Energy & Fuels 1995,9, 995-998
995
Preparation of Highly Dispersed NiMo Catalysts Supported on Hollow Spherical Carbon Black Particles Kinya Sakanishi, Ham-umi Hasuo, Isao Mochida," and Osamu Okumat Institute of Advanced Material Study, Kyushu University,Kasuga, Fukuoka 81 6, Japan Received May 5, 1995@
A special carbon black, Ketjen Black (KB), which has an extremely high surface area and low specific gravity, was selected as a catalyst support to prepare a highly dispersed NiMo catalyst for the hydrogenation of 1-methylnaphthalene, using a 50 mL magnetically-stirred autoclave under the standard conditions of 380 "C, 40 min, and 9.5 MPa of Ha reaction pressure. The catalyst, prepared from molybdenum dioxyacetylacetonate and nickel acetate in methanol solution by successive impregnations of Mo (10 wt %) and Ni (2 wt %) in that order, provided the highest conversion of 84% to methyltetralins. Combinations of soluble metal salts, impregnation solvents, and surface properties of carbon black are suggested to be very important for the preparation of a highly active catalyst. KB-supported NiMo catalysts showed a much higher activity for 1-methylnaphthalene hydrogenation than a commercial NiMo/AlzOs.
Introduction NiMo and CoMo supported on alumina extrudates are extensively applied in petroleum refineries as hydrotreating catalysts. Alumina is believed t o be one of the best supports because of its large surface area for high dispersion of catalyst species and high mechanical strength for the conventional fxed bed flow reactors. However, such alumina-supported Mo-based catalysts often suffer from coking and plugging problems due t o the acidity or polarity of alumina and the limited activity for heavy polyaromatic hydrocarb~ns.l-~ Hence, modification of the alumina support, or other supports such as T i 0 2 and carbon, have been e ~ a m i n e d . ~ - ~ Furthermore, fine particles of a Mo-based catalyst are applied in a moving bed.*-1° The recovery of the fine particle catalyst from the moving bed is one of the problems t o be solved. The present authors have proposed that carbon-supported catalysts can be recovered after the reactions by gravimetric separation due to their low specific gravity and hydrophobic properties for phase separation.'lJ2 Polymer and Chemical Technology Lab., Kobe Steel, Ltd., Kobe, Hyogo 651-22, Japan. @Abstractpublished in Advance ACS Abstracts, October 15, 1995. (l)Groot, C. K.;de Beer, V. H. J.; Prins, R.; Stolarski, M.; Niedzwiedz, W. S. Ind. Eng. Chem. Prod. Res. Dev. 1986,25,522530. (2) Hillerova, E.;Vit, Z.; Zdrazil, M.; Shkuripat, S. A.; Bogdanets, E. N.; Startsev, A. N. Appl. Catal. 1991,67,231-236. (3)Louwers, S. P. A,; Prins, R. J. Catal. 1992,133,94-111. (4) Mochida., I.: ~,Oishi. T.: Korai. Y.: Fuiitsu. H. Ind. Ene. Chem. Prod. Res. Dev. 1984,23,203-205.' (5)Japanese Patent, Showa57-132547 (1982). (6) Paradhan, V.R.; Hemck, D.E.; Tierney, J. W.; Wender, I. Energy Fuels 1991,5,712-720. (7) Duchet, J. C.; van Oers, E. M.; de Beer, V. H. J.; Prins, R. J. Catal. 1983,80,386-402. (8)Kagevama, Y.;Masuvama, T. Proc. Int. Conf. Coal Sci. 1986, 157-160: (9) Kim, S. I.; Woo, S. I. J. Catal. 1992,133,124-135. (10)Derbyshire, F. J.; DeBeer, V. H. J.; Abotsi, G . M. K.; Scaroni, A. W.; Solar, J. M.; Skrovanok, D. J . Appl.Cata1. 1986,27,117-131. (11)Mochida, I.; Sakanishi, K.; Taniguchi, H.; Hasuo, H.; Okuma, 0.Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1995,40, 329. (12) Sakanishi, K.;Hasuo, H.; Mochida, I.; OKuma, 0. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1996,40,377. +
~~I
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I
