Energy & Fuels 1995,9, 38-44
Competitive Reactions during Plasma Arcing of Carbonaceous Materials Louis S. K. Pang,? Luke Prochazka,? Robinson A. Quezada,?Michael A. Wilson,*>+ Robert Pallasser,+Keith J. Fisher,* John D. FitzGerald,§Geoffrey H. Taylor,§ Gary D. Willett,$ and Ian G. Dance* CSIRO Division of Petroleum Resources, P.O. Box 136, North Ryde, NSW 2113, Australia, School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia, and Research School of Earth Sciences, Australian National University, Canberra, ACT 2600, Australia Received May 19, 1994. Revised Manuscript Received September 21, 1994@
Fullerene and pencil production has been studied by electrical arcing in various atmospheres. A range of different materials have been used as anode and the products have been studied using high-pressure liquid chromatography, gas chromatography-mass spectrometry, stable isotope mass spectrometry, and electron and light microscopy. In a methane atmosphere with graphite, the residual methane carbon is isotopically heavy because lighter methane is consumed. A different result is obtained with anodes containing hydrogen because the anode generates light methane, and depending on the amount of available hydrogen the carbon of the product gas can be slightly isotopically lighter or heavier than the original anode material. When materials containing hydrogen are used as anode, polycyclic hydrocarbons are produced. This is also true if graphite is used with a hydrogen atmosphere. It appears that different ratios of polycyclic hydrocarbons are produced when different materials are used as anodes. The results offer strong evidence that fullerenes can form from materials other than graphite through a process which does not involve total breakdown to individual carbon atoms.
Introduction Minute quantities of fullerenes can be produced by laser ablation (pyrolysis) of graphite, coal, kerogen, or other carbonaceous materials and detected by mass spectrometry.l-13 Preparative scale quantities are produced electrically by plasma arc pyrolysis of graphite IfO or coals in an atmosphere of helium or a r g ~ n . l ~ - ~
* To whom correspondence should be addressed.
t CSIRO.
* University of New South Wales. P Australian
National University. Abstract published in Advance ACS Abstracts, November 1,1994. (1) Kroto, H. W.; Allaf, A. W.; Balm, S. P. Chem Rev. 1991,91,1213. (2)Wilson, M. A.; Pang, L. S. K.; Willett, G. D.; Fisher, K. J.;Dance, I. G. Carbon 1992,30,675. (3)Schwartz, H. Agnew. Chem., Znt. Ed. Engl. 1992,31,293. (4)So,H. Y.;Wilkins, C. L. J.Phys. Chem. 1989,93,1184. (5)Gerhardt, P.; Loffler, S.;Hofmann, K. H. Chem. Phys. Lett. 1987, 137,306. (6)Lineman, D. H.; Somayajula, K. V.; Sharkey, A. G.; Hercules, D. M. J.Phys. Chem. 1989,93,5029. (7)Weltner Jr., W.; van Zee, R. J. Chem. Rev. 1989,89,1713. (8)Brown, C. E.; Kovacic, P.; Welch, K. J.;Cody, R. B.; Hein, R. E.; Kinsinger, J. A. J.Polym. Sci., P a r t A 1988,26,131. (9)Brenna, J. T.; Creasey, W. R. Appl. Spectrosc. 1991,45,80. (10) Greenwood, P. F.; Strachan, M. G.; El-Nakat, H. J.;Willett, G. D.;Wilson, M. A.; Attalla, M. I. Fuel 1990,69,257. (11)Greenwood, P. F.; Strachan, M. G.; Willett, G. D.; Wilson, M. A. Org. Mass Spectrom. 1990,25,353. (12)Rose, H. R.; Smith, D. R.; Fisher, K. J.; Dance, I. G.; Willett, G. D.;Wilson, M. A. Org. Mass Spectrom. 