Catalyst beds explanation

Because any individual boundary scale is in the domains of two disciplines, one as the element scale, and the other as the system, the experimental results, such as product distribution, would be influenced by both sides. As well known, the FTS process is very complex and includes several scales or levels. Except experiment method, as mentioned above, the combination of the molecular scale, the particle scale of active phase, and the catalyst bed or reactor scale results very complex reaction performance and modified ASF product distribution of FTS. Although there have been some divergence of these explanations, it can be clearly seen that without the coupling of difier-ent scales, the product distribution of FTS cannot be explained properly. It is... 

GL 18] ]R 6a]]P 17/Using the same experimental conditions and catalysts with the same geometric surface area, the performance of micro-channel processing was compared with that of a fixed-bed reactor composed of short wires [17]. The conversion was 89% in the case of the fixed bed the micro channels gave a 58% yield. One possible explanation for this is phase separation, i.e. that some micro channels were filled with liquids only, and some with gas. This is unlikely to occur in a fixed bed. Another explanation is the difference in residence time between the two types of reactors, as the fixed bed had voids three times larger than the micro channel volume. It could not definitively be decided which of these explanations is correct. 

Nickel-platinum bimetallic catalysts showed higher activity during ATR than nickel and platinum catalysts blended in the same bed. It was hypothesized that nickel catalyzes SR, whereas platinum catalyzes POX and, when they are added to the same support, the heat transfer between the two sites is enhanced [59, 60]. Advanced explanations were reported by Dias and Assaf [60] in a study on ATR of methane catalyzed by Ni/y-Al203 with the addition of small amounts of Pd, Pt or Ir. An increase in methane conversion was observed, ascribed to the increase in exposed Ni surface area favored by the noble metal under the reaction conditions. 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

The percentage desulfurization versus liquid flow rate (and, hence, length of the reactor, since LHSV was kept constant) data obtained with this catalyst are shown in Fig. 4-19. As one explanation for the effect shown in this figure, it has been suggested that the axial dispersion in shorter beds causes their poor performance. Is this a viable explanation Based on Mears criterion, what is the... 

It is well established that eventually the catalytic activity dies away rapidly (figure 2). The most probably explanation of this involves the migration of the wave of heavy metal sulphide deposits through the bed. Examination of spent catalyst removed from a trickle bed reactor shows clearly that the top layer of the bed is very heavily contaminated and that the contamination decreases down the bed. If the reaction is allowed to proceed to the point where heavy deposits spread throughout the bed, then catastrophic deactivation can be expected. 

When the reactor contains a solid catalyst the flow pattern is strongly determined by the presence of the solid. It would be impossible to rigorously express the influence of the packing but again the flux of j resulting from the mixing effect caused by its presence is expressed in the form of Pick s law. Consequently, the form of Eq. 7.2.a-6 is not altered, but the effective diffusivity now also contains the effect of the packing. This topic is dealt with extensively in Chapter 11 on fixed bed catalytic reactors. For further explanation of the effective transport coefficients see Himmelblau and Bischoff [3] and Slattery [4]. 

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