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Table 1. Some Properties of Ketjen Blacks KB EC KB EC600 J D surface area (m2/g) 800 1270 volatile matter (%) 0.5 0.7 9.0 9.0 PH 30 30 particle size (nm) 145 115 apparent density (g/L) 0.1 0.1 ash (%) 1.5 1.5 Ni (ppm) 20 30 V (ppm) 50 100 Fe (ppm) 1 1 Cu (ppm) 1 1 Mn (ppm)
In the present study, Ketjen Black (KB), a unique carbon black, was selected as the support for NiMo. Ketjen Black (KB) is available in the form of hollow spheres of 30 nm in diameter, a surface area of ca. 1000 m2/g, and a low specific gravity (115 g/L) suitable for the catalyst recovery.13J4 Although carbon blacks have been reported to exhibit some catalytic activity for hydrocracking due to its positively charged surface, its high surface area, and its functional g r ~ u p s , ~ sup~J~ ported NiMo is expected to show a much higher activity for the hydrogenation. The supporting procedures to obtain the higher activity were major concerns in the present study. The application of NiMo/KB catalysts to coal liquefaction as a potentially recoverable catalyst will be reported in following papers.14J7
Experimental Section Catalyst. Some properties of Ketjen Black EC (KB EC) and Ketjen Black EC 600JD (KB JD) provided by Mitsubishi
Chemical Co. are summarized in Table 1. N i and Mo salts were applied by several impregnating methods using N i ( N 0 3 ) ~ or Ni(OAc)z, and (N&)a0&4, Mo(CO)6, or Mo dioxyacetyl(13)Nelson, J. R.;Wissing, W. K. Carbon 1986,24,115-121. (14) Sakanishi, K; Hasuo, H.; Kishino, M.; Mochida, I. Energy Fuels,
manuscript in preparation. (15)Farcasiu, M.; Smith, C. Energy Fuels 1991, 5 , 83-87. (16) Farcasiu, M.; Smith, C. Prepr. Pup.-Am. Chem. Soc., Diu. Fuel Chem. 1990,35,404. (17) Sakanishi, K.;Taniguchi, H.; Hasuo, H.; Mochida, I. Energy Fuels, manuscript in preparation.
0887-0624/95/2509-0995$09.00/0 0 1995 American Chemical Society
996 Energy & Fuels, Vol. 9,No. 6, 1995
Sakanishi et al.
Table 2. Catalysts Prepared in the Present Study catalysts A B C D E F G H I J K L M
.5
support
solvent
KB EC KBJD KBJD KBJD KB J D KBJD KB J D KB J D KB J D KBJD KBJD KBJD KB J D
H20MeOH = 9/1 H20MeOH = 9/1 H20/MeOH = 9/1 H20/MeOH = 9/1 H20MeOH = 9/1 H20MeOH = 9/1 H20MeOH = 9/1 H20/MeOH = 9/1 H20/MeOH = 9/1 CsHldMeOH = 111 CsHldMeOH = 111 MeOH MeOH
preparation method simult impregn simult impregn simult impregn simult impregn simult impregn simult impregn simult impregn successive impregn incipient wetness successive impregn successive impregn successive impregn successive impregn
n
40
Ni salt
Mo salt
Ni(N03)2 (1wt %) Ni(N03)2 (1wt %) Ni(N03)2 (1wt %) Ni(N03)2 (2 wt %) Ni(N03)2 (3 wt %) Ni(N03)2 (5 wt %) Ni(N0312 (7 wt %) Ni(N03)2 (2 w t %) Ni(N03)2 (2 wt %) Ni(N03)2 (2 w t %) Ni(0Ac)z (2 wt %) Ni(N03)~(2 wt %) Ni(0Ac)a (2 wt %)
40
1
v1
a
=
8
30
20 10
0 (a)
(h)
(c)
(d)
(e) catalyst
(0
(g)
(h)
(I)
Figure 1. Hydrogenation activities of Ni-Mo/Kl3 catalysts prepared by different supporting procedures: (a) catalyst A; (b) catalyst B; (c) catalyst D; (d) catalyst H; (e) catalyst I; (0 catalyst J; (g)catalyst K, (h)catalyst L; (i)catalyst M. Reaction conditions: l-MN/DHN = 119; reaction temperature 380 "C; reaction pressure 9.5 MPa; reaction time 40 min; catalyst 1 wt % addition to 1-MN. acetonate(MoO2-AA) in water, methanol, and their 9:1mixture, or n-hexane according to the solubility of the salts. In the case of successive impregnation, molybdenum was first impregnated. The list of catalysts prepared in t h e present study is summarized in Table 2. The catalyst precursors were dried at 120 "C for 12 h in uacuo and presulfided i n a 5% H2S/H2 flow at 