12
Energy & Fuels 2002, 16, 12-17
Catalytic Hydrogenation of Extracts from Coal and Their
Thermal Reactivity
Hideyuki Takagi*
National Institute of Advanced Industrial Science and Technology, AIST Tsukuba West,
Tsukuba 305-8569, Japan
Takaaki Isoda, Katsuki Kusakabe, and Shigeharu Morooka
Department of Applied Chemistry, Graduate School of Engineering, Kyushu University,
Fukuoka 812-8581, Japan
Received June 26, 2001. Revised Manuscript Received September 5, 2001
Upper Freeport coal was extracted using a mixture of carbon disulfide and N-methyl-2pyrrolidinone (CS2/NMP) under ultrasonic irradiation at room temperature. The CS2/NMP-soluble
fraction (CS2/NMP-S) was further extracted with THF, leading to THF-soluble fraction (THF-S)
and -insoluble fraction (THF-IS). The thermal reactivity of these extracts from coal was evaluated
by flash pyrolysis at 170-764 °C under an inert atmosphere using a Curie-point pyrolyzer (CPP).
The volatile yield for the soluble fraction after CS2/NMP extraction, as well as THF extraction,
was higher than that for the insoluble fraction. The CS2/NMP-soluble fraction was hydrogenated
using a Ru/Al2O3 catalyst at 120 °C at a hydrogen pressure of 10 MPa. The aromatic structures
in extracts were partially hydrogenated and the acetic acid was introduced into extracts without
significant decomposition of the structure during the catalytic hydrogenation. The thermal
reactivity of extracts was enhanced by this catalytic hydrogenation. This can be explained by
the conversion of CdC bonds to C-C bonds in aromatic structure and the release of compounds
with carboxy groups introduced into extracts.
Introduction
Coal is composed of aromatic units, which are connected by methylene and ether bonds. The aromatic
units also associate with one another by noncovalent
bonds, which consist of hydrogen bonds and π-π
interactions between aromatic structures. The change
in the associated structure of coal has an effect on its
thermal reactivity. The relaxation of the associated
structure by the solvent swelling increased the thermal
reactivity.1 We reported that the ethanol-soluble fraction
of Yallourn coal, which had been oxidized with aqueous
H2O2 at 70 °C, was pyrolyzed, and the result was an
increase in the yield of volatile matter.2 This can be
explained by the cleavage of bridging structures during
the H2O2 treatment. However, the effect of the aromatic
structures in coal on its thermal reactivity is not
sufficiently clarified.
In previous studies,3,4 we developed the method that
the aromatic structures in coal can be changed using
the catalytic hydrogenation under mild conditions without decomposition of the coal structure. The ethanol* Author to whom correspondence should be addressed. Telephone:
+81-298-61-8298. Fax: +81-298-61-8408. E-mail: hide-takagi@aist.go.jp.
(1) Mae, K.; Hoshika, N.; Hashimoto, K.; Miura, K. Energy Fuels
1994, 8, 868-873.
(2) Isoda, T.; Takagi, H.; Kusakabe, K.; Morooka, S. Energy Fuels
1998, 12, 503-511.
(3) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels
1999, 13, 1191-1196.
(4) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Prepr. Pap.s
Am. Chem. Soc., Div. Fuel Chem. 1999, 44, 1029-1032.
