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Energy & Fuels 2003, 17, 172-178
Possibility of Increased Oil Yield in the NEDOL Process Sadao Wasaka,* Shouichi Ibaragi, and Masumi Itonaga New Energy and Industrial Technology Development Organization (NEDO), Higashi-Ikebukuro, Toshima-Ku, Tokyo 170-6028, Japan
Kouji Sakawaki and Kenji Inokuchi Mitsui SRC Development Co., Ltd., Chiyoda-Ku, Tokyo 101-0063, Japan
Michiharu Mochizuki Nippon Steel Corporation, Futtsu-Shi, Chiba 293-8511, Japan
Hirokazu Oda and Toshimitsu Suzuki Faculty of Engineering, Kansai University, Suita-Shi, Osaka 564-8680, Japan Received April 5, 2002
A maximum oil yield in the NEDOL coal liquefaction process was obtained with coal containing 76-78% carbon, while gas and water yields decreased with an increase in the carbon content. On the other hand, residue yield increased with an increase in the carbon content and this was attributed to an increase in asphaltene [(hexane insoluble)-(toluene soluble)] in the residue. From the experimental results, it was inferred that decomposition of the asphaltene is inevitable for improvement of the oil yield and that prolonged residence time in the liquefaction reactors is the most effective and practical measure for decomposing the asphaltene under the operating conditions of the NEDOL process. The average structure of the hexane soluble, asphaltene and preasphaltene [(toluene insoluble)-(THF soluble)] in the liquefaction residue exhibited the similar structural parameters in coals tested in the NEDOL coal liquefaction plants. The asphaltene fraction was then extracted from the residue by commercially applicable extraction conditions following which the extract was hydrotreated. About 35% of the extract was recovered as oil, which is lighter than 811K boiling point, by hydrotreatment. Furthermore, coal liquefaction experiments that used the extract as a part of solvent were conducted and an increase in total liquefaction oil yield was confirmed comparing with a coal liquefaction experiment without the extract.
Introduction The New Energy and Industrial Technology Development Organization (NEDO) has been carrying out the development of coal liquefaction technology as part of the “New Sunshine Program” under the direction of the Agency of Industrial Science and Technology, a division of the former Ministry of International Trade and Industry of Japan. NEDO started basic research for coal liquefaction development in 1980 and subsequently developed the NEDOL coal liquefaction process.1,2 The economics study of the NEDOL coal liquefaction plant, for commercial scale-plants, was conducted after the 150t/d pilot plant operation had been completed. The * To whom correspondence should be addressed. Energy and Environment Technology Development Department, New Energy and Industrial Technology Development Organization, SUNSHINE 60, 30F, 1-1, 3-Chome Higashi-Ikebukuro Toshima-ku, Tokyo, 170-6028, Japan. E-mail:
[email protected]. Telephone: +81-3-3987-9441. Fax: +81-3-5992-3206. (1) Wasaka, S. In Proceedings of the 9th Japan/Australia Joint Technical Meeting on Coal, June 1-2, 1999, Melbourne. (2) Wasaka, S.; Ibaragi, S. In Proceedings of the 17th Pittsburgh Coal Conference, September 11-14, 2000.
results showed that feasibility of the NEDOL plant can be assured, depending on the conditions of the plant site.3 However, further improvement of the economics seems to be desirable for commercialization. In the direct coal liquefaction process, liquefaction residue yield amounted to 25-30 wt % of raw coal. The residue, which was produced by the NEDOL process, includes about 40 wt % of toluene soluble fraction and further improvement of the economics is expected through the effective use of the residue except for its use as a raw material for the hydrogen production. Efforts for reducing the liquefaction residue by controlling the liquefaction conditions are also required. Shenhua coal from China showed a tendency to produce coke in the bottom of liquefaction reactors at a high reaction temperature (higher than 738 K), and difficulty in plant operation was reported at a high reaction temperature.4 Improvement of the oil yield seems to be (3) Maruyama, H.; Nomura, K.; Wasaka, S.; Ibaraki, S.; Tu Zhuming. In Proceedings of 18th World Energy Congress, October 21-25, 2001, Buenos Aires; paper 01-01-16.
