Chemical Reactions on Solid Surfaces - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 439

FIGURE E9-4.2 Excel worksheet for Example 9-4.

We first examine a case where the surface reaction rate is limiting. For this case, we scale
the time with the surface reaction rate constant. The solutions for C A0 ¼ 10 C s ; k A C s ¼ 10 k S ;

K A ¼ 10 k S are shown in Fig. E9-4.3 .Onecanobserve

that in the batch operation, the concentration of the reactant in the bulk fluid phase expe-
riences a quick drop before the product formation is observed ( Fig. E9-4.3 Aand
Fig. E9-4.3 C). The decrease is simply due to the adsorption of reactants on the catalyst
surface and thus is dependent on the amount of catalysts or total amount of adsorption
sites. Since the product B is also adsorbed on the surface, the coverage of A increases
sharply at the start, reaches a maximum, and then decreases, as the product B is being
formed and adsorbed on the surface. The coverage of B increases with time, and as more
product B is formed, it also desorbs to the bulk phase and cause the concentration B in
the bulk phase to increase.
In the second case, we examine the situation where the adsorption of A and surface reac-
tion are the same, but the desorption rate of B is fast. The results are shown in Fig. E9-4.4 . One
can observe that there is a drop in the concentration of A initially, but the drop is gradual or at
much slower speed that Fig. E9-4.3 .

1/ C s ; K C ¼ 4; K B ¼ 1/ C ;and k B C

s ¼

s

q A reached maximummore gradually and not as obvious
as compared Fig. E9-4.4 C with Fig. E9-4.3 B. After q A reached maximum, and the vacant site
fraction become “steady” at about k S t ¼ 0.3 ( Fig. E9-4.4 D).