Influence of particle size distribution on kinetic characteristics

4 INFLUENCE OF PARTICLE SIZE DISTRIBUTION ON KINETIC CHARACTERISTICS 

Theoretical formulation of kinetic expressions from specified geometry and/or mechanisms of reaction have often assumed particles to be of a regular, perhaps defined, shape and of uniform size. Equations developed in this way have frequently been found to give a satisfactory representation of observed isothermal kinetic characteristics in many reactions of interest. Other authors have, however, introduced an allowance for particle size distribution [480—482] into kinetic analyses. 

The first term allows for particles of radius less than or equal to Rlt which are completely decomposed at time t, and the second term includes particles which are only partially reacted at the same time. The expression for a(t) must be solved separately, by numerical integration, for each value of t. The parameters C and k/p were shown to be largely ( 10%) independent of particle size. Other features of the treatment are considered in the article [483]. 

Mcllvried and Massoth [484] applied essentially the same approach as Hutchinson et al. [483] to both the contracting volume and diffusion-controlled models with normal and log—normal particle size distributions. They produced generalized plots of a against reduced time r (defined by t = kt/p) for various values of the standard deviation of the distribution, a (log—normal distribution) or the dispersion ratio, a/p (normal distribution with mean particle radius, p). 

In general, for decreasing interface reactions, the rate coefficients ft, and the exponent, n, are dependent on particle dimensions and shape 

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