Energy & Fuels 1990,4,608-626
608
extract bitumen from Athabasca tar sand. The self-generated surfactant is mainly in the form of a microemulsion of the polar micelles dispersed in the aqueous phase. Lee et al.= used sonication and electrolytic dissociation processes to further enhance the generation of surfactants in oil shale. The polar bitumen components are carried into the aqueous phase by the action of the outer anions on the micelles associating with the polar (25) Lee, A. S.; Sadeghi, M.-A.; Yen, T. F. Energy Fuels 1988,2,88.
components of the bitumen. Separation results as the micelles containing the lighter components form a layer. The heavier preasphaltenes and asphaltenes complexed with metals precipitate and agglomerate to form charcoal-like materials. The microemulsion of micelles remains stable and can repeatedly be utilized as a true surfactant.
Acknowledgment. We thank Energy and Environmental Research Laboratories, Inc., for partial financial support. Registry No. Sodium silicate, 1344-09-8.
Characterization of North Sea Petroleum Fractions: Aromatic Ring Class Distribution Hans Petter Ranningsen* and Ingun Skjevrak Statoil as., Production Laboratories, Forus, N-4001 Stavanger, Norway Received March 28, 1990. Revised Manuscript Received June 29, 1990
The retention behavior of about 50 model hydrocarbons, mainly unsubstituted and alkylated aromatics, on an aminopropylsilane (silica-RNHJ liquid chromatographic stationary phase has been investigated. The study included the effect of aromatic structure as well as various substituent effects. The aromatic subfractions of Clo to C29 distillate fractions from a biodegraded North Sea crude oil have been further fractionated according to number of aromatic carbon atoms. These ring-class fractions have been quantified by off-line gas chromatographywith an internal standard. The reliability of the method has been found satisfactory by comparison with gravimetric quantitation. On-line HPLC/GC and GC/MS group type analyses have been evaluated briefly as alternative quantitation techniques. Monocyclic aromatics were found to be the most abundant group below Cmwhile monoand diaromatics together constituted 8040% of the aromatic fractions above Cm C14 and C19aromatic fractions from a series of North Sea crude oils and condensateswere compared with respect to ring-class distribution by using UV detection at 254 nm and response factors. This quantitation technique was also evaluated against gravimetry. It had obvious limitations but was considered useful for the purpose of rough comparison. The differences between the oils were rather small. Finally, the retention behavior of several aromatic hydrocarbons present in crude oil has been examined on two gas chromatographic stationary phases, and the identity of a large number of compounds has been established and related to carbon number.
Introduction Knowledge of the distribution of major structural classes of hydrocarbons (HC) in crude oils as well as distillates (gasoline, kerosine, diesel) and heavy residues, is frequently needed in various fields of the petroleum industry. Such compositional information may be of value in studies related to reservoir evaluation, petroleum origin, migration and maturity, degradation processes, processing and feedstock utilization, and environmental effects. Due to the immense complexity of petroleum fluids, their characterization has been facilitated by steadily more effecient separation techniques (HPLC, HRGC) and more reliable methods of identification (GC/MS). Traditionally alumina has been the preferred adsorbent for liquid chromatographic ring-class separation of aromatic HC.1-3 Irreproducible retention, due to small (1) Radke, M.; Willsch, H.; Welte, D. H. Anal. Chem. 1984, 56, 2538-2546. (2) Popl, M.; Dolansky, V.; Mostecky, J. J. Chromatogr. 1974, 91, 649-658.
changes in the water content of the nonpolar mobile phase and the possibility of irreversible adsorption, has, however, limited the applicability of this adsorbent for routine analysis. In recent years, many papers have focused on the use of polar, chemically bonded phases as alternative adsorbents for ring-class separations. Several adsorbents have been evaluated, including silica-bonded alkylamine (sili~a-RNH~),4-~ alkyldiamine (sili~a-R(NH~)~),'*~J~ alkanenitrile ( ~ y a n o ) , ' J ~alkanediol,14 -~~ alkylphenyl,14 ni(3) Snyder, L. R. Anal. Chem. 1961,33, 1527-1534. (4) Wise, S. A.; Cheder, S. N.; Hertz, H. S.; Hilpert, L. R.; May, W. E.Anal. Chem. 1977,49, 2306-2310. (5) Grizzle, P. L.; Sablotny; D. M. Anal. Chem. 1986,58,2389-2396. ( 6 ) Oetman, C. E.; Colmsje, A. L. Fuel 1989,68, 1248-1250. (7) Chmielowiec, J.; George, A. E. Anal. Chem. 1980,52 1154-1157.
(8) Boduezyneki, M. M.; Hurtubise, R. J.; Todd, W. A.; Silver, H. F. Anal. Chem. 1983,55, 225-231. (9) Grizzle, P. L.; Thomson, J. S. Anal. Chem. 1982,54, 1071-1078. (10) George, A. E.; Beshai, J. E. Fuel, 1983, 62, 345-349. (11) Bollet, C.; Escalier, J.4.; Souteyrand, C.; Caude, M.; Rosset, R. J . Chromatogr. 1981,206,289-300. (12) Robinson, S. C. F. Chromatographia 1979, 12, 439-442.
0887-0624/90/2504-0608$02.50/0 0 1990 American Chemical Society
Characterization of N o r t h S e a Petroleum Fractions
trophenyl,15 sulfonic acid,15 pyrollidone,16 and organomercury." Thomson et al.18 compared different chargetransfer bonded phases, like 3-(2,Cdinitroanilino)propylsilica. The retentive properties of these adsorbents toward polycyclic aromatic HC (PAH)have been studied, and they show varying degrees of sensitivity to aromatic structure, alkyl substitution, and steric effects. Most of them offer satisfactory separation of aromatics according to number of aromatic rings, or more specifically the number of aromatic carbons, but the alkylamine or -diamine phases seem to have most widespread use today. Miller,14however, concluded in a comparative study that a dual-functional alkanenitrile-secondary alkylamine phase was superior with respect to selectivity toward aromatics. This phase has also been used by other^.'^,^^ In the present work an aminopropylsilane (silica-RNH,) phase has been used. The major advantage of the chemically bonded stationary phases over the classical alumina is less sensitivity to changes in moisture content of the mobile phase. Moreover, the chromatographic system can be operated without the need for gradient elution. A certain disadvantage of the amino bonded phases is their relatively low retention strength compared to most of the others. This may give somewhat increased cross-contaminationbetween ring-class fractions, particularly when broad, complex distillates or residues are analyzed. Analysis of aromatics and alkylated derivatives in petroleum and geological samples has received much attention in recent years. The aromatic content of a crude oil and the distribution of aromatic classes and single compounds are determined by a combination of several factors, such as source material, thermal maturation, biodegradation, and water washing. Each of these factors influences the aromatic constituents (and also the saturates) in various, more or less specific ways. For example, the relative abundance of thermally less stable a-substituted isomers and more stable &isomers changes with increasing maturity. Numerous papers have dealt with the use of aromatic compounds as indicators of m a t ~ r i t y , , l -bio~~ degradation, et^.^^ Furthermore, the gas and liquid chromatographicanalyses of particular classes of aromatics have been treated: Alkylnaphthalenes,2628 alkylbiphenyls,29 diaromatics in genera1,30-32 alkyl(13)Crowley, R. J.; Siggia, s.;Uden, P. C. Anal. Chem. 1980, 52, 1224-1228. (14)Miller, R. Anal. Chem. 1982,54,1742-1746. (15)Matsunaga, A. Anal. Chem. 1983,55,1375-1379. (16)Mourey, T. H.; Siggia, S.; Uden, P. C.; Crowley, R. J. Anal. Chem. 1980,52,885-891. (17)Chmielowiec,J. 3.Chromatogr. Sci. 1981,19,296-307. (18)Thomson, J. S.;Reynolds, J. W. Anal. Chem. 1984,56,2434-2441. (19)Killops,S. D.; Readman, J. W. Org. Geochem. 1985,8(4),247-257. (20)Killops, S.D. HRC & CC, High Resolut. Chromatogr. Chromatogr. Commun. 1986,9,302-303. (21)Alexander, R.; Kagi, R. I.; Rowland, S. J.; Sheppard, P. N.; Chirila, T. V. Geochim. Cosmochim. Acta 1985,49,385-395. (22)Radke, M.; Welte, D. H.; Willsch, H. Geochim. Cosmochim.Acta 1982,46, 1-10. (23)George, A. E.; Bauerjee, R. C.; Smiley, G. T.; Sawatzky, H. Bull. Can. Pet. Geol. 1977,25(5),1085-1096. (24)Radke, M.; Welte, D. H. In Advances in Organic Geochemistry 1981; Bjor~y,M., et al., Eds.; Wiley: Chichester, 1983; pp 504-512. (25)Volkman, J. K.; Alexander, R.; Kagi, R. I.; Rowland, S. J.; Sheppard, P. N. Org. Geochem. 1984,6,619-632. (26)Rowland, S. J.; Alexander, R.; Kagi, R. I. J. Chromatogr. 1984, 294,407-412. (27)Mutton, I. M. J. Chromatogr. 1979,172,438-440. (28)Duswalt, J. M.; Mayer, T. J. Anal. Chem. 1970,42,1789-1794. (29)Cumbers, K. M.; Alexander, R.; Kagi, R. I. J. Chromatogr. 1986, 361,385-390. (30)Mair, B.; Mayer, T. J. Anal. Chem. 1964,36,351-362. (31)Yew, F. F.-H.; Mair, B. Anal. Chem. 1966,38,231-237. (32)Triska, J.; Kriz, J.; Kuras, M.; Adamcova, E.; Brezina, M.; Vodicka, L. Fresenius Z . Anal. Chem. 1982,311,696-697.
