Catalytic Direct Liquefaction of High-Sulfur Coals and Their Blends

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Energy & Fuels 2007, 21, 2216-2225

Catalytic Direct Liquefaction of High-Sulfur Coals and Their Blends with Asphaltite in the Absence of a Solvent O ¨ mer Gu¨l,*,†,‡ Parvana Gafarova,†,‡ Arif Hesenov,† Harold H. Schobert,‡ and Oktay Erbatur† C¸ ukuroVa U ¨ niVersitesi, Fen Edebiyat Faku¨ltesi, Kimya Bo¨lu¨mu¨, 01330 Adana, Turkey, and The Energy Institute, The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802 ReceiVed August 30, 2006. ReVised Manuscript ReceiVed March 15, 2007

Two high-sulfur Turkish coals (Mengen and Kangal) and an asphaltite (Avgamasya) were liquefied with and without the catalyst precursors ammonium heptamolybdate (AHM) and ammonium tetrathiomolybdate (ATTM) at 300, 350, 400, and 450 °C. Blends of these coals with the asphaltite were also liquefied using ATTM. Effective conversions of both coals into oils and into asphaltene and preasphaltene fractions were achieved with both catalyst precursors, although ATTM was more effective than AHM. Maximum conversion for Mengen coal with ATTM (89.2%) was achieved at 400 °C, although the maximum yield of oils (56.9%) was obtained at 450 °C. Kangal, in the presence of ATTM, gave maximum conversion (87.7%) at 400 °C; the corresponding oil yield (49.6%) was not much less than that obtained at 450 °C (49.9%). Some retrogressive reactions toward the formation of aromatics were observed during liquefaction at 450 °C in the presence of AHM or ATTM with both coals. Also, using these catalyst precursors results in effective hydrogenation of two-ring or higher condensed aromatics and effective hydrogenolysis of the alicyclic part of hydroaromatic structures. On the other hand, these catalyst precursors do not provide effective saturation of monoaromatic rings, although the use of ATTM yielded partial reduction of these compounds. The distribution of main product fractions obtained from these reactions and the detailed analysis of oils obtained are reported here.

1. Introduction Conversion of coal to useful liquid fuels or chemical feedstocks requires the release of the mobile phase, the breaking of aliphatic or heteroatomic cross-links, and the removal of heteroatoms.1,2 In general, most covalent bonds in coal cleave between 375 and 450 °C; therefore, most direct liquefaction schemes use temperatures around these values.3,4 Catalyst, a catalyst precursor, or combinations of catalysts can also be used to facilitate the breakdown of the coal structure, the hydrogenation of the structural fragments, or both.1-3,5-20 * To whom correspondence should be addressed. E-mail: [email protected] and/or [email protected]. †C ¸ ukurova U ¨ niversitesi. ‡ The Pennsylvania State University. (1) Derbyshire, F. J. Catalysis in Coal Liquefaction: New Directions for Research; IEA Coal Research: London, U.K., 1988; IEA CR/08. (2) Derbyshire, F. J.; Davis, A.; Lin, R. Energy Fuels 1989, 3, 431437. (3) Vernon, L. W. Fuel 1980, 59, 102-106. (4) Derbyshire, F. J.; Whitehurst, D. D. Fuel 1981, 60, 655-662. (5) Artok, L.; Davis, A.; Mitchell, G. D.; Schobert, H. H. Energy Fuels 1993, 7, 67-77. (6) Garcia, A. G.; Schobert, H. H., Fuel Process. Technol. 1990, 24, 179-185. (7) Song, C.; Saini, A. K.; Yoneyama, Y. Fuel 2000, 79, 249-261. (8) Anderson, L. L. Clean Utilization of Coal; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; NATO ASI Series 370, pp 49-64. (9) Zhao, J.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Energy Fuels 1996, 10, 250-253. (10) Shah, N.; Zhao, J.; Huggins, F. E.; Huffman, G. P. Energy Fuels 1996, 10, 417-420. (11) Ikenaga, N.; Sakoda, T.; Matsui; T.; Ohno, K.; Suzuki, T. Energy Fuels 1997, 11, 183-189. (12) Kotanigawa, T.; Yamamoto, M.; Sasaki, M.; Wang, N.; Nagaishi, H.; Yoshida, T. Energy Fuels 1997, 11, 190-193. (13) Cugini, A. V.; Rothenberger, K. S.; Ciocco, M. V.; Veloski, G. V. Energy Fuels 1997, 11, 213-220. (14) Sakanishi, K.; Hasuo, H.-u.; Mochida, I. Energy Fuels 1998, 12, 284-288.

Using a catalyst, hydrogen can quickly be transferred to the thermally liberated fragments of coal, stabilizing them at these reaction conditions and yielding products having relatively high H/C ratios. Dispersed catalysts, especially those based on the sulfides of molybdenum, are often used in direct liquefaction.1,21-36 (15) Sharma, R. K.; MacFadden, J. S.; Stiller, A. H.; Dadyburjor, D. B. Energy Fuels 1998, 12, 312-319. (16) Priyanto, U.; Sakanishi, K.; Mochida, I. Energy Fuels 2000, 14, 801-805. (17) Qian, V.; Shirai, H.; Ifuku, M.; Ishihara, A.; Kabe, T. Energy Fuels 2000, 14, 1205-1211. (18) Mochida, I.; Sakanishi, K. Fuel 2000, 79, 221-228. (19) Zhang, C.; Lee, C. W.; Keogh, R. A.; Demirel, B.; Davis, B. H. Fuel 2001, 80, 1131-1146. (20) Demirel, B.; Givens, E. N. Energy Fuels 1998, 12, 607611. (21) Demirel, B.; Givens, E. N. Fuel 2000, 79, 1975-1980. (22) Derbyshire, F. J. Energy Fuels 1989, 3, 273-277. (23) Weller, S.; Pelipetz, M. G.; Friedman, S.; Storch, H. H. Ind. Eng. Chem. 1950, 42, 330-334. (24) Weller, S. W.; Pelipetz, M. G. Ind. Eng. Chem. 1951, 43, 12431246. (25) Weller, S. W. Coal liquefaction with molybdenum catalysts. In Chemistry and Uses of Molybdenum; Barry, H. F., Ed.; Climax Molybdenum: Ann Arbor, MI, 1982; p 179. (26) Weller, S. W. Energy Fuels 1994, 8, 415-420. (27) Donath, E. E. In Chemistry of Coal Utilization. Supplemental Volume; Lowry, H. H., Ed.; Wiley: New York, 1963; Chapter 22. (28) Artok, L.; Davis, A.; Mitchell, G. D.; Schobert, H. H. Fuel 1992, 71, 981-991. (29) Artok, L.; Schobert, H. H.; Mitchell, G. D.; Davis, A. Prepr. Symp.s Am. Chem. Soc., DiV. Fuel Chem. 1991, 36, 36. (30) Anderson, R. K.; Lim, S. C.; Ni, H.; Derbyshire, F. J.; Givens, E. N. Fuel Process. Technol. 1995, 45, 109-122. (31) Zhan, X.; Givens, E. N. Catal. Today 1999, 50, 141-148. (32) Demirel, B.; Givens, E. N. Fuel Process. Technol. 2000, 64, 177187. (33) Derbyshire, F. J.; Hager, T. Fuel 1994, 73, 1087-1092. (34) Lastra, B.; Garcia, R.; Moinelo, S. R. Energy Fuels 1997, 11, 411415.