soluble fraction of the low rank coal, which had been
oxidized with aqueous H2O2, was hydrogenated using
a Ru/Al2O3 catalyst in a mixed solvent of ethanol and
acetic acid at 120 °C.2 This catalytic hydrogenation
altered the aromatic structure of the coal and increased
its reactivity with respect to pyrolysis. Further, a THFsoluble fraction of a subbituminous coal, which had been
depolymerized by treatment with a superacid, along
with several model polymers which contained aromatic
structures, was hydrogenated over a Ru catalyst at 120
°C.5 A good correlation was observed between the
thermal reactivity and the aromaticity in the skeletal
structure, which was substantially modified by the
hydrogenation reactions. Since this hydrogenation is
effective in the soluble fraction, this method has not
been applied to the higher rank coal, which contains
more aromatic rings than the low rank coal. On the
other hand, Iino et al.6,7 reported that treatment with
a mixture of carbon disulfide and N-methyl-2-pyrrolidinone (hereafter, referred to as CS2/NMP) gave extraction yields as high as 30-66 wt % for bituminous coals
at room temperature. Therefore, it would be possible to
investigate the role of the associated structure in terms
of the thermal reactivity of higher rank coals by
(5) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels
2000, 14, 646-653.
(6) Iino, M.; Takanohashi, T.; Ohsuga, H.; Toda, K. Fuel 1988, 67,
1639-1647.
(7) Iino, M.; Takanohashi, T.; Obara, S.; Tsueta, H.; Sanokawa, Y.
Fuel 1989, 68, 1588-1593.
10.1021/ef010142u CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/30/2001
Catalytic Hydrogenation of Extracts from Coal
Figure 1. Extraction procedure for Upper Freeport coal.
conducting the extraction using the CS2/NMP mixed
solvent and hydrogenation over a Ru catalyst.
In the present study, Upper Freeport (UF) coal, whose
carbon content was 85.3 wt %, was extracted with a CS2/
NMP mixed solvent under ultrasonic irradiation at room
temperature. The CS2/NMP-soluble fraction was extracted with THF under ultrasonic irradiation at room
temperature, to investigate the change in thermal
reactivity before and after the extraction. The CS2/NMPsoluble fraction was further hydrogenated over a Ru
catalyst at 120 °C under a hydrogen pressure of 10 MPa.
The thermal reactivity of these extracted and hydrogenated fractions was then evaluated by flash pyrolysis
at 170-764 °C in an inert atmosphere, using a Curiepoint pyrolyzer (CPP). The effect of the extraction and
the hydrogenation on thermal reactivity was discussed
from the viewpoint of structural changes.
Experimental Section
Extraction. Upper Freeport (UF) coal used in the present
study was selected from the Argonne Premium Coal Sample
Program. Figure 1 shows the extraction procedure for UF coal
with the CS2/NMP mixed solvent (1:1 in volume). UF coal was
ground into particles smaller than 149 µm in size, and vacuumdried at 70 °C for 12 h. The coal sample was extracted with
the CS2/NMP mixed solvent under ultrasonic irradiation at
room temperature.6,7 The CS2/NMP-soluble fraction (CS2/NMPS) was washed with an acetone-water mixture (1:4 in volume)
and was subjected to extraction with THF and hydrogenation
using the catalyst. The CS2/NMP-insoluble fraction (CS2/NMPIS) was washed with acetone. CS2/NMP-S was extracted with
THF under ultrasonic irradiation at room temperature, giving
THF-soluble fraction (THF-S) and -insoluble fraction (THFIS). Each fraction was dried at 70 °C for 6 h under vacuum.
Hydrogenation. Figure 2 shows an outline of the scheme
used for the hydrogenation of the extracts from UF coal. A
0.5 g sample of CS2/NMP-S was dissolved in a mixture of 3
mL of acetic acid and 6 mL of THF.3,4 Hydrogenation was then
performed using 0.5 g of an alumina-supported ruthenium
catalyst (metal content ) 5 wt %, Wako Chemical Co.;
hereafter referred to as Ru/Al2O3 catalyst) at 120 °C for 1224 h under a hydrogen pressure of 10 MPa, in a 25 mL
autoclave equipped with a magnetic stirrer. After hydrogenation, the catalyst was separated by centrifugation, and the
Energy & Fuels, Vol. 16, No. 1, 2002 13
Figure 2. Hydrogenation procedure for extracts; atemperature: 120 °C; H2 pressure: 10MPa; time: 12-24 h; catalyst:
Ru/Al2O3 (0.5 g); solvent: THF (6 mL) + acetic acid (3 mL).
acetic acid was removed by washing with water. The product
was then extracted with THF under ultrasonic irradiation,
leading to the hydrogenated THF-soluble fraction (H-THF-S)
and a THF-insoluble fraction. Each fraction was dried at 70
°C for 6 h under vacuum.
