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Optimized Solvent Amount in the Liquefaction of Adaro Coal with Binary Sulfide Catalyst Supported on Carbon Nanoparticles Unggul Priyanto,† Kinya Sakanishi,‡ and Isao Mochida*,† Institute of Material Study, Kyushu University, Kasuga, Fukuoka 816-8580, Japan, and National Institute for Resources and Environment, Tsukuba, Ibaraki 305-8567, Japan Received August 18, 1999
Liquefaction of Adaro coal was performed in an autoclave of 50 mL capacity, at variable solvent (tetralin)/coal ratios from 0 to 2 in single and two stages under the reaction hydrogen pressure of 15 MPa by using FeNi and NiMo catalysts supported on carbon nano particles (Ketjen Black). The maximum oil yield (68%) was obtained at the donor solvent/coal ratio of 1, while the solvent/ coal ratio of 0.5 gave the minimum oil yield (38%) in the single- and two-stage liquefaction with FeNi/KB catalyst. Solvent-free liquefaction maximized the hydrocarbon gas/oil yield ratio with FeNi/KB. The catalyst giving a high oil yield (68%) in the liquefaction with tetralin as an H-donor solvent was forced to give a low oil yield when 1-methylnaphthalene was used as non-H-donor solvent. In a marked contrast, NiMo/KB catalyst gave the minimum oil yield at the ratio of zero for the single stage and provided high oil yield (73%) with the nondonor as well as H-donor solvent.
Introduction Many efforts have been spent to reduce the cost and improve the efficiency in the development of coal liquefaction. The catalyst is a key to develop more efficient liquefaction. Highly dispersed and fine particles of Fe and Mo sulfides have been explored, their high activity being reported.1-6 The present authors have also proposed NiMo and FeNi supported on carbon nano particles (Ketjen Black, KB), which exhibited very high activity and recovery for the repeated use.6-11 Such catalysts may not penetrate into the pore of the solid coal. However, they can be highly dispersed into the swollen or softened coal at the initial stage liquefaction. The solvent is another important device to improve the efficiency of the coal liquefaction. The highest oil yield is expected to be achieved with the lowest amount * Corresponding authors. † Kyushu University. ‡ National Institute for Resources and Environment. (1) Derbyshire, F. J.; Catalysis in Coal Liquefaction: New directions for research; IEA Coal Research: London, June 1988. (2) Whitehurst, D. D.; Mitchell, T. O., Farcasiu, M. Coal Liquefaction-The Chemistry and Technology of Thermal Processes; Academic Press: New York, 1980. (3) Derbyshire, F. J. Energy Fuels 1989, 3, 273. (4) Mochida, I.; Sakanishi, K. Advances in Catalysis; Academic Press: San Diego, CA, 1994; p 39. (5) Mochida, I.; Sakanishi, K.; Sakata, R.; Honda, K.; Umezawa, T. Energy Fuels 1994, 8, 25. (6) Mochida, I.; Sakanishi, K.; Suzuki, N.; Sakurai, M.; Tsukui, Y.; Kaneko, T. Catal. Surv. Jpn. 1998, 2, 17. (7) Sakanishi, K.; Hasuo, H.; Mochida, I.; Okuma, O. Energy Fuels, 1995, 9, 995. (8) Sakanishi, K.; Hasuo, H.; Kishino, M.; Mochida, I. Energy Fuels 1996, 10, 216-219. (9) Sakanishi, K.; Taniguchi, H.; Hasuo, H.; Mochida, I. Energy Fuels 1996, 10, 260. (10) Sakanishi, K.; Taniguchi, H.; Hasuo, H.; Mochida, I. Ind. Eng. Chem. Res. 1997, 36, 1453. (11) Sakanishi, K; Taniguchi, H.; Hasuo, H.; Mochida, I. Ind. Eng. Chem. Res. 1997, 36, 306.