10.1021/ef060440x CCC: $37.00 © 2007 American Chemical Society Published on Web 05/16/2007

Catalytic Direct Liquefaction of High-Sulfur Coals

They serve several functions; for MoS2 catalysts in particular, these include the promotion of hydrogenation and the removal of heteroatoms.1,7,25,26,33,35-42 Model compound studies have demonstrated that sulfides of molybdenum, ruthenium, and iron are very effective in supplying hydrogen. These catalysts with high activity (e.g., MoS2) dissociate molecular hydrogen molecules into active hydrogen atoms that stabilize radicals promptly and facilitate hydrogenolysis of carbon-carbon and carbon-oxygen bonds.5,43 This is one of the most critical roles of catalysts during the initial phase of liquefaction: preventing retrogressive reactions that would lead to the formation of high-molecular-mass residues resistant to further reaction.44-47 Preventing radical recombination has been recognized as an important factor in the upgrading of heavy petroleums48 as well as in coal liquefaction.49,50 Early work on the role of molybdenum compounds as liquefaction catalysts has been summarized by Storch.51 The effectiveness of molybdenum and iron catalysts dispersed on coal has been known for many years,5,24,26,28,52-55 although their chemical and structural forms and the specific reactions that they catalyze are, in many cases, still not exactly known. Catalyst activity has been attributed to improved dispersion on the coal surface.39,56 Introducing water or oil-soluble metal precursors by impregnating them onto the coal57-61 generates finely divided active catalysts during liquefaction. Ammonium heptamolybdate (AHM)32,41,62 and ammonium tetrathiomolyb(35) Gu¨l. O ¨ .; Atanur, O. M.; Artok, L.; Erbatur, O. Fuel Process. Technol. 2006, in press. (36) Warzinski, R. P.; Bockrath, B. C. Energy Fuels 1996, 10, 612622. (37) Schroeder, K.; Bockrath, B. C.; Miller, R.; Davis, H. Energy Fuels 1997, 11, 221-226. (38) Derbyshire, F. J.; Davis, A.; Lin, R.; Stansberry, P. G.; Terrer, M. Fuel Process. Technol. 1986, 12, 127-141. (39) Garcia, A.; Schobert, H. H. Fuel 1989, 68, 1613-1616. (40) Artok, L.; Schobert, H. H.; Erbatur, O. Fuel Process. Technol. 1994, 37, 211-236. (41) Go¨zmen, B.; Artok, L.; Erbatur, G.; Erbatur, O. Energy Fuels 2002, 16, 1040-1047. (42) Bockrath, B. C.; Finseth, D. H.; Illig, E. G. Fuel Process. Technol. 1986, 12, 175-188. (43) Ikenaga, N.; Kobayashi, Y.; Saeki, S.; Sakota, T.; Watanabe, Y.; Yamada, H., Suzuki, T. Energy Fuels 1994, 8, 947-952. (44) Yu, J.; Eser, S. Ind. Eng. Chem. Res. 1998, 37, 4601-4608. (45) Burgess, C. E.; Schobert, H. H. Fuel Process. Technol. 2000, 64, 57-72. (46) Glen, R. A. Fuel 1949, 28, 32-40. (47) Glen, R. A.; De Walt, C. W., Jr. Fuel 1953, 32, 157-168. (48) Bearden, R.; Aldridge, C. L. Energy Prog. 1981, 1, 44-48. (49) Charcosset, H.; Bacaud, R.; Besson, M.; Jeunet, A.; Nickel, B.; Oberson, M. Fuel Process. Technol. 1986, 12, 189-201. (50) Suzuki, T. Energy Fuels 1994, 8, 341-347. (51) Storch, H. H. In Chemistry of Coal Utilization; Lowry, H. H., Ed.; Wiley: New York, 1945; Chapter 38. (52) Weisser, O.; Landa, S. Sulphide Catalysts, Their Properties and Applications; Pergamon Press: New York, 1973; pp 46-49. (53) Given, P. H.; Cronauer, D. C.; Spackman, W.; Lovell, H. L.; Davis, A. Fuel 1975, 54, 34-39. (54) Given, P. H.; Cronauer, D. C.; Spackman, W.; Lovell, H. L.; Davis, A.; Biswas, B. Fuel 1975, 54, 40-49. (55) Gorin, E. In Chemistry of Coal Utilization. Second Supplemental Volume; Elliott, M. A., Ed.; Wiley: New York, 1981; Chapter 27. (56) Cugini, A. V.; Krastman, D.; Martello, D. V.; Frommell, E. F.; Wells, A. W.; Holder, G. D. Energy Fuels 1993, 8, 83-87. (57) Weller, S. W. Catalysis in the Liquid-Phase Hydrogenation of Coal and Tar. In Catalysis; Emmett, P. H., Ed.; Reinhold: New York, 1956; Vol. 4, p 513. (58) Hawk, C. O.; Hiteshue, R. W. Hydrogenation of Coal in the Batch AutoclaVe; U.S. Bureau of Mines Bulletin, 1965; p 622. (59) Bodily, D. M.; Wann, J.-P. Prepr. Symp.sAm. Chem. Soc., DiV. Fuel Chem. 1986, 31, 119. (60) Joseph, J. Fuel 1991, 70, 459-464. (61) Vittal, M.; Boehman, A. L. Energy Fuels 1996, 10, 1028-1029.

