Energy Fuels 2009, 23, 4553–4561 Published on Web 08/13/2009
: DOI:10.1021/ef9006092
Solvent Extraction of Bituminous Coals Using Light Cycle Oil: Characterization of Diaromatic Products in Liquids Josefa M. Griffith,‡ Caroline E. Burgess Clifford,*,† Leslie R. Rudnick,§ and Harold H Schobert† †
The EMS Energy Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA, ‡Rentech Inc, 4150 East 60th Avenue, Commerce City, Colorado 80022, and §Ultrachem Inc., 900 Centerpoint Blvd., New Castle, Delaware 19720 Received June 15, 2009. Revised Manuscript Received July 29, 2009
Many studies of the pyrolytic degradation of coal-derived and petroleum-derived aviation fuels have demonstrated that the coal-derived fuels show better thermal stability, both with respect to deposition of carbonaceous solids and cracking to gases. Much previous work at our institute has focused on the use of refined chemical oil (RCO), a distillate from the refining of coal tar, blended with light cycle oil (LCO) from catalytic cracking of vacuum gas oil. Hydroprocessing of this blend forms high concentrations of tetralin and decalin derivatives that confer particularly good thermal stability on the fuel. However, possible supply constraints for RCO make it important to consider alternative ways to produce an “RCO-like” product from coal in an inexpensive process. This study shows the results of coal extraction using LCO as a solvent. At 350 °C at a solvent-to-coal ratio of 10:1, the conversions were 30-50 wt % and extract yields 28-40 wt % when testing five different coals. When using lower LCO/coal ratios, conversions and extract yields were much smaller; lower LCO/coal ratios also caused mechanical issues. LCO is thought to behave similarly to a nonpolar, non-hydrogen donor solvent, which would facilitate heat-induced structural relaxation of the coal followed by solubilization. The main components contributed from the coal to the extract when using Pittsburgh coal are di- and triaromatic compounds.
and alkylnaphthalenes.8 Cycloalkanes are more resistant to thermal degradation under these conditions than are longchain alkanes.9 In coal-derived jet fuel, hydrogen donors such as tetralin and decalin inhibit degradation by stabilizing radicals formed during the reactions that take place in the pyrolytic temperature regime.5,10-15 We and our colleagues have been involved for some years in the development of a jet fuel having greater thermal stability than JP-8 or JP-8 þ 100, notionally called JP-900 from its intended resistance to degradation at 900 °F. Direct liquefaction has been shown to be a potential process route to make coal-derived JP-900.16 In the liquefaction research, we evaluated Pittsburgh and Blind Canyon coals structurally to determine the relationship of the coal structure to the types of products produced.16-19 Both coals showed good conversions in direct liquefaction experiments.16-19 Blind Canyon
Introduction The thermal stability of jet fuel refers to its resistance to breaking down at high temperatures to form solid deposits. Emerging aircraft designs continue to increase the operational capabilities, and at the same time have a requirement for using the fuel as an on-board coolant. In some applications, the fuel is expected to experience temperatures in the range of 900 °F (482 °C).1-4 Coal-derived aviation fuels are more pyrolytically stable than petroleum-derived aviation fuels.5,6 Composition plays a strong role in the thermal stabilization of jet fuels. The seminal work in this field was the detailed characterization of coal-derived jet fuel made by deep hydrotreating of byproduct tars from gasification of lignite at the Dakota Gasification Plant, Beulah, ND.7 This fuel was mainly composed of cycloalkanes, such as decalin and alkyldecalins, hydroaromatic compounds such as tetralin, and alkylaromatics. In comparison, petroleum-derived jet fuel is a complex assemblage of aliphatic hydrocarbons, with trace amounts of alkylbenzenes
(8) Song, C.; Hatcher, P. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 1992, 37 (2), 529–539. (9) Lai, W. C.; Song, C. Fuel Proc. Technol. 1996, 48, 1–27. (10) Andresen, J. M.; Strohm, J. J.; Sun, L.; Song, C. Energy Fuels 2001, 15, 714–723. (11) Song, C.; Peng, Y.; Jiang, H.; Schobert, H. H. Prepr. - Am. Chem. Soc., Div. Fuel Chem. 1992, 37 (2), 485–493. (12) Song, C.; Lai, W.-C.; Schobert, H. Ind. Eng. Chem. Res. 1994, 33, 548–557. (13) Andresen, J.; Strohm, J. J.; Coleman, M. M.; Song, C. Prepr. Am. Chem. Soc., Div. Fuel Chem. 1999, 44 (1), 94–198. (14) Andresen, J.; Strohm, J. J.; Song, C. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 1998, 43 (3), 412–414. (15) Song, C.; Eser, E.; Schobert, H. H.; Hatcher, P. G. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 1992, 37 (2), 541–548. (16) Burgess, C. E.; Schobert, H. H. Fuel Process. Technol. 2000, 64 (1-3), 57–72. (17) Burgess, C. E.; Schobert, H. H. Energy Fuels 1996, 10 (3), 718–725. (18) Burgess, C. E.; Redlich, P. J.; Sakurovs, R. J.; Jackson, W. R.; Marshall, M. Energy Fuels 1998, 12 (3), 570–573. (19) Burgess, C. E.; Schobert, H. H. Energy Fuels 1998, 12 (6), 1212– 1222.
