Chapter 5 - Diffusion control

Abstract

Chapter 4 briefly discussed the transport limitations that are encountered in heterogeneous catalysis. Those were associated with specific length scales: the reactor diameter, the pellet diameter, the pore diameter, etc. This chapter discusses a different type of diffusion control – one which sets a fundamental speed limit on bimolecular reactions in a liquid solution. The only length scale involved is the range of interactions between the reactants and solvent molecules. The earliest version of the theory, by Smoluchowski in 1917 [1], is simple and yet surprisingly accurate for many real reactions. This chapter also presents a few of the many theories [Weiss (1986) [2]] for partial diffusion control and diffusion control under the influence of long range interactions. Finally, we present the method of Northrup, Allison, and McCammon for computing the rates of diffusion controlled reactions between species with non-spherically symmetric interactions [Northrup et al. (1984) [3], McCammon et al. (1986) [4]].