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Liquefaction reaction of coal
Liquefaction
reaction
of coal
1. Depolymerization methylene bridges
of coal by cleavages
Tadashi
Tokuhashi*
Yoshida,
Kazuaki
and Yosuke
of ether
and
Maekawa
Government Industrial Development laboratory, Hokkaido, 2- 17 Tsukisamu- Higashi, Toyohira-ku, Sapporo 061-07, Japan *National Chemical Laboratory for Industry, I- 1 Higashi, Yatabe, Tsukuba, lbaragi Prefecture 305, Japan (Received 25 June 1964)
The roles of ether and methylene bridges in the depolymerization of coal have been reevaluated on the basis of the results of a mild liquefaction reaction (4OOC, 30 min) and the distributions of oxygen and carbon atoms obtained by cross-polarization, magic angle spinning (CP/MAS) ’ %Zn.m.r. spectrometry. Coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as sample coals. The content of etheric oxygen was < 3.7 per 100 carbon atoms and the cleavage of ether bridges contributed to the formation of preasphaltene. The conversion to hexane solubles in the mild liquefaction reaction correlated well with CH, carbon content of coal, though the conversion to pyridine solubles did not. These results suggest that the formation of oil from preasphaltene is caused by the scission of CH, bridges and some naphthenic CH, bonds. The phenolic OH oxygen-rich portions in coal tended to remain as a residue formed by the condensation reaction of phenolic OH groups. (Keywords: coal; liquefaction; depolymerization;
CP/MAS
“C n.mr.)
The reactivity of coal in liquefaction reactions must be influenced by its chemical structure’ and hence a knowledge of the relationship between reactivity and structure is useful for the elucidation of the liquefaction mechanism, and eventually for the appraisal of coal as the material for liquefaction processes. The relations between such coal parameters as carbon content, atomic H/C ratio, volatile matter and volatile carbon, and the reactivity of coal have already been studied 2-4 . However, these parameters do not directly reflect chemical structure of coal, and therefore even if some relation is found between one of these parameters and reactivity, it is impossible to know what structure of the coal is responsible for the observed reaction. Coal is considered to contain relatively small polycyclic aromatic and hydroaromatic rings as structural units, connected by ether and methylene bridges to form a macromolecular structure. The depolymerization of coal is therefore believed to proceed through cleavage of these bridges5v6. In the present Paper, the roles of ether and CH, bridges in the depolymerization of different ranks of coal have been reevaluated on the basis of the results of a mild liquefaction reaction and the distributions of carbon and oxygen atoms obtained from their CP/MAS ’ 3C n.m.r. spectra. EXPERIMENTAL Briquettes of Yallourn brown coal (from Australia) and live Japanese coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as samples. The coals were pulverized to > 149 pm (100 mesh ASTM sieve) and dried in a vacuum at 107°C for 12 h before being used in the autoclave 001&2361/85/070890-07%3.00 0 1985 Buttenvorth & Co. (Publishers) Ltd 890 FUEL, 1985, Vol 64, July
experiments. Ultimate analysis of coal and reaction products was performed using a C,H,N analyser (MT-3, Yanagimoto Co. Ltd) and an 0 analyser (MOX-10, Yanagimoto Co. Ltd). The liquefaction reaction was carried out in a rotating 10 dm3 autoclave. A well shaken mixture of 200 g coal with 20 g Adkins catalyst was charged into the autoclave together with 20 stainless steel balls for stirring. Heating was started under an initial hydrogen pressure of 9.81 MPa, and continued to give a temperature rise of 3°C min-’ until 400°C was reached. This temperature was held for 30 min. During heating, the autoclave was rotated at a rate of 80 rev min-‘. To facilitate the analysis of reaction products, no vehicle oil was used. After the heating period was completed, volatile hydrocarbons (C,C,) and carbon oxide gases (CO,) produced were analysed by g.c. Hydrogen consumption and the yields of gases were calculated from the composition and volume of product gases. Water formed was determined by the distillation method (ASTM D1160). About 30g of nongaseous products were separated into oil (soluble in hexane), asphaltene (insoluble in hexane but soluble in benzene), preasphaltene (insoluble in benzene but soluble in pyridine) and residue (insoluble in pyridine) by the solvent extraction method. Carbon distribution in coal and solid products was examined by using CP/MAS 13C n.m.r. Measurement conditions were based on the results of preliminary experiments. The contact time employed was 2 ms for Yallourn, Soya-koishi and Taiheiyo coals, and 3 ms for Horonai, Akabira and Shin-yubari coals, which gave a maximal carbon aromaticity (f,) for every coal. Pulse repetition times were 8-l 2 s, which caused no reduction of f, value due to the progressive saturation of aromatic
Liquefaction
reaction
et al.
of coal. 7: T. Yoshida
Table 1 Proximate and ultimate analyses of coals Ultimate analysis (wt%>dmmf)
Proximate analysis (wt%)
Atomic ratio
Coal
Volatile matter
Fixed carbon
Low temperature ash
C
H
0”
H/C
O/C
Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
43.2 33.6 49.6 47.9 41.7 34.7
37.6 35.3 33.8 46.1 51.2 56.7
1.7 22.9 13.8 7.0 5.7 9.6
66.2 72.0 76.6 81.1 83.2 87.4
3.9 5.5 6.2 6.5 6.3 6.2
29.4 21.1 15.9 10.9 8.6 4.6
0.701 0.909 0.964 0.954 0.901 0.845
0.333 0.220 0.156 0.101 0.078 0.039
0 Value determined by an oxygen analyser Table 2
Distribution of carbon atoms in coal Distribution (74)
Yallourn
Coal
Polar
Aromatic
CH,
c&H,
B-CH,
f,
Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
22 19 13 5 6 6
57 51 54 61 66 71
12 18 21 22 15 12
5 7 8 8 7 6
4 5 4 4 5 5
0.57 0.51 0.54 0.61 0.66 0.71
Soya - kolshl C
72 0 “I.
Shin - yubori c
a7 4%
I 240
I
I 160 Chemical
1
I
80 shift
I
I 0
( ppm)
Figure 1 CP/MAS t3C n.m.r. spectra of sample coals
carbon signals. Assignments of carbon atoms have been described in a previous paper7. The acetylation method for determining phenolic OH oxygen has been reported elsewhere’. RESULTS Table I shows the proximate
and ultimate analyses and atomic H/C and O/C ratios of the coals. Figure 1 shows the CP/MAS i3C n.m.r. spectra of Yallourn, Soya-koishi, Taiheiyo and Shin-yubari coals.