10.1021/ef020085k CCC: $25.00 © 2003 American Chemical Society Published on Web 12/05/2002
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Figure 1. Simplified process flow sheet of NEDOL process employed in the 1 t/d PSU for the liquefaction tests.
quite difficult to achieve by employing higher reaction temperatures. Therefore, the production and decomposition characteristics of asphaltene in the residue produced at the 1t/d process supporting unit (PSU) were analyzed and methods for reducing the residue yield were studied. Moreover, the characteristics of the residues produced from several kinds of coals were analyzed and residue treatment procedures for improving the oil yield were examined. Extraction of the coal liquefaction residue using toluene was conducted and the extract was hydrotreated in the presence of solvent to study the possibility of decomposition of the extract under the same conditions as the coal liquefaction conditions. Moreover, the extract was treated under the coal liquefaction conditions with solvent and coal to examine the effects of addition of the extract on the improvement of coal liquefaction oil yield. Experimental Section Coal Liquefaction Apparatus. Figure 1 shows a simplified process flow of the NEDOL process employed in the 1t/d PSU, which can process 1 ton of coal a day. Experimental data and samples employed in this study were acquired from the plant. The NEDOL coal liquefaction process consists of four sections: coal preparation section, liquefaction section, distillation section and solvent hydrogenation section. In the coal preparation section, coal is dried and pulverized. The pulverized coal is mixed with hydrogenated solvent and catalyst. The (4) Mochizuki, M.; Namiki, Y.; Higuchi, M.; Inokuchi, K.; Nokami, Y.; Yoshida, S.; Wasaka, S.; Tu Zhuming. In Proceedings of the 7th Japan-China Symposium on Coal and C1 Chemistry, Haikou, China, 2001; pp 249-252.
mixture is fed to the liquefaction reactors and coal is liquefied in the reactors. Products from the reactors are separated into product oils and recycle solvent. The recycle solvent is hydrogenated in a solvent hydrogenation reactor for improving the solvent quality and recycled to the slurry preparation section as hydrogenated solvent. The 1t/d PSU precisely represents the NEDOL process and the data from the unit correlate with those from the 150t/d pilot plant constructed and operated for acquiring data for design and construction of commercial- or demonstration-scale plants.5 Therefore, the 1t/d PSU can be used to provide additional accurate data for commercial plants. Properties of Coals for Liquefaction. The eight kinds of coals shown in Table 1 were selected for coal liquefaction studies. Adaro coal from Indonesia has the lowest carbon content among the eight. Wyoming coal from the U.S.A., Tanito-Harum coal from Indonesia, Wandoan coal from Australia, Illinois coal from the U.S.A., and Yilan coal from China are classified as subbituminous coal. Ikeshima coal from Japan has the highest carbon content, and Shenhua coal from China indicates the highest fixed carbon (FC) and the lowest H/C atomic ratio among the coals tested. Liquefaction Conditions. The eight kinds of coals shown in Table 1 were processed in the 1t/d PSU, which employs the NEDOL process, under the conditions shown in Table 2. To investigate the effect of the coal properties on the residue, each coal was liquefied under the same conditions of the runs that have “465” as a suffix in Table 2. Moreover, the runs having “M” as a suffix indicate conditions of increased reaction pressure, gas liquid ratio, slurry residence time, etc. These conditions were tried for attaining an increase in oil yields. (5) Onozaki, M.; Ishibashi, H.; Aramaki, T.; Sakai, N.; Kobayashi, M.; Chiba, T.; Morooka, S.; Mochida, I. J. Jpn. Inst. Energy 2000, 79, 1159.