Energy & Fuels, Vol. 4, No. 5, 1990 609
phenanthrene^,^^-^ and aromatic HC in crude oils in general,B~lB~379B Characterization of North Sea crude oils in terms of saturate/aromatic distribution, density, and molecular weight as functions of carbon number in the 150-450 "C boiling point range was dealt with in a previous paper.40 In the present paper, the ring-class distribution of aromatics as a function of carbon number in the same boiling point range is discussed. Ring-class separation of aromatic carbon number fractions has been conducted by semipreparative HPLC with off-line GC quantitation. This method has been compared to alternative methods of quantitation: gravimetry and GC/MS. Use of UV-absorption detection with response factors has been evaluated and compared to gravimetry. In addition to the quantitative work, the retention characteristics of different aromatics on the aminopropylsilane column has been studied and single compounds in aromatic subfractions have been identified by GC (spiking with standards), GC/MS, and use of published retention data. Experimental Section Samples Studied. Aromatic carbon number fractions C!, through Cm from a moderately biodegraded North Sea crude oil were prepared by distillation and preparative liquid chromatography, as described in a previous paper.a In addition, CI4and CISaromatic fractions from 12 other North Sea oils, prepared in the same way, have been analyzed. Physical and chemical properties of these oils are found in ref 40. The same numbering of the oils is used in this paper. T h e carbon number fractions were collected between the boiling points of n-alkanes and are designated by C, where n represents the highest boiling n-alkane in the fraction. T h e oils investigated cover a wide spectrum of different North Sea crude oils and condensates found on the Norwegian continental shelf. A Cl0+ aromatic fraction was fractionated into mono-, di-, and tri- tetraaromatics and analyzed by GC and GC/MS for single compound identification. Semipreparative Liquid Chromatography. Aromatic carbon number fractions were separated according to number of aromatic rings by using the following chromatographic system: pump, Waters Associates Model 590, dual reciprocating; detector, Waters Model 490 UV detector monitoring at 254 nm; column, Waters Energy Analysis, aminopropylsilane chemically bonded to 10-rm fully porous silica particles, 300 mm X 7.8 mm i.d., t o = 3.65 min (determined by injecting pentane in hexane with RI detector), N = 10900 (Nes= 2100) for k' = 0.789 (biphenyl) and N = 9900 (Nes = 4100) for k' = 1.77 (phenanthrene); injection, loop injector (Rheodyne Model 7125) with 1OO-rL loop, approximately 30 mg/mL samples injected; mobile phase, hexane (Fisons HPLC grade) passed through a 500 mm X 23 mm i.d. drying column filled with ICN Alumina B-Super I in front of the separation column; flow rate, 3.0 mL/min; temperature, ambient; data acquisition and handling, Nelson Model 763 intelligent interface in combination with Nelson 3000 series chromatography software run on an IBM PC/AT computer. Areas were determined by slice integration. Fractions were collected according to cut points established by injecting standard compounds (see
+
(33)Ewald, M.; Lamotte, M.; Garrigues, P.; Rima, J.; Veyres, A.; Lapouyade, R. In Advances in Organic Geochemistry 1981;Bjoroy, M.,et al., Eds.; Wiley: Chichester, 1983;pp 705-709. (34)Garrigues, P.; Parlanti, E.; Radke, M.; Bellocq, J.; Willsch, H.; Ewald, M. J . Chromatogr. 1987,395,217-228. (35)Schomburg, G.; Weeke, F.; Schaefer, R. G. HRC & CC, High
Resolut. Chromatogr. Chromatogr. Commun. 1985,8,388-390. (36)Radke, M.; Willsch, H.; Garrigues, P.; de Sury, R.; Ewald, M. Chromatographia 1984,19,355-361. (37)Garrigues, P.; de Sury, R.; Angelin, M. L.; Ewald, M.; Oudin, J. L.; Connan, J. Org. Geochem. 1984,6,829-837. (38)Poirer, M.-A,; Das, B. S. Fuel 1984,63,361-367. (39)Rawasmany, V.; Kumar, P.; Gupta, P. L. Fresenius 2. Anal. Chem. 1984,317,37-41. (40)Ronningsen, H. P.; Skjevrak,I.; Osjord, E. H. Energy Fuels 1989, 3,144-755.
Rmningsen and Skjeurak
610 Energy & Fuels, Vol. 4, No. 5, 1990 Table 11). Because of minor variations in the activity of the adsorbent, the standard mixture was run regularly to adjust the cut points. However, during a 3-month period the retention time of benzo[a]pyrene (k'= 5.86) varied by less than 1.5%. Model compounds were run in triplicate to determine capacity factors and retention indices. Prior t o GC quantitation, most of the hexane was removed from the collected fractions by gentle nitrogen flushing and slight heating for fractions above C14. Fractions prepared for weighing were generally based on eight to ten injections. Quantitation of Aromatic Subfractions with Off-Line GC. An exact amount (2-4% by weight) of toluene (dissolved in hexane) was added as an internal standard (ISTD) in each subfraction. The fractions were then analyzed with the following chromatographic system: Gas chromatograph, Perkin-Elmer Sigma 2000; column, Chrompack CpSil5, 25 m x 0.22 mm i.d., 0.13-pm film thickness; carrier gas, helium; flow rate, 1.2 mL/min (linear velocity 38.0 cm/s) at 120 "C; injection, splitless 30 s a t 300 OC, 1.0 pL injected; temperature program, 25 OC isothermal 4 min, 10 "C/min to 100 "C, 7 "C/min to 300 "C; detector, FID, 350 "C; data acquisition and handling, Perkin-Elmer Sigma 15 connected to a Model 3600 chromatography data station. The total area of the fractions was corrected with an average blank run, and the weight was calculated by an ISTD calculation. Response factors were not used. The weight percents of the subfractions were normalized to 100%. The repeatability and accuracy of the combined LC/GC method is discussed in a later paragraph. On-Line HPLC/GC. (1) HPLC: pump, ISCO pLC-500 microflow syringe pump; detection, Waters Model 490 UV detector monitoring at 254 nm; column, silica-NH2 (Scientific Glass Engineering), 5 p m particles, 15 cm X 2 mm i.d.; injection, Rheodyne Model 7410 injector with 1-pL-loop disk, 4.7 pg/pL injected; mobile phase, pentane, Rathburn HPLC grade; flow rate, 100 pL/min. A VICI N4W 4-port switching valve was used to direct the effluent into an on-column injection syringe via a 0.17-mm-o.d. deactivated fused silica capillary. (2) G C column, BP1 (Scientific Glass Engineering), 25 m X 0.32 mm i.d., 0.50-pm film thickness; carrier gas, helium; flow rate, 6.0 mL/min a t 100 "C; injection, on-column, temperature programmed from 50 t o 100 "C at 20 "C/min, 100 or 150 p L injected into a 2 X 5 m retention gap (deactivated fused silica, 0.20-mm i.d.); temperature program, 45 "C isothermal 5 min, 15 "C/min to 160 "C, 4 "C/min to 210 "C, 15 "C/min t o 300 "C; detector, FID, 300 "C; integrator, PerkinElmer LCI-100. Preparative Liquid Chromatography. Separation of a Clo+ aromatic fraction according t o ring number was conducted on a preparative liquid chromatographic system (Waters, Model LC 500 A) with a radial compression column (300 mm X 57 mm i.d., PrepPAK NH2, 55-105-pm porous particles, Waters Associates) and a built-in refractive index detector. Separation conditions: mobile phase, hexane (Rathburn, HPLC grade); flow rate, 250 mL/min. Fractions were collected according to retention times of injected standards: saturates (residual), 2.00-2.92 min; monoaromatics, 2.93-3.67 min; diaromatics, 3.68-6.50 min; triaromatics peri-condensed tetraaromatics, 6.50-11.30 min; kata-condensed tetraaromatics, 11.30-16.50 min; pentaaromatics, backflushed. Hexane was removed in a rotary evaporator and with nitrogen flushing. As seen in Figure 7, a considerable overlap between fractions resulted on the preparative column, hence triaromatics and peri-condensed tetraaromatics were collected together, and this fraction also contained some kata-condensed tetraaromatics. Gas Chromatography. The whole Clo+ saturate and aromatic fractions and aromatic subfractions were analyzed by capillary gas chromatography. Chromatographic system and conditions: gas chromatograph, Varian Vista 6000; column 1, Chrompack CpSil5 CB (10070 dimethylpolysiloxane), 25 m X 0.25 mm i.d., 0.12-pm film thickness, N = 105000 (NeR= 67800) for k' = 4.09 (n-C13), = 505; column 2, Chrompack CpSil 8 CB (5% phenylpolysiloxane, 95% methylpolysiloxane), 25 m X 0.25 mm i.d., 0.12-pm film thickness, N = 83900 (Neff= 55500) for k ' = 4.36 (n-C13), p = 479; carrier gas, helium; flow rate, 0.63 mL/min (column 1) or 0.59 mL/min (column 2); linear gas velocity; 21.3 cm/s (column 1) or 20.2 cm/s (column 2) at 100 "C; injection, split, 0.1 pL injected; split ratio, 1:140 (column 1)or 1:97 (column
+
p
2); temperature program A, 10 "C isothermal 2 min, 4 OC/min to 85 "C, 6 "C/min to 240 "C, 15 "C/min to 300 "C; temperature program B, 15 "C/min from 10 to 100 "C, 2 "C/min to 250 "C, 15 "C/min to 300 "C; detector, FID, 320 "C. T o illustrate the stability of the GC system, the retention time of phenanthrene ( t =~ 36.29 min) varied by less than 0.5% during a 3-month period. Retention times and indices were determined as averages of three injections. The retention index system proposed by Lee e t al.41 for temperature-programmed GC was used: IG(X)
= lW[(tR(X)- tR(h$/(tR(N+l) - tR(N))I + 1OoN
(1)
where N a n d N + 1 refer t o aromatic standards eluting before and after compound X, respectively. N = 1 ( I = 100) for benzene, N = 2 (I = 200) for naphthalene, N = 3 (I = 300) for phenanthrene, N = 4 ( I = 400) for chrysene, N = 5 ( I = 500) for picene. Gas Chromatography/Mass Spectrometry. For quantitation of aromatic subgroups, a VG TS-250 double focusing mass spectrometer was used. The method, which is a modified version of ASTM D2425, has been described p r e v i o u ~ l y . Aromatic ~~ carbon number fractions were analyzed instead of unseparated fractions to avoid interference between certain aromatics and saturates. Experimental conditions: gas chromatograph, H P 5890, splitless injection a t 300 "C; column, Chrompack CpSil 5 CB; temperature program, 60 OC isothermal 2 min, 5 "C/min to 300 "C; interface temperature 280 O C . MS conditions: accelerating voltage, 4 kV; ionization potential, 70 eV; resolution, 500; scan range, 50-450; ion source temperature 220 O C ; scan speed, 1s/scan. This GC/MS system was also used for identification of some compounds. In addition, a VG 7250 HS double focusing mass spectrometer was used for identification purposes.
Results and Discussion Retention Characteristics of Aromatic Hydrocarbons on the Aminopropylsilane Stationary Phase. Several studies on structure, substituent, and steric effects on the retention characteristics of aromatic HC on amino bonded phases have been published: on pBondapak NH2,4,8Nucleosil NH2,15Waters Energy Analysis,42LiChrosorb NH,,' and Chromegabond diamine.5-7 As discussed in detail by Grizzle and Sablotny? quite significant variations in retention strength and selectivity have been observed between silica-RNH2 and s i l i ~ a - R ( N H ~but )~, also between columns containing the same adsorbent from different manufacturers and even columns from the same manufacturer. Such differences are likely to be related in part to the amount of residual silanol groups. Felix et recently reported on the use of a homemade silica-RNH2 bonded phase with a high degree of end-capping that had substantially different selectivity characteristics as compared to a commercial phase. For example, long alkyl chains on benzene retarded elution and hence promoted a better resolution of olefins, which are present in gasoline, and monoaromatics. In view of these facts, it was necessary to carry out an examination of the retentive properties of the particular silica-RNH2 bonded phase used, to be able to establish cut points between aromatic ring class fractions accurately and assess possible cross-contaminationbetween fractions. A series of model compounds were selected so as to provide a range of paraffinic, naphthenic, and unsubstituted aromatic HC encountered in fossil fuel, as well as compounds with dual functions, i.e., alkylaromatics, alkylnaphthenes, and naphthenoaromatics. Capacity factors, k' = tR - t o / t o ,and retention indices were calculated for ~~
(41)Lee, M. L.; Vassilaros, D. L.; White, C. M.; Novotny, M. Anal. Chem. 1979,51,168-174. (42)Dark, W . A. J. Liq. Chromatogr. 1982,5(9), 1645-1652. (43)Felix, G.;Thoumazeau, E.; Colin, J.-M.; Vion, G . J. Liq. Chromatogr. 1987,10(10), 2115-2132.
