Comparison of Fractional Conversions by CSTR and PFR

In the CSTR, the reactants in the feed are instantaneously diluted to the concentrations in the reactor, whereas in the PFR there is no mixing in the axial direction. Thus, the concentrations of the reactants in the PFR are generally higher than those in the CSTR, and reactions of a higher order proceed under favorable conditions. Naturally, the performance for zero-order reactions is not affected by the type of reactor. 

Effects of Mass Transfer Around and Within Catalyst or Enzymatic Particles on the Apparent Reaction Rates 

For liquid-phase catalytic or enzymatic reactions, catalysts or enzymes are used as homogeneous solutes in the liquid, or as solids particles suspended in the liquid phase. In the latter case (i) the particles per se may be catalysts (ii) the catalysts or enzymes are uniformly distributed within inert particles or (in) the catalysts or enzymes exist at the surface of pores, inside the particles. In such heterogeneous catalytic or enzymatic systems, a variety of factors which include the mass transfer of reactants and products, heat effects accompanying the reactions, and/or some surface phenomena, may affect the apparent reaction rates. For example, in situation (iii) above, the reactants must move to the catalytic reaction sites within catalyst particles by various mechanisms of diffusion through the pores. In general, the apparent rates of reactions with catalyst or enzymatic particles are lower than the intrinsic reaction rates this is due to the various mass transfer resistances, as will be discussed below. 

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