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Table 1. Properties of Coals Used in the 1 t/d PSU for Coal Liquefaction Testsa proximate analysis (wt % dry coal)
elemental analysis (wt % daf coal)
coal
ash
VM
FC
C
H
N
O
S
H/C (-)
O/C (-)
Adaro Tanito-Harum Ikeshima Shenhua Yilan Wandoan Illinois Wyoming
1.2 4.3 9.7 5.5 3.3 9.9 12.2 8.3
49.4 47.0 40.7 36.5 45.6 45.9 39.8 41.9
49.4 48.7 49.6 58.0 51.1 44.2 48.0 49.8
73.8 76.9 83.0 81.4 80.1 77.1 77.9 75.4
5.4 5.9 6.1 5.0 5.9 6.4 5.7 5.0
1.0 1.6 2.1 1.0 1.4 1.2 1.5 1.0
19.7 15.6 7.9 12.4 12.4 15.0 11.6 18.5
0.1 0.3 0.9 0.2 0.2 0.3 3.3 0.1
0.88 0.91 0.89 0.74 0.88 1.00 0.87 0.80
0.20 0.15 0.07 0.12 0.12 0.15 0.11 0.18
a VM: volatile matter. FC: fixed carbon. daf: dry ash free. H/C: hydrogen and carbon atomic ratio. O/C: oxygen and carbon atomic ratio.
Table 2. Coal Liquefaction Conditions Employed in the 1t/d PSUa run name
coal
cat. addition (wt %)
coal concentration (wt % slurry)
feed rate (t/d)
temperature (K)
pressure (MPa)
G/L (NL/kg)
H2 concentration (vol %)
RA-465 RT-450 RT-465 RT-465M RT-GL5 RT-GL11 RT-HC85 RT-HC-90 RI-465 RS-465 RS-455M RW-465 RIS-460 RY-465 RWY-465
Adaro Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Ikeshima Shenhua Shenhua Wandoan Illinois Yilan Wyoming
3 3 3 4 3 3 3 3 3 3 4 3 3 3.2 3
40 40 40 40 40 40 45 45 40 40 45 40 40 40 40
2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.0 2.5 2.5 2.5 2.5
738 723 738 738 738 738 738 738 738 738 728 738 728 738 738
16.8 16.8 16.8 18.7 16.8 16.8 16.8 16.8 16.8 16.8 18.7 16.8 16.8 16.8 16.8
700 700 700 900 500 1100 700 700 700 700 900 700 700 700 700
85 85 85 85 85 85 85 90 85 85 85 85 85 85 85
a Cat. addition: amount of catalyst (natural pyrite) addition against dry coal. Coal concentrated: coal concentration in slurry. Feed rate: slurry feed rate. Temperature: reaction temperature. Pressure: reaction pressure. G/L: feed gas and feed slurry ratio. H2 concentration: hydrogen concentration in feed gas.
Table 3. Solvent Extraction Conditions of the Residue Produced in RS-455M liquefaction run name
coal
solvent
solvent/residue (-)
extraction temperature (K)
extraction pressure (MPa)
extraction time (min)
RS-455M
Shenhua
toluene
5
383
atmosphere
90
Table 4. Hydrogenation Conditions of Extract from the Residue Produced in RS-455M catalyst
reaction conditions
solvent name
extract/solvent (-)
name
amount (wt % dry sample)
temperature (K)
pressure (MPa)
residence time (min)
coal derived oila coal derived oila
0.45 0.45
NPb NPb
4 4
733 728
18.7 18.7
30, 60, 90 60
a Solvent used as coal liquefaction recycle solvent in the NEDOL process. b Natural pyrite used as liquefaction catalyst in the NEDOL process.
Structural Analysis of Coal Liquefaction Residue. Coal liquefaction residue was separated using n-hexane, toluene and tetrahydrofran (THF) into hexane soluble (HS: n-hexane soluble), asphaltene (HI-TS: toluene soluble in n-hexane insoluble), preasphaltene (TI-THFS: THF soluble in toluene insoluble), and IOM (insoluble organic matter) (THFI: THF insoluble). On the bases of the results of 1H NMR (by JEOL’s JNM-GX400 and 399.65 MHz of observing frequency) and elemental analysis (by Yanaco’s MT-5 CNM for C, H and N, and by Tanaka Chemical Instrument’s AQS-WD for S), structural analysis was performed using the Brown-Ladner procedure.13 Solvent Extraction of Residue and Liquefaction of the Extract. Extraction with toluene under the conditions shown in Table 3 was conducted using the residue produced from Shenhua coal with low liquefaction oil yield and high residue yield. The extract was hydrotreated and decomposed in an autoclave with a volume of 0.5 L under the conditions shown in Table 4. Moreover, coal liquefaction tests employing the extract as a part of solvent were conducted using an autoclave with a volume of 0.5 L under the conditions shown in Table 5.