*To whom correspondence should be addressed. Telephone: 814-8658673; Fax: 814-865-3573 E-mail:
[email protected]. (1) Edwards, T.; Atria, J. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 1995, 40 (4), 649–654. (2) Edwards, T. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 2000, 45 (3), 436–439. (3) Edwards, T. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 1996, 41 (2), 481–487. (4) Maurice, L. Q.; Lander, H.; Edwards, T.; Harrison, W. E. Fuel 2001, 80, 747–756. (5) Song, C.; Eser, E.; Schobert, H. H.; Hatcher, P. G. Energy Fuels 1993, 7, 234–243. (6) Coleman, M. M.; Schobert, H. H.; Song, C. Chem. Britain 1993, 29, 760–763. (7) Furlong, M.; Fox, J.; Masin, J. Production of Jet Fuels from CoalDerived Liquids: Interim Report, AFWAL-TR-87-2042; 1989; Vol IX, pp 52 (available from NTIS). r 2009 American Chemical Society
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: DOI:10.1021/ef9006092
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Table 1. Ultimate and Proximate Analyses and Thermoplastic Properties for the Following Coals: Pittsburgh, Powellton, Upper Freeport, Blind Canyon, and Illinois No. 6 Pittsburgh
% carbon % hydrogen % nitrogen % sulfur
74.8 5.1 1.2 1.1
% ash % volatile matter % fixed carbon
10.3 36.0 53.7
initial softening temp, °C max. fluidity temp, °C solidification temp, °C fluid temp range, °C maximum fluidity (ddpm) free-swelling index
total vitrinite, % vol. total liptinite, % vol. total inertinite vol., %
Powellton
Upper Free Port
Blind Canyon
Illinois No. 6
85.5 4.7 1.6 2.3
76.5 5.9 1.5 0.4
66.0 4.6 1.1 5.5
Proximate Analyses (dry) 5.0 10.6 29.9 35.0 65.1 54.4
5.8 44.5 49.7
13.4 40.8 45.8
400 419 438 38 3 2
366 410 444 78 49 3
79.7 12.2 8.1
90.2 3.0 6.8
Ultimate Analyses (dry) 87.6 5.8 1.6 0.9
Thermoplastic Properties (Gieseler Plastometer and Free Swelling Index) 387 385 373 440 448 450 477 488 497 90 103 124 20 002 30 000 30 000 7.5 7.5 8.5
83.0 8.1 8.9
Petrographic Properties 68.0 nd 8.6 nd 23.4 nd
study by Bartis and Flint25 called attention to the fact that coaltar chemicals such as RCO would likely be supply constrained in the future, at least in the United States.24 Therefore, solvent extraction of coal is a process under consideration for production of a “RCO-like” coal-based material. Some extraction methods show excellent extraction yields, but the solvents used are very expensive.26 Given our interest in integrating coal-based liquid fuel production into oil refineries, and given that we would wish to blend the RCO-like material with LCO, then LCO became a clear choice for a prospective solvent. We report here the first results of a study directed at making an “RCO-like” material from coal by solvent extraction. In the present study, liquids obtained from LCO and from LCO/Pittsburgh were characterized to determine the contribution of the coal to the liquid.
was one of the coals tested that had the highest conversions, while Pittsburgh coal conversions were typically a little lower than Blind Canyon.16-19 However, direct liquefaction of these coals produced liquids of very different character.16-19 Hexane-soluble liquids from Blind Canyon coal contained oneand two-ring aromatics as well as long-chain alkanes (up to C32); while hexane-solubles from Pittsburgh coal were mainly two-ring compounds, an attractive characteristic for thermally stable jet fuel once the liquid was hydrogenated.16-19 However, there were issues with using direct liquefaction. The previous research was done using pure solvents, that is, phenanthrene, dihydrophenanthrene, and pyrene.16-19 Another constraint was that long construction times and high capital costs for a grass-roots liquefaction plant made it prudent to examine the possibility of incorporating coal, or coal-derived materials, into existing oil refinery operations. Subsequent research showed that hydrotreating a blend of refined chemical oil (RCO), a coal tar from metallurgical coking, with light cycle oil (LCO), followed by fractionation, would produce a 180-270 °C distillation cut that both met the thermal stability requirement of JP-900 and could likely be a drop-in coal-based replacement for Jet A or JP-8.20,21 We have shown that when RCO is blended with LCO from catalytic cracking of vacuum gas oil and hydroprocessed, the product is very rich in tetralin and decalin compounds.22,23 However, a review paper by Song and Schobert24 and an independent
Experimental Section Samples. The ultimate and proximate analyses, fluidity data, and petrographic data for the coals used in this work are shown in Table 1. Four of the coals were supplied by The Pennsylvania State University Coal Sample Bank: Pittsburgh, Blind Canyon, Illinois No. 6, and Powellton. One coal, Upper Free Port, was provided by Argonne National Laboratory. The coals were ground to -60 mesh. They were also dried in a vacuum oven at 100 °C and 4 kPa overnight and cooled for 1 h in a desiccator prior to the experiments. LCO used as a solvent to extract organic components from this coal was obtained from United Refining Company, Warren PA. The properties of this solvent are listed in Table 2. Extraction. The LCO/coal extractions were carried out using a 165 mL stirred batch reactor with a fitted impeller. The extractions were carried out according to Figure 1. The reaction conditions were 350 °C, 0.7 MPa, and 1 h. The appropriate amounts of LCO and coal loaded in the reactor are shown in Table 3. The reactor was sealed and then placed in the heater.
