Energy & Fuels 1987, 1, 343-348
343
SRC and residue. The dimerization and adduction of fluorenyl radical with coal fragments are expected to be facile reactions. As shown in Figure 6 and Table 11, the addition of tetralin to fluorene lowered the yield of SRC and raised the solvent recovery. That is, the dimerization or the adduction of fluorene was suppressed by tetralin. This is partly explained by the radical stabilization reaction depicted by eq 6 in Figure 10. An alternative explanation could be that the fluorene dimer is attacked by tetralin to produce two fluorene molecules. The hydrogen-transfer reaction from the solvent to coal was accelerated by the interactions between the donor and another solvent such as fluorene. It is possible that the acceleration of the hydrogen transfer from tetralin by fluorene and phenanthrene is due to their higher physical affmity with coal as well as their improved hydrogen donor ability. The hydrogen donor ability of the binary solvent as defined by DHA/(DHA + AN) clearly demonstrates the interactions between solvents. The calculated solubility parameter of anthracene is 11.3 and is larger than those of the solvents similar to coal. This is one reason why anthracene is a better physical coal model.
1. Conversions of Yallourn coal in the mixtures of fluorene or phenanthrene and tetralin were larger than those of the mixtures of 1-methylnaphthalene or naphthalene and tetralin, regardless of atmosphere and the reaction time from 20 to 60 min. 2. It was suggested that the physical affinity of phenanthrene or fluorene with Yallourn coal was large and shuttled hydrogen to coal efficiently. It was also c o n f i i e d that fluorene donated hydrogen to coal. 3. The hydrogen donor ability of solvent was evaluated quantitatively by using anthracene as the coal model as shown in Figure 7. The hydrogen donor abilities thus defined for fluorene-tetralin mixtures were larger than those of the other binary solvent, just as the fluorenetetralin mixtures were the best for coal conversion. The chemistry of the liquefaction solvent was very complex. However, the study of the solvent-solvent interactions promises to identify the ideal liquefaction solvent.
Summary and Conclusions Important conclusions derived from this work are as follows.
Registry No. Tetralin, 119-64-2; anthracene, 120-12-7; 1methylnaphthalene, 90-12-0; naphthalene, 91-20-3; fluorene, 8673-7; phenanthrene, 85-01-8.
Acknowledgment. The authors thank K. Ito and T. Suzuki for their technical assistance.
Liquefaction Reactivities of Three Subbituminous Coals in Tetrahydrofluoranthene as a Hydrogen Donor Isao Mochida, Masahiro Kishino,*t Kinya Sakanishi, Yozo Korai, and Ryohei Takahashi** Research Institute of Industrial Science, Department of Molecular Technology, Graduate School of Industrial Sciences, Kyushu University 86, Kasuga, Fukuoka 816, Japan, and Department of Geology, Faculty of Science, Kyushu University 86, Hakozaki, Fukuoka 813, Japan Received October 3, 1986. Revised Manuscript Received April 20, 1987 Three subbituminous coals (Indiana V, Wandoan, and Wabamun coals) of different ranks were reacted in tetrahydrofluoranthene (4HFL) under variable temperature-time conditions. Indiana V (the highest rank coal in this study) gave the highest total yield of oil and asphaltene (greater than 90%) a t 450 OC/30 min, whereas the other two coals of lower rank gave the highest total yield a t 510 OCI2.5 min (90% and 83%) respectively). The highest oil yield was always obtained under the more severe conditions, regardless of coals. Although low concentrations of 4HFL in the solvent decreased the yield under all conditions examined, the relative decrease was greater with the high-rank coal a t higher temperatures. Indiana V and Wandoan coals were almost completely liquefied to THF-soluble products under their respective optimum conditions, whereas 9 % of Wabamun coal remained quinoline insoluble under all conditions tested, even though all coals contained considerable amounts of inert macerals. Inert macerals in Wabamun coal were compared microscopically to those in Indiana V and Wandoan coals, suggesting that characterization of "true inerts" in the hydrogen-transferring liquefaction should be established. Introduction Subbituminous coals of which carbon contents range from 70 to 80 wt % are expected to be sources for coal liquefaction in the near future.l Since the nature and Department of Molecular Technology. *Departmentof Geology.
