Structural units of Athabasca asphaltene: the aromatics with a linear

Citation data is made available by participants in Crossref's Cited-by Linking service. ... Otto P. Strausz , I. Safarik , E. M. Lown and A. Morales-I...
0 downloads 0 Views 1MB Size
Download PDF
Energy & Fuels 1991,5,445-453

445

Structural Units of Athabasca Asphaltene: The Aromatics with a Linear Carbon Framework J. D. Payzant, E. M. Lom, and 0. P. Strausz* Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2 Received October 31, 1990. Revised Manuscript Received February 11, 1991

A flash pyrolysis method has been employed, allowing the production of pyrolysis oil from Athabasca asphaltene on the multigram scale, for the identification of homologous series of n-alkylbenzenes, 9-n-alkylfluorenes1and 1-n-alkyldibenzothiophenes.These aromatic classes of compounds were concentrated from the pyrolysis oil by a sequence of selective oxidative and chromatographic steps. Identification was based on comparison of GC retention times and mass spectra with those of synthetic standards or with literature values. The 1-n-alkyldibenzothiopheneswere also found in the maltene fractions of several heavy oils and bitumens of northern Alberta and the 9-n-akylfluorenes were found before in the maltene fraction of Athabasca bitumen. These aromatic compounds all possess alkyl substitution patterns which suggest that they have been derived by the cyclization and aromatization of precursor substances which possessed a linear carbon framework. The linear carbon framework of these and other compounds previously identified in the pyrolysis oil of Athabasca asphaltene contrasts with the terpenoid carbon framework which characterizes the compounds identified in the distillable portion of the maltene of the same bitumen and points to an n-alkanoic origin of the asphaltene. Introduction Many of the technological difficulties associated with the production and upgrading of heavy oils and bitumens in the worldwide commercial exploitation of nonconventional oil resources are related to their high content of nondistillable, high molecular weight materials. The highest molecular weight portion of these materials, present in a colloidally suspended form in the oil, representing the benzene (or methylene chloride, etc.)-soluble but n-pentane-insoluble fraction of petroleum, the asphaltene, is a dark, amorphous solid. It comprises about 15-20% of Athabasca bitumen and is characterized by a low H/C atomic ratio and a high content of heteroatoms (N, 0, S)and metals (V,Ni, Fe). Considerable effort has been expended on attempts to elucidate the molecular structure, size distribution and modes of intermolecular association giving rise to micellar structures of petroleum asphaltenes.' These investigations, like the structural investigations of organic geomacromolecules in general, are hampered by the high values and broad distributions of their molecular weights and the extreme diversity of structural elements within the constituent molecules. The common features in the many generalized structures proposed for petroleum asphaltenes over the years involve variable sizes of polycondensed aromatic nuclei, naphthenic rings, sulfide linkages, alkyl side chains, and bridges between rings.2-6 Systematic compositional studies on asphaltene have followed two broad approaches, one involving nondestructive instrumental studies and the other chemical degradation of the asphaltene brought about by reductive, oxidative, or thermal means and accompanied by detailed compositional-structural investigation of the resultant degradation products. The molecules identified in the products may then be regarded as structural units covalently bound in the asphaltene molecules. Following an oxidative degradation route involving Ru ions catalyzed oxidation of Alberta asphaltenes, we have *Towhom all correspondence is to be directed. 0887-0624/91/2505-0445$02.50/0

recently shown that the aromatic-attached alkyl side chains and bridges in petroleum fractions including asphaltenes can be converted to their carboxylic acids by ruthenium ions catalyzed oxidation yielding homologous series of n-allranoic and cY,w-n-dicarboxylic acids, thereby permitting the determination of the concentration and size distribution of alkyl chains and bridges in the asphaltene moleculesm6In Athabasca asphaltene essentially all the side chains and bridges are the normal type in the carbon range 1-32 for side chains with monotonously declining concentrations from C1 on, and from probably Co to Czs for bridges with monotonously declining concentrations from C4 on.' With the thermal degradation route, mild thermolysis of asphaltene can yield up to -38% of a distillable oil which can be subjected to detailed compositional studies to yield information on the structure of the polymeric asphaltene m o l e c ~ l e s . Investigations ~~~ on Alberta and other asphaltenes by this method have shown the presence of homologous series of n-alkanes, n-alkenes, cyclic hydrocarbons, a great variety of biological marker molecules, and terpenoid and aromatic hydrocarbons, along with some tentatively identified thiophenes and benzenes."ls As has (1) Yen, T. F. In Chemistry of Asphaltenes; Bunger, J. W., Li,L. C., Eds.; Am. Chem. Soc. Adv. Chem Ser.; American Chemical Society: Washington, DC, 1981; Vol. 195, pp 34-51. (2) Yen, T. F. Proceedings, 1982 Pan-Pacific Synfuels Conference; Japanese Petroleum Institute: Tokyo, 1982; Vol. 11, 547-557. (3) Sagedi, M. A.; Chilingar, G . V.; Yen, T. F. Energy Sources 1986, 8,99-123. (4) Asakoa, S.;Nakata, S.;Shiroto, Y.; Takeuchi, C. Ind. Eng. Chem. Proc. Des. Dev. 1983,22, 242-248. ( 5 ) Tissot, B.;W e b , D. H. Petroleum Formation and Occurrence,2nd ed.; Springer-Verlag: Berlin, 19W, pp 403-410. (6)Mojeleky, T. M.; Montgomery, D. S.; Strausz, 0. P. AOSTRA J. Res. 1986,2, 131-137, 177-184. (7) Mojeleky, T. M.;Igneeiak, T.; Frakman, Z.; McIntyre, D. D.; Low, E. M.; Montgomery, D. S.; Strausz, 0. P. Submitted for publication in Energy Fueb. (8) Rubinstein, I.; S t r a w , 0. P. Ceochim. Cosmochim. Acta 1979,43, 1887-1893. (9) Rubinstein, I.; Spyckerelle, C.; Strausz, 0.P. Ceochim. Coamochim. Acta 1979,43, 1-6. (10) Curiale, J. A.; Harrison, W. E.; Smith, G . Ceochim. Cosmochim. Acta 1983,47, 517-523.

1991 American Chemical Society

Payzant et al.