Pyrolysis. The thermal reactivity of extracted and hydrogenated fractions was evaluated by flash pyrolysis at 170764 °C in an inert atmosphere using a CPP (Japan Analytical
Industry, JHP-22). The heating rate was estimated to be 3000
°C/s, and the total pyrolysis time was 5.0 s. The reaction zone
and tubing were heated at 50 °C. Gaseous products, i.e., CO,
CO2, H2O, and CH4, were analyzed by gas chromatographs
equipped with TCD and FID detectors. Tar was defined as the
products that contained more than two carbon atoms and was
calculated from the difference between the initial mass of the
coal sample and the total yield of residual solid and gaseous
products. In the present study, yields for pyrolysis were
calculated on the basis of the initial mass of each sample.
Analysis of Coal Structure. The H/C atomic ratio of the
coals was calculated from elemental analysis data. The aromaticity, fa, of the extracted and hydrogenated fractions was
defined as the ratio of the number of aromatic carbons to the
total number of carbons, and evaluated from 1H NMR spectral
data and elemental analysis using the Brown-Ladner equation.5,8
FT-IR spectra of the raw coal, extracted, and hydrogenated
fractions were measured by diffusive reflectance method. Each
sample was finely powdered, mixed with dried KBr, in a mass
ratio of 1:50, and then analyzed.
Results
Thermal Reactivity of Extracts from Coal. Table
1 shows the elemental analyses and properties of the
extracts from coal. The yields for CS2/NMP-S and CS2/
NMP-IS were 54.3 and 43.3 wt %, respectively. The fact
that the nitrogen content remained unchanged before
and after extraction shows that no NMP solvent remained in the extracts. An FT-IR peak, corresponding
to the NMP and CS2 solvents, was not observed. Thus,
no solvent was entrapped in either the soluble-fraction
or the insoluble-fraction. Iino et al.6 reported that the
NMP and CS2 solvents were not retained after the
extraction procedure used in the present study. The
minerals in the raw coal were concentrated in CS2/NMP(8) Brown, J. K.; Ladner, W. R. Fuel 1960, 39, 87-96.
14
Energy & Fuels, Vol. 16, No. 1, 2002
Takagi et al.
Table 1. Elemental Analyses and Properties of Extracts from Coal
[wt %-daf]
N
sample
abbreviation
C
H
UF raw coal
CS2/NMP-soluble fraction
CS2/NMP-insoluble fraction
THF-soluble fraction
THF-insoluble fraction
raw coal
CS2/NMP-S
CS2/NMP-IS
THF-S
THF-IS
85.3
86.0
82.7
84.7
84.9
5.3
5.4
5.2
5.2
5.4
a
1.6
1.7
1.7
1.9
1.7
(O + S)a
ash
[wt%]
H/C
extract yield
[wt %-raw coal]
7.8
6.9
10.4
8.2
8.0
15.0
0.9
29.9
1.0
1.5
0.74
0.75
0.75
0.74
0.76
54.3b
43.3b
26.9c
27.3c
Determined by difference. b Extraction using CS2/NMP mixed solvent. c Extraction using THF.
Figure 3. Yields of residual solid from pyrolysis of extracts.
Figure 4. Tar yields from pyrolysis of extracts.
IS. The yields for THF-S and THF-IS, which were
separated by the THF-extraction of CS2/NMP-S, were
26.9 and 27.3 wt %, respectively. The oxygen content of
THF-S or THF-IS was larger than that of CS2/NMP-S.
