Pyrolytic Source

2 Pyrolytic Source Pyrolytic sources can be utilized if radical precursors are available that have very weak bonds so that a thermally induced homolytic bond cleavage process generates two radical species (Fig. 11.3). 

In this way, allyl iodide (C3H5I) and nitrosobenzene (CeHsNO) can be pyrolyzed quantitatively to generate allyl and radicals, respectively. For 

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Therefore, Ph/An> 15 may point to petrogenic sources and Ph/An< 10 to pyrolytic sources. Due to the wide range of values for this index found in the literature, values between 10 and 15 are considered indeterminate relative to source. In petroleum-derived PAHs, pyrene is more abundant than fluoranthene, while at higher combustion temperatures a predominance of fluoranthene over pyrene is characteristic. So the Fl/Pyr values greater than 1 are obviously related to pyrolytic sources, whereas values less than 1 are attributed to petrogenic sources. In order to avoid erroneous conclusions, the two ratios are often combined. When Ph/An> 15 and Fl/Pyr < 1, the PAH input is mainly from crude oil sources and when Ph/An< 10 and Fl/Pyr > 1, the major input may be related to combustion (Wang et ah, 2004b). 

Pyrolytic sources are trimethylamine (22), dimethylnitrosamine (16), dimethyl-nitramine (14), and tetramethyltetrazene (25, 31, 33), the pyrolyses proceeding according to the thermal analogs of Reactions 11, 12, and 13. A further probable source of these radicals is provided by the reaction between dimethylchloramine and copper-bronze in ether at 40° (19). 

The largest quantity of commercial pyrolytic graphite is produced in large, inductively heated furnaces in which natural gas at low pressure is used as the source of carbon. Deposition temperatures usually range from 1800 to 2000°C on a deposition substrate of fine-grain graphite. 

In the method described by Willie et al. [167] atomic absorption measurements were made with a Perkin-Elmer 5000 spectrometer fitted with a Model HGA 500 graphite furnace and Zeeman effect background correction system. Peak absorbance signals were recorded with a Perkin-Elmer PRS-10 printer-sequencer. A selenium electrodeless lamp (Perkin-Elmer Corp.) operated at 6W was used as the source. Absorption was measured at the 196.0nm line. The spectral band-pass was 0.7nm. Standard Perkin-Elmer pyrolytic graphite-coated tubes were used in all studies. 

Demirbas, A. 2005a. Hydrogen production via pyrolytic degradation of agricultural residues. Energy Sources 27 769-775. 

In Curie-point Py-LVMS studies of maceral concentrates (22). vitrinitic moieties were shown to be the main source of the hydroxy aromatic components. Thus, the hydroxy aromatic signals observed in Figure 2d appear to be primarily derived from vitrinite-like components by means of pyrolytic processes. Presumably, therefore, the "nonmobile phase", rather than the "mobile phase , is the main source of the phenols observed in TG/MS and Py-MS studies of Pittsburgh 8 coal (9,16). Further support for this conjecture comes from the observation that phenolic products are also observed in Py-MS analysis of pyridine extracts of Pittsburgh 8 coal known to contain colloidal matter whereas the corresponding tetrahydrofuran extracts, free of colloidal material, produced no phenols (21). 

Pyrolytic-laser-assisted CVD is analogous to thermally driven CVD, but instead of a diffuse heating source, a focused laser beam is used to define deposition areas spatially (32, 38, 39) or to heat the gas phase selectively (228). The use of laser has the added advantages of increased energy flux and rapid heating. To avoid photochemistry, the gas phase must be transparent to the radiation. 

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