(20) Butnark, S. Thermally stable coal-based jet fuel: chemical composition, thermal stability, physical properties, and their relationship; Ph.D. Dissertation, The Pennsylvania State University: University Park, PA, 2004. (21) Balster, L. M.; Corporan, E.; DeWitt, M. J.; Edwards, J. T.; Ervin, J. S.; Graham, J. L.; Lee, S. Y.; Pal, S.; Phelps, D. K.; Rudnick, L. R.; Santoro, R. J.; Schobert, H. H.; Shafer, L. M.; Striebich, R. C.; West, Z. J.; Wilson, G. R.; Woodward, R.; Zabarnick, S. Fuel Proc. Technol. 2008, 89 (4), 364–378. (22) Andresen, J. M.; Strohm, J. J.; Boyer, M. C.; Song, C.; Schobert, H. H.; Butnark, S. Prepr. - Am. Chem. Soc., Div. Fuel Chem. 2001, 46, 208–210. (23) Badger, M. W.; Butnark, S.; Wilson, G. R.; Schobert, H. H. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 2002, 47, 198–200. (24) Schobert, H. H.; Song, C. Fuel 2002, 81, 15–32.
(25) Bartis, J. T.; Flint, Jr., G. T. Constraints on JP-900 Jet Fuel Production Concepts; Technical Report, Project Air Force, Contract FA7014-06-C-0001; Rand Corporation: Pittsburgh, PA, 2007. (26) Takanohashi, T.; Xiao, F. J.; Yoshida, T.; Saito, I. Energy Fuels 2003, 17, 255–256.
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Table 2. Properties of LCO Obtained from United Refining Company propertiesa API gravity @ 60 °F, ASTM D-287 specific gravity (g/mL), ASTM D-1298 sulfur (wt %), ASTM D-5453 nitrogen (ppm), ASTM D-5762 distillation (° C) IBP 10 20 30 50 70 80 90 FBP a
10.3 0.9979 1.92 535 ASTM D-86
ASTM D-2887
220 266 277 286 296 313 324 336 354
146 249 271 279 301 324 341 359 396
Received from United Refining Company.
The sealed reactor was purged three times with 7 MPa of ultrahigh-purity N2 (UHP, 99.999%) and finally pressurized to 0.7 MPa of N2. When the temperature reached 70-80 °C below the desired extraction temperature, the stirrer was started and set at 1500 rpm. After the reaction, the reactor was brought to room temperature by immersing it in a cold water bath for 1 h. The reacted LCO/coal slurry was filtered using a Millipore filter (fine porosity) with a previously weighed PTFE filter. The reactor and the solid were washed with dichloromethane (DCM) until the supernatant became almost colorless. The resulting solid material, which is called the residue hereafter, was quantitatively transferred to a previously weighed Petri dish and then dried in a vacuum oven at 110 °C and 4 kPa for at least 4 h, cooled to room temperature in a desiccator for an hour, and then weighed. This was repeated until a constant weight was obtained. The resulting solution, which is called the extract hereafter, was rotary-evaporated in a water bath at 60 °C until all the visible dichloromethane was separated. To eliminate any remaining dichloromethane, the recovered material was held overnight in a vacuum oven without heating and then weighed. This was repeated until the loss of weight was less than 200 mg. Conversions were calculated from the weight of initial amount of coal and residue on a dry, ash-free basis according to eq 1.26 1 -ðResidueweight ðgÞ=Coalweight ðgÞÞ Conversion ¼ 100 ð1Þ 1 -ðash ðwt%, dbÞ=100Þ
Figure 1. Schematic of reaction and product workup. Table 3. Masses of LCO and Coal in Various Reactions, Including the LCO/Coal Ratio
Extractweight ðgÞ -LCOweight ðgÞ 100 Coalweight ðgÞ -ðCoalweight ðgÞ ðash ðwt%, dbÞ=100ÞÞ ð2Þ
ExtractYieldLCO ¼
LCO/coal
mass coal (g)
mass LCO (g)
10 5 3 10 5 3 10 5 3 10 5 2 10 5 3
