Pyrolysis decomposition, thermal

It is not possible, however, to calculate accurately actual gas composition by using the relationships of reactions (27-14) to (27-19) in Table 27-12. Since the gasification of coal always takes place at elevated temperatures, thermal decomposition (pyrolysis) takes place as coal enters the gasification reactor. Reaction (27-15) treats coal as a compound of carbon and hydrogen and postulates its thermal disintegration to produce carbon (coke) ana methane. Reaction (27-21) assumes the stoichiometiy of hydrogasifying part of the carbon to produce methane and carbon. 

The number of chemical reactions used in CVD is considerable and include thermal decomposition (pyrolysis), reduction, hydrolysis, disproportionation, oxidation, carburization, and nitrida-tion. They can be used either singly or in combination (see Ch. 3 and 4). These reactions can be activated by several methods which are reviewed in Ch. 5. The most important are as follows ... 

The CVD of graphite is theoretically simple and is based on the thermal decomposition (pyrolysis) of a hydrocarbon gas. The actual mechanism of decomposition, however, is complex and still not completely understood. This may be due, in part, to the fact that most of the studies on the subject of hydrocarbon decomposition are focused on the improvement of fuel efficiency and the prevention of carbon formation (e.g., soot), rather than the deposition of a coating. 

Schaber, P.M., Colson, J., Higgins, S., et al. (1999) Study of the Urea Thermal Decomposition (Pyrolysis) Reaction and Importance to Cyanuric Acid Production, American Laboratory,... 

The mechanism of thermal decomposition (pyrolysis) of methane has been extensively studied [90,91]. Because C-H bonds in the methane molecule are significantly stronger than C-H and C-C bonds of the products, the secondary and tertiary reactions contribute at the very early stages of the reaction, which obscure the initial processes. According to Holmen et al. [92], the overall methane thermal decomposition reaction at high temperatures can be described as a stepwise dehydrogenation as follows ... 

The thermal decomposition (pyrolysis) of alkylaryl selenoxides (selenoxide pyrolysis) to an alkene and an aryl selenic acid Ar—Se—OH often takes place even at room temperature (Figure 4.10). This reaction is one of the mildest methods for introducing a C=C double bond by means of a /3-elimination. The mechanism is described by the simultaneous shift of three electron pairs in a five-membered cyclic transition state. One of these electron pairs becomes a nonbonding electron pair on the selenium atom in the selenic acid product. The Se atom is consequently reduced in the course of the pyrolysis. 

Schaber, P. A. Colson, J. Higgins, S. Thielen, D. Anspach, B. Brauer, J. Thermal decomposition (pyrolysis) of urea in an open reaction vessel. Thermochimica Acta 2004, 424, 131-142. 

The terms thermal decomposition, pyrolysis, and carbonization often may be used interchangeably. However, it is more usual to apply the term pyrolysis (a thermochemical decomposition of coal or organic material at elevated temperatures in the absence of oxygen, which typically occurs under pressure and at operating temperatures above 430°C [800°F]) to a process that involves widespread thermal decomposition of coal (with the ensuing production of a char—carbonized residue). 

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