Reaction solid-catalyzed

With many reactions, the rates are affected by materials which are neither reactants nor products. Such materials called catalysts can speed a reaction by a factor of a million or much more, or they may slow a reaction (negative catalyst). 

There are two broad classes of catalysts those that operate at close to ambient temperature with biochemical systems, and the man-made catalysts that operate at high temperature. 

The biochemical catalysts, called enzymes, are found everywhere in the biochemical world and in living creatures, and without their action I doubt that life could exist at all. In addition, in our bodies hundreds of different enzymes and other catalysts are busily at work all the time, keeping us alive. We treat these catalysts in Chapter 27. 

The man-made catalysts, mostly solids, usually aim to cause the high-temperature rupture or synthesis of materials. These reactions play an important role in many industrial processes, such as the production of methanol, sulfuric acid, ammonia, and various petrochemicals, polymers, paints, and plastics. It is estimated that well over 50% of all the chemical products produced today are made with the use of catalysts. These materials, their reaction rates, and the reactors that use them are the concern of this chapter and Chapters 19-22. 

The selection of a catalyst to promote a reaction is not well understood therefore, in practice extensive trial and error may be needed to produce a satisfactory catalyst. 

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However, before extrapolating the arguments from the gross patterns through the reactor for homogeneous reactions to solid-catalyzed reactions, it must be recognized that in catalytic reactions the fluid in the interior of catalyst pellets may diSer from the main body of fluid. The local inhomogeneities caused by lowered reactant concentration within the catalyst pellets result in a product distribution different from that which would otherwise be observed. 

Solid Catalyzed Reaction The pioneers were Langmuir (J. Am. Chem. Soc., 40, 1361 [1918]) and Hinshelwood Kinetics of Chemical Change, Oxford, 1940). For a gas phase reaction A + B Products, catalyzed by a solid, the postulated mechanism consists of the following ... 

Annular flow reactors, such as that illustrated in Figure 3.2, are sometimes used for reversible, adiabatic, solid-catalyzed reactions where pressure near the end of the reactor must be minimized to achieve a favorable equilibrium. Ethylbenzene dehydrogenation fits this situation. Repeat Problem 3.7 but substitute an annular reactor for the tube. The inside (inlet) radius of the annulus is 0.1m and the outside (outlet) radius is 1.1m. 

An observed, gas-solid-catalyzed reaction is A -I- B P. Suppose the surface mechanism is... 

The bubbles play the role of the gas phase. The role of the liquid is played by an emulsion phase that consists of solid particles and suspending gas in a configuration similar to that at incipient fluidization. The quasi-phases are in cocurrent flow, with mass transfer between the phases and with a solid-catalyzed reaction occurring only in the emulsion phase. The downward flow of solids that occurs near the walls is not explicitly considered in this simplified model. 

In heterogeneous catalysis, solids catalyze reactions of molecules in gas or solution. As solids - unless they are porous - are commonly impenetrable, catalytic reactions occur at the surface. To use the often expensive materials (e.g. platinum) in an economical way, catalysts are usually nanometer-sized particles, supported on an inert, porous structure (see Fig. 1.4). Heterogeneous catalysts are the workhorses of the chemical and petrochemical industry and we will discuss many applications of heterogeneous catalysis throughout this book. 

Satterfield, C. N., and Ozel, F., Direct solid-catalyzed reaction of a vapor in an apparently completely wetted trickle bed reactor. AIChEJ. 19, 1259-1261 (1973). 

More often than not, solid-catalyzed reactions are multiple... 

REACTOR CONFIGURATION FOR HETEROGENEOUS SOLID-CATALYZED REACTIONS... 

As in the case of a batch reactor for commercial operation, a CSTR is normally used for a liquid-phase reaction. In the laboratory, it may also be used for a gas-phase reaction for experimental measurements, particularly for a solid-catalyzed reaction, as in Figure 1.2. The operation is normally one of steady-state, except for startup, shutdown, and operational disturbances or upsets, in which cases unsteady-state operation has to be taken into account. 

In a series arrangement, all changes in properties are taken into account, such as adjustment of T (without reaction) by a heat exchanger between stages (lengths). Such adjustment is more common for solid-catalyzed reactions than for homogeneous gas-phase reactions. 

Selective epoxidation of one of the double bonds in dialkenes is of practical interest (Table XVI). Although monoepoxides predominate at low H2O2 concentrations, the diepoxides are also formed at higher concentrations. The diallyl epoxides of bisphenol A are major intermediates in the adhesives industry, and their synthesis in solid-catalyzed reactions in an eco-friendly manner remains a challenge. 

Solid catalyzed reaction. Langmuir-Hinshelwood mechanism... 

For the solid catalyzed reaction, 2A B+C, initial rate data were obtained as tabulated, starting with pure A. Consider these three reaction mechanisms,... 

Data for the solid catalyzed reaction, A o B, are tabulated. Adsorption of B is small compared with that of A. Check the validity of these mechanisms ... 

The rate of a solid catalyzed reaction, A2 surface reaction controlled. With the aid of the given is the dissociated or molecular species that reaction. The equilibrium constant is Ke = Pbe Pae With dissociation,... 

The rate of a solid catalyzed reaction, 2A B, is controlled by three simultaneous factors,... 

The solid catalyzed reaction, A2 + B => Products, takes place with a large excess of substance B so its partial pressure does not change appreciably. The rate of diffusion is rdiff = 0.015(pag pM)... 

The rate of solid catalyzed reaction is controlled by external diffusion and surface reaction, with equation... 

The rate of a solid catalyzed reaction, A => B, is determined by the rate of diffusion to the surface, rd, and the rate of a first order surface reaction, rs. At steady state,... 

The rate of a second order solid catalyzed reaction is controlled by diffusion to the external surface, by diffusion into the pores and by reaction on the pore surface. The rate relations are... 

Site Density and Entropy Criteria in Identifying Rate-Determining Steps in Solid-Catalyzed Reactions... 

For a solid-catalyzed reaction between two different molecules all the possibilities for the rate-determining step of the one-molecule reaction still exist. Thus, adsorption of either molecule can be rate determining a surface reaction involving only one of the molecules can be the rate-determining step and so forth. The two-molecule case introduces some new possibilities for the rate-determining step. In both the one-molecule and the two-molecule case the rate-determining step can be a surface bimolecular reaction. With the surface reaction in the two-molecule case, however, the reaction depends upon the relative abilities of the molecules to adsorb on the active sites. There are several possible cases. Both can adsorb weakly one can adsorb moderately well as the other adsorbs weakly they can both adsorb moderately well, competing effectively with each other for sites and one can adsorb very well as the other adsorbs weakly. Another problem arises when the two... 

For a solid-catalyzed reaction in which a single gaseous reactant is transformed to either of two products via a common surface complex, the reaction scheme is... 

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