5 10 6 5 10 6 5 10 6 5 5 5 5 10 6
50 50 18 50 50 18 50 50 18 50 25 10 50 50 18
separation into eight discrete fractions with chemical identity well-defined.28-30 This method has been used previously to characterize hydrocarbons produce from coal processing.31-33 To carry out the fractionation, approximately 300 mg of sample was dissolved in a minimal amount of THF, stirred with 2 g of silica gel (Merck, grade 10181, 35-70 mesh), preactivated for 4 h at 180 °C, and then the solvent was evaporated. The sample-coated silica gel was placed on the top of the column. The separation was carried out by triplicate using three 50 cm long, 11 mm i.d. glass columns fitted with Teflon stopcocks. The columns were slurry packed, as follows: the packing of the
Extract yields were calculated with respect to the initial amount of coal according to eq 2 and with respect to the initial amount of LCO according to eq 3.27 ExtractYieldcoal ¼
sample LCO/Pitt 10:1 LCO/Pitt 5:1 LCO/Pitt 3:1 LCO/Pow 10:1 LCO/Pow 5:1 LCO/Pow 3:1 LCO/Ill 10:1 LCO/Ill 5:1 LCO/Ill 3:1 LCO/UFP 10:1 LCO/UFP 5:1 LCO/UFP 2:1 LCO/BC 10:1 LCO/BC 5:1 LCO/BC 3:1
Extractweight ðgÞ -LCOweight ðgÞ 100 ð3Þ LCOweight ðgÞ
(28) Lanc-as, F. M.; Karam, H. S.; McNair, H. M. LC-GC, Mag. Liq. Gas Chromatogr. 1987, 5 (1), 41–48. (29) Lanc-as, F. M.; Vilegas, J. H. Y.; Martins, S.; Gobato, E. A. F. J. High Resolut. Chromatogr. 1994, 17, 237–244. (30) Assis, L. M.; Silva Pinto, J. S.; Lanc-as, F. M. J. Microcolumn Sep. 2000, 12 (5), 292–301. (31) Dariva, C.; Oliveira, J. V.; Pinto, J. S.; Vale, M. G. R.; Caram~ao, E. B. J. Supercrit. Fluids 1998, 13, 343–350. (32) Dariva, C.; de Oliveira, J. V.; Vale, M. G. R.; Caram~ ao, E. B. Fuel 1997, 76 (7), 585–591. (33) Assis, L. M.; Lanc-as, F. M. J. Microcolumn Sep. 1999, 11 (7), 501–512.
Fractionation of LCO and LCO/Coal Extract. To characterize the material extracted from coal, the original LCO and the coal extract obtained at 350 °C with LCO/coal 10:1 were fractionated using preparative liquid chromatography (PLC). The method used is PLC-8, which permits sample (27) Guillen, M. D.; Blanco, J.; Canga, J. S.; Blanco, C. G. Energy Fuels 1991, 5, 188–192.
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Table 4. Fractionation of the Samples fraction F-1 F-2 F-3 F-4 F-5 F-6 F-7 F-8
fraction eluted
eluent
volume (mL)
vials
saturated hydrocarbon monoaromatic hydrocarbon diaromatic hydrocarbon di-,triaromatic hydrocarbon di-, triaromatic hydrocarbon resins (oxygen, nitrogen atoms) asphaltenes asphaltols
Hexane Hexane 11.5% v/v benzene in hexane 32% v/v benzene in hexane 32% v/v benzene in hexane 3:4:3 v/v benzene/acetone/CH2Cl2 2:8 v/v acetone/THF methanol
40 27 36 24 25 65 60 65
1-4 5-7 8-11 12-14 15-17 18-23 24-29 30-35
Table 5. Volatile Matter Content for Five Coals, and Conversion, Extract Yieldcoal, and Extract YieldLCO for Reactions with Five Coals Pittsburgh
Powellton
Upper Free Port
Blind Canyon
Illinois No. 6
volatile matter (wt %)
36.0
29.9
35.0
44.5
40.8
conversion (wt %) extract yieldCoal extract yieldLCO
39.4 32.7 2.9
29.3 28.5 2.8
35.8 32.3 2.8
45.9 37.5 3.3
51.2 39.2 3.4
conversion (wt %) extract yieldCoal extract yieldLCO
14.4 10.3 1.8
30.2 26.8 5.1
30.5 19.3 3.4
32.8 21.4 3.8
37.6 16.8 3
conversion (wt %) extract yieldCoal extract yieldLCO
6.6 1.1 0.3
6 1.7 0.5
18.3a 20.7a 5.1a
24.2 22.6 6.8
20 19.1 4.9
10:1 Solvent/Coal
5:1 Solvent/Coal
3:1 Solvent/Coal
a
Solvent to coal ratio 2:1 for this reaction only.
