Coal asphaltenes

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. 

Thus, based on material applications, the following polymers are important natural rubber, coal, asphaltenes (bitumens), cellulose, chitin, starch, lignin, humus, shellac, amber, and certain proteins. Figure 4 shows the primary structures of some of the above polymers. For detailed information on their occurrence, conventional utilization, etc., refer to the references cited previously. 

Most coal liquids are composed of similar major chemical species, which may differ in exact composition. Liquid sulfur dioxide can be used to extract all the aromatic species of the coal liquid, free of saturated hydrocarbons and ash percursors. After removing the SO2 by degassing, distillation under reduced pressure can yield all the phenols and aromatic from the S02-solu-bles of the coal liquid. The residue, which is similar to GPC -fraction 2 of the S02 solubles, can be called coal asphaltenes. 

The average molecular size of coal asphaltenes (linear molecular size is more precise since it is derived from GPC data) is smaller than that of petroleum derived asphaltenes. 

In Table I, a comparison is made of the elemental composition of typical asphaltenes from petroleum and coal liquids. This table shows the typical lower H/C ratio and higher oxygen content for the coal asphaltenes. Furthermore, the GPC molecular-weight distributions shown in Figure 7 illustrate the higher molecular-weight of petroleum asphaltenes as well as the wider molecular-weight distribution. 

Figure 7. Comparison of molecular weight distribution off o) coal asphaltenes and Jobo petroleum asphaltenes (-------) vacuum residuum and (%) atmo-...

The molecular weight of petroleum-derived asphaltene is about ten times higher than that of the coal-derived asphaltene. Unit molecular weight of coal asphaltene is 400-600 whereas that of petroleum asphaltene is 800-2500. 

Composition of H-Coal Asphaltenes and Preasphaltenes Acid-Base Separations and Oxidative Degradation... 

A qualitative survey of the ability of common acids in concentrated aqueous solution to precipitate readily filterable salts from solution of H-coal asphaltenes in toluene suggested perchloric acid as a particularly promising candidate for further examination. The salt that formed at the interface of the solutions was crisply granular, possibly crystalline, although nearly black, and was easily collected and washed. Experiments with this reagent showed that approximately one-third of an asphaltene sample could be precipitated. Because attempts to dry the salts to constant weight by heating led to... 

The presence of hydrocarbons and of low molecular weight heterocompounds identical to those found in the cyclohexane- or pentane-soluble fractions of coal liquids was rather unexpected. However, neutral hydrocarbons have been identified in other coal asphaltenes (10), and more recently,... 

The data obtained on the asphaltene samples examined give considerable insight into both the average and the detailed structure of coal asphaltenes. 

FIGURE 10.36 Representation of the petroleum asphaltene fraction and the coal asphaltene fraction on the basis of molecular weight and polarity. 

The origin of coal asphaltene constituents has been the subject of much speculation insofar as they have been considered to be not only the initial products of coal liquefaction but also the secondary products of coal liquefaction ... 

Coal asphaltene constituents oil Coal - oil asphaltene constituents... 

Coal asphaltene constituents are quite different in nature from petroleum asphaltene constituents (Table 18.7). The molecular weight of asphaltene constituents from coal liquids may be some 8-10 times lower than the observed molecular weight of petroleum asphaltene constituents, although this latter can be revised to lower values for a variety of reasons (Steedman, 1985). 

Coal asphaltene constituents have frequently been defined in terms of an acid-base complex with the asphaltene existing as a composite of the two systems, acid and base ... 

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