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The Moving Bed Continuous Chromatography System The idea of a continuous moving bed extraction process as a means of large scale separation is almost as old as gas chromatography itself. The first description of a continuous gas-solid extraction process that was reported in the chromatography literature was in 1956 by Freund et al. (10). However, much of the experimental work had been reported considerably earlier but in the 'not readily available' Hungarian technical literature.  Shortly afterwards, the use of a moving bed for the continuous preparative scale product isolation using gas-liquid chromatography was reported by Scott (11,12) The principle of the moving  bed separating system is basically simple, but can be quite difficult to carry out in practice.

Moving Bed Continuous Chromatography System The concept of the moving bed extraction process was originally introduced for hydrocarbon gas adsorption by Freund et al. (13) and was first applied to gas liquid chromatography by Scott (14). A diagram of the moving bed system suitable for GC was proposed by Scott and is shown in figure 39. The feasibility of this process was established for a gas chromatographic system, subsequently, its viability was also confirmed for liquid chromatography which will be discussed in Book 19. The moving bed system takes a continuous sample feed and operates in the following way. The stationary phase, coated on a suitable support, is allowed to fall down a column against and upward stream of carrier gas. In the original device of Scott, the packing (dinonyl phthalate coated on brick dust) was contained in a hopper at the top of the column and was taken off from the bottom the column by a rotating disc feed table and returned to

The Continuous Moving Bed Process for the Isolation of Pure Benzene from Coal Gas The moving bed technique was first applied to gas-liquid chromatography by Scott (11,12). A diagram of the moving bed system suitable for gas-liquid chromatography (GLC) was proposed by Scott also in 1956, and the basic system is depicted in figure 25. The original GC system will be used here to explain the principal of the separating process. Figure 25. A Continuous Chromatography Separation System

Although chromatography was discovered late in the 1890s its development was almost negligible until the 1940s and this was largely due to the lack of an inline sensitive detector. The first, effective inline liquid chromatography (LC) detectors were the refractive index detector reported by Tiselius and Claesson (1) in 1942 and the conductivity detector described by Martin and Randall (2) in 1951. These two devices should have evoked a growth in LC development, but, in the early fifties, gas chromatography (GC) was invented which completely eclipsed the development of LC. It was not until the early 1960s that the renaissance of LC took place, initially based on the use of the refractive index of Tiselius and Claesson. Although a significant number of GC detectors were developed over two or three years, the development of LC detectors was much slower, largely due to the fact that low concentrations of solute in a liquid do not change the properties of a liquid nearly as much as they

Considering the very limited chromatography knowledge that was available in 1956, together with the limitations of the equipment that was accessible, the process and plant design was a very impressive achievement at that time.     Figure 24. Apparatus for the Extraction of Pure Acetylene from a Gaseous Hydrocarbon Mixture By Continuous Adsorption Chromatography

the next thrust. The inlet from the solvent supply and the outlet to the column are fitted with non-return valves in the usual manner. Due to the large volume of the pumping cavity, any gradient profile would be seriously distorted so this type of pump is not often used for analytical purposes but is often used in preparative chromatography. The Sample Valve In general, LC sample valves must be able to sustain pressures up to 10,000 p.s.i., although they are most likely to operate on a continuous basis, at pressures of 3,000 p.s.i. or less. The higher the operating pressure the tighter the valve seating surfaces must be forced together to eliminate any leak. It follows that any abrasive material, however fine, that passes into the valve can cause the valve seating to become scored each time it is rotated which will ultimately lead to leaks. This will cause the sample size to vary between samples and eventually affect the accuracy of the analysis. It follows that any solid