conversion tended to be lower than when using industrial solvents that were derived from coal.34,35 Takanohashi et al. also noted that the extraction yields obtained with industrial, nonpolar and nonhydrogen donor solvents such as LCO may be the result of heat-induced structural relaxation followed by solubilization of coal components in the solvent.35 The highest conversions were obtained using a LCO/coal ratio of 10:1 (Table 5); the greater the LCO/coal ratio, the better the conversion and extract yields. Under these conditions, conversions were 39 wt % for Pittsburgh, 29 wt % for Powellton, 51 wt % for Illinois, 36 wt % for Upper Freeport, and 46 wt % for Blind Canyon. We calculated extract yields in two ways, with respect to the initial amount of coal and with respect to initial amount of LCO. The extract yield relative to the coal followed a similar trend to the conversion, with the lowest yield 28 wt % for Powellton up to 39 wt % for Illinois No. 6. The extract yield with respect to the initial amount of LCO provides information about how much coal was dissolved in the LCO. The extract yield relative to LCO solvent was ∼3-4% for all the reactions with the LCO/coal ratio of 10:1. Conversions obtained using the LCO/coal ratio of 5:1 (Table 5) were significantly lower, 14-38 wt %, with Pittsburgh having the lowest conversion and extract yield relative to the other coals. The yield of the coal relative to LCO was ∼2-5%, which is not significantly higher than results obtained for the 10:1 LCO/coal ratio. Conversions obtained using an LCO/coal ratio of 3:1 (Table 5) were lower, 6-24 wt %, with yields calculated on an LCO basis of 0.3-7.0 wt %. Not only were conversions lower at lower LCO/coal ratios, but mechanical operation of the extraction unit was compromised due to plugging in lines and difficulty in separation of the coal and residue in subsequent in-house research. Other studies of flow type systems suggest that problems in handling coal slurries arise when coal slurries are at high
column was performed by first adding the preactivated silica gel (18 g) a little at a time to hexane (60 mL) in a beaker, swirling the beaker, and placing the slurry into a draining column previously filled about 1/3 full with hexane that was mechanically agitated. A plug of glass wool on the end and a layer of white sand on the top were used to support the solid adsorbent. Elution was performed with the mobile phases and the volumes listed in Table 4. The flow rate at the column outlet was maintained at 1.2 mL/min. The 10 mL fractions were collected in vials that were previously weighed. The solvents were evaporated to constant weight in a vacuum oven and then weighed to determine the mass of each fraction. GC/MS Analysis of Fractions from LCO and LCO/Coal Extract. The GC/MS analyses were conducted on a Shimadzu GC-17A coupled with a Shimadzu QP-5000 MS detector. The column was a Restek XTI5 (5% diphenyl/95% dimethylsiloxane). Starting temperature was 40 °C. The column was held at this temperature for 4 min, then heated to 150 at 6 °C/min, then from 150 to 290 at 4 °C/min, and finally held for 10 min. The initial and final pressures in the column were 48.9 and 144 kPa, respectively.
Results and Discussion Conversion of Coal and Yield of Liquids in LCO. The conversion and extract yields at 350 °C and different LCO/ coal ratios are shown in Table 5 (10:1, 5:1, and 3:1 or 2:1). The conversion ranges from 6 to 51 wt %. These results are comparable to the results reported by Takanohashi et al. using LCO and crude methylnaphthalene oil at 360 °C to extract bituminous and subbituminous coals to produce an ashless coal (HyperCoal).34,35 In their work, they obtained conversions between 34 and 42 wt %.34,35 It should also be noted that when LCO has been used as a coal solvent, the (34) Masaki, K.; Yoshida, T.; Li, C. Q.; Takanohashi, T.; Saito, I. Energy Fuels 2004, 18, 995–1000. (35) Yoshida, T.; Takanohashi, T.; Sakanishi, K.; Saito, I.; Fujita, M.; Mashimo, K. Energy Fuels 2002, 16, 1006–1007.