The low-rank coals such as Yallourn and Soya-koishi coals indicated line structures especially in the aromatic regions of their spectra, which were due to the presence of carbonyl, carboxyl, phenolic OH, methoxy groups and aromatic ether bridges. However, Shin-yubari coal showed no signal in the region beyond z 170 ppm, providing a simple spectral feature in the aromatic regions. Table 2 indicates carbon distributions obtained from the n.m.r. spectra. The amounts of polar groups, particularly carboxyl and carbonyl groups, decreased rapidly with increase in the carbon content of the coal. Aromatic carbon was least abundant in Soya-koishi coal and increased with increasing carbon content of coal except for Yallourn coal. Briquettes of Yallourn coal had a relatively large amount of aromatic carbon despite having the lowest carbon content among the coals used. Atiphatic carbon was most abundant in Taiheiyo and Horonai coals. These coals showed the highest CH, carbon content. All coals used had almost the same level of CH, carbon content. Table 3 shows the results of the coal liquefaction reaction under mild conditions (4C!O“C,30 min). Yield of hydrocarbon gases (C,C,) was small for every coal. The yields of CO, and water decreased markedly as the carbon content of the coal increased. The ratio of deoxygenation ranged between 39 and 70”/ and decreased with increase in the carbon content of coal except for Yallourn coal. The yield of oil was high for Taiheiyo, Horonai and Akabira coals, and small for Yallourn, Soya-koishi and Shinyubari coals. DISCUSSION Distributions
of carbon and oxygen
atoms
The change in f, value with rank of coal except for Yallourn coal (Table 2) agrees well with the results reported by other authors9,10. Briquettes of Yallourn coal showed anf, value higher than that for Soya-koishi coal. This unexpected observation may be interpreted as the
FUEL,
1985, Vol 64, July
891
Liquefaction Table 3
reaction
of coal. 1: T. Yoshida
et al.
Experimental results for liquefaction reaction of coal (wt”,;, dmmf coal basis) Yallourn
Soya-koishi
Taiheiyo
Horonai
Akabira
Shin-yubari
Hydrogen consumption Gas CIC7, CO, Water Oil Asphaltene Preasphaltene Residue + loss
4.0 17.0 4.3 12.7 9.1 28.8 16.7 6.7 21.7
4.8 11.8 2.6 9.2 9.2 21.9 14.1 11.2 36.6
3.8 5.8 3.7 2.1 6.3 54.1 15.6 5.0 16.3
2.9 4.2 3.2 1.0 4.0 52.7 15.5 3.8 22.6
2.8 4.0 3.3 0.7 3.3 43.0 20.7 10.8 21.1
1.1 1.8 1.2 0.6 1.6 11.1 35.7 26.7 24.2
Ratio of deoxygenation (%) GCOX 0 Hz0
51.9 30.4 27.5
69.3 30.5 38.8
44.1 8.9 35.2
38.9 6.3 32.6
39.2 5.1 34.1
39.3 8.4 30.9
Table 4
Distribution of oxygen atoms in coal”
o/c
x 100 (“/,)
Coal
=CO,
COOH
ArrOH
*CH,
Ar-O-Ar
c-o-c
Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
7.9 3.3 1.9 0 0 0
7.7 5.5 3.2 1.7 1.2 0
9.7 9.1 7.0 5.6 4.7 2.5
4.0 2.3 1.6 2.3 1.1 0.7
2.9 1.1 1.2 0.2 0.55 0.66
0.8 0.7 0.5 0.2 0.1 0
oOH/“corl
W 29 41 45 55 60 64
“Vafues obtained by assuming that alcohols are not present in coal
result of the dehydrogenation from hydroaromatic structures by heat treatment at the time of briquette preparation. Untreated Yallourn coal gave an fa value (% 0.50) close to that of Soya-koishi coal. The content of CH, carbon is dependent on the rank of coal, though that of CH, carbon is independent. Therefore the difference in atomic H/C ratio found among the coals is mainly due to the content of CH, group, not that of CH, group. This behaviour agrees with the results of Fourier transform infrared (FT-i.r.) spectrometry reported by Painter et al.“. Table 4 shows the amounts of various types of oxygen atom in the coals determined by the combined use of the CP/MAS 13C n.m.r. spectrometry and the acetylation method”. Phenolic OH oxygen is most abundant in every coal and the ratio of phenolic OH oxygen to total oxygen (O,,/O,,,,) increases with the increase in carbon content of coal, ranging from 29% for Yallourn coal to 64% for Shin-yubari coal. Carbonyl and carboxyl groups are also abundant in low-rank coals. However, they decrease rapidly with increasing carbon content of coal, suggesting that they are easily eliminated in the course of coalilication. It is particularly noteworthy that etheric oxygens are present in a smaller amount than expected in every coal and are distributed as aromatic rather than aliphatic ether. The slight increase in the amount of aromatic etheric oxygen in Akabira and Shin-yubari coals is probably caused by the presence of oxygencontaining heterocyclics such as dibenzofurani3. Role
ofether bridges in the depolymerization of coal
The role of ether bridges in the depolymerization of coal is examined on the basis of the amount of etheric oxygen in Table 4. The ether bridges in coal are assumed to be distributed homogeneously because the conversion to pyridine solubles, produced by the cleavage of ether
892
FUEL, 1985, Vol 64, July
bridges at the early stages of depolymerization, amounts to 7&80 wt%i4. Table 5 shows the calculated molecular weights of reaction intermediates produced by the cleavage of ether bridges. Here the average aromatic ring size of structural units of coal is assumed to be l-2 for Yallourn, Soya-koishi and Taiheiyo coals, 2-3 for Horonai and Akabira coals, and 34 for Shin-yubari coal, based on many works 11’13.15*16. Themolecular weightsof the reaction intermediates can be calculated as follows, taking Soya-koishi coal as an example. Soya-koishi coal (ji = 0.5 1) has an average aromatic ring size equal to one to two, corresponding to 12-20 carbon atoms in an average structural unit. Based on the results of ultimate analysis of the coal, the structural unit is formulated to be between C,,H,,.,02.6 (MW= 197) and C20Hl,,,04,4 (MW = 329). Hence, there should be one ether oxygen per 2.884.6 structural units, namely per molecular weight of z 910. Table 5 indicates that the calculated molecular weights of the intermediates from all coals except for Taiheiyo coal are larger than the vapour pressure osmometry (v.p.0.) values for asphaltenes obtained from the liquefaction reaction. As described previously, the content of aromatic ether in Akabira and Shin-yubari coals is overestimated due to the presence of heterocyclic compounds and, therefore, the true molecular weights of the intermediates should be larger than the values in Table 5. These results suggest that the cleavage of ether bridges contributes to the formation of preasphaltene. Figure 2 illustrates the model structure for the reaction intermediate of Soya-koishi coal produced by the cleavage of ether bridges. The model is produced in an effort to understand the depolymerization mechanism of coal. The numbers of CH, bridges and naphthenic CH, carbons are estimated on the basis of CH, carbon distribution in Figure 3. Figure 3 shows the percentages of various types of CH, carbon to total CH, carbon content
Liquefaction Table 5
Calculated
molecular
weights
of reaction
intermediates
produced
by cleavage
reaction
of coal. 1: T. Yoshida
et al.