of solvent. The present authors reported that the NiMo/ KB catalyst gave a relatively high oil yield even under solvent-free conditions by controlling the stirring speed in the two-stage liquefaction consisting of lower temperature hydrogenation and higher temperature hydrocracking.12 The interaction of the catalyst and liquefaction solvent has been also recognized to play an important role in the catalytic liquefaction process.13,14 The solvent has several functions: (1) transportation medium for solid coal as slurry into reactor; (2) swelling and softening coal particles; (3) a source of H-donor to provide the principal pathway for H-transfer to the coal; (4) medium for dissolution of gaseous hydrogen; (5) medium to enhance catalyst activity by facilitating catalyst dispersion and extracting the strongly adsorbed poisons. Nevertheless, the reduction of solvent amount improves the reactor efficiency of the coal liquefaction.15 Recently, recycled solvent, which consists of lighter and heavier solvents, has been proposed for the brown coal liquefaction process.16 The lighter solvent is vaporized and removed from the coal slurry before the first reactor to concentrate the catalyst as well as the coal in the reactor. In this study, liquefaction of Adaro coal, an Indonesian sub-bituminous coal was examined at variable solvent (tetralin)/coal ratios by using FeNi/KB and (12) Sakanishi, K.; Hasuo, H.; Kishino, M.; Mochida, I. Energy Fuels 1998, 12, 284. (13) Mochida, I.; Sakata, R.; Sakanishi, K. Fuel 1989, 68, 306. (14) Derbyshire, F. J.; Davis, A.; Lin, R.; Stansberry, P. G.; Terrer, M. T. Fuel Process. Technol. 1986, 12, 127. (15) Hulston, C. K.; Redlich, P. J.; Jackson, W. R.; Larkins, F. P.; Marshall, M. Fuel 1996, 75, 1387. (16) Yasumuro, M.; Katsushima, S.; Kageyama, Y.; Matsumura, T. Coal Science; Pajares, J. A., Tascon, J. M. D., Eds.; Elsevier Science: New York, 1995; p 1371.
10.1021/ef9901802 CCC: $19.00 © 2000 American Chemical Society Published on Web 06/07/2000
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Table 1. Properties of Catalysts NiMo/KB
FeNi/KB
1270 30 115 2 10
1270 30
(m2/g)
surface area particle size (nm) apparent density Ni (wt %) Mo (wt %) Fe (wt %)
NiMo/Al2O3 400 < 250 000
10
FeS2 12 10 000
2.4 10
10
Table 2. Elemental Analysis of Coal Adaro coal a
Ca
Ha
Na
(O + S)a
ashb
70.22
5.15
0.99
23.57
1.3
b
In wt % (daf). In wt %.
NiMo/KB catalysts to clarify the interaction of the catalysts with solvent and the solvent roles in the production of oil from coal yield. Since the present two catalysts are very contrasting in their hydrogenation activity, their characteristics can be determined by observing the liquefaction at different solvents and solvent/coal ratios.
Figure 1. Influence of solvent (TL)/coal ratio on the singlestage liquefaction of Adaro coal using FeNi/KB catalyst. Reaction conditions: single-stage 450 °C; 60 min; reaction H2 pressure 15 MPa; coal/solvent/catalyst ) 3 g/X g/0.09 g (X ) 0, 1.5, 3, 4.5, 6); stirring speed 1300 rpm; heating rate 20 °C/min.
