Pyrolysis, flash product composition

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

Table 10.24 Plastic mixtures composition and flash pyrolysis products (%)...

The quality of the product is of primary importance in developing a recycling technology converting plastics into fuels by pyrolysis. Today the characterization of a liquid fuel from any sources is obviously based on the qualification methods and standards of fuels from mineral oil. The properties of the pyrolysis-derived fuels from plastics are expected to be similar to conventional fuels (energy content, viscosity, density, octane and cetane number, flash-point, etc.). However, in addition to the familiar ranking values it is necessary to know more about the chemical composition of the plastic pyrolysis oil, because of the peculiarities as follows ... 

The composition of the plastic feedstock for pyrolysis processes has a direct bearing on the quality of the resultant fuel products, especially flash point, cetane index, low-temperature properties and heteroatom content (e.g. sulphur, chlorine and nitrogen). 

Description of the process. The process involves the utilization of two separate CFBs, both operated at ambient pressure (Figure 16.11). The first is a flash pyrolysis reactor in which waste is converted with the addition of steam, at a temperature between 700 and 900°C, into product gas and tar. The reducing atmosphere avoids the dioxins formation. The prodnct stream, made of fuel gas and HCl in a composition strongly dependent on feed/steam ratio, is quenched to recover HCl, which is then further purified. The second CFB is a combustor that provides heat for flash pyrolysis by burning the residnal tar the... 

TABLE 8.10 Flash Pyrolysis Products and Compositions from Softwood and Hardwood"... 

The dependence of the composition of the pyrolysis products on temperature can be exemplified by the study of the monomer and dimer formation during the flash pyrolysis of natural rubber at different temperatures [1]. Figure 4.1.2 shows the plot of monomer/dimer ratio for flash pyrolysis of rubber at discrete temperatures between 300° C and 500° C. The figure indicates the increase in monomer formation at higher temperatures. More examples will be given when pyrolysis for particular biopolymers is discussed. 

Flash vacuum pyrolysis of 2-azidodiphenylmethane (8) affords a mixture of acridine and its 9,10-dilqrdro derivative, the composition of the product varying with the reaction temperature (M.G. Hicks and G. Jones, Chem. Comm., 1983, 1277). 

One of the methods of studying the composition of macromolecular sedimentary organic matter in more detail is the molecular analysis of pyrolysis products. For this purpose, the pyrolysis products are transferred to a gas chromatographic column and analyzed as described for extractable organic matter in Sect. 4.5.5, with or without the combination with a mass spectrometer. Both flash pyrolysis (Curie-point pyrolysis samples are heated on a magnetic wire by electrical induction almost instantaneously, e.g., to 610°C) or off-line pyrolysis at various heating rates have been applied to geological samples (see Larter and Horsfield 1993 for an overview of various pyrolysis techniques). 

The comparison of the peat and wood flash pyrolysis products by Elliott ( ) is a good example of the effect of feedstock on product oil composition. The poplar oil typically was composed of phenolic, ketone and furan compounds with a substantial fraction of low molecular weight organic acids. The main components of the peat oil were hydrocarbons, mostly straight chain olefins. Minor quantities of ketones were noted but no acids, aldehydes or furans were identified by mass spectrometry. Phenols were also present in significant quantities. 

The reliability of simultaneous detection of minor flash-pyrolysis products is often quite insufficient. In composite materials polymer and mineral fillers are often contained in large amounts and the con-centfation of other components is not high, typically... 

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