Energy & Fuels, Vol. 21, No. 4, 2007 2217

date (ATTM)5,7,28,34,37,39,40,63-69 have commonly been used as precursors, but other Mo compounds have also been used.7,20,21,26,28,32,34,36,43 The highly dispersed catalyst provides effective contact with coal-solvent slurries even at low catalyst concentrations, reducing intraparticle diffusion limitations, and provides effective contact with primary liquids released from the coal.70 The addition of hydrogen sulfide to the reactor has also been found to enhance the liquefaction of coals.3,5,20,28,71-76 The low-rank coal reserves in Turkey are about 8.1 billion tons.77 Many of these coals are not used because of their high sulfur content (5-10%). Their possible utilization for oil production is now being evaluated in a series of research projects.62,78 In the present study, two sub-bituminous coals (Mengen and Kangal) and one asphaltite (Avgamasya) having high sulfur contents were liquefied in the absence of a solvent using AHM and ATTM as catalyst precursors. Coal/asphaltite blends were also liquefied to determine the possibility of coprocessing these two feedstocks. 2. Experimental Section The proximate and ultimate analyses of the coals and asphaltite are given in Table 1. The coals were ground to pass 60 mesh, dried at 50 °C under reduced nitrogen pressure until moisture contents fell below 3%, sealed in glass ampoules under nitrogen, and kept at -20 °C until they were used in the liquefaction experiment. All solvents and chemicals were bought from Merck and used as received. For liquefaction, coal samples impregnated with AHM, (NH4)6Mo7O24‚4H2O, or ATTM, (NH4)2MoS4, were used. For coals, noncatalytic runs were also carried out at two temperatures as baseline experiments to determine the performances of the catalyst precursors used. AHM was used as received. ATTM was synthesized in our laboratory using the procedure described by Naumann et al.79 The catalyst precursor [1% Mo by mass of dry, ash-free (daf) coal] was dissolved in 30 mL of distilled water and added onto 100 g of dry coal dropwise, while the coal was mixed with a spatula to achieve a homogeneous mixture. After the addition was completed, the impregnated coal was dried at 50 °C under reduced nitrogen (62) Erbatur, O.; Gu¨l, O ¨ .; Hesenov, A.; Gafarova, P. MISAG-233, Final Report; TUBITAK: Ankara, Turkey, 2004. (63) Solomon, P. R.; Deshpande, G. V.; Serio, M. A.; Kroo, E.; Schobert, H. H.; Burgess, C. E. In Coal Science II; Schobert, H. H., Bartle K. D., Lynch, L. J., Eds.; American Chemical Society: Washington, D.C., 1991; Chapter 15. (64) Wildervanck, J. C.; Jellinek, F. Z. Anorg. Allg. Chem. 1964, 328, 309-318. (65) Snape, C. E.; Bolton, C.; Dosch, R. G.; Stephens, H. P. Energy Fuels 1989, 3, 421-425. (66) Derbyshire, F. J.; Davis, A.; Epstein, E.; Stansberry, P. Fuel 1986, 65, 1233-1239. (67) Garcia, A. B.; Schobert, H. H. Fuel Process. Technol. 1990, 26, 99-109. (68) Hirschon, A. S.; Wilson, R. B., Jr. Prepr. Symp.sAm. Chem. Soc., DiV. Fuel Chem. 1991, 36, 103. (69) Hirschon, A. S.; Wilson, R. B., Jr. Fuel 1992, 71, 1025-1031. (70) Chamberlin, P. L.; Schobert, H. H. Fuel Process. Technol. 1991, 28, 67-76. (71) Abdel-Baset, M. B.; Ratcliffe, C. T. Prepr. Symp.sAm. Chem. Soc., DiV. Fuel Chem. 1980, 25, 1-7. (72) Baldwin, R. M.; Vinciguerra, S. Fuel 1983, 62, 498-501. (73) Demirel, B.; Fang, S.; Givens, E. N. Appl. Catal., A 2000, 201, 177-190. (74) Artok, L.; Schobert, H. H.; Davis, A. Fuel Process. Technol. 1992, 32, 87-100. (75) Murakami, K.; Yokono, T.; Sanada, Y. Fuel 1986, 65, 1079-1080. (76) Willson, W. G.; Hei, R.; Riskedahl, D.; Stenberg, V. I. Fuel 1985, 64, 128-130. (77) Kural, O. Coal; Istanbul, Turkey, 1991; pp 294-332. (78) Erbatur, O.; Erbatur, G. KTCAG-126, Final Report; TUBITAK: Ankara, Turkey, 2002. (79) Naumann, A. W. U.S. Patent 4,243,554, 1981

2218 Energy & Fuels, Vol. 21, No. 4, 2007

Gu¨l et al.

Table 1. Proximate and Ultimate Analytical Data of Coals coals ASTM classification calorific value (kJ/kg) ash (wt % dry) V. M. (wt % dry) F. C. (wt % dry) elemental analysis (wt % daf)a C H N S Ob forms of sulfur (wt % dry) total pyritic sulfatic orgb a

Mengen

Kangal

Avgamasya

sub-bituminous A 24 586 20.96 45.42 31.33

sub-bituminous C 20 753 18.14 53.37 20.75

asphaltite 20 741 39.93 50.27 7.85

74.72 5.91 1.86 10.34 7.17

66.58 5.94 1.88 4.05 21.55

79.82 7.74 1.33 9.19 1.92

13.08 1.98 0.14 10.96

4.95 1.07 0.22 3.66

15.30 0.61 0.14 14.55

daf ) dry, ash-free. b Calculated from difference.

pressure until the moisture content fell below 3%. The incipient wetness water values of all coal samples were adjusted between 2 and 3%. A quantity of ground coal was subjected to this procedure with the same relative amounts of AHM or ATTM added to coal; the impregnated samples, after drying under reduced nitrogen pressure, were sealed in a number of glass ampoules under nitrogen, so that all catalytic liquefaction experiments would be carried out with coal samples having identical AHM or ATTM loading and identical incipient wetness. Microautoclave reactors (tubing bombs) of 25 mL volume were used. In a typical experiment, 2.5 g of coal (whether impregnated or not) or a coal/asphaltite mixture was charged into the reactor. After the reactor was sealed, air was swept out by successive pressurizing (6.9 MPa cold) and depressurizing twice with nitrogen and twice with hydrogen. Finally, the reactor was pressurized with hydrogen (6.9 MPa cold) and submerged into a eutectic salt bath after attaching it to a horizontally oscillating system. The bath, having a temperature of 5 °C above the desired reaction temperature, heats the reactor to the desired temperature in 1-2 min. The horizontally oscillating system shakes the reactor through an amplitude of 2 cm at 400 cycles/min. The duration of all experiments was 30 min. All experiments were carried out at least 3 times; thus, the data reported here are the means of three values. The yields of oil + gas fractions were calculated by difference. Gas analyses were not performed, except H2S measurements. At the end of the reaction, the reactor was taken out of the salt bath and immediately plunged into a cold-water bath. The gas in the reactor was bubbled through a cadmium acetate solution, so that H2S precipitated quantitatively as CdS. Gravimetric determination of precipitated CdS gave the H2S yield by back calculation. The slurry content of the reactor was removed with n-hexane into an extraction thimble and sequentially extracted in a Soxhlet apparatus with n-hexane, toluene, and tetrahydrofuran; oils, asphaltenes (AS), and preasphaltenes (PAS) were the materials solubilized in these solvents, respectively. The mass of oil + gas products was calculated by subtracting the total mass of asphaltene + preasphaltene + char (residue) from the mass of the original dry coal subjected to liquefaction. The oils obtained from three parallel runs were combined and subjected to gas chromatography-mass-selective detector (GCMSD; HP-5970 MSD coupled to a HP-5980 GC) analysis to obtain detailed chemical compositions. The MSD was equipped with a quadrupole analyzer operated in electron-impact (70 eV) mode. The GC was equipped with a TC-17 50/50% phenyl methyl siloxane column (30 m × 0.32 mm i.d.; 0.5 µm film thickness). The oven temperature program started at 50 °C (5 min hold), increased to 280 °C with a 4 °C/min ramp, and was then held at this final value for 15 min.

Separate experiments were carried out in a 500 mL reactor having a magnedrive stirrer, for determining the oil yields from coals at 400 and 450 °C and from the asphaltite at 450 °C. In a typical experiment in this system, 50 g of ATTM-impregnated coal was loaded into the reactor. After the reactor was sealed, the air content of the reactor was minimized using the same sequential purging with nitrogen and hydrogen as described above for the microautoclaves. The reactor was pressurized with 6.9 MPa of hydrogen at room temperature. It was then heated to the desired temperature (400 or 450 °C) and maintained there for 30 min. At the end of the run, the reactor was quenched with cold water for cooling to ambient temperature.