0887-0624/87/2501-0343$01.50/0
reactivity of such coals may differ considerably due to their the optimum conditions for the highest geological hi~tory,28~ oil or oil plus asphaltene yields should be carefully re(1)Whitehurst, D. D.; Mitchell, T. o.; Farcasiu, M. In Coal Liquefaction; Academic: New York, 1980; p 207. (2) Goodarzi, F. Fuel 1985, 64, 1294. (3) Shibaoka, M. Fuel 1983, 62, 639.
0 1987 American Chemical Society
344 Energy & Fuels, Vol. 1, No. 4, 1987
Mochida et al.
Table I. Ultimate Analyses of Sample Coals anal., wt % (daf) coal C H N S O(diff.) H/C wt ?% ash Wabamun 72.8 5.2 1.6 0.4 20.0 0.86 19.0 Wandoan 76.6 6.3 1.1 0.4 15.6 0.99 10.0 0.88 7.0 Indiana V 79.0 5.8 1.6 5.0 8.6 Table 11. Maceral Analysis of Sample Coals anal., vol % (daf) coal SF F Mca TIb Wabamun 30.0 7.5 0.8 28.3 15.0 0.8 20.6 Wandoan 7.2 11.7 1.1 14.2 Indiana V 2.1 "micrinite. TI = 2/3SF + F
b
+ Mc (SF includes Sc and ID).
searched for each coal. Some coals contain a considerable amount of inert macerals. It has been recognized that some inert macerals in subbituminous coals are different from those in higher rank coals and can be liquefied under proper A systematic study on the reactivities of such coals in the hydrogen donor liquefaction using tetrahydrofluoranthene8 (4HFL) is described in the present study. Different reaction conditions (changes in liquefaction temperature, time, and amounts of the donor) were examined to determine how the coals behave. The inert macerals in the starting coals and liquefaction residues were compared microscopically to correlate their reactivity with their microscopic characteristics.
Experimental Section Materials. Tables I and I1 summarize the ultimate and macera1 analyses of the coals used. Macerals were quantified by means of automatic reflectance measurements. The technique was widely applied in the Japanese coking industry. Total inerts (TI)are defined by the following equation according to Shapiro?
TI = 2/3SF+ F + Mc
(1)
SF = semifusinite including sclerotinite (Sc) and inertodetrinite (ID), F = fusinite, and Mc = micrinite. Tetrahydrofluoranthene (4HFL) was prepared by catalytic hydrogenation of fluoranthene (FL), using a commercial nickel/molybdenum/alumina catalyst? Liquefaction solvents were prepared as follows: solvent A, pure 4HFL; solvent B, 4HFL/ (4HFL + FL) = 2/3 by weight; solvent C, 4HFL/(4HFL + FL) = 1/3 by weight. Procedure. Liquefaction was carried out in a tubing bomb (20 mL volume). The solvent (6.0 g) and coal (2.0 g) were thoroughly mixed. The coal was ground to less than 250 pm (60 mesh) and dried a t 100 "C under vacuum before being transferred to the bomb, together with a small iron ball to assist stirring. The bomb was then pressurized with nitrogen gas to 0.5 MPa a t room temperature, immersed in a molten tin bath a t a prescribed temperature, and agitated axially. After the reaction was quenched rapidly by cooling in water, the products, including solids, were washed out from the bomb with tetrahydrofuran (THF). The product, after T H F was evaporated off, was extracted with hexane and then benzene by using a Soxhlet extraction apparatus. The yields (liquefaction yield, LY) of oil (hexane soluble, HS), asphaltene (hexane in(4) Mitchell, G. D.; Davis, A.; Spackman, W. M. In Liquid Fuels from Coal; Ellington, R. T., Ed.; Academic: New York, 1977; p 255. (5) Given, P. H.; Spackman, W.;Davis, A.; Jenkins, R. G. In Coal Liquefaction Fundamentals; Whitehurst, D. D., Ed.; ACS Symposium Series 139; American Chemical Society: Washington, DC, 1980; p 3. (6) Mochida, I.; Iwamoto, K.; Tahara, T.; Fujitsu, H.; Takeshita, K. Fuel 1982, 61, 603. (7) Heng, S.; Shibaoka, M. Fuel 1983,62, 610. (8) Mochida, I.; Otani, K.; Korai, Y. Fuel 1985, 64, 906. (9) Schapiro, N. J. Inst. Fuel 1964, 37, 234.