Characterization of North Sea Petroleum Fractions each model compound. The retention index under isocratic conditions, ZL(x), is given by2 log zL(X) = log I N + [(log tR(X)’- log tR(M’)/(log tR(N+l)’- log tR(N)’)I (2) where N and N + 1 refer to standard compounds eluting before and after compound X (Z = 10 for benzene, Z = 100 for naphthalene, Z = 1000 for phenanthrene, Z = 10OOO for benz[a]anthracene). The retention indices for compounds eluting before benzene were calculated as if they eluted between benzene and naphthalene. Retention data of 49 compounds are summarized in Table I, and a chromatogram of 31 selected aromatics is shown in Figure 1A. The structure and numbering of aromatic molecules is shown in Figure 14. Fifteen monoaromatic compounds (i.e., with six aromatic carbons) with alkyl substituents of various number, lengths, positions, and branching as well as cycloalkyl substituents all had retention indices between 0.27 (1,3,5-triisopropylbenzene) and 1.14 (1,2,3,4-tetrahydronaphthalene). Futhermore, the large, mixed molecule dodecahydrotriphenylene had log Zx = 1.60, meaning that it eluted early in the diaromatic fraction, together with indene. Compared to benzene, all straight-chain substituents accelerated elution, more the longer the n-alkyl chain, at least up to n-pentadecylbenzene. It was further seen that polymethyl-substituted benzenes, such as 1,2,3,5tetramethylbenzene,were slightly retarded while larger substituents, such as isopropyl groups, gave highly accelerated elution. Naphthenic type substituents, both cyclohexyl and rings fused to the aromatic nucleus, such as in tetralin and indan, all were seen to increase retention. In dodecahydrotriphenylene the effect of three fused, saturated rings in fact exceeded the effect of the two extra unsaturated carbons in 1,2-dihydronaphthalene, although the retention on amino bonded phases is believed to be governed primarily by *-electron interactions. With the cut points used in the semipreparative fractionations (see Table 11), the dihydronaphthalenes were collected in the monoaromatic fraction. This was confirmed by GC/MS analysis of collected CIgmono-, di-, and triaromatic subfractions (see Table V). The above findings agree in general good with those of Grizzle and Thomsong and Wise et ala4for silica-RNH2 phases. It is here interesting to note the differences Grizzle and Thomson found between amino and diamine phases; e.g., 1,3,5-triisopropylbenzenewas more retarded than benzene on the diamine phase while it is highly accelerated on the amino phase. The general trend seen for the monoaromatics, namely, that alkyl substituents in general accelerated elution, was also seen for the condensed aromatics although the data are rather limited. Phenyl groups substituted adjacent to condensed ring junctions were seen to highly decrease retention compared to what could be expected on the basis of the number of aromatic carbons. For example, 1phenylnaphthalene (16 aromatic carbons) had retention similar to fluorene (12 aromatic carbons) and was hence collected in the diaromatic fraction. Similarly, 9phenylanthracene and 9,lO-diphenylanthracene were collected as tri- and tetraaromatics, respectively. This effect has been explained by Grizzle et al.9 as a result of nonplanarity of the aromatic molecules. An analogous effect was observed by the same authors for biphenyls substituted in the 2-position. On the other hand, a noncondensed triaromatic compound like p-terphenyl (1,4-diphenylbenzene) had a retention similar to the condensed phenanthrene. According to Chmielowiec,’ the ortho isomer is somewhat less re-
Energy & Fuels, Vol. 4, No. 5, 1990 611 Table I. Retention Characteristics of Some Aliphatic, Alicyclic, and Aromatic Hydrocarbons on Silica-RNH2 (Waters Energy Analysis) peak n0.O compoundb N6.2 C.,d k’e log Zi’ Aliphatics 0.008 n-cm n-C8 0.014 Alicyclics nonadecylcyclohexane cholestane
1
2
3
4 5 6 7 8
9 10 11 12 13 14 15 16 17 18 19 20
Monoaromatics 1,3,5-triisopropylbenzene 1,3-diisopropylbenzene 1,3,5-triethylbenzene n-pentadecylbenzene n-nonadecylbenzene n-decylbenzene n-octylbenzene n-butylbenzene isopentylbenzene toluene benzene 1,2,3,5-tetramethylbenzene cyclohexylbenzene indan 1,2,3,4-tetrahydronaphthalene Diaromatics 1,2-dihydronaphthalene dodecahydrotriphenylene indene I-methylnaphthalene naphthalene acenaphthene 4-pentylbiphenyl 4-ethylbiphenyl 4-methylbiphenyl biphenyl 9-ethylfluorene 9,10-dihydrophenanthrene fluorene 1-phenylnaphthalene acenaphthylene Triaromatics 2-tert-butylanthracene dibenzothiophene anthracene 3,6-dimethylphehanthrene phehanthrene 9-phenylanthracene 1,4-diphenylbenzene (p-terphenyl)
0.022 0.047 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
0.101 0.142 0.148 0.164 0.167 0.175 0.178 0.186 0.186 0.211 0.227 0.236 0.241 0.255 0.266
0.27 0.58 0.61 0.71 0.72 0.77 0.78 0.82 0.82 0.93 1.00 1.03 1.05 1.10 1.14
1 1 1 2 2 2 2 2 2 2 2 2 2 3 2
6 0.378 6 0.441 6 0.460 10 0.657 10 0.688 10 0.740 12 0.674 12 0.742 12 0.784 12 0.789 12 0.871 12 0.967 12 1.10 16 1.14 10 1.20
1.46 1.60 1.79 1.96 2.00 2.08 1.98 2.08 2.14 2.15 2.25 2.36 2.50 2.54 2.59
3 2 3 3 3 4 3
14 12 14 14 14 20 18
1.45 1.50 1.71 1.72 1.77 2.04 2.06
2.79 2.83 2.97 2.97 3.00 3.16 3.17
5 4 3 4 3 4
26 16 16 16 16 18
2.33 2.36 2.61 2.66 2.73 3.61
3.30 3.32 3.43 3.45 3.48 3.79
27 28 29 30
Tetraaromatics 9,lO-diphenylanthracene pyrene 1,2-benzofluorene fluoranthene 2,3-benzofluorene 9,10-dimethylbenz[a]anthracene naphthacene triphenylene benz [a ]anthracene chrysene
4 4 4 4
18 18 18 18
4.14 4.33 4.37 4.44
3.94 3.99 4.00 4.02
31
Pentaaromatics benzo[a]pyrene 5
20
5.86
g
21 22 23 24 25 26
a Refers to Figure 1A. *The ring-class designations refer to the LC fractions in which the compounds were collected. ‘Number of aromatic rings. dNumber of aromatic carbons. CCapacityfactor k’ = t R - to/t,,. /Logarithm (base IO) of retention index (eq 2). Z t R of reference compound benzo[a]chrysene was not measured; hence log I,, could not be calculated.
tarded than the meta and para isomers on silica-R(NH&. Good separation was achieved between peri-condensed
Rmningsen and Skjevrak
612 Energy & Fuels, Vol. 4, No. 5, 1990 1-
I
/
~
.
Ill,I
i
l
H
'I
t
i
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c
~-
Mono.aromatics Di-aromrtw
J L hi-aromatcs Figure 1. Separation of (A) aromatic standards and (B)CIS aromatic ring class subfractions from oil no. 1 on semipreparative silica-RNH,. 1, monoaromatics; 2, diaromatics; 3, triaromatics; 4-P, peri-condensed tetraaromatics; 4-K, kata-condensed tetraaromatics; 5+, pentaaromatics and higher. For identification of labeled peaks, see Table I. L
Table 11. Aromatic Subfractions Collected from the Semipreparative Silica-RNH, HPLC Column" fraction retention time interval, min monoaromatics diaromatics
triaromatics tetraaromatics (peri-condensed (kata-condensed
3.92-5.00 5.01-9.00 9.01-11.50 11.51-23.00 11.51-15.70) 15.71-23.00)
Conditions: See Experimental Section.
tetraaromatics, such as pyrene, and kata-condensed molecules of the chrysene type. Hence, two tetraaromatic subfractions could have been collected. However, in the quantitative work discussed later, all the tetraaromatics were collected in one common fraction. A heteroatom like sulfur appeared to increase retention slightly. Dibenzothiophene (DBT), as an example, eluted after its parent HC, fluorene. DBT was hence collected with the triaromatics (although its alkylated derivatives may have overlapped in part with the diaromatics) while fluorene was collected in the diaromatic fraction. It is further seen in Table I that the silica-RNH2 stationary phase gave a reasonably good separation between the last eluting saturated compounds, such as cholestane (a four-ring naphthene), and the earliest eluting monoaromatics, such as triisopropylbenzene. A certain overlap must, however, be expected for real samples containing a large number of isomers. The retention characteristics reported here in essence agree well with those reported by Dark4* for a smaller diameter column from the same
10
1:
44.7
I
Y
WPLI. (;I
15 IMNT [ I S CI-rllOMTEY
:R
:i
(mm)
rim
Figure 2. Off-line GC quantitation of CIS aromatic ring class subfractionswith intend standard (ISTD)using splitless injection and FID detection. (A) Monoaromatics; (B)diaromatics. manufacturer, but he observed generally somewhat lower retention. The higher capacity factors reported here could indicate either a higher retention strength of the stationary phase or lower moisture content in the mobile phase, both being advantageous with respect to reducing cross-contamination. In Table I it is indicated to which of the collected subfractions each compound belonged. As we recall from above, for some compounds the exact classification may be uncertain. Furthermore, there are, of course, numerous other possible structures that are likely to be present in crude oils in varying amounts. Evaluation of Methods for Quantitation of Aromatic Ring Class Distribution. 1. Off-Line GC. Aromatic fractions Clo through Ca were fractionated according to the cut points established by using standards and quantified off-line by cappillary GC with toluene added as internal standard to each subfraction after removal of the solvent. Gas chromatograms of the CI5 subfractions are shown in Figure 2 as a typical example. The weight of material was calculated from the total area assuming equal FID response for all aromatic compounds. This assumption is, of course, not strictly correct. Tong and K a r a ~ e found k ~ ~ a single characteristic FID response factor for a range of PAHs and alkylated PAHs with a standard deviation of 5.7%. However, toluene has a theoretical "equal per carbon" response which is between the highly alkylated aromatics (about 3% lower) and the unsubtituted, condensed aromatics (about 3 % higher). Hence, possible errors introduced by response differences are likely to be more or less cancelled out in complex mixtures. (44)Tong, H.Y.;Karasek, F. W.Anal. Chem. 1984,56,2129-2134.
