It is well known that, in the high temperature region, the diffusional resistances within the boundary film and that within the pores of catalyst pellet have an important effect on the overall effective reaction rate. In reactor design, it is essential to analyze the experimental data and to distinguish the effect of diffusion from the chemical reaction rate so as to predict the over-all effective reaction rate for the given industrial conditions.
Previously, Kubota and Shindo⁵⁾ presented a method for calculating effectiveness factor of the porous catalyst, which is applicable to any reaction but which involves considerable complicated computations.
In this paper, the authors present a new method for calculating effectiveness factor, based on the approximation of reaction rate to a kind of first-order reaction as expressed by Eq. (6) or (7). When this method was applied to ammonia synthesis, whose rate was expressed by Eq. (13) and which was far from the first-order reaction, the value of Ef' obtained was found to be a very good approximation to the value of Ef obtained by the previous method (Fig. 2).
Other proposals the authors make in this paper are (i) a general analytical procedure for predicting the effective reaction rate by taking into account the diffusional resistances within the boundary film and that within pores of catalyst pellet, and (ii) two other methods for estimating the chemical reaction rate from the experimental data, by taking into account the above-mentioned diffusional resistances. Of these two methods, the first one is applicable when v_eA (pAG) can be obtained from the reaction, viz. when the reaction is carried on in a differential reactor, and the second one is applicable when v_eA (pAG) cannot be obtained directly from the experiment, viz., when the reaction is carried on in an integral reactor. When the latter was applied to the ammonia synthesis data, obtained by one of the authors⁴⁾, great difference was found in the range of above 475°C or so, between the apparent values of reaction rate constant and their corrected values given according to this procedure.