Hydrogenation polyaromatic

The kinetics associated with catalytic reactions are complex however, some general trends can be determined. Reactions are often first order with respect to the reactant, and the rates of hydrodechlorination are faster than hydrogenation. Polyaromatic compounds react faster than monoaromatic compounds, and chlorinated alkenes react faster than their corresponding alkanes. Finally, the reaction rate often increases with increasing degree of chlorination, though this does not hold true for the chlorinated ethylenes. 

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. 

Beyond this easily converted portion of the coal even at short times, the composition of the solvent is important - high concentrations of H-donors and polyaromatics are beneficial. Over hydrogenation is detrimental. 

Direct conversion of target compounds (sulfur and nitrogen compounds, hydrogen sulfide, polyaromatics, etc.) to an easily removable or desirable product. 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

Progress is being made in the search for catalysts to hydrogenate aromatic systems (see Section VII). This area is likely to become increasingly important if coal, which contains polyaromatic compounds, is utilized more for production of petrochemicals. Stereospecific production of fully m-C6D6H6 from perdeuterobenzene has been reported catalysts for selective hydrogenation of benzene to cyclohexene would be valuable. 

Unlike 36, 37 is not carcinogenic because the fluorine atom at position 1 blocks bioactivation of the 1,2-position and, hence, the 1,2-epoxide metabolite is not formed [74]. Replacement of the hydrogen atom at position 2 of 36 with a fluorine atom also abolishes carcinogenicity [74]. Similar observations have been made with fluorine substitution of specific hydrogen atoms of other anthracenes, and of other polyaromatic compounds such as chrysenes and benzo[a]pyrenes [75]. 

Another consequence of increased reaction temperatures is the shift in the equilibrium concentrations of polyaromatic hydrocarbons and their hydrogenated derivatives. At high temperatures, the fully aromatic hydrocarbons are thermodynamically favored, especially at the pressures of today s HDS reactors. As the concentration of polyaromatics increases, the fluorescence of the finished fuel increases. This may cause problems with other specifications, as discussed shortly. 

Historically aromatic compounds were produced from hard coal by coking. The polyaromatics present in coal are released under the pyrolytic conditions and are absorbed in oil or on activated charcoal to separate them from the other coal gases. The components are freed by codistillation with steam or by simple distillation. The contaminant nitrogen- and sulfur-containing compounds are removed by washing with sulfuric acid or by hydrogenation. 

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