Characterization of North Sea Petroleum Fractions Table 111. Repeatability of Combined HPLC/Off-Line GC Method for Quantitation of Ring-Class Distribution in Aromatic Fractions of Oil No. 1 aromatic fraction, normalized wt % of fraction monoditri- recovery,' % c 1 5
mean av dev from mean, % c16
mean av dev from mean, % ClB mean av dev from mean, %
55.6 56.4 56.6 56.2
0.7 52.6 50.0 53.5 52.0 2.6 53.8 54.8 54.3 0.9
44.4 43.6 43.4 43.8 0.9 47.4 50.0 46.5 48.0 2.8 38.1 37.5 37.8 0.8
Energy & Fuels, Vol. 4, No. 5, 1990 613 Table IV. Comparison of Different Methods for Quantitation of Aromatic Ring Class Distribution in Oil No. 1
fraction C1,
102.6 103.1 102.9
CIS 1
107.9 91.2 123.1 8.1 7.7 7.9 2.5
102.8 103.4
a Relative to amount injected in 100 pL, quantified by the same GC method as the subfractions.
The repeatability of the quantitation procedure was examined by running two fractions (Cl5and C16)in triplicate and one (Clg) in duplicate. The results are summarized in Table 111. Taking into account the several steps in the procedure, involving fractionation, solvent removal, and splitless GC sample introduction, the repeatability was quite acceptable. For some reason, the recovery, calculated by comparing added subfraction weights and the weight of material in 1OO-pL HPLC sample solution, quantified by the same ISTD GC procedure, was generally higher than 100%. This is believed to be due in part to inaccuracy in the HPLC injection and partly due to difficulties with integration of the more complex chromatograms of whole aromatic fractions. Hence the normalized weight distributions were likely not much affected by the recovery, as indicated by the C16 results, where the repeatability of the normalized distribution is reasonably good despite the highly scattered recoveries. The accuracy of a quantitation method has to be assessed by comparison with other accepted methods, of which gravimetry in this case is the most accurate. Ten injections of C1, and Clg fractions were made, collected subfractions were combined, solvent was removed, and subfractions were weighed. It is seen in Table IV that off-line GC results in both cases agreed with the gravimetric results within 2-490 relative, which is considered satisfactory. Although the off-line GC technique was used later, it was of some interest to evaluate two other methods of quantitation briefly as well, namely, GC/MS group type analysis and on-line HPLC/GC. 2. Gas Chromatography/Mass Spectrometry. The GC/MS method is a slightly modified version of ASTM D2425 and was in a previous paperq0 applied for PNA analysis of distillation fractions. It actually identifies "2" series of compounds, where 2 refers to the general hydrocarbon formula CnHzn+Z.The main groups of compounds in the series identified are listed in Table V. As indicated in the footnotes, some additional compound types may be present. It is seen in Table IV that the GC/MS data agreed reasonably well with gravimetric data for the CI4aromatic fraction (about 6.5% relative underestimation) but highly underestimated the monoaromatics (about 14% relative) in the Clg aromatic fraction. The observed discrepancies probably are due mainly to errors in the weighting elements of the correction matrix used in the calculations. This tendency to underestimate monocyclic aromatics has been confirmed by analyzing
method HPLC/off-line GC HPLC/on-line GC gravimetry GC/MS' HPLC/off-line GC gravimetry GC/MSb
aromatics, wt % monoditri59.8 62.0 57.3 53.5 54.3 54.9 47.1
40.2 38.0 42.7 45.9 37.8 38.3 48.9
0.0 0.0 0.0 0.6 7.9 6.8 4.0
'0.2% was identified as paraffins and 1.2% as naphthenes, but the results are normalized to the sum of aromatics. b0.5% paraffins and 4.0% naphthenes; the results are normalized to the sum of aromatics. Averages of two parallels (see Table V).
standard mixtures and appears to be a general flaw of this method. The repeatability of the method is seen in Table V to be good. In conclusion, this method is satisfactory for ordinary PNA analysis but has major drawbacks when applied to quantitation of aromatic subgroups, although it may be useful for comparison purposes. An advantage is, of course, that no prior LC fractionation is necessary. The detailed distribution of C19aromatic subgroups, as reported by the GC/MS method, is shown in Table V. In spite of the errors involved, the results clearly indicate the main groups of compounds in the different subfractions. Some observations are worth mentioning: (1)There was some cross-contaminationof monocyclic naphthenes in the mono- and diaromatic fractions. The high content of naphthenes in the triaromatic fraction seems suspect, although it was reproducible. (2) Dihydronaphthalenes were found exlcusively in the monoaromatic fraction. No indenes were present because they would have been collected with the diaromatics. (3) In the whole aromatic fractions, alkylbenzenes and alkylnaphthalenes were the most abundant mono- and diaromatic classes. However, in the C19diaromatic fraction analyzed, acenaphthenesl biphenyls were dominating because some of the alkylnaphthalenes were collected with the monoaromatics. 3. On-Line HPLC/GC (and SFC). On-line capillary GC is an attractive quantitation method because no solvent-removal step is involved. The main problem is, of course, the large injection volumes when conventional HPLC systems are applied for fractionation. This can, however, to some extent be overcome by using micro-LC or microbore-HPLC columns and long retention gaps in combination with on-column GC injection. This two-dimensional HPLC/GC technique has recently been applied for fractionation of gasolineqs@and kerosineldiesel fue1.4'~~ Applications of the technique in general have been reviewed by Davies et al.49 Figure 3 shows FID gas chromatograms of mono- and diaromatic subfractions separated on a microbore silica-RNHz HPLC column. Duplicate analyses gave 60.1 and 64.0% monoaromatics, respectively. It is seen in Table IV that the average result was about 3% (relative) higher than the off-line GC result (45) Munari, F.; Trisciani, A,; Mapelli, G.; Trestianu, S.; Grob, K., Jr.; Colin, J. M. HRC & CC, High Resolut. Chromatogr. Chromatogr. Com-
mun. 1985, 8, 601-606. (46) Duquet, D.; Dewaele, C.; Verzele, M. HRC & CC, High Resolut. Chromatogr. Chromatogr. Commun. 1988, I I , 252-256. (47) Davies, I. L.; Bartle, K. D.; Williams, P. T.; Andrews, G. E. Anal. Chem. 1988,60, 204-209. (48) Davies, I. L.; Bartle, K. D.; Andrews, G. E.; Williams, P. T. J. Chromatogr. Sci. 1988,26, 125-130. (49) Davies, I. L.; Markides, K. E.; Lee, M.; Raynor, M. W.; Bartle, K. D. HRC & CC, High Resolut. Chromatogr. Chromatogr. Commun. 1989, 12, 193-207.
Rsnningsen and Skjevrak
614 Energy & Fuels, Vol. 4, No. 5, 1990
Table V. Detailed Composition of C14and C19Aromatic Fractions and CI9Aromatic Subfractions” (in wt % ) from Oil No. 1 Determined by GC/MS CIg aromaticsc C1, aromatics‘ Zb C19monoClg diClg trihydrocarbon group 2 0.0 0.2 0.0 0.5 0.3 0.0 0.0 paraffins 4.2 4.0 4.0 1.1 9.5 0.9 1.2 0 monocyclic naphthenes 40.4 23.2 23.8 2.3 0.0 25.9 27.3 -6 alkylbenzenes 25.4 13.7 13.8 24.9 25.6 1.2 3.1 indans + tetralins -8 16.7 0.9 1.2 7.8 7.7 0.0 0.0 indenes + dihydronaphthalenes -10 -12 1.4 1.1 0.0 0.0 0.0 0.0 0.0 naphthalene -12 37.3 34.9 19.3 19.0 10.8 27.2 3.5 alkylnaphthalenes 17.5 17.3 -14 6.4 6.4 1.6 39.2 0.0 acenaphthenes + biphenylsd 25.6 1.7 1.4 10.5 10.3 0.0 acenaphthylenes fluorenese -16 0.0 -18 0.5 0.6 4.0 3.7 0.4 3.6 83.9 triaromatics
+
Analysis in duplicate. a From semipreparative LC NH2 fractionation. *Refers to the general hydrocarbon formula C,H2,+z contain, e.g., tetrahydrophenanthrenes and -anthracenes. e May also contain, e.g., dihydrophenanthrenes and -anthracenes.
I
A C14 MONO:: -e , -..
C14 DI-
lb
L
(min) 2‘0
Figure 3. On-line microbore HPLC fractionation/GC quantitation of C1,aromatic ring class subfractions using direct oncolumn injection with retention gap and FID detection. Gas chromatograms of (A) monoaromatics; (B)diaromatics.
and about 8% higher than the gravimetric result. Hence, a certain overestimation of the monoaromatics seemed to take place. However, a more extensive comparison of the two GC methods would have to be carried out to draw safe conclusions. But the on-line GC method is definitely an attractive alternative to the off-line method. An even more attractive separation/quantitation technique would be supercritical fluid chromatography (SFC) with a microbore amino HPLC column eluted with COz in combination with FID detection. This technique, which has been applied by, e.g., Lundanes and Greibrokkm and Norris51for saturate-aromatic-polar separations, involves
May also
neither solvent removal nor transfer of collected fractions between two chromatographic systems. It has not yet been tested on real petroleum samples in our laboratory. 4. UV Detection with Response Factors. This method has to be calibrated with an accepted method of quantitation, in order to calculate characteristic response factors. The method is discussed in a later paragraph. RingClass Distribution of Cloto CB Aromatics in a Biodegraded North Sea Crude Oil. Aromatic fractions Clo through CZswere first chromatographed qualitatively on the silica-RNH2 column with UV monitoring a t 254 nm. The chromatograms are shown in Figure 4, starting with Clo which contained monoaromatics (C3benzenes) only. The appearance of additional, higher molecular weight groups of aromatics with increasing carbon number can be followed. Table VI summarizes in which carbon number fractions different groups of compounds are encountered. The information in this table is based in part on comparison with the standard chromatogram (Figure 1)and partly on gas chromatography, because the elution order of aromatic hydrocarbons relative to n-alkanes on nonpolar stationary phases corresponds well with the boiling order during distillation (see discussion below). The same fractions (except four) were fractionated as described above and the subfractions quantified by off-line GC. The results are summarized in Table VII. Monoaromatics are seen to dominate betweed Clo and Cm while mono- and diaromatics constituted about equal parts (totally 80-90%) betweed CzOand CZ7. The main monoaromatic subgroup was alkylbenzenes, but also alkylindans and -tetralins were present in these fractions. Moreover, as seen in Table V, a certain amount of residual saturates, mainly monocyclic naphthenes, were present in the whole aromatic fractions and most of these seemed to be carried over with the monoaromatics. The complexity of the monoaromatic fractions is illustrated in Figure 5 with a C13fraction as an example. The molecular masses of the main peaks are listed. The m / z 148, 162, and 176 peaks are C5-, C6-, and C7-benzenes while the m/z 160 and 174 peaks are C3- and C4-indans/tetralins. Several compounds with different masses are seen to coelute, and in view of the huge number of possible isomers, numerous other compounds are likely to be present. C13is, in fact, among the simplest of the monoaromatic fractions. Figure 10 shows a gas chromatogram of a Clo+ monoaromatic fraction with some of the most abundant compounds labeled (see Table XI11 for identification). Most of the labeled peaks were alkylbenzenes, but three large peaks (no. 42,47 and 56) eluting between n-Clz and n-C14 (50) Lundanes, E.; Greibrokk, T. J . Chromatogr. 1985,349,439-446. (51) Norris, T. A.; Rawdon, M. G. Anal. Chem. 1984,56, 1767-1769.