of ether bridge
Coal
R,
f,
NC
Formula”
MW,
Yallourn
1-2
0.57
11-18
C,,H,.KL, C,,HIL&,.,
(199) (325)
Soya-koishi
1-2
0.51
12-20
C,,H,,.,% &HI s.t%.,
Taiheiyo
l-2
0.54
11-19
Horonai
2-3
0.61
Akabira
2-3
Shin-yubari
34
V.p.o.6
Ne
MWi
2.5 1.5
3.7
490
356
(197) (329)
4.6 2.8
1.8
910
446
C,,H,,.,%, C,,H,s.,%
(171) (294)
5.3 3.1
1.7
910
917
16-23
C16H15.301.6 CZ~HZI.@Z.~
(233) (335)
15.6 10.9
0.4
3640
681
0.66
15-21
C,,H,,.,& [email protected]
(213) (297)
10.3 7.3
0.65
2180
707
0.71
20-23
C,,H,,.,O,.s C,,H,,.,%,
(270) (310)
7.6 6.6
0.66
2040
618
N”
“Formula for structural units b V.p.0. value of asphaltene obtained by mild liquefaction reaction R,, Number of aromatic rings in a structural unit; NC, number of carbon atoms in a structural unit; MW,, molecular weight of structural number of structural units per etheric oxygen atom; N,, number of etheric oxygen atoms per 100 carbon atoms; MW,, calculated molecular reaction intermediate produced by cleavage of ether bridge
r___---__------_-----------
unit; N,, weight of
1
I
I
I
Naphthenrc (lncludlng
CH, CH2 bridge
)
I I I
I I I I I
I
I L__________________________J
I
Figure 2 Model structure coal produced by cleavage
for the reaction intermediate of ether bridges
I-
Paraffinlc CH2 + cycloparafflnlc CH2
‘.
of Soya-koishi
\
\a
I--
for various ranks of coal. The content of paraftinic CH, carbon is calculated from the yield of saturated hydrocarbon (paraffins and cycloparafhns) fraction obtained from the liquefaction reaction at 400°C for 30 min. The yield of the fraction is considered to correspond roughly to the amount of saturated components in coal, as it has been reported that the fraction is formed at the early stages of the reaction I7 . The content of alkyl CH, carbon is estimated by the amount of B-CH, group in Table 2, with the assumption that alkyl groups in coal consist mainly of methyl and ethyl groups. The sum of these methylene carbons amounts to 35553% of total CH, carbon content for various ranks of coal. Therefore, the residual methylene carbons should be assigned to naphthenic CH, carbon, including CH, bridges, which are sensitive to scission. Thus, on average, the reaction intermediates of Soya-koishi coal have 6.2 CH, bridges and naphthenic CH, carbon atoms. The model structure in Figure 2 indicates that the scission of CH2 bridges and some naphthenic CH2 bonds is involved when the reaction intermediate is further depolymerized to oil molecules. Formation of oil molecules Figure 4 shows the relationship between aliphatic carbon contents of various ranks of coal and the oil yields obtained. Figure 4a shows that there is a poor correlation between the oil yield and total aliphatic carbon content
‘\ o\
,-
Alkyl
I
I
I
65
75
85 dmmf)
Carbon
Figure 3
CH,
Distribution
content
of various
of coal
(wt%,
types of methylene
carbon
in coal
(CH, +CH,). On the other hand, Figure 4b indicates that the oil yield gives a better correlation with CH, carbon content (solid line). This is in agreement with the results of an FT-i.r. spectrometric study recently reported by Senftle et al.‘*. However, the graph of oil yield against CH, carbon content does not go through the origin, indicating that ~8% of the CH2 groups are not involved in the production of oil. Methylene bridges play an important role in the depolymerization of coal to oil, and naphthenic CH2 and paraflinic CH2 groups contribute to an increase in the yield of oil. In contrast, alkyl CH2 groups are consumed only for the generation of hydrocarbon gas. Therefore, the oil yield should correlate with the amount
FUEL, 1985, Vol 64, July
893
Liquefaction
reaction
of coal.
1: T. Yoshida
et al asphaltene on the CH, carbon content of coal is considered to arise from: 1. the increase in the amounts of CH, bridges and naphthenic CH, carbons being sensitive to scission, 2. the increase in the solubility of oil components with the increase in the number of naphthenic rings, and 3. the increase in the amount of transferable hydrogen with the increase in naphthenic CH2 content. It would appear, therefore, that oil and asphaltene are produced by the scission of CH2 bridges and some naphthenic CH2 bonds. Table 6 shows the calculated molecular weight of oil produced by the scission of 20 or 500/,of CH2 bridges and naphthenic CH2 bonds. The calculated molecular weight of oil agrees roughly with the field ionization mass
a 60 t
I
0 12
I
I
I
20
I
28
(CH2+CH3)/Cx100
I 36
(“1.) SY -0
01 0
I
I
I CH,
L
I
8 /C
16 x 100
HO
I
(“1.1
of CH, carbons excluding alkyl CH, carbon. The broken line in Figure 4b represents such a plot on the basis of the CH, carbon distribution in Figure 3 and shows that the yield of oil is directly proportional to the sum of CH, groups other than alkyl CH2. Figure 5 shows the relationships between CH2 carbon content of coal and conversions to pyridine solubles and benzene solubles. The conversion to pyridine solubles is independent of CH, carbon content except for Yallourn and Soya-koishi coals, in contrast to the conversion to benzene solubles. The formation of a reaction intermediate such as preasphaltene appears to be achieved by the cleavage of ether bridges alone and hence is not dependent on the CH2 carbon content of the coal. However, dependence of the yields of extractable oil and
FUEL, 1985, Vol 64, July
TAfi
24
Figure 4 Relationship between oil yield and aliphatic carbon content ofcoal. (a), Ya, Yallourn; SK, Soya-koishi; TA, Taiheiyo; HO, Horonai; AK, Akabira; SY, Shin-yubari. (b), 0, plots of oil yield against total CH z carbon content; 0, plots of oil yield against sum of CH, carbons excluding alkyl CH,
894
AK a
01
0
I
I
I 8 CH2/C
I
I 16 x 100 (“I.)
