Coal fractionation

Cationic polymerization of coal-tar fractions has been commercially achieved through the use of strong protic acids, as well as various Lewis acids. Sulfuric acid was the first polymerization catalyst (11). More recent technology has focused on the Friedel-Crafts polymerization of coal fractions to yield resins with higher softening points and better color. Typical Lewis acid catalysts used in these processes are aluminum chloride, boron trifluoride, and various boron trifluoride complexes (12). Cmde feedstocks typically contain 25—75% reactive components and may be refined prior to polymerization (eg, acid or alkali treatment) to remove sulfur and other undesired components. Table 1 illustrates the typical components found in coal-tar fractions and their corresponding properties. 

In the work now reported coal fractions derived from a solubilised coal were reacted individually with Tetralin, without any additions of catalyst or gaseous hydrogen, and the reaction products studied to determine the effect that chemical type had on the reaction. The untreated whole coal was also reacted to test whether phenol, present in the coal fractions as a result of the fractionation procedure, was having any significant effect on the reaction with the fractions. 

Approximately 3g samples of the coal fractions and of the whole coal were then reacted separately with 25 - 30 ml of tetra-lin at 450°C in a type 316 stainless steel, sealed reactor, 13 cm high by 2 cm diameter. The reactor was heated by plunging it into a preheated fluidised sand bath after 4 hours it was removed and quenched rapidly. 

TABLE I. Structural Characteristics of Coal Fractions Separated from Solubilized... 

Yields of Original Coal Fractions and their Products of Reaction with Tetralin, g/lOOg Original Dry Coal. 

Calculation of hydrogen transferred to the coal fractions, g/lOOg of dry brown coal... 

TRW Gravichem A modification of the TRW Meyers process (see next entry) in which the coal fraction which contains less pyrites is first removed by sedimentation in the ferric sulfate solution. 

The coals and coal fractions which have been examined by NMR thermal analysis are subdivided Into two sets ... 

In another series of e q>eriments in this laboratory (U), it was found that the particle size of the coal fraction used affected the ash level in the filtered coal extract solution. In these e q>eriments, the coal sample, which is nominally < 200 pm, was divided into different size fractions by sieving, and each fraction digested using the normal procedure. Table 3 shows the results obtained with Point of Ayr and Calverton coals. Note that the Point of Ayr coal was a different batch to that used for the results described previously, with a simil analysis except for ash, which was higher at 19 %. 

The results in Table 5 show a large increase in proportion of Mn and Ti, and increases for Mg and Ca from coal to extract. Fe stays about the same and all the others decrease. Previous work Q) has also shown that the elements which increase in proportion also deposit readily and steadily on the hydrocracking catalyst. Thus, any method which reduces the ash level in the filtered extract solution needs to be, if at all posible, selective towards Mn, Ti, Ca, Mg, and Fe. In the case of digestion pressure, as shown by the results above, most trace elements do not significantly change their proportion as the ash level decreases, except for Mn where the situation becomes worse and Mg where there is some improvement. Liquefaction of different-sized coal fractions has little effect on the distribution of elements in the ash as the overall ash level decreases. However, with the use of HAO with different saturates levels, there is a distinct increase in the levels of Ti with decreasing ash level, but a significant decrease in Mn. 

Previous work has shown that the 3.3-5.5 /xm coal fraction has a particle size distribution similar to that of respirable mine dust collected on personal samplers during mining operations (13). This fraction was used for the spark-source analyses. The coals used in this investigation are identified in Table I. The respirable dusts were obtained from personal sampler filters submitted to the Dust Group, Pittsburgh Technical Support Center, Federal Bureau of Mines. The samples were collected during actual mining operations. 

Along similar lines, carbon-13 magnetic resonance has been applied to coal and to the elucidation of the character of soluble coal fractions and other coal-derived materials (Bartuska et ah, 1978 Ladner and Snape, 1978 Miknis, 1988). In fact, it is the advances in carbon-13 magnetic resonance that have brought new thoughts to the chemical nature of, and structural types in, coal. The technique brought with it the innovative solid-state techniques that allowed coal to be viewed in its natural solid state without invoking the criterion of sample solubility. This removed the need for dissolution of coal fractions and the often... 

Figure 2. GPC separation of SO 2-solubles of SRC from West Virginia subbituminous coal. Fraction 3 and 4 are ...

Glycerophosphoric acid proved to be interesting in that approximately 5% of the preasphaltene bases had water-soluble glycerophosphate salts. It appears that the highly hydrophilic glycerophosphate anion can act as a phase-transfer agent for a fraction of preasphaltene bases that must be distinguished from the other H-coal fractions in some structural way. 

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