360 "C for 3 h prior to t h e reaction. A commercially available NiMo/AlzOs (Ni0;3 wt %, Mo03;15 wt %), provided by Nippon Ketjen Co., was used for comparison. Activity Test. 1-Methylnaphthalene(1-MN; 1.0 g), decalin (9.0 g), and catalyst (1 wt % based on 1-MN) were charged into a 50 mL magnetically-stirred autoclave. Standard conditions for the hydrogenation were 40 min at 380 "C and 9.5 MPa of H2 of reaction pressure. The hydrogenated 1- and 5-methyltetralin products a n d a trace of tetralin were identified and quantified by GC and GC-MS to calculate t h e hydrogenation activity and selectivity over t h e respective catalyst. About 5% error with t h e experimental d a t a was estimated based on t h e triplicate experiments.
Results Catalytic Activity of NiMo KB Catalysts. Figure 1illustrates the catalytic activities of a series of NiMo/ KB catalysts prepared by different procedures, using KB EC and KB ECGOOJD (KB JD). The catalytic reaction with the present catalysts produced 1- and 5-methyltetralins (MT), the latter always being the major product. The 1-/5-MT selectivity was around 0.5, although it depends on the reaction conditions. The activity of the KB JD supported catalyst (catalyst B) was always greater than that of KB EC (catalyst A,
Figure 2. Activity of t h e NiMo/KB with variable Ni content. Reaction conditions: 1-MN/DHN = 1/9; reaction temperature 380 "C; reaction pressure 9.5 MPa; reaction time 40 min; caalyst catalyst B-catalystG, 1 wt % addition to 1-MN.
Figure l), reflecting the higher surface area and higher dispersion of metal species. Activities of catalysts D, H, and I reflected the catalyst preparation procedures. Catalysts H prepared by successive impregnations of Mo and Ni in this order and catalyst I by incipient wetness method were certainly more active than catalyst D by simultaneous impregnation of Ni and Mo salts, suggesting that preference of Mo active sites over Ni and better contact between metal salts and KB are essential to the preparation of highly active NiMo/KB catalysts. Activities of the catalysts H, J , K, L and M reflected the influences of the metal salts and solvents in the successive impregnation procedures due to the hydrophobic nature of KB. The largest activity was obtained with Ni(OAc)2 and Mo02-AA in methanol. Ni(NO& and Mo02-AA in methanol provided the second best activity. These activities were much larger than those obtained with other combinations of salts and solvents, indicating that better wettability may be achieved by the combinations of soluble metal salts in organic solvent and hydrophobic KB support. Figure 2 compares the catalytic activities of NiMo/ KB catalyst with variable nickel contents at a fixed Mo content (catalysts B-G) prepared by simultaneous impregnation. The catalytic activity increased with increasing nickel content up to 2-3%. More nickel reduced the activity very gradually, 7% of nickel providing two-thirds of the maximum activity obtained with the 2% nickel catalyst. The ratio of Ni (2 wt %) and Mo (10 wt %) coincides with the ratio of conventional NiMo/AlaOs catalysts which shows the best activity for the hydrogenation of aromatics. Reaction Conditions in the Catalyses by Catalyst M. Figure 3 illustrates the conversion of 1-MN over catalyst M at 380 "C for 40 min by changing the
Preparation of Highly Dispersed NiMo Catalysts
4
6 7 8 9 Reaction p r e s s u d P s
5
10
Figure 3. Effect of reaction pressure on the conversion of 1-MN with NiMo/KB J D or NiMo/AlzO3 catalyst. Reaction conditions: l-MN/DHN = 1/9; reaction temperature 380 "C; reaction time 40 min; catalyst 1 wt % addition to 1-MN.