1993,28,825. (13)Dance, I. G.; Fisher, K. J.;Willett, G. D.; Wilson, M. A. J.Phys. Chem. 1991,95,8425. (14)Taylor, R.; Hare, J. P.; Abdul-Sada, A. K.; Krotq H. W. J. Chem. SOC.,Chem. Commun. 1990,1423. (15)Kratschmer, W.; Lamb, L. D.; Fostirououlos. K.; Huffman, D. R.Nature 1990,347,354. (16)Haufler, R.E.; Conceicao, J.; Chibante, L. P. F.; Chai, Y.; Byme, N. E.; Flanagan, S.; Haiey, M. M.; O'Brien, S. C.; Pan, C.; Xiao, Z.; Billups, W. E.; Ciufolini, M. A.; Hauge, R. H.; Margrave, J. L.; Wilson, L. J.; Curl, R. F.; Smalley, R. E. J.Phys. Chem. 1990,94,8634. @
an alternating current is used for arc pyrolysis, and the electrodes are equally cooled, only soot containing fullerenes is produced since any material deposited on a cathode is immediately vaporized as that cathode becomes an anode. However, if direct current rather than alternating current is used, carbon builds up on the cathode electrode of the arcing apparatus as a pencil and as filaments.21 The carbon pencil consists of a number of different forms of carbon including pyrolytic and nanotubes and n a n o p ~ l y h e d r a . ~ ~ - ~ ~ The mechanism by which fullerenes and nanotubes are formed is not understood. At arc temperatures exceeding 3000 "C,highly ordered fullerenes and nanotubes might be expected to be less stable than graphite, and yet they are the major products of the arcing reaction. Although fullerenes can be observed from laser pyrolysis of mesophase (a liquid crystal carbonaceous material, which is a precursor to coke) in a hydrogen or methane atmosphere,13fullerenes are not (17)Pang, L. S.K; Vassallo, A. M.; Wilson, M. A. Nature 1991,352, 480. (18)Pang, L. S.K.; Vassallo, A. M.; Wilson, M. A. Energy Fuels 1992, 6,176. (19)Wilson, M. A.; Pang, L. S. K.; Quezada, R. A.; Fisher, K. J.; Dance, I. G.; Willett, G. D. Carbon 1993,31,393. (20)Pallasser, R.; Pang, L. S. K.; Prochazka, L.; Rigby, D.; Wilson, M. A. J.Am. Chem. SOC.1995,115,11634. (21)Fitzgerald, J. D.; Taylor, G. H.; Brunckhorst, L. F.; Pang, L. S. K.;Wilson, M. A. Carbon 1993,31,239. (22)Taylor, G. H.; Fitzgerald, J. D.; Brunckhorst, L. F.; Pang, L. S. K.;Wilson, M. A. J. Crystal Growth 1994,135,157-164. (23)Seraphim, S.;Zhou, D.; Jiao, J.; Withers, J. C.; Loutfy, R. Carbon 1993,31,685. (24)Pang, L. S.K.; Wilson, M. A. Energy Fuels 1993,7,436. (25)Iijima, S.;Ichihashi, J.; Ando, Y. Nature 1992,356,776. (26)Ebbesen, J. W.;Ajayan, P. M. Nature 1992,358,220. (27)Lenosky, T.; Gonze, X.; Teter, M. Nature 1992,355,333. (28)Ajayan, P. M.;Iijima, S. Nature 1993,361,333.
0 1995 American Chemical Society
Energy & Fuels, Vol. 9,No. 1, 1995 39
Plasma Arcing of Carbonaceous Materials
Table 1. Elemental Composition (Dry)Basis of Carbonaceous Material Used in Plasma Arcing Experiments element (% w/w) Loy Yang Ca exchanged Loy Yang Rundle kerogen Rundle shale Queensborough No. 2 DM Baerami Creek No. 2 DM Bayswater vitrinite Bayswater inertinite a
Ca
H
N
Ca
59.0 67.4
4.2 4.7
0.50 0.80
0.00 0.54
63.1 2.3 21.8 48.4 82.8 83.8
8.0 1.3 2.5 3.2 5.5 4.7
1.54 0.4 nd nd 2.1 1.9
nd nd nd nd nd nd
maceral analysisb (%, v/v) ash
V
I
L
elemental C/H ratio
1.40 1.54
nd nd
nd nd
nd nd
1.17 1.18
10.26 nd 2 nd 5.8 15.2
0 0 7 18 78 21
0 0 45 63 16 71
100 100 48 19 6 8
0.66 0.15c 0.73 1.26 1.25 1.48
Organic carbon. V = vitrinite, I = inertinite, L = liptinite. Value reflects inorganic hydrogen in rock. nd = not determined.