Experimental Section Catalyst and Materials. A prescribed amount of Ketjen Black was dispersed in methanol by ultrasonic irradiation for 15 min. Then, iron(II) fumarate and Ni(NO3)2 dissolved in methanol were mixed into the KB-methanol slurry with a small amount of nitric acid (1% vol.) as an additive to prepare FeNi/KB catalyst.11 The slurry was dispersed by ultrasonic methods and then heated at 40 °C for 2 h before the slurry was dried at 120 °C for 12 h in vacuo. Other combinations of metals, Ni/Mo/KB, MoO2-acetyl acetonate, and Ni-acetate, were also prepared by simultaneous impregnation of their salts, using methanol as the solvent.7 A commercial catalyst of NiMo/Al2O3 and synthetic pyrite supplied from NEDO was examined for comparison. These catalysts were presulfided by flowing 5% vol. H2S/H2 at 360 °C for 2 h prior to the reaction. Some properties of catalysts are shown in Table 1. The elemental analysis of Adaro coal is summarized in Table 2. Commercially guaranteed grade tetralin (TL) and 1-methylnaphthalene were used as liquefaction solvents. Liquefaction Procedure. Coal liquefaction was performed in an electromagnetic-driven autoclave of 50 mL capacity at 450 °C for single-stage and 360 and 450 °C for two-stage liquefaction. A 3 g amount of coal, solvent (0, 1.5, 3, 4.5, 6 g), and 0.09 g of catalyst were charged to the autoclave. The single- and two-stage liquefactions were performed under 15 MPa of hydrogen pressure at the reaction temperature for 60 min. The heating rate to the reaction temperature was 20 °C/ min. The stirring speed was 1300 rpm. In case of solvent-free liquefaction, the stirring speed was set at 500 rpm until the temperature reached 300 °C in order to get good mixing between coal and catalyst. Afterward, the stirring speed was increased to 1300 rpm. For two-stage liquefaction, the first stage was performed first at 360 °C for 60 min, and then the reactor was cooled. Hydrogen gas was renewed after releasing outgaseous products. The second-stage reaction was carried out at 450 °C, 15 MPa, for 60 min. The liquid and solid products of coal liquefaction were recovered with THF. After THF was removed by evaporation, the product was extracted in sequence with n-hexane, acetone, and THF. The n-hexane-soluble (HS), hexane-insoluble but acetone-soluble (HI-ACS), acetone-insoluble but THF-soluble (ACI-THFS), and THF-insoluble(THFI) substances were defined as oil (O) and solvent, asphaltene (A), preasphaltene (PA), and residue (R),respectively. The gas yield was calculated
Figure 2. Influence of solvent(TL)/coal ratio on the two-stage liquefaction of Adaro coal using FeNi/KB catalyst. Reaction conditions: two-stage conditions; 360 °C-60 min/450 °C-60 min; reaction presure 15 MPa; coal/solvent/catalyst ) 3 g/X g/0.09 g (X ) 0, 1.5, 3, 4.5, 6); stirring speed 1300 rpm; heating rate 20 °C/min. by weight difference between initial coal and recovered product. The oil yield was calculated by subtracting the solvent weight from the total weight of HS. The reaction under the same conditions was repeated at least three times to make sure the experimental errors that were with 1 wt % daf coal base. Analysis of Gas Products. Gas products were identified and quantified by using GC-TCD (GC-140 Shimadzu) and FID (GC-2800 Yanaco) by sampling from the autoclave.
Results Single- and Two-Stage Liquefaction of Adaro Coal by Variable Solvent/Coal Ratios Using FeNi/ KB Catalyst. Figures 1 and 2 describe the products in the single- and two-stage liquefaction of Adaro coal, using FeNi/KB catalyst by variable tetralin/coal ratios. In the single-stage liquefaction, the maximum oil yield of 68% was obtained at solvent/coal ratio of 1. The oil yield decreased sharply to 38%, when the solvent/coal ratio was reduced from 1 to 0.5. However, the oil yield increased to 48% by decreasing the solvent/coal ratio from 0.5 to 0. Under solvent-free conditions, the control of stirring speed up to 300 °C is suggested to disperse effectively the catalyst onto the coal particles. In the
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Energy & Fuels, Vol. 14, No. 4, 2000 803
Figure 3. Influence of solvent (TL)/coal ratio on the singlestage liquefaction of Adaro coal using NiMo/KB catalyst. Reaction conditions: single-stage 450 °C; 60 min; reaction H2 pressure 15 MPa; coal/solvent/catalyst ) 3 g/X g/0.09 g (X ) 0, 1.5, 3, 4.5, 6); stirring speed 1300 rpm; heating rate 20 °C/min.
