Energy & Fuels 1989,3, 707-713
707
Hydrogenation and Hydrogenolysis of Coal Model Compounds by Using Finely Dispersed Catalysts Toshimitsu Suzuki,* Hiroshi Yamada, Paul L. Sears,? and Yoshihisa Watanabe Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Kyoto, 606 Japan, and Energy Research Laboratories, Canada Centre for Minerals and Energy Technology ( C A N M E T ) , Ottawa, Ontario, Canada K I A OG1 Received J u l y 14, 1989. Revised Manuscript Received September 12, 1989
In order to understand differences in the catalytic activities of various iron and molybdenum catalysts for coal liquefaction, model reactions such as hydrogenation of phenanthrene and pyrene and hydrogenolysis of diphenylmethane, dibenzyl ether, and benzyl phenyl ether were investigated. The high catalytic activities of Fe(CO)5or Fe(C0I5-S in coal liquefaction were closely correlated to the higher activity of the catalyst for the hydrogenation of phenanthrene and pyrene. MO(CO)~-Sstrongly promoted hydrogenation of polycyclic aromatic compounds. Only MO(CO)~-Sexhibited high catalytic activity for the hydrogenolysis of dibenzyl ether and benzyl phenyl ether. Slight catalytic effects of Fe(C0)5-S on the hydrogenolysis of diphenylmethane was observed. Mossbauer spectra of the Fe(C0)5-S deposited on the active carbon, which was used for dispersing Fe(CO)5-S-derivedcatalyst during hydrogenolysis of diphenylmethane, exhibited an unidentified doublet peak that could not be seen for other iron-sulfur catalysts. The doublet peak seemed to be responsible for the higher activity of the highly dispersed iron species.
Introduction In the direct coal liquefaction process, the role of catalyst has not been fully understood because of complicated reactions involving cleavages of C-C and C-0 bonds and hydrogenation of the resulting polycyclic aromatic compounds. Also hydrogen-transfer reactions from a donor solvent made it difficult to understand the true function of the catalyst. The functions required for a coal liquefaction catalyst may be classified into three categories: (1)activity for hydrogenation of polycyclic aromatic compounds, (2) activity for cleavage of C-C or C-0 bonds through hydrocracking reactions, and (3) desulfurization and denitrogenation activities.l Hydrogenation and hydrocracking of polycyclic aromatic compounds have been carried out with Ni-Mo-Al,O, catalyst by Badilla-Ohlbaum,2 and Johnston3 and with iron-based catalyst by Ogata et al.4 Hydrocracking of diphenylmethane, l,Zdiphenylethane, dibenzyl ether, and benzyl phenyl ether have been intensively studied by a number of research group^,^@^ as has their thermal decomposition.'*12 We have reported that iron pentacarbonyl (Fe(C0)5)or Fe(CO)5-molecular sulfur catalysts showed higher catalytic activity than the Fe203-S or red-mud-sulfur systems.13 The higher catalytic activity was assumed to be due to the finely dispersed state of pyrrhotite which was formed from Fe(C0)5and sulfur from coal or molecular sulfur added during the r e a ~ t i 0 n . l ~ The purpose of this work is to understand the higher catalytic activity of Fe(CO)sS and/or MO(C0)e-S for the hydroliquefaction of coal by examining different model reactions such as hydrogenation of polycyclic aromatic compounds and the hydrogenolysis of C-C and C-O bonds. Mossbauer spectra of iron species remaining after the reaction were investigated to understand the differences in the catalysts derived from Fe(CO),-S, FeSz, and Fe203-S. t CANMET.
0887-0624/89/2503-0707$01.50/0
Experimental Section Materials. Reagents were commercially available materials and were used without further purification. Natural pyrite (Matsumine Japan, pulverized to less than 2.0 pm, supplied by Dr. H. Naruta of the Government Industrial Development Laboratory, Hokkaido) was used as a source of FeSp catalyst. Hydrogenation of P y r e n e a n d Phenanthrene. The hydrogenation of model compounds was carried out in a 50-mL batch autoclave at an initial hydrogen pressure (at 20 "C) of 5.0 MPa. Pyrene or phenanthrene (1.0 g) and active carbon (0.5 g) as a dispersing agent for the catalyst were placed into the autoclave with 4.0 mL of decalin. In catalyzed runs, 0.025-1.0 mmol of catalyst was added with or without sulfur. Competitive Hydrogenation of Pyrene and Phenanthrene. Equal amounts of pyrene and phenanthrene (2.8 mmol) and 0.5 g of active carbon were placed into the autoclave with 4.0 mL of catalyst was added decalin, and 0.25 mmol of Fe(CO)5or MO(CO)~ with sulfur. Hydrogenolysis of Diphenylmethane, Dibenzyl Ether, and (1) Tanabe, T.; Hattori, H.; Yamaguchi, T.; Iizuka, T.; Matauhashi, H.; Kimura, A.; Nagase, Y. Fuel Process. Technol. 1986, 14, 247-260. (2) Baldilla-Ohlbaum, R.; Pratt, K. C.; Trimm, D. L. Fuel 1979, 58, 309-314. (3) Johnston, K. P. Fuel 1984, 63, 463-468. (4) Ogata, E.; Tamura, R.; Kamiya, Y. Proceedings International
Conference on Coal Science; Moulijn, J. A., et al., Eds.; Elsevier: Amsterdam, 1987; pp 243-246. (5) Utoh, S.; Hirata, T.; Oda, H.; Yokokawa, C. Fuel Process. Technol. 1986,14, 221-229. (6) Cassidy, P. J.; Jackson, W. R.; Larkins, F. P. Fuel 1983, 62, 1404-1411. (7) Ogawa, T.; Stenberg, V. I.; Montano, P. A. Fuel 1984, 63, 1660-1663.
