Aromatic of coals

Aromaticity of coal molecules increases with coal rank. Calculations based on several models indicate that the number of aromatic carbons per cluster varies from nine for lignite to 20 for low volatile bituminous coal, and the number of attachments per cluster varies from three for lignite to five for subbituminous through medium bituminous coal. The value is four for low volatile bituminous (21). 

On the subject of carbon aromaticity of coal, 13C magnetic resonance spectroscopy has also found use in determining the fraction of carbon atoms that are in aromatic locations (fa) as well as attempting to define the structure of the aromatic ring system. However, there is a possibility of serious underestimation of aromaticity by this method (Miknis, 1988 Snape et al., 1989 Sfihi and Legrand, 1990). 

The study of the aromaticity of coal has included infrared spectroscopy (7 ) and various chemical methods (8, 9), but the most... 

Generally, raising the temperature increases the aromaticity of coal liquefaction products. However, there were no significant changes in either the H/C atomic ratios or the hydrogen aromaticities (see Table VII) of the oils or asphaltenes with temperature. Though there was a decrease in the H/C atomic ratio of the extraction residue and possibly of the pre-asphaltene with temperature (see Table VII). The pre-asphaltene content also appears to decrease with increasing extraction temperature. 

For fish and wildlife, the aromatics of coal tar pose the most danger. The aquatic toxicity in the water-soluble fraction is mostly from the aromatics. 

Table I. Elemental Analysis (Z) and Aromaticity of Coal. Catalytic Incorporated (Cat. Inc.) Coal Liquid, and Cat. Inc. Asphaltene and A240 Petroleum Pitch...

Mazumdar, B.K. (1988) Aromaticity of coal A reappraisal of the graphical-densimetric approach. Fuel Processing Technology, 19 (2), 179-202. 

The composition of coal tar varies with the carbonization method but consists, largely, of mononuclear and polynuclear aromatic compounds and their derivatives. Coke oven tars are relatively low in aliphatic and phenolic content while low-temperature tars have much higher contents of both. 

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

The organic chemical structural types believed to be characteristic of coals include complex polycyclic aromatic ring systems with connecting bridges and varied oxygen-, sulfur-, and nitrogen-containing functionalities. 

Proof of the existence of benzene in the light oil derived from coal tar (8) first estabHshed coal tar and coal as chemical raw materials (see Eeedstocks, COAL chemicals). Soon thereafter the separation of coal-tar light oil into substantially pure fractions produced a number of the aromatic components now known to be present in significant quantities in petroleum-derived Hquid fuels. Indeed, these separation procedures were for the recovery of benzene—toluene—xylene (BTX) and related substances, ie, benzol or motor benzol, from coke-oven operations (8) (see BTX processing). 

G-9 Aromatic Petroleum Resins. Feedstocks typically used for aromatic petroleum resin synthesis boil in the approximate range of 100—300°C at atmospheric pressure, with most boiling in the 130—200°C range. The C-9 designation actually includes styrene (C-8) through C-10 hydrocarbons (eg, methylindene). Many of the polymerizable monomers identified in Table 1 for coumarone—indene type cmdes from coal tar are also present in aromatic fractions from cracked petroleum distillates. Therefore, the technology developed for the polymerization of coal-tar cmdes is also appHcable to petroleum-derived aromatic feedstocks. In addition to availabiHty, aromatic petroleum resins offer several advantages over coumarone—indene resins. These include improved color and odor, as weU as uv and thermal stabiHty (46). 

Trimesic acid is also referred to as 5-carboxyisophthahc acid [554-95-0] trimesinic acid, or trimesitinic acid. It is a smaH-volume, synthetic chemical and is sold commercially. Traces of trimesic acid as well as other aromatic carboxyUc acids with three or more carboxyUc acid groups are found in lignite (137), and when various types of coals or coal components such as brown coal, asphaltene, or coal-tar pitch are oxidized. 

Coal tar is the condensation product obtained by cooling to approximately ambient temperature, the gas evolved in the destmctive distillation of coal. It is a black viscous Hquid denser than water and composed primarily of a complex mixture of condensed ring aromatic hydrocarbons. It may contain phenoHc compounds, aromatic nitrogen bases and their alkyl derivatives, and paraffinic and olefinic hydrocarbons. Coal-tar pitch is the residue from the distillation of coal tar. It is a black soHd having a softening point of 30—180°C (86—359°F). 

Antimony trichloride is used as a catalyst or as a component of catalysts to effect polymerisation of hydrocarbons and to chlorinate olefins. It is also used in hydrocracking of coal (qv) and heavy hydrocarbons (qv), as an analytic reagent for chloral, aromatic hydrocarbons, and vitamin A, and in the microscopic identification of dmgs. Liquid SbCl is used as a nonaqueous solvent. 

Vitrinite Reflectance. The amount of light reflected from a poHshed plane surface of a coal particle under specified illumination conditions increases with the aromaticity of the sample and the rank of the coal or maceral. Precise measurements of reflectance, usually expressed as a percentage, ate used as an indication of coal rank. 

Only a limited number of coal-denved pitches were examined by H NMR because of their low solubility in solvents commonly used m conventional proton magnetic resonance. Table 12 reports the distribution of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the matenals listed in Table 12 are characterized by a high content of aliphatic hydrogen. 

The polymerization process of coal tar and petroleum fraction (from which aromatic hydrocarbon resins are obtained) are similar. The process is extensively described in the book by Mildenberg et al. [25]. There are three basic steps in the polymerization of coumarone-indene and hydrocarbon resins. 

Aromatics are petrochemicals. Fixed-bed reforming of virgin naphthas is one source of these materials. Aromatics fiom the high temperature of coking of coal, the main source prior to 1940, now only account but for a small proportion of the total production. 

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