Results and Discussion Liquefaction Yield. Figure 2 shows the relationship between the carbon content in coal and product yields of oil, gas, water, and residue obtained in the tests conducted under the same conditions (reaction temperature, 738 K; reaction pressure, 16.8 MPa; G/L, 700 NL/ kg; and hydrogen concentration, 85 vol %). Gas and water yields decreased with any increase in carbon content. Oil (C4 to 811 K fraction) yield showed a maximum point at a 76-78% of carbon content and then decreased with an increase in carbon content. On the other hand, residue yield increased with an increase in carbon content. Figure 3 shows the relationship between carbon content and fraction yields of hexane soluble, asphaltene, preasphaltene, and IOM in the residue. Hexane soluble, preasphaltene, and IOM yields were nearly constant in the range of the carbon content in coals used in this experiment. However, the amount of
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Energy & Fuels, Vol. 17, No. 1, 2003 175
Table 5. Conditions of Coal Liquefaction Tests with Extract from the Residue Produced in RS-455M
run without extract (control) with extract high G/L with extract a
coal (amount/ extract (amount/ initial H2 pressure coal slurry ratio) solvent extract coal ratio) catalyst temperature residence G/La (MPa) (daf g/wt %) (g) (daf g/wt %) (wt % dry coal) (K) time (min) (NL/kg) 56.8/45 56.8/45 37.9/45
73.8 67.4 44.7
0.0/0.0 6.4/11.3 4.3/11.3
4.0 4.0 4.0
728 728 728
60 60 60
207 207 350
7.8 7.8 7.8
Hydrogen coal slurry (coal + solvent + extract + catalyst) ratio.
Figure 2. Relationship between carbon content in coals and product yields (gas, oil, water, and residue) in the tests carried out at a reaction temperature of 738 K.
Figure 4. Relationship between liquefaction conditions for Shenhua coal and fraction yields in oil and residue.
Figure 3. Relationship between carbon content in coal and each component yield(hexane soluble, asphaltene, preasphaltene, and insoluble organic matter) in residue.
asphaltene did increase with an increase in carbon content. Therefore, the increase of the residue yield shown in Figure 2 seems to depend on the increase of the asphaltene fraction. Kidoguchi et al.6 and Itoh et al.7 have proposed the reaction scheme of the NEDOL process and calculated the reaction rate constant for each reaction path and that, in the initial stage of the liquefaction reaction, heavy oil (623-811 K of boiling range) and asphaltene are formed from coal, and that the asphaltene and heavy oil decompose slowly. Therefore, extension of the residence time in coal liquefaction reactors seems to be an effective measure for reducing the asphaltene yield in high carbon content coals. Figure 4 shows the effects of liquefaction conditions on yields in oil fractions and residues produced under (6) Kidoguchi, A.; Itoh, H.; Hiraide, M.; Kaneda, E.; Ishibashi, H.; Kobayashi, M.; Ikeda, K.; Imada, K.; Inokuchi, K. Fuel 2001, 80, 13251331. (7) Itoh, H.; Hiraide, M.; Kidoguchi, A.; Onozaki, M.; Ishibashi, H.; Namiki, Y.; Ikeda, K.; Inokuchi, K.; Morooka, S. Ind. Eng. Chem. Res. 2001, 40, 210-217.
