Energy & Fuels 1990, 4 , 81-84 the reduction is highest at the high processing temperature. The adjusted H/C ratio is improved from 1.0 to 1.5 in the best case.
Acknowledgment. We gratefully acknowledge the
81
Swedish National Board of Energy, who sponsored this project. Registry No. Co, 7440-48-4; Mo, 7439-98-7; Ni, 7440-02-0; isooctane, 26635-64-3; xylene, 1330-20-7.
Hydrogen-Transferring Liquefaction of an Australian Brown Coal with Polyhydrogenated Condensed Aromatics: Roles of Donor in the Liquefaction Isao Mochida,*yt Akihisa Takayama,t Ryuji Sakata,f and Kinya Sakanishit Institute of Advanced Material Study and Department of Molecular Science Engineering, Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816, Japan Received July 13, 1989. Revised Manuscript Received November 14, 1989
Several donors with different numbers and reactivities of donorable hydrogens were examined in the hydrogen-transferring liquefaction of an Australian brown coal. Tetrahydrofluoranthene (4HFL), which liberated all of the hydrogens in 5 min at 450 "C, suffered a shortage of donorable hydrogens at a solvent/coal weight ratio of 1/1 (S/C = l),providing poor yields of oil and asphaltene. The dehydrogenation from hexahydroanthracene (6HAn) was too early to stabilize the coal fragment radicals. Octahydroanthracene (8HAn) and dodecahydrotriphenylene (12HTp) provided more oil and asphaltene at S/C = 1, while significant amounts remained unreacted even after the longer reaction time of 15 min. More 8HAn (S/C = 1.5-3) was less effective than the same amount of 4HFL in increasing the oil yield, suggesting different efficiencies in the hydrogen-transferring liquefaction. 12HTp and 8HAn are not stable enough at 450 and 480 "C, respectively. The reactivities of donors, as well as the solvent/coal ratio, are very important for the yields of oil and asphaltene. The design of a donor solvent is proposed.
Introduction The hydrogen-transferring depolymerization of coal macromolecules may be the most efficient first step in coal liquefaction.' Naphthenes derived from condensed aromatics of three to five rings are superior because of their hydrogen-releasing reactivity and dissolving ability for coal-derived molecules.2 In spite of an extensive study of hydrogen-transferringliquefaction, several problems still How much is the minimum amount of the donor solvent? How can we determine the best solvent from its structure and reactivity? In previous papers,*lo the present authors reported the influence of donor (4HFL) concentration and amount on the liquefaction of an Australian Brown coal. Major results were as follows: (1) There is an optimum amount of donor a t a fixed solvent/coal ratio for the largest oil plus asphaltene yield. Excess donor tends to produce more gas, decreasing the oil yield. (2) Nondonor solvent plays an important role in increasing the yield by suppressing the coking and gas production. (3) A donor solvent/coal ratio of 1.5 appears to be the minimum to obtain sufficient oil yield. On the basis of these results, the roles of donor were assumed to be multi-fold, suggesting the bimolecular interactions between the donor and coal-derived molecules. In the present study, polyhydrogenated aromatics of three to four rings were examined as donors for coal lit Institute
of Advanced Material Study.