(8)Sweeny, P. G.; Stenberg, V. I.; Hei, R. D.; Montano, P. A. Fuel
1987, 66, 532-541. (9) Matsuhashi, H.; Hattori, H.; Tanabe, K. Fuel 1985,64,1224-1228. (10) Kamiya, Y.; Ogata, E.; Goto, K.; Nomi, T. Fuel 1986,65,586-590. (11) (a) Korobkov, V. Y.; Grigorieava, E. N.; Bykov, V. I.; Senko, 0. V.; Kalechitz, I. V. Fuel 1988,67,657-662. (b) Korobkov, V. Y.; Grigorieava. E. N.: Bvkov. V. I.: Kalechitz. I. V. Fuel 1988, 67. 663-665. (12) Scholosberg,'R. H.; Ash, T. R.; Paneirov, R. J.; Donaldson, M. Fuel 1981,60, 155-157. (13) Watanabe, Y.; Yamada, 0.; Fujita, K.; Takegami, Y.; Suzuki, T. Fuel 1984,63, 752-755. (14) Suzuki, T.; Yamada, 0.;Takahashi, Y.; Watanabe, Y. Fuel Process. Technol. 1985, 10, 33-43.
0 1989 American Chemical Society
Suzuki et al.
708 Energy & Fuels, Vol. 3, No. 6,1989
run le 2c
3c 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20d 21 22
catalyst none
Table I. Catalytic Hydrogenation of Pyrene" metal, mmol S, mmol conv, % DHP,b 70 THP,b % 16.6 14.4 0.7 19.7 16.4 0.28 1.0 0.26 20.0 16.7 1.0 8.4 8.8 0.2 15.4 0.26 17.2 0.8 19.5 1.5 1.0 23.2 19.2 1.3 0.26 22.1 1.0 19.2 1.4 1.0 22.3 2.0 18.3 1.3 0.25 21.9 0.51 20.8 30.0 2.0 1.0 2.2 23.4 28.2 0.25 2.1 22.9 29.0 0.25 0.51 2.3 23.1 27.9 0.26 2.1 23.4 31.4 0.29 0.49 2.3 23.0 34.6 0.26 2.4 23.6 42.0 0.25 0.48 2.7 25.0 33.5 0.026 3.0 0.1 22.3 40.8 0.25 2.7 0.50 12.5 13.5 0.25 0.5 21.6 0.25 38.6 2.7 0.50 16.5 17.2 0.25 0.8 10.7 11.4 0.25 0.4
HHP-1,b 7O 0.7 1.0 1.0 0.1 0.5 0.1 0.9 0.9 1.2 3.2 1.4 1.9 1.2
2.4 3.8 6.5 2.6 7.0 0.3 6.5 0.5 0.2
HHP-2,b % 0.8 1.3 1.3 0.1
0.6 1.1 0.8 0.8 1.2 3.8 1.3 1.9 1.4 3.2 5.4 9.2 2.9 8.9 0.2 7.8 0.5 0.2
"At 375 "C, P(H2) = 5.0 MPa, reaction time 60 min, pyrene 1.0 g, active carbon 0.5 g, decalin 4.0 mL. bAbbreviations: DHP, 4,5-dihydropyrene; THP, 4,5,9,10-tetrahydropyrene;HHP-1, 1,2,3,6,7,8-hexahydropyrene;HHP-2, 1,2,3,3a,4,5-hexahydropyrene.c425 OC. dReaction time 120 min. Benzyl P h e n y l Ether. Diphenylmethane or dibenzyl ether or benzyl phenyl ether (4.0 g) and 0.5 g of active carbon were placed into the autoclave. In catalyzed runs, 0.25 mmol of catalyst was added with or without sulfur. Procedure. The reactants were heated to the desired temperature (350-445 "C) within 7 min by using an electrical heater equipped with a shaker which can be shaken 110 cycle/min. Nominal reaction time was estimated from the time when the temperature of the reaction mixture had reached 20 "C below the desired temperature. After maintaining the desired reaction temperature for 20-60 min, the autoclave was cooled to room temperature by air blowing. Products were recovered from the autoclave by filtering off the active carbon with a glass filter, followed by repeated washing with THF. Analyses of Products. Reaction products were identified by using a QP-1000 gas chromatograph mass spectrometer (Shimadzu) equipped with a column containing OV-17 (2%, 3 mm i.d. X 1.5 m). 1,2,3,6,7,8-Hexahydropyrene(HHP-1) and 1,2,3,3a,4,5-hexahydropyrene(HHP-2) were isolated with a medium-pressure liquid chromatograph on a n alumina column (74-154 pm, 400 g, 5 cm 0.d. X 40 cm) with a hexane and CH2C12 (15:l) mixture as an eluent.16 Fractions from 118 to 138 (10 mL each) gave 1,2,3,6,7,8-hexahy&opyrene:'H NMR (270 MHz JEOL GSX 270), 6 = 1.76-2.03 (4 H, q, H-2,7), 2.92 (8 H, t, H-1,3,6,8), 6.97 (4 H, 9, H-4,5,9,10); 13C NMR (67.5 MHz) 6 = 23.33 (C-2,7), 31.47 (C-1,3,6,8), 123.34 (C-4,5,9,10), 130.0 (C-lOb,lOc), 133.91 (C-3a,5a,8a,lOa). Fractions from 154 to 176 gave 1,2,3,3a,4,5hexahydropyrene: 'H NMR, 6 = 1.24-1.27 (2 H, m, H-3), 1.8-2.16 (4 H , m, H-2,4), 2.90 (5 H, m, H-l,3a,5), 7.02-7.56 (5 H, m); 13C NMR, 6 = 22.9 (C-3), 29.96, 30.71, 30.98, 31.20 (C-1,2,4,5), 37.80 (C-3a). The product distribution was analyzed by a Model GC-8APF gas chromatograph (Shimadzu) equipped with an FID detector by using a SE-30 (5%) glass column (3 mm i.d. x 3 m) in a temperature-programmed mode, from 100 to 200 OC a t a heating rate of 2 OC/min for the analyses of hydrogenation products and from 45 to 200 "C for hydrogenolysis products. The molar ratios of hydrogenated products were estimated from their peak areas. Yields of hydrogenolysis products were determined by using two internal standard substances (ethylbenzene and naphthalene).
