Static bed

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

Calcination can be completed in an inclined rotary calciner, a heated fluidized bed, or by simply bea ting a static bed of powder in a refractory cmcible. 

All the foregoing pertains to sohds of approximately the same physical characteristics. There is evidence that sohds of widely different characleristics wih classify one from the other at certain gas flow rates [Geldart, Baeyens, Pope, and van de Wijer, Powder Technol., 30(2), 195 (1981)]. Two fluidized beds, one on top of the other, may be formed, or a lower static bed with a fluidized bed above may result. The latter frequently occurs when agglomeration takes place because of either fusion in the bed or poor dispersion of sticl feed solids. 

Polyethylene beads of relatively narrow size distribution with a harmonic mean diameter of 2800 mm and a particle density of 910 kg/m3 were used as the bed material. A static bed height of 1.4 m was employed. 

Figure 6. Influence of the static bed height on jet attrition of spent FCC catalyst in a submerged jet test facility (Dt = 0.05 m, uor= 100 ms 1, dor = 2 mm. (Werther andXi. 1993.)...

Again, as in the case of jet attrition, attention must be paid in the experimental determination of Ra bub to the isolation of the attrition that is due to bubbles. There are basically two ways to do this. The one is to use a porous plate distributor in order to avoid any grid jets. The other is the procedure suggested by Ghadiri et al. (1992a) which is depicted in Fig. 7 the measurement of the production rate of fines at different values of the static bed height permits to eliminate the grid jet effects. 

Figure 29 (Qin and Liu, 1982) shows the behavior of individual particles above the distributor recorded by video camera of small clusters of particles, coated with a fluorescent material and spot-illuminated by a pulse of ultra violet light from an optical fiber. The sequential images, of which Fig. 29 just represents exposures after stated time intervals, were reconstructed to form the track of motion of the particle cluster shown in Fig. 30. Neither this track nor visual observation of the shallow bed while fluidized, reveal any vestige of bubbles. Instead, the particles are thrown up by the high velocity jets issuing from the distributor orifices to several times their static bed height.

Figure 4.7 Static-bed solid polymerization rates of 0.45 dl/g IV PET prepolymers [39]. From Duh, B., US Patent, 4 238 593 (1980)...

In entrainer sublimation, an entrainer gas is blown into the vaporisation chamber of a sublimer in order to increase the vapour flowrate to the condensing equipment, thereby increasing the yield. Air is the most commonly used entrainer, though superheated steam can be employed for substances such as anthracene that are relatively insoluble in water. If steam is used, the vapour may be cooled and condensed by direct contact with a spray of cold water. Although the recovery of the sublimate is efficient, the product is wet. The use of an entrainer gas in a sublimation process also provides the heat needed for sublimation and an efficient means of temperature control. If necessary, it may also provide dilution for the fractional condensation at the desublimation stage. Entrainer sublimation, whether by gas flow over a static bed of solid particles or through a fluidised bed, is ideally suited to continuous operation. 

Recently, Hays et al. [26] reported on of several cases where particle clustering was inferred in flnidized bed systems. In the first case, they attempted to reproduce why highly variable entrainment rates were observed in a commercial-scale fluidized bed even though steady-state was presumed. Tests were conducted in a 6 inch (15-cm) diameter fluidized column with a static bed height of 52 inches (132 cm) of the same Geldart Gronp A powder (dp5o of 55-60 microns) used in the commercial process. The test unit was operated in batch mode at a superficial gas velocity of 0.66 ft/sec (0.2 m/sec). 

Inlet air volume Nozzle height (with respect to static bed surface)... 

General Concept. The development of the fixed-bed process was based upon the idea of using a static bed of catalyst and maintaining a continuous flow of hydrocarbon vapor by the use of multiple reactors (17). Each reactor was submitted to a cycle of operations consisting of ... 

When carbon with low crystallinity and a large surface area is fluorinated, the reaction rate is normally very high as a result, deflagration decomposition of the product can occur with only a slight temperature increase. For the fluorination of such carbons, the flow system is recommended because it is convenient to remove the heat of reaction effectively. This type of process is used on an industrial scale. The static bed system is used for the preparation of small amounts of custom fluorinated products on a development scale with a wide variety of carbons and various degrees of fluorinations.6 In both systems, fluorine gas is diluted with an inert gas such as nitrogen to improve control of reaction exotherms. 

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