Pyrolysis initial rates

Mechanisms and Rates of Combustion. AH soHd fuels and wastes bum according to a general global mechanism (Fig. 2). The soHd particle is first heated. FoHowing heating, the particle dries as the moisture bound in the pore stmcture and on the surface of the particle evaporates. Only after moisture evolution does pyrolysis initiate to any great extent. The pyrolysis process is foHowed by char oxidation, which completes the process. 

Fig. 6. Comparison of initial rate with titama particles prepared by flame spray pyrolysis and spray pyrolysis.

Some semi-quantitative confirmation of these A factors comes from the consideration that the pyrolysis of C2H8 at 900°K. is a chain reaction in which the data on maximal inhibition indicate a chain length X of the order of 10. Since the only likely homogeneous, initiation process is the fission of C2H8 into 2CH3, the hypothetical first-order rate constant for the pyrolysis can be set equal to this initiation rate constant multiplied by X ... 

Results for pyrolysis of the acid-washed samples in the three atmospheres can be seen in Figure 5. In the case of this sample, the same effect of atmosphere on initial weight loss can be observed. That is, initial rates of weight loss in nitrogen and carbon dioxide are similar and greater than the rates in wet nitrogen. However, it can be seen that there is little, if any, effect of the atmospheres on final weight loss. 

Thermal Decomposition of Liquid Gun Propellant The Liquid Gun Propellant (LGP) tested in the solids recirculation was LP XM-46, which is 24% TEAN (triethanol ammonium nitrate) and 76% HAN (hydroxy-ammonium nitrate. The mixture was diluted 1 3 in water. The diluted LGP was injected at an initial rate of 0.06 gal/min and later increased to 0.1 gal/min. The operation was run in pyrolysis and combustion modes. 

Figure 2. Influence of initial concentration of HCl on the initial rate of formation of CH (or i-C Hg) in the pyrolysis of neopentane. -p neo-csHit iQQ mmHg T = 480°C.

Figure 8. Influence of initial concentration of HBr on the initial rates of formation of CH4 (or CsHe), curve (A ), and i-C Hs (or Hg), curve (B ) in the pyrolysis of isobutane, = 50 mmHg T = 480°C.

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Cracking temperatures are somewhat less than those observed with thermal pyrolysis. Most of these catalysts affect the initiation of pyrolysis reactions and increase the overall reaction rate of feed decomposition (85). AppHcabiUty of this process to ethane cracking is questionable since equiUbrium of ethane to ethylene and hydrogen is not altered by a catalyst, and hence selectivity to olefins at lower catalyst temperatures may be inferior to that of conventional thermal cracking. SuitabiUty of this process for heavy feeds like condensates and gas oils has yet to be demonstrated. 

The energy available in various forms of irradiation (ultraviolet, X-rays, 7-rays) may be sufficient to produce in the reactant effects comparable with those which result from mechanical treatment. A continuous exposure of the crystal to radiation of appropriate intensity will result in radiolysis [394] (or photolysis [29]). Shorter exposures can influence the kinetics of subsequent thermal decomposition since the products of the initial reaction can act as nuclei in the pyrolysis process. Irradiation during heating (co-irradiation [395,396]) may exert an appreciable effect on rate behaviour. The consequences of pre-irradiation can often be reduced or eliminated by annealing [397], If it is demonstrated that irradiation can produce or can destroy a particular defect structure (from EPR measurements [398], for example), and if decomposition of pre-irradiated material differs from the behaviour of untreated solid, then it is a reasonable supposition that the defect concerned participates in the normal decomposition mechanism. 

Kinetic observations for decomposition of some representative transition metal sulphides are summarized in Table 13. Several instances of an advancing interface [contracting volume, eqn. (7), n = 3] rate process have been identified and the rate may be diminished by the presence of sulphur. Diffusion control is, however, believed to be important in the reactions of two lower sulphides (Ni0.9sS. [687] and Cu1-8S [688]). These solids have attracted particular interest since both are commercially valuable ores and pyrolysis constitutes one possible initial step in metal extraction. 

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