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Figure 2. Correlation between conversion of coals at solvent to coal ratio of 10:1 and volatile matter of the coals. Table 6. Mass Results from Preparative Liquid Chromatography (PL-8) fraction
fraction eluted
vials
LCO (wt %)
LCO/Pitts (wt %)
F-1 F-2 F-3 F-4 F-5 F-6 F-7 F-8 uneluted sample
saturated hydrocarbon monoaromatic hydrocarbon diaromatic hydrocarbon di-,triaromatic hydrocarbon di-, triaromatic hydrocarbon resins (oxygen, nitrogen atoms) asphaltenes asphaltols high molecular weight compounds
1-4 5-7 8-11 12-14 15-17 18-23 24-29 30-35
6.2 1.3 25.3 43.6 3.1 3.8 5.7 2.5 8.5
3.7 3.6 24.1 39.6 17.3 5.0 3.9 1.2 1.6
solids loadings.36-38 With higher LCO/coal ratios, slightly less coal-derived material is incorporated into the liquid. In a process in which the entire liquid stream would be upgraded, the coal-derived material may not have a great impact on the properties of the final fuel product. Alternatively, excess LCO solvent could be stripped and recycled, allowing downstream processing of a liquid having a relatively high concentration of coal-derived material. Effect of Coal on Conversion and Yield. Ultimate, proximate, and fluidity analyses of the coals are shown in Table 1. Figure 2 (numerical data shown in Table 5) shows the
relationship of conversion to volatile matter of the coals and the conversion of the coals in LCO at 10:1 solvent-tocoal ratio. As noted on the figure, the R2 of the trend line is 0.81, with Blind Canyon and Illinois No. 6 not quite fitting the trend; these two coals are low fluidity coals. Although the volatile matter is sufficient to determine the extent of conversion using LCO, it will not provide information as to the character of the products made. Influence of Coal on the Character of the Extract Product. The liquids that were characterized were from reaction at 350 °C, 1 h, using LCO and Pittsburgh coal in a 10:1 solventto-coal ratio. The products were subjected to PLC-828-30 to separate them into fractions based on polarity. The solvents used and the types of compounds extracted are shown in Table 4. Table 6 shows the mass of each fraction from LCO reacted alone and LCO/Pittsburgh coal. Figure 3 shows the chromatograms of the various fractions from LCO and LCO/Pittsburgh coal reactions, and Tables 7-12 show the compounds identified in each fraction.
(36) Burgess Clifford, C. E.; Boehman, A.; Miller, B. G.; Mitchell, G.; Rudnick, L. R.; Song, C.; Schobert, H. H. Refinery Integration of ByProducts from Coal-Derived Jet Fuels, Grant DE-FC26-03NT41828, Final Report, September 18, 2003 - March 31, 2008, Date Issued: July 25, 2008. (37) Huang, H.; Wang, K.; Wang, S.; Klein, M. T.; Calkins, W. H. Energy Fuels 1996, 10 (3), 641–648. (38) Huang, H.; Wang, K.; Wang, S.; Klein, M. T.; Calkins, W. H. Energy Fuels 1998, 12 (1), 95–101.
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Figure 3. Chromatograms comparing chemical nature of reaction of LCO alone and LCO/Pittsburgh extract; Tables 7-12 show retention times and the identity of the likely structures of the major peaks.
Fractions F-1 and F-2 represent ≈6-7% of the liquid product, and both LCO alone and LCO/Pittsburgh extract have near identical compositions (Tables 7-8). For both the LCO alone and the LCO/Pittsburgh extract, ≈70-80% of the liquids eluted in fractions F-3, F-4, and F-5 (Table 6). There were differences between the amounts eluted from LCO and LCO/Pittsburgh extract in these fractions as well as
the identity of the compounds eluted. The amount eluted in the F-3 fraction for both LCO and LCO/Pittsburgh were similar in mass (≈25%, Table 6) and in the types of compounds, mainly two-ring aromatics (Table 9). The amount eluted from LCO in F-4 was ≈45% (Table 6), the compounds dominantly alkylated two- and three-ring compounds (Table 10). A slightly smaller amount, ≈40%, 4558
