Falling Film Catalytic Wall Reactor

This problem can be recognized as a variation of the tube wall reactor of Chapter 7, where the reactants flowing down the tube had to migrate to and into the porous catalyst on the wall to react. The only difference here is that the reactant must first migrate through the film, which coats the waU before it can enter the catalyst and react. 

If the second reactant 5 is in high concentration (Hquids have much hi er densities than gases even at high pressures) and the reaction is not limited by its mass transfer, then this becomes a pseudo-first-order reaction r = k CA. If all mass transfer steps are fast compared to the reaction, then this problem would simplify to be identical to the tube waU catalytic reactor, which gave 

We can continue to write other expressions for different Hmiting cases, for example, with reaction on a nonporous catalyst film, which coats the wall. 

In the preceding expression we include an effectiveness factor r to account for pore diffusion limitations of A. Hi fact, if the catalyst film thickness on the wall of the reactor is small enough that we can assume it planar, then the effectiveness factor becomes 

It is evident, however, that this problem can be much more comphcated than either the wetted wall column or the catalytic wall reactor, because it combines the complexities of both. In fact, there are numerous additional complexities with this reactor beyond those simplified cases. 

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Figure 12-13 A falling film catalytic wall reactor in which reactant in the gas must diffuse through a liquid film to react L...

As with the falling film reactor, the rate of mass transfer to the catalyst goes as R, while the size of the reactor goes as R, so this reactor becomes very inefficient except for very small-diameter tubes. However, we can overcome this problem, not by using many small tubes in parallel, but by allowing the gas and liquid to flow (trickle) over porous catalyst pellets in a trickle bed reactor rather than down a vertical wall, as in the catalytic wall reactor. 

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