different liquefaction conditions using Shenhua coal from China. It seems difficult to obtain a higher oil yield with Shenhua coal because of its high Inertinite content, classified by petrographical analysis and amounting to about 40%.8 RS-455M has a lower residue yield because of its lower IOM and asphaltene yields compared with RS-465. With regard to oil yields, naphtha (C4 to 493K of boiling range) yield of RS-455M is lower than that of RS-465. On the other hand, light oil (493-623 K of boiling range) and heavy oil yields of RS-455M are higher than those of RS-465. Despite the lower reaction temperature applied to RS-455M compared with RS465, the longer residence time of the heavy fraction in the liquefaction reactors using higher G/L and lower slurry feed rate seems to have afforded higher light oil and heavy oil yields. Sakawaki et al.9 reported that a higher G/L tends to prolong residence time of the heavy distillate in the liquefaction reactors. In previous experiments with the 1 t/d PSU, higher reaction temperatures of up to 738 K resulted in lower residue yield and higher oil yield.10 However, in the experiments with Shenhua coal shown in Figure 4, a longer residence time seems to be effective to improve the oil yield through (8) Okada, K. Japan’s New Sunshine Project, 1998 Annual Summary of Coal Liquefaction and Gasification. 1999; pp 111-114. (9) Sakawaki, K.; Nokami, Y.; Inokuchi, K.; Kawabata, M.; Imada, K.; Tachikawa, N.; Moki, T.; Ishikawa, I. In Proceedings of the 34th Sekitan Kagaku Kaigi in Japan, Sendai, 1997; pp 119-122. (10) Ikeda, K.; Sakawaki, K.; Nogami, Y.; Inokuchi, K.; Imada, K. Fuel 2000, 79, 373-378.
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Figure 5. Relationship between carbon content in coal and degree of aromatic ring condensation (Haus/Caus) in each fraction produced under the same liquefaction conditions (reaction temperature, 738 K; reaction pressure, 16.8 MPa; gas and slurry feed ratio, 700 NL/kg; catalyst addition, 3 wt % daf coal basis).
conversion of asphaltene to heavy oil and conversion of heavy oil to light oil. Therefore, it was confirmed that, in the experiments at the 1 t/d PSU, precisely representing the NEDOL process, using higher Inertinite content coal, like Shenhua coal, a longer residence time is effective in achieving a higher oil yield, especially a higher light oil yield. It has also been reported that for the liquefaction of high Inertinite content coals, a longer residence time is effective to increase oil yield in the experiments in a small-scale plant, which can process 0.1 ton of coal a day, using various kinds of Chinese coals.11,12 Properties of Liquefaction Residue. Structural analysis of the liquefaction residue was conducted using 1H NMR.13 Figure 5 shows the number of aromatic rings (Raus) and aromatic ring condensation (Haus/Caus: hydrogen and carbon atomic ratio in aromatic rings not having substituent group) of the hexane soluble, asphaltene and preasphaltene in the residues produced under the same conditions (reaction temperature, 738 K; reaction pressure, 16.8 MPa; G/L, 700 NL/kg; and amount of catalyst, 3 wt % daf coal basis) corresponding to the carbon content of the coals used in the liquefaction tests in the 1 t/d PSU. The Raus and Haus/Caus of each fraction were almost constant within the range of these carbon contents of raw coals. The Raus of the hexane soluble fraction ranged from 3 to 4, asphaltene from 3.5 to 4.5, and preasphaltene from 4.5 to 5.5. Haus/Caus of hexane soluble fraction ranged from 0.65 to 0.7, asphaltene from 0.6 to 0.65, and preasphaltene from 0.5 to 0.6. Takeya et al.14 and Yokoyama et al.15 reported (11) Wasaka, S.; Ibaragi, S.; Hashimoto, T.; Tsukui, Y.; Katsuyama, T.; Shi Shidong. In Proceedings of the 7th Japan-China Symposium on Coal and C1 Chemistry, Haikou, China, 2001; pp 245-248. (12) Wasaka, S.; Ibaragi, S.; Hashimoto, T.; Tsukui, Y.; Katsuyama, T.; Shi Shidong. Fuel 2002, 81, 1551-1557. (13) Brown, J. K.; Ladner, W. R.; Sheppard N. Fuel 1960, 39, 79, 87.