d
C
Figure 1. Microphotographs of inert macerals in Wabamun coal. Table 111. Inert Macerals in Coals coals photo type maceral Wabamun Figure l-a A fusinite 1 B fusinite 2 C ulminite-vitrinite Figure l-b A fungal tissue Figure l-c A fusinite 2 B semifusinite Figure l-d A inertodetrinite B sclerotinite Wandoan Figure 2-a A fusinite 1 B fusinite 2 Figure 2-b A inertodetrinite Figure 2-c A text-ulminite Figure 2-d A fungal tissue Indiana V Figure 3-a A fungal tissue Figure 3-b A fusinite 1 B sclerotinite Figure 3-c A fungal tissue soluble-benzene soluble, HI-BS) and residue (benzene insoluble, BI) were calculated according to eq 2-4. The amount of gaseous HS-gas LY(oi1) = initial coal (daf) LY (asphaltene) = HI-BS (3) initial coal (daf) LY (residue) =
BI (daf) initial coal (daf)
(4)
product was estimated from the material balance (charged coal minus liquid and solid products); hence, it included material loss. The benzene-insoluble products and starting coals were examined by a refleded polarized light microscope after conventional mounting and polishing of the sample.
Results Inert Macerals in Original Coals. Wabamun coal contained a large amount of inert macerals as shown in Table 11. The majorities of the inert macerals were classified as semifusinite (SF) according to the automatic
Energy & Fuels, Vol. 1, No. 4, 1987 345
Reactivities of Subbituminous Coals
5;ii
b
a
1 4HFL Contents (weight ratio)
Figure 4. Influence of 4HFL content in solvent on sum yield of oil and asphalthene a t variable conditions a t 450 "C/30 min: (A)Wabamun; (0) Wandoan; (0)Indiana V.
4HFL Contens(weight ratio)
d
C
Figure 2. Microphotographs of inert macerals in Wandoan coals.
a
b
A
.I
C Figure 3. Microphotographs of inert macerals in Indiana V coal.
analysis of reflectance measurements. Microphotographs of the inertlike macerals from Wabamun coal appear in Figure 1. Their identifications are summarized in Table 111. There were fusinites (F) 1(no texture, Figure la-A) and 2 (texture, Figure la-B,c-A), inertodetrinite (Figure 1d-A), sclerotinite (Figure Id-B), fungal tissue (a kind of Sc, Figure lb-A), and semifusinite (Figure lc-B). An intermediate between ulminite and vitrinite (Figure la-C) was also included. Semifusinite showed relatively high reflectance. Wandoan coal contained a fairly large amount of inert macerals as shown in Table 11. The major inert maceral was fusinite. In addition to fusinites 1and 2 (Figure 2a-
Figure 5. Influence of 4HFL content in solvent on the sum yield of oil and asphalthene a t variable conditions a t 480 OC/5 min: (A) Wabamun; (0) Wandoan; (0) Indiana V.
Figure 6. Influence of 4HFL content in solvent on the sum yield of oil and asphalthene a t variable conditions a t 510 OC/2.5 min: (A) Wabamun; (0) Wandoan; (0) Indiana V.