* Department of Molecular Science Engineering. 0887-0624/90/2504-0081$02.50/0
Table I. Elemental Analysis of Morwell Coal w t % (daf) C H N o+s ash 63.7 4.9 0.9 30.5 2.3
quefaction of Morwell brown coal to reduce the solvent/ coal ratio to unity. More than four hydrogen atoms in the donors are assumed to be transferred to the coal molecules. At the same time, the role of donors in liquefaction is discussed because they should show different reactivities for hydrogen liberation. (1)Mochida, I.; Moriguchi, Y.; Korai, Y.; Fujitsu, H.; Takeshita, K. Fuel 1981,60, 746-147. (2)Mochida, I.; Otani, K.; Korai, Y.; Fujitsu, H. Chem. Lett. 1983, 1025-1028. (3)Neuworth, M. B.;Moroni, E. C. In Proceedings of the IGT Symposium Advances in Coal Utilization Technology, Louisville, KY, May 1979; pp 354-364. (4)Varghese, P.;Derbyshire, F. J.; Odoerfer, G. A.; Whitehurst, D. D. in Proceedings of the International Conference on Coal Science, Pittsburgh, 1983; pp 37-40. (5) Taunton, J. W.; Trachte, K. L.; Williams, R. D. Fuel 1981, 60, 788-194. (6)Rosenthal, J. W.; Dahlberg, A. J.; Kuehler, C. W.; Cash, D. R.; Freedman, W.Fuel 1982, 61, 1045-1050. (7)Mochida, I.; Sakanishi, K.; Korai, Y.; Fujitau, H. Fuel Process. Technol. 1986, 14, 113-124. (8) Mochida, I.; Yufu, A.; Sakanishi, K.; Korai, Y.; Shimohara, T. J. Fuel SOC.Jpn. 1986,65, 1020-1026. (9)Mochida, I.; Yufu, A.; Sakanishi, K.; Korai, Y. Fuel 1988, 67, 114-118. (10) Mochida, I.; Sakata, R.; Sakanishi, K. Fuel 1989, 68, 306-310.
0 1990 American Chemical Society
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82 Energy & Fuels, Vol. 4, No. 1, 1990
Mochida et al.
501
50
097iT+o*
reactiontim&nn) (c 1
0'
i
2:5
i
7:s
W i n time(snin)
(d 1
7t?
1b ' mtim timdmin)
(b)
Figure 1. Liquefaction yields at 450 "C and 1/1 (solvent/coal) using various solvents: (a) 4HFL; (b) 8 W , (c) 12HTp; (d) 6%. 0 , (oil + asphaltene);0,oil; 8,gas; 0 ,preasphaltene; a, residue.
Experimental Section Materials. The ultimate analysis of Morwell coal is summarized in Table I. 1,2,3,4,5,6,7,&Octahydroanthracene(8HAn), 1,2,3,4,5,6,7,8,9,10,11,12-dodecahydrotriphenylene (12HTp),and 1,4,5,8,9,10-hexahydroanthracene (6HAn) were commercial reagents. 1,2,3,lObTetrahydrofluoranthene(4HFL) was prepared by catalytic hydrogenation of commercially available fluoranthene (FL) using a commercial Ni-Mo catalyst." Liquefaction Procedure. Liquefaction was carried out in a tube bomb (20-mLvolume). The ground coal (2 g) and the solvent (2, 3, 4, or 6 g), after thorough mixing, were transferred to the bomb. The bomb was then pressurized with nitrogen gas to 1.0 MPa at room temperature, immersed in a molten tin bath at the prescribed temperature,and agitated axially. The liquid and solid products recovered from the bomb were subsequently extracted with THF, benzene, and hexane. The hexane-soluble (HS), hexane-insoluble but benzene-soluble (HI-BS), benzene-insoluble but THF-soluble (BI-THFS),and THF-insoluble (THFI) substances were defined as oil, asphaltene,preasphaltene,and residue, respectively. The oil yield was calculated as the difference between the HS and solvent-derivedproducts identified by GC. The yield of oil plus asphaltene was used to indicate the efficiency of liquefaction, since both products are favorable for the second upgrading stage. The gas yield was calculated by the difference between the initial and recovered residual weights. Thus, the weight loss during the experiment was included in the gas yield. Results Liquefaction at the Solvent/Coal Ratio of 1/1 at 450 "C. Figure 1illustrates the product distribution against the reaction time in the liquefaction of the brown coal at 450 "C, using various hydrogen donors at the solventfcoal ratio of 1/1. 4HFL, as reported in a previous paper,1° provided in 5 min 40% oil plus asphaltene (0 A), 30% preasphaltene (P), 20% oil (0)and gas (G), and 10% residue (R). A longer reaction time of 10 min very slightly increased the yield of (0 + A), while the yield of P decreased significantly, R and G increased to compensate for the decrease of P. Further extension of the reaction time to 15 min changed the product distribution very slightly. 8HAn provided slightly better results, giving 50% yield of (0 + A) and a smaller yield of P, 20%. Extension of the reaction time slightly decreased yields of P and R,
+
(11) Mochida, I.; Otani, K.; Korai, Y. Fuel 1985, 64, 906-910.