Table 2. Experiments Using Various Organic Matter Types Embedded in Graphite Rods and Various Atmospheres expt no.
wt. of
organic matter
additive ( g )
gas
press? (Wa)
He 148 127 60 ndf He 1.31 142 125 60 1.03 141 123 30 He 0.54 192 125 19 He/CHp 0.064 He/CW 143 17 210 0.041 160 153 15 Hz 0.57 153 142 14 H2 0.066 152 9 165 Hz 161 150 0.066 10 Hz 1.35 He 130 121 115 0.43 25 0.42 123 112 Hz He 143 124 45 0.37 1.40 128 116 13 0.43 0.91 Hz He 1.79 125 45 145 0.46 He 133 114 57 1.39 0.43 124 113 13 1.64 0.59 Hz 1.78 142 122 60 He 0.53 nd 121 115 15 0.47 H2 a 50% mixture. Nanotubes detected but core mainly pyrolytic carbon. Calcium exchanged. f n d = not determined. 1 Loy Yang coal
2 3 4 5 6 7 8 9 10
Rundle oil shale Rundle kerogen Loy Yang coal graphite graphite Loy Yang Coal Rundle oil shale Rundle kerogen Loy Yang Cac 11 Bayswater vitrinite 12 Bayswater vitrinite 13 Bayswater inertinite 14 Bayswater inertinite 15 Queensborough source rock 16 Queensborough source rock 17 Baerami Creek source rock 18 Baerami Creek source rock
0.58 0.63 0.60 0.31 0.30 0.62 0.06
nanotubes and press.e time yield of yield of fullerene-Cso nanopolyhedra (Wa) (min) soot ( g ) extract (9) detected detected
produced in arcing experiments with graphite under methane.lg Fullerenes are also not produced using brown coals that have first been ion exchanged with metal ions, mixed with pitch, and then made into coke rods.29 Thus it is appropriate t o study a range of different carbonaceous materials under different arcing atmospheres to elucidate the importance of both atmosphere and fdlerene feedstock material on fullerene and nanotube production. Fullerene production has been monitored by high-pressure liquid chromatography3O and by infrared s p e c t r o ~ c o p y ~and J ~ -laser ~ ~ ~desorp~~ tion mass s p e c t r ~ m e t r y .Nanotube ~ ~ ~ ~ and nanopolyhedra production has been studied by electron and light microscopy.22~2*-28
Experimental Section Materials. Lay Yang coal and its calcium-exchanged salt, Bayswater inertinite and vitrinite concentrate, Rundle Shale and its kerogen concentrate, and two dispersed organic matter (DM) source rocks Queensborough No. 2 and Baerami Creek No. 2 were used as carbon sources. All samples are of Australian origin. Elemental and maceral data for these materials are listed in Table 1. Electrode Preparation. I n experiments using materials other than graphite several preparative procedures were used (29) Pang, L. S. K. Fuel Process. Technol. 1993, 34, 147. (30)Pang, L. S. K.; Wilson, M. A. J . Phys. Chem. 1993, 97, 4761. (31) Vassallo, A. M.; Pang, L. S. K.; Cole-Clarke, P. A.; Wilson, M. A. J . Am. Chem. SOC.1991,113, 7820. (32)Greenwood, P. F.; Dance, I. G.; Fisher, K. J.; Willett, G. D.; Pang, L. S. K.; Wilson, M. A. Org. Mass Spectrom. 1991,26, 920.
0.06 0.05 0.03 0.02 0.03 0.01 0.01 0.01 0.02 0.02 0.01 0.05 0.01 0.03 0.03 0.01 0.05 0.02
Yes Yes Yes no no no no no no no no Yes no Yes Yes no Yes no
Operating pressure. e Charge pressure.
to form the electrodes. I n these experiments, graphite (13 mm x 30 mm) was always used as the cathode; however, the anode was prepared in two different ways. I n one series of experiments graphite rods (8 mm x 100 mm) were drilled out to form a 3 mm cylindrical passage. Powdered coal, shale, kerogen, or dispersed organic matter in petroleum source rocks was then poured into the cylinder void and the ends plugged with a 2 mm x 3 mm graphite plug. Generally about 0.40-0.60 g could be packed into the hollow graphite rod (Table 2). In the second series of experiments, anode was prepared from char which was prepared from calcium-exchanged brown coal. The exchanged coal was prepared by stirring Loy Yang brown coal (La Trobe Valley, Australia) (25 g) previously crushed and sieved through a 212 pm mesh screen, in excess ( 1 L 0.1 M) hydrochloric acid for 20 h. The coal (25 g) was then filtered and washed with distilled water (about 2 L until neutral). After filtering the coal was calcium exchanged by stirring in 600 mL 0.2 M calcium chloride solution for 20 h. The exchanged coal was filtered, washed with distilled water, and dried in a vacuum oven at 80 “C for 1h. Samples (about 12 g) were mixed with finely ground pitch (Koppers “pencil”) (20 wt %, elemental composition 93.2% C, 4.69% H, 1.27% N, 0.46% S, 0.20% ash) as a binder. The coalpitch mixture was packed into a stainless steel tube and sealed. The tube was then heated t o 450 “C for 20 h to obtain a rod-shaped semichar. Further carbonization of the semichar at 1200 “C for 5 h in argon resulted in the formation of a conductive char rod. Arcing Procedures. The method used to prepare both fullerenes and nanotubes has been described e l s e ~ h e r e . ~ ~ ~ ~ ~ The graphite cathode and graphite anode or anode containing other materials were enclosed in a chamber. The chamber was evacuated and purged with helium or other gas a t ca. 112-
40 Energy &Fuels, Vol. 9,No. 1, 1995
Pang et al.