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eluted from the LCO/Pittsburgh with similar types of compounds, except for the presence in the coal extract of 1-3 ring sulfur-containing compounds that were not present in LCO alone. The amount eluted from LCO in F-5 was less than 5% (Table 6) and was mainly three-ring compounds, while the amount eluted from the LCO/Pittsburgh extract was ≈17% and consisted of two- and three-ring compounds as well as compounds containing sulfur and oxygen (Table 11). While the amounts eluted from LCO and LCO/ Pittsburgh extracts in F-6 were similar (≈4-5%), the coal extract fraction contained more oxygen and nitrogen compounds (Table 12). The types of compounds contributed by the coal are the precursors for production of a thermally stable jet fuel, and once hydrotreated to remove sulfur, nitrogen, and oxygen, followed by hydrogenation of the ring compounds, will produce an extremely high quality jet fuel.16,24 Butnark et al.39,40 and Burgess Clifford et al.36 demonstrated that the 180-270 °C or 180-300 °C fractions of hydrotreated LCO/coal liquid (25:75 or 50:50) blends jet fuel with excellent thermal stability. These results were achieved using RCO as the coal-derived liquid. The results presented
Table 7. Compounds Identified in Fraction F-1 for LCO and LCO/ Pittsburgh peak molecular formula m/z C13H28 C14H30 C15H32 C16H34 C17H36 C18H38 C19H40 C20H42 C21H44 C22H46 C23H48
1 2 3 4 5 6 7 9 10 11 12
compound
184 198 212 226 240 254 268 282 296 310 324
n-tridecane n-tetradecane n-pentadecane n-hexadecane n-heptadecane n-octadecane n-nonadecane n-eicosane n-heneicosane n-docosane n-tricosane
LCO LCO/Pitts coal X X X X X X X X X X X
X X X X X X X X X X X
Table 8. Compounds Identified in Fraction F-2 for LCO and LCO/ Pittsburgh peak molecular formula m/z C15H24 C16H26 C17H28 C18H30 C19H32 C20H34 C21H36
1 2 3 4 5 6 7
204 218 232 246 260 274 288
compound C9-benzene C10-benzene C11-benzene C12-benzene C13-benzene C14-benzene C15-benzene
LCO LCO/Pitts coal X X X X X X X
X X X X X
Table 9. Compounds Identified in Fraction F-3 for LCO and LCO/Pittsburgh Coal peak
molecular formula
m/z
compound
LCO
1 2 3 4 5 6 7 8 9 10 11 12
C10H8 C11H14 C11H10 C12H16 C12H12 C10H10S C13H18 C13H14 C13H16 C14H16 C15H18 C16H20
128 146 142 160 156 162 174 170 172 184 198 212
naphthalene C2-indan C1-naphthalene C2-1,2,3,4-tetrahydronaphthalene C2-naphthalene C2-benzothiophene C3-1,2,3,4-tetrahydronaphthalene C3-naphthalene C3-1,2,-dihydronaphthalene C4-naphthalene C5-naphthalene C6-naphthalene
X X X X X X X X X X X
LCO/Pitts coal X X X X X X X X X X X
Table 10. Compounds Identified in Fraction F-4 for LCO and LCO/Pittsburgh Coal MF
m/z
retention time
compound names
LCO
LCO/Pitts coal
C11H10 C12H12 C13H12 C13H14 C15H24O C11H12S C13H12 C13H10 C14H12 C13H12 C13H10O C14H12 C14H12 C14H16 C14H14 C14H12 C14H12 C15H18 C12H8S C14H10 C15H14 C13H10S C15H12 C16H16 C14H12S C15H14S C16H14 C17H16 C18H18 C17H12
142 156 168 170 220 176 168 166 180 168 182 180 180 184 182 180 180 198 184 178 194 198 192 208 212 226 206 220 234 216
13.674, 13.873 14.570-15.782 15.683-16.186 16.014-17.78 16.233 16.875 17.698-18.501 17.579 17.868 17.698-18.501 18.362, 18.562 19.107 19.273-20.342 17.505-20.966 19.571-21.079 19.107 19.273-20.342 22.418-23.537 20.709 21.185 21.481-22.776 22.483-23.473 23.272-24.128 24.158-25.358 24.261-25.184 26.203-27.637 25.546-27.578 28.318-29-838 28.318-29-838 30.179-31.024
C1-naphthalene C2-naphthalene C1-biphenyl C3-naphthalene butylated hydroxytoluene C3-benzothiophene C1-biphenyl fluorene C1-fluorene C1-biphenyl C1-dibenzofuran 9,10-dihydro-phenanthrene/anthracene C1-fluorene C4-naphthalene C2-biphenyl 9,10-dihydro-phenanthrene/anthracene C1-fluorene C5-naphthalene dibenzothiophene phenanthrene /anthracene C2-fluorene C1-dibenzothiophene C1-phenanthrene /anthracene 1,2,5,6-tetramethylacenaphthylenes C2-dibenzothiophene 1,1-methylthio(ethenylidene)-benzene C2-phenanthrene/anthracene C3-phenanthrene/anthracene C4-phenanthrene/anthracene C1-pyrene
X X X X X
X X
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X X X X X X X X X X X X X X X X X X X X X X X
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: DOI:10.1021/ef9006092
Griffith et al.
