Chromatography simulated countercurrent

Both GC and LC may be operated in one of several modes. The principal modes currently used for large-scale separations are elution, selective adsorption or desorption, and simulated countercurrent chromatography. In addition, reaction and separation can be combined in a single column with unique advantages. Elution is the most used and best developed form of the technique and is described first. 

The three main modes of chromatographic operation are elution chromatography, selective adsorption/desorption, and simulated countercurrent chromatography. Of these, elution chromatography, used as a cyclic batch process, was the first to be developed for large-scale separations. 

Compared with elution chromatography, the advantage of both the SMB and SCCR forms of simulated countercurrent operation is that each product is taken off as soon as it is separated. The disadvantages are mechanical complexity and the fact that the number of pure products readily obtainable from one column is limited to two at most. Elution chromatography allows many components to be separated on one column. If no components are taken off before reaching the column exit, however, any components that are much more easily separated than the key components occupy space in... 

Computer-aided experimentation in counter-current reaction chromatography and simulated countercurrent chromatography (with B.B. Fish and R.W. Carr). Chem. Eng. Sci. 43,1867-1873 (1988). 

A typical chemical engineering approach to a large-scale separation problem is to try to devise a steady-state, oounteroussent system. This has led to methods that are quite different from the scale-up of analytical elution chromatography. First, approaches where the solid is moved are considered and iheo methods where the solid does not move but movement is simulated are discussed. Finally, the different systems are compared. In all cases the countercurrent or simulated countercurrent Systran replaces the column in Figure 14.2-1. The equipment for product and solvent recovery still is required. 

Extensive experimental studies of simulated countercurrent gas-liquid chromatography have been dons.11 A system with 12 chromatography columns was enclosed in an oven. The system did not use a zone IV. Figure 14.3-51,1 shows one run for the separation of elhylcaprate from ethyl lauraie. The columns were packed with 15% OV-275 on chromosorb P and were operated at 160°C with nitrogen as tbe earner. This is a fairly difficult separation with a separation factor of 1.44. For a feed flow rate of 75 cm /h (Fig, ]4,3-5) the ethyl cap rate product was 94,2% pure and the ethyl laurate was 91.2% pure. When the feed flow rale was lowered to 25 crtrVh, the products were 99.4 and 99.3% pure, respectively. The results taken... 

Ballanec B. and Hotter G. 1993. From batch to simulated countercurrent chromatography. In, Preparative and production scale chromatography, Ganetsos G. and Barker P.E. (Eds.), Marcel Dekker, New York, pp. 301-357. 

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. 

Scaled-up elution chromatography and simulated countercurrent systems both have advantages and disadvantages. It makes sense to try to combine these two methods and develop hybrid systems that have some of the characteristics of both the other types. 

U(VI) Pu(IV) Simulated spent fuel TBP, MIBK, DMDOHEMA, etc. Recovery of U(VI), Pu(IV) demonstrated Countercurrent chromatography used (247)... 

Myasoedov, B.F. Kulyako, Y.M. Trofimov, T.I. Samsonov, M.D. Malikov D.A. Recovery of U and Pu from simulated spent nuclear fuel by adducts of organic reagents with HN03 followed by their separation from fission products by countercurrent chromatography, Plutonium Futures - The Science 2008, Dijon, France, July 7-11. 

The countercurrent movement of a stationary phase is cumbersome in practice but it can be circumvented by an array of short columns connected by multi-position valves connected with eluent, feed, extract and raffinate, a method referred to as simulated moving bed chromatography (SMB) (Schulte and Strube, 2001). In SMB chromatography, the continuous countercurrent flow of the fluid and of the solid adsorbent is simulated by periodically switching the different inlets and outlets in the multi-column unit. Enantioselective SMB-LC has first been demonstrated for racemic 1-phenylethanol resolved on the polysaccharide CSP Chiralcel OD. In this pioneering work the principle of the method and the set-up has been depicted in a lucid educational fashion (cf. Figures 22 23) (Negawa and Shoji, 1992). 

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],... 

---