Diffusion model reaction

Both questions have been recently addressed via a surface diffusion-reaction model developed and solved to describe the effect of electrochemical promotion on porous conductive catalyst films supported on solid electrolyte supports.23 The model accounts for the migration (backspillover) of promoting anionic, O5, species from the solid electrolyte onto the catalyst surface. The... 

The conversion process within the biofilm is described by a substrate diffusion-reaction model. 

The biofilm thickness (Lf) and density (X = 50 g/L) were assumed uniform and the biofilm treated as a continuum. A substrate diffusion-reaction model assuming spherical particle was used. Diffusion coefficient of phenol and oxygen in the biofilm were assessed according to Fan et al. [64] ... 

This study was carried out to simulate the 3D temperature field in and around the large steam reforming catalyst particles at the wall of a reformer tube, under various conditions (Dixon et al., 2003). We wanted to use this study with spherical catalyst particles to find an approach to incorporate thermal effects into the pellets, within reasonable constraints of computational effort and realism. This was our first look at the problem of bringing together CFD and heterogeneously catalyzed reactions. To have included species transport in the particles would have required a 3D diffusion-reaction model for each particle to be included in the flow simulation. The computational burden of this approach would have been very large. For the purposes of this first study, therefore, species transport was not incorporated in the model, and diffusion and mass transfer limitations were not directly represented. 

Satisfactory agreement between the predictions of the diffusion-reaction model with the experimental data, particularly the ensuing estimate of a consistent interlayer distance, provides evidence of the spatial order resulting from the step-by-step construction of the multilayered coating. 

The ratio vJD can then be used to calculate a chemical reaction rate for a nonconservative solute, S. To do this, the one-dimensional advection-diffusion model is modified to include a chemical reaction term, J. This new equation is called the one-dimensional advection-diffusion-reaction model and has the following form ... 

Doremus, R. H. 2000. Diffusion of water in rhyolite glass Diffusion-reaction model. Journal of Non-Crystalline Solids, 261, 101-107. 

Steam reformers are used industrially to produce syngas, i.e., synthetic gas formed of CO, CO2, 11-2, and/or hydrogen. In this section we present models for both top-fired and side-fired industrial steam reformers by using three different diffusion-reaction models for the catalyst pellet. The dusty gas model gives the simplest effective method to describe the intermediate region of diffusion and reaction in the reformer, where all modes of transport are significant. This model can predict the behavior of the catalyst pellet in difficult circumstances. Two simplified models (A) and (B) can also be used, as well as a kinetic model for both steam reforming and methanation. The results obtained for these models are compared with industrial results near the thermodynamic equilibrium as well as far from it. 

Note that all three models give almost the same exit conversion and yield for methane and carbon dioxide and that the second unit (2) is also operating relatively closely to its thermodynamic equilibrium, though further away from it when compared to Plant (1). The close agreement between the industrial performance data and the simulated data for the reformers (1) and (2) that was obtained by three different diffusion-reaction models validates the models that we have used, at least for plants operating near their thermodynamic equilibria. 

The predictions from the three models for steam reforming are equally reliable for industrial reactors that operate near their thermodynamic equilibrium. Significant deviations occur when the system is operating far from thermodynamic equilibrium, though. In this case the dusty gas model is still quite accurate while the simplified diffusion-reaction models are no longer accurate enough. 

The six reactions described in (7.151) to (7.156) with their rate equations (7.157) to (7.162) take place in the catalyst pellet. Reactants and products are diffusing simultaneously through the pores of the catalyst. In our development of the diffusion-reaction model equations we make the following assumptions. 

PAMC (Parameterized ADM Mathematica Code) for diffusion-reaction models ... 

Diffusion 127 -, anomalous 39, 42-43, 65 Diffusion-reaction model 141 Diffusivity, thermal 149 Diglycidylether of bisphenol-A (DGEBA) 141 Disordered structure 12 Dispersion 9-10,30,32,36,48 Dynamic plowing lithography 153... 

II. Spatial Averaging of Convection-diffusion-reaction Models using the L-S Method 217... 

Doremus R. H. (1999) Diffusion of water in crystalline and glassy oxides diffusion-reaction model. J. Material. Res. 14, 3754-3758. 

There is a large body of literature that deals with the proper definition of the diffusivity used in the intraparticle diffusion-reaction model, especially in multicomponent mixtures found in many practical reaction systems. The reader should consult references, e.g.. Bird, Stewart, and Lightfoot, Transport Phenomena, 2d ed., John Wiley Sons, New York, 2002 Taylor and Krishna, Multicomponent Mass Transfer, Wiley, 1993 and Cussler, Diffusion Mass Transfer in Fluid Systems, Cambridge University Press, 1997. 

We illustrate the above point with an example from the hydrogen oxidation on a single Pt(l 11) crystal. This system was recently studied experimentally by Ertl, Wintterlin, and coworkers, and motivated simulation because the corresponding continuum diffusion-reaction model was unable to capture some experimental features. Their experiments entailed predosing the... 

Here the basic concepts of system theory and principles for mathematical modelling are presented for the development of diffusion reaction models for fixed bed catalytic reactors. 

B.l SIMPLE APPLICATION OF THE ORTHOGONAL COLLOCATION TECHNIQUES FOR A FICKIAN-TYPE DIFFUSION-REACTION MODEL FOR POROUS CATALYST PELLETS... 

Techniques for a Fickian-type Diffusion-Reaction Model for Porous Catalyst Pellets 436... 

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