I 24
Figure 5 Relationships between conversions to pyridine solubles and benzene solubles and CH, carbon content of coal. 0, Pyridine solubles; 0, benzene solubles. (Symbols for coals are the same as in Figure 4) Table 6 Calculated molecular weights of oil produced CH, bridges and naphthenic CH, bonds
by scissions
of
Coal
MWt
Nb
;:;a,
MW
Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
490 910 910 3640 2180 2040
1.7 6.2 6.7 35.8 12.2 8.6
26(t370 22&410 21&390 190-450 31&630 38t3-750
320 340 325 320 360 350
MW,, Calculated molecular weight of reaction by cleavage of ether bridges; N,, number of CH, CH, carbon atoms per reaction intermediate; cular weight of oil produced by scission of 20 or
intermediate produced bridges and naphthenic MW,, calculated moleSOA of CH, bridges and
naphthenic CHZ bonds; MW, mean molecular fraction determined by f.i.m.s.
weight of the neutral
oil
Liquefaction
reaction of coal. I: T. Yoshida et al.
spectrometry (f.i.m.s.) value for the neutral oil fraction obtained from the liquefaction reaction. This value is close to the calculated molecular weight of oil produced by the cleavage of 20”/, CH2 bonds for lower-rank coals, and to that of oil produced by the cleavage of 50% CH2 bonds for higher-rank coals. In conclusion, the depolymerization of coal to oil proceeds essentially through the cleavage of ether and CH2 bridges including naphthenic CH2 bonds. Formation of residue Figure 6 shows the oxygen balance between phenolic OH groups in coal and water produced during the liquefaction. All of the phenolic OH oxygen and half the carboxylic oxygen are considered to be sources of water. Therefore, the subtraction of half the carboxylic oxygen from the amount of oxygen in water produced (OHI, - l/2 0 coo”) gives the amount of phenolic OH oxygen converted to water. As shown in Figure 6, the ratio of phenolic OH oxygen converted to water to total oxygen in coal C(0” 0 - l/2 %0HY%%J increases with increase in ratio. However, the conversion of phenolic OH Ool4/fOc0,1 oxygen to water (broken line in Figure 6) is 44-64x and is larger in lower-rank than in higher-rank coals. Thus, it has become apparent that zSoO/, of the phenolic OH oxygen in coal remains unreacted. Figure 7 shows the relationship between the OoH/Ocoa, ratio and the ratio of O/C of each product to that of coal [(O/C,,)/(O/C,,,)]. In the ultimate analysis of residue, the contents of C, H and 0 were corrected for the effects of ash and catalyst. The atomic O/C ratio of the product increases in the order asphaltene, preasphaltene and residue, and the (0&,)/(0/C,,,,) ratio of each product increases with increase in OOH/O,.Oal.Furthermore, the ratio is larger than 1.0 in all the residues except for that from Yallourn coal, and in preasphaltenes from high-rank coals. These results lead to the following conclusions.
1. The phenolic OH oxygen tends to remain in the residues and preasphaltenes. This is supported by the fact that the signals of aromatic carbons substituted by
.-. 80
1
I
80 -
Figure 7 Relationship between ratio of phenolic OH oxygen to total oxygen and ratio of O/C of each product to that of coal. 0, Residue; A, preasphaltene; 0, asphaltene
the phenolic OH oxygen or aromatic ether oxygen are clearly observed in the CP/MAS ’ 3C n.m.r. spectra of residues and preasphaltenes. The presence of phenolic OH oxygen results in the depression of depolymerization of coal due to the hydrogen bonding” or promotes the production of more stable and higher molecular weight materials (residue) via oxygen-bridging by the condensation reaction of phenolic OH groups”. The phenolic OH oxygen atoms are distributed heterogeneously in coal. If they are distributed homogeneously, the (O/C,,,)/(O/C,,,,) ratios of the residues and preasphaltenes must be < 1.0 because of deoxygenation during liquefaction. In conclusion, phenolic OH oxygen-rich portions in coal produce higher molecular weight materials by the formation of new oxygen bridges and hence are apt to remain as residue.
REFERENCES 1 2 3 4 5 6 7 8 9 10
Owl
0
Figure 6
I
I
20
I
I
40 o,,/o,,,
I
I
60 , (%/.)
I
I
80
JO
100
Oxygen atom balance Between phenolic OH groups in coal
and water produced. 0, (OH,0 - l/2 QmB)/Ocod
0, (o,@ - l/2 @mH)/aH the same as in Figure 4)
uersus OOB/Oooat;
11 12 13
uersus@,H&,,l. (Symbdsfor coals are 14
Whitehurst, D. D., Mitchell, T. 0. and Farcasiu, M. in ‘Coal Liquefaction, The Chemistry and Technology of Thermal Processes’, Academic Press, 1980, ch. 5 Imuta, K., Yamakawa, T., Ouchi, K., Tsukada, K., Morotomi, H., Shimura, K. and Miyazu, T. J. Fuel Sot. Jpn. 1979, 58, 754 Given. P. H., Cronauer, D. C., Spackman, W., Lovell, H. L., Davis, A. and Biswas, B. Fuel 1975, 54, 40 Whitehurst, D. D. Am. Chem. Sot. Symp. Ser. 1980, 139, 75 Takegami, Y., Kajiyama, S. and Yokokawa, C. Fue[ 1963,42,291 Maekawa, Y., Shimokawa, K., Ishii, T. and Takeya, G. J. Fuel Sot. Jpn. 1967,&i, 927 Yoshida, T., Nakata, Y., Yoshida, R., Ueda, S., Kanda, N. and Maekawa, Y. Fuel 1982,61, 824 Hasegawa, Y., Tokuhashi, K. and Maekawa, Y. in ‘Proc. 17th Conf. Coal Sci.‘, Fuel Sot. Jpn, 1980, p. 5 Maciel, G. E., Bartuska, V. J. and Miknis, F. P. Fuel 1979,58,391 Dereppe, J. M., Boudou, J. P., Moreaux, C. and Durand, B. Fuel 1983,62, 575 Painter, P. C., Kuehn, D. W., Starsinic, M., Davis, A., Havens, J. R. and Koenig, J. L. Fuel 1983, 62, 103 Yoshida, T., Tokuhashi, K., Narita, H., Hasegawa, Y. and Maekawa, Y. Fuel 1984,63, 282 Hayatsu, R., Winans, R. E., Scott, R. G., Moore, L. P. and Studier, M. H. Fuel 1978,57, 541 Whitehurst, D. D. Am. Chem. Sot. Symp. Ser. 1980,139, 316
FUEL, 1985, Vol 64, July
895
liquefaction 15 16 17
896
reaction
of coal. 1: T. Yoshida et al.
