Close Similarities of Chemical Structures between Light (Hexane-Soluble) andHeavy (Hexane-Insoluble and Benzene-Soluble) Fractions of Solvent-Refined Coal
Masakatsu NOMURA,* Toru IDA, Mikio MIYAKE, Takashi KIKUKAWA, and Tatsuhisa SHIHONO+Department of Chemistry, Faculty of Engineering, Osaka University,2-l, Yamada-oka, Suita, Osaka 565+Department of Clothing Faculty of Domestic Science

Teikoku Women's University, 6-173, Fujita-cho, Moriguchi, Osaka 570
Curie-point pyrolysis-GC analyses were applied for structural analysesof hexane-soluble (HS) and hexane-insoluble and ben2:ene-SOluble (HI-BS)
fractions from two SRC samples. pyrograms of HS and HI-BS fractions are
strikingly similar, indicating that they are composed of similar aromaticconstituents, although the molecular weight distributions between the two
fractions are different. The difference in coal rank for the two SRC
samples was reflected as the profiles of pyrograms.
Although many works1-3) have been carried out on the characterization ofcoal-derived liquids, however, most of which give only averaged, partly detailed,structural information about the constituents in these complex samples. Recently,
FI- and FD-MS measurements have been applied to the characterization ofcoal-derived liquids4-8) because these techniques provide fragment-free mass
spectra and, subsequently, Simplified compound-type distribution of complex
organic materials. Another powerful method is Curie-point pyrolysis combined withgas chromatography and mass spectrometry (PY-GC-MS), which is now widely used in
the characterization of complex organic materials, such as oil shales,9)coals10-11), and coal-tar pitches.12)
In the present study, constituents in Solvent-Refined Coal (SRC) wereelucidated by PY-GC-MS analyses. Furthermore, the results were assessed by thecomparison with those obtained by FI- and FD-MS measurements.
Akabira and Wandoan SRC were provided by Sumitomo Metal Mining Co., Ltd. SRC
was further fractioned as follows: 10 g of SRC was extracted with boilingbenzene (300 ml) for 3 h being separated to benzene-soluble (BS) andbenzene-insoluble (BI) fractions, respectively. The BS fraction, concentrated toabout 20 ml by evaporating benzene, was poured into hexane (1000 ml) to precipitate
hexane-insolubles (HI-BS).
Hexane-soluble (HS) was obtainedby evaporating hexane from thefiltrate. The HS and HI-BS
fractions were subjected toanalyses. The elemental

