Mechanism of pyrocarbon formation from propylene

Conference · Wed Jan 01 04:00:00 EST 1975

OSTI ID:4114490

Gower, R P; Hill, J; Blocher, Jr, J M; Hintermann, H E; Hall, L H ^[1]

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1. eds.

The pyrolysis of propylene was investigated at 100 mm Hg pressure over a carbon filament heated to 1000--1400$sup 0$C. The major products of reaction were carbon and hydrogen together with methane, ethylene, and acetylene. Large quantities of tars were also formed as by-products. The tars consist of polynuclear aromatic hydrocarbons. Disappearance of propylene was first order with E/sub A/ = 4.8 kcal mole$sup -1$ and a pre-exponential factor (A) of 3.5 x 10$sup 9$ s$sup -1$. The rate of rise of vessel pressure gave similar results (E/ sub A/ = 6.4 kcal mole$sup -1$; A = 4.1 x 10$sup 9$ s$sup -1$). Results suggest activation of propylene at the surface is the rate determining step followed by the formation of the propenyl radical (C$sub 3$$H$$sub 5$). The variation of the concentrations of hydrocarbons in the gas phase with time is cyclic and it is concluded that opposing the formation reactions are other reactions such as formation of pyrocarbon at the filament. Formation of methane and ethylene have activation energies of 12 and 5 kcal mole$sup -1$ respectively while the removals of these gases have activation energies of 2 and approximately zero. Physical adsorption is suggested as the removal step. The formation of pyrocarbon has E/ sub A/ approximately 20 kcal mole$sup -1$, suggesting a reaction via formation of tars on the filament surface or one in which surface diffusion is rate determining. Pyrocarbon produced from propylene is well ordered, indicating the occurrence of a meso-phase and supporting a formation mechanism involving tars. (auth)

• Research Organization: Atomic Weapon Research Establishment, Aldermaston, Eng.
• NSA Number: NSA-33-015360
• OSTI ID: 4114490
• Country of Publication: United States
• Language: English

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