Other Reactors

Other reactors and processes include the hot oil bath, molten salt bath, microwave, and plasma. These processes have been researched on laboratory and some cases pilot plant scale. None have proven commercially successful. 

Besides the MPCVD reactors, other CVD reactors are also used for diamond deposition. They are hot filament, DC plasma, radio-frequency (rf) plasma, thermal rf plasma, plasma jet, and combustion CVD reactors. In the following, hot filament and DC plasma CVD reactors will be described, because they have been used for oriented growth of diamond. 

Other types of fermenters have been developed for specific applications. Anaerobic bioreactors are used when microorganisms do the conversions in the absence of oxygen. Examples are the acetone-butanol-ethanol (ABE) fermentation with Clostridium species, the production of lactic acid with lactic acid bacteria, and bioethanol fermentation with Saccharomyces cerevisiae. Because of the need for large volumes with these low-cost products, and the ease of construction, these 

no single best solution seems at hand. 

If the fermentation contains sohds, then special precautions may be required to prevent sedimentation. One is a fluidized bed, where a dense slurry phase in the bottom of the tank is kept in gentle motion via upflow of the hquid or some induced gas/liquid momentum. The upflow anaerobic sludge bed (UASB) reactor is an example. In biogas installations, sohds may sediment and bacterial consortia may take several months to convert ah the material into methane and CO2. Because of the slow reaction rates, these instahations can be extremely large, up to 20 000 m. Other devices are packed-bed bioreactors, where ceUs are immobihzed on a solid support and the liquid is percolated or trickled down to supply nutrients and remove products. These can be found in specific antibiotic or food fermentations. Because of the lack of free fluid flow, the performance characteristics of such vessels are usually poor compared to suspensions. 

A special application, evolved in parahel in the medical community, is found in tissue engineering. Cell tissues in humans and animal models are getting more and more important in medical research and studies on the performance of cells in an environment where supply of nutrients and removal of waste products use similar approaches as in solid-state fermentations. Although an important emerging field, and the communities may converge in the future, this topic is left out of scope of this chapter. 

Tray columns, with perforated plates, have also occasionally been encountered. 

Diagnostic experiments such as those described above can be carried out in a straightforward manner when the velocity of the fluid relative to the catalyst can be controlled by the experimenter, and can be varied without changing any other parameters that affect the reaction rate. Unfortunately, this is not always the case. 

Consider abatchreactor where very small particles of a solid catalyst are suspended in a liquid and kept in suspension by mechanical agitation. The reaction takes place between components of the liquid, and the products are soluble in the liquid. What is the velocity of the liquid relative to the catalyst particles, and how can it be varied in a systematic fashion  

We might be tempted to say that the velocity of the liquid relative to the particles was related to the design and rotational velocity of the agitator, and that the relative velocity could be changed by changing the rotational speed of the agitator. Unfortunately, this approach is not 

For this case, gravitational settling is the primary cause of a relative velocity between the hquid and the catalyst particles. The settling velocity can be calculated, at least approximately. However, it cannot be changed without changing the physical properties of the catalyst and/or the hquid. It is essentiahy impossible to perform the kind of diagnostic experiments described in the previous section with this kind of reactor. 

In order to evaluate the influence of external transport in a reactor that contains a slurry of catalyst, it is necessary to perform a calculation. This approach wiU be described in the following sections. 

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In the first step cumene is oxidized to cumene hydroperoxide with atmospheric air or air enriched with oxygen ia one or a series of oxidizers. The temperature is generally between 80 and 130°C and pressure and promoters, such as sodium hydroxide, may be used (17). A typical process iavolves the use of three or four oxidation reactors ia series. Feed to the first reactor is fresh cumene and cumene recycled from the concentrator and other reactors. Each reactor is partitioned. At the bottom there may be a layer of fresh 2—3% sodium hydroxide if a promoter (stabilizer) is used. Cumene enters the side of the reactor, overflows the partition to the other side, and then goes on to the next reactor. The air (oxygen) is bubbled ia at the bottom and leaves at the top of each reactor. 

Additionally, two other reactors, the international thermonuclear experimental reactor (ITER) for which the location is under negotiation, and the Tokamak Physics Experiment at PPPL, Princeton, New Jersey, are proposed. The most impressive advances have been obtained on the three biggest tokamaks, TETR, JET, andJT-60, which are located in the United States, Europe, and Japan, respectively. As of this writing fusion energy development in the United States is dependent on federal binding (10—12). 

The third control is by use of a fixed burnable poison. This consists of rods containing a mixture of aluminum oxide and boron carbide, included in the initial fuel loading using the vacant spaces in some of the fuel assembhes that do not have control clusters. The burnable poison is consumed during operation, causing a reactivity increase that helps counteract the drop owing to fuel consumption. It also reduces the need for excessive initial soluble boron. Other reactors use gadolinium as burnable poison, sometimes mixed with the fuel. 

