Catalyst particles analogy

This model is equivalent to the model for a first-order reaction in an infinite cylinder of catalysts (214). Analogous to the solution of the catalyst particle problem, the notation of an effectiveness factor can be introduced as the ratio of reaction on each pair of wafers (back and front) to the deposition rate at the wafer edge, that is,... 

Equation (4.97) is usually satisfied for mass transfer in the gas phase, such as transport of oxygen or hydrogen to the outer surface of a small catalyst particle which is stagnant relative to the surrounding gas. In this case, when Eq. (4.98) is also satisfied, Sh of 2 is a good approximation, which is analogous to the heat transfer counterpart given in Eq. (4.15). Equation (4.97) is especially important when there is simultaneous heat transfer and mass transfer. 

The mass-transfer coefficient with a reactive solvent can be represented by multiplying the purely physical mass-transfer coefficient by an enhancement factor E that depends on a parameter called the Hatta number (analogous to the Thiele modulus in porous catalyst particles). 

Similar to normal catalyst synthesis whereby ion exchange methods can result in egg-shell structures, in the preparation of monolith catalysts the majority of the metal can be deposited at the entrance of the monolith. Egg-shell structures can be attractive for catalyst particles, but for monoliths, analogous uneven distributions of the active phase are a disaster. Fortunately, extensive literature is available describing ion-exchange procedures for conventional catalysts that yield homogeneous metal distributions. This literature can be used as a guide for preparing satisfactory monolithic catalysts. 

P1-6a What is the difference between the rate of reaction for a homogeneous system, —ta, and the rate of reaction for a heterogeneous system, — ri Use the mole balance to derive an equation analogous to Equation (1-6) for a fluidized CSTR containing catalyst particles in terms of the catalyst weight, IV, and other appropriate terms. 

The limited rate of mass transport through the bed can give rise to incomplete utilization of the catalyst in the bed, in analogy with the incomplete utilization of a catalyst particle due to pore diffusion limitation. 

In practice, the effects of heat transfer from the bulk of a fluid phase to the external surface of a solid catalyst particle are more important than the effects of mass transfer. An approach analogous to that of mass transfer, for a single reactant, leads to ... 

Steps 3 and 4 cannot, in general, be separated from each other the transport away from the interface occurs simultaneously with the chemical reaction, just as with transport and reaction inside catalyst particles. The following section offers a quantitative analysis analogous to the analysis in Section 8.4.1. 

Packed-betl reactoi-s are tubular reactors filled with catalyst particles. The der-ivaiion of the differential and integral forms of the de.sign equations for packed-bed reactors are analogous to those for a PFR [cf. Equations (2-15) and (2-16)]. That is, substituting Equation (2-12) for in Equation (M5) gives... 

In any catalytic system not only chemical reactions per se but mass and heat transfer effects should be considered. For example, mass and heat transfer effects are present inside the porous catalyst particles as well as at the surrounding fluid films. In addition, heat transfer from and to the catalytic reactor gives an essential contribution to the energy balance. The core of modelling a two-phase catalytic reactor is the catalyst particle, namely simultaneous reaction and diffusion in the pores of the particle should be accounted for. These effects are completely analogous to reaction-diffusion effects in liquid films appearing in gas-liquid systems. Thus, the formulae presented in the next section are valid for both catalytic reactions and gas-liquid processes. 

Slurry reactors are popular in industry where the solids either take part in the reaction or act as catalyst.Many aspects of these reactors,particularly for catalytic systems,have been discussed at length in 1iterature(1,2).Catalytic slurry reactors are also reviewed in this proceedings by Hofmann(3).However,there are still aspects which have not been treated in the literature in sufficient detail.Firstly,until recently little attention has been paid to slurry reactors involving reactive solids.Secondly, it is often assumed that steps of diffusion of the dissolved gas from the gas-liquid interface to the bulk liquid phase bulk liquid phase to the solid catalyst surface and surface reaction are steps in series.This leads of course to a specific gas absorption rate which is always smaller than k.A. While this is a representative picture in a majority of cases of industrial relevance,we can conceive situations,where the catalyst particle size may be smaller than the diffusion film(liquid film next to gas-liquid interface) thickness.We may then have steps of the transport of the dissolved gas from the gas-liquid interface and reaction on the catalyst particle in parallel,that is,while the dissolved gas diffuses it reacts on the catalyst surface.This is then in many ways analogous to normal gas-liquid reactions and may lead to the enhancement of specific gas absorption rate so that it exceeds k.A. This point is also relevant to reactive solid systems indeed in an earlier paper,Ramachandran and Sharma(4) had shown that the specific rate of absorption accompanied by an instantaneous reaction in a slurry containing sparingly soluble fine particle size was considerably smaller than the film thickness. Finally,there is substantial information in the literature on the combined effect of solid particles on k a.However,the information... 

The heat transfer coefficient was obtained by using the analogy for mass and heat transfer iD-jn)- The overall heat of cracking reactions was assumed to be 380 kJ/kg gas oil converted. In addition, the heat flux by radiation from the reactor tube to the surface of the catalyst particles was accounted for by the Stefan-Boltzmann law [10]. 

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