280
300 320 340 360 380 400 Reaction temperaturd'C
Figure 4. Effect of reaction temperature on the conversion of 1-MN with NiMo/KB J D or KF-842 a s the catalyst. Reaction conditions: 1-MN/DHN = 1/9; reaction temperature 300-380 "C; reaction pressure 9.5 MPa; reaction time 40 min; catalyst 1 wt % addition t o 1-MN. Table 3. Rate Constant of NiMo/KB JD and KF-842at 5.0, 7.0, and 9.5 MPa of Hz Pressurea rate (k x io3) (min-l) catalyst 5MPa 7MPa 9.5MPa 1.1 2.2 3.2 NiMo/AlzO3 NiMo/KB J D (catalyst M) 4.5 7.4 14.1 a
Energy & Fuels, Vol. 9, No. 6, 1995 997
Reaction temperature 380 "C.
hydrogen pressure from 5 to 9.5 MPa. A sharp increase in conversion proportional to the hydrogen pressure was observed. The reaction order in H2 was calculated to be first order. Figure 4 illustrates the conversions at several reaction temperatures of 300-380 "C over the catalyst M. The conversion leveled off or slightly decreased a t higher temperature, as is often experienced.ls Table 3 summarizes the rates of hydrogenation at 380 "C at three different hydrogen pressures. The hydrogenation reaction was found to be first order in 1-MN as well as in H2 pressure under the present conditions. Catalytic Activity of a Commercial NiMo/AlzOs Catalyst. The activity of catalyst M is compared with that of a commercial NiMo/AlzOs catalyst in Figure 5. The conversion of 1-MN by NiMo/AlzOs increased sharply with increasing catalyst amounts. Catalyst M provided 1-MN conversion of 87 and 57%a t catalyst amounts of 5 and 1w t %based on 1-MN, respectively. On the other hand, ground commercial NiMo/AlzOs ( ~ 6 mesh) 0 exhibited a lower conversion of 65 and 18%when 5 and 1 wt % of the catalyst was applied, respectively. A larger difference was found a t lower catalyst loading. The catalytic activity of a commercial NiMo/AlzOs catalyst at 380 "C under variable hydrogen pressures is shown (18) Groot, C. K., de Beer, V. H. J., Prim, R.Ind. Eng. Chem. Prod. Res. Dev. 1986,25, 522-530.
Catalyst M 0
Ni-MolAIZOJ
Figure 5. Effect of catalyst amount on the hydrogenation conversion of 1-methylnaphthalenewith NiMo/KB J D or NiMo/ Al203. Reaction conditions: 1-MN/DHN = 1/9; reaction temperature 380 "C; reaction pressure 9.5 MPa; reaction time 40 min; catalyst catalyst M or NiMo/AlzOa, 1-5 w t % addition to 1-MN.
in Figure 3 for comparison with that of catalyst M. The commercial catalyst provided conversion of 10-20% a t 5-9.5 MPa. The activity difference between the two catalysts was most emphasized under the highest hydrogen pressure of 9.5 MPa. The catalytic activities are also compared in the temperature range of 300-380 "C in Figure 4. The commercial catalyst basically exhibited an activity only above 340 "C, with increasing conversion up t o 360 "C. Conversion stayed at 5%below 320 "C regardless of the reaction temperature. On the other hand, the catalytic activity of the KB-supported catalyst was significant at lower temperature, while the activity at higher temperature was 3-4 times higher than that of the commercial catalyst. Table 3 summarizes the rate of hydrogenation over the commercial catalyst at 380 "C under variable hydrogen pressures. The rates were found to be first order in 1-MN under these conditions, being one-fourth of those for catalyst M under variable H2 pressures.