3. Results and Discussion 3.1. Distribution of Main Product Fractions. 3.1.1. Effect of the Process Temperature in the Presence of the Catalyst Precursor AHM. Both AHM-impregnated coals were liquefied at 300, 350, 400, and 450 °C. The distributions of main product fractions are given in Tables 2 and 3. Noncatalytic runs were also carried out at two different temperatures, so that a comparison of the results would show the effect of AHM in liquefying these two low-rank coals, whose constitutions are rather different. The product distributions in Table 2 show that, as the temperature is increased, liquefaction becomes more effective, as expected. The data indicate that substantial decomposition of the matrix of this coal starts around 350 °C, whereas effective formation of oil + gas takes place around 400 °C. At this temperature, conversion of PAS into AS also takes place.5,80 These observations suggest that AHM converted into a catalytically active form around this temperature.81 Conversion increased remarkably at 450 °C, producing oil + gas effectively as well as the PAS and AS. Conversion reached 79.8%, similar to the results of Kaneko et al.82 Because the conversions at 400 and 450 °C were of most interest, noncatalytic runs were also carried out at these temperatures with both coals. The product distributions given in Table 2 show that the mineral matter in Mengen coal and the high sulfur content play a self-catalytic role and that conversions of 12.1% at 400 °C and 11.6% at 450 °C less than the corresponding values obtained in the catalytic runs were achieved. This agrees with work by O ¨ ner et al.83,84 and Olcay et al.85 on the effect of the ash value of Turkish lignites and asphaltites on conversion, including an increased yield of hexane solubles.84 However, even when the minerals in the coal help catalyze liquefaction, yields are always better if MoS2 is also added.86 There is a substantial increase in the oil + gas fraction, 50.9-61.0% at 450 °C, for noncatalytic and catalytic reactions, respectively, but visual observations during the experiments implied that gaseous products made up a considerable amount of the product slate at this temperature. One can expect that the interaction of hydrogen sulfide formed from sulfur-containing groups with iron in the coal matrix should form iron sulfides that could act as catalysts during the process. Mengen coal has 10.98% organic sulfur, 1.98% pyritic sulfur, and 0.96% iron (80) Aleksic, B. R.; Ercegovac, M. D.; Cvetkovic, O. G.; Branislav Zˇ . Markovic, B. Z.; Aleksic, B. D.; Vitorovic, D. K. Fuel Process. Technol. 1998, 58, 33-43. (81) Lopez, J.; Pasek, E. A.; Cugini, A. V. U.S. Patent 4,762,812, 1988. (82) Kaneko, T.; Tazawa, K.; Okuyama, N.; Tamura, M.; Shimasaki, K. Fuel 2000, 79, 263-271. (83) O ¨ ner, M.; Bolat, E.; Dincer, S. Energy Sources 1992, 14, 81-94. (84) O ¨ ner, M.; O ¨ ner, G.; Bolat, E.; Yalin, G.; Kavlak, C.; Dincer, S. Fuel 1994, 73, 1658-1666. (85) Olcay, A.; O ¨ ner, M. In Coal; Kural, O., Ed.; Istanbul Technical University: Istanbul, Turkey, 1994; Chapter 28. (86) Sustmann, H.; Weinrotter, F. Brennst.-Chem. 1941, 22, 229-236.



Table 2. Percent Distribution of Main Product Fractions Following Liquefaction of Mengen Coal with or without the Catalyst Precursor (AHM) at Different Reaction Temperatures

a

catalyst precursor

T (°C)

gas + oila,b

ASa

PASa

total conversiona

Sgc

AHM AHM AHM AHM

300 350 400 450 400 450

1.5 ( 0.5 17.3 ( 8.6 41.5 ( 2.1 61.0 ( 2.8 34.7 ( 0.3 50.9 ( 3.8

3.4 ( 0.3 13.6 ( 1.1 20.7 ( 1.1 13.7 ( 2.1 14.9 ( 0.7 10.2 ( 1.3

11.9 ( 1.4 20.6 ( 4.6 12.0 ( 1.3 5.1 ( 0.8 12.5 ( 0.7 7.1 ( 1.0

16.7 ( 3.9 51.5 ( 1.5 74.2 ( 3.9 79.8 ( 1.3 62.1 ( 0.2 68.2 ( 3.1

0.9 ( 0.1 2.2 ( 0.5 5.1 ( 0.4 6.0 ( 0.6 6.1 ( 0.6 7.1 ( 1.0

wt % (daf). b Calculated from difference. c wt % of sulfur in the gas phase.

Table 3. Percent Distribution of Main Product Fractions Following Liquefaction of Kangal Coal with or without the Catalyst Precursor (AHM) at Different Reaction Temperatures

a

catalyst precursor

T (°C)

gas + oila,b

ASa

PASa

total conversiona

Sgc

AHM AHM AHM AHM

300 350 400 450 400 450

7.4 ( 0.8 35.0 ( 3.4 63.1 ( 1.6 70.2 ( 3.9 37.3 ( 0.1 54.0 ( 1.8

3.5 ( 1.9 8.8 ( 1.8 8.8 ( 1.3 3.7 ( 1.2 6.7 ( 1.9 9.3 ( 0.1

2.0 ( 0.4 9.6 ( 5.6 2.2 ( 0.3 2.1 ( 0.4 8.5 ( 1.3 4.3 ( 0.1

12.8 ( 1.3 53.3 ( 5.5 74.1 ( 0.3 75.9 ( 3.6 52.5 ( 0.5 67.6 ( 1.8

0.9 ( 0.5 2.4 ( 0.6 3.3 ( 0.4 3.0 ( 0.9 4.3 ( 0.4 7.0 ( 1.8


(dry basis). Iron compounds as catalyst precursors, even if they were sulfur-containing compounds, were found less active with regard to hydrogen consumption than molybdenum catalyst precursors.5 However, in the presence of H2S, a remarkable activity was reported for iron compounds. The increased activity of iron compounds has been attributed to the transformation of pyrite to pyrrhotite in an H2S atmosphere.5 Furthermore, H2S itself is also a good hydrogen donor.5,6,74 However, these effects were not as noticeable as in the catalytic runs with AHM.87,88 Molybdenum-containing catalyst precursors enhance hydrogen consumption, coal conversion, and oil and asphaltene yields.5 Desulfurization, in the form of hydrogen sulfide evolution, was even more effective in noncatalytic runs (Table 2). A H2S yield decrease was reported when AHM was used as a catalyst precursor.41 This effect was explained by the consumption of H2S in the reaction with AHM to activate this catalyst precursor.41 The product distributions from Kangal are given in Table 3. Substantial decomposition of the coal again started around 350 °C, as observed with Mengen. Although the conversions of both coals with AHM at 400 °C are about equal, distributions of the product fractions are rather different. The yield of oil + gas from Kangal is 21.6% higher than the corresponding value obtained with Mengen. Kangal has a very high oxygen content (21.55%); therefore, one can expect that a considerable fraction of the oil + gas product obtained from this coal should be CO2 from the cleavage of carboxylic groups from the coal structure.89 It was reported that, if a coal has less carbon and more oxygen content, it would have a larger population of carboxylic groups.90 When the AS and PAS formations were compared, Mengen gave higher AS and PAS yields than Kangal under all conditions tested. Kangal coal is younger and has a lower fixed carbon and higher oxygen content than Mengen coal. When younger coals break up, they will likely have a considerable amount of lower molecular-weight hydrocarbons. On the other hand, higher rank coals will yield higher molecular-weight products, which will contribute to AS and PAS. These results are consistent with (87) Tomic, J.; Schobert, H. H., Energy Fuels 1997, 11, 116-125. (88) Burgess, C. E.; Schobert, H. H. Energy Fuels 1996, 10, 718-725. (89) Ruberto, R. G.; Cronauer, D. C. In Organic Chemistry of Coal; Larsen, J. W., Ed.; American Chemical Society: Washington, D.C., 1978; Chapter 3. (90) Blom, L. Ph.D. Thesis, Delft University of Technology, Delft, The Netherlands, 1960.

