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Liquefaction reaction of coal
Liquefaction 2. Structural products
reaction
correlation
of coal
between
coal and its liquefaction
Tadashi Yoshida, Kazuaki Tokuhashi*, Hideo Narita, Shin-ichi Yokoyama, and Yosuke Maekawa Government Industrial Development Laboratory, Hokkaido, 2-l 7 Jsukisamu-Higashi, Joyohira-ku, Sapporo 061-01, Japan * National Chemical Laboratory for Industry, I- 1 Higashi, Yatabe, Jsukuba, lbaragi Prefecture 305, Japan (Received 25 June 1984)
The structural correlation between coal and its liquefaction products has been examined using crosspolarization, magic angle spinning (CP/MAS) 13C n.m.r. and field ionization mass spectrometry (f.i.m.s.). The CHJaromatic carbon ratios of all solid products (asphaltene, preasphaltene and residue) were close to the corrected CHJaromatic carbon ratio for the coal. This suggests that the ring structure of the structural unit of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. The CHJaromatic carbon ratios of aromatic ring-type oil fractions also correlated with the corrected ratio for the coal, although they were larger. The z series distribution obtained from the f.i.m.s. of oil fractions revealed that coal with a higher CH,/aromatic carbon ratio produced
an oil rich in naphthenic structures. (Keywords: coal; liquefaction; f.i.ms.;
CP/MAS
“C n.m.r.)
In a previous paper’, the mechanism of depolymerization of coal was described on the basis of the results of a mild liquefaction reaction and distributions of oxygen and carbon atoms determined by CP/MAS 13C n.m.r. spectrometry. One of the most important results obtained in the study was that, under the experimental conditions used, the depolymerization of coal to oil proceeded essentially through the cleavage of ether bridges and subsequently CH, bridges, including some naphthenic CH, bonds. This suggests that the chemical structures of liquefaction products are closely related to that of the parent coal. Therefore, the elucidation of structural correlation between coal and its liquefaction products should be useful for the selection of raw coal for liquefaction and the evaluation of the oil produced. In this work, the structural correlation between coal and its liquefaction products has been examined using CP/MAS 13C n.m.r. and f.i.m.s.
from Fr-PP by washing with lOvol.% NaOH and with 10 vol.% H,SO, solution, respectively. The resultant neutral oil was named Fr-PP,,. Solution 13C n.m.r. spectra of ring-type oil fractions were obtained by a gateddecoupling technique which
Soyo-kolshl
Talhelyo
coal
coal
EXPERIMENTAL Briquettes of Yallourn coal and live Japanese coals ranging from 66.2 to 87.4 wt% C were used as sample coals. Details of the characteristics of the coals and the results of a mild liquefaction reaction with subsequent fractionation of products by solvent extraction have been described previously’. The oil (hexane solubles) was further separated, using a double-layered packed column of silica and alumina’, into five fractions of different ring type, namely saturates (Fr-P), monoaromatics (Fr-M), diaromatics (Fr-D), triand tetraaromatics (Fr-T), and poly- and polar aromatic compounds (Fr-PP). Acidic and basic oils were removed 00162361/85/070897-05$3.00 0 1985 Butterworth & Co. (Publishers)
Ltd
Chemical
shift
(ppm)
Figure 1 CP/MAS 13C n.m.r. spectra of residue, preasphaltene asphaltene from Soya-koishi and Taiheiyo coals
FUEL, 1985, Vol 64, July
and
897
Liquefaction
of coal. 2: T. Yoshida et al.