Figure 3 shows the yields of residual solid from the
pyrolysis of extracts. The yield of residual solid at 386
°C was 98 wt % for the raw coal, 97 wt % for CS2/NMPS, and 96 wt % for CS2/NMP-IS. Each of the yields
decreased with increasing pyrolysis temperature. The
yield of residual solid for CS2/NMP-S was smaller, and
that for CS2/NMP-IS was larger, than that for the raw
coal. At 764 °C, the yield of residual solid reached 82
wt % for CS2/NMP-IS, 73 wt % for the raw coal, and 66
wt % for CS2/NMP-S. This suggests that the coal is
composed of two parts with higher and lower thermal
reactivities. The yields of residual solid for THF-S and
THF-IS were smaller than that for CS2/NMP-S, and, at
764 °C, it was 51 wt % for THF-S, and 64 wt % for THFIS.
Figure 4 shows the tar yields from the pyrolysis of
extracts. The tar yield for CS2/NMP-S was larger than
that for the raw coal, and reached 18 wt % for the raw
coal, 25 wt % for CS2/NMP-S at a pyrolysis temperature
of 764 °C. However, the tar yield for CS2/NMP-IS was
smaller than that for the raw coal (11 wt % at 764 °C).
The tar yields for THF-S and THF-IS, which were the
extracts of CS2/NMP-S, were larger than the tar yield
of CS2/NMP-S. At 764 °C, the tar yield approached 29
wt % for THF-IS and 41 wt % for THF-S, while the tar
yield of CS2/NMP-S was 25 wt %.
Table 2 shows the yields of gaseous products from the
pyrolysis of the raw coal and extracts. CO, CO2, and CH4
were substantially produced at temperatures above 386
°C, while H2O was produced at temperatures as low as
170 °C. The yields of gaseous products were nearly the
same for all fractions.
Structures of Hydrogenated Extracts and Their
Thermal Reactivity. Table 3 shows the elemental
analyses and acetone-extracted yields of THF-S and
Catalytic Hydrogenation of Extracts from Coal
Energy & Fuels, Vol. 16, No. 1, 2002 15
Table 2. Gasesous Products from Pyrolysis of Raw Coal
and Extracts
yield [wt %]
sample
temperature [°C]
CO
CO2
H2O
CH4
raw coal
170
386
500
590
764
0.1
0.2
0.2
0.3
0.5
0.1
0.2
0.6
0.5
0.6
1.2
1.2
2.0
2.4
3.5
0.0
0.0
0.2
1.5
4.1
CS2/NMP-S
170
386
500
590
764
0.0
0.0
0.0
0.0
0.2
0.2
0.2
0.2
0.2
0.3
3.0
3.6
4.4
4.4
5.1
0.0
0.0
0.1
1.2
3.6
CS2/NMP-IS
386
590
764
0.0
0.1
0.3
0.1
1.0
1.3
0.6
3.3
4.9
0.0
0.5
1.9
THF-S
386
590
764
0.0
0.1
0.3
0.6
1.0
1.3
3.0
3.3
4.9
0.0
0.5
1.9
THF-IS
386
590
764
0.0
0.1
0.3
0.6
0.2
0.5
2.5
2.1
2.7
0.0
0.7
2.4
Figure 5. Changes of H/C atomic ratios and aromaticity, fa,
for H-THF-S.
Table 3. Elemental Analyses and Acetone-Extracted
Yields of THF-S and H-THF-S
hydroextract
[wt %-daf]
genation
yieldb [wt
sample
time [h]
C
H N (O + S)a H/C %-raw coal]
THF-S
H-THF-S
H-THF-S
a
12
24
84.7 5.2 1.9
80.0 6.4 1.5
79.1 6.8 1.4
8.2
12.1
12.7
0.74
0.96
1.03
7.2
7.1
6.9
Determined by difference. b Extraction using acetone.
