The Effect of Mass Transfer on Observed Rates

Equation (10-47) shows that the relative importance of diffusion resistances from bubbles to bulk liquid and from liquid to catalyst particle depends on the area ratio. If a large concentration of very small particles is used, afOg is so large that only the first term is important. Then Eq. (10-47) reduces to 

Calderbank et al. studied the hydrogenation of ethylene using a large concentration of Raney nickel particles in a slurry reactor in order to approach these conditions. Analysis of the data indicated that the controlling step was the mass transfer of hydrogen from gas bubble to bulk liquid. 

Equation (10-51) indicates that the important parameters for this case are ki and the gas-liquid interfacial area Cg. The latter depends on the size and concentration of bubbles in the slurry. Alternately, it may be expressed in terms of the bubble diameter and gas holdup. The volume of the gas bubbles is the difference between the volume of the bubbling slurry n. and that of the bubble-free slurry Vq. Both Vf, and Vq can be measured directly. Then for spherical particles of diameter dj, 

Koide et al. give the following equation for bubbles formed over a porous plate  

Massimilla, Calderbank, and others also have reported experimental data on bubble sizes.  

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SECTION 10-8 THE EFFECT OF MASS TRANSFER ON OBSERVED RATES... 

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