FLOW PATTERN IN LABORATORY REACTORS

FIGURE A9.1 (a) Flow pattern and different Peclet numbers (Data from Kangas, M., Salmi, T., and Murzin, D., Ind. Eng. Chem. Res., 47, 5413-5426, 2008) and (b) a laboratory-scale fixed bed. 

A best way is to determine the residence time distribution experimentally as described in Chapter 4. From the experimentally determined variance (a) of a pulse experiment, the longitudinal Peclet number is easily obtained by an iterative solution o = 

The role of external mass transfer resistance can be checked by the estimation of the Biot number and the mass transfer coefficient as described in Appendix 5. For experimental determination of the role of external mass transfer in fixed beds, a simple test is recommended the reaction is carried out in the fixed bed with different amounts of catalyst 

To suppress the internal mass transfer resistance in the pores of the solid material, small enough particles should be used. The role of internal mass transfer resistance can be evaluated using the concepts described in Chapter 5, that is, by evaluating the generalized Thiele modulus and the effectiveness factor. 

A good experimental approach to check the presence/absence of internal mass transfer resistance is to carry out experiments with various particle sizes. By gradually minimizing the particle size, the conversions, yields, and selectivities should approach a limiting value corresponding to the intrinsic kinetics. Sometimes this approach can, however, lead to a cul-de-saq the pressure drop increases, as the particle size is diminished and the kinetic conditions are not attained. Another type of test reactor should then be considered, for instance, a fluidized bed (for gas-phase reactions) or a slurry reactor (for liquid-phase reactions). 

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