The pencil deposit on the cathode was sectioned and analyzed 152 kPa. A Lincoln d.c. arc welder was used to supply the by light and electromicroscopy as described elsewhere.22 power for the experiments. Currents of ca. 130A at 18-21 V were applied. Sawtooth waveforms were supplied from the arc welder. Results and Discussion After 10-60 min arcing the weights of the anode and the cathode were recorded, together with the weight of soot. By Exchanged Brown Coal. As previously noted,29 comparison with their initial weight before the experiments, calcium-exchangedbrown coals which have been mixed the weight of mass transfer from the anode to the cathode with pitch, charred, and made into coke rods do not could be calculated, and the yield of soot calculated by ] in a plasma produce [c60] fullerene and [ C ~ Ofullerene difference. arc experiment, yet unexchanged brown coals will The soot product was collected and extracted with toluene. produce fullerenes, under otherwise the same condiThe presence of fullerenes in the toluene extract was detected tions. This result was confirmed here (experiment 10, by high-pressure liquid chromatography3O from the four charTable 21, although it was also found that if the pitch acteristic [CSO] fullerene absorptions in the infrared spectrum31 and by laser desorption mass s p e c t r ~ m e t r y ~ ~of, ~the ~ , ~ ~ - was ~ ~ added after charring, fullerenes were produced, original soot. Other products were identified by gas chromaprobably from the pitch. One explanation for the tography-mass spectrometry. absence of Merenes could be that endohedral fullerenes Experimental conditions, yields and the nature of products are produced instead, i.e., fullerenes with exchanged ion formed during pyrolysis are listed in Tables 2-5. (in this case Ca2+)inside the fullerene ball. In laser Analysis. High-pressure liquid chromatography was carablation experiments with alkenic geopolymers such as ried out using a Waters instrument equipped with a 486 coorongite (an algal kerogen precursor from South tunable W detector at 590 nm, a 590 programmable pump, Australia) we have found that endohedral calcium and a Waters Nova Pak (2-18reverse phase column. Toluene complexes such as Ca@Cso are formed when the (40% v/v) and 2-propanol (60% v/v) mixtures were used as geopolymer is pyrolyzed with calcium salts.39 Also laser mobile phase. A flow rate of 2 m u m i n was used. Fullerenes ablation of kerogen residues in the presence of metal were identified by comparison of retention time with authentic ions produces endohedral f u l l e r e n e ~ .However, ~~ we samples. Infrared spectra were obtained on a Digilab FTS 201 80 Fourier transform spectrometer using the potassium browere unable t o detect the presence of these compounds mide pellet technique. About 5 mg of sample and 150 mg of by HPLC in the arcing experiments reported here. potassium bromide were used t o prepare the pellet. Moreover, when the calcium-exchangedcoal was studied Gas chromatography-mass spectrometry was carried out by using laser ablation (i.e., using the conditions used using a Hewlett-Packard 5970 instrument with a 5890 gas for forming Ca@Cso from coorongite with power chromatograph and chemical data system. Chromatography ranging from 20 kW/cm2 to 4000 MW/cm2)endohedral was carried out on a 50 m x 0.22 mm i.d. BPX5 (phenylcomplexes were not detected. Thus it is clear that it is methylsilicone type) column. The gas chromatograph was not some intrinsic factor concerning the arcing experiprogrammed from 40 "C a t 4 "C/min and held at 300 "C for 45 ment that is preventing endohedral complex or fullerene min. The products were identified by comparison with library I and [ C ~ O ] formation. Rather, endohedral [ C ~ Ofullerene spectra. Laser desorption and ablation Fourier transform ion cyclofullerene complexes are not formed from calciumtron resonance mass spectrometry was carried out using a Nd: exchanged coals under arcing or laser ablation condiYAG (Spectra-Physics DCR-11) laser operating at a fundations. mental frequency of 1064 nm. The laser was focussed to a n Experiments in the Presence of Various Hydroarea of 0.1 mm2 on the sample. After ablation or desorption, gen Sources. Table 2 shows that fullerenes were ions were detected using a Spectrospin (CMS-47FT) ion produced from all the substrates as anodes when helium cyclotron resonance instrument equipped with a 4.7 T superwas used as atmosphere, and this includes hydrogenconducting magnet and Aspect 3000 ~ o m p u t e r . ~ ~In - ~studies ' rich material (Table 1) such as Rundle kerogen, alof the soots, low powers (-5 kW) were used to laser desorb though one cannot be sure how much fullerene origifullerenes from the soot samples.32 Some studies were carried nates from the graphite container. out on the ion exchanged coals to determine if fullerenes could be produced from these materials. I n these studies much Fullerenes were not formed when graphite was used higher (up to 4200 MW) power was used. as anode and hydrogen or methane was used as atmoIsotope distributions in gaseous products were measured sphere. However, GC/MS indicated the presence of using the method described by Jenden and Kap1a1-1.~~The polycyclic hydrocarbons as products. The various comisotope distribution was measured using a Finnigan MAT252 pounds identified are listed in Table 3 (structures are isotope ratio mass spectrometer and is reported in the 6 shown in Figure l),and amounts normalized relative notation relative to the international standard Peedee Belemto phenanthrene are shown in Table 4. In addition to nite (PDB) as
(33)Hiura, H.;Ebbesen, T. W.; Tanigaki, K.; Takhashi, H. Chem. Phys. Lett. 1993,202,509. (34)Greenwood, P.F. Ph.D. Thesis, University of New South Wales, Australia, 1992. (35)Rose, H.R.; Dance, I. G.; Fisher, K. J.; Smith, D. R.; Willett, G. D.; Wilson, M. A. Org.Mass Spectrom., in press. (36)Hopwood, F. G.; Dance, I. G.; Fisher, K. J.; Willett, G. D.; Wilson, M. A,; Pang, L. S. K.; Hanna, J. V. Org. Mass Spectrom. 1992, 27,1006. (37)Nguyen, T. H.; Clezy, P. S.; Willett, G. D.; Paul, G. L.; Tann, J.; Derrick, P. J. Org. Mass Spectrom. 1991,26,215. (38)Jenden, P. D.; Kaplan, I. R. Am. Assoc. Pet. Geol. Bull. 1989, 73,431.
those compounds listed in Table 4,an unknown, possibly containing a polyene structure, was found t o be an important component of many of the extracts prepared under hydrogen. Polycyclic hydrocarbons cannot be produced from pure graphite under helium because of the absence of hydrogen. However, when a helium atmosphere is used and Loy Yang coal, Bayswater inertinite or vitrinite, dispersed organic matter source rocks, and Rundle Shale or its kerogen are arced, polycyclic hydrocarbons are (39)Rose, H. R.; Dance, I. G.; Fisher, K. J.; Smith, D. R.; Willett, G. D.; Wilson, M. A. J. Chem. SOC.,Chem. Commun. 1993,941. (40)Rose, H. R.; Dance, I. G.; Fisher, K. J.; Smith, D. R.; Willett, G. D.; Wilson, M. A. J. Chem. Soc., Chem. Commun. 1993,1361.
Energy &Fuels, Vol. 9, No. 1, 1995 41
Plasma Arcing of Carbonaceous Materials Table 3. Compounds Identified in Extracts from Plasma Arcing Experiments under Various Conditions" compd naphthalene biphenyl biphenylene acenaphthylene fluorene dibenzothiophene phenanthrene anthracene cyclopentaphenanthrene fluoranthene Pyrene benzo[g,h,ilfluoranthene cyclopenta[c,dlpyrene methylnaphthalenes methylpyrene
number 1 2 3
4 5
6 7 8 9 10
11 12 13 14 15
See Figure 1 for structures of compounds 1-13.