H-THF-S. The H/C ratio, as well as the hydrogen
content, in THF-S increased as a result of hydrogenation. The yield of H-THF-S was fundamentally equal to
that of THF-S. The hydrogen content without hydrotreatment was 5.2 wt % for THF-S. After hydrogenation
for 24 h, the hydrogen content of H-THF-S increased to
6.8 wt %. The oxygen content was also increased after
hydrogenation. This can be attributed to the introduction of acetic acid, which was used as the additive, into
the coal structure.5 Meanwhile, the nitrogen content was
decreased as a result of hydrogenation. This can be
explained, in part, by a slight amount of cracking of the
heterocyclic structure and by the deposition of nitrogencontaining matter on the surface of the catalyst.9
To evaluate the degree of cracking during the hydrogenation, THF-S and H-THF-S, representing the THFsolubles before and after hydrogenation, were further
extracted with acetone under ultrasonic irradiation at
room temperature. The yields are listed in Table 3. It
has been reported that an acetone-soluble fraction of UF
coal was composed of small components, of which the
molecular weight was approximately 520.10 The yield
of the acetone extract, based on the mass of the dry raw
coal, was 6.9-7.2 wt % and remained unchanged. This
result suggests that the extent of cracking of the coal
structure is negligible during the hydrogenation.
Figure 5 shows the changes of the H/C atomic ratios
and aromaticity, fa, for H-THF-S during the hydrogenation over the Ru/Al2O3 catalyst at 120 °C. The H/C ratio
(9) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels
1999, 13, 934-940.
(10) Takanohashi, T.; Iino, M.; Nakamura, K. Energy Fuels 1998,
12, 1168-1173.
Figure 6. FT-IR spectra of raw coal (a), THF-S (b), H-THF-S
[12 h] (c), H-THF-S [24 h] (d).
was 0.74 for the extract before hydrogenation, and 1.03
after hydrogenation for 24 h, and the fa value was 0.67
and 0.58, respectively.
Figure 6 shows the FT-IR spectra of the raw coal (a),
THF-S (b), H-THF-S after hydrogenation for 12 h (c),
and H-THF-S for 24 h (d). The peak at 1250 cm-1 of
THF-S is assigned to the ether bonds. After hydrogenation for 24 h, the shape of the peak at 1602 cm-1, which
was assigned to aromatic C-C bonds, was changed. The
small peak at 1722 cm-1, assigned to the CdO group of
carboxy or ester groups, was observed, especially for
H-THF-S after hydrogenation for 24 h.
Figure 7 shows the effect of aromaticity, fa, on yields
of residual solid and tar from pyrolysis of THF-S and
16
Energy & Fuels, Vol. 16, No. 1, 2002
Takagi et al.
Discussion
Figure 7. Effect of aromaticity, fa, on yields of residual solid
and tar from pyrolysis of THF-S and H-THF-S.
Table 4. Gasesous Products from Pyrolysis of THF-S and
H-THF-S
sample
yield [wt %]
hydrogenation temperature
time [h]
[°C]
CO CO2 H2O CH4
THF-S
THF-S
THF-S
386
590
764
0.0
0.1
0.3
0.6
1.0
1.3
3.0
3.3
4.9
0.0
0.5
1.9
H-THF-S
H-THF-S
H-THF-S
12
12
12
386
590
764
0.1
0.3
1.3
0.8
1.0
1.2
2.3
3.0
3.1
0.0
0.4
1.8
H-THF-S
H-THF-S
H-THF-S
24
24
24
386
590
764
0.1
0.4
1.2
0.6
0.8
1.8
2.9
3.1
4.4
0.0
0.5
1.9
H-THF-S at pyrolysis temperatures of 386, 590, and 764
°C. The yield of residual solid for THF-S at a pyrolysis
temperature of 590 °C was 64 wt %, and decreased to
54 wt % for H-THF-S after hydrogenation for 24 h. At
764 °C, the yield of residual solid also decreased to 41
wt % from 51 wt % as a result of hydrogenation for 24
h. This indicates that the thermal reactivity of extracts
is enhanced by the catalytic hydrogenation. The decrease in the yield of residual solid at 386 °C, however,
was 1.5 wt % after hydrogenation. The tar yields at 590
and 764 °C increased with decreasing the fa values.