Results and Discussion Hydrogenation of Pyrene. Pyrene was chosen as a model compound for coal-derived polycyclic aromatic (15) Minabe, M.; Nakada, K. Bull. Chem. SOC.Jpn. 1985, 58, 1962-1966.
Scheme I
&p-@-@ Pyrene
\
DHP
\
HHP-1
substances. It was hydrogenated in a poor hydrogen donating solvent (decalin) with several catalysts used for coal hydroliquefaction. The products obtained by hydrogenation are shown in Scheme I, and yields of products are summarized in Table I. At 425 "C, little effect of the catalyst on the product distribution was observed (runs 1-3). Further studies were carried out at lower temperatures (375 "C). Finely pulverized natural pyrite is an effective catalyst for coal liquefaction.16 It promoted hydrogenation of pyrene as compared to the uncatalyzed run (runs 4 and 5). Catalytic activity of Fe203-S (run 7) was almost the same as that of iron(I1) oxalate (Fe(ox))-S (run 9), and both were slightly higher than that of pyrite (runs 5, 7, and 9). When the amounts of catalysts were increased to 1 mmol (runs 8 and lo), the conversion of pyrene with pyrite and Fe(ox)-S increased from 17.2 to 23.2% and from 21.9 to 30.0%, respectively (runs 6 and lo), but the conversion with Fe203-S catalyst did not change (runs 7 and 8). Moderate activity of Fe(ox) catalyst for the liquefaction of Yallourn coal was recently reported." The activity of Fe(C0)5was higher in the hydrogenation of pyrene. In the presence of sulfur, this catalyst further promoted hydrogenation of pyrene and increased the concentrations of hexahydropyrenes. In the absence of an active carbon, Fe(CO), decomposed to give very thin shining metallic iron flakes. This form of iron exhibited catalytic activity for the hydrogenation of pyrene. How(16) Baldwin, R. M.; Vinciguerra, S. Fuel 1982, 62, 498-501. (17) Kamiya, Y.; Nobusawa, T.; Futamura, S. Fuel Process. Technol. 1988, 18, 1-10,
Hydrogenation and Hydrogenolysis of Model Compounds
run 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Energy & Fuels, Vol. 3, No. 6,1989 709
Table 11. Catalytic Hydrogenation of Phenanthrene" S, mmol conv, % DHPH,b % THPH,b %
catalyst metal, mmol none FeS2 0.25 Fe203-S 0.25 Fe,04-S 0.25 Fe(ox)-S 0.25 Fe(a~ac)~-S 0.25 Fe(CO), 0.25 Fe(CO),-S 0.24 Mo(C0)G 0.25 MO(CO)G-S 0.25 MO(CO)& 0.025 M ~ O ~ ( a c a c ) ~ - S 0.25 MoS~ 0.25 n-Bu,Sn 0.25
0.50 0.50 0.50 0.50 0.50 0.50 0.1 0.50
8.7 14.4 17.8 17.1 18.9 10.1 25.5 25.4 40.0 53.7 31.7 54.9 9.5 13.6
6.3 10.9 13.1 13.1 13.7 7.2 19.2 19.2 19.6 16.5 21.4 15.3 6.9 10.0
2.4 3.6 4.5 4.0 5.0 2.9 6.0 5.9 15.6 20.7 9.2 22.4 2.6 3.6
OHP,b % 0 0 0.1 0 0.1 0 0.1 0.2 3.3 10.9 0.6 11.6 0 0
PHP,b % 0 0 0.1 0 0.1 0 0.2 0.2 1.5 5.6 0.5 5.6 0 0
'At 375 O C , P(H,) = 5.0 MPa, reaction time 60 min, phenanthrene 1.0 g, active carbon 0.5 g, decalin 4.0 mL. bAbbreviations: DHPH, 9,lO-dihydrophenanthrene;THPH, 1,2,3,4-tetrahydrophenanthrene; OHP, 1,2,3,4,5,6,7,8-octahydrophenanthrene; PHP, perhydrophenanthrene.