the structural differences of these two coals regarding rank, fixed carbon, and oxygen and sulfur functionalities.91 In noncatalytic runs, Mengen gave a higher conversion than Kangal. The role of oxygen functional groups, specifically, their loss during the thermally induced breakdown of the coal structure, in promoting recombination reactions during liquefaction has been described.63,92-94 This loss of oxygen functional groups generates reactive sites that, if not readily capped by hydrogen, can combine to form new structures that resist further reaction. The observed dependence of conversion on oxygen content agrees with this conceptual model of the loss of oxygen functional groups triggering retrogressive reactions when effective capping of the reactive sites cannot occur. Further, Storch et al.95 showed that there was a general similarity between the rates of oxygen elimination and liquefaction for the catalytic reactions that they tested. We did not obtain kinetic data in the present work; however, there is a reasonable linear relationship between the increase in the oil + gas yield and the increase in conversion with the reaction temperature from 350 to 400 °C for both coals and both catalyst precursors. Because the oxygen functional groups, particularly carboxyl groups that we expect to be abundant in low-rank coals, would contribute to the gas yield, their loss, followed by effective capping of the nascent reactive sites by hydrogen, would enhance overall conversion of the macromolecular structure of the coal. The formation of CO2 is thought to coincide with the primary thermal decomposition of the coal.95 3.1.2. Effect of the Process Temperature in the Presence of the Catalyst Precursor ATTM. Both coals and the asphaltite were impregnated with ATTM and liquefied; results are given in Tables 4, 5, and 6, respectively. Conversion of Mengen with ATTM is highest at 400 °C, but when oil + gas yields are compared, the highest yield (67.1%) is obtained at 450 °C (Table 4). Oil yields were also determined directly for these two runs. (91) Artok, L.; Schobert, H. H.; Nomura, M.; Erbatur, O.; Kidena, K. Energy Fuels 1998, 12, 1200-1211. (92) Suuberg, E. M.; Lee, D.; Larsen, J. W. Fuel 1985, 64, 1668-1671. (93) Deshpande, G. V.; Solomon, P. R.; Serio, M. A. Prepr. Symp.s Am. Chem. Soc., DiV. Fuel Chem. 1988, 33, 310. (94) Solomon, P. R.; Serio, M. A.; Deshpande, G. V.; Kroo, E. Energy Fuels 1990, 4, 42-54. (95) Storch, H. H.; Fisher, C. H.; Hawk, C. O.; Eisner, A. U.S. Bureau of Mines Technology Paper, 1943; p 654.


Gu¨l et al.

Table 4. Percent Distribution of Main Product Fractions Following Liquefaction of Mengen Coal with or without the Catalyst Precursor (ATTM) at Different Reaction Temperatures catalyst precursor

T (°C)

ATTM ATTM ATTM

350 400 450 400 450

a

oila 30.9 ( 3.7 56.9 ( 5.9

gas + oila,b

% ASa

% PASa

% total conversiona

% Sgc

8.1 ( 1.2 51.3 ( 4.8 67.1 ( 0.5 34.7 ( 0.3 50.9 ( 3.8

18.7 ( 1.6 29.6 ( 7.8 14.0 ( 0.5 14.9 ( 0.7 10.2 ( 1.3

23.8 ( 1.8 8.2 ( 0.6 5.2 ( 1.0 12.5 ( 0.7 7.1 ( 1.0

50.7 ( 2.2 89.2 ( 2.6 86.3 ( 0.1 62.1 ( 0.2 68.2 ( 3.1

3.2 ( 0.3 6.0 ( 0.4 9.2 ( 1.0 6.1 ( 0.6 7.1 ( 1.0

wt % (daf). b Calculated from difference. c wt % of sulfur in the gas phase. Table 5. Percent Distribution of Main Product Fractions Following Liquefaction of Kangal Coal with or without the Catalyst Precursor (ATTM) at Different Reaction Temperatures

catalyst precursor

T (°C)

ATTM ATTM ATTM ATTM

300 350 400 450 400 450

a

oila

gas + oila,b

ASa

PASa

total conversiona

Sgc

49.6 ( 3.1 49.9 ( 2.2

11.3 ( 5.1 38.6 ( 0.8 78.7 ( 2.2 80.4 ( 2.2 37.3 ( 0.1 54.0 ( 1.8

1.6 ( 0.5 9.4 ( 0.5 7.0 ( 1.3 2.5 ( 1.6 6.7 ( 1.9 9.3 ( 0.1

3.3 ( 1.1 3.4 ( 0.4 2.0 ( 0.4 3.1 ( 0.7 8.5 ( 1.3 4.3 ( 0.1

16.3 ( 6.0 51.3 ( 1.0 87.7 ( 3.3 85.9 ( 1.8 52.5 ( 0.5 67.6 ( 1.8

1.2 ( 0.6 3.3 ( 0.1 4.2 ( 0.3 5.1 ( 0.1 4.3 ( 0.4 7.0 ( 1.8


Table 6. Percent Distribution of Main Product Fractions Following Liquefaction of Avgamasya Asphaltite with the Catalyst Precursor (ATTM) at Different Reaction Temperatures catalyst precursor

T (°C)

P (atm)

ATTM ATTM ATTM ATTM

350 400 400 450

70 70 90 70

a

oila

gas + oila,b

ASa

PASa

total conversiona

Sgc

52.9 ( 2.3

19.1 ( 0.3 42.4 ( 1.4 48.4 ( 1.0 74.4 ( 2.0

19.4 ( 0.5 45.5 ( 0.8 46.3 ( 0.01 12.5 ( 0.6

1.5 ( 0.03 4.2 ( 1.9 4.3 ( 1.0 4.0 ( 0.4

40.0 ( 0.7 92.0 ( 1.6 99.0 ( 0.03 90.9 ( 1.6

2.4 ( 0.2 3.9 ( 0.6 4.9 ( 0.9 4.9 ( 0.6


The highest oil yield (56.9%) was obtained at 450 °C; the corresponding yield at 400 °C was about 30.9%. ATTM is more effective in liquefaction of Mengen coal than AHM, consistent with a general observation that, for heavy metals, the sulfide forms are more active than oxides as liquefaction catalysts.96,97 To obtain the maximum yield of oil, a process temperature of 450 °C would be needed for this coal. On the other hand, because the conversion at 450 °C is 2.9% lower than at 400 °C, there may be a slight formation of char via retrogressive reactions at 450 °C. Pott et al.98 have shown that temperatures of 390-410 °C appeared to be optimum for solvent extraction of most of the coals with which they worked; above this range, retrogressive reactions occurred. In catalytic hydroprocessing of heavy oils, thermal pyrolysis becomes increasingly important above about 410 °C.87,99-105 Also, the most effective desulfurization took place at this temperature. The conversions obtained without using ATTM were lower, as would be expected for a noncatalytic reaction. Table 5 summarizes the product distributions from liquefaction of Kangal with ATTM. Again, conversions are higher with ATTM compared to those with AHM. The highest conversion (96) Storch, H. H. J. Ind. Eng. Chem. 1945, 37, 340-351. (97) Redlich, P. J.; Hulston, C. K. J.; Jackson, W. R.; Larkins, F. P.; Marshall, M. Fuel 1999, 78, 83-88. (98) Pott, A.; Broche, H.; Nedelmann, H.; Schmitz, H.; Scheer, W. Fuel 1934, 13, 91-95. (99) LePage, J. F.; Chatila, S. G.; Davidson, M. Resid and HeaVy Oil Processing; EÄ ditions Technip: Paris, France, 1992; Chapter II.2. (100) Tomic, J.; Schobert, H. H. Energy Fuels 1996, 10, 709-717. (101) Huang, L. Ph.D. Dissertation, The Pennsylvania State University, University Park, PA, 1995. (102) Moschopedis, S. E.; Hawkins, R. W.; Speight, J. G. Fuel Process. Technol. 1982, 5, 213-228. (103) Rosal, R.; Cabo, L. F.; Diez, F. V.; Sastre, H. Fuel Process. Technol. 1992, 31, 209-220. (104) Speight, J. G. The Chemistry and Technology of Petroleum, 2d ed.; Dekker: New York, 1991; p 760. (105) Bolat, E.; Kavlak, C.; Yalin, G.; Dincer, S. Fuel Process. Technol. 1992, 31, 55.