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Figure 6. Effect of liquefaction conditions on number of aromatic rings (Raus) and degree of aromatic rings condensation (Haus/Caus) for each fraction.
that the Haus/Caus of extracts from coal and coal hydrogenated oil decreased with an increase in carbon content in raw coals, and that the Raus increased with the carbon content of raw coals. However, such tendencies reported by Takeya et al.14 and Yokoyama et al.15 were not observed in the present coals. This seems to be due to the use of a narrow range of carbon content (74-83 wt %), of which range is applicable for the NEDOL process, compared with the range (60-86 wt %) employed in the studies by Takeya et al.14 and Yokoyama et al.15 Figure 6 shows the Raus and Haus/Caus of hexane soluble, asphaltene and preasphaltene in the residues produced under different liquefaction conditions. The Raus of hexane soluble, asphaltene and preasphaltene increased by raising the reaction temperature and the Haus/Caus decreased with an increase in the reaction temperature (comparison of RT-450, RT-465, and RT465M). On the other hand, no effect of reaction pressure or G/L was observed on the Raus and Haus/ Caus (comparison of RT-465 and RT-465M). Figure 7 shows the average numbers of naphtenic rings (Rnus) and carbon numbers of side chains (Csideus) of hexane soluble, asphaltene, and preasphaltene fractions in the residues produced under different liquefaction conditions. From Figure 7, it is clear that Rnus decreases with a rasing reaction temperature. However, no significant difference in Csideus except for hexane soluble was observed depending upon the reaction conditions. Csideus of hexane soluble slightly decreased with an increase in the reaction temperature. Therefore, structural parameters of the residues produced from coals applicable to the NEDOL process and under the condi(14) Takeya, G.; Itoh, M.; Suzuki, A.; Yokoyama, S. Memories of Faculty of Engineering; Hokkaido University: Hokkaido, Japan, 1965; Vol. XI, p 613. (15) Sanada, Y.; Sasaki, M.; Obara, T.; Chiba, T.; Nagaishi, H.; Yokoyama, S.; Sato, M. Sekitan Tenkan Riyo Gijyutsu; IPC Co., Ltd.: Tokyo, Japan; 1994, p 370.
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Energy & Fuels, Vol. 17, No. 1, 2003 177 Table 6. Properties of Extract from the Residue Produced in RS-455M ultimate analysis (wt % daf) C
H
N
S
O
H/C (atoms/atoms)
MWa (g/mol)
90.91
6.09
0.91
0.04
1.51
0.797
260
a
Figure 7. Numbers of naphtenic rings and carbon numbers of side chain for each fraction (hexane soluble, asphaltene, and preasphaltene) in residue produced under different liquefaction conditions.
Figure 8. Relationship between number of aromatic rings and degree of aromatic ring condensation for each fraction in the residue produced from various kinds of coals.
tions of the NEDOL process seem to be similar except for Rnus of the residue under different temperatures. Figure 8 shows the relationship between the Raus and Haus/Caus of hexane soluble, asphaltene and preasphaltene fractions in the residues produced from several kinds of coals under the same liquefaction conditions (reaction temperature 738 K; reaction pressure, 16.8 MPa; G/L, 700NL/kg; and amount of catalyst, 3 wt % daf coal basis). In Figure 8, the relationship between the Raus and Haus/Caus of aromatic compounds as categorized in the peri type (benzene, naphthalene, anthracene, naphthacene, etc.) and kata type (pyrene, perylene, coronene, ovalene, etc.), and the relationship between the Raus and Haus/Caus of recycle solvent used in the liquefaction are shown. Asphaltene and preasphaltene were on the line of the kata type compounds, and hexane soluble was on the line of the peri type compounds. Therefore, the average structure of asphaltene and preasphaltene seems to consist of mainly the kata type compounds, and the average structure of hexane soluble seems to consist of mainly the peri type compounds. Moreover, the relationship between the
Analyzed by GPC with normal paraffine as standard reagent.
Figure 9. Influence of residence time and reaction temperature on conversion of extract (weight ratio of extract converted to below 811 K boiling point fractions and raw extract).