Gas-cooled, graphite moderated reactors have several significant advantages over other reactor designs by virtue of their inherent passive safety characteristics. These are the result of the large thermal mass of the graphite core, the high... 

Its unique design suggests several accident scenarios that could not occur at other reactors. For example, failure to supply ECC to 1/16 of the core due to the failure of an ECC inlet valve. On the other hand, some phenomena of concern to other types of reactors seem impossible (e.g., core-concrete interactions). The list of phenomena for consideration came from previous studies, comments of an external review group and from literature review. From this, came the issues selected for the accident progression event tree (APET) according to uncertainty and point estimates. 

Other reactor sources with instruments like D4C but with much lower flux, and hence longer data collection times, are the Laboratoire Leon Brillouin (LLB, Saclay, France), on the instrument 7C2, and the NFL (Studsvik, Sweden), on the instrument SLAD... 

I. ------Mass of initiator entering reactor j from other reactors. 

Polymer of chain length n from other reactors (mass) entering reactor j. 

Molecules must come into contact for a reaction to occur, and the mechanism for the contact is molecular motion. This is also the mechanism for diffusion. Diffusion is inherently important whenever reactions occur, but there are some reactor design problems where diffusion need not be explicitly considered, e.g., tubular reactors that satisfy the Merrill and Hamrin criterion. Equation (8.3). For other reactors, a detailed accounting for molecular diffusion may be critical to the design. 

Among several types of reactors investigated, the microstructured reactor was successfully applied to the synthesis of a pharmaceutical intermediate via a fast exothermic Boc protecting reaction step. The reaction temperature was isothermally controlled at 15°C. By using the microstructured reactor the heat of reaction was completely removed so that virtually no byproducts were produced during the reaction. Conversions as high as 96% were achieved. The micro-reactor operation can be compared with other reactors, however, which need to be operated at 0°C or -20°C to avoid side reactions. 

Other reactor types are also used for gas-liquid reactions, but they are not very common in fine chemicals manufacture. Spray towers and jet reactors are used when the liquid phase is to be dispersed. In spray towers the liquid is sprayed at the top of the reactor while the gas is flowing upward. The spray reactor is useful when a solid product, possibly suspended in the liquid, is formed, or if the gas-phase pressure drop must be minimized. In a jet reactor, the liquid is introduced to the reaction zone through a nozzle. The gas flows in, being sucked by the liquid. 

Obviously, the least experience has been accumulated with monoliths, particularly in three-phase applications. They are also more expensive than the other reactors. Therefore, the use of monoliths can only be economically ju.stified for three-phase processes in which it offers a distinct advantage, like higher yield, improved. selectivity, increased throughput of a plant, or lower overall investment or operating costs. Of particular interest are situations in which a MR substantially simplifies the design or operation of a unit. 

Finally, the reactor vessel has been assumed to be perfectly mixed. Imperfect mixing and a flow pattern created by different types of agitators, baffles, feed locations and other reactor vessel configurations will cause the performance to be below that indicated by perfect mixing. 

Thus we may construct straight line GH in Figure 8.11, by drawing a line of slope ( —1/t2) through the point with an ordinate of zero and an abscissa of CA1. The intersectiom of this line with curve I gives us the effluent concentration from the second reactor. This same procedure can be repeated for any other reactors that may be part of the cascade. The straight line JK was constructed in this fashion for the present case. 

A fixed bed reactor has many unique and valuable advantages relative to other reactor... 

For a constant-volume batch reactor operated at constant T and pH, an exact solution can be obtained numerically (but not analytically) from the two-step mechanism in Section 10.2.1 for the concentrations of the four species S, E, ES, and P as functions of time t, without the assumptions of fast and slow steps. An approximate analytical solution, in the form of a rate law, can be obtained, applicable to this and other reactor types, by use of the stationary-state hypothesis (SSH). We consider these in turn. 

There are many other reactors of various types not included among those discussed above. These include tower reactors (Chapter 24), which may be modeled as PF or modified PF reactors. We describe one further example in this section. 

Including 20 ft2 for miscellaneous items not identified in this section, 110.3 ft2 must be rented, at an annual cost of 44,100/yr. Note that this moderately sized complex is added to an existing electronic materials manufacturing facility. Hence, no direct charges are added for infrastructure, such as non-clean room and office space. The total purchase cost, 6,492,100, provides equipment modules that require small installation costs, on the order of 1% that is, 65,000. Note also that two PECVD reactors are provided to assure uninterrupted operation when the plant is in operation, around the clock, 330 day/yr. While the robot loads and unloads one of the reactors, the other reactor is in operation. 

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