reaction
suppressed nuclear Overhauser enhancement3. Carbon atom distributions of asphaltene, preasphaltene and residue were obtained from their CP/MAS r3C n.m.r. spectra. Details of the measurement conditions and the Table
1
Carbon
distribution,
f, value and CHJaromatic
carbon
assignments of carbon atoms have been reported elsewhere’*4. The compound type analysis of oil components was carried out on the basis of the f.i.m.s. of fractions P, M, D and T5. No correction for the difference
ratio of coal and its solid products _
Carbon
distribution
(%)
Polar
Aromatic
CH,
CH,
f,
CH,/aromatic
Coal Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
22 19 13 5 6 6
57 51 54 61 66 71
I2 18 21 22 I5 12
9 12 12 12 12 11
0.57 0.51 0.54 0.61 0.66 0.71
0.21 0.35 0.39 0.36 0.23 0.17
Residue Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
17 17 14 12 9 8
67 63 62 60 68 72
8 12 14 17 13 I1
8 9 10 11 10 9
0.67 0.63 0.62 0.60 0.68 0.72
0.12 0.19 0.23 0.28 0.19 0.15
Preasphaltene Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
11 11 10 12 11 7
68 67 65 68 69 74
10 IO 12 10 10 9
11 13 I3 IO 10 10
0.68 0.67 0.65 0.68 0.69 0.74
0.15 0.15 0.18 0.15 0.14 0.12
69 68 69 67 70 71
16 16 17 18 I4 14
IO I1 IO II 13 12
0.69 0.68 0.69 0.67 0.70 0.71
0.23 0.24 0.25 0.27 0.20 0.20
Asphaltene Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari ” Values in parentheses
Table 2
are corrected
for alkyl CH,
Yield, f, value and CH,/aromatic
carbon
and paraflinic
CH,
ratio of ring-type
carbons
oil fraction
D
T
PP”
ratio
1.4 0 _
1.4 0.34 1.23
0.9 0.52 0.62
0.9 0.59 0.44
24.4 0.61 0.38
ratio
1.3 0 _
1.5 0.30 1.56
0.8 0.51 0.59
0.5 0.60 0.46
17.7 0.60 0.46
4.9 0
3.6 0.28 1.88
2.0 0.50 0.66
1.7 0.56 0.46
42.5 0.57 0.50
ratio
3.6 0 _
3.7 0.31 1.50
1.7 0.50 0.60
1.2 0.57 0.43
42.6 0.58 0.50
2.1
ratio
2.0 0 _
_
1.6 0.52 0.60
1.1 0.61 0.41
36.3 0.61 0.42
0.8 0.32 1.41
0.7 0.56 0.49
0.5 0.66 0.26
7.7 0.61 0.39
Soya-koishi Yield” carbon
Taiheiyo Yield” f, CH,/aromatic
carbon
ratio
Horonai Yield” f, CH,/aromatic Akabira Yield” .f, CHJaromatic
carbon
carbon
Shin-yubari Yield” f, CHJaromatic
1.4 0 carbon
ratio
y Wt%, dmmf coal basis
898
fraction
M
Yallourn Yield”
/, CH,/aromatic
(0.11) (0.22) (0.21) (0.23) (0.12) (0.08)
P
Coal
carbon
ratio
in coal
Ring-type
f, CH,/aromatic
carbon
FUEL, 1985, Vol 64, July
Liquefaction
reaction of coat. 2: T. Yoshida et al.
considerably higher in the asphaltenes. Considerable amounts of aliphatic carbon remained in the residue. Table 2 summarizes the yield, f, value and CH,/aromatic carbon ratio of the ring-type fraction of oil. Fraction PP, amounted to 7&85 wt% of the oil obtained and the yields of other fractions decreased in the order P, M, D and T. Thef, value increased in the order P, M. D. and T for every oil. Figure Zshows the f.i.m.s. of ring-type oil fractions from Soya-koishi coal. The molecular weight distribution of the fraction P covered an m/z range of 15&5OO.Aromatic ring-type fractions M and D had a similar mass range (m/z 130-370) and molecular weight distribution to each other, but the distributions of Fr-T and PP, were distinctly different from those of Fr-M and D. The number-average molecular weights of Fr-T and PP, were higher than those of Fr-M and D7. Figure 3 gives the distribution (z series distribution) of molar ratios of various compound types in the ring-type fractions of oils from Yallourn, Taiheiyo and Shin-yubari coals as obtained by the compound type analysis of f.i.m.s. The z series distribution of oil from Yallourn coal revealed the following major components: paraffins (z = + 2) for Fr-P, alkyl-substituted mononaphthenobenzenes (z = - 8) for Fr-M, alkyl-substituted mononaphthenonaphthalenes and biphenyls (z= - 14) for Fr-D, and alkyl-substituted phenanthrenes (z= - 18) and alkylsubstituted (poly)naphthenophenanthrenes (z = - 20, - 22) for Fr-T. For every aromatic ring-type fraction the contents of hydroaromatic compound types were larger than those of aromatic compound types.
