Flash Pyrolytic Study on Chemical Structures of Akabira Coal
Extracts and Residue
Kenji MTSUBAYASH, Masakatsu NOURA,* and Mikio MIYAkE
Department of Applied Chemistry, Faculty Of Engineering,Osaka University, 2-1, Yamada-oka, Suita, Osaka 565
Akabira coal extracts [ Pyridine soluble fraction (PS)and Acetone soluble fraction (AS) ] and residue [ CS2-Nmethy1-2-pyrrolidone (NMP) insoluble fraction (Residue) ]were analyzed to get detailed information about components
contained in three fractions using curie-point pyrolyser-GC(Py-GC) and -GC-MS (Py-GC-MS). The pyrograms obtained fromthese fractions by Py-GC showed close similarities among
them. The examination by PY-GC-MS resulted in theidentification of 130 compounds.
Structural estimation of coal organic materials has been approached fromdifferent angles over the last thirty or forty years, however, most of theseanalyses of coal were usually Carried out after the chemical degradation:hydrogenation,1) oxidation,2) or alkylation. Although these methods are useful
to make coal organic materials soluble in common organic solvents, from a point ofview to get intrinsic structural information of original coal, these chemicaldegradations are not appropriate. Solvent extraction under mild conditions canprovide valuable information on coal structures through characteri2:ation of ,theextracts and the residue because such extraction is believed not to accompany 'any
chemical reactions. Py-GC and Py-GC-MS are regarded as one of the most powerful
methods to evaluate chemical structures of solid organic materials, on molecularlevel, such as oil shale,3) coals,4) and many natural and synthetic polymers.5)
In the present work, the extracts and the residue obtained from Akabira coalby solvent extraction were analyzed by means of Py-GC and Py-GC-MS.
Akabira coal was ground under 200 mesh and subjected to solvent extraction
after drying in vacuo at 110 ℃ for 24 h. Coal (g) was extracted With 200 ml ofCS2-NMP mixed solvent (1:1) under ultrasonic irradiation for 30 min at room
temperature because, at present time, this binary solvent system6) is known very
powerful for extracting coal organic materials. After centrifugation for 60 min
the supernatant was separated by decantation. These procedures repeated until thesupernatant became almost colorless (7 times). CS2-NMP insoluble (Residue)
fraction was then washed with acetone three times under ultrasonic irradiation(30 min). The above supernatant was filtered and the solvent was evapolated invacuo. The CS2-NMP wet extract was put into a thimble in a soxhlet extractor andsubsequently extractedwith 200 ml of acetone for
24 h, and then with 200 m1
of pyridine for 48 h.
After stripping of thesolvents, theacetone-soluble fraction
and the pyridine-soluble(PS) fraction wereobtained. The small
amount of residue ln thethimble was designated MS
fraction. The acetone
extract was, further,washed with 8:2 wateracetone solution, then thewater-acetone soluble (WS)and water-acetone
insoluble (AS) fraction
was obtained. The AS (l4wt%), PS (15 wt%) andResidue (67 wt%) fractions
were subjected to analyses
after dealing with hotwater (100℃) for 5, 10,
and 15 days, respectively,
to remove NMP completely.
The ultimate analyses ofraw coal, Residue, PS and
AS were shown in Table l.
Curie-Point Pyrolysis
was performed with anequipment of Japan
Analytical Industry Co. ,Ltd. (Model JHP-2 or JHP3). The curie-pointtemperature and pyrolytic
time were selected 670℃
(heating rate 3350 ℃/s)
and 3 s, respectively.
Structural analyses were performed using a JEOL DX303 double focusing mass
spectrometer combined with a Hewlett-Packerd 5970 GC and a JHP-3 pyrolyser. For
compositional determination, a Shimadzu GC-8APF equipped with fused silica
capillary Column was combined with JHP-2 pyrolyser. Conditions were described indetail elsewhere.7)
The pyrograms of three fractions are presented in Fig. 1 and thecorresponding compoundsof AS, which wereidentified by mass
spectroscopy, are listed
in Table 2. In thesepyrolysates, benzene,
pheno1, naphthalene' andtheir series of alkyl
homologues were observedin addition toalkanes /alkenes (C1 C22). Relatively
smaller nuclei such as
benzene and naphthalene
were most abundant andover three-ringaromatics were present
only in small amount.
The remarkable peaks ofphenol derivatives foundare seemed to beconnected with lignin
structure.8)
Figures la, b, andc show the pyrograms ofAS, PS, and Residue
fractions of Akabiracoal, respectively. Itshould be noteworthy
that these pyrograms areroughly the same except
peaks appeared after
retention time of 22 minon the pyrogram of AS
fraction, which
considered to beisoprenoid derivatives.
Therefore, as to GCanalyzed volatilematerials, the close
similarity of chemical structure among the coal extracts and the residue could bestrongly supported. This similarity Was also found in the previous work7) about
Akabira SRC. The volatile materials were evaluated quantitatively by weighting,carefully, both the pyro-tube and the pyro-foil before and after pyrolysis,respectively. The amount of volatile materials to be analyzed directly by GC andGC-MS were established as 34% (AS), 29% (PS),and 31% (Residue) from eachfraction.

This observation that the volatile materials were obtained almost same amount,also, seems to indicate the structural similarities among the extracts and theresidue.
The results obtained here using Curie-Point Pyrolyser may be interpreted by
the following two ways: (i) All of the compounds on the pyrograms arose frompyrolysis of coal macro-molecule. (ii) These had been trapped in the coal
physically Or h61d by weak-bond like hydrogen-bonding were released by activateddiffusion or some breakdown of the network due to shock heating. The former
assumption means that the similarity of pyrograms reflects the three fractions arecomposed of similar unit skeletons' and the latter means that the similar kinds
and quantities of low-molecular-weight materials are held in the three fractions
by some interactions. However, these arguments need to await further
clarification to be concluded. Some workers9-10) found that small compounds;
aromatic hydrocarbons and phenols were trapped in the coal network as clathrates
and were not extractable with common organic solvents at their normal boilingpoint. Therefore, present authors consider that most of the compounds observed on
pyrograrns originated from the collapse of physical or weak-chemical bond rather
than covalent bond. Now, the relationship between the low-molecular-weightmaterials obtained by Py-GC and “mobile phase”11) which is discussed on the basisof coal-two-component model are, also, under investigation.
By application of this analytical system, ca. 30% of the coal extracts (AS,ps) and the residue (Residue) composed high-molecular-weight materials (over m/z2000) could be analyzed by GC and GC-MS, and it is found that the pyrograms
obtained by the method described above revealed almost same appearance. There
have been few reports being related to comparison of chemical structure among coalextracts and residue. Consequently, these structural information among them seemto be of great importance.