Design equation heterogeneous catalytic

After the rates have been determined at a series of reactant concentrations, the differential method of testing rate equations is applied. Smith [3] and Carberry [4] have adequately reviewed the designs of heterogeneous catalytic reactors. The following examples review design problems in a plug flow reactor with a homogeneous phase. 

The design equation for a heterogeneous catalytic reaction for which the kinetics is described by eq. (10.15) is almost the same as for an enzymatic kinetics (10.11), with the only exception being that the catalyst density should be taken into account... 

The type of the catalytic reactor in cormnon use is the fluidized-bed. The flui-dized-bed reactor is analogous to the CSTR in that its contents, though heterogeneous, are well mixed, resulting in a uniform concentration and temperature distribution throughout the bed. The fluidized-bed reactor can therefore be modeled, as a first approximation, as a CSTR. For the ideal CSTR, the reactor design equation based on volume is... 

Design equation— ideal batch reactor— heterogeneous catalytic reaction (moles)... 

Appendix 3.II gives the forms of the design equation for a heterogeneous catalytic reaction that are equivalent to Eqns. (3-17) and (3-18). These equations are labeled Eqns. (3-17a) and (3-18a). 

Equation (3-16a) is the most fundamental form of the design equation for a heterogeneous catalytic reaction in an ideal CSTR. 

Equations (3-26)-(3-28) are various forms of the design equation for a homogeneous reaction in an ideal, plug-flow reactor, in differential form. The equivalents of Eqns. (3-26)-(3-28) for a heterogeneous catalytic reaction are given in Appendix 3.Ill A as Eqns. (3-26a), (3-27a), and (3-28a). Be sure that you can derive them. 

Suppose that we were asked to estimate the amount of catalyst required to reach a final n-Cs conversion of 55%. From Chapter 3, the design equation for an ideal stirred-tank reactor with a heterogeneous catalytic reaction taking place is... 

Chemical Reactions and Chemical Reactors takes a different approach. The design equations are derived in Chapter 3 for both catalytic and non-catalytic reactions. In Chapter 4, which deals with the use of the design equations to size and analyze ideal reactors, transport effects are discussed qualitatively and conceptually. The student is then able to size and analyze ideal, heterogeneous catalytic reactors, for situations where transport effects are not important. This builds an important conceptual base for the detailed treatment of transport effects in Chapter 9. 

In this sequence R represents the active center, which normally is an atom or radical in homogeneous reactions and a catalytic site in heterogeneous reactions. Other molecules in each step are not shown explicitly, and we let the product of their concentrations with the appropriate rate constants (requiring unit stoichiometric coefficient for R) be designated by r for the initiation step, tp for the propagation step, and for the termination step. The rate equation for the active center R is... 

To address these limitations, additional -tests have been designed. In one experiment called the "three-phase test," a substrate is attached to an insoluble support, such as a polymer. If the catalyst is also a solid, then the supported substrate reacts much more slowly than the analogous soluble substrate, but if the catalyst is dissolved, then the two substrates will react with more similar rates. The polymer-bonded substrate must be swollen in a solvent which is compatible with the homogeneous catalyst. Applications of this test for homogeneity are Illustrated in Equation 10.54. The virtue of this test is that it is based on the catalytic process itself, rather than on detection of hypothetical catalysts. A variation of this theme involves the use of polymeric catalyst poisons, such as polythiols. These were found to have no effect on heterogeneous catalysts but to retard homogeneous catalysts.- ... 

The basic problem in the design of a heterogeneous reactor is to determine the quantity of catalyst and/or reactor size required for a given conversion and flow rate. In order to obtain this, information on the rate equaiion(s) and their parameter(s) must be made available. A rigorous approach to the evaluation of reaction velocity constants has yet to be accomplished for catalytic reactions at this time, industry still relies on the procedures set forth in the previous chapter. For example, in catalytic combustion leac-tioas, the rate equation is extremely complex and cannot be obtained either analytically or numerically. A number of equations may result and some simplification is often warranted. As mentioned earlier, in many cases it is safe to assume that the expression may be satisfactorily expressed by the rate equation of a single step. 

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