ever, as described later, Mossbauer spectrum of Fe(CO),-S without active carbon demonstrated quite a different pattern as compared to that with active carbon. Therefore, to simulate coal liquefaction conditions, active carbon is added throughout the experiments. The most active Mo(CO), catalyst in coal liquefaction18showed the highest activity together with sulfur in the hydrogenation of pyrene. A decrease in the catalyst level to 1/10 (run 17) of that used in run 16 still resulted in higher catalytic activiy than Fe(CO),-S catalyst at a higher concentration (0.26 mmol). The catalytic effect of molybdenum-sulfur compounds such as Mo(CO),-S and a hexavalent soluble molybdenum ( M ~ O ~ ( a c a c ) ~ system )-S gave nearly the same level of conversion in the hydrogenation of pyrene. However, that of MoSz (finely pulverized) was quite low compared to those found for soluble molybdenumsulfur systems. Although n-Bu,Sn exhibited almost the same catalytic activity as Fe(CO),-S and n-Bu4Ge had a lower activity than n-Bu4Snin the liquefaction of Yallourn and Wandoan C O ~ ~group S , ~IVb ~ 'metal ~ based catalysts showed very low activities in the hydrogenation of pyrene. This indicates that the major function of these catalysts would be different from hydrogenation of polycyclic aromatic compounds in the coal direct liquefaction stage. Moritomi et a1.21claimed that the role of catalyst in the direct coal liquefaction process is to increase hydrogen donor abilities of coal-derived liquids or a coal slurry vehicle oil. Our observation is that enhancement of the coal liquefaction reaction, with the catalyst derived from a tin compound or a germanium compound, was not due to the increase in the donor ability of the vehicle oil. The amount of dihydropyrene increased with the addition of catalysts and leveled off at -25% at an initial hydrogen pressure of 5.0 MPa even in the presence of highly active Fe(CO),-S, Mo(CO),, and Mo(CO),-S catalysts (runs 11-18). Minabe et al.15 suggested that hydrogenation of dihydropyrene proceeded further to HHP-1 and HHP-2 and that the amount of HHP-1 formed was 2-3 times larger than the amount of HHP-2, due to the differences in the thermodynamic stabilities of HHP-1 and HHP-2. In the (18) Yamada, 0.; Suzuki, T.; Then, J. H.; Ando, T.; Watanabe,Y. Fuel Process. Technol. 1985,11,297. (19) Suzuki, T.;Ando, T.; Yamada, 0.; Watanabe, Y. Fuel 1986,65,
--.
7* A f i
(20)Suzuki. T.:Yasuhisa.. M.:. Ando,. T.:. Watanabe, Y. J . Fuel SOC. Jpn. 1987,66,'128-133. (21) Moritomi, H.; Nagaishi, H.; Naruse, M.; Sanada, Y.; Chiba, T. J . Fuel SOC.Jpn. 1983,62, 245-262.
Scheme I1
&&
@g \& DHP
OHP
Phenanthrene
THP
OH P
present work the ratio of HHP-1 to HHP-2 was about 1:1, when less active catalysts such as FeS, or Fez03-S were used. With more active catalysts (Fe(CO),, Mo(CO)~-S), the amount of HHP-2 increased. The differences in the product distribution between the results of Minabe et al.I5 and our results may be partly due to the differences in the reaction temperature. Even with increases in the reaction time from 60 to 120 min conversion and product distribution were only slightly changed (run 18). This suggests that hydrogenation of pyrene reaches thermodynamic equilibrium conditions at the elevated temperature. However, at 375 "C, differences in the catalytic activity could be observed, indicating that at this temperature the equilibrium preferably shifted to the hydrogenation side. At 425 "C, however, thermodynamic equilibrium ruled the reaction and, irrespective of the activity of the catalyst, almost the same product distributions were obtained. Johnston also reported a slight change in product distribution of partially hydrogenated pyrenes at 425 "C by using Co-M0-A1203 catalyst. The amounts of DHP, THP, HHP-1, and HHP-2 increased when the reaction temperature was decreased to 375 OC over Co-Mo c a t a l y ~ t . ~ Hydrogenation of Phenanthrene. Hydrogenation of phenanthrene was carried out under the same conditions as the hydrogenation of pyrene, in order to find out the differences in the hydrogen acceptabilities between three-membered and four-membered polycyclic aromatic compounds. Partially hydrogenated phenanthrenes are shown in Scheme 11, and the results are summarized in Table 11. Major products were 9,lO-dihydrophenanthrene(DHP) and 1,2,3,4-tetrahydrophenanthrene(THP). When active catalysts (Mo(CO),, Mo(CO),-S, MoOz(acac)z-S) were employed, 1,2,3,4,5,6,7,8-octahydrophenanthrene (OHP) perhydrophenanthrene (PHP) were obtained. As in the hydrogenation of pyrene, Fe(C05-S, Mo(CO),-S, and Mo02(acac)2-Sshowed high catalytic activity in the hy-
Suzuki et al.
710 Energy & Fuels, Vol. 3, No. 6,1989
catalyst Fe(C0)6-S MO(CO)gS
conv, % 32.4 33.9
Table 111. Comoetitive Hydrogenation of P s r e n e and Phenanthrene" pyrene phenanthrene DHP, % THP, % HHP-1, % HHP-2, % conv, % DHPH, % THPH, % OHP, % 32.4 2.8 3.1 2.8 29.5 22.3 6.9 0.1 22.1 2.9 6.8 8.2 47.0 19.0 17.3 6.9
PHP, % 0.2 3.8
"At 375 "C, P(H,) = 5.0 MPa, reaction time 60 min, pyrene 2.8 mmol, phenanthrene 2.8 mmol, active carbon 0.5 g, decalin 4.0 mL. Abbreviations are the same as those in Tables I and 11.