Figure 2. Liquefaction yields with 8HAn at 1/1: (a) 430 "C; (b) 480 "C. Symbols are the same as in Figure 1.
0'
'/1 '9.3
vi"y 3 4 "1 coal
'
Figure 3. Influence of solvent/coal ratio on the liquefaction yields: - - -,4HFL; -, 8HAn, 0 and A, (oil + asphaltene);0 and A, oil; 8 , gas; 0 , preasphaltene; a, residue. while the G yield increased significantly, keeping the level of the (0 A) yield at 50%. 12HTp provided more reasonable results, giving 40% (0 + A) (20% 01, 25% G and P, and 10% R in 5 min. Extension of the reaction time to 10 and 15 min decreased P, increasing mostly A and considerable 0, while R and G stayed almost unchanged. 6HAn provided the worst yield of (0 A), 35% a t 5 min. Extension of the reaction time slightly increased the yield of (0+ A) to 40% by decreasing P rapidly. However, 0 decreased slightly and G and R also increased slightly. Further extension of the reaction time decreased 0 and A, increasing G with the unchanged yield of P. Thus, more hydrogens in the donor at the solvent/coal ratio of 1/1 are favorable to produce more (0 + A) and to prohibit retrogressive reactions which lead to increasing gas and residue yields, although their number in the donor is not the sole factor in determining the yield. Figure 2 illustrates the results at 430 and 480 "C, using 8HAn. The liquefaction at 430 "C appeared to be over at 30 min, providing a product distribution similar to that obtained at 450 "C for 10 min, although the rate was slow at the former temperature. The reaction was almost over in 5 min at 480 "C, providing much the same product distribution, although P decreased further at 20 min. Thus, the reaction temperature slightly influenced the product distribution with 8HAn. Liquefaction with More Amount of Donors. Figure 3 illustrates the product distribution at 450 " C for 10 min with increasing solvent/coal ratios, using 4HFL and 8HAn.
+
+
Energy & Fuels, Vol. 4, No. I, 1990 83
Liquefaction of Australian Brown Coal Table 11. Composition of Solvents a f t e r Liquefaction at 450 "C hydrogen composition, % consumption reacn time, min 4HFLa FL mol % 5 0 100 0.019 100 10 0 100 0.019 100 15 0 100 0.019 100 hydrogen composition, % consumption reacn time. min 8HAnn 4HAn An mol % 0.016 34 5 42 42 16 0.018 42 10 33 49 18 0.019 44 15 31 50 19 hydrogen consumpcomposition, % tion reacn % time. min ~ ~ H T D ~" H T D ~ H T D others mol 5 14 28 39 18 0.020 40 10 11 20 42 27 0.020 41 15 7 13 45 35 0.021 41 hydrogen consumpcomposition, % tion reacn time.min 6HAn" 2HAn 4HAn An mol % 5 0 10 24 66 0.026 80 10 0 13 17 70 0.028 84 15 0 13 16 70 0.028 84 Starting solvent.
