Journal of the Japan Society of Powder and Powder Metallurgy

The relation between the grain size of catalyst and reaction rate, measuring the dehydrating rate of-butanol on the various space velocity with the acidclay catalyst, which are tabulated in various sizes, was investigated.
As the result of experiment (shown in Fig. 1 and 2) it was recognized that the reaction rate increases with the increase of space velocity, and with the decrease of the grain size. Also the mechanism was explained that the reaction rate was controlled by the diffusion rate of reactant into grain inside through pore, and that the space velocity affects not directly the reactant concentration of the grain inside, but its outside concentration.

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The available surface area of grain catalyst, accompanied by volume expansion of fluid, was studied for single grain and packed reactor.
Reaction mechanism was assumed that the amount of the reactant, diffusing into inside from outside of grain, is equal to the amount of reactant reacting on the pore wall of. the catalyst. In this case the following differencial equation is derived.
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x=distance from the grain centre, y=reactant concentration, t=total number of moles per c.c in the fluid, n= ??, C=reaction rate in the pore wall, r=area of pore cross section per unit length of perimeter of pore cross section. D=diffusion constant.
From this equation, ko the ratio of available surface to actual surface is obtained as the function of nx, and y, (s is the surface note). Also the available surface ratio ko of packed catalyst is as follows.
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kj=packed degree of grain, L=length of reactor. As the result of calculation its value coincided with experimental value.

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