A,B), inertodetrinite (Figure 2b-A) and text-ulminite (Figure 2c-A), a considerable amount of fungal tissue (Figure 2d-A) having high reflectance, which may be misclassified into the fusinite by the automatic analysis, was observed in the coal. Text-ulminite may be also misclassified into fusinite and should actually be semifusinite. Indiana V coal contained less inert macerals as shown in Table 11. The major inert maceral was again fusinite. However Figure 3 shows that it also contained appreciable amounts of fungal tissue that has a high reflectance (Figure 3a-A,c-A). This maceral may also be misclassified into fusinite. The coal contained fusinite 1 (Figure 3b-A) and sclerotinite macerals (Figure 3b-B); however, their contents were rather limited. This coal also contained some intermediates between ulminite and vitrinite. Liquefaction Reactivities of Coals. The sums of oil and asphaltene yields (sum yield) using solvents containing different amounts of 4HFL (solvents A, B, and C, of which the 4HFL contents are 1, 2/3 and 1/3 (weight ratio), respectively) are illustrated in Figures 4-6, where the liquefaction temperature and time were varied (450 OC/30 min, 480 "C/5 min and 510 OC/2.5 min). At 450 "C/30 min, solvent A (pure 4HFL) gave a sum yield of 90% from Indiana V. Only 3% remained as BI from the coal as shown in Table IV. The yields from
Mochida et al.
346 Energy & Fuels, Vol. 1, No. 4, 1987 Table IV. Yield ( % of Oil and BI" solvent solvent A B oil BI oil BI 45OoC/30min Wabamun 61 10 57 11 Wandoan 69 9 62 10 Indiana V 64 3 53 6 480 OC/5 min Wabamun 60 10 54 14 Wandoan 73 5 58 6 Indiana V 57 1 39 9 510 OC/2.5min Wabamun 64 10 61 9 Wandoan 69 1 54 6 IndianaV 57 7 39 11 "olvent A, pure 4HFL; solvent B, (by weight); solvent C, 4HFL/(4HFL
solvent C -
oil 50 50 44
BI
40 43 37
23 9 15
47 44 37
19 15 21
12 11 11
4HFL/(4HFL + FL) = 2/3 (by weight).
+ FL) = * / 3
Wabamun and Wandoan coals were definitely lower than that of Indiana V under these conditions, but were still above 80%. Although decreasing 4HFL in the solvent reduced the yield regardless of coals, yields for Indiana V decreased the most. Similar yields (ca. 72 % ) were obtained from all coals with solvent C. BI from Indiana V coal increased very rapidly from 3% (solvent A) to 11% (solvent C), whereas those from other coals stayed around 10%. Wandoan coal gave the largest oil yield of 69% among the coals with solvent A under the conditions shown in Table IV. Less donor in the solvent reduced the oil yield to 50% with solvent C. Wabamun coal behaved like Wandoan coal, although its oil yield was definitely less when solvents A and B were used. Indiana V produced less oil than Wandoan coal despite its higher conversion. At 480 OC/5 min, Indiana V gave s u m yields similar to those at 450 OC/30 min when solvents A and B were used as shown in Figure 5. However, the total yield decreased sharply when solvent C was used. Wandoan coal gave slightly higher yields a t 480 OC/5 min with solvents A and B; however, solvent C gave slightly poorer results. Under these conditions, Wandoan coal was still less reactive than Indiana V coal. Wabamun coal gave lower yields than the former two coals, especially when solvent C was used. Wandoan coal provided the highest oil yield of 73% when solvent A was used, as shown in Table IV; however, the reduction of oil yield with poorer solvents was more marked under these conditions than that a t a lower temperature. Indiana V coal produced less oil under these conditions. At 510 OC/2.5 min, Wandoan coal gave the highest sum yield of 90% with solvent A as shown in Figure 6, whereas the yield from Indiana V was reduced to 809'0, which was lower than that obtained under less severe conditions. Some coking of Indiana V coal and its liquefied products may take place. Wabamun coal provided the same sum yield as that obtained at 480 OC/5 min. The oil yields from Indiana V and Wandoan coals were similar to those obtained a t 480 OC/5 min. It is worthwhile to note that the total yield decreased more markedly with less 4HFL in the solvent a t 510 "C for Indiana V and Wandoan coals, although the decrease in oil yields were similar for all three coals, regardless of reaction temperature. The BI contents in the products are summarized in Table IV, indicating some interesting features of liquefaction reactivity. When the best solvent A was applied, Wandoan coal gave less BI material with increasing liquefaction temperatures. Indiana V gave the lowest value a t 480 OC/5 min. In contrast, Wabamun coal gave 9% BI regardless of the temperatures.
