John R. Kershaw

The effect of solvent properties on the supercritical gas extraction of coal

Abstract Supercritical gas extraction of the same coal was carried out using various solvents. Correlations between the conversion and the critical temperature, the density at the experimental conditions and the Hildebrand solubility parameter at the experimental conditions were found. For toluene, the conversion increases with an increase in the Hildebrand solubility parameter until a maximum is reached when a further increase in the solubility parameter results in a decrease in conversion. The solubility parameter was varied by changing the pressure.

Identification of large polycyclic aromatic hydrocarbons in a coal tar pitch

Abstract High-performance liquid chromatography using a shape-selective reversed phase and a diode-array absorbance detector was used to identify several 7–10-ring polycyclic aromatic hydrocarbons (PAHs) in coal tar pitches. The structures of these PAHs suggest that many different reaction pathways occur in the production of coal tar pitches.

Relations between hydroliquefaction behaviour and the organic properties of a variety of South African coals

Abstract A selection of twenty South African coals was subjected to liquefaction using direct hydrogenation procedures. The overall conversion data and yields of oil obtained in these experiments were correlated against the hydrogen to carbon ratio, volatile matter and the concentration of reactive macerals present in the coal. The conventional assessment of reactive macerals (the sum of vitrinite and exinite) was found to be inadequate for these coals. These correlations, obtained using simple linear regression analysis, were generally good and allowed for prediction to be made about the behaviour of a coal during processing using readily obtainable coal parameters.

Supercritical Gas Extraction of South African Coals

Abstract The supercritical gas extraction of South African coals was carried out using semi-continuous reactors. The conversion (to liquid and gaseous products) increases as the volatile matter yield or the H/C atomic ratio of the coal increases and as the critical temperature or the Hildebrand solubility parameter of the solvent increases. The effect of pressure and temperature on the conversion is discussed. The chemical nature of the oils (hexane soluble product) from supercritical gas extraction at 350°C and 450°C is also reported.

Supercritical fluids in coal processing

Abstract The extraction of coals with supercritical fluids is reviewed. Possible strategies for the liquefaction of coal with supercritical fluids are emphasized. The effect of coal properties, solvent properties, pressure, temperature, and particle size are discussed.

Supercritical gas extraction of Victorian brown coals: The effect of coal properties

Abstract A selection of fifteen Victorian brown coals, which varied in lithotype but only slightly in rank, were subjected to supercritical gas extraction with toluene. Seven of these coals were also extracted with 5% tetralin/toluene under the same conditions of temperature and pressure (400 °C and 10 MPa). The overall conversion, the extract yield and the yield of toluene solubles (oil and asphaltene) were correlated with more easily obtained coal properties using simple linear regression analysis. Good correlations were obtained between the total conversions and the volatile matter content of the coals, and for the toluene extractions between both the extract yield and the yield of toluene solubles and the H/C atomic ratio. For the toluene solubles from the toluene extractions, the aromaticity decreased and the molecular weight increased as the H/C atomic ratio of the coal increased. Inorganic constituents of the coals did not appear to have a marked effect on total conversion and liquid yields. Removal of the cations from two coals increased conversion and liquid yields in one case and decreased these in the other, but in both instances the changes were not large.

Supercritical gas extraction of coal with hydrogen-donor solvents

Abstract An investigation of the effect of a hydrogen-donor component in the solvent used for supercritical gas extraction was undertaken. Extraction of three Australian coals with toluene, with decalin and with these solvents containing small amounts of tetralin was investigated. There was a significant improvement in conversion by addition of 5% tetralin to the solvent. Other hydrogen donors were also effective. The improvement in conversion was shown to be due to hydrogen donation rather than to a change in the physical properties of the solvent. The increase in conversion was greater for a brown coal than for a bituminous coal of the same hydrogen to carbon atomic ratio. The pre-asphaltene content of the extract increased with conversion.

Fluorescence spectroscopy in the characterization of coal-derived liquids

Abstract The use of fluorescence spectroscopy as a qualitative analytical technique for the analysis of polyaromatic hydrocarbons in coal-derived liquids is reported. Examples of fluorescence emission and fluorescence excitation spectra obtained from aromatic ring systems in coal hydrogenation oils and solvent extracts are shown. Twelve aromatic ring systems were identified. The separation scheme was simple and, therefore, the method has potential for routine analysis.

Extraction of victorian brown coals with supercritical water

Abstract Extraction of five Victorian brown coals with supercritical water in a semi-continuous reactor was investigated. At 380°C and 22 MPa conversions of 42–54% and extract yields of 20–26% were obtained, significantly higher than with toluene under the same conditions. The extracts were separated into oils, asphaltenes and pre-asphaltenes and these were studied by NMR spectroscopy combined with elemental, OH and molecular weight analyses. The extacts have a high asphaltene and pre-asphaltene content, together with a high oxygen content, especially in the asphaltene and pre-asphaltene fractions. Long alkyl chains were present in the oils and asphaltenes. Temperature had little effect on the extraction, whereas pressure has a marked effect on both the conversion and the composition of the extract. The major difference between the toluene and water extracts is the higher oxygen content of the latter. There was a considerable improvement in the conversion using 0.5 M NaOH rather than water. Analyses of some of the chars were also carried out.

Extraction of brown coals with supercritical fluid mixtures: Implications for coal structure

Abstract Supercritical fluid extractions of brown coals with mixtures of hydrocarbon and polar solvents showed that aliphatic alcohols and amines are beneficial in the extraction of these coals. Conversions of > 90% were obtained for extraction with benzene-amine mixtures (80:20 w/w) at 300 °C. The results are consistent with the view that ester bond cleavage is an important step in dissolution of low-rank coals.