methylacetate. Falk and Seidel-Morgenstern (2002) have investigated the hydrolysis of methyl formate. 

SMB allows a drastic reduction of the costs of chiral separations, mainly due to a reduction of chiral stationary phase (50-60% lower than in HPLC) and of eluent consumption (up to 10 times compared with the batch chromatographic process). It allows production scales of 10-100 tons per year, with separation costs as low as US 30 per kg of pure enantiomer [155], The coupling of SMB with racemization and/or enantioselective crystallization techniques is even more promising. 

Analytical preparative-scale batch chromatographs will satisfactorily separate and isolate individual components from mixtures in amounts sufficient for tentative identification or structural elucidation (spectroscopic and C, H, N analysis ... 

Analytical preparative-scale batch chromatographs are widely used. For analytical preparative operation on columns up to about 10 mm or more in diameter, one can use analytical instruments designed specifically for this purpose. The following components should be adapted to the preparative specifications of large analytical columns reservoir, pump, sample introduction device, detector and outlet. 

The most reliable system is probably that with time- and concentration-dependent control. Fig. 3 shows a block diagram for such a type of automatic batch chromatograph fitted with a control system. 

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