446 Energy & Fuels, Vol. 5, No. 3, 1991

been shown recently many of the terpenoid compounds originated not from the asphaltene, but from the asphaltene-complexed resins which coprecipitated with the asphaltene.I2 In addition to these compounds we have recently reportedl7 the presence of isomeric homologous series of thiolanes, thianes, thiophenes, and benzo[b]thiophenes, all mono- or disubstituted with n-alkyl groups up to a total carbon number of -30. They all featured a uniform, characteristic substitution pattern revealing a normal alkanoic carbon skeleton and a normal alkanoic biotic source material for their origin. Similar series of compounds have been reported when various types of macromolecular sedimentary organic matter (kerogen, coal, and asphaltene) were investigated by flash pyrolysis-gas chromat~graphy.'~J~ Thiolanes, thianes, and thiophenes possessing a linear carbon framework have been identified in a variety of petroleums and sediments*a and this had led to the suggestion that inorganic sulfur species are incorporated into functionalized lipids early in the sedimentation process,uim although a statistical method for the formation of organosulfur compounds in petroleum has been suggested.26 The bicyclic 2,4-di-n-alkylbenzo[b]thiophenes which have a linear carbon framework have been reported in the pyrolysis oil of a~phaltenes'~J" and occur in various petroleum^.'^*^^ Finally, a large number of sulfides and thiophenes possessing terpenoid or isoprenoid carbon frameworks have been identified in the geo~phere.~~-~~ (11) Behar, F. J.; Pelet, R.; Roucache, J. Org. Geochem. 1984, 6, 587-595. (12) Mchtyre, D. D.; Montgomery,D. 5.;Strausz, 0. P. AOSTRA J. Res. 1986,2, 251-265. (13) Cawmi, F.; Eglington, G. Chem. Geol. 1986,56,167-183. (14) Fowler, M. G.; Brooks, P. W. Energy Fuels 1987, 1, 459-467. (15) Jones, D. M.; Douglas, A. G.; Connan, J. Energy Fuels 1987,1, 468-476. (16) Ritchie, R. G. S.;Roche, R. S.;Stedman, W. Fuel 1979, 58, 523-530. (17) Payzant, J. D.; Montgomery, D. S.; Strausz, 0. P. AOSTRA J. Res. 1988, 4, 117-131. (18) Sinninghe Dames, J. S.;Kock-van Dalen, A. C.;De Leeuw, J. W.; Schenck, P. A. J. Chromatogr. 1988,435,435-452. (19) Sinninghe Damss, J. S.; Rijpstra, W. I. C.; De Leeuw, J. W.; Schenck, P. A. Geochim. Cosmochim. Acta 1989,53, 1323-1341. (20) Sinninghe Dames, J. S.; Ten Haven, H. L.; De Leeuw, J. W.; Schenck, P.A. Org. Geochem. 1986,10,791-805. (21) Sinninghe Dames, J. S.;De Leeuw, J. W.; Kock-van Dalen, A. C.;

De Zeeuw, M. A.; De Lange, F.; Rijpstra, W. I. C.;Schenck, P. A. Geo-

chim. Cosmochim. Acta 1987,51, 236-239. (22) Schmid, J. C.; Connan, J.; Albrecht, P. Nature 1987,329,54-56. (23) Payzant, J. D.; McIntyre, D. D.; Mojelsky, T.W.; Torres,M.; Montgomery, D. S.; Strausz, 0. P. Org. Geochem. 1989, 14, 461-473. (24) Sinninghe Dames, J. 5.;Rijpstra, W. I. C.; Kock-van Dalen, A. C.; De Leeuw, J. W.; Schenck,P. A. Geochim. Cosmochim. Acta 1989,53, 1343-1355. (25) Vairavamurthy, A.; Mopper, K. Nature 1987,329,623425. (26) Arpino, P. J.; Ignatiadas, I.; DeRycke, G. J. Chromatogr. 1987, 390,329-348. (27) Sinninghe Damst.4, J. S.;Eglinton, T. I.; De Leeuw, J. W.; Schenck, P. A. Geochim. Cosmochim. Acta 1989,53,873-889. (28) Payzant, J. D.; Montgomery, D. S.;Strausz, 0. P. Tetrahedron Lett. 1983,24,651464. (29) Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.;Strausz, 0. P. Tetrahedron Lett. 1986,26,4175-4178. (30) Payzant, J. D.; Montgomery, D. S.; Strausz, 0. P. Org. Geochem. 1986,10, 357-369. (31) Cyr, T. D.; Payzant, J. D.; Montgomery, D.S.; Straw, 0. P. Org. Geochem. 1986,9, 139-143. (32) Valisolalao,J.; Perkis, N.; Chappe, B.; Albrecht, P. Tetrahedron Lett. 1984,25, 1183-1186. (33) BraeseI1, S. C.; Lewis, C. A.; De Leeuw, J. W.;De Lange, F.; Sinninghe Dames, J. S. Nature 1986,320,160-162. (34) Siinghe Dames, J. S.; Kock-van Dalen, A. C.; De Leeuw, J. W.; Schenck. P. A. Tetrahedron Lett. 1986.10.791-806. (35) Sinninghe Damns, J. S.; De LeeUw,'J. W. Int. J. Environ. Anal. Chem. 1987, 28, 1-19.

Table I. Average Prowrtids of Athabasca Aophaltene' elemental 'H and lacNMR analysis, w t % C 79.9 aromatic C per 100 C 37 H 8.3 saturated C per 100 C 63 N 1.2 aromatic H per 100 C 8 s 7.8 saturated H per 100 C 116 0 2.8

(H/C).tOfiC a

1.24

~UOUldCUOIMtiC molecular weight

0.23 6000

Data from refs 37 and 38.

Recently we have reported methods for the isolation of sulfides and thiophenes from petroleum based on the selective oxidation of the sulfur atom in the different chemical environments. The large difference in polarity between the oxidized and unoxidized forms and their ease of interconversion permits the isolation of these compound classes in high purity.B* The present work employs these methods and is a continuation of our previous studyI7 on the pyrolysis oil of Athabasca asphaltene. Here we report the occurrence of additional aromatic compounds having a linear carbon framework in Athabasca asphaltene and in the maltene fraction of several heavy oils and bitumens from northern Alberta.

Experimental Section Materials. All solvents were reagent grade and were distilled in an all-glass-Teflon apparatus prior to use. Toluene, n-pentane, and dichloromethanewere distilled from CaHz and dioxane from LiAlH4. GC-FID Analysis. The fractions were examined with an HP-5830A gas chromatograph (GC) employing hydrogen carrier gas, an injector with a split ratio of ca.151,and a flame ionizetion detector (FID). The column used was J&W fused silica 60 m X 0.25 mm coated with 0.25-rm DB-5. Samples were injected in the form of a toluene solution and the GC was temperature programmed from 70 to 300 "C at 6 "C/min. GC-MSAnalysis. A Varian V i t a GC with a splitless injector was used with a J&W fused silica column 60 m X 0.32 mm coated with 0 . 2 5 DB-5. ~ Sampleswere injected in the form of a toluene solution. The GC was temperature programmed from 50 to 300 OC at 3 OC/min. The end of the column was introduced directly into the ion source of a VG 7070E mass spectrometer. Typical mass spectrometer conditions employed were 250 "C ion source and 70 eV electron energy. Data acquisition was done with VG 11-250software using a PDP 11/24 computer. The mass range m / z = 50-600 Da was scanned every 1.0 s. Sample Description and Asphaltene Preparation. The sample of Athabasca bitumen, Suncor Coker Feed sample no. 86-02,location 23-92-10-W4M, was obtained from the Oil Sands Sample Bank of the Alberta Research Council and was produced by the Hot Water Process. In a typical procedure, asphaltene was prepared by dissolving 130 g of Suncor Coker Feed bitumen in a mixture of 50 mL of dichloromethane and 50 mL of n-pentane. The resulting homogenous solution was agitated and diluted to 3.5 L with npentane. After standing overnight at 5 "C, the suspension was filtered and the crude asphaltene washed repeatedly with npentane until the washings were colorless. The crude asphaltene was air-dried to yield 20.8 g (15.5% of the bitumen). The crude asphaltene was dissolved in 200 mL of dichloromethane and centrifuged to remove fine particles of mineral matter. The resulting solution was decanted into 2.5 L of n-pentane with agitation. After standing overnight at 5 "C, the suspension was filtered and the asphaltene washed repeatedly with n-pentane and dried to give 17.4 g of purified asphaltene which was stored in a sealed container at -10 "C until use. The average propertie^^',^ of Athabasca asphaltene are summarized in Table I. (36) Payzant, J. D.; Mojelsky, T.W.; Straw, 0. P. Energy Fuels 1989,

