Kinetics of Homogeneously or Enzyme Catalyzed Reactions

Mass and heat transport may influence the effective rate of heterogeneously catalyzed and gas-solid reactions. External profiles of concentration and temperature may be established in the boundary layer between the surface of the particles and the fluid, and internal gradients may develop in the particles (although for industrial practice the influence of internal heat transfer can be usually neglected). Deviations from the ideal zero-gradient situation are usually considered by effectiveness factors. 

To predict significant transport effects, respective criteria are needed. This is particularly important for kinetic studies in laboratory reactors to minimize the intrusion of diffusion and heat conduction. The concept used to derive such criteria is the following Since gradients of concentration and temperature always exist in and around a particle (although they are sometimes negligibly small), an assumption has to be made about the deviation up to which the reaction can considered to be uninfluenced by mass and heat transport. Commonly, the criterion is that the deviation of the mean reaction rate from the zero-gradient rate should be within 5%. 

The following two sections give only a very brief introduction to the kinetics of homogeneously and enzyme-catalyzed reactions. For details see Bhaduri and Mukesh (2000), Behr (2008), Cornils and Herrmann (2002), Parshall and Ittel (1992), Cornils et al. (2005), Bommarius and Riebel-Bommarius (2004), Garcia-Junceda (2008), and Hou and Shaw (2008). 

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