F
I
Yallourn
16
1
M/L
Figure 2
F.i.m.s. of ring-type oil fractions from Soya-koishi coal
in relative ion sensitivities among oil components6 applied.
was Tal helyo
RESULTS CP/MAS ‘.‘C n.m.r. spectra of residue, preasphaltene and asphaltene from Soya-koishi and Taiheiyo coals are shown in Figure I. As illustrated in the spectra of products from Soya-koishi coal, the residue was rich in polar groups such as phenolic OH (including aromatic ether), COOH, =CO and -OCH, groups, and had a significant amount of aliphatic carbon. The asphaltene contained virtually no polar groups other than phenolic OH. Table 1 shows the carbon atom distribution, carbon aromaticity, fa, and CH,/aromatic carbon ratio of the parent coal, residue, preasphaltene and asphaltene, obtained from their CP/MAS *‘C n.m.r. spectra. The f, values of residue, preasphaltene and asphaltene were larger than that of the parent coal and the difference inf, value between coal and solid products was large in lowerrank coals and small in higher-rank coals. The variation of f, value with rank of coal increased in the order asphaltene, preasphaltene and residue. The CH, carbon content was lowest in the preasphaltenes and
Shin-yubarl
12 -
.z
Figure 3 z series distribution of oil from Yallourn, Taiheiyo and Shinyubari coals
FUEL, 1985, Vol 64, July
899
Liquefaction
reaction
of coal. 2: T. Yoshida
et al.
DISCUSSION As the liquefaction reaction of coal is accompanied by the elimination of functional groups and alkyl side chains, a parameter CH,/aromatic carbon ratio, which represents the ratio of naphthenic CH, to aromatic carbons in the unit ring structure, should be used to demonstrate the structural correlation between coal and its liquefaction products. Here, the amounts of naphthenic CH, and aromatic carbons for the solid products were obtained from the area intensities of z 25-51 and z 93-171 ppm in the CP/MAS i3C n.m.r. spectra, respectively. However, as the sum of alkyl CH, and paraffmic CH, carbons in various ranks of coal amounts to 35-53x of total CH, carbon content’, the CH,/aromatic carbon ratio of coal in Table I should be corrected for the presence of these CH, carbons. The corrected ratio is designated in parentheses. Figure 4 shows the plots of CH,/aromatic carbon ratios of solid products (residue, preasphaltene and asphaltene) against the corrected ratio for the parent coal. The dotted line shows a 1:l correlation. Although Figure 4 shows some scatter, the CH,/aromatic carbon ratios of all solid products clearly increase with the increase in corrected CH,/aromatic carbon ratio of the coal. It is noteworthy that the CH,/aromatic carbon ratios of all the solid products are close to that of the parent coal. These results suggest that the unit ring structure of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. Hence, the solid products are considered to be formed by the cleavage of bridges between structural units. The oil obtained under the mild liquefaction reaction conditions used is considered to retain some of the structural characteristics of the parent coal, although the
01 CH,/aromotlc
J 0.2 ratio
03
of coal
Figure 5 Variation of CHJaromatic carbon ratios of aromatic ringtype oil fractions with corrected CH,/aromatic carbon ratio of coal. 0, Fr-D; 0, Fr-T; A, Fr-PP,. (Symbols for coals are the same as in Figure 4
/’
U.L
U.1
CH,/aromatlc
ratlo
”
of coal
Figure 4 Variation of CH,/aromatic carbon ratios of solid products with corrected CHJaromatic carbon ratio of coal. 0, Asphaltene; 0, preasphaltene; A, residue; YA, Yallourn; SK, Soya-koishi; TA, Taiheiyo; HO, Horonai; AK, Akabira; SY, Shin-yubari
900
FUEL, 1985, Vol 64, July
oil is the most highly hydrogenated fraction. Figure 5 shows the plots of CH,/aromatic carbon ratios of aromatic ring-type oil fractions (except for Fr-M) against the corrected ratio for the coal. The amounts of naphthenic CH, and aromatic carbons for ring-type oil fractions were obtained from the area intensities of z 25-54 and zz 107-157 ppm in their solution 13C n.m.r. spectra, respectively. However, as the compound type analysis based on f.i.m.s. of ring-type oil fractions has proved that individual oil components have long alkyl side chains, considerable amounts of alkyl CH, carbon are probably included in the content of naphthenic CH, carbon obtained from the i3C n.m.r. spectra. Therefore, the CH,/aromatic carbon ratio in Table 2 is an overestimate. Nevertheless, correlations are clearly observed between coal and the fractions. The result indicates that oil fractions also reflect the structure of the parent coal. The fact that CHJaromatic carbon ratios of the oil fractions are significantly larger than those of the coals is due to the overestimation of naphthenic CH, carbon content due to the presence of alkyl CH, carbon or the hydrogenation of aromatic rings. The z series distribution in Figure 3 provides information on the distribution of compound types (ring structure) of oil components without being influenced by the presence of alkyl substituents. The pattern of the z
Liquefaction
I 75
I 70
I 65
Carbon
Figure 6 Variation with carbon content
content
I
I 80
of coal
( wt
of cycloparaIIins/parafns of coal
85 %, dmmf
)
molar
ratio
<
of Fr-P
- -
reaction
of coal. 2: T. Yoshida
et al.
