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A selective, low temperature depolymerization procedure has been applied to four coals of different rank to obtain products that are representative of the original structural units (monoclusters) of the coal macromolecular component, and that are amenable to Chromatographic analysis. The monocluster products of this depolymerization procedure retain most of their original aromatic-hydroaromatic structures, whereas functional groups serving as intercluster linkages, e.g. alkylene and etheric groups, undergo predictable modification. A comparison of liquid 13C n.m.r. spectra of the products and solid state 13C n.m.r. spectra of the original coals showed only minor changes in the aromaticities between the solid and depolymerized products, but some loss of carbonyl carbons was detected in all of the coals. Both the tetrahydrofuran pre-extract and the depolymerized products of the four coals were separated into chemical classes by adsorption chromatography. Two of these fractions were found to consist predominantly of aliphatic hydrocarbons (paraffins and naphthenes) and alkylsubstituted bi-, tri- and (some) tetracyclic arenes. The fractions were analysed using gas chromatography-mass spectrometry. Structural identifications were based on a combination of Chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized coal products, and contained various molecular biological markers. The compositions of the pre-extracts became closer to those of the depolymerized coal products as rank increased.

Wandoan Australian coal was extracted with benzene-ethanol and part of the residue was further extracted with pyridine at 350 °C. The n -hexane-soluble fractions of the two extracts have similar distributions of n -alkanes, methyl esters of straight-chain carboxylic acids and unidentified homologues C n H 2 n − 2 O 2 (or C n H 2 n O). This suggests that a large amount of extractable organic material is trapped in the coal matrix so tightly that it cannot be fully extracted using ordinary methods. Another part of the residue from the benzene-ethanol extraction was hydrogenated and the hexane-soluble part was separated into saturate, aromatic and polar fractions. The polar fraction was again hydrogenated in the same way. From the results of analysis it was concluded that paraffins in the hydrogenation product represented the reduction or decarboxylation products of straight-chain esters.

Wandoan Australian coal was separated into three parts by the float and sink method. The light(I) and medium(II) density fractions were extracted both by benzene-ethanol using ultrasonic irradiation and at 200 °C in an autoclave. The residue was hydrogenated in steps to obtain the n-hexane soluble part, raising the reaction temperature from 320 to 390 °C. The n-paraffins were analysed for each extract. Those from ambient extraction showed a bimodal distribution in the C12-C31 region with odd carbon numbers predominating in the C23-C31 region. In the case of the 200 °C extract a smooth distribution appeared at C12-C31. For the first hydrogenation, the paraffins were distributed at C12-C32 with a slight predominance of odd-paraffins in the C23-C31 region, and only one maximum at C26. When the temperature was increased from 320 to 390 °C the distribution approached two maxima at C12 and C26, with the former increasing in amount with the temperature. At the final stage there is a slight predominance of even paraffins in the region C14-C20 which is believed to originate from esters, acids, alcohols etc. It was also found that there was no serious difference between part I and II in the distribution of n-paraffins, but part I yielded greater amounts of saturated hydrocarbons than the corresponding part II.

Wandoan coal, after exhausting extraction by benzene/ethanol, has been liquefied by mild hydrogenation, and the hexane solubles were fractionated into saturate, aromatic and polar fractions. The polar fraction was vacuum distilled. The polar distillate was fully hydrogenated, dehydrogenated and separated to saturate (Fr. 31-1) and aromatic (Fr. 31-2) fractions. The non-distillable polar fraction was similarly hydrogenated and separated. All the aromatic fraction was dehydrogenated under 400 °C using palladium. The components in sub-fraction Fr. 31-2 were found to be similar to those of aromatics in other fractions, suggesting that aromatics in the hydrogenation product were probably derived from reduction of the polar fraction. The chemical structure of parent coal is composed mostly of polar compounds as found in the polar fraction.

The reaction of lignin with n-C 14 alcohol (as a model of hydrolysate of lipid) at 120–180 °C using active clay as catalyst was studied. The n-hexane insoluble product and lignin itself were then hydrogenated under mild conditions. The benzene soluble fractions of reacted product contained n-C 14 substituted phenols and C 1 -C 3 substituted phenols. The latter have also been found in the hydrogenation product of lignin itself. Therefore alcohol could link to the benzene nuclei of lignin. As long alkyl chain substituted phenols are found abundantly in coal liquids, pyrolysates or extracts and are regarded as the main constituent of coal, it is suggested that the early diagenesis process includes the reaction between lignin and alcohol (or fatty acid) which may be the hydrolysation product of lipids widely occurring in nature.