Surface and Enzyme Reaction Rates

The moving fluid in these reactors is fi equenfly well mixed within the reactor so the mass balance on reactant species A is that of a CSTR, 

The flow proflle of this reactor is incompletely mixed, and in the limit there is no mixing at aU to yield the PFTR, 

We will develop the rest of this chapter assuming that the catalyst is in a sohd phase with the reactants and products in a gas or liquid phase. In Chapter 12 we will consider some of the more complex reactor types, called multiphase reactors, where each phase has a specific residence time. Examples are the riser reactor, the moving bed reactor, and the transport bed reactor. 

In catalytic reactors we assume that there is no reaction in the fluid phase, and all reaction occurs on the surface of the catalyst. The surface reaction rate has the units of moles per unit area of catalyst per unit time, which we will call r . We need a homogeneous rate r to insert in the mass balances, and we can write this as 

Suppose we have a packed bed reactor filled with pellets with surface area per unit volume of pellet (units of cm-i, for example). Here we define Sg as the surface area per unit weight of catalyst (area per gram is a common set of units) and Pc as the density of a catalyst pellet. We therefore have 

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