260
Energy & Fuels 1996, 10, 260-261
Communications Remarkable Oil Yield from an Indonesian Subbituminuous Coal in Liquefaction Using NiMo Supported on a Carbon Black under Rapid Stirring Kinya Sakanishi, Hideki Taniguchi, Haru-umi Hasuo, and Isao Mochida* Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan Received June 20, 1995 Introduction Unceasing efforts to cut the cost of coal liquefaction process have been continuing to meet the demand of liquid fuel in the next century. A catalyst that produces higher oil yield at lower cost is recognized as a key to develop such a process. The present authors have proposed NiMo catalyst supported on a particular carbon black of Ketjen Black (KB) which has been proved to exhibit excellent activity for the liquefaction of an American bituminous coal at its recovery from the product by the gravimetric separation based on its hollow sphere of low gravity.1-3 The very fine particles of the carbon black around 30 nm provided a large surface for supporting Ni and Mo; however they tend to agglomerate, lowering their contact with substrate. In the present study, the effect of stirring speed on oil yield was examined in the liquefaction of Tanitoharum coal, an Indonesian bituminous coal, because high-speed stirring appears to be very effective to disperse the carbon black particles.
Figure 1. Effect of reaction time, pressure, and stirring speed on the liquefaction yields of Tanitoharum coal with NiMo/KB as the catalyst. Reaction conditions: temperature, 450 °C; pressure, 13, 15 MPa; time, 60, 90 min; stirring speed, 500, 1300 rpm; heating rate, ca. 20 °C/min; catalyst: NiMo/KB (Ni, 2 wt %, Mo 10 wt %), 0.1g; solvent: tetralin, 4.5 g; coal: Tanitoharum coal, 3.0 g. Table 1. Properties of Ketjen Black particle size (nm)
surface area (m2/g)
apparent density (g/L)
30
1270
115
Experimental Section Catalysts and Materials. Some properties of KB are shown in Table 1. Ni(2 wt %),Mo(10 wt %)-supported KB catalyst (NiMo/KB) was prepared by impregnating Ni(OAc)2 and molybdenum dioxyacetylacetonate (MoO2-AA) in methanol solution. The catalyst precursor was dried at 120 °C for 12 h in vacuo. The catalyst was presulfided in 5% H2S/H2 flow at 360 °C for 2 h prior to the reaction. A synthetic pyrite powder provided by NEDO was used as a reference catalyst for comparison. The elemental analysis of Tanitoharum coal is summarized in Table 2. Tetralin (TL) of commercial guaranteed grade (>95% purity) was used as a liquefaction (hydrogen donating) solvent. Liquefaction Procedure. The liquefaction was carried out using a 50 mL magnetic-stirred autoclave at a prescribed temperature of 450 °C. Stirring speeds were set at 500 and 1300 rpm. The coal (3.0 g), the solvent (4.5 g), and the catalyst (0.1 g, NiMo/KB or pyrite) were charged into the autoclave, which was then pressurized with hydrogen to 9.3-11 MPa at room temperature after replacing the air with nitrogen gas. The heating rate was ca. 20 °C/min. After the reaction, the (1) Mochida, I.; Sakanishi, K.; Sakata, R.; Honda, K.; Umezawa, T. Energy Fuels 1994, 8, 25. (2) Mochida, I.; Sakanishi, K.; Taniguchi, H.; Hasuo, H.; Okuma, O. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40(2), 329. (3) Sakanishi, K.; Hasuo, H.; Mochida, I.; Okuma, O. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40(2), 377.
0887-0624/96/2510-0260$12.00/0
Table 2. Elemental Analyses of Tanitoharum Coal wt % (daf) C
H
N
(O + S)
ash (wt %)
71.6
5.6
1.6
21.2
3.9
product remaining in the autoclave was recovered with THF and extracted in sequence with n-hexane, acetone, and THF after the evaporation of THF. The n-hexane-soluble (HS), n-hexane-insoluble-acetone-soluble (HI-AcS), acetone-insoluble-THF-soluble (AcI-THFS), and THF-insoluble (THFI) substances were defined as oil (O), asphaltene (A), preasphltene (PA), and residue (R), respectively. The gas yield (G) was calculated by the difference between weights of the initial raw materials and recovered products.
Results Figure 1 illustrates the liquefaction yields from Tanitoharum coal at 450 °C, 13 or 15 MPa of H2, 60 or 90 min, and stirring speeds of 500 or 1300 rpm. An oil yield of 63% was obtained at 13 MPa of H2 for 60 min reaction time and at a stirring speed of 500 rpm. The yield was much superior to that (50%) obtained by synthetic pyrite of the same weight under the same © 1996 American Chemical Society
Communications
Energy & Fuels, Vol. 10, No. 1, 1996 261
conditions. A longer reaction time of 90 min reduced the yields of asphaltene and preasphaltene to 8 and 3.8%, respectively, from 14.7 and 5.3%. No increase of gas yield was noted with a longer reaction time. The oil yield reached as high as 71.3%. THFI residue was as low as 1.3% regardless of the reaction conditions, reflecting very low inert content and effective hydrogen donating. Stirring at 1300 rpm under the same liquefaction conditions at the reaction time of 60 min increased the oil yield to 67.2% and slightly reduced the yields of gas, asphaltene, and preasphaltene. Longer reaction time of 90 min increased the oil yield to 71.0% which was much the same as that obtained by slower stirring. Higher pressure of 15 MPa with faster stirring was effective to achieve the oil yield as high as 70.2% at 60 min and 74.4% at 90 min. Significant reduction of asphaltene and preasphaltene yields with unchanged gas yield was the reason for such a high oil yield. Discussion The present Communication reports the very high oil yield of 74.4% from an Indonesian subbituminous coal under conventional liquefaction conditions except for the rapid stirring in an autoclave. The reaction time of 90 min of the reaction time may appear a little too long. However, a large gas/liquid ratio in a flow reactor will allow such a reaction time.4
High oil yield was obtained by conversion of asphaltene and preasphaltene without increase of gas yield, indicating that the catalyst may accelerate the conversion very effectively. Fine particles of NiMo/KB catalyst are better dispersed in the liquefaction system than the pyrite due to the low apparent density and the lypophilic nature of the carbon black. Such a high dispersion of the catalyst allows better contact with the substrate for higher conversion to oil. Further devices to disperse the catalyst particles better may further increase the conversion. The present coal has a very low inert maceral content. The present liquefaction results suggest the possibility of the extremely high conversion into oil. The catalyst can be easily separated from the minerals if no binding substrates in the organic residue are present. Thus, the catalyst can be recycled, reducing its cost markedly. The present Communication indicates that the selection of starting coal and catalyst design may further reduce the cost of coal liquefaction through the higher oil yield, catalyst recycle, and smaller reactor. Lower catalyst loading also may benefit the potential process. EF9501206
(4) Yasumuro, M.; Shindo, A.; Ida, T.; Hirano, T.; Katsushima, S.; Kageyama,Y. Proc. 31st Coal Sci. Meet. Jpn. 1994, 127.
