lecture 16 - CHE 349 Lecture 23-24 CHE 349 Kinetics and...

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y Jing Wu CHE 349: Kinetics and Reactor Design CHE 349: Kinetics and Reactor Design Lecture 23 Lecture 23 - 24 Jing Wu 350 Tiernan Department of Chemical Engineering ± [email protected] ² 973-642-7064 CHE 349 - Lecture 23-24 by Jing Wu 2 Assignment Homework P10-3, 10-4, 10-11 Carefully Read 10.3.3, so that you can derive the rate limiting desorption case. CHE 349 - Lecture 23-24 by Jing Wu 3 Catalysts --- Definitions(I) • A catalyst is a substance that affects the rate of a reaction but emerges from the process unchanged. A catalyst usually changes a reaction rate by promoting a different molecular path(“mechanism”) for the reaction. Figure 10-1 on P582 CHE 349 - Lecture 23-24 by Jing Wu 4 Catalysts --- Definitions(II) Catalysis is the occurrence, study, and use of catalysts and catalytic processes. The development and use of catalysts is a major part of the constant search for new ways of increasing product yield and selectivity from chemical reactions. Because a catalyst makes it possible to obtain an end product by a different pathway (e.g. a lower energy barrier), it can affect both the yield and the selectivity. Normally when we talk about a catalyst, we mean one that speeds up a reaction, although strictly speaking, a catalyst can either accelerate or slow the formation of a particular product species. A catalyst changes only the rate of a reaction; it does not affect the equilibrium.
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y Jing Wu CHE 349 - Lecture 23-24 by Jing Wu 5 Classification of Catalytic Processes Homogeneous catalysis concerns processes in which a catalyst is in solution with at least one of the reactants. Heterogeneous catalytic process involves more that one phase; usually the catalyst is a solid and the reactants and products are in liquid or gaseous form. Reaction 1 on P583 Reaction 2 on P583 CHE 349 - Lecture 23-24 by Jing Wu 6 Note … • Only heterogeneous catalyst will be considered in this chapter. • A heterogeneous catalytic reaction occurs at or very near the fluid-solid interface. • The principles that govern heterogeneous catalytic reactions can be applied to both catalytic and noncatalytic fluid-solid reactions. • Heterogeneous reaction involve gas-liquid and gas-liquid-solid systems. Reactions between gases and liquids are usually mass- transfer limited. CHE 349 - Lecture 23-24 by Jing Wu 7 Classification of Catalysts According to Catalyst types (I) Porous Molecular sieves Monolithic Supported Unsupported CHE 349 - Lecture 23-24 by Jing Wu 8 Porous Catalysts • A catalyst that has a large area resulting from pores. Raney nickel -- hydrogenation of vegetable and animal oils. • A catalytic reaction occurs at the fluid-solid interface. A large interfacial area can be helpful or even essential in attaining a significant reaction rate.
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