is obtained at 400 °C, whereas the oil yields are almost the same at both 400 and 450 °C. There is a slight decrease in conversion at 450 °C, again suggesting some possible char formation because of retrogressive reactions at this temperature. These results show that 400 °C is the optimum temperature for liquefaction of this coal when using ATTM. Similar to observations made using AHM, extensive gaseous product formation (around 30%) occurs with this coal, likely because of decarboxylation reactions. Avgamasya asphaltite, from southeastern Turkey (around Sirnak), is an aliphatic-rich material with almost no oxygen but a high sulfur content (9.2%, daf basis). The product distribution from liquefaction of this material in the presence of ATTM is given in Table 6. Conversions of about 90% were obtained at both 400 and 450 °C, but the yield of oil + gas (74.4%) was much higher in the latter case, in which around 52.9% was the oil product. Garcia and Schobert6 correlated the liquid yields with the organic sulfur content, and they suggested that the thermolysis of relatively weak C-S bonds is important in disrupting the macromolecular structure to produce lighter materials. Avgamasya asphaltite was blended with Mengen coal at various ratios and liquefied in the presence of ATTM at 450 °C. The distributions of product fractions are given in Table 7 (Figure 1a). In no cases were better results achieved than those obtained with a single coal or with the asphaltite alone, either in terms of conversion or in terms of oil + gas yields. As the mass ratio of the coal in the blend was increased, both the conversions and the oil + gas yields decreased. However, no linear relationship was seen between the mass ratio of the coal and conversions or oil + gas yields (parts a and b of Figure 1). Similar experiments were carried out with blends of Kangal and the asphaltite (Table 8; Figure 1b) but at 400 °C, because Kangal itself liquefied most efficiently at this temperature in the presence of ATTM. Results were obtained similar to those from Mengen + asphaltite blends. The presence of even 25%



Table 7. Percent Distribution of Main Product Fractions Following Liquefaction of ATTM Impregnated Mengen Coal/Avgamasya Asphaltite Blends at 450 °C

a

coal/asphaltite

gas + oila,b

ASa

PASa

total conversiona

Sgc

0:1 1:3 1:1 3:1 1:0

74.4 ( 2.0 66.0 ( 1.0 63.3 ( 3.0 51.0 ( 6.1 67.1 ( 0.5

12.5 ( 0.6 11.8 ( 1.3 11.4 ( 0.6 11.1 ( 2.0 14.0 ( 0.5

4.0 ( 0.4 4.0 ( 0.4 3.6 ( 0.5 5.9 ( 0.6 5.2 ( 1.0

90.9 ( 1.6 81.8 ( 2.3 78.6 ( 2.6 67.1 ( 4.0 86.3 ( 0.1

4.9 ( 0.6 7.5 ( 1.0 8.3 ( 0.9 12.7 ( 0.2 9.2 ( 1.0


Table 8. Percent Distribution of Main Product Fractions Following Liquefaction of ATTM Impregnated Kangal Coal/Avgamasya Asphaltite Blends at 400 °C

a

coal/asphaltite

gas + oila,b

ASa

PASa

total conversiona

Sgc

0:1 1:3 1:1 3:1 1:0

42.4 ( 1.4 41.2 ( 2.3 46.8 ( 1.3 45.2 ( 2.0 78.7 ( 2.2

45.5 ( 0.8 37.5 ( 0.9 21.0 ( 1.3 11.9 ( 1.1 7.0 ( 1.3

4.2 ( 1.9 2.9 ( 0.3 2.4 ( 0.1 3.3 ( 0.4 2.0 ( 0.4

92.0 ( 1.6 81.6 ( 1.5 70.2 ( 0.8 60.3 ( 0.7 87.7 ( 3.3

3.9 ( 0.6 3.8 ( 0.02 4.5 ( 0.2 5.4 ( 0.3 4.2 ( 0.3


Figure 1. (a) Total conversion and oil + gas changes versus the Mengen coal ratio. (b) Total conversion and oil + gas changes versus the Kangal coal ratio.

of the asphaltite in the blend decreased both conversion and the oil + gas yield dramatically. Assuming that asphaltite serves as the liquid vehicle in this system, this observation is consistent with the work of Warren et al.,106 who showed that, with catalyst loadings g 0.5%, the addition of a liquid vehicle can have a negative effect on conversions.96 Tomic et al.87 also reported that, in the co-processing of coal and a petroleum residue, the residue behaved like a liquid medium for the coal fragments and did not have properties of a hydrogen donor or hydrogen shuttler. In our work, the addition of asphaltite would make it (106) Warren, T. E.; Bowles, K. W.; Gilmore, R. E. Ind. Eng. Chem. 1939, 11, 415-419.

likely that hydrogen would need to diffuse through a film of liquid covering the surface of the coal + catalyst particles. This hydrogen diffusion process has been shown to be critical, albeit at lower temperatures, by Storch et al.95 Blending has suppressed coal conversions obtained in combination with the asphaltite at 400 °C (Kangal) and 450 °C (Mengen) relative to the conversions obtained with coals or asphaltite alone. This is expected, because in co-processing, reactive species are generated both by the coal and the asphaltite. Residual solids are usually a result of the reactive species recombining and cross-linking before they have been hydrogenated.87 It is a likely consequence that the residual solids have increased. 3.2. Chemical Composition of Oils. 3.2.1. Oils Obtained when AHM or ATTM Was Used as the Catalyst Precursor. Table 9 summarizes the results from GC-MSD analysis of oils from the liquefaction of Mengen with AHM and from noncatalytic runs at 400 and 450 °C. The most striking observation was that, while the amounts of naphthalene and alkyl-substituted naphthalenes and tetralin and alkyl-substituted tetralins were substantial when AHM was not used, there were significant decreases in the amounts of these compounds in the reactions performed using AHM. Also, in contrast to the case where AHM was not used, the amount of alkyl-substituted benzenes increased substantially. These data indicate that AHM is very effective in catalyzing the hydrogenation of naphthalene and alkylsubstituted naphthalenes and in catalyzing the hydrocracking of tetralin and alkyl-substituted tetralins. Hydrogenation of naphthalene over AHM to produce tetralin is accompanied by ring opening to alkylbenzenes above 400 °C.107 Ring-opening reactions in catalytic hydrogenation of coal have been noted.108 Our findings are in general agreement with Sweeney et al.,109 albeit at slightly lower temperatures (400-450 °C instead of 450-480 °C) and higher hydrogen pressures (1000 psi instead of 150 psi). Aliphatic side chains on aromatic systems are also cleaved at g450 °C.108 On the other hand, the reduction of the monoaromatic ring of alkyl-substituted benzenes was not observed.43 Tetralin and alkyl-substituted tetralins almost disappeared from the products when AHM was used, which showed that AHM was very effective in catalyzing the cleavage of the hydroaromatic ring. (107) Hall, C. C. Fuel 1933, 12, 76-93. (108) Speight, J. G. The Chemistry and Technology of Coal; Dekker: New York, 1994; Chapter 16, part I. (109) Sweeney, W. J.; Voorhies, A. Ind. Eng. Chem. 1934, 26, 195198.


