Fluidised heterogeneous

Industrial reactors generally operate at very high velocities (of order 1 m/s) much in excess of terminal falling velocity for at least the finest powder fractions. Powder is continually elutriated and returned to the bed via cyclones. Under these conditions there is disagreement as to whether or not bubbles retain their identity and such beds have been described as "turbulent" or "fast fluidised". What little evidence there is supports the continued existence of bubbles but now in a much disturbed or heterogeneous dense phase and with a less definite shape. Until more is known about this physical situation it is not easy to see how the bubbling bed reactor models should be modified correctly to describe this flow regime. 

At velocities above the minimum fluidisation velocity the fluidised bed expands. Its height and void fraction increase. Solid-liquid systems expand continuously with increasing liquid velocity, and the solid particles are homogeneously distributed. In solid-gas systems gas bubbles form inside the fluidised bed, so that a heterogeneous system exists. 

The regeneration of B-MFI as the heterogeneous catalyst for the gas phase Beckmann-rearrangement of cyclohexanone oxime to e-caprolactam in a continuous fluidised bed was investigated. 

As gas and solid phases are involved in this reaction, any gas-solid-containing equipment such as a fluidised bed can be used to carry out this reaction. Here, the heterogeneous reactor is the fluidised bed reactor (Figure 2.30). 

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