3, 449-454.

Structural Units of Athabasca Asphaltene

n-Pentane

n-Pentane

5% Tol.

508 T 0 1 . l

10% Tol.

"1

Figure 1. Flow diagram for the separation of various classes of compounds from the pyrolpis oil of A t h a w asphaltene. Details of the separation procedure are given in the Experimental Section. Flash Pyrolysis Apparatus and Procedure. The pyrolysis apparatus consisted of a 125-mL Erlenmeyer flask, the mouth of which was attached to a 2.5-cm-diameter Pyrex tube and then to a dropping funnel, and a 1.5-cm exit tube was attached to the side of the flask. The bottom 15 cm of the apparatus was immersed in a fluidized sand bath heated to the desired pyrolysis temperature. A solution of asphaltene (3-4%) in toluene was added from a dropping funnel through the vertical large tube which was adjusted so that the falling drops initially struck the bottom of the flask. A flow of 30-50 mL/min of nitrogen was maintained through the the vessel to sweep the reaction vapors out the side arm, which was attached to a collection flask immersed in ice water and equipped with a condenser. The rate of addition of the toluene solution was maintained at less than 1 mL/min. A faster rate of addition was found to give a lower yield of pyrolysis oil. This rate of addition of the toluene solution corresponds to a flow of toluene vapor of about 0.5 L/min at the reactor temperature and a residence time in the hot zone of roughly 20 8. In a typical procedure, a solution of asphaltene (11.5 g) in toluene (300 mL) was added dropwise over a period of 5 h to the flash pyrolysie apparatus while the fluidized sand bath was heated to 430 OC. Concentration of the collected liquids on a rotary evaporator gave the pyrolysis oil as a mobile dark red oil (4.0 g, 34% of asphaltene). From the pyrolysis apparatus was recovered a black vuggy char (6.1 g, 53% of asphaltene), leaving a loss of 1.4 or 13% of asphaltene in the form of gases and volatiles. Removal of the Olefins. To a 100-mL round-bottom flask equipped with a reflux condensor and a magnetic stirring bar was added pyrolysis oil (5.8 g) and toluene (20 mL). The vessel was flushed with nitrogen, cooled in ice water, and 1M BH3.THF (10 mL) was added slowly by syringe. The reaction mixture was allowed to come to room temperature and stirring was continued for 1h after which 30% H202(5 mL) was slowly added, followed by KOH (0.5 g). The resulting mixture was refluxed for 45 min, cooled to room temperature,and transferred to a separatory funnel with n-pentane (100 mL) and water (25 mL). The aqueous layer was withdrawn and the organic phase washed with water (2 x 25 mL), dried (Na,SO,), concentrated, and applied to a column of 100-g silica gel (Figure 1). Elution with n-pentane (150 mL) (37) Ignerriak, T. M.;Kotlyar, L.; Samman, N.; Montgomery, D. S.; S t r a w , 0.P. Fuel 1983,62, 363-369. (38) Cyr, N.;McIntyre, D. D.; Toth, C.; Strauez, 0. P. Fuel 1987,66, 17W1714.

Energy & Fuels, Vol. 5,No. 3,1991 447 gave a saturate fraction (1.65 g, 28% of the pyrolysis oil), 50% toluene/n-pentane (150 mL) gave an aromatic fraction (2.4 g, 42% of the pyrolysis oil), and methanol (25 mL) followed by 15% methanol/toluene (150 mL) gave a polar fraction (1.77 g, 30% of the pyrolysis oil). Oxidation of Thiophenes to Sulfones. To a 125-mL Erlenmeyer flask equipped with a magnetic stirring bar was added m-chloroperbenzoic acid (50-60%, 1.5 g), NaHC03 (2.5 g), and dichloromethane (40 mL). The mixture was stirred for 30 min after which a portion of the n-pentane eluent from the silica gel column (0.205 g) was added using dichloromethane (10 mL). The mixture was stirred for 24 h, after which a solution of Na& 0&H20 (2.0 g) in water (20 mL) was added and stirring continued for 30 min. The reaction mixture was transferred to a separatory funnel using n-pentane (75 mL) and the aqueous layer was withdrawn. The organic phase was extracted with 10% KOH (2 x 50 mL) and water (2 X 50 mL), dried (NaaO,), concentrated, and applied to a column of silica gel (8 g) which was then eluted with n-pentane (25 mL). The n-pentane fraction from this column was concentrated and applied to an activity I alumina column (4 g). Elution with n-pentane (25 mL) gave the alkanes (0.136 g, 18.5% of the pyrolysis oil), while subsequent elution with 5% tolueneln-pentane (25 mLJ gave the alkylbenzenes (5.8 mg,0.8% of the pyrolysis oil).

Sulfides and Condensed Thiophenes from the Aromatic Fraction. The procedure for the isolation of the sulfides and thiophenes from the pyrolysis oil is outlined in Figure 1. The sulfides and condensed thiophenes were isolated in 2.0% and 14% yields of the pyrolysis oil, respectively. Sulfides and condensed thiophenes were also isolated from the maltene fraction of several of the heavy oils and bitumens of northern Alberta. The experimental procedure for their isolation has been previously described in detai1.29*3s Separation of Fluorenes by Oxidation to Fluorenones and Fluorenols. The present procedure is similar to that previously described.m A portion of the aromatic fraction (Figure 1)after removal of the sulfides and thiophenes by oxidation (0.194 g) was placed in a 50-mL flask with a magnetic stirring bar, 18-crown-6 ether (0.03 g), powdered KOH (0.3 g), and toluene (25 mL). The mixture was stirred overnight at room temperature, after which it was transferred to a separatory funnel with n-pentane (25 mL) and water (40 mL). The aqueous layer was withdrawn and the organic phase extracted with 10% KOH (40 mL) and water (40 mL), concentrated, and chromatographed on silica gel (8 g) ( F i i 1). Elution with 10% tolueneln-pentane (25 mL) gave aromatics I (95.5 mg), 50% tolueneln-pentane (25 mL) aromatics I1 (29.6 mg), CHzC12(25 mL), fluorenones (4.7 mg), and 10% EtOAc/ CH2C12fluorenols (5.7 mg). Synthesis of 1-n-Alkyldibenzothiophenes. The l-n-alkyldibenzothiophenes were prepared from l-carboxyethyldibewthiophene according to Ashby et al." via the corresponding aldehyde as illustrated in eq 1 for 1-ethyldibenzothiophene. &\a b ,I c \, d , a/