Iwata, K., Itoh, H. and Ouchi, K. Fuel Process. Technol. 1980,3, 25 Iwata, K., Itoh, H., Ouchi, K. and Yoshida, T. Fuel Process. Technol. 1980, 3, 221 Inoue, K., Yokoyama, S. and Sanada, Y. Fuel 1982,61, 245
FUEL, 1985, Vol 64, July
18 19 20
Senftle, J. T., Kuehn, D., Davis, A., Brozoski, B., Rhoads, C. and Painter, P. C. Fuel 1984.63, 245 Szladow, A. J. and Given, P. H. Am. Chem. Sot. Div. Fuel Chem. Prepr. 1978, 23(4), 161 Ouchi, K. Carbon 1966, 4, 59
reaction
of coal
1. Depolymerization methylene bridges
of coal by cleavages
Tadashi
Tokuhashi*
Yoshida,
Kazuaki
and Yosuke
of ether
and
Maekawa
Government Industrial Development laboratory, Hokkaido, 2- 17 Tsukisamu- Higashi, Toyohira-ku, Sapporo 061-07, Japan *National Chemical Laboratory for Industry, I- 1 Higashi, Yatabe, Tsukuba, lbaragi Prefecture 305, Japan (Received 25 June 1964)
The roles of ether and methylene bridges in the depolymerization of coal have been reevaluated on the basis of the results of a mild liquefaction reaction (4OOC, 30 min) and the distributions of oxygen and carbon atoms obtained by cross-polarization, magic angle spinning (CP/MAS) ’ %Zn.m.r. spectrometry. Coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as sample coals. The content of etheric oxygen was < 3.7 per 100 carbon atoms and the cleavage of ether bridges contributed to the formation of preasphaltene. The conversion to hexane solubles in the mild liquefaction reaction correlated well with CH, carbon content of coal, though the conversion to pyridine solubles did not. These results suggest that the formation of oil from preasphaltene is caused by the scission of CH, bridges and some naphthenic CH, bonds. The phenolic OH oxygen-rich portions in coal tended to remain as a residue formed by the condensation reaction of phenolic OH groups. (Keywords: coal; liquefaction; depolymerization;
CP/MAS
“C n.mr.)
The reactivity of coal in liquefaction reactions must be influenced by its chemical structure’ and hence a knowledge of the relationship between reactivity and structure is useful for the elucidation of the liquefaction mechanism, and eventually for the appraisal of coal as the material for liquefaction processes. The relations between such coal parameters as carbon content, atomic H/C ratio, volatile matter and volatile carbon, and the reactivity of coal have already been studied 2-4 . However, these parameters do not directly reflect chemical structure of coal, and therefore even if some relation is found between one of these parameters and reactivity, it is impossible to know what structure of the coal is responsible for the observed reaction. Coal is considered to contain relatively small polycyclic aromatic and hydroaromatic rings as structural units, connected by ether and methylene bridges to form a macromolecular structure. The depolymerization of coal is therefore believed to proceed through cleavage of these bridges5v6. In the present Paper, the roles of ether and CH, bridges in the depolymerization of different ranks of coal have been reevaluated on the basis of the results of a mild liquefaction reaction and the distributions of carbon and oxygen atoms obtained from their CP/MAS ’ 3C n.m.r. spectra. EXPERIMENTAL Briquettes of Yallourn brown coal (from Australia) and live Japanese coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as samples. The coals were pulverized to > 149 pm (100 mesh ASTM sieve) and dried in a vacuum at 107°C for 12 h before being used in the autoclave 001&2361/85/070890-07%3.00 0 1985 Buttenvorth & Co. (Publishers) Ltd 890 FUEL, 1985, Vol 64, July
experiments. Ultimate analysis of coal and reaction products was performed using a C,H,N analyser (MT-3, Yanagimoto Co. Ltd) and an 0 analyser (MOX-10, Yanagimoto Co. Ltd). The liquefaction reaction was carried out in a rotating 10 dm3 autoclave. A well shaken mixture of 200 g coal with 20 g Adkins catalyst was charged into the autoclave together with 20 stainless steel balls for stirring. Heating was started under an initial hydrogen pressure of 9.81 MPa, and continued to give a temperature rise of 3°C min-’ until 400°C was reached. This temperature was held for 30 min. During heating, the autoclave was rotated at a rate of 80 rev min-‘. To facilitate the analysis of reaction products, no vehicle oil was used. After the heating period was completed, volatile hydrocarbons (C,C,) and carbon oxide gases (CO,) produced were analysed by g.c. Hydrogen consumption and the yields of gases were calculated from the composition and volume of product gases. Water formed was determined by the distillation method (ASTM D1160). About 30g of nongaseous products were separated into oil (soluble in hexane), asphaltene (insoluble in hexane but soluble in benzene), preasphaltene (insoluble in benzene but soluble in pyridine) and residue (insoluble in pyridine) by the solvent extraction method. Carbon distribution in coal and solid products was examined by using CP/MAS 13C n.m.r. Measurement conditions were based on the results of preliminary experiments. The contact time employed was 2 ms for Yallourn, Soya-koishi and Taiheiyo coals, and 3 ms for Horonai, Akabira and Shin-yubari coals, which gave a maximal carbon aromaticity (f,) for every coal. Pulse repetition times were 8-l 2 s, which caused no reduction of f, value due to the progressive saturation of aromatic
Liquefaction
reaction
et al.
of coal. 7: T. Yoshida
Table 1 Proximate and ultimate analyses of coals Ultimate analysis (wt%>dmmf)
Proximate analysis (wt%)
Atomic ratio
Coal
Volatile matter
Fixed carbon
Low temperature ash
C
H
0”
H/C
O/C
Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
43.2 33.6 49.6 47.9 41.7 34.7
37.6 35.3 33.8 46.1 51.2 56.7
1.7 22.9 13.8 7.0 5.7 9.6
66.2 72.0 76.6 81.1 83.2 87.4
3.9 5.5 6.2 6.5 6.3 6.2
29.4 21.1 15.9 10.9 8.6 4.6
0.701 0.909 0.964 0.954 0.901 0.845
0.333 0.220 0.156 0.101 0.078 0.039
0 Value determined by an oxygen analyser Table 2
Distribution of carbon atoms in coal Distribution (74)
Yallourn
Coal
Polar
Aromatic
CH,
c&H,
B-CH,
f,
Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
22 19 13 5 6 6
57 51 54 61 66 71
12 18 21 22 15 12
5 7 8 8 7 6
4 5 4 4 5 5
0.57 0.51 0.54 0.61 0.66 0.71
Soya - kolshl C
72 0 “I.
Shin - yubori c
a7 4%
I 240
I
I 160 Chemical
1
I
80 shift
I
I 0
( ppm)
Figure 1 CP/MAS t3C n.m.r. spectra of sample coals
carbon signals. Assignments of carbon atoms have been described in a previous paper7. The acetylation method for determining phenolic OH oxygen has been reported elsewhere’. RESULTS Table I shows the proximate
and ultimate analyses and atomic H/C and O/C ratios of the coals. Figure 1 shows the CP/MAS i3C n.m.r. spectra of Yallourn, Soya-koishi, Taiheiyo and Shin-yubari coals.
