Effect of Scale on Performance

Developments in experimental and mathematical techniques in the 1970s have initiated an interest in the development of better laboratory reactors for catal5d ic studies. Besides the many publications on new reactors for general or special tasks, quite a few review articles have been published on the general subject of laboratory reactors for catalytic studies. 

In reaction engineering, laboratory catal54ic reactors are tools or instruments to study how catalysts behave in some desired reaction. Quantitatively, the investigator wants to know how much of the desired product can be made per unit weight of catalyst, how much raw material will be used, and what byproducts will be made. This is the basic information needed to estimate the costs and profitability of the process. The economic consequence of our estimates also forces us to clarify what the rate limiting steps are, and how much transfer processes influence the rates, i.e., everything that is needed for a secure scale-up. Making the 

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From the earliest days when unsuccessful attempts were made to scale up the Fischer-Tropsch reaction (38), it has been recognized that conversion decreases strongly as many fluidized bed processes are scaled up. The effect of scale on performance according to the two-phase bubbling bed model (19) and the Orcutt model (17,18) with perfect mixing in the dense phase are shown in... 

Finally, the scale of the reactors is significant. The experiments reported here were performed only with one family of models on one scale (about 1 40, relative to real-world reactors). Another investigation (8) of the effect of scale on hydraulic characteristics of coagulation reactors showed that as the scale increased, the flow regime or the energy dissipation became less ho-... 

T-Y Koo, K-O Kim, M O Mahony. Effects of forgetting on performance on various intensity scaling protocols Magnitude estimation and labeled magnitude scale (Green scale). J Sens Stud 17 177 192, 2002. 

Findings with Bench-Scale Unit. We performed this type of process variable scan for several sets of catalyst-liquid pairs (e.g., Figure 2). In all cases, the data supported the proposed mechanism. Examination of the effect of temperature on the kinetic rate constant produced a typical Arrhenius plot (Figure 3). The activation energy calculated for all of the systems run in the bench-scale unit was 18,000-24,000 cal/g mole. 

In this volume not all stress types are treated. Various aspects have been reviewed recently by various authors e.g. The effects of oxygen on recombinant protein expression by Konz et al. [2]. The Mechanisms by which bacterial cells respond to pH was considered in a Symposium in 1999 [3] and solvent effects were reviewed by de Bont in the article Solvent-tolerant bacteria in biocatalysis [4]. Therefore, these aspects are not considered in this volume. Influence of fluid dynamical stresses on micro-organism, animal and plant cells are in center of interest in this volume. In chapter 2, H.-J. Henzler discusses the quantitative evaluation of fluid dynamical stresses in various type of reactors with different methods based on investigations performed on laboratory an pilot plant scales. S. S. Yim and A. Shamlou give a general review on the effects of fluid dynamical and mechanical stresses on micro-organisms and bio-polymers in chapter 3. G. Ketzmer describes the effects of shear stress on adherent cells in chapter 4. Finally, in chapter 5, P. Kieran considers the influence of stress on plant cells. 

As a final point, we note that typical surfaces are usually not crystalline but instead are covered by amorphous layers. These layers are much rougher at the atomic scale than the model crystalline surfaces that one would typically use for computational convenience or for fundamental research. The additional roughness at the microscopic level from disorder increases the friction between surfaces considerably, even when they are separated by a boundary lubricant.15 Flowever, no systematic studies have been performed to explore the effect of roughness on boundary-lubricated systems, and only a few attempts have been made to investigate dissipation mechanisms in the amorphous layers under sliding conditions from an atomistic point of view. 

The effects of miniaturization on the performance of an analytical separation system are often discussed in terms of a reduction of a characteristic length parameter (e.g., column diameter dc or particle diameter dp) and the associated consequences for lateral zone dispersion processes and their interplay with longitudinal (axial) zone dispersion. A rigid discussion of the physical-chemical basis is beyond the scope of this chapter. For a general account in terms of scaling laws and proportionality considerations, the reader is referred to the references [12,14]. A comprehensive and detailed description with emphasis on the underlying physical-chemical processes can be found in the book by Giddings [20]. 

In some cases, it is not possible to evaluate a material or product (combination of materials) in a bench-scale test in a manner that is representative of its end-use. For example, it is difficult to use a bench-scale test method to evaluate the effect of joints on the fire performance of a thick sandwich panel that consists of a plastic foam core and metal skins. In this case, a room test is used to assess the reaction to fire of the materials. It is also very difficult to assess the fire performance of complex objects such as upholstered furniture based on the reaction-to-hre characteristics of the object s components. Large-scale reaction-to-hre tests have been developed to evaluate these complex objects. 

Liquid distribution in trickle bed reactors has been mainly discussed from the aspect of flow channels between particles [6, 7]. However, since most of the commercial catalysts are extrudates, an effect of the particle orientation on liquid distribution is much more important than flow channel, which relates to mass flow rate and a particle size. Shaped catalysts have a higher volume activity than cylindrical catalysts when an effect of diffusion on the reaction rate is large [8]. Therefore, the shaped catalysts have been commonly used for hydrodemetallation of residue. However, since an effect of liquid distribution on the catalyst performance is important in large-scale commercial reactors, catalyst shape should be carefully selected to maximize the effectiveness of the catalyst usage in a commercial application. 

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