Monoaromatics

A typical catalytic hydrodealkylation scheme is shown ia Figure 3 (49). The most common feedstock is toluene, but xylenes can also be used. Recent studies have demonstrated that and heavier monoaromatics produce benzene ia a conventional hydrodealkylation unit ia yields comparable to that of toluene (51). The use of feeds containing up to 100% of C —aromatics iacreases the flexibiUty of the hydrodealkylation procedure which is sensitive to the price differential of benzene and toluene. When toluene is ia demand, benzene suppHes can be maintained from dealkylation of heavy feedstocks. 

Zebiihr et al. (29) developed an automated system for determining PAHs, PCBs and PCDD/Fs by using an aminopropyl silica column coupled to a porous graphitic carbon column. This method gives five fractions, i.e. aliphatic and monoaromatic hydrocarbons, polycyclic aromatic hydrocarbons, PCBs with two or more ortho-chlorines, mono-ort/io PCBs, and non-ortho PCBs and PCDD/Fs. This method employed five switching valves and was successfully used with extracts of sediments, biological samples and electrostatic filter precipitates. 

Up to now, far more than 5000 retinoic acid analogs have been synthesized, out of which the following three generations have been established for therapy of various disorders First, the nonaromatic retinoids (3-carotene (provitamin A), alWraras-retinoic acid (RA) (tretinoin) and 13-cis-RA (isotretinoin), second, the monoaromatic retinoid derivatives trimethyl-methoxyphenyl analog of RA (etretinate) and9-(4-methoxy-2,3,6-trimethylphenyl)-... 

Hutchins SR (1991) Biodegradation of monoaromatic hydrocarbons by aquifer microorganisms using oxygen, nitrate or nitrous oxide as the terminal electron acceptors. Appl Environ Microbiol 57 2403-2407. 

Haggblom M (1990) Mechanisms of bacterial degradation and transformation of chlorinated monoaromatic compounds. J Basic Microbiol 30 115-141. 

Amor, L., Kennes, C., and Veiga, M., Kinetics of inhibition in the biodegradation of monoaromatic hydrocarbons in presence of heavy metals, Bioresour Technol, 78 (2), 181-185, 2001. 

Table IV shows the proton ratios obtained from the nmr spectra on the original fractions A, B and C and all the bottoms products. The proton ratios for the bottoms products have been adjusted to eliminate absorptions due to residual naphthalene. Note that the original fractions contained hydrogen present from combined phenol. Most of this hydrogen appears as monoaromatic hydrogen, but when the phenol-OH is still intact, one proton will appear as OH hydrogen.

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

The monoaromatic compounds benzene, toluene, ethylbenzene and xylene, commonly found in crude oil, are often jointly called BTEX compounds. The most harmful of these compounds is benzene, which is a known carcinogen. BTEX compounds occur naturally near natural gas and petroleum deposits and are detected in the fumes of forest fires. Most of the highly volatile BTEX compounds released by human activity originate from fuel use and end up as pollutants in the air. Inhaling BTEX-polluted air is also the greatest hazard to humans by these compounds. BTEX compounds are water-soluble, and therefore, improper handling can also cause groundwater contamination. 

The chemical objectives of naphtha and gasoline hydrotreatment are essentially the removal of S and N, and up to whether possible, to saturate the monoaromatic rings. One collateral requirement has to do with achieving the objective with no octane losses. The chemistry of the HDN of nitrogen compounds, commonly found in gasoline, has been the subject of studies, some of which are considered in this section. 

Figures 1.7.1 to 1.7.4 show the dependence of the physical-chemical properties on Le Bas molar volume. Figure 1.7.1 shows that the solubilities of the monoaromatics decrease steadily with increasing molar volume. The vapor pressure data in Figure 1.7.2 are similar, but log KoW in Figure 1.7.3 increases with increasing molar volume also in a linear fashion.

Mackay, D., Shiu, W.Y., Ma, K.C. (1992a) Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Vol. 1, Monoaromatic Hydrocarbons, Chlorobenzenes and PCBs. Lewis Publishers, Inc., Chelsea, Michigan. 

There are several chemical compounds found in the waste waters of a wide variety of industries that must be removed because of the danger they represent to human health. Among the major classes of contaminants, several aromatic molecules, including phenols and aromatic amines, have been reported. Enzymatic treatment has been proposed by many researchers as an alternative to conventional methods. In this respect, PX has the ability to coprecipitate certain difficult-to-remove contaminants by inducing the formation of mixed polymers that behave similarly to the polymeric products of easily removable contaminants. Thus, several types of PX, including HRP C, LiP, and a number of other PXs from different sources, have been used for treatment of aqueous aromatic contaminants and decolorization of dyes. Thus, LiP was shown to mineralize a variety of recalcitrant aromatic compounds and to oxidize a number of polycyclic aromatic and phenolic compounds. Furthermore, MnP and a microbial PX from Coprinus macrorhizus have also been observed to catalyze the oxidation of several monoaromatic phenols and aromatic dyes (Hamid and Khalil-ur-Rehman 2009). 

Together with singly charged ions doubly and multiply charged ions may also arise in the ionization process. However, the number of doubly charged and especially of multiply charged species is much lower. The yield of these ions depends on the structure of a molecule and on the experimental conditions. For example, polycyclic aromatic hydrocarbons give more ions of these types compared to aliphatic or monoaromatic compounds. 

Terpenoids are susceptible to a number of alterations mediated by oxidation and reduction reactions. For example, the most abundant molecule in aged Pinus samples is dehydroabietic acid [Structure 7.10], a monoaromatic diterpenoid based on the abietane skeleton which occurs in fresh (bleed) resins only as a minor component. This molecule forms during the oxidative dehydrogenation of abietic acid, which predominates in rosins. Further atmospheric oxidation (autoxidation) leads to 7-oxodehydroabietic acid [Structure 7.11]. This molecule has been identified in many aged coniferous resins such as those used to line transport vessels in the Roman period (Heron and Pollard, 1988 Beck et al., 1989), in thinly spread resins used in paint media (Mills and White, 1994 172-174) and as a component of resin recovered from Egyptian mummy wrappings (Proefke and Rinehart, 1992). 

Exceptionally facile elimination of CO also takes place from the following structure in which monoaromaticity can stabilize the transition state. 

Seifirt, W. K. and Moldowan, J. M., 1979, Applications of Steranes, Terpanes and Monoaromatics to the Maturation, Migration and Source of Crude Oils Geochemica et Cosmo-chimica Acta, Vol. 42, No. 1, pp. 77-95. 

TCDD may be in a state of flux, resulting from dechlorination of octa-and hepta-CDD and being further dechlorinated to 2-mono-CDD [54]. Beside dechlorination reactions in sediments [4],dioxin dechlorination reactions have been demonstrated in the presence of microorganisms ([5, 12, 13, 431-433], dihydroxylated monoaromatic compounds [433], vitamin B12, and zero valent metals [3]. 

Soluble in ethanol, ether, acetone, benzene (U.S. EPA, 1985), toluene, xylenes, and other monoaromatic hydrocarbons. 

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