Gas Chromatography - Preparative Gas Chromatography > The Moving Bed Continuous Chromatography System > Page 61

The maximum pressure that can be tolerated by large diameter columns is considerably less than their analytical equivalents. Thus to allow adequate gas flow rate through the column, the particle diameter of the packing must be relatively large. In turn, this means that the efficiency obtainable from preparative GC columns is relatively low and, thus, for effective separations, the stationary phase must be chosen to have the maximum selectivity for the solutes concerned. Compared with analytical GC, preparative GC can be far more difficult, The challenge is to achieve both adequate resolution and a satisfactory throughput.

The 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 hopper by a simple air-lift device.

Courtesy of Butterworths Scientific Publications Ltd. [Ref. 10]

 

Figure 39 The Moving Bed Continuous Chromatography System