Reactor design structure

The hierarchical approach is a simple but powerful methodology for the development of process flowsheets. It consists of a top-down analysis organized as clearly defined sequence of tasks aggregated in levels. Each level handles a fundamental conceptual problem input/output structure, reactor design, structure of separa-... 

The use of excess reactants, diluents, or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes the recycling of unwanted byproduct to the reactor can inhibit its formation at the source. If this can be achieved, it improves the overall use of raw materials and eliminates effluent disposal problems. Of course, the recycling does in itself reuse some of the other costs. The general tradeoffs are discussed in Chap. 8. 

Reactor design can have a significant influence on reactor performance in a number of ways. Some aspects of reactor design such as heat transfer, structural design, etc., are reasonably well-understood. Other phenomena such as mixing details, latex flocculation, and the formation wall polymer are not completely understood. 

The quality and yield of carbon black depends on the quality of the feedstock, reactor design, and input variables. The structure is controlled by the addition of alkali metals to the reaction or mixing zones. Usual practice is to use aqueous solutions of alkali metal salts such as potassium chloride or potassium hydroxide sprayed into the combustion chamber or added to the make oil in the oil injector. Alkaline-earth compounds such as calcium acetate that increase the specific surface area are introduced in a similar manner. 

The CVD reactor must be designed and operated in such a manner that changes in film thickness, crystal structure, surface morphology, and interface composition can be accurately controlled. The overall process performance depends on the reactor design and process variables such as reactant concentrations, flow rates, energy input, pressure, and substrate conditions. 

Like the literature of plasma-assisted etching, the literature on the PECVD of specific materials is considerable. Because film properties are ultimately determined by chemical reaction mechanisms, reactor design, and film structure (Figure 5), the determination of the exact relationships between properties and processing is difficult. At present, the fundamental understanding of such relationships is limited, and thus, empirical efforts have been the norm. In this chapter, the more widely studied film materials deposited by PECVD will be briefly discussed. More extensive information on these and other films can be found in a number of review articles (9-14, 32, 50, 200-203) and references therein. 

The investigation of the mechanism of olefin oxidation over oxide catalysts has paralleled catalyst development work, but with somewhat less success. Despite extensive efforts in this area which have been recently reviewed by several authors (9-13), there continues to be a good deal of uncertainty concerning the structure of the reactive intermediates, the nature of the active sites, and the relationship of catalyst structure with catalytic activity and selectivity. Some of this uncertainty is due to the fact that comparisons between various studies are frequently difficult to make because of the use of ill-defined catalysts or different catalytic systems, different reaction conditions, or different reactor designs. Thus, rather than reviewing the broader area of selective oxidation of hydrocarbons, this review will attempt to focus on a single aspect of selective hydrocarbon oxidation, the selective oxidation of propylene to acrolein, with the following questions in mind ... 

Fixed-bed catalytic reactors and reactive distillation columns are widely used in many industrial processes. Recently, structured packing (e.g., monoliths, katapak, mella-pak etc.) has been suggested for various chemical processes [1-4,14].One of the major challenges in the design and operation of reactors with structured packing is the prevention of liquid flow maldistribution, which could cause portions of the bed to be incompletely wetted. Such maldistribution, when it occurs, causes severe under-performance of reactors or catalytic distillation columns. It also can lead to hot spot formation, reactor runaway in exothermic reactions, decreased selectivity to desired products, in addition to the general underutilization of the catalyst bed. 

Experiments performed with the reactor, in that case made of titanium, by Worz at BASF in a proprietary reaction revealed 60% yield for the desired product at residence times as low as 40 ms in the micro reactor. This performance was superior to that of the experiments performed in an aluminum capillary, which corresponds well with the reactor design of the industrial process (Figure 3.24). A 2000% gain in space-time yield was found for the porous coated micro structures compared with the aluminum capillaries. 

It must be pointed out again that even today confusion of terms can be observed when chemical engineers discuss miniplants or microplants . In most of these cases they identify with the terms mentioned above chemical plants made of glassware with volumes in the range of up to a few liters. To summarize, at that early stage no specialized micro structured reactors for production purposes were available. Most of the fabricated micro structured devices were made in terms of micro fabrication capabilities and not adapted to the chosen chemical process. It is no wonder that at first visionary theoretical work either had to be based on conventionally fabricated chemical reactors or did not outline reactor design in detail [30],... 

Most reliable are the data on neutron fluxes which are determined by the plasma power density, reactor geometry and structural parameters. Most of the conceptual power reactor design studies contain a detailed neutronics analysis giving the energy as well as the spatial distribution of neutron fluxes. 

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