Condensed aromatics

Because they contain many islets of condensed aromatics, the carbon-rich asphaltenes can begin to acquire the spatial organization of graphite layers. 

Comparing the overall concentrations of these different carbons designated generally as structural patterns , measured before and after a process such as FCC or hydrocracking (see Chapter 10), enables the conversion to be monitored the simple knowledge of the percentage of condensed aromatic carbon of a feedstock gives an indication of its tendency to form coke. 

Condensed aromatic hydrocarbons may be brominated directly with bromine in the presence of a solvent, such as carbon tetrachloride ... 

Benzoin condensation. Aromatic aldehydes when treated with an alkali cyanide, usually in aqueous solution, undergo condensation to the -hydroxyketone or benzoin. The best known example is the conversion of benzaldehyde to benzoin ... 

Condensed aromatic compounds (benzoselenazoles) are considered much more stable, and they are in fact more commonly used in the area of cyanine-type photographic dyes. 

A wide variety of guest molecules may be trapped by the Wemer-type crystalline host lattice, ranging, eg, from noble gases to condensed aromatic hydrocarbons. These clathrates may be formed from solution or by sorption. Kinetics of sorption—desorption have been studied (83). 

The main chain of these polymers contains, as the principal component, five- or six-membered heteroaromatic rings, ie, imides, which are usually present as condensed aromatic systems, such as with benzene (phthalimides, 3) and naphthalene (naphthalimides, 4) rings. 

At pressures of 13 GPa many carbonaceous materials decompose when heated and the carbon eventually turns into diamond. The molecular stmcture of the starting material strongly affects this process. Thus condensed aromatic molecules, such as naphthalene or anthracene, first form graphite even though diamond is the stable form. On the other hand, aUphatic substances such as camphor, paraffin wax, or polyethylene lose hydrogen and condense to diamond via soft, white, soHd intermediates with a rudimentary diamond stmcture (29). 

The Schiemann reaction seems to be the best method for the selective introduction of a fluorine substituent onto an aromatic ring. The reaction works with many aromatic amines, including condensed aromatic amines. It is however of limited synthetic importance, since the yield usually decreases with additional substituents present at the aromatic ring. 

Also including aminonaphthols and hydroxy derivatives of higher condensed aromatic systems. 

Solid-state [4 + 2] cycloaddition of fullerene C60 with condensed aromatics using a high-speed vibration milling technique [100]... 

Although cracking also occurs on chlorine-treated clays and amorphous silica-aluminas, the application of zeolites has resulted in a significant improvement in gasoline yield. The finite size of the zeolite micropores prohibits the formation of large condensed aromatic molecules. This beneficial shape-selectivity improves the carbon efficiency of the process and also the lifetime of the catalyst. 

The substitution of condensed aromatic rings is possible at various sites. This leads to regioisomerism, already when the first substituent is introduced. There are first hints that the distributions between regioisomers of condensed aromatics differ when conducted in a micro reactor as compared with conventional processing. The reason for this is not understood even suggestions on this are lacking in the literature. 

The structure of a-C H films may be thus pictured as sp--carbon atoms in condensed aromatic clusters, dispersed in an sp- -rich matrix, which confers to the network its characteristic rigidity. This situation can also be regarded as a random covalent network in which the sp" clusters of a defined size take part in the structure as an individual composed atom with its corresponding coordination number [17]. Such kinds of models have been successfully used to describe the dependence of a-C H film mechanical properties on composition, hybridization, and sp" clustering [23]. 

Based on the IR spectroscopy, evidence that nitrogen incorporation into a-C H films may occur in the periphery of condensed aromatic rings [10], Mansur and... 

Hydrogen donors are, however, not the only important components of solvents in short contact time reactions. We have shown (4,7,16) that condensed aromatic hydrocarbons also promote coal conversion. Figure 18 shows the results of a series of conversions of West Kentucky 9,14 coal in a variety of process-derived solvents, all of which contained only small amounts of hydroaromatic hydrocarbons. The concentration of di- and polyaromatic ring structures were obtained by a liquid chromatographic technique (4c). It is interesting to note that a number of these process-derived solvents were as effective or were more effective than a synthetic solvent which contained 40% tetralin. The balance between the concentration of H-donors and condensed aromatic hydrocarbons may be an important criterion in adjusting solvent effectiveness at short times. 

Kleinpeter and Burke have recently reported (24) that solvents can also be over hydrogenated and thus become less effective in short time processes. Figure 19 shows some of their work in which a process-derived SRC recycle solvent was hydrogenated to various severities and used for the conversion of an Indian V bituminous coal. The results clearly show a maximum at intermediate hydrogenation severities. Our assessment of this observation is that the loss in conversion was due primarily to the loss in condensed aromatic nucleii rather than conversion of hydrogen donors to saturates. 

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