Table 4 shows gaseous products from pyrolysis of
THF-S and H-THF-S. The yields of CO and CO2 slightly
increased after hydrogenation, whereas the yields of
H2O and CH4 remained unchanged before and after
hydrogenation.
Effects of Extraction on Thermal Reactivity. The
thermal reactivity of CS2/NMP-S was higher than that
of CS2/NMP-IS. This suggests that the coal contains two
components, one of which shows a high and the other a
low thermal reactivity. Based on the results in Figures
3 and 4 and Table 2, the average of the volatile yields
for CS2/NMP-S and CS2/NMP-IS was approximately
equal to that of the raw coal. The tar yield for the soluble
fraction after THF extraction, as well as CS2/NMP
extraction, was higher than that for the insoluble
fraction.
When THF-S or THF-IS was pyrolyzed at 386 °C, the
tar yield was 10-12 wt %. On the other hand, the tar
yield for the raw coal, CS2/NMP-S and CS2/NMP-IS at
this temperature was negligible. Except for H2O, the
yields of gases were also very low. Covalent bonds are
not much cleaved during flash pyrolysis at temperatures
below 400 °C.11,12 Thus, formation of tar for THF-S or
THF-IS during pyrolysis at 386 °C can be related to the
release of volatile components in extracts. However, as
shown in Table 1, the oxygen content of THF-S or THFIS was larger than that of CS2/NMP-S. FT-IR analysis
indicates the increase in ether bonds after the THF
extraction. These suggest that THF solvent remained
in extracts. The amount of residual THF, which was
estimated from the increase in the oxygen content after
the THF extraction, was 8.5 wt % for THF-S, and 7.2
wt % for THF-IS. Therefore, the modified yields of
residual solid and tar from pyrolysis of extracts after
THF extraction are shown in Figure 8, based on the
assumption that the residual THF corresponds to tar
after pyrolysis. After the modification of yield, the
average of tar yields for THF-S and THF-IS was larger
than that for CS2/NMP-S. This can be related to the
relaxation of the structures and suppressing the crosslinking reactions during the pyrolysis by the swelling
of residual THF, as reported by Mae et al.1
Effect of Hydrogenation for Coal Extracts. As
shown in Figures 5 and 6 and Table 3, the changes of
elemental analyses, fa values, and FT-IR spectra suggest
that the aromatic structures of the extract were partially hydrogenated and the acetic acid was introduced
into the structure under mild conditions with only
negligible cracking of the overall structure during this
catalytic hydrogenation. However, the mechanism of the
incorporation of acetic acid was unknown from the
result in this study. In previous studies,3,4 we reported
that a Ru catalyst exhibited a high activity for the
hydrogenation of aromatic compounds, which were
dissolved in polar solvents, such as alcohol and THF.
However, both NMP and dimethyl sulfoxide, which
contain nitrogen and sulfur atoms, respectively, strongly
inhibited the hydrogenation activity of the Ru catalyst.
The hydrogenation activity of the Ru catalyst was
markedly enhanced by the addition of acetic acid. Thus,
THF with acetic acid was used as the solvent for the
hydrogenation of extracts in the present study.
The amounts of hydrogen and acetic acid introduced
into the extract were calculated by using the following
(11) Isoda, T.; Takagi, H.; Kusakabe, K.; Morooka, S. Prepr. Pap.s
Am. Chem. Soc., Div. Fuel Chem. 2000, 45, 234-237.
(12) Isoda, T.; Takagi, H.; Kusakabe, K.; Morooka, S. J. Jpn. Inst.