series distribution varies with increase in the rank of coal. Namely, paraffins decrease and cycloparaffins increase in Fr-P, and the major components (z= - 8) in Fr-M decrease and the major components (z= - 14) in Fr-D increase with increase in the rank of coal. These observations indicate that the average aromatic ring size of the structural unit in coal increases with increase in the rank of coal. Thus, the z series distribution reveals the dependence of oil composition on the rank of coal. Hence a quantitative study of the structural correlation between coal and oil was undertaken. In Figure 6, the cycloparalXns/parafns molar ratio of Fr-P is plotted against the carbon content of coal. The cycloparaff~ns/parafns molar ratio of Fr-P is calculated from the amounts of paraffins (z = + 2) and cycloparaflins (z=O to - 10) in Figure 3. The positive relation obtained indicates that the saturated fraction from lowrank coals is rich in free paraffins and that from high-rank coals is rich in cycloparafflns. These results are probably caused by the difference in the composition of saturated components contained in various ranks of coal. In Figure 7 the hydroaromatics/aromatics molar ratios of fractions M, D and T are plotted against the corrected CH,/aromatic carbon ratio of coal. The hydroaromatics/aromatics molar ratio of Fr-M, for example, is calculated from the amounts of aromatic compound type (z = - 6) and hydroaromatic compound types (z = - 8 to -18) in Figure 3. Although Figure 7 shows some scatter of results, the ratios of all aromatic ring-type fractions tend to increase with the increase in the corrected CHJaromatic carbon ratio of the parent coal. F.i.m.s. of the fraction PP, is too complicated to obtain the z series distribution and hence the estimation of hydroaromatics/aromatics molar ratio of the fraction is difficult. However, the fraction PP,, has the same tendency as the fractions D and T in Figure 5, suggesting that the hydroaromatics/aromatics molar ratio of the fraction PP, is also proportional to the corrected CH,/aromatic carbon ratio of the parent coal. These results indicate that coal having a higher CH,/aromatic carbon ratio produces an oil rich in naphthenic structures. REFERENCES
CH,/aromatlc
mtto
of coal
Figure 7 Variation of hydroaromatics/aromatics molar ratio of ringtype oil fractions with corrected CHJaromatic carbon ratio of coal. 0, Fr-M; A, Fr-D; 0, Fr-T. (Symbols for coals are the same as in Figure 4)
Yoshida, T., Tokuhashi, K. and Maekawa, Y. Fuel 1985,64, 890 Yokoyama, S., Tsuzuki, N., Kato, T. and Sanada, Y. J. Fuel Sot. Jpn. 1978,57, 748 Yoshida, T., Maekawa, Y., Uchino, H. and Yokoyama, S. Ann/. Chem. 1980, 52, 817 Yoshida, T., Nakata, Y., Yoshida, R., Ueda, S., Kanda, N. and Maekawa, Y. Fuel 1982, 61, 824 Yoshida, T., Maekawa, Y., Higuchi, T., Kubota, E., Itagaki, Y. and Yokoyama, S. Bull. Chem. Sot. Jpn. 1981, 54, 1171 Yoshida, T., Maekawa, Y. and Shimada,T. Anal. Gem. 1982,54,967 Yokoyama, S., Uchino, H., Kato, T., Sanada, Y. and Yoshida, T. J. Fuel Sot. Jpn. 1979, 58, 837
FUEL,
1985,
Vol 64, July
901
reaction
correlation
of coal
between
coal and its liquefaction