s m a 5
-
3 5 0
$ O
1
2
3
Wabamun
1 2 3 Wandoan
1 2 3 Indian V
Figure 7. Solubility of BI residue: (a) QI;(0) QS (Liquefaction conditions: run 1,450 OC/30 min, solvent A; run 2,510 OC/2.5 min, solvent A; run 3, 510 OCl2.5 min, solvent B).
The poorer solvents produced more BI regardless of coals and temperatures, although the extent of the increase depended strongly on the coal. The increases of BI from Wandoan and Wabamun coals with poorer solvents at 450 OC/30 min were small, whereas that from Indiana V was large. The coals behaved similarly a t 480 OC/5 min. At 510 OC, the increase for Indiana V was most marked. The increase for Wandoan coal was slightly emphasized under the conditions, because solvent A produced no BI. In contrast, the increase for Wabamun coal was similar to that a t 480 OC/5 min. It should be noted that Indiana V and Wandoan coals gave no BI under their respective best conditions, whereas the lowest amount from Wabamun coal was 9%. The former two coals consist only of reactive macerals having different reactivities and requiring different conditions for their complete conversion. Thus, all of the inert macerals quantified (based on the reflectance data) in Indiana V and Wandoan coals were liquefied, whereas half of those in Wabamun coal were never liquefied. Characterization of BI. The quinoline solubilities (QS) of BI products for the three coals are summarized in Figure 7. The majority of BI products from Indiana V and Wandoan coals, under all conditions tested when solvent A was used, were soluble in quinoline. Thus, essentially all portions of these coals are reactive under these hydrogen-transferring liquefaction conditions and give at least a preasphaltene-type material. However, deficient amounts of hydrogen donor under severe conditions provided quinoline insolubles (QI), as observed in the case of liquefaction a t 510 OC/2.5 min using solvent C. Severe conditions with less donor may fail to depolymerize coal molecules of low reactivity or accelerate the conversion of the preasphaltene (produced from both coals) into isotropic cokes. In contrast to the two coals discussed, BI from Wabamun coal always contained some QI under all conditions examined. The shape of &I ruled out its fusion during the liquefaction. It is suggested that Wabamun coal contains completely unreactive macerals. Figures 8-10 show microphotographs of benzene-insoluble residues from Wabamun, Wandoan, and Indiana V coals (liquefaction conditions, 510 OC/2.5 min, solvent B), respectively. Considerable amounts of benzene-insoluble residues were produced from all coals with the solvent containing less donor. Unreactive macerals found in the residues were identified in Table V. Reacted Wabamun coal contained inerts of fusinite (Figure 8a-A,b-A,B),inert deterinite (Figure 8c-A) and sclerotinite (Figure 8c-B). In addition, semifusinite (Figure 8c-E) and ulminite (Figure 8d-B) were found undissolved in the residue. The ulminite grains left a net structure. Wandoan and Indiana V coals left fine grains of fusinite (Figures Sa-A,b-A and loa-A,b-B,c-A) and sclerotinite
Energy & Fuels, Vol. 1 , No. 4, 1987 347
Reactivities of Subbituminous Coals
'I.
b
a
a
C
b
d
Figure 10. Microphotographs of BI residue from Indiana V coal.
d
C
Figure 8. Microphotographs of BI residue from Wabamun coal.
b
Q
C Figure 9. Microphotographs of BI residue from Wandoan coal.
