Catalyst balance

The common further treatment of the approach - assumption of steady-state conditions for the intermediate substrate complexes, consideration of the catalyst balance ([catalyst]0=[solvent complex] + [IRe] + [Isi] + [IIRe] + [Hsi]) and of the stoichiometry of the hydrogenation - provides the rate of hydrogen consumption under isobaric conditions (Eq. (13)) [57f]. A more general derivation can be found in [59]. 

With the catalyst balance 8.16 and rate equation 8.17 this gives... 

The total catalyst balance, if including only the species containing significant fractions of cobalt, is... 

The rate -rA can now be obtained from the catalyst balance and the concentrations. The catalyst balance is... 

Analogously to the treatment of ligand deficient catalysis we introduce the concentration of C>u into the total catalyst balance and by defining Cx through Dj, the reaction rate is... 

We resolve this dilemma by writing a conservation equation called a site balance, which expresses the fact that the number of occupied sites plus the number of unoccupied sites is constant. In other branches of catalysis, a site balance is referred to as a catalyst balance or an enzyme balance. If Sj is the total number of sites in the system, the site balance for this example is... 

In view of the preceding discussion of catalyst balances, Step 3 of the procedure for using the steady-state approximation on page 314 requires modification as follows ... 

Step 3 For a catalytic reaction, eliminate the active center concentrations from the equation for the net reaction rate by writing a combination of SSAs and catalyst balances. The number of such expressions must equal the number of active centers. 

More that one catalyst balance will be required if there is more than one distinct catalyst species in the reaction mechanism. Several of the end-of-chapter problems contain this extension. 

Eliminate the concentrations of the active centers from the rate equation using equilibrium expressions for the reactions that are not the RLS. If the reaction is catalytic, one or more catalyst balances also will be required to eliminate the concentrations of the active centers. 

Cracking reactions are endothermic the energy balance is obtained by the production of coke that deposits on the catalyst and that is burned in the regenerator. 

Chapter 11. STEADY STATE MATERIAL AND ENTHALPY BALANCES IN POROUS catalyst PELLETS... 

Having discussed at some length the formulation and testing of flux models for porous media, we will now review v at Is, perhaps, their most Important application - the formulation of material balances In porous catalyst pellets. 

Interest has been generated by the advances made in the homogeneously cataly2ed polymerisation of propylene using metallocenes (10). Polymers produced with these catalyst systems have an unusual balance of properties that may become commercially attractive. 

Liquid crystal polyesters are made by a different route. Because they are phenoHc esters, they cannot be made by direct ester exchange between a diphenol and a lower dialkyl ester due to unfavorable reactivities. The usual method is the so-called reverse ester exchange or acidolysis reaction (96) where the phenoHc hydroxyl groups are acylated with a lower aHphatic acid anhydride, eg, acetic or propionic anhydride, and the acetate or propionate ester is heated with an aromatic dicarboxyHc acid, sometimes in the presence of a catalyst. The phenoHc polyester forms readily as the volatile lower acid distills from the reaction mixture. Many Hquid crystal polymers are derived formally from hydroxyacids (97,98) and thein acetates readily undergo self-condensation in the melt, stoichiometric balance being automatically obtained. 

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