Energy & Fuels, Vol. 4, No. 5, 1990 615
Characterization of North Sea Petroleum Fractions 0
5
10
15
20
10
5
10
25(mk)30
0
5
10
20
5
0
25 Ink) 30
10
1
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20
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5
25 frh)30
lo
15
20
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15
25 lml 30
20
0
5
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5
10
15
20
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5
c19
15
25 Wl) 30
20
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i
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0
c27
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15
io
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15
20
25 fnk)30
20
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10
20
. 5
5
25 fml 30
MTHYLPHXNANTMENS
'13
0
20
R
C18
r 0
0
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i'
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25 fmkl 30
'24
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o
20
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15
10
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5
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20
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0
15
0
5
10
15
20
25 (ml 30
25 f"Ll 30
C28
0
5
10
15
20
25 fm)30
h
b 0
5
10
15
20
c22
25 (mn) 30
3 2 '
'16
?: :
Figure 4. Aromatic carbon number fractions chromatographed on silica-RNH2 column with W detection at 254 nm. 1, monmmatics; 2, diaromatics; 3, triaromatics; 4-P, peri-condensed tetraaromatics; 4-K, kata-condensed tetraaromatics; 5, pentaaromatics.
were identified as alkylindans. Above CI5three homologous series (XI Y, and Z) of alkylbenzenes are seen to be
present, of which the Y series was the n-alkylbenzenes (base peak m / z 92 in mass spectrum). The X-series com-
616 Energy & Fuels, Vol. 4, No. 5, 1990 Table VI. Main Groups of Aromatic Compounds in the Different Carbon Number Fractions' fraction subfraction compound type MWb monobenzene 78 92 monotoluene monoxylenes 106 monoC3-benzenes 120 C4-/C5-benzenes 1341148 monoindanlmethylindans 1181132 indene di116 C5-1C6-benzenes mono1481162 1461160 C2-1C3-indans di128 naphthalene mono1621176 CG-/C7-benzenes 1601174 CS-lC4-indans di142 methylnaphthalenes mono1761190 C7-/C8-benzenes 1741188 C4-1C5-indans di156 C2-naphthalenes 154 biphenyl 152 acenaphthylene 1901204 C8-/CS-benzenes mono170 diC3-naphthalenes 168 methylbiphenyls 154 acenaphthene 2041218 C9-1C10-benzenes monodiC4-naphthalenes 184 182 C2-biphenyls 166 fluorene 2181232 ClO-/Cll-benzenes mono198 C5-naphthalenes di196 C3-biphenyls 1801194 methyl-/CZ-fluorenes 184 dibenzothiophene tri212 C6-naphthalenes di210 C4-biphenyls C3-fluorenes 208 178 phenanthrene tri198 methyldibenzothiophenes di226 C7-naphthalenes 224 C5-biphenyls C4-fluorenes 222 tri192 methylphenanthrenes phenylnaphthalene 204 C8-naphthalenes di240 C2-phenanthrenes tri206 218 methylphenylnaphthalenes 202 tetrafluoranthene tri220 C3-phenanthrenes 202 tetrapyrene 216 methylfluoranthenes 2201234 C3-1C4-phenanthrenes tri216 methylpyrenes tetrabenzofluorenes 216 C4-1C5-phenanthrenes tri2341248 230 tetraC2-pyrenes/fluoranthenes tetrabenz[a]anthracene 228 228 chrysene triphenylene 228 methylchrysenes etc. tetra242 penta252 benzo[a]pyrene 252 per y1ene 276 hexabenzo[ghi]perylene a As collected between successive n-alkanes; see definition in Samples Studied paragraph. *Molecular weight.
pounds (base peak m/z 106) probably have a methyl group branching in the a-position, and the Z-series compounds (base peak m/z 105) probably have a methyl substituent in addition to a straight chain alkyl substituent. The subscripts indicate the number of carbon atoms in the substituents. Usually the most abundant single monoaromatic compound is toluene. It occurs in the CBfraction and constitutes more than 2% by weight of some light North Sea oils and condensates. It is seen in Table VI11 that oil no. 1 used in this study contained 0.60% toluene and 1.31%
Runningsen and Skjeurak Table VII. Ring-Class Distribution of Aromatics in Carbon Number Fractions from Oil No. la aromatic fraction,b wt % carbon no. monoditritetra10 100.0 11 92.5 7.5 12 85.9 14.1 13 60.5 39.5 14 59.8 40.2 15 56.2 43.8 52.0 48.0 16 17 56.5 41.8 1.7 18 56.5 39.2 4.3 19 54.3 37.8 7.9 20 47.2 42.9 8.5 1.4 21 c 22
47.9
44.3
6.1
1.7
23c 24 25 26 27
43.0 35.4 40.8 45.6
46.0 43.9 42.1 32.5
10.0 12.9 7.4 10.9
5.0 7.8 9.7 11.0
a Determined by combined HPLC separation and off-line GC quantitation. Normalized to 100%. Not analyzed.
of the three xylene isomers together (in C9). The monoaromatic content, as a percentage of whole crude, is seen to decrease gradually from Cs to Czs. The decrease in relative monoaromatic content from 100% to about 40% corresponded with the progressive appearance of di-, tri-, and tetraaromatics. The diaromatics first appeared in the Cll fraction. This was mainly cross-contamination of naphthalene from CI2, where the major part of naphthalene occurred, in agreement with the GC elution order. The C13 diaromatics are methylnaphthalenes exclusively. The subsequent classes of alkylnaphthalenes overlap with biphenyls/ acenaphthylenes (from C14) and fluorenes (from c16). The relative, total diaromatic content is seen in Table VI1 to be constant about 40-45% from C13 to c26, while the diaromatics as a percentage of whole oil are seen in Table VI11 to reach a peak in C16 to c16 (mainly C3- and C4naphthalenes) and decrease slowly from there on. Some of the most abundant diaromatics are labeled in Figure 11. A high degree of coelution certainly occurs above CIS. Hence, only the positions of some trimethylnaphthalenes (TMN) are indicated, because the peaks identified as C3-naphthalenes may well contain other trimethyl isomers as well as propyl- and ethylmethylnaphthalenes. Alexander et a1.21have proposed to use several ratios between DMNs and TMNs as indicators of thermal maturity, the argument being that the DMN and TMN isomers with the highest degree of a-substitution, such as l,&DMN, are less stable and consequently most susceptible to changes as a result of thermal influence. One advantage is that the DMNs and TMNs undergo a regular change through the region of the oil window while other maturity indicators, such as C-20 epimer ratios of ethylcholestane, have narrower dynamic ranges. The triaromatics first appeared in CI7 as dibenzothiophene (DBT) and some cross-contamination of phenanthrene (P) from C18. Methylphenanthrenes (MP) were found in Cls, C2-Ps mainly in Cmand C3-Ps mainly in Czl. In these fractions phenylnaphthalenes also occurred. In the Clo+tri- + tetraaromatic fraction shown in Figure 12, 1-phenylnaphthalene (peak no. 92) was in fact more abundant than the MPs. C2-Ps have been analyzed in great detail by Garrigues et a1.34and Radke et al.,24*36 and ratios involving C2-Ps as well as MPs are considered to have geochemical significance similar to the DMN and TMN ratios. In Figure 13, which shows a segment of
Energy & Fuels, Vol. 4, No. 5, 1990 617
Characterization of North Sea Petroleum Fractions
1624 1598
I
Scan no.:
mlz
1413 1426 1444 1446 1461 1473 1401 1491 1500 1515 1529 1539 1551 1564 1576 1590 1607 1624 1650 1676 1668
162 146 1621160 1621160 1621174 162 146 162 162 162 16011621174 1481162 14611621174 1601176 16Ql174 160 174 1601176 1501176 16011741176 1741176
1
1500 15
1
1491
1
'S I
in
1.
in
I I
I(.
IP
im
im
in
Scan no.
Figure 5. Detailed gas chromatogram (totalion monitoring) of CI3monoaromatics and molecular masses of the main peaks obtained by GC/MS. Table VIII. Detailed Composition of Biodegraded North Sea Crude Oil (Oil No. 1) Based on Capillary GCP Distillation,b Preparative LC.' and Combined LC/GCd whole fraction saturateah aromatics aromatic subgroup, wt % C. wt %' MWf d wt % MW d wt % MW OB monoditritetra0.88 58.0 0.567 0.88 58.0 0.567 0.75 0.674 0.75 83.5 0.674 83.5 2.50 91.7 0.742 2.44 92.1 0.740 0.06 78.1 0.884 0.06 4.20 107.5 0.753 0.60 92.1 0.871 0.60 105.0 0.768 3.60 124.6 3.87 117.7 0.793 2.56 0.757 1.31 106.2 0.872 1.31 87.80 296 0.904 46.62 37.23' 2.93 132 0.808 1.99 138 0.785 0.94 120 0.850 0.94 3.23 0.796 134 0.79 148 0.815 2.38 153 0.85 0.858 0.06 2.98 159 0.836 2.12 167 0.811 0.86 145 0.892 0.74 0.12 3.73 172 2.64 0.818 1.09 153 0.66 0.43 0.850 182 0.933 3.58 185 0.861 2.42 196 0.826 1.16 165 0.944 0.69 0.47 2.27 212 0.834 1.32 177 0.949 0.74 0.58 3.59 197 0.873 3.05 0.882 1.87 222 0.838 1.18 188 0.957 0.61 0.57 209 2.19 242 1.20 3.39 227 0.873 0.834 202 0.953 0.68 0.50 0.02 3.09 0.875 2.07 259 0.837 1.02 220 0.58 0.40 0.04 0.965 243 2.83 1.84 254 0.885 270 0.843 0.99 230 0.54 0.37 0.08 0.973 55.23 461 0.934 24.83 26.62 2.79 1.14 241 0.10 0.01 262 0.903 1.65 282 0.855 0.983 0.54 0.49 2.23 1.34 281 0.898 298 0.849 0.978 0.89 256 1 1 j 1 293 0.898 0.851 0.46 2.45 0.96 266 0.01 1.49 314 0.978 0.43 0.06 2.09 1.26 307 0.899 330 0.853 0.978 0.83 281 1 1 1 1 0.900 0.854 2.12 0.01 1.28 320 335 0.977 0.36 0.39 0.08 0.84 294 1.94 1.13 333 0.905 356 0.862 0.978 0.81 306 0.29 0.36 0.10 0.01 1.75 346 0.907 1.02 370 0.859 0.980 0.73 308 0.05 0.07 0.30 0.31 2.11 0.10 0.09 361 0.910 1.22 383 0.865 0.974 0.89 329 0.41 0.29 2.06 0.920 1.23 0.874 374 0.83 335 394 0.988 1 1 1 1 2.03 381 404 0.978 0.920 1.26 0.881 0.77 359 1 1 1 1 33.86 624 0.953 11.95 17.93' a Below n-CB,i.e., C4 to CD.Determined by method described in ref 53. * Clo to (2%. For details, see ref 40. Saturatearomatic distribution. dAromatic ring class distribution. e Weight percent of whole stabilized oil. f Molecular weight determined by freezing point depression above Clo and from single compound molecular weights below Cl0. BDensity (g/cmg);calculated from single compound densities below Clo. hUp to Cal the saturates can be divided into paraffins and naphthenes; see ref 40 and discussion in text. 'In addition, 4.0% polars (resins) and 0.4% pentane insolubles. "Ringclasses not determined.