The low-rank coals such as Yallourn and Soya-koishi coals indicated line structures especially in the aromatic regions of their spectra, which were due to the presence of carbonyl, carboxyl, phenolic OH, methoxy groups and aromatic ether bridges. However, Shin-yubari coal showed no signal in the region beyond z 170 ppm, providing a simple spectral feature in the aromatic regions. Table 2 indicates carbon distributions obtained from the n.m.r. spectra. The amounts of polar groups, particularly carboxyl and carbonyl groups, decreased rapidly with increase in the carbon content of the coal. Aromatic carbon was least abundant in Soya-koishi coal and increased with increasing carbon content of coal except for Yallourn coal. Briquettes of Yallourn coal had a relatively large amount of aromatic carbon despite having the lowest carbon content among the coals used. Atiphatic carbon was most abundant in Taiheiyo and Horonai coals. These coals showed the highest CH, carbon content. All coals used had almost the same level of CH, carbon content. Table 3 shows the results of the coal liquefaction reaction under mild conditions (4C!O“C,30 min). Yield of hydrocarbon gases (C,C,) was small for every coal. The yields of CO, and water decreased markedly as the carbon content of the coal increased. The ratio of deoxygenation ranged between 39 and 70”/ and decreased with increase in the carbon content of coal except for Yallourn coal. The yield of oil was high for Taiheiyo, Horonai and Akabira coals, and small for Yallourn, Soya-koishi and Shinyubari coals. DISCUSSION Distributions
of carbon and oxygen
atoms
The change in f, value with rank of coal except for Yallourn coal (Table 2) agrees well with the results reported by other authors9,10. Briquettes of Yallourn coal showed anf, value higher than that for Soya-koishi coal. This unexpected observation may be interpreted as the
FUEL,
1985, Vol 64, July
891
Liquefaction Table 3
reaction
of coal. 1: T. Yoshida
et al.
Experimental results for liquefaction reaction of coal (wt”,;, dmmf coal basis) Yallourn
Soya-koishi
Taiheiyo
Horonai
Akabira
Shin-yubari
Hydrogen consumption Gas CIC7, CO, Water Oil Asphaltene Preasphaltene Residue + loss
4.0 17.0 4.3 12.7 9.1 28.8 16.7 6.7 21.7
4.8 11.8 2.6 9.2 9.2 21.9 14.1 11.2 36.6
3.8 5.8 3.7 2.1 6.3 54.1 15.6 5.0 16.3
2.9 4.2 3.2 1.0 4.0 52.7 15.5 3.8 22.6
2.8 4.0 3.3 0.7 3.3 43.0 20.7 10.8 21.1
1.1 1.8 1.2 0.6 1.6 11.1 35.7 26.7 24.2
Ratio of deoxygenation (%) GCOX 0 Hz0
51.9 30.4 27.5
69.3 30.5 38.8
44.1 8.9 35.2
38.9 6.3 32.6
39.2 5.1 34.1
39.3 8.4 30.9
Table 4
Distribution of oxygen atoms in coal”
o/c
x 100 (“/,)
Coal
=CO,
COOH
ArrOH
*CH,
Ar-O-Ar
c-o-c
Yallourn Soya-koishi Tai hei yo Horonai Akabira Shin-yubari
7.9 3.3 1.9 0 0 0
7.7 5.5 3.2 1.7 1.2 0
9.7 9.1 7.0 5.6 4.7 2.5
4.0 2.3 1.6 2.3 1.1 0.7
2.9 1.1 1.2 0.2 0.55 0.66
0.8 0.7 0.5 0.2 0.1 0
oOH/“corl
W 29 41 45 55 60 64
“Vafues obtained by assuming that alcohols are not present in coal
result of the dehydrogenation from hydroaromatic structures by heat treatment at the time of briquette preparation. Untreated Yallourn coal gave an fa value (% 0.50) close to that of Soya-koishi coal. The content of CH, carbon is dependent on the rank of coal, though that of CH, carbon is independent. Therefore the difference in atomic H/C ratio found among the coals is mainly due to the content of CH, group, not that of CH, group. This behaviour agrees with the results of Fourier transform infrared (FT-i.r.) spectrometry reported by Painter et al.“. Table 4 shows the amounts of various types of oxygen atom in the coals determined by the combined use of the CP/MAS 13C n.m.r. spectrometry and the acetylation method”. Phenolic OH oxygen is most abundant in every coal and the ratio of phenolic OH oxygen to total oxygen (O,,/O,,,,) increases with the increase in carbon content of coal, ranging from 29% for Yallourn coal to 64% for Shin-yubari coal. Carbonyl and carboxyl groups are also abundant in low-rank coals. However, they decrease rapidly with increasing carbon content of coal, suggesting that they are easily eliminated in the course of coalilication. It is particularly noteworthy that etheric oxygens are present in a smaller amount than expected in every coal and are distributed as aromatic rather than aliphatic ether. The slight increase in the amount of aromatic etheric oxygen in Akabira and Shin-yubari coals is probably caused by the presence of oxygencontaining heterocyclics such as dibenzofurani3. Role
ofether bridges in the depolymerization of coal
The role of ether bridges in the depolymerization of coal is examined on the basis of the amount of etheric oxygen in Table 4. The ether bridges in coal are assumed to be distributed homogeneously because the conversion to pyridine solubles, produced by the cleavage of ether
892
FUEL, 1985, Vol 64, July
bridges at the early stages of depolymerization, amounts to 7&80 wt%i4. Table 5 shows the calculated molecular weights of reaction intermediates produced by the cleavage of ether bridges. Here the average aromatic ring size of structural units of coal is assumed to be l-2 for Yallourn, Soya-koishi and Taiheiyo coals, 2-3 for Horonai and Akabira coals, and 34 for Shin-yubari coal, based on many works 11’13.15*16. Themolecular weightsof the reaction intermediates can be calculated as follows, taking Soya-koishi coal as an example. Soya-koishi coal (ji = 0.5 1) has an average aromatic ring size equal to one to two, corresponding to 12-20 carbon atoms in an average structural unit. Based on the results of ultimate analysis of the coal, the structural unit is formulated to be between C,,H,,.,02.6 (MW= 197) and C20Hl,,,04,4 (MW = 329). Hence, there should be one ether oxygen per 2.884.6 structural units, namely per molecular weight of z 910. Table 5 indicates that the calculated molecular weights of the intermediates from all coals except for Taiheiyo coal are larger than the vapour pressure osmometry (v.p.0.) values for asphaltenes obtained from the liquefaction reaction. As described previously, the content of aromatic ether in Akabira and Shin-yubari coals is overestimated due to the presence of heterocyclic compounds and, therefore, the true molecular weights of the intermediates should be larger than the values in Table 5. These results suggest that the cleavage of ether bridges contributes to the formation of preasphaltene. Figure 2 illustrates the model structure for the reaction intermediate of Soya-koishi coal produced by the cleavage of ether bridges. The model is produced in an effort to understand the depolymerization mechanism of coal. The numbers of CH, bridges and naphthenic CH, carbons are estimated on the basis of CH, carbon distribution in Figure 3. Figure 3 shows the percentages of various types of CH, carbon to total CH, carbon content
Liquefaction Table 5
Calculated
molecular
weights
of reaction
intermediates
produced
by cleavage
reaction
of coal. 1: T. Yoshida
et al.