Tadashi Yoshida, Kazuaki Tokuhashi*, Hideo Narita, Shin-ichi Yokoyama, and Yosuke Maekawa Government Industrial Development Laboratory, Hokkaido, 2-l 7 Jsukisamu-Higashi, Joyohira-ku, Sapporo 061-01, Japan * National Chemical Laboratory for Industry, I- 1 Higashi, Yatabe, Jsukuba, lbaragi Prefecture 305, Japan (Received 25 June 1984)
The structural correlation between coal and its liquefaction products has been examined using crosspolarization, magic angle spinning (CP/MAS) 13C n.m.r. and field ionization mass spectrometry (f.i.m.s.). The CHJaromatic carbon ratios of all solid products (asphaltene, preasphaltene and residue) were close to the corrected CHJaromatic carbon ratio for the coal. This suggests that the ring structure of the structural unit of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. The CHJaromatic carbon ratios of aromatic ring-type oil fractions also correlated with the corrected ratio for the coal, although they were larger. The z series distribution obtained from the f.i.m.s. of oil fractions revealed that coal with a higher CH,/aromatic carbon ratio produced
an oil rich in naphthenic structures. (Keywords: coal; liquefaction; f.i.ms.;
CP/MAS
“C n.m.r.)
In a previous paper’, the mechanism of depolymerization of coal was described on the basis of the results of a mild liquefaction reaction and distributions of oxygen and carbon atoms determined by CP/MAS 13C n.m.r. spectrometry. One of the most important results obtained in the study was that, under the experimental conditions used, the depolymerization of coal to oil proceeded essentially through the cleavage of ether bridges and subsequently CH, bridges, including some naphthenic CH, bonds. This suggests that the chemical structures of liquefaction products are closely related to that of the parent coal. Therefore, the elucidation of structural correlation between coal and its liquefaction products should be useful for the selection of raw coal for liquefaction and the evaluation of the oil produced. In this work, the structural correlation between coal and its liquefaction products has been examined using CP/MAS 13C n.m.r. and f.i.m.s.
from Fr-PP by washing with lOvol.% NaOH and with 10 vol.% H,SO, solution, respectively. The resultant neutral oil was named Fr-PP,,. Solution 13C n.m.r. spectra of ring-type oil fractions were obtained by a gateddecoupling technique which
Soyo-kolshl
Talhelyo
coal
coal
EXPERIMENTAL Briquettes of Yallourn coal and live Japanese coals ranging from 66.2 to 87.4 wt% C were used as sample coals. Details of the characteristics of the coals and the results of a mild liquefaction reaction with subsequent fractionation of products by solvent extraction have been described previously’. The oil (hexane solubles) was further separated, using a double-layered packed column of silica and alumina’, into five fractions of different ring type, namely saturates (Fr-P), monoaromatics (Fr-M), diaromatics (Fr-D), triand tetraaromatics (Fr-T), and poly- and polar aromatic compounds (Fr-PP). Acidic and basic oils were removed 00162361/85/070897-05$3.00 0 1985 Butterworth & Co. (Publishers)
Ltd
Chemical
shift
(ppm)
Figure 1 CP/MAS 13C n.m.r. spectra of residue, preasphaltene asphaltene from Soya-koishi and Taiheiyo coals
FUEL, 1985, Vol 64, July
and
897
Liquefaction
of coal. 2: T. Yoshida et al.
