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

solutes (S1) and (S2) which are continuously fed on to the center of the column, having retention volumes Vr(1) and Vr(2), respectively, then if       one solute (S2) will be eluted with the mobile phase at the end of the column and the other (S1) will be eluted with stationary phase and support at the front of the column. The basic principles given above will apply to all moving bed or simulated moving bed systems irrespective of the complex nature of the experimental design. The Continuous Moving Process for the Isolation of Pure Acetylene Using Gas-Solid Chromatography The moving bed process described in 1956 by Freund et al. (10) was developed to isolate pure acetylene from the gaseous product obtained from methane oxidation. The actual feed mixture contained 8-9% of acetylene, 4-5% of carbon dioxide, 4-5% of methane, 25% of carbon monoxide, and about 50% of hydrogen. The apparatus shown in figure 24 produces relatively pure acetylene as a direct product. The

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