618 Energy & Fuels, Vol. 4, No. 5, 1990
R~nningsenand Skjeurak
Table IX. UV Response Factors and Relative Response of C14and CISMono-, Di-, and Triaromatics a t 254 nm response factor,' relative fraction wt %" UV area % b wt/area responsed 7.86 1.00 CI4mono57.3 7.61 92.39 0.435 18.1 CI4 di42.7 28.58 1.00 Clg mono54.9 1.90 36.10 1.047 27.2 CIg di38.3 62.00 0.127 263 C19tri6.8 a Gravimetric. bAt wavelength 254 nm. Based on gravimetric results and UV area percents of oil no. 1. UV area percents of other ring-class subfractions should be multiplied by these factors before renormalization. dRelative to the monoaromatics.
Table X. Comparison of HPLC-UV" and Gravimetric Quantitation of Ring-Class Distribution in Some C14and Cl0 Fractions aromatics, wt % monoditrioil no. fraction method 48.4 51.6 0.0 2 C14 HPLC-UV gravimetry 51.9 48.1 0.0 30.3 69.7 0.0 5 CL4 HPLC-UV 47.8 52.2 0.0 gravimetry 47.4 44.8 7.8 5 C1g HPLC-UV 50.0 42.9 7.1 gravimetry 41.7 58.3 0.0 9 CI4 HPLC-UV gravimetry 42.9 57.1 0.0 9 Cis HPLC-UV 42.6 41.5 15.9 _gravimetry 48.0 39.9 12.1 10 C,, HPLC-UV 75.3 24.7 0.0 82.5 17.5 0.0 gravimetry 11 C1g HPLC-UV 36.6 52.1 11.3 gravimetry 44.5 45.3 10.2
Table XI. RingClass Distribution of Aromatics in C14and CISFractions from Various North Sea Crude Oils C14 aromatics, wt% CISaromatics, wt % oil no. monodimonoditri1' 57.2 42.8 54.9 38.3 6.8 26 48.4 51.6 53.1 39.0 7.9 3b 52.4 47.6 53.3 39.1 7.6 46 62.2 37.8 5" 47.8 52.2 50.0 42.9 7.1 6b 44.5 55.5 44.1 48.0 7.9 7b 57.1 42.9 47.2 46.0 6.8 8b 58.4 41.6 48.9 44.8 6.3 9" 42.9 57.1 48.0 39.9 12.1 10" 82.5 17.5 11' 48.9 51.1 44.5 45.3 10.2 12b 53.1 46.9 51.3 41.7 7.0 13b 61.0 39.0 54.7 40.3 5.0 50.0 42.3 7.7 52.8d 47.2d mean std dev 6.4 6.4 3.8 3.3 1.9 Gravimetric results. Calculated from UV 254-nm area percents using response factors. 'Gravimetric results for C19 only. dOil no. 10 not included.
11
"The response factors in Table IX have been used to calculate weight percents for these oils.
d IC.
C2-NAPHTHALENES 4 1
BIPHENYL Di-aromatics
F i g u r e 7. Clo+ aromatic subfractions from preparative fractionation chromatographed on semipreparative silica-RNH2. These eing-class fractions were analyzed by capillary GC; see Figures 9-13.
n
I '
/
F
Figure 6. C,, aromatic fractions from six different oils chromatographed on the semipreparative silica-RNHp column: (A) oil no. 5;(B)oil no. 10; (C) oil no. 1 (used to calculate response factors); (D)oil no. 7; (E)oil no. 13; (F) oil no. 9. Note the different ratios between alkylnaphthalene and biphenyl areas, which in some cases makes use of UV response factors difficult.
Figure 12 in more detail, the elution order of 17 of the 25 possible DMP isomers on the nonpolar stationary phase is indicated. The positions of nine trimethyl isomers are indicated as well. They coeluted with 2,3-benzofluorene and some methylpyrenes/fluoranthenes. Below Czethe triaromatics never constituted more than about 12% of the aromatic fractions (about 0.10% of whole crude). Also the tetraaromatics constituted a rather small part, less than ll%,of the aromatic fractions below Czs and only about 0.01 ?& of whole crude. Fluoranthene is the earliest eluting four-ring compound. It occurred in the Czofraction, pyrene occurred in Czl, and the 1,2- and 2,3-benzofluorenes occurred in C,?. The kata-condensed four-ring compounds, such as chrysene, triphenylene, and benz[a]anthracene, first appeared in the Cz4fraction. The geochemical significance of alkylated chrysenes has been discussed by Garrigues et aL3' As seen in Figure 4, the first traces of pentacyclic aromatics appeared in Cm This corresponded well with the HPLC retention time of benzo[a]pyrene and also with its GC retention time (see Figure 9). On the nonpolar stationary phase, benzo[a]pyrene and perylene both more or
Characterization of North Sea Petroleum Fractions
Energy & Fuels, Vol. 4 , No. 5 , 1990 619
Table XII. Retention Behavior of Polycyclic Aromatic Hydrocarbons Relative to n -Alkanes on Two Stationary Phases" CpSil5 CB' CpSil8 CBd compound bPb tFle bPd A P tRe bPd A P 174 16.89 18.18 n-C10 196 20.88 22.19 n-C11 22.31 204.4 218 24.70 naphthalene 14 211.1 7 216 24.28 25.51 n-C,2 235 27.12 28.33 n-C13 241.1 256 biphenyl 27.96 15 30.18 248.3 8 270 29.46 acenaphthylene 252.1 32.01 18 262.2 8 29.60 253 30.83 n-C14 279 30.26 acenaphthene 21 258.2 31.87 271 33.13 n-cls 32.50 fluorene 277.1 34.85 294 17 284.0 10 33.97 287 35.25 n-Cl6 dibenzothiophene 35.93 303.9 333 29 35.94 303 37.27 nG7 36.29 phenanthrene 340 305.6 34 38.78 314.1 26 37.81 317 39.17 n-Cl8 39.59 331 40.98 n-C19 fluoranthene 41.06 375 43.80 342.2 33 352.4 23 41.29 344 42.71 n-CX 41.94 44 393 44.78 349.2 pyrene 360.0 33 357 42.92 44.38 n-Cz1 413 1,2-benzofluorene 46.30 43.48 371.8 361.3 52 41 413 43.70 2,3-benzofluorene 363.0 50 369 44.48 45.97 n-czz 381 45.98 47.41 n-C23 benz [alanthracene 435 387.9 47 46.83 448 46.99 389.2 chrysene 59 49.46 399.9 48 425 389.2 46.99 triphenylene 36 49.46 399.9 25 392 47.34 48.63 n-C24 402 48.48 49.68 n425 413 49.44 50.60 n-CZ6 423 50.28 51.48 n-CZ7 432 52.36 51.08 n-CZ8 441 51.88 53.02 n-Cz9 52.70 n-Cm 450 54.23 a Temperature program A (see Experimental Section). Atmospheric boiling point ("C).@ Dimethylsilicone phase. Methylphenylsilicone phase. e Retention time (min). 'Elution boiling point relative to n-alkanes (interpolated). RDifference between bp and bp,,.
less coeluted with n-C2&However, aromatic subfractions higher than CZ7were not quantified in this work. Table VI11 shows the detailed composition of oil no. 1 as determined by a combination of capillary GC, distillation, preparative LC, and semipreparative LC/GC. Oil no. 1is rather heavy, biodegraded oil with an aromatic content somewhat higher than most other North Sea oils. Of a total of 66.14 wt % below C30, 21.27wt 9'0 was aromatics of which 12.9 w t % was monoaromatics, 6.7 wt 9% diaromatics, 1.1 w t 5% triaromatics and only 0.5 wt % tetraaromatics. The aromatic ring class distribution must be expected to shift toward more condensed aromatics in the C30+ fraction, but the mono- and diaromatics probably contribute significantly up to quite high carbon numbers. The subdivision of saturates into paraffins and naphthenes could be obtained by GC/MS analysis or from empirical correlations based on the saturate density.40 Further information concerning ring-class distribution of the naphthenes is also achievable by GC/MS. This has been discussed in more detail in ref 40. Comparison of Different North Sea Oils Using UV Absorbance Chromatograms. The use of UV detection for quantitation of aromatic hydrocarbons is restricted due to the great differences in absorptivity between different compounds and in particular between groups of compounds with different degree of condensation. However, response factors characteristic of each class may be established. Rawasmany et al.39used UV response factors based on UV spectra of typical mono-, di-, and triaromatic compounds to calculate the ring-class distribution among gas-oil aromatics and Dark42used UV and refractive index response factors in SARA analysis of crude oils. A similar
technique was used by Cookson et al.53 for ring-class quantitation with refractive index detection. In the present work UV response factors at 254 nm were established by using the weight percents for oil no. 1 determined gravimetrically (see Table IV) and area percents determined by slice integration. The evaluation of the technique was limited to CI4 and C19 fractions. Response factors and relative responses for the aromatic subfractions are summarized in Table IX. Normalized area percents had to be multiplied by these response factors before renormalization. The relative responses between mono-, di-, and triaromatics in the CI9fraction agreed quite well with the gas-oil UV data reported by Rawasmany et al.39 To test the reliability of the method, the distribution of subfractions in a series of C,, and Clg aromatic fractions, calculated by using the response factors in Table IX, were compared to gravimetric data. The results are summarized in Table X. The calculated content of triaromatics generally agreed quite well with the gravimetric data. The monoaromatics were generally somewhat underestimated and the diaromatics correspondingly overestimated. A particular large error was observed for the C14 fraction of oil no. 5. This error illustrates a general problem with the UV method, especially for fractions containing relatively few compounds with highly different UV absorbance. As illustrated in Figure 6, the biphenyl area in the C14 fraction of oil no. 5 was much larger than that in oil no. 1, which (52) Osjord, E. H.; Ronningsen, H. P.; Tau, L. Aa. HRC & CC, High Resolut. Chromatogr. Chromatogr. Commun. 1985,8,683-690. (53) Cookson, D. J.; Rix, C.J.; Shaw, I. M.; Smith, B. E. J. Chromatogr. 1984,312, 237-246.