Additional amounts of 4HFL, as reported before,'O increased the yield of (0 + A) most markedly a t the ratio of 1.5/1 and gradually in the range of 1.5/1 to 3/1, providing 65% at 3/1. The increase in oil yield is very distinct and proportionate with the increase in ratio, reaching 50% at 3/1. Most of 4HFL present under liquefaction conditions can react with the coal and its products until its complete consumption, converting the asphaltene and the heavier products into lighter ones. Larger amounts of 8HAn to 1.5/1 increased the yield of (0+ A) significantly to 55%; however, further increases failed to provide larger yields. The oil yield increased very slightly from 25 to 32% by increasing the ratio from 1.5/1 to 3/1. No increase in the oil yield was obtained by further increasing the ratio. The yields of other products were influenced by the ratio only in its range of 1/1-1.5/1. Thus, only a restricted portion of 8HAn appears to react with a fixed amount of coal and its products, providing the plateau yield of oil and asphaltene in the raoge of 1.5/ 1-3/1. Excess 8HAn appears to be effective to prohibit the coking reactions of asphaltene, preasphaltene, and residue. Reactivity of Donors. Figure 4 illustrates the produds from the donors reacted after the liquefaction at 450 "C. 4HFL was converted exclusively into FL; no other product
FL
LliFL
m -m-c B@ 8 M 4HAn
An
I
xf others
olhers
Figure 4. Dehydrogenation schemes of donor solvents a t 450 "C. *, dehydrogenation scheme a t 480 "C.
was found. 8HAn yielded 4HAn and An. 12HTp suffered isomerization of its cyclohexane ring into a methylcyclopentane ring as well as dehydrogenation. 6HAn was dehydrogenated into An through 2HAn and 4HAn. Table I1 summarizes the composition of donors and their derivatives in the course of liquefaction when the starting solvent/coal ratio was unity. 4HFL was consumed in 5 min. 8HAn was much less reactive, producing 42% 4HAn and 16% in 5 min, and after 5 min 4HAn slowly increased to 49% and An increased to 18%. Very little conversion took place in the following 5 min, with essentially no hydrogen transfer occurring. 12HTp was fairly reactive to produce 8HTp and 4HTp by releasing hydrogens. The latter substance, however, appeared to stay unreacted. Nonreactive or very unreactive methylcyclopentane ring substances were also produced. 6HAn was as reactive as 4HFL, disappearing completely in 5 min and providing 2HAn, 4HAn, and An, which appeared rather stable and non-hydrogen donative, and remained for 15 min. Table I11 shows the reactivity of 8HAn a t 430 and 480 "C. At a lower temperature, the concentration of 8HAn became 32% at 20 min, providing 4HAn, and An, and further decreased very slowly after 20 min. The fact that 8HAn was reactive only a t the initial stage of the liquefaction indicates that it can react only with a very reactive portion of the coal. A t 480 "C, 8HAn disappeared completely in 20 min. However, the major portions of the dehydrogenated products of 4HAn and An were produced essentially a t the initial stage, methylcyclopentane ring
Table 111. Hydrogen Consumption of 8HAn under Various Liquefaction Conditions
reacn time. min 20 30 40
temD. "C 430
1
480
2.5 5 7.5 10
20
8HAn 32 29 24 58 41 23 11 6 0
composition, % 4HAn An 2HAn 47 21 0 24 0 47 48 0 28 0 10 32 0 42 17 4 17 52 6 21 48 27 8 44 14 29 38
others 0 0
0 0 0 4 14 15 19
hydrogen consumption mol 90 44 0.019 49 0.021 0.022 51 0.011 26 38 0.016 48 0.020 56 0.024 0.026 60 69 0.030
84 Energy & Fuels, Vol. 4 , No. 1, 1990
derivatives becoming substantial in the latter stage of the reaction as is shown in Table 111and Figure 4.