analyses of the HS and HI-BS fractions are listed in Table l.
Curie-point pyrolysis was performed with an equipment of Japan AnalyticalIndustryCo.,Ltd (Model JHP-2 or JHP-3). In order to perform efficient pyrolysisof the sample, ferro-magnetic foil (pyro-foil) was used with Curie-pointtemperature at 690 ℃. structural analyses were performed using a JEOL DX303
double focusing mass spectrometer combined with a Hewlett-Packard 5970 GC anda JHP-3 pyrolyser. Conditions used were: 0.25 mm i.d. X 25 m OV-101 Fused Silicacolumn; 50 ℃ for 2 min and 10 ℃/min to 300℃; ionization potential 70eV; scanspeed 0.5 see from m/I 35 to 500. For compositional determination, a Shirnadzu 7AGC equipped with 0.32 mm i.d. X 25 m ULBONHR-101 Bonded Fused Silica column(equivalent to OV-101 column; Chromato Packing Co., Ltd.) was combined with JHP-2pyrolyser. Conditions were: 50 ℃ for 2 min and 10 ℃/min to 300 ℃. FI- andFD-MS spectra were recorded for HS and HI-BS fractions using a JEOL DX300 double
focusing mass spectrometer. The conditions for FI-MS measurements were as
follows: cathode potential -5.5 kV, emitter current 10 mA. Scanning (2 s/cycle)
was repeated 600-700 times(FI-FAS) or 230 times (FD-MS).
For FD-MS analysis, emittercurrent was elevated at a rateof 4.2 mA/min.
Figures l a and b show theFT-MS spectra of HS fractions
from Akabira and Wandoan SRC,
respectively. The compound-type
distributions are also indicatedin these figures as z numbers
which refer to the formulaCnH2+z Most of the ions wereassigned to the series ofz=-12(+2), -14, -16, -18, and-22, which could correspond tothe homologues of naphthalene(alkane), biphenyl, fluorene,
phenanthrene, and pyrene,
respectively. In comparison
with the spectra of Akabira HS,
the components of Wandoan HS
have relatively higher m/z
number and the homologues ofz=+2 series appear in the rangeof higher m/z, which could
correspond to alkanes.
Figure 2 shows the FD-MS
spectrum of Akabira HI-BS, whichindicates the complexity ofchemical composition of the HI-BS fraction. In case of Wandoan HI-BS fraction, noreproducible spectra were obtained by FD- and FI-MS analyses, probably due tothermal lability or non-volatility.
Thus, FI-MS analyses give information about the molecular-mass distribution of
constituents with different compound-types. However, it is impossible todistinguish compounds with the same molecular-mass but different structures; forexample, distinction between phenanthrene and anthracene (m/z=178). Furthermore,
it is difficult to assess compound-type distributions for very complex FD-MS
spectrum of Akabira HI-BS (Fig. 2). Therefore, it seems to be very difficult toassign the chemical structures ofconstituents in HS and HI-BS
fractions by measuring only FI- andFD-MS spectra.
Figures 3a and b show thepyrograms of HS and HI-BS fractionsof Akabira SRC, respectively. Itshould be noted that these pyrograms
are strikingly Similar after 11 minof the retention time. Figures 4aand b show the pyrograms of HS andHI-BS fractions of Wandoan SRC,respectively. A close similarity
between two fractions alsoestablished. These similarities
refer not only to the profiles ofpyrograms, but also to the relative
abundances of the dominant peaks.
Accordingly both HS and HI-BS
fractions are composed of very
similar aromatic components, asregard to GC-analyzed volatilematerials. Larger amounts of gas,
alkYlben2:eneS, and hydroaromatics,
such as tetralin anddihydrophenanthrene, were detectedin the pyrogram of the HS than thatof the HI-BS. This would suggestthat constituents in HI-BS is more
complex, having more substituentsand more bridging groups.
Although the original Akabiraand Wandoan coals are of different
ranks, the major components in theirpyrograms are very similar, in theway that compounds detected have

simple aromatic skeletons, such as naphthalene, bipheny1, fluorene, dibenzofuran.
phenanthrene, anthracene, and their homologues. The differences in coal rank
appeared in the relative concentrations of these compounds on pyrograms: ( i )Naphthalenes and biphenyls had C2-C3 substituents in the pyrograms of wandoan
whereas C1-naphthalenes were dominant in that of Akabira. (ii) Several peaks
appeared with a certain regularity on the pyrograms of wandoan at retention time
longer than 20 min. These peaks would be assigned to n-alkane homologous series
because these compounds were also observed on the FI-MS spectrum (Fig. la).
The yields of GC-analyzed volatile materials were estimated by the weight
difference between the charged sample and the pyrolysis residue. The HI-BS
fraction showed low Yield than the HS fraction for both wandoan and Akabira
samples. This result indicates that the HI-BS fractions are composed of larger
molecules than the FS fractions. By considering the similarity of the pyrograms
between the HS and HI-BS fractions mentioned above, it is suggested that
constituents in both the HS and HI-BS fractions have similar aromatic structuralunits, however, the number of structural units per one molecule would be different.
The nature of Curie-point pyrolysis technique, quick and reproducible
Heating13,14) and rapid removal of the pyrolyzed products from the heated zone,
ensure that the products observed are primary products, and not secondary Or
rearrangement products.
This research was supported in part by the Ministry Of Education, Science andCulture, Grant-in-Aid for Scientific Research (C)(No. 62550611). We also thank Mr.
Hisaji Matsui, Osaka Gas Co. Ltd., for FI- and FD-HS measurements.