No abstract

The solvolytic conversion of softening bituminous coal at 380 °C in solvents derived from the commercial hydrocarbon byproducts and residues from coal and petroleum processing was studied. Hydrogen-donor tetrahydronaphthalene (THN) and nondonor 1-methylnaphthalene (MN) were also used for comparison. The high-boiling solvents of different chemical classes (highly aromatic coal tar, its anthracene fraction, and low-aromatic heavy gas oil of catalytic cracking of the oil residue) and the H-donor THN solvent were found to exhibit high efficiency for coal conversion into quinoline-soluble products. The chemical and molecular compositions of coal, solvents, and dissolved products were characterized in detail by different techniques, including chemical analysis, group analysis, infrared Fourier transform (IRFT) spectroscopy, X-ray diffraction (XRD), liquid chromatography, and thermal analysis to reveal the chemical transformations of the coal–solvent mixture during the dissolution reaction. The solvolysis of coal in the liquid phase of both highly aromatic and low-aromatic solvents was found to involve selective depolymerization of polymer-like coal via breaking of weak linkages between the aromatic units, resulting in the formation of soluble pitchlike products. The effective dissolution of coal in the H-donor THN solvent resulted probably from a combination of the nonselective thermal fragmentation of the coal structure to smaller radical intermediates and their stabilization by hydrogen from THN, producing mainly tar and a few gases. The low-boiling solvents of both predominantly aromatic and aliphatic classes (gas oils from naphtha pyrolysis and delayed coking of the petroleum residue) and MN exhibited poor efficiency for coal dissolution. The concentrations of carcinogenic benzo­(a)­pyrene (BaP) in the solvents used and in the toluene fractions of the resulting extracts were analyzed. The remarkable result was that coal extracts, compared to solvents, contained much less BaP, probably due to its conversion with coal and/or solvent molecules during coal dissolution.

Three extractive pitches were produced by using thermal dissolution of the medium-ranked coals at 380 °C in anthracene oil. The empirical properties such as the chemical composition, solubility in quinoline and toluene, softening point, and content of carcinogenic polycyclic hydrocarbons, and also molecular and structural parameters of the extractive pitches were characterized in comparison with three commercially available pitches, including typical coal-tar pitch, petroleum-derived pitch, and blended pitch derived from the mixture of coal tar with petroleum feedstock. The molecular and structural properties of pitches were studied using FTIR, 1H and 13C NMR, and XRD techniques. It was shown that the average molecule of the extractive pitches was composed of predominantly aromatic rarely substituted pericondensed nuclei, such as that in coal-tar pitch. The spatial structures of both the extractive and reference pitches consisted of predominantly disordered carbon matter with a small amount of rather ordered nanosized “graphite-like” stacks. In terms of the technical specifications, the extractive pitches irrespective of the coal used met the requirements for the pitch binder and resembled commercial blended petro-coal-tar pitch. A remarkable merit of the extractive pitches compared to coal-tar pitch was low carcinogenicity (two to three times as low).

No abstract