Figure 4. Effect of solvent/coal ratios on the ratio of hydrocarbon gas/oil fraction in the single-stage liquefaction of Adaro coal using FeNi/KB catalyst. Reaction conditions: single stage; 450 °C; 15 MPa; 60 min; stirring speed 1300 rpm; heating rate 20 °C/min.
two-stage liquefaction, the maximum oil yield (73%) was also obtained at the solvent /coal ratio of 1, while the solvent/coal ratio of 0.5 gave the lowest yield (43%). Single-Stage Liquefaction of Adaro Coal with Variable Solvent/Coal Ratios Using NiMo Catalyst. Figure 3 describes the product distribution in the singlestage liquefaction of Adaro coal using NiMo/KB catalyst by variable tetralin/coal ratios. The highest oil yield (75%) was obtained at a solvent/coal ratio of 1. From the solvent/coal ratio of 1-2, the oil yield decreased moderately to 71%. The asphaltene and preasphaltene yields increased in line with the rise of solvent/coal ratio while the gas yield decreased. Unlike FeNi catalyst, NiMo catalyst in the coal liquefaction at the coal/solvent ratio of 0.5 gave higher oil yield (65%) compared to that
Figure 5. Activities of catalysts in the single-stage liquefaction of Adaro coal with tetralin solvent: (a) NiMo/KB; (b) FeNi/ KB; (c) NiMo/Al2O3; (d) FeS2. Reaction conditions: 450 °C; 60 min; reaction H2 pressure ) 15 MPa; coal/solvent/catalyst ) 3 g/3 g/0.09 g; stirring speed ) 1300 rpm; heating rate ) 20 °C/min.
of solvent-free liquefaction. The high activity of NiMo/ KB could hydrogenate the radical species formed at coal dissolution. In general, the NiMo/KB catalyst in tetralin solvent provided a higher oil yield of 6% than FeNi/KB catalyst in the same solvent. Effect of Solvent (TL)/Coal Ratios in the Liquefaction on the Composition of Gas. Figure 4 shows the ratio of hydrocarbon gas/oil fraction in the singlestage liquefaction of Adaro coal catalyzed by FeNi/KB. The ratio of hydrocarbon gas/oil fraction decreased in order of solvent/coal ratio of 0 > 1 > 1.5 > 2. This means that the more solvent is used, the less hydrocarbon gas/ oil fraction is obtained in the liquefaction. Table 3 shows the yields of CO plus CO2 and hydrocarbon gases in the single-stage liquefaction. The highest CO + CO2 gas yield was obtained at the solvent/ coal ratio of zero. Comparison of Sulfide Catalysts in the Liquefaction of Adaro Coal. Figure 5 compares the catalytic activities of NiMo/KB, FeNi/KB, commercial NiMo/ Al2O3, and FeS2 catalysts in the single-stage liquefaction. The oil yields produced with NiMo/KB, FeNi/KB, NiMo/Al2O3, and FeS2 catalysts were 75%, 68%, 68%, and 58%, respectively. The highest activity of NiMo/KB was confirmed. The FeNi supported on KB of a large surface area should be noted to give oil yields comparable to those of the NiMo/Al2O3 catalyst even though NiMo/Al2O3 carried expensive Mo. FeS2 catalyst gave the lowest oil yield, reflecting its smallest surface area and the poor activity of iron sulfide itself. The support of a very high surface area can significantly improve the activity of supported metal sulfides. Table 4 summarizes the conversion of tetralin into naphthalene after the liquefaction at 450 °C and 15 MPa for 60 min. The FeNi/KB catalyst allowed only 21% conversion, which is almost the same as that of NiMo/
Table 3. Gaseous Products in the Single-Stage Coal Liquefaction with FeNi/KB Catalyst at Variable Solvent/Coal Ratiosa gas product
solvent/coal ratio of 0 (wt %) (daf base)
solvent/coal ratio of 1 (wt %) (daf base)
solvent/coal ratio of 1.5 (wt %) (daf base)
solvent/coal ratio of 2 (wt %) (daf base)
CO + CO2 hydrocarbon gas total
11.6 9.8 21.4
6.9 9.3 16.2
7.0 8.4 15.4
7.1 7.5 14.6
a
Reaction conditions: 450 °C; 15 MPa; 60 min; stirring speed 1300 rpm.
