SOLIDS REACTORS Thermal Decomposition

Fig 5 The Effect of Reactor Irradiation on the Thermal Decomposition of Colloidal o -Pb Azide. (Ref 110). Fraction of total decomposition a against time. Solid circles experimental points for unirradiated material at 240.9 open circles experimental points for irradiated material at 238.5°C other points are the attempted fits indicated by arrows... 

Reactions of solids are typically feasible only at elevated temperatures. High temperatures are achieved by direct contact with combustion gases. Often, the product of reaction is a gas. The gas has to diffuse away from the reactant, sometimes through a solid product. Thermal and mass-transfer resistances are major factors in the performance of solids reactors. There are a number of commercial processes that utilize solid reactors. Reactor analysis and design appear to rely on empirical models that are used to fit the kinetics of solids decomposition. Most of the information on commercial reactors is proprietary. 

There have been attempts to use catalysts in order to reduce the maximum temperature of thermal decomposition of methane. In the 1960s, Universal Oil Products Co. developed the HYPROd process for continuous production of hydrogen by catalytic decomposition of a gaseous hydrocarbon streams.15 Methane decomposition was carried out in a fluidized bed catalytic reactor from 815 to 1093°C. Supported Ni, Fe and Co catalysts (preferably Ni/Al203) were used in the process. The coked catalyst was continuously removed from the reactor to the regeneration section where carbon was burned off by air, and the regenerated catalyst returned to the reactor. Unfortunately, the system with two fluidized beds and the solids-circulation system was too complex and expensive and could not compete with the SR process. 

We successfully demonstrated that hydrogen could be efficiently produced by catalytic steam reforming of carbohydrate-derived bio-oil fractions in a fluidized bed reactor using a commercial nickel-based catalyst. Greater steam excess than that used for natural gas reforming was necessary to minimize the formation of char and coke (or to gasify these carbonaceous solids) resulting from thermal decomposition of complex carbohydrate-derived compounds. 

As there are no suitable organometallic precursors commercially available, initial work dealt with the synthesis of such a precursor [4]. 2,5-Bis(rbutyl)-2,5-diaza-l-germa-cyclopentane is a monomeric solid with a melting point of 45 °C and a sufficient vapour pressure of 0.40 mbar at 40 °C to allow its introduction into the CVD reactor. For the details about the synthesis and properties of this precursor we refer to a recent paper [4]. The present work deals with the investigation of the thermal decomposition of the precursor, the deposition of amorphous germanium (a-Ge) and the characterization of the deposited thin films. Finally some data should try to give some understanding about the deposition mechanism. 

Von Sacken and Dahn [89], using TG-MS, showed that below 523 K the thermal decomposition of AMV proceeds by simultaneous release of ammonia and water in a constant proportion, regardless of whether the atmosphere is inert or oxidizing. Above 523 K, residual ammonia reduces the solid products so that the stoichiometry of the final residue is dependent upon the sample size, gas flow, heating rate and reactor design. 

The thermal decomposition of organic compounds can also be employed to generate small carbon clusters or atoms. The borderline with chemical vapor deposition (CVD) as presented in the next section is not really fix. In both cases, the method is based on the thermal decomposition of organic precursors. Processes both with and without catalyst have been reported. Contrary to the chemical vapor deposition, however, the catalyst (if applied) is not coated onto a substrate, but the substance or a precursor is added directly to the starting material ( floating catalyst ). The resulting mixture is then introduced into the reactor either in solid or in liquid state by a gas stream. From this point of view the HiPCo-process could also be considered a pyrolytic preparation of SWNT, but due to its importance it is usually regarded as autonomous method. 

During the last 25 years a variety of processes have been developed for the thermal degradation of tyres in order to recover valuable components from rubber wastes.120-125 Stirred tanks, rotary kilns, fixed beds, fluidized beds and tray systems are examples of reactor types used for the thermal degradation of tyres. Several of these processes are now being used on a pilot plant and industrial scale. Basically, three fractions are derived from the thermal decomposition of tyres gases, liquid oils and solid residues. In the past, the influence of the reaction conditions and the reactor type were studied in order to maximize... 

Removal of the primary reactor heads revealed warpage over approximately one-half of the upper tube sheet and showed evidence of leakage at a number of points on the bottom tube sheet. Many tubes in the area of the upper tube sheet warpage were burned through while the space between these tubes was solidly blocked with carbon from thermal decomposition of the organic coolant. Review of the reactor design indicated that cooling of the reactor should have been more than... 

The generic apparatus used in a vapor precursor process is very similar to that used in spray pyrolysis, except that the precursor material is introduced to the reactor as a vapor (see Figure 2.1, 2. la). If the precursor is a liquid, carrier gas is typically bubbled through it. If the precursor is a solid, then the carrier gas is often passed through a heated, packed bed of the material. The vapor-laden carrier gas then flows to a furnace reactor, where thermal decomposition of the precursor occurs and particle formation results. Product powder is collected or measured at the reactor outlet. Flame processes also fall into the vapor precursor/thermal decomposition category of gas-phase powder synthesis. The only difference is that the thermal energy is provided by combustion as opposed to an external source. 

Several aerosol nanoparticle reactors have been built and characterized in which one or more convenient process parameters can be used to control the particle size distribution, including particle diameter and number concentration. To address the diverse needs of the NOSH Consortium membership, various aerosol nanoparticle synthesis methods have been employed, including thermal decomposition of hquid precursor vajxrrs, spray atomization of hquids of soluble materials or solid susjjensions, and thermal vaporization of solid metals. These aerosol nanoparticle reactors are used in subsequent NOSH Consortium activities as detailed in the remaining... 

Two different decobaiting methods are used in a number of variations. One is the thermal decomposition of the carbonyls after releasing the product from the reactor with simultaneous reduction of the CO-partial pressure. The decomposition is effected by recycling cobalt-free hot reaction product or by introducing hot water or steam [838]. An inert stripping gas may be applied simultaneously. The solid cobalt metal, -oxide, or -hydroxide separating is mechanically removed [749, 839]. 

Commercially available bis(phenylsulfonyl)amine (59.4 g, 0.2 mol) in MeCN (150mL) at - 40 C in the presence of powdered NaF in an ambient pressure reactor was reacted with 10% F2/N2 (7.6 g, 0.2 mol) for 3 h. An excess of F2 must be avoided since it leads to fluorination of the aromatic rings. After evaporation of the solvent, the crude mixture was purified by recrystallization (Et20) or by column chromatography (silica gel, CH2C12). A-Fluorobis(phenylsulfonyl)amine was obtained in 70% average yield as a colorless solid which melts without decomposition at 114—116 JC and which is thermally stable up to 180°C. 

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