-

6 \

/ \

/

('1

(a) UAIH,/elher, (b) Cr03/pyridindCH2Clz,(c) CH3MgI, (4Cr03/pyridine/CHzC1z,(e) ZrdHg/HCl

The lH NMR and mass spectra of this substance have been reported." The 13C NMR (75.5 MHz, CDC13) had signals at (ppm) 141.2, 140.1, 139.7, 135.9, 133.1, 126.4, 125.2, 125.1, 124.3, 122.8, 120.6, 28.2, 14.2. A mixture of various 1-n-alkyldibenzothiopheneswas prepared by reacting a mixed Grignard reagent prepared from a halide mixture (methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-octyl halides) with the aldehyde as outlined in step c above. The final Clemmenson reduction gave a mixture of the desired l-n-alkyl(39) Mojeleky, T.M.; Strausz, 0. P. Org. Ceochem. 1986, 9,31-39, 39-45. (40) Ashby, J.; Ayad, M.; Meth-Cohn, 0.J.Chem. Soc., Perkin 7 h n e . 1 1974, 1744-1747. (41) Tedjamulia, M. L.;Tominaga, Y.; Castle, R. N.; Lee, M. L. J. Heterocycl. Chem. 1983,20, 1485-1495.

Payzant et al.

448 Energy & Fuels, Vol. 5, No.3, 1991 dibenzothiophenesand some olefins. The mixture was catalytically hydrogenated (HS(1 atm), PtO,, n-pentane) to give the

corresponding 1-n-alkyldibenzothiophenes.

Table 11. Gravimetric Results for the Separation of Various Fractions from Athabasca Asphaltene Pyrolysis Oil wt%

wt%

Results and Discussion fractiona pyrolysis oil* asphaltene Flash Pyrolysis. In previous studies flow pyrolysis of saturates 28 9.5 asphaltene has been conducted in a stream of helium, with diphatics 18 6.1 9 3.1 the asphaltene supported as a thin film on q u a r t ~ . ~ * ~ J ~ thiophenes alkylbenzenes 0.8 0.3 Reaction products are quickly swept from the reaction zone aromatics 42 14 in this experimental arrangement and thus secondary sulfides 2 0.7 pyrolysis of the initially produced fragments is minimized. condensed thiophenes 14 4.8 Yields of pyrolysis oil can be as high as 38%. In contrast, 5.1 1.7 aromatics I pyrolysis of bulk asphaltene affords only a low and variable aromatics I1 1.6 0.5 fluorenones 0.25 0.1 ( 10% ) yield of pyrolysis oil. The pyrolysis of asphaltene fluorenols 0.3 0.1 as a thin film on quartz, while affording high and reproP O h 30 10 ducible yields of pyrolysis oil, is cumbersome and limited to small quantities (0.1-0.2 g) of asphaltene. In contrast, a See Figure 1. *Isolated yield. the present flash pyrolysis method is convenient to employ considerable amounts of alkylthiophenes and minor and can readily be done on the 10-g scale, thus permitting amounts of alkylbenzenes. The alkylthiophenes may be the generation of pyrolysis oil on the multigram d e . This separated from the alkanes by chromatography on 10% pyrolysis procedure affords reproducible (110% relative) AgN03/silica gel and the distribution by carbon number yields of pyrolysis oil. At a pyrolysis sand bath temperaof the thiophenes may be observed directly by GC-MS ture of 410 OC, the yield of pyrolysis oil was 18%, at 430 since the n-alkyl-substituted thiophenes possess base peaks OC 3470, and at 460 OC 37%. Examination of the pyrolysis in their mass spectra corresponding to cleavage of the side oil at 460 OC suggested that the average side chain length chain @ to the thiophene ring. The GC-FID and GC-MS in the pyrolysis oil was considerably shorter at this pyrotraces for the thiophenes have been published." The lysis temperature than at 430 OC, while the pyrolysis oil thiophenes are dominated by three homologous series at 410 "C was similar to that obtained at 430 "C. A pywhich have H, CH3, or C2H6in position 2 and an n-alkyl rolysis temperature of 430 OC was selected as a suitable substituent of chain length from C6 to Czoin position 5. compromise between maximum yield and minimum secThe identity of these compounds has been established by ondary pyrolysis reactions. It is assumed in these experGC-MS comparison with synthetic materials." Similar iments that secondary pyrolysis reactions are relatively homologous series of thiophenes have been reported in minor and therefore the fragments generated on pyrolysis pet~oleums~~ and 1 ~have ~ a been identified in the pyrolysis reflect the molecular architecture of the asphaltene. fragments of various asphaltenes and kerogens.'W A high The toluene solvent used to transport the asphaltene relative abundance of the 2,5 substitution pattem has been into the hot zone was found not to produce a significant interpreted as indicating that the precursor to these quantity of polymerization products when examined in thiophenes possessed a linear carbon f r a m e ~ o r k . ' ~ J ~ * ~ blank pyrolysis experiments at 430 "C. No evidence was Benzenes. The n-alkyl-substituted benzenes have a found to suggest the incorporation of toluene into the mass spectrum which is qualitatively similar to that of the asphaltene pyrolysis products. n-alkylthiophenes; that is, the mass spectrum is dominated Separation Scheme-General. The method used to by the base peak which is due to cleavage of the n-alkyl separate the pyrolysis oil into its various fractions is side chain at the carbon j3 to the aromatic ring. The aloutlined in Figure 1. The initial step of removing the kylbenzenes comprise only c a 4% of the saturate fraction olefins was found to simplify the subsequent oxidation and unambiguous direct deterinination by GC-MS is difreactions since the olefins gave complex reaction products ficult since fragment ions from other substances appear and interfered with the separation in some steps. The on the mass chromatograms of the base peaks of the nolefins were removed from the mixture by converting them alkylbenzenes. into alcohols by reaction with diborane followed by oxiThe thiophenes and benzenes have similar chromatodation with basic hydrogen peroxide as described previgraphic behavior and are thus difficult to separate. Sep0usly.1~Subsequent chromatagraphy on silica gel produced aration of these classes was achieved by oxidizing the a 'saturates" fraction (28% pyrolysis oil; elemental analthiophenes to their corresponding sulfones by using mysis, S = 2.9%), an aromatic fraction (42% pyrolysis oil), chloroperbenzoic acid as outlined in the Experimental and a polar fraction (30% pyrolysis oil) which contained Section and in Figure 1. Chromatography on silica gel the alcohols derived from the olefins and other polar removed the sulfones and a subsequent chromatography substances from the pyrolysis oil. on activity I alumina separated the alkanes from the A series of selective oxidation reactions followed by benzenes. That alkylbenzenes are unaffected by the oxchromatography, as outlined in Figure 1, permitted the idation reaction under the experimental conditions emseparation of various classes of compounds from the two ployed was shown in a separate experiment using 1main fractions, thus simplifying the analysis by gas chrophenyltridecane. The GC-FID trace of the benzenes is matography. The gravimetric results on the fractions and shown in Figure 2. The assignment of the major peaks subfractions isolated are presented in Table 11. The nto n-alkylbenzenes and the various isometric monomethyl pentane eluant which is labeled as saturates contains, in n-alkylbenzenes is based on their mass spectra and comaddition to saturates, thiophenes and alkylbenzenes, and parison with the reported relative GC retention indexes the aromatic fraction contains thianes, thiolanes, and of the isomers.42 The maximum concentrations occur condensed thiophenes in addition to the aromatic class around CI6-Cl7;however, the true distribution is altered compounds. by progressively increasing losses on going to lower moSaturate Fraction. Thiophenes. The n-pentane eluant (S= 2.9%) from the first silica gel chromatography, (42) Hayea Jr., P. C.; Pitzer, E. w. J. Chromatogr. 1982,259,179-198. Figure 1, contains, in addition to aliphatic compounds,

