A computational study of the chemical kinetic effects of oxygen addition on the process of soot formation from hot acetylene is reported. The results, which are supported by trends observed in shock-tube experiments, reveal that the reaction pathway to soot identified previously for acetylene pyrolysis remains essentially unchanged in an oxidative environment. The main effects of oxygen are: (1) promotion of fuel decomposition, which alters the initiation route to soot; (2) supplementary rapid production of hydrogen atoms in the initial, small-molecule reactions, which drives the concentration of hydrogen above the equilibrium value with respect to H2 and thus enhances polymeric growth of polycyclic aromatics; (3)oxidation of aromatic radicals by molecular oxygen, which removes them from the polymeric growth. The computational results indicate a crucial need for kinetic studies of high temperature reactions between molecular oxygen and hydrocarbon radicals.

Mechanism of Soot Formation in Acetylene-Oxygen Mixtures

The experimental literature on the pyrolysis of C 2 H 2 is reviewed and summarized. These observations divide naturally into three temperature regimes: (i) T 1800 K, where a fragment chain carried by C 2 H and H drives a polymerization to polyacetylenes. A combined molecular/fragment chain mechanism is developed and applied to the modeling of three shock-tube studies which span the two higher-temperature regimes. The core of the mechanism is a set of 5 mainly molecular reactions whose rates are derived from an application of unimolecular rate theory and detailed balance to recent measurements on the decomposition of vinylacetylene. The combination of this core with consequent fragment radical reactions provides a satisfactory description of most features of the chosen experiments including several-isotope exchange, hydrogenation ot C 2 H 4 , and C 6 H 2 formation-which are almost entirely the result of fragment radical chain reaction. Possible detailed paths for the molecular dimerization are suggested and some possible molecular paths for the Berthelot synthesis of benzene are also proposed

The mechanism of the homogeneous pyrolysis of acetylene

The pyrolyses of the guaiacols or methoxyphenols (o-, m-, and p-HOC6H4OCH3) have been studied using a heated SiC microtubular (μ-tubular) reactor. The decomposition products are detected by both photoionization time-of-flight mass spectroscopy (PIMS) and matrix isolation infrared spectroscopy (IR). Gas exiting the heated SiC μ-tubular reactor is subject to a free expansion after a residence time of approximately 50–100 μs. The PIMS reveals that, for all three guaiacols, the initial decomposition step is loss of methyl radical: HOC6H4OCH3 → HOC6H4O + CH3. Decarbonylation of the HOC6H4O radical produces the hydroxycyclopentadienyl radical, C5H4OH. As the temperature of the μ-tubular reactor is raised to 1275 K, the C5H4OH radical loses a H atom to produce cyclopentadienone, C5H4═O. Loss of CO from cyclopentadienone leads to the final products, acetylene and vinylacetylene: C5H4═O → [CO + 2 HC≡CH] or [CO + HC≡C–CH═CH2]. The formation of C5H4═O, HCCH, and CH2CHCCH is confirmed with IR spectroscopy. In separat...

Thermal decomposition mechanisms of the methoxyphenols: formation of phenol, cyclopentadienone, vinylacetylene, and acetylene.

The kinetics of pyrolysis of furan vapour diluted in argon have been studied behind reflected shock waves in a shock tube both by time-resolved infrared CO2 laser absorption spectrometry and by single pulse shock techniques of product analysis over the temperature range 1100–1700 K, at pressures of ca. 20 atm and at uniform residence times of ca. 300 µs. The rate of overall disappearance of furan, as measured by absorption spectrometry, was found to be first order in furan concentration, with a rate constant of koverall= 1015.3±0.3 exp[–326(±8) kJ mol–1/RT] s–1 in agreement with a previous determination by Lifshitz et al.(A. Lifshitz, M. Bidani and S. Bidani, J. Phys. Chem., 1986, 90, 5373). Principal products were carbon monoxide, C3H4(propyne and allene) and acetylene. Ketene was identified in the products by FTIR spectroscopy.A detailed chemical reaction model for the pyrolysis was developed and shown to give good predictions of the concentration profiles of furan and the major products. Modelling and thermochemical considerations led to the postulate that the initiation of pyrolysis takes place by C—O bond scission to a biradical which can undergo decomposition, via parallel reaction paths, to the observed products.

Kinetics of pyrolysis of furan

Conformational studies by vibrational spectroscopy: a review of various methods

The i.r., Raman and microwave spectra of 1-butene-3-yne (vinylacetylene) and 1-butene-3-yne-4d

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Abstract The infrared spectra of 1-cyano-3-butyne were recorded in the region 4000-50 cm-1 in the vapour and liquid states, as an amorphous and as two different crystalline solids at 90 K. In addition the compound was studied as a high pressure crystalline solid at ambient temperature. Raman spectra of the liquid, including polarization measurements, and of the amorphous and the two crystalline solids at 90 K, were obtained. The spectra revealed the existence of two conformers, anti (Cs) and gauche (C1 symmetry) in the vapour, liquid and in the amorphous solid. When annealed to ca. 140 K a metastable crystal containing one conformer (probably the gauche) was formed, when annealed to ca. 190 K a stable crystal was obtained having the other conformer (probably the anti). The latter conformer was present in the high pressure crystal. Very accurate spectral data for each conformer were collected from the two crystalline solids, making complete assignments for the anti and gauche conformers feasible. The assignments were checked by a normal coordinate analysis. A simple diagonal force field was derived in which the same force constants were employed for the anti and gauche conformers. The mean amplitudes of vibration were calculated for both conformers.

E. Tørneng

Papers

The i.r., Raman and microwave spectra of 1-butene-3-yne (vinylacetylene) and 1-butene-3-yne-4d

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

The Conformation and Vibrational Spectra of 1-Cyano-3-Butyne