Gu¨l et al.

Table 9. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of Mengen Coal with or without the Catalyst Precursor (AHM) at Different Reaction Temperaturesa catalyst precursor

temp. (°C)

openchain paraffins

cycloparaffins

alkylbenzenes

naphthalene and derivative

tetralin and derivative

decalin and derivative

other two-ring aromatics

AHM AHM AHM AHM

300 350 400 450 400 450

11.6 8.6 21.3 17.6 22.6 19.9

4.6 2.3 1.4 1.7 0.0 0.0

31.0 47.8 16.1 17.5 4.1 3.9

9.1 3.8 4.7 7.8 20.0 14.8

2.3 10.6 0.0 1.9 16.9 39.5

0.0 0.6 0.0 0.0 0.0 0.0

2.3 6.5 6.9 8.5 6.3 1.9

a

phenols

three-ring or higher aromatics

othersb

36.3 11.4 13.8 18.9 16.4 17.4

0.0 0.1 1.2 6.7 0.3 0.0

3.0 8.5 34.6 19.5 13.4 2.7

Percent distributions belong to the ratio of GC-MS peak areas. b Total area of unidentified peaks spread throughout the chromatogram. Table 10. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of Kangal Coal with or without the Catalyst Precursor (AHM) at Different Reaction Temperatures

catalyst precursor

temp. (°C)

openchain paraffins

cycloparaffins

alkylbenzenes





AHM AHM AHM AHM

300 350 400 450 400 450

21.2 16.0 27.1 16.2 4.5 5.0

7.5 4.5 1.7 5.4 0.2 0.5

26.7 29.0 20.5 24.1 12.8 10.8

5.7 2.2 4.3 9.1 25.0 26.7

0.0 1.1 0.4 1.8 39.5 35.3

0.0 0.0 0.0 0.0 0.0 0.0

2.1 3.8 5.5 6.3 1.8 2.1

phenols


others

34.7 26.7 19.6 14.6 8.9 11.8

0.0 0.0 0.0 0.0 0.0 1.2

2.3 16.7 21.0 22.5 7.3 6.6

Table 11. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of Mengen Coal with or without the Catalyst Precursor (ATTM) at Different Reaction Temperatures catalyst precursor

temp. (°C)

openchain paraffins

cycloparaffins

alkylbenzenes





ATTM ATTM ATTM

350 400 450 400 450

44.6 41.9 16.8 22.6 19.9

0.6 0.4 0.9 0.0 0.0

6.1 9.0 14.8 4.1 3.9

4.4 5.2 8.8 20.0 14.8

0.0 1.7 1.5 16.9 39.5

0.0 0.0 0.0 0.0 0.0

9.2 8.0 6.8 6.3 1.9

phenols


others

23.7 21.0 15.1 16.4 17.4

0.0 0.0 6.8 0.3 0.0

11.6 12.8 28.5 13.4 2.7

Table 12. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of Kangal Coal with or without the Catalyst Precursor (ATTM) at Different Reaction Temperatures catalyst precursor

temp. (°C)

openchain paraffins

cycloparaffins

alkylbenzenes





ATTM ATTM ATTM ATTM

300 350 400 450 400 450

29.6 34.0 32.2 14.6 4.5 5.0

9.6 13.4 5.8 17.0 0.2 0.5

42.0 24.2 14.4 31.5 12.8 10.8

0.3 0.7 3.2 5.4 25.0 26.7

1.2 0.3 0.8 1.3 39.5 35.3

0.0 0.0 0.0 0.0 0.0 0.0

1.5 3.8 2.8 3.9 1.8 2.1

The amounts of naphthalene and alkyl-substituted naphthalenes, tetralin and alkyl- substituted tetralins, and higher condensed aromatics formed at 450 °C in the presence of AHM were higher than the corresponding values obtained at 400 °C. It is obvious that cleavage of the coal structure accelerates, and therefore, high yields of oil are obtained at 450 °C. On the other hand, the increase of the three-ring or higher aromatics in the liquid at higher liquefaction temperatures also indicate the possibility of enhancement of retrogressive reactions toward aromatization at 450 °C.110,111 The relative amounts of phenolic products obtained following reactions at 400 and 450 °C, both with and without AHM, vary around 15% with this coal. Of the common oxygen functional groups in coal, phenolic groups are the most resistant to reaction during liquefaction.89,95,112 Table 10 gives compositions of oils obtained from Kangal in the presence of AHM. The results of noncatalytic runs are (110) Dutta, R. P.; Schobert, H. H. Catal. Today 1996, 31, 65-77. (111) Peng, Y. Ph.D. Dissertation, The Pennsylvania State University, University Park, PA, 1995. (112) Kirby, S. R.; Song, C.; Schobert, H. H. Catal. Today 1996, 31, 121-135.

phenols


others

13.3 17.9 18.6 17.4 8.9 11.8

0.0 0.0 0.5 1.1 0.0 1.2

2.5 5.6 21.6 7.9 7.3 6.6

also given. Generally, similar results were observed with respect to reactions of naphthalene and its alkyl-substituted derivatives, tetralin and its alkylated derivatives, and alkyl-substituted benzenes. These observations are consistent with the results from Mengen. The relative amount of phenols among the products from both coals is similar, despite the extremely high oxygen content of Kangal, suggesting that most of the oxygen in this coal occurs as carboxyl, carbonyl, and ether functional groups. These observations are also consistent with the distribution of main product fractions and Blom’s90 oxygen functional group distributions. Further characterization to determine the functional groups of coals will be reported in future studies. Tables 11 and 12 summarize the compositions of oils obtained from Mengen and Kangal with ATTM. In general, the trends observed in the compositions of oils obtained using AHM were also observed in the oils obtained with ATTM, but GC-MSD data indicate that there was some saturation of monoaromatic rings when ATTM had been used with Kangal coal, which was not the case with AHM.5,96 Because the reduction of monoaromatics is more difficult compared to aromatics containing two



Table 13. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of ATTM Impregnated Avgamasya Aphaltite with the Catalyst Precursor ATTM at Different Reaction Temperatures catalyst precursor

temp. (°C)

openchain paraffins

cycloparaffins

alkylbenzenes





ATTM ATTM ATTM

350 400 450

21.2 27.1 30.5

8.6 3.7 3.9

23.9 19.5 10.0

6.2 8.4 4.1

9.3 10.6 1.4

0.1 0.7 0.0

5.2 2.1 7.2

phenols


others

6.4 4.3 0.0

2.2 0.6 4.4

16.8 23.1 38.5

Table 14. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of ATTM Impregnated Blends of Mengen Coal/ Avgamasya Asphaltite at 450 °C coal/ asphaltite

open-chain paraffins

cycloparaffins

alkylbenzenes





0:1 1:3 1:1 3:1 1:0

30.5 29.8 22.4 21.6 16.8

3.9 1.1 4.2 7.7 0.9

10.0 12.9 15.1 15.3 14.8

4.1 4.8 7.0 8.2 8.8

1.4 1.4 1.8 2.3 1.5

0.0 0.0 0.0 0.0 0.0

7.2 7.2 3.4 3.3 6.8

phenols


others

0.0 4.8 8.4 15.5 15.1

4.4 4.1 4.2 6.8 6.8

38.5 33.9 33.6 19.3 28.5

Table 15. Percent Distribution of the Product Fractions of Oils Obtained from Liquefaction of ATTM Impregnated Blends of Kangal Coal/ Avgamasya Asphaltite at 400 °C coal/ asphaltite