-

Structural Units of Athabasca Asphaltene

Energy & Fuels, Vol. 5, No.3, 1991 449

c19

I

& c 2 1

GC Retention Time

GC Retention Time

-

Figure 2. GC-FID trace of the alkylbenzenes isolated from A t h a h asphaltene pyrolysis oil. Numbers above the clusters of peaks indicate the total number of carbon atoms in the corresponding benzenes. The insert is an expansion of the area about Cmrecorded with a temperature program of 3 OC/min. Peak a, m-monomethyl-n-akylbenzene; b, p-monomethyl-n-akylbenzene; c, n-alkylbenzene; d, o-monomethyl-n-alkylbenzene. Scheme I. Compound Classes in Athabasca Asphaltene Having an n -AIkanoic Carbon Framework

lecular weight material owing to volatility. The most abundant of the benzenes possess an n-alkyl substituent on the ring and either no other substituent or a methyl group on the ring. The most abundant of the monomethyl n-alkylbenzene isomers at most carbon numbers is the ortho isomer followed by the meta and then para isomers. The ortho-substituted benzene would have arisen at some stage in the petroleum generation process by aromatization involving the cyclization of a suitably functionalized linear strand of carbon, in much the same way as the n-alkylthiophenes have been postulated to be f ~ r m e d . ' ~ The J ~ ortho monomethyl isomer is the most abundant monomethyl isomer at most carbon numbers and the one which corresponds to the linear carbon framework (Scheme I). The unsubstituted n-alkylbenzenes may also be fragments derived from a precursor possessing a linear carbon framework. The meta and para isomers are of lower abundance than the ortho and could have been formed by isomerization of the ortho isomer in the pyrolysis process, or by transformation over geologic timea during the maturation of the petroleum, or they may reflect the presence of more complex molecular types in the original source material. Alkanes. The GC-FID trace of the alkanes after removal of the benzenes and thiophenes is shown in Figure 3. The trace is dominated by a series of peaks corresponding to n-alkanes which is smooth and round with respect to carbon number and extends from CI1to Ca and beyond. In addition to the n-alkanes and other acyclic compounds, this fraction contains minor amounts of ho-

w

Figure 3. GC-FIDtrace of the alkanes isolated from Athabasca asphaltene pyrolysis oil. The numbers above the peaks indicate the number of carbon atoms in the corresponding n-alkane. Pr = pristane and Py = phytane. panes and other terpenoid hydrocarbons as has been reported previously.8J0J2 As with the n-alkylbenzenes the true concentration distribution of the n-alkanes is distorted owing to progressively increasing losses a t lower carbon numbers and, on the basis of the results obtained from the ruthenium ions catalyzed oxidation of Athabasca as~ h a l t e n e it , ~is probable that the concentrations of the alkanes would keep on increasing with lower carbon numbers below CISdown to C1. Aromatic Fraction. Sulfides. The 50% toluenelnpentane eluant from the first silica gel column (Figure 1) contains a variety of sulfur-containing compounds in addition to aromatic hydrocarbons. The sulfides were removed first from this mixture by oxidation with tetrabutylammonium periodate to the corresponding sulfoxides as described p r e v i o ~ s l y . ~The ~ * polar ~ ~ * sulfoxides ~ were chromatographed from the mixture and reduced to the corresponding sulfides as outlined in Figure 1. The GCMS data for the sulfides isolated from the Athabasca asphaltene pyrolysis oil have been published previo~ly.'~ The mixture is dominated by series of thiolanes possessing an H, CH3, or C2H5in paition 2 and an n-alkyl chain from about c6 to Cmin position 5 in a manner analogous to the thiophenes. Minor amounts of 2,6-di-n-alkyl-substituted thianes were also observed. Similiar series of sulfides possessing a linear carbon framework have been reported in a variety of p e t r o l e ~ m s . ' ~ * ~ ~ ~ ~ 3 Condensed Thiophenes. The condensed thiophenes were isolated from the aromatic fraction of the pyrolysis oil, as outlined in Figure 1, by oxidation to the corresponding sulfones with m-chloroperbenzoic acid.% The polar sulfones and other oxidation products were readily separated from the reaction mixture by chromatography on silica gel. The sulfones were reduced back to thiophenes with LiAlH, in refluxing dioxane and were isolated by a subsequent chromatography on silica gel. The procedure for the isolation of the condensed thiophenes from the maltene fractions of various heavy oils and bitumens was as previously described36and the results of the analyses are summarized in Table 11. Benzo[b]thiophenes are of such high abundance in Athabasca asphaltene pyrolysis oil that they are easily concentrated from the pyrolysis oil by a simple chromatographic procedure and this mixture is dominated by series of 2,4-di-n-alkyl-substituted benzo[blthi~phenes.'~ This substitution pattern suggests that these benzo[b]thiophenes have been produced by sulfur atom addition, cyclization, and aromatization processes on a precursor substance having a linear carbon framework. This underlying linear carbon framework is illustrated by the heavy line in the benzo[blthiophene structure in Scheme

Payzant et al.