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Table 4. Conversion of Tetralin during Coal Liquefactiona catalyst
tetralin conv (%)
NiMo/KB FeNi/KB NiMo/Al2O3 FeS2
20 21 27 42
a Reaction conditions: 450 °C; 60 min; 15 MPa; stirring speed 1300 rpm.
Figure 7. Activities of FeNi, NiMo/Al2O3, and NiMo/KB catalysts using 1-methylnaphthalene as solvent in the singlestage liquefaction. Parts a-c are liquefaction products using FeNi/KB, NiMo/Al2O3, and NiMo/KB catalysts, respectively. Reaction conditions: single stage; 450 °C; 60 min; reaction H2 pressure ) 15 MPa; coal/solvent/catalyst ) 3 g/3 g/0.09 g; stirring speed ) 1300 rpm; heating rate ) 20 °C/min.
Discussion
Figure 6. Effect of catalyst activity on the ratio of hydrocarbon gas/oil fraction in the Adaro coal liquefaction. Reaction conditions: single stage; 450 °C; 15 MPa; 60 min; stirring speed 1300 rpm; coal/solvent/catalyst: 3 g/3 g/0.09 g; heating rate 20 °C/min.
KB catalyst. Low consumption of H-donor should be noted. In contrast, NiMo/Al2O3 and FeS2 provided 27% and 42% conversions, respectively, indicating limited hydrogenation to the coal. Figure 6 shows the effects of catalyst on the ratio of hydrocarbon gas/oil fractions in the liquefaction of Adaro coal. The ratio increased in the order of NiMo/KB ) NiMo/Al2O3 < FeNi/KB < FeS2. The Mo-based catalysts gave smaller gas yields than those with Fe-based catalysts. The loading of Ni can also reduce the gas formation. Table 5 summarizes CO + CO2 and hydrocarbon gas product in the single-stage liquefaction with variable catalysts. The NiMo/KB and NiMo/Al2O3 catalysts produced less CO + CO2 than FeNi/KB and FeS2. Coal Liquefaction in 1-Methylnaphthalene by Using Sulfide Catalysts. Figure 7 illustrates the activities of FeNi/KB, NiMo/KB, and NiMo/Al2O3 catalysts in the single-stage liquefaction of Adaro coal, using 1-methylnaphthalene as the solvent. The oil yields obtained with NiMo/KB and NiMo/Al2O3 were 74% and 63%, respectively. Such values were similar to those produced by using tetralin solvent (see Figure 5). In contrast, the FeNi/KB catalyst in methylnaphthalene gave a much lower oil yield (18%) than that in tetralin (68%). Table 6 summarizes the hydrogenation conversions of 1-methylnaphthalene with FeNi/KB and NiMo/KB catalyst at 360 and 450 °C. NiMo/KB and FeNi/KB catalysts gave conversions of about 96% and 11%, respectively, at 360 °C; however, they did about 81% and 46%, respectively, at 450 °C, indicating that Mobased and Fe-based catalysts are more effective at lower and higher temperatures, respectively, for the hydrogenation of aromatic ring.
The present study described very high activity of NiMo and FeNi both supported on carbon nano particles (Ketjen Black, KB) in both single- and two-stage liquefaction although NiMo and FeNi exhibited their own characteristic features in their catalytic functions. The carbon particles allow high dispersion of catalysts into the swollen or softened coal particles to provide intimate contact between catalyst and coal. The high oil yield is ascribed to less production of hydrocarbon gases as well as asphaltene and preasphaltene. The hydrocarbon gases are produced through hydrogenative dealkylation. Extensive hydrogenation of the aromatic ring before dealkylation reduces the gaseous product. Hence, NiMo gives less gas yield than FeNi because Fe-based catalyst is rather active for the dealkylation reaction of alkyl aromatics.17 Such hydrogenation activity of NiMo reduces also CO2/CO production by hydrogenative deoxygenation of oxygen functional groups. Two-stage liquefaction is always effective to increase the oil yield especially with NiMo/KB catalyst. Hydrogenation of substrates and high dispersion of catalyst during the first stage is effective by the aid of an H-donor to reduce both heavy and gaseous products. The roles of solvent are of value for discussion. First of all, the optimum amount of H-donor (tetralin) was found at the solvent/coal ratio of 1 over both NiMo/KB and FeNi/KB catalysts. Less or more solvent reduces the oil yield. More solvent may retard the catalytic hydrocracking of asphaltene or preasphaltene because more solvent may reduce the intimate contact among the catalyst and the asphaltene or preasphaltene.18 It is rather peculiar that the tetralin/coal ratio of 0.5 gave the minimum oil yield over FeNi/KB, which was smaller than that obtained without solvent. NiMo/KB exhibited the minimum yield without solvent as expected. The hydroaromatic content of the solvent that is not sufficiently present may cause deleterious side reactions such as solvent dimerization and char forma(17) Montano, P. A.; Granoff, B. Fuel 1980, 59, 214. (18) Ikenaga, N.; Sakoda, T.; Matsui, T.; Ohno, K.; Suzuki, T. Energy Fuels 1997, 11, 183-189.