Energy 2000, 79, 511-521.
Catalytic Hydrogenation of Extracts from Coal
Energy & Fuels, Vol. 16, No. 1, 2002 17
increased as a result of hydrogenation. The analysis of
tar from pyrolysis of hydrogenated extracts by using a
GC-MS equipped with a CPP indicated the inclusion of
saturated aromatic structures and compounds with
carboxy groups. In the previous study,5 we hydrogenated
the aromatic structures in phenolic resin and polystyrene, which were used as model compounds for coal and
extracts. The yield of volatile matters from pyrolysis of
hydrogenated compounds at 500 °C increased with
increasing the amount of hydrogen introduced into the
structure. Thus, the increase in tar yield as a result of
catalytic hydrogenation can be attributed to the conversion of CdC bonds to C-C bonds and the release of
compounds with carboxy groups introduced into extracts. On the other hand, the increase in the tar yield
of extracts after hydrogenation for 24 h was 1.5 wt %
at a pyrolysis temperature of 386 °C, while 10 wt % at
590 °C. This can be related to the difficulty in the
cleavage of covalent bonds at low temperature.
Figure 8. Modified yields of residual solid and tar from
pyrolysis of extracts after THF extraction.
assumptions: (1) H-THF-S (24 h) was composed of THFS, CH3COOH, and H (hydrogen). (2) (O + S) was treated
as oxygen. (3) Only three elements, C, H, and O, were
considered. (4) Molar ratio of THF-S (CH0.74O0.073),
C2H4O2, and H was assumed to be 1, x, and y, respectively. Using the above assumptions, H/C and O/C of
H-THF-S (24 h) could be calculated by the following
equations:
H/C ) (0.74 + 4x + y)/(1 + 2x) ) 1.03
O/C ) (0.073 + 2x)/(1 + 2x) ) 0.120
From these equations, the values of 0.027 for x and
0.237 for y could be obtained. Thus, the molar ratios of
THF-S, CH3COOH, and hydrogen were 1, 0.027, and
0.237, respectively.
This catalytic hydrogenation resulted in changes in
the thermal reactivity of extracts. At pyrolysis temperature of 590 and 764 °C, the tar yield of the extracts
Conclusions
(1) Upper Freeport coal was extracted with a CS2/
NMP mixed solvent under ultrasonic irradiation at room
temperature. The CS2/NMP-soluble fraction (CS2/NMPS) was further extracted with THF under ultrasonic
irradiation at room temperature, leading to THF-soluble
fraction (THF-S) and -insoluble fraction (THF-IS). The
thermal reactivity of these extracts from coal was
evaluated by flash pyrolysis at 170-764 °C under an
inert atmosphere using a Curie-point pyrolyzer (CPP).
The thermal reactivity of CS2/NMP-S was higher than
that of CS2/NMP-insoluble fraction (CS2/NMP-IS), and
the average of the volatile yields for CS2/NMP-S and
CS2/NMP-IS was approximately equal to that of the raw
coal. The volatile yields for THF-S was larger than that
for THF-IS.
(2) The CS2/NMP-soluble fraction was further hydrogenated over a Ru catalyst at 120 °C at a hydrogen
pressure of 10 MPa, and was pyrolyzed using CPP. The
aromatic structures of extracts were partially hydrogenated and the acetic acid was introduced into the
structure under mild conditions with only negligible
cracking of the overall structure during the catalytic
hydrogenation. This hydrogenation caused an alternation in the thermal reactivity of the extracts. At pyrolysis temperatures of 590 and 764 °C, the tar yield of the
extracts increased with decreasing the fa values. This
can be attributed to the conversion of CdC bonds to
C-C bonds and the release of compounds with carboxy
groups introduced into extracts.
Acknowledgment. This work was supported by a
“Research for the Future” projects of the Japan Society
for the Promotion of Science (JSPS), through the 148th
Committee on Coal Utilization Technology.
EF010142U