450 Energy & Fuels, Vol. 5, No. 3, 1991 3

Table 111. Weight Peroent Recovery of Sulfides and ThioDhenes in the Maltene Fractions

of maltene sulfides thiophenes (Th) S/Th (S) 2.0 14.0 0.14 wt %

Athabasca asphaltene pyrolysis oil surfaceo Athabasca surface Athabasca Syncrude pit surfaceb Athabasca Suncor 23-92-10-W4M surface Peace River 4-21-85-18W5M-500 m Peace River 4-21-8618W5668 mb Cold Lake 4-65-3-W4M-500 m Lloydminster 700 m Lloydminster 16-3-40-1W3 670 mb Wolf Lake -500 mb Bellehill Lake 12-28-41-12W4 920 mb N

(?I

I /

3.8 6.9 3.8

4.4 6.4 4.4

0.86 1.1 0.86

4.3 16 4.6 3.9 2.6 3.6 3.1C

11.8 7.6 6.1 6.7 5.7 2.9 5.5

0.36 2.1 0.75 0.46 0.47 1.2 0.56

O Asphaltene pyrolysis oil; sulfides are n-alkyl-substituted thianes and thiolanes. From ref 36. Sulfides are mainly n-alkyl-substituted thianes and thiolanes with some cyclic terpenoid sulfides. The sulfides in the rest of the samples are cyclic terpenoid sulfides.

Table IV. Dibenzothiophenes Identified on m l z = 197 Mass Chromatomamr of Figure 4 proposed compound/isomer -peak no. mol w t 1 198 4-methvldibenzothio~hene 2- and ?I-methyldibekothiophene 2 198 3 198 1-methyldibenzothiophene 4 212,226 C2- and C,-dibenzothiophenes 5 240 n-C,-dibenzothiophene 6 254 n-C5-dibenzothiophene n-CcDibenzothiophene 7 268 8 282 n-C,-dibenzothiophene n-C8-dibenzothiophene 9 296 n-C9-dibenzothiophene 10 310 11 324 n-C,,,-dibenzothiophene n-CI1-dibenzothiophene 12 338 n-CI2-dibenzothiophene 13 352

I. Similar 2,4-di-n-alkyl-substituted benzo[blthiophenes have been reported in various petroleums and pyrolysates.183%21,27 In addition to the mixture of 2,4-n-alkyl-substituted benzo[blthiophenes, a variety of dibenzothiophenes were also observed. The maltenes of the petroleums examined (Table ID)contain only minor amounts of benzothiophenes compared to dibenzothiophenes;98however, in Athabasca asphaltene pyrolysis oil, benzothiophenes are somewhat more abundant than dibenzothiophenes. The dibenzothiophenes are a complex mixture and the GC-FID traces for the condensed thiophene fraction of several heavy oils and bitumens of northern Alberta have been reported previously.98 The most abundant homologous series of n-alkyl-substituted dibenzothiophenes are the l-n-alkyldibenzothiophenes and they are conveniently observed by GC-MS as their m / z = 197 mass chromatogram as displayed in Figure 4. The m/z = 197 fragment ion corresponds to cleavage of the n-alkyl side chain at the carbon atom in the position /3 to the aromatic ring.

The identity of the compounds was confirmed in GC-MS coinjection experiments with synthetic l-n-alkyldibenzothiophenes prepared as described in the Experimental Section. In Athabasca asphaltene pyrolysis oil the most abundant dibenzothiophene is l-methyldibenzothiophene.As may

I

4

n

1 ,

Asphaltene pyrolysis oil

-

Suncor maltene

I,

Cold Lake maltene

I

Peace River maltene

I

Lloydminster maltene

-GC

Retention Time

-

Figure 4. GC-MSmass chromatograms of m / z = 197 for the condensed thiophene fractions isolated from various maltenes and Athabasca asphaltene pyrolysis oil. For peak assignments see Table IV.

be seen from Figure 4, the abundance of the l-methyl isomer relative to the other monomethyl isomers decreases with increasing depth of burial or thermal maturity of the various petroleums, as the thermodynamically least stable l-methyl isomer is converted into the other isomers. This trend in relative abundance of the various monomethyldibenzothiophenes as a function of depth of burial has been noted p r e v i o ~ s l y . ~ . ~ ~ In addition to the monomethyldibenzothiophenes,all samples contained a complex mixture of isomeric C2and C3 dibenzothiophenes as shown in the m / z = 197 mass chromatogram (Figure 4) followed by a series of l-n-alkyldibenzothiophenes with the side chain extending in length to n-C13 in some samples. In the m/z = 197 mass chromatogram of the Athabasca asphaltene pyrolysis oil these extended side chain compounds appear as an incompletely resolved doublet. The first peak of these doublets corresponds to the l-n-alkyldibenzothiophenes, while the second peak is unidentified. The condensed thiophenes from the maltene fraction of the same petroleum re the asphaltene, however, contain mainly the series corresponding to l-n-alkyldibenzothiophenes. The l-n-alkyldibenzothiopheneseries truncates at n-C,+ for the maltenes of the highly biodegraded Athabasca, Cold Lake, and Peace River bitumens, while long (>n-C& side chain dibenzothiophenes are found in Athabasca asphaltene pyrolysis oil and in the more deeply buried, and therefore less biodegraded, Lloydminster heavy oil (Figure 4). The absence of dibenzothiophenes with side chains >n-C8 in Athabasca maltene is probably due to biodegradation since certain microorganisms will attack n-alkylated aromatic molecules when the n-alkyl side chain exceeds a critical length.14 (43)Albaiges, J.; Algaba, J.; Clavell, E.; Grimalt, J. Org. Geochem. 1986,10,441-450. (44)Fedorak, P.M.;Westlake, D.W.S.Appl. Enuiron. Microbiol. 1986,51,435-437.

Energy & Fuels, Vol. 5,No.3, 1991 451

Structural Units of Athabasca Asphaltene The preference for the n-alkyl substituent in position 1 in the dibenzothiophene nucleus may be explained by their formation by sulfur introduction, cyclization, and aromatization of a precursor which initially possessed a linear carbon framework in a manner analogous to the thiophenes and benzo[ blthiophenes. The numbering system of dibenzothiophene is shown in Scheme I and the underlying proposed linear carbon framework has been highlighted with a heavy line. In Table I11 are given the weight percentages of the sulfides and thiophenes in some Alberta oil sand, heavy oil, and the Bellshill Lake conventional oil maltenes along with the corresponding values for the pyrolysis oil of Athabasca asphaltene. The individual values and the ratios of the values of sulfides over thiophenes show considerable variations even when the samples were from the same bore hole, as in the case of Peace River bitumen, but from somewhat different depths. It should also be kept in mind that the sulfides may comprise two distinctly different structural classes of molecules, the n-alkyl-substituted thianes and thiolanes on the one hand, and the cyclic terpenoid sulfides on the The sulfides in the asphaltene pyrolysis oil are made up entirely of the former class, in the Bellshill Lake maltene mainly of the former class, and in the rest of the samples listed in Table 111,they are exclusively of the latter type. These structural differences in the sulfide composition of the various samples in Table I11 are in agreement with the principal conclusions of the present and earlier studies,= namely, that the asphaltene and nondistillable portions of these oils are of normal alkanoic origin, while the lower molecular weight distillable portion is of isoprenoid/terpenoid origin. Fluorenes. The fluorenes were isolated from the aromatic fraction of Athabasca asphaltene pyrolysis oil by silica gel chromatography,after removal of the condensed thiophenes, followed by an oxidation step to convert them to fluorenones and fluorenols (Figure 1). The method of oxidation, the base-catalyzed autooxidation with molecular oxygen in the presence of the phase transfer catalyst 18crown-6 ether, quantitatively converts nuclear alkylated fluorenes to fluorenones and 9-n-alkylfluorenes to 9-nalkylfluorenols as was reported p r e v i o ~ s l y . ~ ~ The fluorenones and fluoren-9-01s were isolated from Athabasca asphaltene pyrolysis oil in yields of 0.25% and 0.3%, respectively, corresponding to 0.1% each of the asphaltene. The GCMS data for the fluoren-9-01s are shown in Figure 5. The 9-n-alkylfluoren-9-01s have a characteristic base peak in their mass spectra corresponding to the loss of the 9-n-alkyl side chain:

