7. Conclusion

Downdraft-fed fixed-bed catalytic reactors are widespread in industrial practice. The hydrodynamics of gas-liquid flows are complex and lead to the appearance of different flow regimes, depending on the flow rates applied. Measuring and estimating transfer quantities is not easy, and the correlations proposed in the literature do not lead to precise evaluations of these quantities.

Millimetre-sized catalyst particles are usually impregnated with liquid, and slow intraparticle diffusion frequently limits the rate of chemical transformation. In commercial installations, we usually work with flow rates high enough to ensure complete wetting of the catalyst and high external transfer coefficients, which are therefore not or only slightly limiting.

For experiments carried out on a reduced scale, compliance with chemical similarity (u _...