Specialized reactors, described

As is the case with pure bubble columns and gas-operated loop reactors, most bioreactors in technical use are aerated with oxygen or air. Reactors with pure surface aeration, such as roller bottles, shake flasks and small stirred reactors or special reactors with membrane aeration, are exceptions. The latter are used for the cultivation of cells and organisms which are particularly sensitive to shearing (see e. g. [28 - 29]). The influence of gas bubbles in increasing stress has been described in many publications (see e.g. [4, 27, 29, 30]). In principle it can be caused by the following processes ... 

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

In addition to the laboratory-scale reactors described here, there are numerous more specialized reactors in use. However, as mentioned previously, the performance of these reactors must lie somewhere between the mixing limits of the PFR and the CSTR. Additionally, when using small laboratory reactors, it is often difficult to maintain ideal mixing conditions, and the state of mixing should always be verified (see Chapter 8 for more details) prior to use. A common problem is that flow rates sufficiently large to achieve PFR behavior cannot be obtained in a small laboratory system, and the flow is laminar rather than turbulent (necessary for PFR behavior). If such is the case, the velocity profile across the reactor diameter is parabolic rather than constant. 

A special reactor for gas-liquid interaction is described by the authors in patent [18]. Due to the holes in the stirrer, C02 is involved intensively in the epoxy compound. 

Ideal mixing and plug flow. The batch, contlnuous-stirred-tank, and plug-flow reactors are defined by certain idealized assumptions on the fluid flow. The batch and continuous-stirred-tank reactors are assumed to be ideally well mixed, which means that the temperature, pressure and species concentrations are independent of spatial position within the reactor. The plug-flow reactor describes a special type of flow in a itube in which the fluid.is well.mixed in the radial direction and varies... 

Despite the details of gel-particle formation inside a micro-reactor channel having been reported previously by Zhan et al. [23], the continuous production of such particles was first described by Sugiura et al. [31]. For this, the design of a special reactor was described, that employed micro-hthographically prepared micro-nozzles (Figure 14.23). These nozzles ensured that the droplets were formed... 

To see that the model works properly it is instructive to consider several special cases. Putting the constant a = 0 we have the case of a batch reactor described by... 

Another very useful solvent for polymerization of (semi)fluorinated monomers in homogeneous solution is supercritical carbon dioxide (SCCO2) due to its high ability to dissolve fluorinated compounds. CO2 reaches the critical point at = 31°C and= 73.75 bar. Thus, high pressure cells are needed and special equipment, such as tubular reactors described by Beuermann et al. [69], has to be used. This type of reactor was also applied for the (controlled) radical polymerization of sf... 

Several patents describe solvent-free bulk-phase halogenation (67—69). Dry soHd butyl mbber is fed into a specially designed extmder reactor and contacted with chlorine or bromine vapor. The by-product HCl or HBr ate vented directly without a separate neutralization step. Halogenated butyl mbbers produced are essentially comparable in composition and properties to commercial products made by the solution process. 

Topics that acquire special importance on the industrial scale are the quality of mixing in tanks and the residence time distribution in vessels where plug flow may be the goal. The information about agitation in tanks described for gas/liquid and slurry reactions is largely apphcable here. The relation between heat transfer and agitation also is discussed elsewhere in this Handbook. Residence time distribution is covered at length under Reactor Efficiency. A special case is that of laminar and related flow distributions characteristic of non-Newtonian fluids, which often occiu s in polymerization reactors. 

Apparatus for carrying out hydrogenation at several atmospheres can be constructed readily (1,78,93), but there seems little point in this exercise since good commercial equipment is available. The most commonly used commercial low-pressure equipment is the Parr hydrogenator (manufactured by Parr Instrument Co., Moline, Illinois). This equipment (Fig. 1) has withstood the test of time it was first described in 1922 and offered commercially in 1926. It comes in two sizes one for 500-ml reactor bottles and one for 1000-and 2000-ml reactor bottles. Specially made smaller bottles, down to 50 ml, can be used also but require special holders to compensate for differences in bottle heights. Shaker bottles should not be more than half full to ensure good mixing, a consideration in selection of bottle size. 

Substantial heat-transfer intensification was also described for a special micro heat exchanger reactor [104]. By appropriate distribution of the gas-coolant stream, the axial temperature gradient can be decreased considerably, even under conditions corresponding to very large adiabatic temperature rises, e.g. of about 1400 °C. 

Attrition of particulate materials occurs wherever solids are handled and processed. In contrast to the term comminution, which describes the intentional particle degradation, the term attrition condenses all phenomena of unwanted particle degradation which may lead to a lot of different problems. The present chapter focuses on two particular process types where attrition is of special relevance, namely fluidized beds and pneumatic conveying lines. The problems caused by attrition can be divided into two broad categories. On the one hand, there is the generation of fines. In the case of fluidized bed catalytic reactors, this will lead to a loss of valuable catalyst material. Moreover, attrition may cause dust problems like explosion hazards or additional burden on the filtration systems. On the other hand, attrition causes changes in physical properties of the material such as particle size distribution or surface area. This can result in a reduction of product quality or in difficulties with operation of the plant. 

AChE-biotests are located in a special column-reactor connected with the peristaltic pump and the incubation is done in flowing conditions. For this purpose special flowing, termistatic column-reactor is used (described in Supplement 2). 

After essential revision, and description of wave-material interactions, microwave technology, and equipment (Chapt. 1) the concepts of microwave-assisted organic chemistry in pressurized reactors are described (Chapt. 2). Special emphasis on the possible intervention of a specific (non-purely thermal) microwave effect is discussed in Chapt. 3 and this is followed by up-to-date reviews of microwave-assisted organic... 

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