reaction
suppressed nuclear Overhauser enhancement3. Carbon atom distributions of asphaltene, preasphaltene and residue were obtained from their CP/MAS r3C n.m.r. spectra. Details of the measurement conditions and the Table
1
Carbon
distribution,
f, value and CHJaromatic
carbon
assignments of carbon atoms have been reported elsewhere’*4. The compound type analysis of oil components was carried out on the basis of the f.i.m.s. of fractions P, M, D and T5. No correction for the difference
ratio of coal and its solid products _
Carbon
distribution
(%)
Polar
Aromatic
CH,
CH,
f,
CH,/aromatic
Coal Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
22 19 13 5 6 6
57 51 54 61 66 71
I2 18 21 22 I5 12
9 12 12 12 12 11
0.57 0.51 0.54 0.61 0.66 0.71
0.21 0.35 0.39 0.36 0.23 0.17
Residue Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
17 17 14 12 9 8
67 63 62 60 68 72
8 12 14 17 13 I1
8 9 10 11 10 9
0.67 0.63 0.62 0.60 0.68 0.72
0.12 0.19 0.23 0.28 0.19 0.15
Preasphaltene Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
11 11 10 12 11 7
68 67 65 68 69 74
10 IO 12 10 10 9
11 13 I3 IO 10 10
0.68 0.67 0.65 0.68 0.69 0.74
0.15 0.15 0.18 0.15 0.14 0.12
69 68 69 67 70 71
16 16 17 18 I4 14
IO I1 IO II 13 12
0.69 0.68 0.69 0.67 0.70 0.71
0.23 0.24 0.25 0.27 0.20 0.20
Asphaltene Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari ” Values in parentheses
Table 2
are corrected
for alkyl CH,
Yield, f, value and CH,/aromatic
carbon
and paraflinic
CH,
ratio of ring-type
carbons
oil fraction
D
T
PP”
ratio
1.4 0 _
1.4 0.34 1.23
0.9 0.52 0.62
0.9 0.59 0.44
24.4 0.61 0.38
ratio
1.3 0 _
1.5 0.30 1.56
0.8 0.51 0.59
0.5 0.60 0.46
17.7 0.60 0.46
4.9 0
3.6 0.28 1.88
2.0 0.50 0.66
1.7 0.56 0.46
42.5 0.57 0.50
ratio
3.6 0 _
3.7 0.31 1.50
1.7 0.50 0.60
1.2 0.57 0.43
42.6 0.58 0.50
2.1
ratio
2.0 0 _
_
1.6 0.52 0.60
1.1 0.61 0.41
36.3 0.61 0.42
0.8 0.32 1.41
0.7 0.56 0.49
0.5 0.66 0.26
7.7 0.61 0.39
Soya-koishi Yield” carbon
Taiheiyo Yield” f, CH,/aromatic
carbon
ratio
Horonai Yield” f, CH,/aromatic Akabira Yield” .f, CHJaromatic
carbon
carbon
Shin-yubari Yield” f, CHJaromatic
1.4 0 carbon
ratio
y Wt%, dmmf coal basis
898
fraction
M
Yallourn Yield”
/, CH,/aromatic
(0.11) (0.22) (0.21) (0.23) (0.12) (0.08)
P
Coal
carbon
ratio
in coal
Ring-type
f, CH,/aromatic
carbon
FUEL, 1985, Vol 64, July
Liquefaction
reaction of coat. 2: T. Yoshida et al.
considerably higher in the asphaltenes. Considerable amounts of aliphatic carbon remained in the residue. Table 2 summarizes the yield, f, value and CH,/aromatic carbon ratio of the ring-type fraction of oil. Fraction PP, amounted to 7&85 wt% of the oil obtained and the yields of other fractions decreased in the order P, M, D and T. Thef, value increased in the order P, M. D. and T for every oil. Figure Zshows the f.i.m.s. of ring-type oil fractions from Soya-koishi coal. The molecular weight distribution of the fraction P covered an m/z range of 15&5OO.Aromatic ring-type fractions M and D had a similar mass range (m/z 130-370) and molecular weight distribution to each other, but the distributions of Fr-T and PP, were distinctly different from those of Fr-M and D. The number-average molecular weights of Fr-T and PP, were higher than those of Fr-M and D7. Figure 3 gives the distribution (z series distribution) of molar ratios of various compound types in the ring-type fractions of oils from Yallourn, Taiheiyo and Shin-yubari coals as obtained by the compound type analysis of f.i.m.s. The z series distribution of oil from Yallourn coal revealed the following major components: paraffins (z = + 2) for Fr-P, alkyl-substituted mononaphthenobenzenes (z = - 8) for Fr-M, alkyl-substituted mononaphthenonaphthalenes and biphenyls (z= - 14) for Fr-D, and alkyl-substituted phenanthrenes (z= - 18) and alkylsubstituted (poly)naphthenophenanthrenes (z = - 20, - 22) for Fr-T. For every aromatic ring-type fraction the contents of hydroaromatic compound types were larger than those of aromatic compound types.
