Pyrolysis-oxidation apparatus

Automatic recording infrared apparatus can also be used in studying the kinetics of both complex reactions and intermediates if their concentrations are not less than 1 per cent. In this way, ketene, CH2CO, and acetaldehyde, CIIsCHO, have been identified as intermediates in the pyrolysis of ethylene oxide, C2H40. ... 

Two other systems that produce high-temperature molecules should be mentioued shock waves and flames. Shock waves are typically formed by the rapid release of a high pressure of gas in a shock-tube apparatus. A shock wave is formed that can travel at several times the speed of sound temperatures as high as 20 000 K have been produced in shock tubes. Thus the method is ideal for monitoring pyrolysis and oxidation reactions. Flames are gaseous systems where a flow of gas combines with a self-supporting reaction to produce a steady-state situation. Again, oxidation reactions are amenable to this approach. In particular, short-hved intermediates in hydrocarbon oxidation, such as C2, OH, and CHO+, have been identified in flames. 

Specihcally with regard to the pyrolysis of plastics, new patents have been filed recently containing variable degrees of process description and equipment detail. For example, a process is described for the microwave pyrolysis of polymers to their constituent monomers with particular emphasis on the decomposition of poly (methylmethacrylate) (PMMA). A comprehensive list is presented of possible microwave-absorbents, including carbon black, silicon carbide, ferrites, barium titanate and sodium oxide. Furthermore, detailed descriptions of apparatus to perform the process at different scales are presented [120]. Similarly, Patent US 6,184,427 presents a process for the microwave cracking of plastics with detailed descriptions of equipment. However, as with some earlier patents, this document claims that the process is initiated by the direct action of microwaves initiating free-radical reactions on the surface of catalysts or sensitizers (i.e. microwave-absorbents) [121]. Even though the catalytic pyrolysis of plastics does involve free-radical chain reaction on the surface of catalysts, it is unlikely that the microwaves on their own are responsible for their initiation. 

NH4 was synthesized first via DeVarda s alloy. When the tracer NOs" was used directly, it was reduced in volume to 1 mL by rotary evaporation, then 1 mmol of NH4NO3 was added, followed by 25 mL of H2SO4. Nitrous oxide was evolved at 260 C in a pyrolysis apparatus swept by N2. When NH3 was used, it was mixed with 4 mmol of NH4NO3 and the same cold H2SO4. A temperature was selected at which the rate of evolution of gas approximately balanced the rate of decay of the N20 collected. When either of these synthetic routes were used, the N20 was contaminated with 30% 10% produced directly from a... 

One of the great issues in the field of silicon clusters is to understand their photoluminescence (PL) and finally to tune the PL emission by controlling the synthetic parameters. The last two chapters deal with this problem. In experiments described by F. Huisken et al. in Chapter 22, thin films of size-separated Si nanoparticles were produced by SiLL pyrolysis in a gas-flow reactor and molecular beam apparatus. The PL varies with the size of the crystalline core, in perfect agreement with the quantum confinement model. In order to observe an intense PL, the nanocrystals must be perfectly passivated. In experiments described by S. Veprek and D. Azinovic in Chapter 23, nanocrystalline silicon was prepared by CVD of SiH4 diluted by H2 and post-oxidized for surface passivation. The mechanism of the PL of such samples includes energy transfer to hole centers within the passivated surface. Impurities within the nanocrystalline material are often responsible for erroneous interpretation of PL phenomena. 

Both methods require minimal if any sample preparation, and extensively automated systems are available. The highly corrosive chemicals and the harsh conditions used in the Kjeldahl digestion call for appropriate fume hoods and exhaust systems, and standardization of the digestion itself may sometimes be difficult. The relatively low sensitivity and the fairly large amount of sample required are usually no problem in the food industry. As for chromatographic methods, controlled oxidative pyrolysis of food releases a number of volatile compounds that may foul the separation columns. This requires careful maintenance of the equipment, and in particular of the precolumn that guards the separation apparatus. 

The application oiflame spray pyrolysis to NP synthesis generally resulted in the production of metal oxides and salts [54—57]. Recently, Athanassiou et al. proposed the use of a flame-SP apparatus which operated in continuous fashion in a nitrogen-filled glovebox to produce carbon-coated Cu NPs with a good size uniformity [58]. 

Ciajolo, A., Barhella, R. 1984. Pyrolysis and oxidation of heavy fuel oils and their fi-actions in a thermogravimetric apparatus. Fuel 63 657-661. 

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