Pyrolysis-oxidation studies

Bench-Scale Pyrolysis-Oxidation Studies of Coal-Derived Liquids... 

FIGURE 12.1. Schematic of tubular reactor setup for pyrolysis/catalytic/oxidation studies coupled to a molecular-beam mass spectrometer sampling system. 

Further developments of the work include a more accurate study of the mechanisms of desulfurization processes using instrumental improvements. This will enable an easy quantitation of gas yield and a thermochemical approach of elemental processes. We also have been using model polymers to better study the interactions of pyrite and sulfur with the organic matrix during coal pyrolysis, oxidation and combustion (34 and to examine more accurately the specific role of organic sulfur in thermal degradation processes. 

Oxidation studies on Athabasca and other oil sand asphaltenes have shown the presence of aliphatic sulfides in amounts of up to 25% of the total sulfur (25). The structure of these sulfides has been established using mild thermolysis to liberate them from the polymeric framework of the asphaltene molecules. The produced pyrolysis oil contains significant concentrations of the sulfides and can be readily subjected to analysis. SIR-GC/MS traces of the homologous series of sulfides identified are... 

Significantly, Equations 8 and 9 show no oxygen dependence. Previous measurements of methanol pyrolysis by Aronowitz et al., (IS) indicated that rates of pyrolysis are an order of magnitude lower than oxidation rates. This is in agreement with our oxidation studies in which pyrolysis at 550 0 was an order of magnitude slower than oxidation at 550 0. It is therefore surprising to... 

Indaconitine, isolated (59) from A. chasmanihum Stapf, is the fourth naturally occurring ester-alkaloid derived from pseudaconine. It is the acetate benzoate, as shown by its hydrolysis to pseudaconine and acetic and benzoic acids. Pyrolysis of indaconitine proceeds, as usual, with elimination of acetic acid, but two isomeric pyroindaconitines have been described (59), the a-isomer derived from the alkaloid itself, and the iS-isomer from indaconitine hydrochloride. No oxidative studies are on record. 

Curie-point pyrolysis/combustion chamber in which sub-/u.gs of plastic are burned in air atmosphere in the chamber the exhausted combustion gas is then cryofocused by a purge-and-trap (PT) device and analysed by GC-MS. In this way air-pyrograms are easily obtained. Lehrle et al. [598] have proposed PyGC-MS in oxidative pyrolysis conditions. Pyrolysis is then performed whilst air still remains within the pyrolysis chamber (before complete evacuation). This approach offers advantages over the so-called Enclosed Curie-Point (ECP) pyrolysis method for polymer and oil oxidation studies [511]. The latter procedure suffers from the limitation that secondary reactions may arise due to the fact that it is effectively a two-stage process, in which the analysis follows the oxidation stage. 

The techniques most commonly used in thermo-oxidative studies on polymers are mainly based on thermal analysis methods such as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and on pyrolysis-gas chromatographic studies (particularly if they are linked to complimentary techniques such as mass spectrometry or infrared spectroscopy). Other techniques that have been used to a much lesser extent include chemiluminescence analysis, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance, and positron annihilation lifetime mass spectrometry. 

Continual use of decabromidiphenyl oxide has been placed ia question based on the discovery that under certain laboratory conditions brominated dibenzo- -dioxias are generated (63). The condition most often employed ia such studies is pyrolysis of milligram-scale samples at 600°C. This temperature is higher than polymer processiag conditions and lower than fire temperatures, ie, the conditions are not representative of actual conditions to which flame-retardant polymers are exposed. 

Guaiacols. Cresote, obtained from the pyrolysis of beechwood, and its active principles guaiacol [90-05-1] (1) and cresol [93-51-6] (2) have long been used ia expectorant mixtures. The compounds are usually classed as direct-acting or stimulant expectorants, but their mechanisms of action have not been well studied. Cresol is obtained by the Clemmensen reduction of vanillin (3), whereas guaiacol can be prepared by a number of methods including the mercuric oxide oxidation of lignin (qv) (4), the ziac chloride reduction of acetovanillone (5), and the diazotization and hydrolysis of o-anisidine (6). 

Kinetic studies of pyrolysis of azides, giving oxadiazole A-oxides in near-quantitative yields, showed that the 5-azido-6-nitroquinoline pyrolyzed in acetic acid 27.6 times faster than did 5-azidoquinolines, because of the -M effect of the group adjacent to the azide group (85AJC1045). 

Spectroscopic techniques as 13C-NMR [28], ESR [29], pyrolysis-GC/MS, and pyrolysis-Fourier transform infrared (FTIR) [30], x-ray diffraction [31], and SEM [32] techniques are also used to study mbber oxidation. 

Recently, Stair and coworkers [10, 11] developed a method to produce gas-phase methyl radicals, and used this to study reactions of methyl groups on Pt surfaces [12] and on molybdenum oxide thin films [13]. In this approach, methyl radicals are produced by pyrolysis of azomethane in a tubular reactor locat inside an ulttahigh vacuum chamber. This method avoids the complications of co-adsorbcd halide atoms, it allows higher covraages to be reached, and it allows tiie study of reactions on oxide and other surfaces that do not dissociate methyl halides effectively. 

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