F
I
Yallourn
16
1
M/L
Figure 2
F.i.m.s. of ring-type oil fractions from Soya-koishi coal
in relative ion sensitivities among oil components6 applied.
was Tal helyo
RESULTS CP/MAS ‘.‘C n.m.r. spectra of residue, preasphaltene and asphaltene from Soya-koishi and Taiheiyo coals are shown in Figure I. As illustrated in the spectra of products from Soya-koishi coal, the residue was rich in polar groups such as phenolic OH (including aromatic ether), COOH, =CO and -OCH, groups, and had a significant amount of aliphatic carbon. The asphaltene contained virtually no polar groups other than phenolic OH. Table 1 shows the carbon atom distribution, carbon aromaticity, fa, and CH,/aromatic carbon ratio of the parent coal, residue, preasphaltene and asphaltene, obtained from their CP/MAS *‘C n.m.r. spectra. The f, values of residue, preasphaltene and asphaltene were larger than that of the parent coal and the difference inf, value between coal and solid products was large in lowerrank coals and small in higher-rank coals. The variation of f, value with rank of coal increased in the order asphaltene, preasphaltene and residue. The CH, carbon content was lowest in the preasphaltenes and
Shin-yubarl
12 -
.z
Figure 3 z series distribution of oil from Yallourn, Taiheiyo and Shinyubari coals
FUEL, 1985, Vol 64, July
899
Liquefaction
reaction
of coal. 2: T. Yoshida
et al.
DISCUSSION As the liquefaction reaction of coal is accompanied by the elimination of functional groups and alkyl side chains, a parameter CH,/aromatic carbon ratio, which represents the ratio of naphthenic CH, to aromatic carbons in the unit ring structure, should be used to demonstrate the structural correlation between coal and its liquefaction products. Here, the amounts of naphthenic CH, and aromatic carbons for the solid products were obtained from the area intensities of z 25-51 and z 93-171 ppm in the CP/MAS i3C n.m.r. spectra, respectively. However, as the sum of alkyl CH, and paraffmic CH, carbons in various ranks of coal amounts to 35-53x of total CH, carbon content’, the CH,/aromatic carbon ratio of coal in Table I should be corrected for the presence of these CH, carbons. The corrected ratio is designated in parentheses. Figure 4 shows the plots of CH,/aromatic carbon ratios of solid products (residue, preasphaltene and asphaltene) against the corrected ratio for the parent coal. The dotted line shows a 1:l correlation. Although Figure 4 shows some scatter, the CH,/aromatic carbon ratios of all solid products clearly increase with the increase in corrected CH,/aromatic carbon ratio of the coal. It is noteworthy that the CH,/aromatic carbon ratios of all the solid products are close to that of the parent coal. These results suggest that the unit ring structure of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. Hence, the solid products are considered to be formed by the cleavage of bridges between structural units. The oil obtained under the mild liquefaction reaction conditions used is considered to retain some of the structural characteristics of the parent coal, although the
01 CH,/aromotlc
J 0.2 ratio
03
of coal
Figure 5 Variation of CHJaromatic carbon ratios of aromatic ringtype oil fractions with corrected CH,/aromatic carbon ratio of coal. 0, Fr-D; 0, Fr-T; A, Fr-PP,. (Symbols for coals are the same as in Figure 4
/’
U.L
U.1
CH,/aromatlc
ratlo
”
of coal
Figure 4 Variation of CH,/aromatic carbon ratios of solid products with corrected CHJaromatic carbon ratio of coal. 0, Asphaltene; 0, preasphaltene; A, residue; YA, Yallourn; SK, Soya-koishi; TA, Taiheiyo; HO, Horonai; AK, Akabira; SY, Shin-yubari
900
FUEL, 1985, Vol 64, July
oil is the most highly hydrogenated fraction. Figure 5 shows the plots of CH,/aromatic carbon ratios of aromatic ring-type oil fractions (except for Fr-M) against the corrected ratio for the coal. The amounts of naphthenic CH, and aromatic carbons for ring-type oil fractions were obtained from the area intensities of z 25-54 and zz 107-157 ppm in their solution 13C n.m.r. spectra, respectively. However, as the compound type analysis based on f.i.m.s. of ring-type oil fractions has proved that individual oil components have long alkyl side chains, considerable amounts of alkyl CH, carbon are probably included in the content of naphthenic CH, carbon obtained from the i3C n.m.r. spectra. Therefore, the CH,/aromatic carbon ratio in Table 2 is an overestimate. Nevertheless, correlations are clearly observed between coal and the fractions. The result indicates that oil fractions also reflect the structure of the parent coal. The fact that CHJaromatic carbon ratios of the oil fractions are significantly larger than those of the coals is due to the overestimation of naphthenic CH, carbon content due to the presence of alkyl CH, carbon or the hydrogenation of aromatic rings. The z series distribution in Figure 3 provides information on the distribution of compound types (ring structure) of oil components without being influenced by the presence of alkyl substituents. The pattern of the z
Liquefaction
I 75
I 70
I 65
Carbon
Figure 6 Variation with carbon content
content
I
I 80
of coal
( wt
of cycloparaIIins/parafns of coal
85 %, dmmf
)
molar
ratio
<
of Fr-P
- -
reaction
of coal. 2: T. Yoshida
et al.