6 S
7
Figure 1. Structures of compounds 1-13.
produced in addition to fullerenes (Tables 3 and 4). It seems clear that there is sufficient hydrogen in these materials to quench intermediate species and form polycyclic hydrocarbons. Of interest is fluorene (5) and acenaphthylene (4), cyclopentaphenanthrene (91, fluoranthene (lo),and benzofluoranthene (12). These systems contain five-membered rings and hence may derive from intermediates in the formation of CSO and other fullerenes which have 12 five-membered rings. The provision of molecular hydrogen does not seem to affect the relative yields of polycyclic hydrocarbons in a systematic way. Within the reproducibility of the experiment, Loy Yang coal produces greater proportions of 4 and 10, but lesser amounts of 11 and 13 under helium than hydrogen. Rundle kerogen, however, produces greater proportions of 5 under helium than hydrogen but the product under helium is deficient in 10. Rundle shale produces greater proportions of 4,5, and 12 under helium than under hydrogen and the product is again deficient in 10. On the other hand, the product from Bayswater vitrinite under helium has greater proportions of 4 and 5 but is deficient in 11.
Quite the reverse is true of the Queensborough source rock. This is deficient in 4 under helium. From the elemental C/H ratio it is possible to draw up a tentative list among the anode substrates which is a measure of the degree of available hydrogen for capping carbon radicals formed during arcing. The hydrogen-rich Rundle kerogen and its shale (RS) should top this list, then comes the Queensborough, liptiniterich dispersed organic matter, followed by the Loy Yang coal, Bayswater vitrinite, and finally the Baerami Creek inertinite and Bayswater inertinite. Such plots, however, do not show a correlation of abundance of any particular compound with WC ratio. Gas Analysis. Residual gases from the reactions were analyzed. The products are mainly methane and in experiments in which the reactant cathode contained oxygen, small amounts of carbon dioxide were detected. Small amounts of CZcompounds were also detected in experiments using methane as atmosphere indicating that the methane molecule is reactive. Stable carbon isotope ratio measurements were made on gases for some experiments and these are listed in Table 5. It is clear that in experiments with methane, residual methane is isotopically heavy. The fact that 613C values for the gases from experiments under methane are so different from the methane used to fill the reactor is further evidence that methane is reactive. Moreover, large amounts of filaments are formed in these experiments which probably derive from the methane. Few methylated polycyclic aromatics were detected so most of the methane must be consumed in forming carbon. In the experiments with Loy Yang coal, Rundle Shale or kerogen with a hydrogen atmosphere methane is generated. However, the carbon isotope distribution in this methane is closer to that found for methane used to fill the reactor. Chung and Sackett41have shown that the methane generated from pyrolysis of lignitic coals a t 500 "C is of the order of -24.2%0 613C and this is in agreement with the values detected here. The methane generated is isotopically lighter than the original coal because of the preferential cleavage of 12C-12C bonds over 12C-13C bonds. Nanotube and Nanopolyhedra Formation. We have previously reported that nanotubes can be formed from and we now report that they can be formed from other geoorganic matrices (Table 2). An important point to be made here is that nanotubes can be formed under hydrogen (Figure 2, a and b) or methane, although under methane the deposit is mainly pyrolytic carbon, presumably from the methane. Large amounts of pyrolytic carbon were also formed in experiments under hydrogen probably because it was difficult to form a stable arc under these conditions. Under hydrogen, manual feeding of the anode t o the cathode was necessary to maintain the arc, and this could cause uneven heating profiles with time. Nanotube production is not prevented by the use of hydrogen, methane, or alternative anode materials used here, although it is difficult to make a direct measure of relative yield. As already noted, large numbers of filamentsZ1 (not to be confused with nanotubes) are formed in the methane experiments. Pyrolytic carbon is also formed within the depositsZ2which appears to (41)Chung, H. M.; Sackett,W. M. Fuel 1978, 57, 734.
Pang et al.
42 Energy &Fuels, Vol. 9, No. 1, 1995
Table 4. Relative Proportions of Polycyclic H ~ d r o o ~ i bn oExtracts ~ from Plasma Arcing Experiments under Various Condition@ compound no. expt no. 1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18
details
1
2
LoyYang/He Rundle shaleme Rundle k e r o g e f l e Loy Yang/He/C&d Graphite/He/CH4d Graphite/H2b,C LoyYang/H&C Rundle shalelHzbzc Rundle kerogen/H2bsc Loy Yang Cae/Hec BayswatervitriniteEIz Bayswaterinertinite/Hx Bayswatervitriniteme Bayswaterinertinite/He QueensboroughDMDI2 Baerami Creek DM/H2 QueensboroughDWHe BaeramiCreekDMHe
7 40 ‘5 nd 12 (5