I

I

-GC

TIC

134

m/z=181

II I

m/z= 195

Retention Time

-

Figure 5. GC-MSof the fluorenols isolated from Athabasca asphaltene pyrolysis oil. Upper trace, total ion current; middle = 181, the base peak of the mass spectrum of the trace, m? fluoren-9-01s;lower trace, mlz = 195, the base peak of 9-n-alky the monomethyl-9-n-alkylfluoren-9-ols. The numbers above the peaks on the mlz = 181mass fragmentogram indicate the number of carbon atoms of the 9-n-alkylsubstituent of the fluoren-9-01.

Prominent among the various series of fluoren-9-ols are fluoren-9-01s with a 9-n-alkyl substituent which are conveniently observed by GC-MSas the m/z = 181 mass chromatogram of their base peak as shown in Figure 5, middle panel. The n-alkyl side chain extends from methyl to n-CI3with a pronounced maximum in abundance for 9-methylfluoren-9-01and with a monotonous decline with increasing chain length. This distribution by carbon number is different from that previously reported for the fluoren-9-01s and 9-alkylfluorenes from Athabasca maltene4 in that the relative abundance of 9-methylfluoren-9-01

is considerably greater and the 9-n-alkyl chain length is longer in the Athabasca asphaltene pyrolysis oil. Thus, we observe here the same relationship in the side chain distribution of the materials from the asphaltene as compared to the materials from the maltene as we found in the case of the dibenzothiophene series, namely, the side chains are longer in the former materials (up to Cis)than in the latter (to C8only), again pointing to microbial removal of the longer chain members from the maltene. The increased relative abundance of 9-methylfluorene in the laboratory pyrolysis oil is presumed to reflect the preferential production of short side chain molecules during pyrolysis versus thermal maturation. The distribution by carbon number of the nuclear monomethylated fluoren9-01s is shown in the bottom panel of Figure 5 as its characteristic m/z = 195 mass chromatugram. The various monomethyl isomers are incompletely resolved; however, these series, like the nonmethylated series, possess an n-alkyl substitutent at position 9 and the most abundant member of these series is the one with a methyl group at position 9. The structure of the fluorenes corresponding to the fluoren-9-ols is shown in Scheme I and ita potential derivation from a precursor substance possessing a linear carbon framework has been highlighted with a heavy line. The GC-MSdata for the fluorenones are displayed in Figure 6. The fluorenones possess prominent molecular ions in their mass spectraa and mass fragmentograms for the molecular ions corresponding to the various alkylated fluorenones are displayed in Figure 6 in addition to the total ion current. As may be seen from Figure 6, some of the isomeric alkylated fluorenones are more abundant than others, but none of the isomers have been identified. To summarize the results on fluorenes in the present work, it was found that high molecular weight Athabasca asphaltene contains over 0.2% fluorene, 9-n-alkylfluorene and their nuclear methylated derivatives. In previous studies from this laboratorp it was also shown that npentane precipitated Athabasca asphaltene contains nu-

(45) Payzant, J. D.; Mojeleky, T. W.; Cyr, T. D.; Montgomery, D. S.; Strauez, 0. P. Org. Geochem. 1986,8, 177-180.

(46) Frakman, 2.;Ignasiak,T. M.; Lown,E. M.; Strauez, 0. P. Energy Fuels 1990,4, 263-270.

181

e=

Payzant et al.

452 Energy & Fuels, Vol. 5, No. 3, 1991

I

/

TIC

Fluorenone

J C, Fluorenon

C2 Fluorenorm

ZMI

222

II

F1uor(Klone

I I

236

I

C, Fluorenone

Figure 6. GC-MSof the fluorenones isolated from Athabasca asphaltene pyrolysis oil. TIC is total ion current. Descending panels are mass chromatograms of the molecular ions.

clear methylated fluorenones, benzofluorenones, and dibenzofluorenones complexed to the asphaltene micelles in an aggregate amount -0.16%. The maltene fraction of the same oil was shown to contain fluorene, 9-n-alkylfluorene, fluorenone, 9-n-alkyMuoren-9-ols,and their nuclear methylated derivatives.w In the fluorenones and fluorenes from the maltene it was found that the dimethyl derivatives were the most abundant of the nuclear alkylated species and that their relative isomeric importance was in the order 1,4 > 2,4 > 3,4 > 2,3. Other Aromatic Hydrocarbons. The GC-FID traces for the aromatics I and aromatics I1 fractions are shown in Figure 7. The aromatics I fraction, upper panel in Figure 7, is a complex mixture which probably consists mainly of various alkylated naphthalenes and tetralins. The carbon and z numbers (C,Ha+,) indicated above the major clusters of peaks in Figure 7 are derived from the GC-MS data and correspond to the major peaks in the mixture. Many individual isomers are present. The peaks CIll2; z = -12, -14 represent methylnaphthalenes (Cllklo; z = -12) and biphenyl (C12Hlo;z = -141, the next cluster of peaks with ClZI3;t = -12, -14 their methyl derivatives, and the subsequent cluster of peaks their higher alkyl derivatives. The detection of the presence of these structures in the asphaltene is important. The presence of naphthalenes confirms the conclusion drawn before from Ru ions oxidation studies,’’ based on the detection of benzene-1,2dicarboxylic acids, the oxidation products of naphthalenes. Ru ions oxidation is not suitable for the detection of biphenyl structures because the expected product, oxalic acid, if formed, is further oxidized to carbon dioxide. Therefore, prior to the present study, no evidence existed for the presence of biphenyls in asphaltenes. The aromatic I fraction waa obtained from the pyrolysis of the asphaltene in 1.7% yield.

Figure 7. GC-FID traces for the aromatics I, upper panel, and aromatics 11, lower panel, isolated from Athabasca asphaltene pyrolysis oil. The carbon and t numbers above selected clusters of peaks on the traces were derived from GC-MSdata.