Discussion The present study revealed that a particular carbon black with an extremely large surface area was an excellent support for a NiMo sulfide catalyst, and exhibited much higher activity for the hydrogenation of 1-methylnaphthalene in the temperature range of 320-380 "C under hydrogen pressures of 5-9.5 MPa than a commercial NiMo catalyst. The catalyst preparatipn procedure is a key to obtain high catalytic activity. Because of the hydrophobic surface of the particular carbon black, the best preparation procedure uses soluble salts in organic solvent for high dispersion of the catalyst precursor. Nickel acetate and molybdenum dioxyacetylacetonate in methanol is the best combination, while nickel nitrate and ammonium molybdate in aqueous solvent gave a limited activity. It is also pointed out that the combination of organic soluble metal salts and methanol may effectively suppress the agglomeration of Ketjen Black ultrafine particles, which is usually observed in water, during the metal impregnation procedures probably due to the balanced hydrophobic nature of solvent matrix. The interesting points of the present catalyst are its activity at lower temperatures and enhancement by high hydrogen pressure. Such higher activity may reflect a higher dispersion of nickel molybdenum mixed
998 Energy & Fuels, Vol. 9, No. 6, 1995
Sakanishi et al.
Table 4. Selectivity of 1-MT and 5-MT from 1-MN HYD" catalyst KF-842 catalyst M
reaction press. (MPa)
conversion
5.0 7.0 9.5 5.0 7.0 9.5
8.6 10.2 17.9 23.7 36.9 57.8
(%)
(%) l-MT/ 1-MTb 5-MT 5-MT
37 35 33 35 33 33
63 65 67 65 67 67
0.59 0.55 0.50 0.55 0.50 0.49
"Reaction temperature and time are 380 "C and 40 min, respectively. 1-MT tetralin yield.
+
sulfide on the surface of the carbon black. It is suggested that hollow spheres of Ketjen Black particles may provide a large number of metal supporting sites in high dispersion. The XRD spectra showed the evidence of high disperion of metal species on the carbon black. The selectivities of hydrogenation between the methyl-substituted and nonsubstituted ring of l-methylnaphthalene under various hydrogen pressures are summarized in Table 4. Although the ratio of 145methyltetralin over catalyst M was much the same to that over the commercial NiMo/AlzOs catalyst, catalyst M provided higher yield of alkyl-substituted ring(1methyltetralin) because of larger conversion. It is expected that the catalyst M provides a high oil yield in coal liquefaction because selective hydrogenation of substituted aromatic ring at lower temperatures pro-
motes the cleavage of strong linkages in the coal molecules such as Caryl-Carylbonds. The activity of the present catalyst in the coal liquefaction will be reported in due course. Another point is that NiMo/KB catalyst can be recovered from the liquefaction residue because it is highly dispersed in the liquefaction soluble products and solvent fraction. It is expected that KB-supported catalyst can be recycled with recycle solvent. The details on the catalyst recovery will be also reported later.
Conclusion Nickel molybdenum sulfide supported on Ketjen Black was found very active for the hydrogenation of 1-methylnaphthalenein the temperature range of 320400 "C. Under a hydrogen pressure of 9.5 MPa, the catalyst is much more active than commercial nickel molybdenum sulfide catalyst. Ketjen Black of larger surface area provided the highest activity by successive impregnation of MoOz-Mnickel acetate for methanol solution probably because of the high dispersion of the precursor salts on the surface. Impregnation from aqueous solution gave a lower activity, for which the hydrophobic surface of KB may be responsible. EF950088F