Ronningsen and Skjeurak
620 Energy & Fuels, Vol. 4, No. 5, 1990 n - alkane no.
13
14 I
15
16
I
I
17
19
18
I
I
20
A
12
13
14
15
18
17
18
19
20
Figure 8. Retention behavior of Clo+ diaromatic compounds relative to n-alkanes on (A) CpSil5 CB and (B) CpSil8 CB columns (see Table XII). Note that the aromatics are shifted toward a higher carbon number on the CpSil8 phase, without any significantly
improved resolution.
was used to generate response factors. And because biphenyl has a UV absorbance at 254 nm several times higher than the C2-naphthalenes, a small amount of biphenyl contributed with a disproportionately large fraction of the total diaromatic area, hence the large overestimation of the diaromatics. On the other hand, oil no. 9, which had a much smaller biphenyl area than oil no. 1, showed excellent agreement between LC-UV and gravimetric data. This indicated some additional factor that tended to overestimate the diaromatics (or underestimate the monoaromatics) systematically. In fractions with a large number of compounds, such as monoaromatic fractions, the differences in UV absorbance are likely to more or less cancel out. As seen in Table X, the calculated values in most cases were quite satisfactory,
at least for the purpose of rough comparison. The method could, of course, be further improved by using response factors based on several oils, etc., but if very accurate data are desired, one of the other quantitation techniques discussed above would have to be used anyway. Having concluded that this fast method, with its obvious limitations, is applicable for rough comparison of fractions, the response factors in Table IX were used to calculate ring-class distribution in CI4 and CIS fractions from 12 other North Sea oils. These results are summarized in Table XI. The distribution of mono- and diaromatics in CI4 fractions varied between 62-38 and 43-57 with one exception (oil no. 10). In view of the variety of different oil types studied, including “normal”, paraffinic oils (2,3, 11, and 121, aromatic, biodegraded oils (1 and 41, a na-
Characterization of North Sea Petroleum Fractions phthenic, biodegraded oil (13), a waxy oil (5), and condensates of paraffinic (9) and aromatic character (6), the variation was quite small. However, there appeared to be a slight tendency toward more monoaromatics in the biodegraded fractions (1,4, and 13). This tendency was further supported by the very high content of monoaromatics in the biodegraded condensate no. 10. The variation was even less among the 11 CISfractions. An average distribution of 50.0-42.3-7.7 wt 90,with absolute standard deviations amounting to 3.8-3.3-1.9 w t % only, could be calculated. The biodegraded oils seemed to have slightly more monoaromatics and less triaromatics, but the differences were nearly within experimental error limits. These findings are in good agreement with density measurements on aromatic fractions previously reporteda4 The density showed small variation among the different oils, indicating that the ring-class distributions were fairly similar. Gas Chromatographic Analysis of CIWAromatics. The CIWaromatic fraction from a North Sea crude oil was fractionated on a preparative silica-RNH2 column, and the mono-, di-, and tri- + tetraaromatic fractions were chromatographed on the semipreparative column (se Figure 7). The same fractions were analyzed qualitatively by capillary GC, primarily on a nonpolar dimethyl silicone stationary phase, but a methylphenyl silicone phase was also utilized for comparison. The identity of about 110 compounds were established definitely or tentatively by a combination of (1) spiking the oil fractions with pure standards, (2) GC/MS analysis to get molecular mass information, and (3) use of published retention data of alkylated benzene^^^-^^ and PAH compound^.^^ Furthermore, the retention behavior of about 65 additional compounds, which are known to be present in crude oils, was examined. They were not actually identified in the chromatograms, either because they coeluted with other compounds or because they were present in too small amount to be discerned from the unresolved envelope, but their positions in the chromatograms were determined The CIw saturate fraction was chromatographed as well, in order to relate the retention of the aromatics to n-alkanes. This is of interest because fractions between successive n-alkanes are used in the oil characterization. As mentioned above, on nonpolar stationary phases the elution order of aromatics relative to n-alkanes corresponds very well with the boiling order during TBP distillation, although it is well-known5' that, due to distillation, PAH compounds are present in fractions with end points considerably lower than the boiling points of these PAHs. This is illustrated in Table XII, which summarizes the retention behavior of several PAHs on the two stationary phases. As an example, chrysene has a boiling point comparableto n-Cm,while eluting between n-CDand n-CW On both phases there was a gradual increase in the difference, AT, between the actual boiling point and the GC elution boiling point relative to n-alkanes (bp,,,) with increasing molecular weight. AT was, however, generally smaller on the more polar phase because the aromatics were more retarded due to interactions with the phenyl (54) Kumar, B.; Kuchhal, R. K.; Kumar, P.; Gupta, P. L. J. Chromatogr. Sci. 1986,24,99-108. (55)Matisova, E.; Krupcik, J.; Cellar, P.; Kocan, A. J. Chromatogr. 1985,346,177-190. (56) Lubcek, A. J.; Sutton, D. L. HRC & CC, High Resolut. Chromatogr. Chromatogr. Commun. 1983,6, 328-332. (57)Gouw, T.H.;Jentoft, R. E. In Chromatography in Petroleum Analysis; Altgelt, K. H., Gouw, T. H., Eds.; Chromatography Science Series; Marcel Dekker: New York, 1979; p 318. (58)CRC Handbook of Chemistry and Physics, 58th ed.; Weast, R. C., Ed.; CRC Press: Boca Raton, FL, 1977-78.
Energy & Fuels, Vol. 4, No. 5, 1990 621 Bql'Cln..Urr
!I4
271
Y4
402
n.U.nno
10
15
20
25
ELnn4.M(.fl
*
e'Um
4W
*I3 34
I('Clrm 240 300
300
A
r-
Figure 9. Whole Clw aromatic fraction and ring-class subfractions chromawaphed on CpSil5 C B (A) Clw aromatic fraction; (B)Clo+ monoaromatics; (C) Cl0+ diaromatics; (D)Clq+ tri- + tetraaromatics. Temperature program A (see Experimental Section). For identification of labeled peaks, see Table XIII.
groups. The displacement of the diaromatics relative to the n-alkanes is illustrated in Figure 8. Each PAH is seen to be shifted to somewhat less than one carbon number higher on the CpSil8 phase. The relative retention of the aromatics was, however, more or less the same, and because of the complexity of the mixture, hardly any improved
Rsnningsen and Skjeurak
622 Energy & Fuels, Vol. 4, No. 5, 1990 n
io
. alkane no. 9
12
11
13
14
15
16
17
(8
19
20
21
~~
Relention lime (mm)
15
20
30
25
35
40
Figure 10. Details of G o + monoaromatics chromatographed on CpSil 5 CB, temperature program A. For identification of labeled peaks, see Table XIII. n - alkane no.
13
12
,Retention time (min)
14
15
30
25
17
16
35
18
19 40
20
21
22 i
55
Figure 11. Details of Clw diaromatics chromatographed on CpSil5 CB, temperature program A. For identification of labeled peaks, see Table XIII. Positions of some trimethylnaphthalenes are indicated below the chromatogram. overall resolution was achieved. It should here be remembered that even on the nonpolar phase, the retention of aromatics relative to n-alkanes can be changed slightly by manipulating the chromatographic conditions. Careful comparison of Figure 9D and Figure 12 shows that, e.g., fluoranthene (peak no. 96) elutes earlier relative to n-Czo with the slower temperature program (Figure 12). Figure 9 shows the whole ClW aromatic fraction together with the subfractions chromatographed on the nonpolar phase. Figures 10 and 11show the mono- and diaromatics, respectively, in more detail. Figures 12 and 13 show the tri- + tetraaromatic fraction in successively more detail
with the position of several C2- and C3-phenanthrenes indicated in Figure 13. Concerning C2-phenanthrenes, Garrigues at al.34 have reported retention behavior on CpSil8 CB. The tri- + tetraaromatics in Figures 12 and 13 were chromatographed with a slower temperature program in order to improve resolution. In Table XI11 the retention characteristics of the identified compounds on CpSil5 CB with temperature program A (see Experimental Section) are listed. It should be emphasized here, in view of the vast number of possible structures present in crude oils, that other compounds may in some cases coelute with those listed. The identification table should therefore be
Characterization of North Sea Petroleum Fractions n
- alkane no.
17
18
19
20
25
30
35
40
,
Energy & Fuels, Vol. 4, No. 5, 1990 623 20 45
Retention time (min)
Figure 12. Details of Clo+ tripeaks, see Table XIII. n
- alkane no.
21 50
22
23 55
24 60
25 65
70 i
105
+ tetraaromatics chromatographed on CpSil5 CB, temperature program B. For identification of labeled
19
20
Retention time (min) 40
21 45
2,s z,a
4.10
22 50
a,io
Figure 13. Further details of Cl0 tri- + tetraaromatics chromatographed on CpSil5 CB, temperature program B. For identification of labeled peaks, see Table XIII. Positions of some di- and trimethylphenanthrenes are indicated below the chromatogram.
considered more as a guide to where the different compounds are encountered on the carbon number scale. This distinction is of importance if accurate quantitative analysis of single compounds is to be carried out. Then, frequently, further prefractionation and/or use of alternative detectors will be necessary. As an example, the
accurate determination of the isomer distribution of methylphenanthrenes, which is used as a geochemical maturity parameter, may be conducted with simultaneous FID and flame photometric detection24or multidimensional GC35 to avoid interference from coeluting methyldibenzothiophenes.
Rmningsen and Skjeurak
624 Energy I%Fuels, Vol. 4, No. 5, 1990 1 6 5
w
2 3
6 5
4 WANE (15)
BENZENE
/ b
;
7&; 6
4 INDENE ( 16)
5
1 2 m
BENZOTWHENE
B M N Y L (48)
1
m
2
n
6 5 ACENAPHTHENE (85)
ACENAPHTHYLENE (60d)
10
9
7 8
4
NAPHTHALENE (40a)
1
;
5 4 FLUORENE (74)
5 4 DIBENZOTHIOPHENE (84)
6 5 4 ANTHRACENE
PHENANTHRENE (85)
10
6 5 PYRENE (102)
7 6 FLUORANTHENE (98)
7 6 1,2-BENZOFLUORENE(105a)
11
6 5 4 23-BENZOFLUORENE (106b)
1 10
11
12
1
10 8 7 6 BENZ(a)ANTHRACENE (110)
7 6 CHRYSENE ( l l l a )
11
9
&
0 PERYLENE (115)
3
\
8 7 8 5 BENZO(a)PYRENE (1 14)
7 6 5 4 NAPHTHACENE
TRIPHENYLENE (11 l b )
4
\
7
8
5
INDENO(1,2,3-cd)PYRENE (116)
6 BENZO(ghi)PERYLENE (1 17)
Figure 14. Molecular structure and numbering of some polycyclic aromatic hydrocarbons. Numbers in parentheses refer to Table XIII.
