Ind. Eng. Chem. Res. Vol. 26, No. 2, 1987 205 C n ( n = 4.5.6...1
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Figure 5. I3C NMR spectrum of steam extract of run 5. 16
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Figure 6. FIMS of steam extract of run 5.
The group of signals in the 15-20 ppm region is probably due to the methylene carbons attached to aromatic rings. The presence of a broad spectral envelope in addition to the sharp alkane lines demonstrates the extract’s complexity. The spectral complexity is due to the presence of small amounts of polymethylene-type compounds. The complex band of carbon signals in the 120-130 ppm region is due to the aromatic and polycyclic aromatic species. Interestingly, a small but distinctive signal occurs a t 179 ppm which is where the carbonyl carbon of a COOH group appears, suggesting the presence of some carboxylic acids in the extract. FIMS is a mass spectrometry technique which uses a soft ionization mode and allows most molecules to be observed as unfragmented molecular ions (Anbar and Aberth, 1974; St. John et al., 1978). The method can provide a true molecular weight profile for any given complex mixture. Figure 6 represents the field-ionization mass spectrum of the extract. The extract has a very narrow molecular weight distribution with number average (M,) and weight average (M,) molecular weights of 315 and 373, respectively. Since 75% of the material was volatilized in the FIMS probe, the observed molecular weights are a true representation of the extract and the extract is composed of low molecular weight compounds. The most prominent peaks in the spectrum appear at m/z 110,124, and 138 and can be assigned to dihydroxybenzene and its methyl and ethyl analogues, respectively. Surprisingly no prominent peaks due to monohydroxybenzene (phenol) or its C-1 or C-2 analogues are found. The oxygenated compounds present in the extract are best represented by the class of
dihydroxybenzenes and other dihydroxy aromatics. There are a number of other prominent peaks in the higher molecular weight range which, in all probability, arise from the polymethylenes attached to an aromatic ring (identified by NMR), but the FIMS analysis does not allow ready identification of these compounds. In the presence of the highly reactive dihydroxy aromatics, the normally stable alkanes and alkyl aromatics readily undergo transalkylation reactions under the processing conditions studied. The transalkylated products can undergo further condensation and coupling reactions, the net result being an intractable, highly cross-linked coal. Pretreatment with steam, at lower temperatures, allows the breaking of hydrogen bonds, loosening of the coal matrix, and stabilizing of some of the reactive components in the coal. When the temperature increases during the supercritical extraction step, many of these reactive molecules can be steam volatilized or steam extracted, escaping the loosened coal matrix structure before undergoing retrogressive reactions. This explanation is supported since the introduction of a low-temperature pretreatment step before the supercritical steam extraction leads to a 32% increase in conversion. The presence of reactive dihydroxybenzenes in the extract is also supporting evidence. Dihydroxy aromatics have never been reported as occurring in coal liquids obtained under the normal coal processing conditions generally employed. They cannot survive the severe processing conditions. Small amounts of dihydroxy aromatics have been obtained in flash or fast pyrolysis conditions (Meuzelaar et al., 1984). The very rapid heating allows the dihydroxy aromatics to escape the coal matrix before they can undergo retrogressive reactions.
Conclusions The steam pretreatment/extraction process produces enhanced extract yields. The extract has a high H/C ratio due to the presence of long-chain polymethylene compounds which may or may not be attached to aromatic rings. The extract contains significant amounts of oxygenated compounds, some of which are present as dihydroxy aromatics. A highly condensed residue (low H/C ratio) is obtained which can be attractive as a solid fuel for combustion. Acknowledgment This work has supported by the Electric Power Research Institute through research Project 2147-9. Shu-Yen Huang performed the IR and NMR analyses and prepared the FIMS samples. We thank Linda F. Atherton for helpful discussions.
Literature Cited Anbar, M.; Aberth, W. H. Anal Chem. 1974, 46, 59A. Anon. Coal Technology Report Vol. 2, No. 11, May 28, 1984, p 1. Atherton, L. F.; Kulik, C. J. Advanced Coal Liquefaction; Presented at the AIChE Annual Meeting, Nov 1982, Los Angeles, CA. Meuzelaar, H. L. C.; Harper, A. M.; Hill, G. R.; Given, P. H. Fuel 1984, 63, 640. Ross, D. S.; Green, T. K.; Mansani, R. Proceedings of the International Conference on Coal Science, Pittsburgh, PA, Aug 1983; pp 10-13. St. John, G. A.; Buttrill, S. E., Jr.; Anbar, M., ACS Symp. Ser. 1978, 71, 223.
Received for review January 14, 1986 Accepted August 4 , 1986