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Table 5. Gaseous Products in the Single-Stage Coal Liquefaction at the Solvent/Coal Ratio of 1a
a
gas product
NiMo/KB catalyst (wt %) (daf base)
NiMo/Al2O3 catalyst (wt %) (daf base)
FeNi/KB catalyst (wt %) (daf base)
FeS2 catalyst (wt %) (daf base)
CO + CO2 hydrocarbon gas total
6.0 9.5 15.5
6.6 8.9 15.5
6.9 9.3 16.2
7.8 10.9 18.7
Reaction condition: 450 °C; 15 MPa; 60 min; stirring speed 1300 rpm.
Table 6. Hydrogenation of 1-Methylnaphthalenea over FeNi/KB and NiMo/KB Catalysts catalysts
conv %b
conv %c
FeNi/KB NiMo/KB
11 96
46 81
a Catalysts, 0.09 g; 1-methylnaphthalene, 6 g. b Reaction conditions: 360 °C; 15 MPa; 60 min; stirring speed 1300 rpm. c Reaction conditions: 450 °C; 15 MPa; 60 min; stirring speed 1300 rpm.
tion.19 Stable solvent composition can be achieved by rehydrogenating the hydrogen-depleted solvent with gaseous hydrogen. Unfortunately, FeNi/KB catalyst is not so active to hydrogenate the solvent at a sufficient rate. The second point for discussion concerns with the consumption of tetralin through dehydrogenation during the liquefaction. The same conversion of about 20% was obtained with both NiMo and FeNi/KB, indicating similar hydrogenation activity of the catalysts under the liquefaction conditions. NiMo/KB was found much more active for the hydrogenation of 1-methylnaphthalene at 360 °C. However, its preference is reduced at a higher temperature of 450 °C as shown in Table 4, where (19) Shah, Y. T.; Reaction Engineering in Direct Coal Liquefaction; Addison-Wesley Publishing Co., Advanced Book Program/World Science Division: Reading, MA, 1981.
hydrogenation equilibrium and activation energy can govern the conversion on NiMo and FeNi, respectively, counting the similar conversion level of tetralin under the liquefaction conditions. In contrast to tetralin, 1-methylnaphthalene provided much less oil yield with FeNi/KB than that with NiMo/ KB. When coal dissolution starts, 1-methylnaphthalene stays almost unhydrogenated over FeNi/KB, little Hdonor being available at that moment to prevent the retrogressive reactions. In contrast, 1-methylnaphthalene was hydrogenated at almost 100% over NiMo/KB at coal dissolution (see Table 4). Such a situation appears different from that of tetralin solvent where hydrogen required for stabilizing free radicals was provided by tetralin, while naphthalene was regenerated back to the donor by the catalyst.1 Fe sulfide is much less active for hydrogenation than Mo sulfide even though both catalysts are significantly activated with Ni sulfide. Different roles of Ni in Fe sulfide are suggested, for the active site. In contrast, Ni in Mo sulfide is often referred as the promoter. The mixture of Mo and Ni has a higher activity than that of either components. Hence, both Mo and Ni sulfides can be active components in Fe sulfide. EF9901802