Discussion In the present study, the authors aimed to achieve sufficient yields of oil and asphaltene with donors of the more donorable hydrogens at a donor/coal ratio of unity, while the oil yield was always low (ca. 20-30%). 4HFL carried insufficient hydrogens at the ratio, being completely consumed in 5 min because of its high reactivity. Longer times led to retrogressive reactions, decreasing oil and asphaltene. Hence, the solvent/coal ratio of unity was too small for a sufficient yield. More 4HFL was very effective in increasing the oil yield up to 50% by a ratio of 3/1. Considerable amounts of 8HAn and 12HTp remained unreacted a t 450 O C even a t 15 min. No significant reduction of preasphaltene (P)and residue (R) or no increase in oil was achieved after 10 min, although the longer reaction did not necessarily lead to the retrogressive reaction. More 8HAn failed to reduce asphaltene (A) as well as P and R. 8HAn appeared essentially reactive only a t the initial stage when coal macromolecules and their derivatives react vigorously with 8HAn. At a higher temperature of 480 "C, 8HAn tended to isomerize into poor donors, failing in the effective hydrogen donation. 12HTp and its partially dehydrogenated derivatives were rather balanced donors but tended to isomerize into poor donors even a t 450 "C. 6HAn appeared to be very reactive, but its liquefaction performance was very poor, because it loses the hydrogens during the heating before reaching the liquefaction temperature. A summary of the present study suggests some important aspects in the mechanisms of the hydrogentransferring depolymerization of coal macromolecules. As described in previous papersgJOand cited in the literature for model compounds,12-14coal macromolecules may depolymerize not only through unimolecular thermolysis followed by stabilization with radical hydrogens from the (12) McMillen, D. F.; Ogier, W. C.; Chang, S.; Fleming, R. H.; Malhotra, R. In Proceedings of the International Conference on Coal Science, Pittsburgh, 1983; pp 199-202. (13) Kamiya, Y.; Ohta, H.; Fukushima, A.; Aizawa, M.; Mizuki, T. In Proceedings of the International Conference on Coal Science, Pittsburgh, 1983; pp 195-198. (14)Kamiya, Y.; Futamura, S.;Mizuki, T.;Kajioka, M.; Koshi, K. Fuel Process. Technol. 1986, 14, 79-90.
Mochida et al. donor but also through bimolecular reaction routes between coal and donor molecules. These routes have their own reaction features. For the former route, only the reactive and weak bonds in the coal macromolecules and their derivatives may break thermally to react with donors. In this case, the reactivity of naphthenic C-H bonds in donors is not so distinguished, because the coal fragment radicals are very reactive. The conversion by this route will be saturated at a limited level according to number of the weak bonds in the coal. In the latter routes, the bonds strong enough for the thermal pyrolysis can also be fissioned. The amount as well as the reactivity of the donor and the reaction sites (sufficient hydrogenation susceptibility and fissionable bonds after hydrogenation) in the substrates define the liquid yield and conversion of the donor. The contribution of these routes to the product distribution may be subject to the reactivities of donor as well as coal and to liquefaction conditions. The isomerization of the cyclohexane ring which leads to poor donorability is well documented in the 1iterat~re.l~ It is another important point in the evaluation of donors, especially when the liquefaction temperature is over 450 "C. Donors of the present study can be classified in the liquefaction a t 450 "C as follows: 4HFL: very reactive, leading to a shortage of hydrogens at a solvent/coal (S/C) of 1. More 4HFL is necessary to increase the oil yield. 8HAn: rather stable and reactive, but a considerable amount stayed unchanged even at a S/C of 1. More 8HAn slightly increased the oil yield. 12HTp: rather reactive, but not stable enough even at 450 "C. 6HAn: too reactive, losing hydrogen during heating. According to the above discussion, the design of the donor solvent is important to achieve a higher conversion with less solvent. A mixture of solvents of rather high (4HFL) and low (8HAn) reactivities may be effective in reducing the amount of solvent, especially when highly reactive 4HFL is used after the unimolecular depolymerization with 8HAn is finished. The details will be reported later. Registry No. IHFL, 20279-21-4; GHAn, 5910-28-1; 8HAn, 1079-71-6; 12HTp, 1610-39-5. (15)Philip, J. C.; Trevor, D. G.; Horst, R.; Michael, A. W. Fuel 1985, 64, 1280-1285.