Table 11. Compounds Identified in Fraction F-5 for LCO and LCO/Pittsburgh Coal MF
m/z
retention time
compound names
C11H10 C12H12 C13H14 C13H10 C12H12 C13H12 C15H24O C13H14 C14H14 C14H12 C14H12 C14H10 C15H14 C14H10 C13H10S C15H12 C16H16 C16H14 C14H12S C16H14 C17H16 C15H14S
142 156 170 166 156 168 220 170 182 180 180 178 194 178 198 192 208 206 212 206 220 226
13.654-13.855 14.551-15.712 15.971-17.376 17.369 16.512-17.977 15.817-18.176 16.233 15.971-17.376 17.133-20.931 19.083 19.326-20.227 21.031 20.919-22.642 21.221 22.416-23.242 23.273-24.287 24.335-25.366 25.355-26.704 24.709-26.034 26.050-26.730 27.632-30.206 26.690-28.405
C1-naphthalene C2-naphthalene C3-naphthalene fluorene C2-naphthalene C1-biphenyl butylated hydroxytoluene C3-naphthalene C2-biphenyl 9,10-dihydro-phenanthrene-anthracene C1-fluorene phenanthrene/anthracene C2-fluorene phenanthrene/anthracene C1-dibenzothiophene C1-phenanthrene/anthracene 1,2,5,6-tetramethylacenaphthylenes C2-phenanthrene/anthracene C2-dibenzothiophene C2-phenanthrene/anthracene C3-phenanthrene/anthracene 1,1-methylthio(ethenylidene)-benzene
LCO
LCO/Pitts coal X
X X X X X X X X X X X X X X X
X X X X X
X X
Table 12. Compounds Identified in Fraction F-6 for LCO and LCO/Pittsburgh Coal MF
m/z
retention time
compound names
LCO
LCO/Pitts coal
C6H12O C6H14O C6H14O C6H12O C6H14O2 C7H16O2 C6H12O2 C6H6O C7H8O C7H8O C8H10O C9H12O C9H10O C14H12 C14H12 C13H11NO C13H11N C15H14N2O C15H15N
100 102 102 100 118 132 116 94 108 108 122 136 134 180 180 197 182 238 209
6.265 6.387 6.508 7.472 9.369 9.514 9.710 9.891 10.877 11.127 11.985, 12.198 12.812-13.128 14.065 19.468-19.997 21.648-21.943 22.152 23.701-24.736 25.798-26.330 28.265-29.162
2-hexanona 3-hexanol 2-hexanol cyclobutylethanol 1-ethyl-butyl hydroperoxide 1-methyl-hexyl hydroperoxide 3-hexene-2,5-diol phenol 2-methyl-phenol 4-methyl-phenol dimethyl-phenol methyl-ethyl-phenol indenol C1-fluorene C1-fluorene N-hydroxymethylcarbazole C1-carbazol 10,11-dihydrocarbamazepine C3-carbazol
X X X
X
in the present study demonstrated that the fraction of coalderived liquid in the extract is relatively lower. We have found in subsequent work that higher conversions can be obtained from multistage extraction or when recycling solvent that contains coal liquid.36 Likely, either or both of these conditions would pertain to operation at demonstration-plant or commercial scale. However, Strohm et al.41 have shown that only 2 mol % of hydroaromatic and saturated ring compounds were needed to prevent thermal degradation in a petroleum-based jet fuel. Depending on the desired specifications of the finished product, even a modest extraction of coal could confer significant benefits to stability of the final fuel. As thermal solvent extraction with LCO leads to lower conversions than direct coal liquefaction processes, a greater proportion of carbon-based residues
X X X X X X X X X X X X
X X X X X X
must be utilized; carbon-based residues could be processed in other revenue generating processes within a refinery. Conclusions Extraction of coals with LCO at 350 °C, 100 psi N2, 1 h reaction time, at a 10:1 LCO/coal ratio, can provide coal conversions of up to ∼50 wt %. These results are comparable to those of other researchers using LCO.34,35 However, their goal34,35 was to produce a mineral-matter-free coal product, whereas our goal is to produce a liquid that contains primarily one and two-ring compounds, that once hydrotreated would produce a high thermal stability jet fuel. At lower LCO/coal ratios (5:1 and 3:1), lower conversions were obtained. The higher solids loading at these LCO/coal ratios also contributed to mechanical problems. On the basis of the LCO/coal ratios tested here, 10:1 would be the preferred reaction ratio. Extraction of Pittsburgh coal generated the types of precursors desired for production of thermally stable jet fuel. The compounds contributed by this coal were mainly two- and three-ring compounds. With hydrotreating to reduce sulfur and nitrogen and saturation of the
(39) Butnark, S.; Badger, M. W.; Schobert, H. H. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 2000, 45 (3), 493–495. (40) Butnark, S.; Badger, M. W.; Schobert, H. H.; Wilson, G. R. Prepr. - Am. Chem. Soc., Div. Pet. Chem. 2002, 47 (3), 201–203. (41) Strohm, J. J. Novel hydrogen donors for the improved thermal stability of advanced aviation jet fuels; MS Thesis, The Pennsylvania State University: 2003.
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: DOI:10.1021/ef9006092
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aromatics, this extract can be expected to produce highquality jet fuel. While using LCO as solvent may lead to lower conversion than other solvents, carbon-based residues could be utilized in other revenue generating processes. Since LCO is produced in refineries (from the fluid catalytic cracker unit), it could be a useful solvent for process configurations that couple coal conversion upstream with standard downstream hydrotreating, aromatics saturation, and fractionation in a refinery. This offers a route to the production of coal-petroleum blended liquid fuels at
lower capital cost than construction of a grass-roots synthetic fuel plant. Acknowledgment. The authors are pleased to acknowledge the financial support for this work provided by the Air Force Office of Scientific Research and by the Department of Energy. We thank United Refining Company for the sample of LCO used in this work. We would like to acknowledge Gareth Mitchell for characterization of the coals and the late Dr. David Clifford for his help with the characterization of liquid samples.
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