Conclusions The Waters Energy Analysis amino (silica-RNHJ stationary phase generally provided effective separation of aromatic hydrocarbons according to number of aromatic carbons. Benzenes monosubstituted with straight-chain alkyl groups or polysubstituted with branched groups such as isopropyl were accelerated while naphthenic substitutents promoted retarded elution. Phenyl groups substituted adjacent to fused ring junctions (as in l-phenylnaphthalene), increased retention slightly while molecules with nonfused benzene rings (like p-terphenyl) behaved in a manner similar to that of fused molecules with the same number of aromatic carbons. The column provided acceptable separation between the latest eluting saturates, i.e., fused naphthenes, and the earliest eluting monoaromatics, i.e., compounds like 1,3,5-triisopropylbenzene. Off-line capillary GC quantitation of HPLC fractionated ring-class fractions offered results that agreed with gra-
vimetry within 2-4% relative with satisfactory repeatability (better than 3%). GC/MS group type analysis tended to underestimate the monoaromatics (or overestimated the diaromatics). UV detection a t 254 nm could be applied for fast, rough comparison of fractions when response factors characteristic of each ring class, calculated from gravimetric results and UV areas, were used. Agreement with gravimetry within about 10% relative was generally observed. In a biodegraded North Sea crude oil the monoaromatics were the dominating ring class in practically all the Clo to C2, range, from about Czotogether with the diaromatics. The tri- and tetraaromatics, which first appeared in C17 and Cz0,respectively, never constituted more than about 10% each. The ring-class distribution in CI4fractions from 12 North Sea oils and condensates varied between 62-38% and 43-57% (mono-di). The variation among CI9fractions was even smaller. It was difficult to find systematic variation that could be related to type of oil, although the
Characterization of North Sea Petroleum Fractions peak no.b 1 2a 2b 3 4 5 6 7 8 9 10a 10b 11
12a 12b 13 14 15 16 17 18a 18b 19a 19b 19c 20a 20b 21 22
23a 23b 24
25 26a 26b 27 28 29 30 31 32 33 34 35 36 37a 37b 38a 38b 38c 39 40 41 42 43a 43b 44 45 46 47 48 49 50a 50b 51a 51b 52 53 54 55a 55b
Energy & Fuels, Vol. 4 , No. 5, 1990 625
Table XIII. Identity of Aromatic Compounds Eluting between n -Cna n d n-CS2on C p S i l 5 CBa compound t ~min , ZG' peak no.b compound t ~min , 10.11 134.87 ethylbenzene 56 C4-indan 29.21 10.48 136.74 1,4-dimethylbenzene (p-xylene) 57 C8-benzene (C4-indan) 29.33 1,3-dimethylbenzene (m-xylene) 58 C2-biphenyld 29.25 1,2-dimethylbenzene (0-xylene) 11.33 141.28 59 C5-indane (C4-indan) 29.55 60a acenaphthylene 12.75 148.88 isopropylbenzene (cumene) 29.46 60b 13.94 155.24 n-propylbenzene 1,4-dimethylnaphthalene 29.48 14.27 157.01 1-ethyl-3-methylbenzene 60c 1,5-dimethylnaphthalene 1-ethyl-4-methylbenzene 14.34 157.38 60d 2,3-dimethylnaphthalene 61 1,2-dimethylnaphthalene 1,3,5-trimethylbenzene (mesitylene) 14.58 158.66 29.82 1-ethyl-2-methylbenzene 14.92 160.48 62 C3-naphthalene 29.98 63 1,8-dimethylnaphthalene 1,2,4-trimethylbenzene (pseudocumene) 15.54 163.80 30.04 64 2-ethylbiphenyl tert-butylbenzene 30.18 16.19 167.27 65 acenaphthene isobutylbenzene 30.26 66 3-methylbiphenyl sec-butylbenzene 16.28 167.75 30.53 67 1-isopropyl-3-methylbenzene (m-cymene) 4-methylbiphenyl 30.67 68 C3-naphthalene 1,2,3-trimethylbenzene (hemimellitene) 16.56 169.25 31.05 69 1-isopropyl-4-methylbenzene (p-cymene) 16.80 170.53 C3-naphthalene 31.51 indan 70 C3-naphthalene 16.90 171.07 31.64 71 indene 17.40 173.74 C3-naphthalene 31.94 C4-benzene 17.87 C3-naphthalene 72 32.02 1,3-diethylbenzene 17.97 176.79 73 C3-naphthalene 32.31 74 1-methyl-3-n-propylbenzene fluorene 32.50 1,4-diethylbenzene 75 18.11 177.54 C3-(C4-)naphthalene 32.71 1-methyl-4-n-propylbenzene 76 C2-biphenyle (C3-naphthalene) 32.86 n-butylbenzene 4-ethylbiphenyl 77 32.97 78 l,2-diethylbenzene 18.26 178.34 C3-JC4-naphthalene 33.06 1,3-dimethyl-5-ethylbenzene C2-biphenyl' 79 33.20 1-methyl-2-n-propylbenzene 80 18.50 179.63 C2-biphenyl/C4-naphthalene 33.39 1,4-dimethyl-2-ethylbenzene 81 18.95 182.03 C2-biphenyl 33x4 82 9-ethylfluorene 18.99 182.25 1,3-dimethyl-4-ethylbenzene 34.06 methylindan 83a 1-methylfluorene 34.98 1,2-dimethyl-4-ethylbenzene 83b 2-methylfluorene 19.22 183.48 1,3-dimethy1-2-ethylbenzene 19.40 184.44 84 dibenzothiophene 35.93 1,2-dimethyl-3-ethylbenzene 85 phenanthrene 19.92 187.22 36.29 C5-benzene 86 1-phenylnaphthalene 38.10 C5-benzene 87 3-methylphenanthrene 20.07 38.38 C5-benzene 20.26 88 2-methylphenanthrene 38.50 1,3-dimethyl-5-isopropylbenzene 89 9-methylphenanthrene 20.42 189.89 38.78 90 20.54 190.53 1,2,3,5-tetramethylbenzene (isodurene) 1-methylphenanthrene 38.86 20.73 C5-benzene 918 C2-phenanthrene C2-indan 2-phenylnaphthalene 21.05 92 39.67 C5-benzene C2-phenanthrene 21.13 939 21.30 C5-benzene C2-phenanthrene 948 C5-benzene C2-phenanthrene 21.39 95s 21.54 C5-benzene fluoranthene 96 41.06 21.62 196.31 1,2,3,4-tetramethylbenzene (prehnitene) C2-phenanthrene 978 1,2,3,4-tetrahydronaphthalene(tetralin) C2-phenanthrene 988 1,3-diisopropylbenzene C2-phenanthrene 99 21.87 197.65 C5-benzene MW 218h lo@ MW 218h C3-indan 1018 n-pentylbenzene 22.14 199.09 pyrene 102 41.94 naphthalene MW 218h 1038 22.31 200.00 C5-benzene MW 216' 1048 22.86 C2-indan 105 25.09 1,2-benzofluorend 43.48 C3-indan 25.81 2,3-benzofluorene' 106 43.70 C7-benzene MW 216' 1079 2-methylnaphthalene MW 216'/230k 1088 25.80 224.96 C3-indan MW 230k 109 26.26 1-methylnaphthalene 26.19 227.75 benz[alanthracene 110 46.83 C3-indan chrysene llla 26.64 46.99 biphenyl 27.96 240.41 triphenylene lllb 46.99 n-heptylbenzene MW 242' 28.06 1128 C4-indan 28.17 113 benzo[k] fluoranthene 49.90 C7-benzene 114 benzo [ a]pyrene 50.80 1-ethylnaphthalene 28.39 243.49 115 perylene 50.92 2-ethylnaphthalene 116 indeno[ 1,2,3-cd]pyrene 52.84 2,6-dimethylnaphthalene 28.65 245.35 53.20"' picene 2,7-dimethylnaphthalene benzo[ghi] perylene 28.73 245.92 117 53.27 1,3-dimethylnaphthalene alkylbenzene 29.04 248.14 Xn" 1,6-dimethylnaphthalene 29.12 n-alkylbenzene Ynn 1,7-dimethylnaphthalene alkylbenzene Z""
Ioc
251.07 251.29 253.72 255.22 256.23 256.87 258.80 259.80
272.89 276.25
284.05 290.63 297.42 300.00 316.92 319.53 320.65 323.27 324.02 331.59
344.58
352.80 367.20 369.25
398.50 400.00 400.00 446.86 461.35 463.29 494.20 500.00 501.32
a Temperature program A (see Experimental Section). Coeluting compounds are identified with lower-case letters. Retention index (eq 1). dProbably 2,2'-dimethyl. Probably 3,3'-dimethyl. f Probably 4,4'-dimethyl. #Temperature program B used (see Experimental Section). Probably methylphenylnaphthalene. Could also be benzylnaphthalene. Methylpyrenes or 4uoranthenes. j Coelutes with MW 216
compound. Probably C2-pyrene or -fluoranthene. Probably methylchrysene or -triphenylene. Estimated from t R of benzo[ghi]perylene using literature data.41 " Monoaromatic compounds (see Figure 10); n is number of carbon atoms in the alkyl group.
Ronningsen and Skjevrak
626 Energy & Fuels, Vol. 4, No. 5, 1990
biodegraded oils seemed to be slightly richer in monoaromatics. There was good agreement between the elution order of aromatics relative to n-alkanes on a nonpolar GC stationary phase and the boiling order during TBP distillation. On a methylphenylsilicone phase the aromatics eluted less than one carbon number later relative to the n-alkanes.
Acknowledgment. We gratefully acknowledge contribution of GC/MS data for identification purposes by T. Meyer, Rogaland University (now Statoil), the assistance with gas chromatography by B. Bjarndal and A. L. Blilie, both Statoil,and helpful reviewing of the manuscript by Prof. T. Greibrokk a t the University of Oslo. We are also grateful to Statoil for allowing publication of this paper.
Cn
C" DBT DHN DMN DMP FID
Abbreviations alkyl substituent with n carbon atoms carbon number fraction n dibenzothiophene dihydronaphthalene dimethylnaphthalene dimethylphenanthrene flame ionization detector
GC GC/MS HPLC HRGC ISTD MP MW P PAH PNA SARA SFC TBP TMN
gas chromatography gas chromatography/mass spectrometry high-performance liquid chromatography high-resolution gas chromatography internal standard methylphenanthrene molecular weight phenanthrene polycyclic aromatic hydrocarbon paraffin-naphthene-aromatic saturate-aromatic-resin-asphalthene supercritical fluid chromatography true boiling point trimethylnaphthalene
Symbols phase ratio (= Vs/ V I ) retention index in gas chromatography retention index in liquid chromatography capacity factor ( = t R- t o / t o ) number of theoretical plates effective N ( = N ( k ' / k ' + 1)2) density at 15 "C, g/cm3 elution time of unretained compound, min retention time, min adjusted retention time ( = t R - to),min volume occupied by gas phase volume occupied by liquid phase