series distribution varies with increase in the rank of coal. Namely, paraffins decrease and cycloparaffins increase in Fr-P, and the major components (z= - 8) in Fr-M decrease and the major components (z= - 14) in Fr-D increase with increase in the rank of coal. These observations indicate that the average aromatic ring size of the structural unit in coal increases with increase in the rank of coal. Thus, the z series distribution reveals the dependence of oil composition on the rank of coal. Hence a quantitative study of the structural correlation between coal and oil was undertaken. In Figure 6, the cycloparalXns/parafns molar ratio of Fr-P is plotted against the carbon content of coal. The cycloparaff~ns/parafns molar ratio of Fr-P is calculated from the amounts of paraffins (z = + 2) and cycloparaflins (z=O to - 10) in Figure 3. The positive relation obtained indicates that the saturated fraction from lowrank coals is rich in free paraffins and that from high-rank coals is rich in cycloparafflns. These results are probably caused by the difference in the composition of saturated components contained in various ranks of coal. In Figure 7 the hydroaromatics/aromatics molar ratios of fractions M, D and T are plotted against the corrected CH,/aromatic carbon ratio of coal. The hydroaromatics/aromatics molar ratio of Fr-M, for example, is calculated from the amounts of aromatic compound type (z = - 6) and hydroaromatic compound types (z = - 8 to -18) in Figure 3. Although Figure 7 shows some scatter of results, the ratios of all aromatic ring-type fractions tend to increase with the increase in the corrected CHJaromatic carbon ratio of the parent coal. F.i.m.s. of the fraction PP, is too complicated to obtain the z series distribution and hence the estimation of hydroaromatics/aromatics molar ratio of the fraction is difficult. However, the fraction PP,, has the same tendency as the fractions D and T in Figure 5, suggesting that the hydroaromatics/aromatics molar ratio of the fraction PP, is also proportional to the corrected CH,/aromatic carbon ratio of the parent coal. These results indicate that coal having a higher CH,/aromatic carbon ratio produces an oil rich in naphthenic structures. REFERENCES
CH,/aromatlc
mtto
of coal
Figure 7 Variation of hydroaromatics/aromatics molar ratio of ringtype oil fractions with corrected CHJaromatic carbon ratio of coal. 0, Fr-M; A, Fr-D; 0, Fr-T. (Symbols for coals are the same as in Figure 4)
Yoshida, T., Tokuhashi, K. and Maekawa, Y. Fuel 1985,64, 890 Yokoyama, S., Tsuzuki, N., Kato, T. and Sanada, Y. J. Fuel Sot. Jpn. 1978,57, 748 Yoshida, T., Maekawa, Y., Uchino, H. and Yokoyama, S. Ann/. Chem. 1980, 52, 817 Yoshida, T., Nakata, Y., Yoshida, R., Ueda, S., Kanda, N. and Maekawa, Y. Fuel 1982, 61, 824 Yoshida, T., Maekawa, Y., Higuchi, T., Kubota, E., Itagaki, Y. and Yokoyama, S. Bull. Chem. Sot. Jpn. 1981, 54, 1171 Yoshida, T., Maekawa, Y. and Shimada,T. Anal. Gem. 1982,54,967 Yokoyama, S., Uchino, H., Kato, T., Sanada, Y. and Yoshida, T. J. Fuel Sot. Jpn. 1979, 58, 837
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