run 1 2
3 4 5 6 7 8 9 10 11 12
13 14 15 16 17
catalyst noneb none FeSz Fe203-S red mud-S Fe(CO), Fe(CO),-S Mo(CO), Mo(CO)gS n-Bu,Sn none Fe(CO), Fe(CO)6-S Mo(CO), MO(CO)6-Sc MO(CO),-S Mo(C0)3-Sd
Table IV. Catalytic Hydrogenolysis of Diphenylmethane" metal, mmol S, mmol temp, "C benzene, % 425 0.7 425 3.4 0.25 425 4.5 0.25 0.50 425 4.7 0.25 0.50 425 5.7 0.25 425 6.1 0.26 0.50 425 6.2 0.25 425 6.1 0.25 0.50 425 13.9 0.25 425 4.2 445 6.3 0.26 445 10.3 0.26 0.50 445 10.2 0.25 445 12.3 0.25 0.50 445 10.5 0.25 0.50 445 28.9 0.25 0.50 445 45.3
toluene, % 1.0 3.5 4.2 5.0 5.7 6.1 6.4 6.3 13.8 4.5
6.1 10.5 9.6 12.6 10.5 28.2 44.1
" P(Hz) = 5.0 MPa, reaction time 60 min, diphenylmethane 4.0 g, active carbon 0.5 g. *Under argon atmosphere. Reaction time 20 min. dReaction time 120 min. drogenation of phenanthrene. Mo(CO)~-Sand Moo2(acad2-S exhibited the highest catalytic activity, and increases in the amounts of OHP and PHP were remarkable. Ogata et al. reported higher activity of ultrafine metallic iron than for Fe(C0)5catalyst in the hydrogenation of ~henanthrene.~ However, they did not add active carbon for Fe(CO), catalyst to improve the dispersion state. Iron(II1) acetylacetonate is soluble in decalin, but the catalytic activity of this compound with sulfur is smaller than that for the Fe203-S system for the hydrogenation of phenanthrene. On the other hand, the activity of M ~ O ~ ( a c a c ) ~is-comparable S to that of the MO(CO)~-S system. It is difficult to understand the lower activity of the Fe(acac)& system, but the lower activity of the Fe( a ~ a c ) ~ -system S was also observed in the direct liquefaction of ~ 0 a i . l ~ Competitive Hydrogenation of Pyrene and Phenanthrene. Competitive hydrogenation of pyrene and phenanthrene was carried out with Fe(CO),-S or Mo(CO),-S as catalysts, and the results are showed in Table 111. When Fe(CO),-S was used as a catalyst, the amounts of hydrogen absorbed by pyrene and phenanthrene did not differ significantly. When MO(CO)~-Swas employed, phenanthrene absorbed about 1.4 times as much hydrogen as did pyrene. In this comparison, pyrene and phenanthree have a different number of sites that can accept hydrogen, that is, 16 and 14. Therefore, the amount of hydrogen absorbed by phenanthrene was tentatively normalized to pyrene base by multiplying the amount of hydrogen absorbed by phenanthrene by a factor of 16/14. These results suggest that the hydrogen-accepting ability of a polycyclic aromatic compound does not depend solely on the substrate and interactions with the catalyst employed play a significant role. The most active catalyst (MO(CO)~-S)increased the portion of hexahydrogenated compounds in the hydrogenation of pyrene. Further hydrogenation of hexahydropyrenes to polyhydro compounds was promoted slightly, due to the difficulty in the access of hydrogen on the catalyst surface to the sterically hindered fused carbon
in positions 10b and 1Oc. On the other hand, Mo(C0)gS in the hydrogenation of T H P to give OHP and PHP. Consequently, phenanthrene absorbed a larger amount of hydrogen than pyrene. Hydrogenolysis of Diphenylmethane. The hydrogenolysis of diphenylmethane was investigated to elucidate the role of catalyst in the cleavage of the Ph-C-Ph bond, one of the most important bonds in coal structure. The reactions concerning cracking of model compounds were carried out in the absence of solvent. If the reaction were carried out in solvent, it would be difficult to interpret the result encountered because of hydrogenation or dehydrogenation of the solvent used and hydrogen transfer from the solvent to the fragments of starting materials.22 In Table IV, the yields of the main products, benzene and toluene, in the hydrogenolysis of diphenylmethane are listed. At an initial nitrogen pressure of 5.0 MPa, small amounts of benzene and toluene were obtained. Under hydrogen (initial pressure 5.0 MPa) without a catalyst, the yields of benzene and toluene increased with a molar ratio of 1:l. Further increase in the yields of benzene and toluene were observed with the addition of catalyst. At 425 "C, the activity of Fe(C0)5 was slightly higher than that of other iron catalysts such as FeS2,Fe203-S, and red mud-S (runs 2-5). A t 445 "C, the yields of benzene and toluene without catalyst increased and were almost the same as those obtained in the presence of Fe(CO), at 425 "C. Increases in the yields of decomposition products were also remarkable with Fe(CO)5or Fe(C0)5-S catalyst. In the hydrogenolysis of diphenylmethane, the activity of Mo(CO), increased markedly when sulfur was added. On the other hand, the activities of Fe(CO)5and Fe(CO),-S showed almost no difference, in contrast to coal liquefaction. Stenberg et al.23and Sweeny et a1.6 reported the hydrogenolysis of diphenyl ether and diphenylmethane in (22) Kamiya, Y.; Nagae, S.; Oikawa, S. Fuel 1983, 62, 30-33. (23) Stenberg, V. I.; Ogawa, T.; Willison, W. G.; Miller, D. Fuel 1983, 62, 1487-1491.
