Pyrolysis, polynuclear aromatic compound

Primary Conversions and Influence of Mobile Phase Yields for the various H-donor and non-donor solvent extractions of Linby coal at 400% are summarised in Table III the conversions for the THF-extracted coal include the extracted material. Surprisingly, pre-extraction with THF significantly increases primary conversions in the polynuclear aromatic compounds (PACs) investigated. These findings appear to be contrary to those of other liquefaction (16) and pyrolysis (17) studies where prior removal of chloroform-extractable material significantly reduced conversions. However, Rincon and Cruz (18) have reported recently that pre-swelling coals in THF increases conversions for both anthracene oil and tetralin. The fact that Point of Ayr (87% dmmf C) coal yielded over 80% pyridine-solubles in pyrene (C.E. Snape, unpublished data) without pre-extraction is consistent with the earlier results of Qarke et al (19) for anthracene oil extraction where UK coals... 

Flash vacuum pyrolysis of 3-benzoylcinnolines has been presented as an interesting route toward polynuclear aromatic compounds <2001T7377>. 

The presence of free radicals in pyrolytic reactions seems to be a common event, as seen by the increase in certain more stable species as the pyrolysis temperature increases. At elevated temperatures, higher levels of aromatic compounds, polynuclear aromatic compounds, or small molecules tend to be formed. These compounds were not seen in the mass spectra fragments, where only intramolecular rearrangements are more common. 

The formation of radicals at elevated temperatures from the mononuclear aromatic compounds, followed by condensations between them, may explain the presence of polynuclear aromatic compounds in the pyrolysate, as shown in Section 2.4. The generation of small molecules at higher pyrolysis temperatures can be explained by reactions of the type ... 

Many studies of the pyrolysis of individual polynuclear aromatic compounds, particularly polynuclear aromatic hydrocarbons, have been published. The... 

The main process occurring in the pyrolysis of polynuclear aromatic compounds involves polymerization. The carbonaceous residues that form... 

The thermal conversion of polynuclear aromatic compounds to carbon can be considered a free-radical process because it involves a series of bond cleavage reactions. Many of the radical intermediates are expected to be unstable and cannot be detected by conventional spectroscopic techniques. However, the carbonaceous residues from pyrolysis do contain significant amounts of stable free radicals as apparent from EPR experiments. For example, Figure 8 shows the results of EPR measurements of the free-radical content for anthracene and naphthalene pitches after heating from 400 to 700 °C. The concentration of stable free radicals increases with heat treatment temperature as the molecular size grows. The more highly condensed... 

Odd-Alternate Polynuclear Aromatic Hydrocarbon Radicals. Substantial evidence supports the contention that the stable free radicals formed during the pyrolysis of polynuclear aromatic compounds are odd-alternate hydrocarbon radicals. As an example, the phenalenyl radical (5) is formed during pyrolysis of a number of organic compounds including acenaphthylene (3) and dihydronaphthalene (4) (24) (see Scheme III). The... 

Al-Awadi and co-workers investigated unique routes to polynuclear aromatic compounds using flash vacuum pyrolysis (FVP) of 3-arylcinnolines <01T7377>. The FVP of 160 at... 

Large numbers of polynuclear aromatic compounds occur in the tar from hard coal distillation, in products of pyrolysis and in a variety of residues from combustion. These compounds have been separated by TLC on silica gel [46, 47], alumina [46, 59] and acetyl-cellulose [1, 78]. 

Although the great majority of petroleum and coal-based pitch materials, as well as model compounds such as polyvinyl chloride, acenaphthylene, decacyclene and polynuclear aromatic hydrocarbons, form anisotropic graphitizable carbons, it is an almost impossible task to predict the type of optical texture of a coke from an elemental analysis of the pitch. The size, shape and reactivity of peri-condensed polynuclear aromatic molecules in the products of pyrolysis of a pitch play a more important role in determining optical texture. 

Other studies on coal were performed using pyrolysis, such as the measurement of the level of sulfur containing compounds in coal [27,28], or evaluation of polynuclear aromatic hydrocarbons (PAH) in coal [29]. The generation of PAH in coal pyrolysis is an important issue, as some of these compounds are known to have carcinogenic properties. A list of PAHs identified in coal pyrolysates is given in Table 14.2.2. The yield of PAH in coal pyrolysate depends to some extent on the coal type but mainly on the pyrolysis temperature. The variation of PAH levels as a function of temperature for several bituminous coals is shown in Figure 14.2.3. The yields of other pyrolysis products of coal were also shown to be temperature dependent [30]. 

The origin of most compounds with effects on human health in cigarette smoke and in other types of smoke is not well understood. Studies on pyrolysis of pure substances were performed to find the origin of some of these undesirable compounds [39]. For example for the generation of polynuclear aromatic hydrocarbons (PAH), selected... 

The phenols and lignin model compounds follow the calibration quite closely, tending to show slightly higher apparent molecular weights than they actually have, probably because of association with the solvent. This is encouraging for the HPSEC of pyrolysis oils as these types of compounds are more likely to be present. Heavily cracked oils, however, can be rich in polynuclear aromatics. 

Alkylated aromatic hydrocarbons are dominant in the unheated samples and are altered to the parent polynuclear aromatic hydrocarbons (PAHs) with limited or no alkylation at higher pyrolysis temperatures. Similar results for aromatic hydrocarbons were reported for laboratory thermal alteration (150-410°C) of kerogen from recent marine sediments (Ishiwatari and Fukushima, 1979). The pattern for the alkylnaphthalene series is shown in Fig. 5. Naphthalene is a trace component in the unheated samples, but becomes the major compound at 500°C. 

Mixtures of gaseous or liquid hydrocarbons which can be vaporized represent the raw materials preferable for the industrial production of carbon black. Since aliphatic hydrocarbons give lower yields than aromatic hydrocarbons, the latter are primarily used. The best yields are given by unsubstituted polynuclear compounds with 3-4 rings. Certain fractions of coal tar oils and petrochemical oils from petroleum refinement or the production of ethylene from naphtha (aromatic concentrates and pyrolysis oils) are materials rich in these compounds. These aromatic oils, which are mixtures of a variety of substances, are the most important feedstocks today. Oil on a petrochemical basis is predominant. A typical petrochemical oil consists of 10-15% monocyclic, 50-60% bicyclic, 25-35% tricyclic, and 5-10% tetracyclic aroma tes. 

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