The GC-FID trace for the aromatics I1 is shown in the lower panel of Figure 7. Like the aromatics I, it is a complex mixture of alkylated aromatics of the phenanthrene f anthracene type and also more highly condensed materials. The carbon and z numbers indicated above the clusters of peaks in Figure 7 were derived from GC-MS data. The aromatics I1 fraction was obtained in 0.5% yield. Normal Alkanoic Structural Entities in Athabasca Asphaltene. The total amount of material that has been identified as having a normal aliphatic carbon skeleton or that could have arisen from the cyclization of a normal alkanoic precursor in the asphaltene pyrolysis oil (Table 11)amounts to over 15% of the asphaltene. This does not include the terminal n-alkenes which form in a yield which is commensurate with the yield of n-alkanes in the flow pyrolysis of Athabasca asphaltene* but were removed by the hydroboration step in the workup procedure (Figure 1)of the present study. Under the present experimental conditions, however, the yield of olefins could have been substantially reduced owing to the increased importance of hydrogen abstraction by the alkyl radicals from the toluene carrier to form alkanes. In any event, from previous studies>% the amount of normal alkyl moiety content of Athabasca asphaltene is known to be -24%. Adding to this -60% of the sum of weight percentages of the thiophenes, alkylbenzenes, sulfides, fluorenone, fluorenols, and aromatics, -6%, the lower limit that can be placed on the amount of the asphaltene that originated from normal alkanoic biotic source materids is about 30%. The true value must be much higher.

Summary and Conclusions A flash pyrolysis method which permits asphaltene pyrolyses to be conducted on the multigram scale with a high yield of pyrolysis oil has been developed. Athabasca asphdtene was pyrolyzed in this way at 430 OC to give a 34% yield of pyrolysis oil. The dominant classes of compounds in the pyrolysis oil are alkanes and various thiophenes and condensed thiophenes. One of the major classes of compounds identified in this work was the dibenzothiophenes. Among the various isomeric alkylated dibenzothiophenes, the most abundant homologous series was found to be the

Energy & Fuels 1991,5,453-458

l-n-alkyldibenzothiophenes.In addition, the l-n-alkyldibenzothiophenes were found to occur in Athabasca maltene and in the maltene of several of the heavy oils and bitumens of northern Alberta. The predominance of the l-n-alkyl substitution pattern of the dibenzothiophene nucleus suggests that they were derived from a precursor substance possessing a linear carbon framework. Various selective oxidation methods permitted the separation of several classes of compounds which occur in small amounts in the pyrolysis oil. The alkylbenzenes were isolated and n-alkylbenzenes and monomethyl n-alkylbenzenes were found to be the most abundant homologous series. The most abundant of the monomethyl n-alkylbenzenes at most carbon numbers was found to be the o-methyl isomer followed by the m- and p-methyl isomers. The predominance of the o-methyl isomer suggests that the various n-alkylbenzenes were derived by the cyclization of a percursor substance possessing a linear carbon framework. Finally, several series of 9-n-alkylfluorenes were observed by conversion to their corresponding fluoren-9-01s which have previously been observed in Athabasca maltene.99*'6The n-alkyl substituent at position 9 of the fluorene nucleus suggests that it too is derived by the cyclization of a precursor substance possessing a linear carbon framework. Previously, we reported the abundant occurrence of several homologous series of thiophenes, 2,Cdi-n-alkylbenzo[ b]thiophenes, thiolanes, and thianes in Athabasca asphaltene pyrolysis oil, all of which had n-alkyl substituents, suggesting that they were derived from a precursor possessing a linear carbon f r a m e ~ 0 r k . lThe ~ quantity of terpenoid-derived polycyclic systems in Athabasca asphaltene pyrolysis oil is small in comparison with the quantity of material possessing a linear carbon framework.

453

This contrasts with the distillable portions of Athabasca maltene, which are dominated by homologous series of polycyclic systems possessing a terpenoid carbon framework. Field ionization mass spectrometry has shown that the bulk of the distillable portion of the maltene consists of a complex mixture of compounds whose distribution by carbon number suggests that they are derived from terpenoid precursors." Finally, ruthenium-catalyzed oxidation of the nondistillable portion of Athabasca maltene has suggested that it, like the asphaltene, is composed mainly of material possessing a linear carbon framew0rk.u Apparently, the high molecular weight componenta of Athabasca bitumen are composed mainly of material possessing a linear carbon framework while the lower molecular weight portion of the bitumen is dominated by substances derived from an underlying terpenoid carbon framework. This distinction is accentuated in Athabasca bitumen compared to conventional petroleums, since biodegradation has removed most of the n-alkyl-substituted materials from the low molecular weight portion of Athabasca bitumen which resulted from the thermal maturation of asphaltene, leaving the biodegradation-resistant polycyclics and high molecular weight materials behind. Acknowledgment. The financial support of the Alberta Oil Sands Technology and Research Authority is gratefully acknowledged. We thank Dr. Theodore J. Cyr for many helpful discussions and suggestions on asphaltene chemistry and the Oil Sands Sample Bank of the Alberta Research Council for the various heavy oil and bitumen samples. (47) Payzant, J. D.; Hogg, A. M.; Montgomery, D. S.; S t r a w , 0. P. AOSTRA J. Res. 1985,1, 175-182,183-202,203-210.

Influence of Supercritical Fluid Solvent Density on Benzyl Phenyl Ether Pyrolysis: Indications of Diffusional Limitations Benjamin C. Wu,Michael T. Klein,* and Stanley I. Sandler Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716 Received November 28,1990. Revised Manuscript Received February 19, 1991 The influence of supercritical solvent density on the pyrolysis of benzyl phenyl ether (BPE) in tetralin and supercritical toluene is interpreted in terms of transport limitations. Reaction at varying toluene densities highlighted the transport dependence of the BPE fission rate constant. The conversion of BPE decreased from 0.55 to 0.15 as the toluene density increased from 0.0 to 0.75. The yield and selectivity of BPE rearrangement products were also density dependent. These results were explained and modeled quantitatively in terms of the cage effect theory. Introduction The potential for the use of SCF solvents in reaction processes is motivated in part by their extreme compressibility. The density, dielectric constant, solubility parameter, and transport properties of a SCF solvent vary between gas- and liquidlike extremes with modest changes

* Author to whom correspondence should be addressed.

in pressure.'J Thii allows regulation of pressure to control and manipulate SCF solvent properties, which can in turn influence reaction rates and sele~tivities.~In this work (1) Paulaitia, M. E.; Krukonis, K. J.; Kurnik, R. T.; Reid, R. C. Supercritical Fluid Extraction. Reu. Chem. Eng. 1983, 1(2). ( 2 ) Paulaitis, M. E.; Penninger, J. M. L.; Gray, R. D., Jr.; Davidson, P. Chemical Engineering at Supercritical Fluid Conditions; AnnArbor Science: Ann Arbor, MI, 1983.

0SS7-0624/91/2505-0453$02.50/00 1991 American Chemical Society