Energy &Fuels, Vol. 3, No. 6,1989 711
Hydrogenation and Hydrogenolysis of Model Compounds run 1 2 3 4
5
catalyst none Fe(C0I5 Fe(CO),-S Mo(CO), MO(CO),-S
Table V. Catalytic Hydrogenolysis of Dibelizyl EtheP S, mmol PhH, % PhCH,, % PhCHO, % DPM,b %
metal, mmol 0.26 0.25 0.25 0.25
0.50 0.50
5.5 5.2 4.9 4.1 2.7
95.1 100.1 97.8 83.4 151.1
41.3 33.7 26.1 29.9 0
0.4 0.5 0.5 0.8 0.4
DB,* % 2.7 4.5 3.7 5.6 12.3
STB,b % 1.8 2.8 3.0 2.2 0
BB,b % 1.2 0.6 0 0.5 0
" A t 350 OC, P(H2)= 5.0 MPa, 20 min, dibenzyl ether 4.0 g, active carbon 0.5 g. bAbbreviations: DPM, diphenylmethane; DB, 1,2-diphenylethane; STB: cis- and trans-1,2-diphenylethene;BB, benzyl benzoate.
run 1 2 3 4 5
catalyst none Fe(CO), Fe(CO),-S Mo(C0)B MO(CO),-S
metal, mmol
Table VI. Catalytic Hydrogenolysis of Benzyl Phenyl Ethera S, mmol PhH, % PhCH,, % PhOH, % DPM, % DB, %
0.25 0.26 0.25 0.25
0.50 0.50
5.1 4.7 5.8 20.6 54.0
32.9 39.8 51.1 45.8 81.7
48.5 49.5 55.8 46.5 49.5
11.1 10.2 9.2 4.6 3.9
1.7 1.8 2.9 1.5 1.5
DPK," % 0.4 0 0 0 0
HDPM," % 7.1 8.6 9.9 3.0 0
'At 425 OC, P(H2) = 5.0 MPa, 60 min, benzyl phenyl ether 4.0 g, active carbon 0.5 g. bAbbreviations: DPK, diphenyl ketone; HDPM, (hydroxypheny1)phenylmethane.
Table VII. Mossbauer Parameters for Various Iron-Sulfur Catalysts after Hydrocracking of DiDhenylmethane' Fe, mmol S, mmol 6, mm/s A, mm/s c internal field, kOe patternsc iron species
iron FeS2 Fe(COh
2 1
4 1
Fe(C0h
1
2
Fe(CO)5b Fe(C0)5 Fez03
1 1 1
1 0
2
0.74 0.70 0.37 0.73 0.37 0.72 -0.03 0.20 0.36 0.73
-0.04 0.05
297 277
-0.03
301
0.05 0.03
277 331 203
0.05
293
0.75 0.90
0.79
sextet sextet (4) doublet (1) sextet (2.8) doublet (1) sextet sextet 1 (1) sextet 2 (4.8) doublet (5.3) sextet
pyrrhotite pyrrhotite ? pyrrhotite ? pyrrhotite iron metal cementite ?
pyrrhotite
"The Mossbauer spectra were recorded by using a ,"Co source in a rhodium matrix a t room temperature. Center shifts are given relative to the center of the iron metal. All iron sulfur species were dispersed on active carbon. bActive carbon was not used. eNumerals in parentheses indicate relative intensities of sets of peaks.
the presence of iron sulfides and hydrogen sulfide. They found that an increase in the amount of HzS added enhanced the decomposition of DPM both with and without pyrrhotite. They attributed the higher conversion of DPM in the presence of pyrite to the formation of a nonstoichiometric pyrrhotite structure. When the cracking of DPM was carried out in tetralin solvent, the amount of naphthalene formed from tetralin did not decrease irrespective of the addition of catalyst. This is quite a different phenomenon from that observed in coal hydroliq~efaction.'~ If the formation of a benzyl radical and abstraction of hydrogen from tetralin were involved, a decrease in the amount of naphthalene would be expected with the addition of an active catalyst such as MO(CO)~-S.However, this was not observed. Cracking of DPM is accelerated with an increase in the acidic nature of the catalyst in addition to the radical process. Real active sites for hydrogenolysis reaction were due to Mo3+ species with sulfur v a c a n ~ i e s . ~ ~ ~ ~ Hydrogenolysis of Dibenzyl Ether. The hydrogenolysis of dibenzyl ether (DBE) was carried out without solvent by using iron and molybdenum carbonyl derived catalysts. The results are summarized in Table V. Conversion of DBE was 100% in all cases and the yields of products were expressed in mole percent, based on the molar amount of the starting material used. Schlosberg et al. reported that dibenzyl ether decomposed into toluene and benzaldehyde under hydrogen-starved conditions.12 In our case, the main products were toluene and benzaldehyde. In addition to them, several fragment radicals (24)Grag, P.Catal. Rev. Sci. Eng. 1980,21(1),135-181.
produced by the cleavage of the C-0 bond recombined with each other or disproportionated and afforded diphenylmethane, dibenzyl, stilbene, benzyl benzoate, and several other products. No benzyl alcohol was detected. Matsuhashi et aL9reported that iron oxide and metal oxide catalysts such as Fez03-ZnO, Fez03-Zr0, and Fez03-MgO exhibited relatively high activities in the hydrogenolysis of dibenzyl ether and diphenyl ether in xylene. When Fe(C0)6,Fe(CO)5-S, and MO(CO)~ were used in the hydrogenolysis of dibenzyl ether, the effects of catalysts were not remarkable as compared with an uncatalyzed run. However, yields of benzaldehyde decreased slighlty with the addition of catalysts (runs 1-4). When MO(CO)~-Swas employed,considerable hydrogen absorption was observed with a large decrease in the amount of benzaldehyde. The amount of hydrogen absorbed nearly corresponded to that required for the stoichiometry PhCHzOCHzPh + Hz 2PhCH3 + H2O (1) Also, decreases in the amounts of by-products (C13-Ci4 compounds except DB) were remarkable. These results clearly indicate that prompt hydrogen transfer from molecular hydrogen to benzyl and benzyloxy radicals did occur in the presence of Mo-S catalyst. Removal of oxygen as water was promoted only by Mo-S catalyst. The characteristic features of Mo-S catalyst may account for the high activities in coal liquefaction. Hydrogenolysis of Benzyl Phenyl Ether. In Table VI, the results of hydrogenolysis of benzyl phenyl ether at 425 "C are listed. The conversion was 100% even without catalyst, because of the high temperature. The main products were toluene and phenol. Benzene and diphenylmethane, dibenzyl, diphenyl ketone, and isomeric
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Suzuki et al.