of ether bridge
Coal
R,
f,
NC
Formula”
MW,
Yallourn
1-2
0.57
11-18
C,,H,.KL, C,,HIL&,.,
(199) (325)
Soya-koishi
1-2
0.51
12-20
C,,H,,.,% &HI s.t%.,
Taiheiyo
l-2
0.54
11-19
Horonai
2-3
0.61
Akabira
2-3
Shin-yubari
34
V.p.o.6
Ne
MWi
2.5 1.5
3.7
490
356
(197) (329)
4.6 2.8
1.8
910
446
C,,H,,.,%, C,,H,s.,%
(171) (294)
5.3 3.1
1.7
910
917
16-23
C16H15.301.6 CZ~HZI.@Z.~
(233) (335)
15.6 10.9
0.4
3640
681
0.66
15-21
C,,H,,.,& [email protected]
(213) (297)
10.3 7.3
0.65
2180
707
0.71
20-23
C,,H,,.,O,.s C,,H,,.,%,
(270) (310)
7.6 6.6
0.66
2040
618
N”
“Formula for structural units b V.p.0. value of asphaltene obtained by mild liquefaction reaction R,, Number of aromatic rings in a structural unit; NC, number of carbon atoms in a structural unit; MW,, molecular weight of structural number of structural units per etheric oxygen atom; N,, number of etheric oxygen atoms per 100 carbon atoms; MW,, calculated molecular reaction intermediate produced by cleavage of ether bridge
r___---__------_-----------
unit; N,, weight of
1
I
I
I
Naphthenrc (lncludlng
CH, CH2 bridge
)
I I I
I I I I I
I
I L__________________________J
I
Figure 2 Model structure coal produced by cleavage
for the reaction intermediate of ether bridges
I-
Paraffinlc CH2 + cycloparafflnlc CH2
‘.
of Soya-koishi
\
\a
I--
for various ranks of coal. The content of paraftinic CH, carbon is calculated from the yield of saturated hydrocarbon (paraffins and cycloparafhns) fraction obtained from the liquefaction reaction at 400°C for 30 min. The yield of the fraction is considered to correspond roughly to the amount of saturated components in coal, as it has been reported that the fraction is formed at the early stages of the reaction I7 . The content of alkyl CH, carbon is estimated by the amount of B-CH, group in Table 2, with the assumption that alkyl groups in coal consist mainly of methyl and ethyl groups. The sum of these methylene carbons amounts to 35553% of total CH, carbon content for various ranks of coal. Therefore, the residual methylene carbons should be assigned to naphthenic CH, carbon, including CH, bridges, which are sensitive to scission. Thus, on average, the reaction intermediates of Soya-koishi coal have 6.2 CH, bridges and naphthenic CH, carbon atoms. The model structure in Figure 2 indicates that the scission of CH2 bridges and some naphthenic CH2 bonds is involved when the reaction intermediate is further depolymerized to oil molecules. Formation of oil molecules Figure 4 shows the relationship between aliphatic carbon contents of various ranks of coal and the oil yields obtained. Figure 4a shows that there is a poor correlation between the oil yield and total aliphatic carbon content
‘\ o\
,-
Alkyl
I
I
I
65
75
85 dmmf)
Carbon
Figure 3
CH,
Distribution
content
of various
of coal
(wt%,
types of methylene
carbon
in coal
(CH, +CH,). On the other hand, Figure 4b indicates that the oil yield gives a better correlation with CH, carbon content (solid line). This is in agreement with the results of an FT-i.r. spectrometric study recently reported by Senftle et al.‘*. However, the graph of oil yield against CH, carbon content does not go through the origin, indicating that ~8% of the CH2 groups are not involved in the production of oil. Methylene bridges play an important role in the depolymerization of coal to oil, and naphthenic CH2 and paraflinic CH2 groups contribute to an increase in the yield of oil. In contrast, alkyl CH2 groups are consumed only for the generation of hydrocarbon gas. Therefore, the oil yield should correlate with the amount
FUEL, 1985, Vol 64, July
893
Liquefaction
reaction
of coal.
1: T. Yoshida
et al asphaltene on the CH, carbon content of coal is considered to arise from: 1. the increase in the amounts of CH, bridges and naphthenic CH, carbons being sensitive to scission, 2. the increase in the solubility of oil components with the increase in the number of naphthenic rings, and 3. the increase in the amount of transferable hydrogen with the increase in naphthenic CH2 content. It would appear, therefore, that oil and asphaltene are produced by the scission of CH2 bridges and some naphthenic CH2 bonds. Table 6 shows the calculated molecular weight of oil produced by the scission of 20 or 500/,of CH2 bridges and naphthenic CH2 bonds. The calculated molecular weight of oil agrees roughly with the field ionization mass
a 60 t
I
0 12
I
I
I
20
I
28
(CH2+CH3)/Cx100
I 36
(“1.) SY -0
01 0
I
I
I CH,
L
I
8 /C
16 x 100
HO
I
(“1.1
of CH, carbons excluding alkyl CH, carbon. The broken line in Figure 4b represents such a plot on the basis of the CH, carbon distribution in Figure 3 and shows that the yield of oil is directly proportional to the sum of CH, groups other than alkyl CH2. Figure 5 shows the relationships between CH2 carbon content of coal and conversions to pyridine solubles and benzene solubles. The conversion to pyridine solubles is independent of CH, carbon content except for Yallourn and Soya-koishi coals, in contrast to the conversion to benzene solubles. The formation of a reaction intermediate such as preasphaltene appears to be achieved by the cleavage of ether bridges alone and hence is not dependent on the CH2 carbon content of the coal. However, dependence of the yields of extractable oil and
FUEL, 1985, Vol 64, July
TAfi
24
Figure 4 Relationship between oil yield and aliphatic carbon content ofcoal. (a), Ya, Yallourn; SK, Soya-koishi; TA, Taiheiyo; HO, Horonai; AK, Akabira; SY, Shin-yubari. (b), 0, plots of oil yield against total CH z carbon content; 0, plots of oil yield against sum of CH, carbons excluding alkyl CH,
894
AK a
01
0
I
I
I 8 CH2/C
I
I 16 x 100 (“I.)
