Kinetics of carbon deposition in a fluidized bed

Abstract

Rate data have been obtained for the deposition of carbon films from methane and acetylene in fluidized beds of alumina, uranium dioxide, uranium monocarbide, uranium dicarbide, and a solid solution of uranium-thorium dicarbide powders. These carbon films have been shown to provide excellent protection for the powdered fertile material against attack by hot concentrated nitric-acid solutions. The coated uranium-thorium dicarbide particles were also shown to be stable in humid air.

Coke formation in the pyrolysis and oxidative pyrolysis of methane and methyl chloride

“…The value of200 kcal/mol for E determined in our studies is considerably higher than the 103 kcal/mol value reported by Hirt and Palmer (1963) and the value of 90.4 kcal/mol reported by Oxley et al (1961). Since these previous studies did not provide details of the surface morphology of the materials used, we cannot make definitive remarks with regard to the underlying reasons for the differences observed in the activation energies.…”

“…Previously, Hirt and Palmer (1963) studied coke formation from methane in a flow reactor in the temperature range 890-1100 °C, and determined an apparent activation energy value of about 103 kcal/mol for the rate of formation of coke over glazed porcelain walls. Oxley et al (1961) studied methane pyrolysis in a fluidized bed reactor consisting of uranium oxide and carbide particles in the temperature range 850-1025 °C, and based on heterogeneous reaction rate considerations they derived an activation energy of 90.4 kcal/mol. Both of these activation energies are close to the C-H bond dissociation energy of 104 kcal/mol in CH4, thereby suggesting that the unimolecular decomposition of CH4 might have been the ratelimiting step in both studies.…”

Chemical Kinetics of Soot Particle Growth

“…For example, the 100 kcaljmole activation energy that Grisdale et al (5) measured for carbon formation is just the bond dissociation energy of methane; their rates then are presumably unrelated to any heterogeneous process. The results of Foster et al (6,7) and others (8) provide additional examples of this problem. Palmer et al (9)(10)(11) considered heterogeneous reactions and diffusion as well as homogeneous reactions in his experiments; but with the low surface-to-volume ratios used, carbon formation was again controlled by gas phase processes.…”

Microminiaturized Fuel Elements by Vapor-Deposition Techniques

“…The original purpose of coating carbide fuel particles with carbon films was to protect the carbide against attack by humid air during fabrication operations. Thorium dicarbide particles are particularly sensitive to hydrolysis, and precoating them Reprinted from (8) can result in substantial savings in fabrication costs. It has been shown that carbon coatings provide excellent protection for uranium dicarbide-thorium dicarbide solid solution particles against attack by moisture.…”