open-chain paraffins

cycloparaffins

alkylbenzenes





0:1 1:3 1:1 3:1 1:0

27.1 30.7 33.2 31.7 32.2

3.7 3.5 3.5 5.6 5.8

19.5 12.7 7.4 7.3 14.4

8.4 2.0 5.5 1.6 3.2

10.6 5.6 6.0 4.8 0.8

0.7 0.0 0.0 0.0 0.0

2.1 5.8 4.3 6.8 2.8

or more condensed rings113-115 and because monoaromatics are likely formed mainly from hydrogenation and hydrogenolysis of multicyclic aromatics, the reduction of monoaromatics takes place in the later stages of liquefaction, i.e., when liquefied material dominates in the reaction mixture. Under these conditions, most of the interaction of monoaromatics with the catalyst particles may take place in the liquid phase. Thus, we presume that there may be structural differences between the active molybdenum sulfide catalyst obtained from ATTM and the active catalyst obtained from AHM under liquefaction conditions.81,116 However, we cannot rule out particle-size differences between the dispersed catalysts, because the particle size is known to be an important factor in the (NH4)n[X(MoO4)6] family of catalysts (where X represents various elements incorporated as promoters).117 Similar to AHM, some aromatization reactions at 450 °C are also observed with ATTM.110 For both coals, fewer total aromatics (the sum of alkylbenzenes, naphthalene and derivative, tetralin and derivative, other two-ring aromatics, phenols, and three-ring or higher aromatics) were obtained at 400 °C than at 450 °C in the presence of ATTM. On the other hand, when catalytic and noncatalytic reaction products are compared, both coals gave fewer aromatics at 400 and 450 °C in the presence of ATTM than those of noncatalytic reactions (parts a and b of Figure 2). The results from Kangal indicate the highest conversion to oil at 400 °C; if conversion to oils is the most important criterion in the liquefaction process, this temperature should not be exceeded with this coal and ATTM. On the other hand, for (113) Lapinas, A. T.; Klein, M. T.; Gates, B. C.; Macris, A.; Lyons, J. E. Ind. Eng. Chem. Res. 1991, 30, 42-50. (114) Sapre, A. V.; Gates, B. C. Ind. Eng. Chem. Process Des. DeV. 1981, 20, 68-73. (115) Sapre, A. V.; Gates, B. C. Ind. Eng. Chem. Process Des. DeV. 1982, 21, 86-94. (116) Utz, B. R.; Cugini, A. V.; Frommell, E. A. Prepr. Symp.sAm. Chem. Soc., DiV. Fuel Chem. 1989, 34, 1423-1430. (117) Kingman, F. E. T.; Rideal, E. K. Nature 1936, 137, 529.

phenols


others

4.3 15.2 20.5 19.0 18.6

0.6 0.0 0.2 0.0 0.5

23.1 24.5 19.4 23.2 21.6

Mengen, which is of a higher rank than Kangal, a temperature above 400 °C may be needed, but one should be cautious in selecting the processing temperature somewhere between 400 and 450 °C to avoid retrogressive reactions that occur >435 °C. The compositions of oils obtained from ATTM-impregnated Avgamasya asphaltite are given in Table 13. As mentioned above, the composition of this feedstock is rather different from the coals. As expected from the low oxygen content, phenol

Figure 2. Total aromatics at 400 and 450 °C in the presence and absence of ATTM (a) Mengen and (b) Kangal.


Gu¨l et al.

Figure 3. (a) Open-chain paraffins (%), (b) naphthalenes (%), and (c) phenols (%) changes with the increase of the Mengen coal ratio in the blend.

Figure 4. (a) Open-chain paraffins (%), (b) naphthalenes (%), and (c) phenols (%) changes with the increase of the Kangal coal ratio in the blend.

concentrations in the products are rather low and almost disappear upon the reaction at 450 °C. The percentage of alkanes increased steadily up to 450 °C, while the percentages of naphthalene, tetralin, and their alkyl derivatives decreased steadily, indicating that 450 °C is needed to convert this feedstock effectively into aliphatic oil. Tables 14 and 15 summarize the analyses of oils from ATTMimpregnated Mengen + asphaltite and Kangal + asphaltite blends, respectively. On the basis of results from the coals themselves, the temperature for liquefaction of the Mengen + asphaltite blend was chosen as 450 °C and the temperature for liquefaction of Kangal + asphaltite blend was 400 °C. As the ratio of one of the components in the blend was increased, the dominant products expected from that component when it had been liquefied by itself increased. Mengen + asphaltite showed a very good linear relationship between the ratio of one component in the blend and some chemical classes of the oil (i.e., open-chain paraffins, naphthalenes, and phenols) (Figure

3), but Kangal + asphaltite did not show such correlations between the ratio of the component and the chemical classes (Figure 4). There was no deleterious effect of blending these feedstocks as far as the yields of alkanes are concerned, but when the liquefaction conversion efficiencies are taken into account, then blending showed a negative effect, especially when the ratio of coal/asphaltite was high (i.e., 67.1 and 81.8% conversions were obtained from Mengen/asphaltite blends of 3:1 and 1:3, respectively; these values for Kangal/asphaltite blends were 60.3 and 81.6%). If we consider the asphaltite to be a vehicle for introducing the coal into the reactor, then this behavior is similar to other reports on a negative effect of the presence of a vehicle in catalytic liquefaction.106,118 Therefore, it is better to process these feedstocks separately rather then blending, at least for liquefaction in the presence of ATTM. (118) Horton, L.; King, J. G.; Williams, F. A. J. Inst. Fuel 1933, 7, 8597.


4. Summary and Conclusions This study has shown that high-sulfur sub-bituminous coals can be effectively liquefied by impregnating water-soluble AHM or ATTM into these coals. Dependent upon the rank of the coal, a processing temperature between 400 and 450 °C is adequate, but one must be cautious about enhancing the aromatization reactions around 450 °C. Using these catalyst precursors results in effective hydrogenation of two-ring or higher condensed aromatics and effective hydrogenolysis of the alicyclic part of hydroaromatic structures. Using ATTM yields higher conversions compared to AHM. Alkyl-substituted monoaromatic structures were partially saturated when ATTM was used, but this was not observed with AHM. Nevertheless, the active (119) Burgess, C. E. Ph.D. Dissertation. The Pennsylvania State University, University Park, PA, 1994. (120) Song, C.; Schobert, H. H.; Andresen, J. M. Premium carbon products and organic chemicals from coal. International Energy Agency Report CCC/98, 2005.


catalyst formed from ATTM does not provide effective saturation of monoaromatic rings, and therefore, subsequent hydrogenation would be needed by using appropriate catalysts. Because these coals have high oxygen content, considerable phenolic compounds also form during liquefaction. These phenolic compounds could be separated119 and used as feedstocks in the production of a variety of materials.120 The addition of asphaltite to coals resulted a negative effect on both coal conversions and oil yields. One can ascribe this observation to the aliphatic-rich content of asphaltite, such that, when it was blended with the lignites and hydrogenated, the aliphatics coming out from asphaltite in the early stages of treatment inhibit the interaction of coal and catalyst particles, with the active hydrogens coming from both liquid and gas phases. Acknowledgment. This work was funded by the Turkish Scientific and Technical Research Council (TUBITAK). EF060440X

Catalytic Direct Liquefaction of High-Sulfur Coals and Their Blends

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