712 Energy & Fuels, Vol. 3, No. 6, 1989
(hydroxypheny1)phenylmethane were produced due to radical recombination reactions. Compared with uncatalyzed runs, the effect of the addition of Fe(C0)5 was scarcely noticeable. However, in the presence of sulfur, Fe(CO)5slightly increased yields of toluene and phenol (runs 1-3). Even with a Mo(CO)~catalyst, total yields of benzene, toluene, and phenol were the same as with Fe(CO)5-S. In runs 2-4, the proportion of recombination products (including unidentified oligomers) amounted to 106-88% of starting material. However, when sulfur was added to Mo(CO),, the yields of the recombined products decreased. This result indicates that prompt hydrogen transfer from molecular hydrogen to benzyl and phenoxy radicals did occur smoothly and further deoxygenation by hydrogenolysis of phenol to benzene was catalyzed. Final Form of Iron Carbonyl or Iron CarbonylSulfur Catalyst. Since Fe(CO), and sulfur showed very high catalytic activity as described above, the final form of iron species was investigated by X-ray diffraction and Mossbauer spectra. Although differences in the catalytic activities were most pronounced in the hydrogenation of pyrene or phenanthrene, when these reaction were carried out at 375 "C, iron species reacted at 425 "C were subjected to analyses, because coal liquefaction with iron catalyst was carried out a t 425 0C.8J3J4 After the hydrogenolysis of diphenylmethane a t 425 'C, the iron compound was recovered together with the active carbon and successively washed with T H F under argon atmosphere. The results of Mossbauer spectral data are compiled in Table VII. Mossbauer spectra of iron species on the active carbon from the hydrogenation of diphenylmethane with FeS2 or Fe203-S are shown in Figure la,b. From major sextet peaks shown in Figure la,b, the iron compounds in ~ , ~ ~ the the residue were assigned as p y r r h ~ t i t e . ~However, residue from Fe(CO),-S showed a different pattern (Figure IC)from the iron-sulfur catalysts shown above. This spectrum had a sextet of pyrrhotite and a center doublet (6 = 0.36 mm/s, A = 0.75 mm/s). However, the center doublet disappeared when the reaction of Fe(CO),-S was carried out in the absence of an activated carbon, and a spectrum quite similar to that shown in Figure l a was obtained. From the X-ray diffraction pattern, the iron compound found in the residue using FeS2, Fe203-S, and Fe(C0)5-S was assigned as pyrrhotite (20 = 29.9', 33.7', 43.4', 53.1'1, and in the case of Fe(CO), alone the peaks of iron metal were observed (strongest peak 28 = 44.7'). The Mossbauer spectrum of Fe(C0)5 without sulfur (with active carbon) showed sextets belonging to iron metal and cementite and an intense center doublet. The doublet peak of Fe(CO)6-S relates closely to the higher activity of the catalyst in hydrogenation, hydrocarcking of diphenylmethane, or hydroliquefaction of coal. However, the difinite species of iron giving a doublet is not known. This may be a normal paramagnetic species, but it is plausible that it is magnetic material in an extremely finely dispersed state on the active carbon surface, thus giving rise to a superparamagnetic doublet spectrum.
Conclusion The high catalytic activity of Fe(CO)5or Fe(CO),-S in coal liquefaction is closely related to the fact that the active species formed from Fe(CO), had higher activity in the hydrogenation of polycyclic aromatic compounds than did other iron compounds-sulfur systems. (25) Montano, P. A.; Granoff, B. Fuel 1980,59, 214-216. (26) Bommannarar, A.; Montano, P. A. Fuel 1982, 61, 1288-1290.
8
7
6
5
4
3 2
1
0 -1 -2 -3 4 - 5 6 -7 -8
velocitity relative t o
i r o n metal m m l s
Figure 1. Mossbauer spectra of various iron-sulfur catalysts after hydrogenolysis of diphenylmethane at 425 O C , for 60 min. P(H2) = 5.0 MPa (cold). (a) FeSz/active carbon; (b) FeZO3-S(1:2)/active carbon; (c) Fe(CO)5-S (1:2)/active carbon.
A very small amount of Mo(C0)gS (1/10 of Fe(CO),-S) could strongly promote hydrogenation of polycyclic aromatic compounds. Under typical coal liquefaction conditions, 425 'C, 5.0 MPa of H2, however, the differences in F e S and Mo-S catalysts in the hydrogenation of pyrene were not pronounced. Fe(CO),-S and MO(CO)~-Scatalysts showed slight to remarkable effects on the hydrogenolysis of diphenylmethane, and MO(CO)~-Sstrongly promoted the cleavage of Ph-C-Ph bonds more than other catalysts. This reaction seems to be assisted by the hydrocracking ability of the catalyst. With regard to the cleavage of Ph-C-0-C-Ph bonds, only Mo(CO)& exhibited high catalytic activity and promoted prompt hydrogen transfer to radical fragments. Iron-based catalysts did not show high activity, unlike the cases of hydrogenation of polycyclic aromatic compounds and cleavage of Ph-C-Ph bonds. These findings seem to suggest that the enhancement of coal liquefaction reactions by Fe(CO)5-S catalyst is due to a higher ability to hydrogenate polycyclic aromatic compounds and direct hydrogen-transfer ability from
Energy & Fuels 1989, 3, 713-715
713
molecular hydrogen to fragment radicals. The extremely high activity of the Mo(CO)& system is in addition to the greater ability of the above functions. High activities for the hydrocracking reaction must be responsible.
