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Energy & Fuels 1996, 10, 1028-1029
Communications Functionalized Surfactants as Precursors to Dispersed Coal Liquefaction Catalysts Manohar Vittal* and Andre´ L. Boehman Fuel Science Program, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 Received December 11, 1995. Revised Manuscript Received February 5, 1996 Dispersed-phase catalysts for direct coal liquefaction are often introduced as water-soluble or oil-soluble precursors.1,2 Under liquefaction conditions, the metal precursor decomposes, producing fine particles of catalyst which are well dispersed through the coal. Oilsoluble metal compounds have been shown to be particularly effective precursors, probably because they are miscible with the hydrocarbon solvent and thus enjoy a high degree of interaction with the coal surface.3-5 In this work, we explored a functionalized (metal-exchanged) anionic surfactant as a precursor to highly dispersed coal liquefaction catalysts. The functionalized surfactant was oil-miscible and thermally decomposable and was introduced by dissolving it in the reaction solvent. The metal function was chosen from the group of Co, Ni, and Fe, all known to be active for coal liquefaction. The catalyst precursors used in this study were based on the surfactant Aerosol OT-100 (AOT, sodium dioctylsulfosuccinate), obtained from Cytec Industries. AOT was changed into the cobalt, nickel, or iron form by liquid ion exchange. A bituminous coal (Blind Canyon, DECS-17) and a subbituminous coal (Wyodak, PSOC 1401) were used in this study (Table 1). The amount of catalyst required for a particular catalyst loading was first dissolved in the reaction solvent, either 1-methylnaphthalene (1-MN) or 1,2,3,4-tetrahydronaphthalene (tetralin). Coal liquefaction tests were conducted in 25 mL microautoclave reactors (tubing bombs) in a preheated sandbath. Two grams of coal, 2 g of solvent, and 11 mg of sulfur were charged into the reactor. The reactor was pressurized thrice to 6.9 MPa with hydrogen to remove air. Subsequently, the reactor was pressurized to 6.9 MPa (cold) with hydrogen. It was then immersed in the sandbath and agitated at 200 cycles/ min. The reaction temperature of 400 °C was reached in all cases within 6 min of immersion. After 60 min, the reactor was plunged into cold water to quench the reaction. After depressurization, the liquid and solid products were separated by sequential extraction with hexane and THF. THF-solubles and residue were dried for 6 h in vacuum at 110 °C. Conversion was calculated by subtracting the weight of the residue from the weight (1) Derbyshire, F. J. Catalysis in Coal Liquefaction: New Directions for Research; IEA Coal Research: London, 1988. (2) Mochida, I.; Sakanishi, K. Adv. Catal. 1994, 40, 39. (3) Hirschon, A. S.; Wilson, R. B. ACS Symp. Ser. 1991, 461, 273. (4) Hirschon, A. S.; Wilson, R. B. Fuel 1992, 71, 1025. (5) Song, C.; Parfitt, D. S.; Schobert, H. H. Catal. Lett. 1993, 21, 27.
S0887-0624(95)00254-4 CCC: $12.00
Table 1. Elemental Analysis of Coal Samples wt %, moisture and ash-free basis coal
%C
% H % N % Sorganic % Spyritic % Odiff
Wyodak 72.72 4.55 1.07 (PSOC 1401) Blind Canyon 82.05 6.18 1.39 (DECS-17)
0.28
0.01
21.38
0.44
0.02
9.94
of the coal and dividing by the daf weight of the coal. Selected runs were duplicated and indicate that the experimental error for reported conversions is (2.5 wt %. Thermogravimetric data (TGA) for the decomposition of the catalyst precursors was obtained in N2 at 10 °C/ min using a Mettler TA4000 thermal analyzer. The behavior of each catalyst precursor under reaction conditions was also investigated. In these experiments, the precursor was dissolved in the solvent and mixed with active carbon (Supersorb Active Carbon from Amoco, approximately 0 wt % ash) rather than coal. This eliminated interference on X-ray diffraction analysis from the mineral matter in the coal. In addition, the catalyst loading was increased to 4 wt % to make phase identifications possible. The mixture of active carbon, catalyst precursor, solvent, sulfur, and hydrogen gas was heated in the sandbath for 5 min and quenched to room temperature. The products were washed out of the reactor using THF and filtered. The filter cake was dried in vacuum and then analyzed by X-ray diffraction (XRD) using Cu KR radiation set at 40 kV and 20 mA. The TGA profiles in N2 for each precursor indicated that decomposition started at about 240 °C and was essentially complete before 300 °C. Precursors that are easily decomposable thermally are generally activated earlier and at lower temperatures. For XRD analysis, active carbon was used in place of coal to eliminate interference from mineral matter. XRD patterns for the resulting catalyst particles on active carbon are shown in Figure 1. Peaks corresponding to γ-Co6S5, NiS1.03, and Fe1-xS (pyrrhotite) were detected in the Co/C, Ni/ C, and Fe/C samples, respectively. Although these are room temperature sulfide phases, it is evident that the precursors were transformed to the respective metal sulfides within the first 5 min of reaction. We suggest that this method could easily be adapted to the preparation of carbon-supported metal sulfide catalysts for hydrotreating and coal-liquid upgrading operations. © 1996 American Chemical Society
Communications
Energy & Fuels, Vol. 10, No. 4, 1996 1029 Table 3. Liquefaction of PSOC 1401 Coal in 1-MN and Tetralina catalyst
solvent
THF conversion
hexane conversion
none none Co(AOT)2 0.26% Co 0.13% Co 0.065% Co 0.13% Co Ni(AOT)2 0.26% Ni 0.13% Ni 0.065% Ni 0.13% Ni Fe(AOT)2 0.26% Fe 0.26% Fe
1-MN tetralin
32.0 76.2
17.7 50.5
1-MN 1-MN 1-MN tetralin
71.4 64.0 51.0 83.0
36.2 37.2 27.6 56.9
1-MN 1-MN 1-MN tetralin
73.8 73.2 57.4 85.0
48.3 40.7 31.9 57.8
1-MN tetralin
38.3 75.0
24.9 48.5
run no. 7 51 8 14 16 57 11R 15 17 58
Figure 1. XRD patterns of Co, Ni, and Fe catalysts deposited on active carbon. Table 2. Liquefaction of DECS-17 Coal in 1-MN and Tetralina run no.