Raus and Haus/Caus for each fraction produced from different ranks of coal appeared on the same line, indicating that the decomposition to lighter fractions of preasphaltene and asphaltene by hydrogenation seems to be effective, as matter of course, for the residues from the coals tested in the PSU plant employing the NEDOL process. Extraction of Residue and Liquefaction of the Extract. Extraction by toluene of the Shenhua coal liquefaction residue (residue from R455M) was carried out using an autoclave. In this liquefaction run, the high residue yield and low liquefaction oil yield were obtained. In the extraction under the conditions shown in Table 3, 33.5 wt % of the residue was recovered as the extract. Properties of the extract are shown in Table 6. First, the hydrogenation of the extract was conducted under the conditions shown in Table 4, while Figure 9 shows the results of this hydrogenation. At a reaction temperature of 733K, extension of the residence time resulted in higher conversion of the extract and, for 90 min of residence time, the oil yield (fractions of below 811 K boiling point) from the extract reached to around 40 wt %. In the figure, the result of 728 K and a 60minute case is also indicated. The result was almost equivalent to the 733 K case and about 35 wt % of the oil yield from the extract was obtained. The hydrogenation conditions applied here were the same conditions that produced the residue from the original coal and a possibility that further decomposition of the extract would progress under coal liquefaction reaction conditions was indicated. This extract was then processed under the coal liquefaction reaction conditions with coal using an autoclave. The liquefaction examinations with extract and coal were carried out under the coal liquefaction conditions of reaction temperature of 728K and residence time of 60 min as shown in Table 5. An examination with coal only was carried out for a control, and comparison with the case using the extract was performed. In the case using the extract, the amount of solvent equivalent to the added extract was reduced
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Figure 10. Product yields in coal liquefaction experiments with extract and conversion of extract.
from the total amount of the solvent. That is, the added extract was considered to be a part of the solvent. The liquefaction results are shown in Figure 10. In the control, the oil (fractions of below 811K boiling point) yield was 32 wt % daf coal basis. On the other hand, 34 wt % of the oil yield was attained in the examination with the extract (11.3 wt % daf coal base). This means approximately 42 wt % of the extract was converted to the oil. Furthermore, a 3.5 wt % increase of the oil yield, compared with the control, was attained in high G/L with the extract (the increased hydrogen gas case). This increase seems to include the increased oil yield brought by coal itself besides the increased oil from the extract. However, it was confirmed that the coal liquefaction reaction was not impeded and that the oil yield was improved even with the addition of the extract as a part of solvent. Conclusion Liquefaction tests under the same reaction conditions using several kinds of coals were carried out in the 1 t/d PSU which employed the NEDOL process. It was found that there is a maximum liquefaction oil yield at a 76-78% carbon content in coals tested, and that the oil yield reduces with the accretion of carbon content. However, the liquefaction residue yield increased with an increase in carbon content. This increase seems to
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result from an increase of the asphaltene in liquefaction residue. Therefore, it seems that the decomposition of the asphaltene is inevitable for improving the liquefaction oil yield of high-carbon coals. Moreover, it can be inferred that extension of the residence time in the liquefaction reactors rather than higher reaction temperatures is effective in improving the liquefaction oil yield, and that especially for higher Inertinite content coal, extension of the residence time is effective. The number of aromatic rings of hexane soluble, asphaltene and preasphaltene in the liquefaction residue produced in the NEDOL process was 3 to 4, 3.5 to 4.5, and 4.5 to 5.5, respectively, and the condensation of the aromatic rings was 0.65 to 0.7, 0.6 to 0.65, and 0.5 to 0.6, respectively. The number of aromatic rings and the condensation of the aromatic rings did not depend on the carbon content among the raw coals employed for the NEDOL coal liquefaction process. Moreover, the average structure of hexane soluble was the same as that of the peri type compounds and those of asphaltene and preasphaltene were the same as that of the kata type compounds. Extraction by toluene of the residue produced from Shenhua coal, which includes abundant Inertinite and shows a low coal liquefaction oil yield, was conducted. It was confirmed that around 35-40 wt % of the extract was decomposed to the fractions of below 811 K boiling point by the hydrogenation under the conditions employed in the coal liquefaction reaction. Furthermore, the oil yield of 3.5 wt % was improved in this coal liquefaction tests using the extract (11.3 wt % daf coal base) as a part of the solvent comparing with the coal liquefaction without the extract. This indicates the possibility of the use of the extract as a part of the solvent in the NEDOL process. Therefore, since the heavier fractions in the solvent can be withdrawn as part of product oil and the extract can decompose to the oil through the coal liquefaction process, further improvement of the coal liquefaction oil yield is expected in the NEDOL process by using the extract as a part of solvent. EF020085K
