Liquid Chromatography - The Fluidized Bed Method for Bonded Phase Synthesis 1


The Fluidized Bed Method for Bonded Phase Synthesis

The concept of synthesizing bonded phases by means of a fluidized bed reactor was first suggested by Unger (23) and was later implemented by Simpson and Khong (23a). The term fluidization describes a contact process in which particulate matter is transformed into a fluid-like state by a stream of gas or liquid. This state is achieved by the upward passage of a fluid through the bed of particles to a velocity at which the drag force acting on the surface of the particles is equal to the gravitational force downwards. At this point the particles move apart and become suspended by the fluid flow and the bed is said to be fluidized.

The fluidized bed apparatus can be operated in such a way that it allowed far more complex multi-stage syntheses to be carried out rapidly and with relative ease; e.g., the synthesis of oligomeric phases. The fluidized bed apparatus is shown in figure 34. The fluidized bed is enclosed in a tube about 25 cm long, 4.5 cm in diameter situated in a heating jacket. The temperature of the bed is monitored by three thermocouples placed in the center and at either end of the bed. A condenser is situated at the top of the bed which returns unreacted silanizing reagent to the vapor generator. The vapor generator consists of a simple boiling flask that can be provided with a nitrogen stream if the silanizing reagent does not boil at reasonable temperatures. The silanizing reagent vapor passes from the vaporizer to a preheater and then to the base of the fluidizer.

Figure 34. The Fluidized Bed Apparatus for the Synthesis of Bonded Phases