(Figures 9c-A and 10d-A) in the adhered ulminite and vitrinite (Figures 9c-B and lob-A,d-B). The latter macerals may be converted into benzene solubles if enough donor is present, since they appeared once fused as a result of liquefaction. Such macerals are not inert any more.
Table V. BI Residues after Liquefactioii coals Dhoto tvDe macerals Wabamun Figure 8-a A fusinite 1 Figure 8-b A fusinite 1 B fusinite 2 Figure 8-c A inertodetrinite B sclerotinite C intermediate of ulminite and vitrinite D fusinite 2 E semifusinite 2 Figure 8-d A sclerotinite B ulminite Wandoan Figure 9-a A fusinite 2 Figure 9-b A fusinite 2 Figure 9-c A sclerotinite B fused ulminite and vitrinite Indiana V Figure 10-a A fusinite 2 Figure 10-b A fused ulminite and vitrinite B fusinite 2 Figure 10-c A fusinite 1 B anisotropic coke, fused ulminite, and vitrinite Figure 10-d A sclerotinite B fragmental fusinite, fused ulminite, and vitrinite
It should be noted that the fungal tissues present in the original coals were not found in the residues. As mentioned before, this maceral may be misidentified as fusinite by the automatic analysis, since reflectance is the sole means for the maceral identification. Hydrogen Consumption. Hydrogen consumption was estimated from the amount of 4HFL remaining. It ranged from 2.0 to 5.0 w t % (daf coal basis), depending on the conditions and coals. The highest total yield (90%) was achieved with hydrogen consumptions of 5 w t % using Indiana V and Wandoan coals (liquefaction conditions of 450 "C/30 min and 510 OC/2.5 min, respectively). Under both sets of conditions, hydrogen consumption decreased linearly with decreasing yields as the concentration of 4HFL was reduced. Decreasing yields were much more pronounced a t higher temperatures.
348 Energy & Fuels, Vol. 1, No. 4,1987
Discussion Optimum Conditions for Coal Liquefaction. The present liquefaction results showed that solvents using tetrahydrofluoranthene, as a hydrogen donor, were effective in producing oil and asphaltene from subbituminous coals, giving sum yields greater than 80%. Liquefaction yields appear to be rank dependent. Indiana V coal (highest rank) prefers long liquefaction times a t low temperatures, whereas Wandoan and Wabamun coals (lower rank) prefer short times a t high temperatures, although the yield of Wabamun coal appears to be limited by the amount of the reactive macerals. Indiana V coal consists of relatively large aromatic molecular units that are connected by weaker bonds. Hence lower temperatures are sufficient to break these bonds, which can moderately be stabilized by the donor solvent, as observed with bituminous coals.'O At higher temperatures, the condensation reaction of large aromatic molecules is accelerated and the hydrogen donor cannot satisfy the demand for hydrogen to suppress the reaction. This causes the production of cokes or insoluble coke precursors, especially when less hydrogen donor is available. In contrast, higher temperatures are preferable for the lower rank coals in which molecular units are connected by many and stronger bonds. Higher temperatures may also allow more hydrogens available rapidly to satisfy the large demand. Because such coals consist of smaller molecular units, more oil is produced a t the higher temperatures through fissions of more connecting bonds and their effective stabilization. Hydrogen consumption is one of most important factors to control in liquefaction. The reduced amount of 4HFL in the solvent reduces the consumption, but results in decreased yields of oil and asphaltene. The decrease was more marked at higher temperatures, where more light oils tend to be produced. The higher temperatures may require more donor since a greater number of molecular bonds are being broken. With less hydrogen donor available, intermediate radicals may condense into coke or decompose into gaseous products. Coal liquids produced in this stage should be further upgraded by catalytic hydrogenation.ll Liquefaction temperatures and times in the first stage are selected to provide the product that will maximize catalyst performance in the second stage. The quality and quantity of BI in the product may influence appreciably the life of the catalyst and therefore should be controlled or removed before the hydrogenation step. Taking into account all of these factors, the first step of coal liquefaction can be designed. It is of value to note that the optimum conditions may differ significantly from one coal to another, even if they are all classified as subbituminous coals. Reactivity of Coal Macerals. The reactivity of macerals should be defined precisely in order to select a coal (10) Mochida, I.; Kawamoto, N.; Kishino, M.; Korai, Y. Fuel 1986,65, 81. (11) Mochida, I.; Fujitsu, H.; Korai, Y.; Sakanishi, K. Sunshine J. 1985,29/30, 15.
