1994 Volume 73 Issue 6 Pages 404-411
In the previous paper, the initial stage liquefaction of several coals was examined by using a pipe reactor which was designed to recover six heat-treated samples in the heating process up to ca. 450°C and the yield of pyridine insolubles (PI) of the heat-treated slurry was shown to depend on the coal rank and decrease to less than % in some coals. In this paper, solid-state 13C-NMR spectroscopy of PI is applied to examine the mechanism of the initial stage liquefaction of Lingan bituminous coal, Illinois and Wandoan subbituminous coals and Wabamun lignite. The followings are derived from the analysis of NMR spectra. The spectra of PI samples of Lingan coal heat-treated up to 423°C are almost the same and those of Illinois and Wandoan coals are scarcely changed up to 372°C and 409°C, respectively. It is therefore considered that PS (pyridine solubles) of each coal is composed of the compounds with almost the same functional group distribution as that of PI of the raw coal. The PI values of the three coals decrease largely at higher temperatures than the above-mentioned as previously presented. The followings are discussed in this temperature range. It is shown in Lingan coal that the compounds relatively rich in aromaticity become PS and the components with relatively low aromaticity remain as PI. In the case of Illinois coal, the small aromatics with side chains such as alkyl groups become PS and the components composed of the relatively large aromatic ring crosslinked by alkyl chains remain as PI. In the case of Wandoan coal, the compounds with the long alkyl chains are changed to PS and the components relatively rich in aromaticity crosslinked by alkyl chains are recovered as PI. Wabamun coal shows a completely different behavior from these three coals, that is, the aliphatic compounds become PS successively with increasing tempera-ture without an abrupt change and the components with high aromaticity remain as PI.