I 24
Figure 5 Relationships between conversions to pyridine solubles and benzene solubles and CH, carbon content of coal. 0, Pyridine solubles; 0, benzene solubles. (Symbols for coals are the same as in Figure 4) Table 6 Calculated molecular weights of oil produced CH, bridges and naphthenic CH, bonds
by scissions
of
Coal
MWt
Nb
;:;a,
MW
Yallourn Soya-koishi Taiheiyo Horonai Akabira Shin-yubari
490 910 910 3640 2180 2040
1.7 6.2 6.7 35.8 12.2 8.6
26(t370 22&410 21&390 190-450 31&630 38t3-750
320 340 325 320 360 350
MW,, Calculated molecular weight of reaction by cleavage of ether bridges; N,, number of CH, CH, carbon atoms per reaction intermediate; cular weight of oil produced by scission of 20 or
intermediate produced bridges and naphthenic MW,, calculated moleSOA of CH, bridges and
naphthenic CHZ bonds; MW, mean molecular fraction determined by f.i.m.s.
weight of the neutral
oil
Liquefaction
reaction of coal. I: T. Yoshida et al.
spectrometry (f.i.m.s.) value for the neutral oil fraction obtained from the liquefaction reaction. This value is close to the calculated molecular weight of oil produced by the cleavage of 20”/, CH2 bonds for lower-rank coals, and to that of oil produced by the cleavage of 50% CH2 bonds for higher-rank coals. In conclusion, the depolymerization of coal to oil proceeds essentially through the cleavage of ether and CH2 bridges including naphthenic CH2 bonds. Formation of residue Figure 6 shows the oxygen balance between phenolic OH groups in coal and water produced during the liquefaction. All of the phenolic OH oxygen and half the carboxylic oxygen are considered to be sources of water. Therefore, the subtraction of half the carboxylic oxygen from the amount of oxygen in water produced (OHI, - l/2 0 coo”) gives the amount of phenolic OH oxygen converted to water. As shown in Figure 6, the ratio of phenolic OH oxygen converted to water to total oxygen in coal C(0” 0 - l/2 %0HY%%J increases with increase in ratio. However, the conversion of phenolic OH Ool4/fOc0,1 oxygen to water (broken line in Figure 6) is 44-64x and is larger in lower-rank than in higher-rank coals. Thus, it has become apparent that zSoO/, of the phenolic OH oxygen in coal remains unreacted. Figure 7 shows the relationship between the OoH/Ocoa, ratio and the ratio of O/C of each product to that of coal [(O/C,,)/(O/C,,,)]. In the ultimate analysis of residue, the contents of C, H and 0 were corrected for the effects of ash and catalyst. The atomic O/C ratio of the product increases in the order asphaltene, preasphaltene and residue, and the (0&,)/(0/C,,,,) ratio of each product increases with increase in OOH/O,.Oal.Furthermore, the ratio is larger than 1.0 in all the residues except for that from Yallourn coal, and in preasphaltenes from high-rank coals. These results lead to the following conclusions.
1. The phenolic OH oxygen tends to remain in the residues and preasphaltenes. This is supported by the fact that the signals of aromatic carbons substituted by
.-. 80
1
I
80 -
Figure 7 Relationship between ratio of phenolic OH oxygen to total oxygen and ratio of O/C of each product to that of coal. 0, Residue; A, preasphaltene; 0, asphaltene
the phenolic OH oxygen or aromatic ether oxygen are clearly observed in the CP/MAS ’ 3C n.m.r. spectra of residues and preasphaltenes. The presence of phenolic OH oxygen results in the depression of depolymerization of coal due to the hydrogen bonding” or promotes the production of more stable and higher molecular weight materials (residue) via oxygen-bridging by the condensation reaction of phenolic OH groups”. The phenolic OH oxygen atoms are distributed heterogeneously in coal. If they are distributed homogeneously, the (O/C,,,)/(O/C,,,,) ratios of the residues and preasphaltenes must be < 1.0 because of deoxygenation during liquefaction. In conclusion, phenolic OH oxygen-rich portions in coal produce higher molecular weight materials by the formation of new oxygen bridges and hence are apt to remain as residue.
REFERENCES 1 2 3 4 5 6 7 8 9 10
Owl
0
Figure 6
I
I
20
I
I
40 o,,/o,,,
I
I
60 , (%/.)
I
I
80
JO
100
Oxygen atom balance Between phenolic OH groups in coal
and water produced. 0, (OH,0 - l/2 QmB)/Ocod
0, (o,@ - l/2 @mH)/aH the same as in Figure 4)
uersus OOB/Oooat;
11 12 13
uersus@,H&,,l. (Symbdsfor coals are 14
Whitehurst, D. D., Mitchell, T. 0. and Farcasiu, M. in ‘Coal Liquefaction, The Chemistry and Technology of Thermal Processes’, Academic Press, 1980, ch. 5 Imuta, K., Yamakawa, T., Ouchi, K., Tsukada, K., Morotomi, H., Shimura, K. and Miyazu, T. J. Fuel Sot. Jpn. 1979, 58, 754 Given. P. H., Cronauer, D. C., Spackman, W., Lovell, H. L., Davis, A. and Biswas, B. Fuel 1975, 54, 40 Whitehurst, D. D. Am. Chem. Sot. Symp. Ser. 1980, 139, 75 Takegami, Y., Kajiyama, S. and Yokokawa, C. Fue[ 1963,42,291 Maekawa, Y., Shimokawa, K., Ishii, T. and Takeya, G. J. Fuel Sot. Jpn. 1967,&i, 927 Yoshida, T., Nakata, Y., Yoshida, R., Ueda, S., Kanda, N. and Maekawa, Y. Fuel 1982,61, 824 Hasegawa, Y., Tokuhashi, K. and Maekawa, Y. in ‘Proc. 17th Conf. Coal Sci.‘, Fuel Sot. Jpn, 1980, p. 5 Maciel, G. E., Bartuska, V. J. and Miknis, F. P. Fuel 1979,58,391 Dereppe, J. M., Boudou, J. P., Moreaux, C. and Durand, B. Fuel 1983,62, 575 Painter, P. C., Kuehn, D. W., Starsinic, M., Davis, A., Havens, J. R. and Koenig, J. L. Fuel 1983, 62, 103 Yoshida, T., Tokuhashi, K., Narita, H., Hasegawa, Y. and Maekawa, Y. Fuel 1984,63, 282 Hayatsu, R., Winans, R. E., Scott, R. G., Moore, L. P. and Studier, M. H. Fuel 1978,57, 541 Whitehurst, D. D. Am. Chem. Sot. Symp. Ser. 1980,139, 316
FUEL, 1985, Vol 64, July
895
liquefaction 15 16 17
896
reaction
of coal. 1: T. Yoshida et al.
Iwata, K., Itoh, H. and Ouchi, K. Fuel Process. Technol. 1980,3, 25 Iwata, K., Itoh, H., Ouchi, K. and Yoshida, T. Fuel Process. Technol. 1980, 3, 221 Inoue, K., Yokoyama, S. and Sanada, Y. Fuel 1982,61, 245
FUEL, 1985, Vol 64, July
18 19 20
Senftle, J. T., Kuehn, D., Davis, A., Brozoski, B., Rhoads, C. and Painter, P. C. Fuel 1984.63, 245 Szladow, A. J. and Given, P. H. Am. Chem. Sot. Div. Fuel Chem. Prepr. 1978, 23(4), 161 Ouchi, K. Carbon 1966, 4, 59