Mochida et al.
that is suitable for liquefaction. The reactivity of inert macerals has concerned r e s e a r c h e r ~ . ~ + j JRelevant ~ - ~ ~ information has also accumulated in coking technology.16 The conditions and ideal coals in the coking are quite different from those of liquefaction, and therefore additional detailed studies may be of value. Liquefaction reactivities of semifusinite macerals were reported else~here.~J~J~ An excellent hydrogen donor such as tetrahydrofluoranthene under rather severe conditions is found to liquefy some inert macerals that are believed unreactive in the coking process? The maceral analyses by automatic reflectance measurement, which has been established in the coking technology: may not always be appropriate to predict the reactivity of macerals in the coal liquefaction. The present study revealed that all inert macerals found in Indiana V and Wandoan coals were essentially liquefied, or at least were once fused under their respective optimum liquefaction conditions. It should be noted that the inert material in the latter coal becomes reactive a t higher temperature, where the liquefaction time should be short, otherwise coking takes place rapidly, especially after the donor is consumed. In contrast, 9% of Wabamun coal was not liquefied, indicating true inerts in the coal. The residues from Wabamun coal examined after liquefaction revealed that significant portions of fusinite, sclerotinite, and semifusinite macerals remain unchanged. They are true inert macerals. In contrast, Indiana V and Wandoan coals contained a considerable amount of fungal tissue, which may be misidentified as fusinite because of high reflectance. This maceral may be inert in the coking process; however, it reacts during coal liquefaction when enough donor is present. The coals tested may contain a small amount of true inert macerals; however, many of them were degraded into very small pieces, indicating their partial reactivity. At the same time, it can not be fully ruled out that very small particles may pass through the filter when solvent extractions are performed in order to evaluate liquefaction conversions. Reactive macerals of ulminite and vitrinite may remain benzene insoluble when the concentration of donor is not sufficient. They may require higher concentrations of donor for liquefaction. Thus, detailed characterization of inert macerals should be established in order to evaluate coals as liquefaction sources. Fluorescence microscopy can be a tool for such a predi~tion,"-'~although its chemical meaning is not fully understood. (12) Foster, N.R.;McPhearson,W. P.; Tao, C.; Collin, P. J. Fuel 1986, 64, 916.
(13) Shibaoka, M.; Heng, S.;Okada, K. Fuel 1985, 64, 600. (14) Shibaoka, M. Fuel 1985, 64, 606. (15)Takahashi, R.;Sasaki, M. Coal Science in Japan; Tokyo, 1985; p 251. (16) Pitt, G.J. In Coal and Modern Coal Processing: An Zntroduction; Pitt, G. J., Millward, G. R., Eds.;Academic: New York, 1979; p 69. (17) Teichmuller, M. Adu. Org. Chem. 1973, 379. (18) Diesel, C.F.K.; Evamarie, W. F. Proc. Znt. Conf. Coal Sci., 1985 1985,649. (19) Davis, A,; Bensley, D. F.; Derbyshire, F. J. Int. J. Coal Geol. 1986, 6, 215.