Developing Advanced Process for the Efficient Use of Coal (Grants 62041057 and 63043035),sponsored by the Ministry of Education, Science and Culture, Japan. Registry No. Fe(C0)5, 13463-40-6; S, 7704-34-9; MO(CO)~,
Acknowledgment. Part of this work was carried out under the Japan-Canada Joint Research Program-
32312-17-7; FeSz, 12068-85-8;Fez03,1309-37-1;pyrene, 129-00-0; phenanthrene, 8501-8; diphenylmethane, 101-81-5; dibenzyl ether, 103-50-4; benzyl phenyl ether, 946-80-5.
Effect of Water on the Low-Temperature Oxidation of Heavy Oil Donald G. Lee* and Nazih A. Noureldin Department of Chemistry, University of Regina, Regina, Saskatchewan S4S OA2 Canada Received January 2, 1989. Revised Manuscript Received September 11, 1989 When low-temperature oxidation (LTO) occurs, it causes undesirable changes in both the physical properties and the chemical composition of heavy oil. The presence of water, however, seems to decrease the destructive effect of LTO considerably. When LTO is carried out in the presence of water, while all other conditions are held constant, there is a sharp decrease in the amount of tetrahydrofuran solubles and coke formed. Furthermore, liberation of carbon dioxide, with a consequent decrease in both the viscosity and acidity of the produced oil, is much greater in the presence of water.
Introduction We have recently reported' that the heating of heavy oil in the presence of oxygen and the absence of water causes several chemical reactions to occur. Among these are the formation of oxygenated compounds such as carboxylic acids and sulfones. Most such compounds became part of the coke and T H F solubles-fractions that are absent in the virgin heavy oil. In heavy oil reservoirs, crude oil is usually found together with water that was either present in the formation or introduced during secondary recovery techniques. Thus when in situ combustion is used as either a secondary or tertiary recovery technique, it is anticipated that LTO, which involves reaction of oxygen with petroleum below its combustion temperature, will be affected by the presence of water. We have, therefore, examined the effect of steam on the LTO reactions. The products were subjected to five analytical procedures: (i) the composition (gases, maltenes, asphaltenes, THF solubles, and coke) of the produced oil was determined; (ii) the physical properties of the whole products and their components were investigated; (iii) the volatile compounds present were separated and identified by gas chromatography and mass spectrometry; (iv) the nonvolatile components were subjected to analytical pyrolysis; and (v) the water phase was subjected to chemical analysis. It is the intent of this paper to describe the effect that the presence of water has on the chemical composition of the products obtained when heavy oil is subjected to lowtemperature oxidation. In order to do this, samples of heavy oil were treated in a simulator under predetermined (but arbitrary) conditions that were known to cause lowtemperature oxidation. The products obtained in the (1) Noureldin, N. A.; Mourits, F. M.; Lee, D. G.;Jha, K. N. AOSTRA 1987, 3, 155.
J. Res.
0887-0624/89/2503-0713$01.50/0
absence and the presence of water were then compared.
Experimental Section Heavy Oil. Virgin heavy oil was obtained from the Lloydminister area in Saskatchewan by primary recovery methods. It was used after separation of water and particulates by centrifuging a t 9000 rpm and 40 "C. Elemental Analysis. Elemental analyzer Model 240 (Perkin Elmer) was used for carbon, hydrogen, oxygen, and nitrogen analysis. Sulfur content was determined with a Leco Model SC32 sulfur analyzer. Acid Numbers. A Metrohm 636 Titroprocessor and Dosimat E635 were used t o determine acid numbers by titration with alcoholic potassium hydroxide. The reference end points were m-nitrophenol, benzoic acid, and benzenesulfonic acid for the weak, strong, and very strong acids, respectively. Viscosities. A Brookfield digital viscometer Model HBTDCP (Brinkman Scientific), a Precision Scientific kinematic viscosity bath, or Cannon Fenske calibrated viscometer tubes (opaque) were used depending on the viscosity of the sample. Those samples containing particulates were filtered (ASTM 8 wm) before the viscosity was measured. Densities. A Paar Model DMA-45 density meter was used to measure densities. Low-Temperature Oxidation/Aquathermolysis. In a typical experiment, a mixture of heavy oil (120 g) and distilled water (120 g) was placed in a glass liner that was, in turn, positioned in a rocking, high-pressure reactor (Carpenter Steel 20 CBC Parr l-L capacity). The chamber was evacuated, filled with oxygen (117 psi, 7.4 g), warmed to 200 O C , and rocked for 24 h. The final pressure (at room temperature) was 28 psi. Gas analysis indicated the presence of carbon dioxide (1.5 g), carbon monoxide (0.2 g), and oxygen (0.13 g) along with small amounts of hydrocarbons. I t is evident, therefore, that only 16% of the oxygen consumed can be accounted for by the amount of CO and COz produced. After cooling and separation of the aqueous phase by centrifuging, the organic product was separated into components by first adding an equal amount (by weight) of toluene. Then 50 volumes of heptane were added and, after stirring for 24 h, the solution was filtered and concentrated by flash evaporation
0 1989 American Chemical Society