catalyst
solvent
THF conversion
hexane conversion
5R2 53
none none Co(AOT)2 0.26% Co 0.13% Co 0.065% Co 0.0325% Co 0.065% Co Ni(AOT)2 0.26% Ni 0.13% Ni 0.065% Ni 0.0325% Ni 0.065% Ni Fe(AOT)2 0.26% Fe 0.26% Fe
1-MN tetralin
49.9 79.3
9.5 29.5
1-MN 1-MN 1-MN 1-MN tetralin
83.7 82.3 77.9 70.6 90.5
31.6 33.7 32.2 26.4 45.6
1-MN 1-MN 1-MN 1-MN tetralin
84.6 81.9 78.5 69.2 86.4
32.5 35.3 33.4 29.9 43.1
1-MN tetralin
59.8 79.5
14.2 31.4
6R2 13 18 31 55 12R 20R 19 30 56 46 54 a
Conditions: T ) 400 °C, P ) 1000 psi of H2 (cold), t ) 1 h, 1:1 solvent to coal, 10 mg of elemental sulfur added.
Liquefaction of coal was carried out in nondonor 1-MN and H-donor tetralin with varying amounts of catalyst precursor. For Blind Canyon coal (Table 2), the use of only 650 ppm (based on as-received coal) of either Co (run 18) or Ni (run 19) was sufficient to increase THF conversion to 78%, vs 50% for the thermal (uncatalyzed) case (run 5R2). Comparison of runs 18 and 19 with run 53 shows that the conversion in nondonor 1-MN with 650 ppm of Co or Ni catalyst is the same as in H-donor tetralin without catalyst, suggesting that a suitably dispersed active catalyst can substitute for a good H-donor solvent. 3,4,6 The conversion in 1-MN increased only slightly as the catalyst concentration was raised to 0.13%; the oil yield (hexane conversion) remained roughly constant at 32% as the catalyst concentration was raised from 650 ppm to 0.26%. However, the use of 650 ppm of either Co or Ni catalyst in conjunction with tetralin increased the oil yield by about 15% relative to run 53. It appears that for the Blind Canyon coal, the Co and Ni catalysts have very similar liquefaction activities under the conditions employed here. Interestingly, both catalysts are effective even at very low concentration (325 ppm), suggesting that a high level of dispersion is achieved with such a precursor. (6) Lili, H. Ph.D. Thesis, The Pennsylvania State University, 1995.
45 52
a Conditions: T ) 400 °C, P ) 1000 psi of H (cold), t ) 1 h, 1:1 2 solvent to coal, 10 mg of elemental sulfur added.
For Wyodak coal (Table 3), the effect of added catalyst was larger. The use of 0.26% of either Co or Ni catalyst increased the conversion in 1-MN by nearly 40% and doubled the yield of oil (compare run 7 with runs 8 and 11R). In analogy with the Blind Canyon coal, comparison of runs 8 and 11R with run 51 shows that the conversion in nondonor 1-MN with 0.26% of Co or Ni is approximately the same as in H-donor tetralin without catalyst. However, the conversion decreased rapidly as the concentration of catalyst was lowered from 0.26% to 650 ppm. Interestingly, in 1-MN, the Ni catalyst is more effective for the Wyodak coal than the Co catalyst. This is consistent with the order of catalytic activity reported in ref 7, viz., Fe < Co < Ni < Mo. For both coals, the use of as much as 0.26% Fe catalyst could only increase the conversion in 1-MN marginally. This is consistent with the finding that Fe is the least effective catalyst even at high concentrations.7 The conversion in tetralin with 0.26% Fe catalyst is the same as that without any catalyst. This suggests that a good donor solvent like tetralin can mask the effect of added Fe catalyst.3,4,6 In summary, an oil-soluble coal liquefaction catalyst precursor was prepared by functionalizing (ion-exchanging) a commercially available anionic surfactant (Aerosol OT-100, sodium dioctylsulfosuccinate) with Co, Ni, or Fe. During liquefaction, the Co and Ni forms of the surfactant produced catalysts that were active for coal liquefaction at low concentrations even in a nondonor solvent, while the Fe form produced the least effective catalyst. As catalyst precursors, functionalized surfactants offer some advantages in terms of ease of preparation and convenience in use.
Acknowledgment. We thank Dr. Harold H. Schobert for helpful comments and suggestions. EF950254J
(7) Weller, S.; Pellipetz, M. G. Ind. Eng. Chem. 1951, 43, 1243.
