Anal. Chem. 1980, 52, 906-909
906
Shale Oil Hydrocarbon Separation by Preparative Liquid Chromatography and Glass Capillary Gas Chromatography F. P. DiSanzo,' P. C. Uden," and S. Siggia Department of Chemistry, GRC Tower I, University of Massachusetts Amherst, Massachusetts 0 1003
The applicatlon of low pressure high performance preparative liquid chromatography to commercial shale oil hydrocarbons is described. Compound class separation on 32-63 pm Woelm silica gel and silica gel impregnated with silver nitrate yields fractions of alkanes, alkenes, and aromatics. Further characterization of hydrocarbon classes is achieved by glass capillary gas chromatography and vapor phase Molecular Sieve 5 A subtraction techniques. Evldence for the presence of prist-I-ene in commercial shale oils is presented.
leum analytical and spectroscopic techniques to the analysis of the heavy end shale oil fraction. Clark et al. (6) employed Sephadex LH-20 for the large scale separation of shale oil hydrocarbons for physiological testing. In this study, a simple, inexpensive, but efficient separation scheme has been developed employing rapid preparative low pressure high performance liquid chromatography (LPHP-LC) on 32-63 pm Woelm silica gel. T h e liquid chromatographic separation is followed by high performance glass capillary gas chromatography and vapor phase subtraction for the resolution of individual components.
T o follow changes in the various retorting processes and t o assess and characterize the chemicals present in shale oil for petrochemical feedstock applications, it is necessary t o determine as fully as possible most of the constituents of the oil. T h e complexity of the system dictates that a chemical compound class separation scheme giving minimal class overlap be carried out prior t o subsequent detailed high resolution chromatographic analysis. In the identification of individual gas chromatographically separated components, a knowledge of the compound class involved increases the effectiveness of the usual ancillary techniques, and constituent peaks from complex hydrocarbon mixtures can tie studied more readily. Because of the complexity of shale oil, simpie and rapid analytical methods for its analysis have not been extensively developed. Separation schemes for various classes of compounds have been applied t o shale oil b u t these usually are time consuming, require large samples sizes, show overlapping of classes, and/or neglect the isolation and identification of the individual components. Many methods have Seen developed for the quantitative determination of hydrocarbon compound classes. Dinneen e t al. (I)employed adsorption on Florisil together with vacuum distillation, thermal diffusion, and adduct formation for the analysis of hydrocarbons and polar fractions in a high boiling distillate. Dinneen e t al. (2) also performed a very extensive qualitative and quantitative composition analysis of shale oil naphtha. Many paraffins, cycloparaffins, and aliphatic olefins were identified. Poulson et al. ( 3 )pointed out the problems associated with the determination of hydrocarbons in a shale oil distillate fraction; the classical displacement chromatographic method employing silica did not yield clean compound class separation. They also demonstrated the gross overlap t h a t occurred between alkanes and alkenes on efficient high performance liquid chromatographic silica columns. Consequently, they proposed a gas chromatographic readout where fractions are compared before and after wet chemical subtraction techniques have been applied. Jensen e t al. ( 4 ) characterized the saturates and olefins in a shale oil gas oil fraction into compound types. Florisil and silica gel adsorption chromatography were followed by mass spectral analysis. Ruberto et al. ( 5 ) applied modified petro-
Liquid Chromatography. LPHP-LC was performed on Pyrex glass columns, the ends of which were fitted with threaded Teflon fittings (Ace Glass Company, Vineland, N.J.). Florisil (Fisher Scientific Company, Medford, Mass.) was used as received. M'oelm 3243 pm activated silica was obhned from ICN Company (Cleveland, Ohio). The 20% silver nitrate impregnated 32-63 pm Woelin silica was prepared from spectrograde acetonitrile solution according to the procedure of Heath et ai (7). The latter column was covered with aluminum foil to prevent exposure to light. The separations were performed at room temperature without thermostating of the columns. The solvent delivery system was either a nitrogen gas pressurized 500-mL stainless steel reservoir or a high pressure liquid chromatography pump (Tracor, Inc., Austin, Texas). Pentane was distilled and passed through a silica column before use. The collected fractions were concentrated either by rotary evaporation or by careful distillation of the solvent with a Vigreux column. The fractions were not taken to dryness to avoid losses of the lower boiling components. Eluting components were detected with either a refractive index (RI) detector (Varian Associates, Palo Alto, Calif.) or a UV detector (LDC, Inc., Riviera Beach, Fla.). Gas Chromatography. Gas chromatographic analysis was carried out on a Varian 2760 instrument equipped with flame inch ionization detection (FID), employing either a 6 foot X stainless steel column packed with 270 Dexsil 300 GC on Chromosorb 750 (Johns-Manville, Denver, Colo.), or an 18 m X 0.4 mm i.d. glass SCOT column prepared according to the method reported by Cramers et al. (8). The glass capillary was drawn on a Shimadzu GDM-1 machine (Shimadzu Scientific, Columbia, Md.) and was coated with OV 101 (Analabs, North Haven, Conn.) on Cab-0-Si1 (Cabot Corp., Rillerica, Mass.). A splitter injection port was packed with approximately 2 cm of Tenax GC (60-80 mesh) and maintained at 300 "C (9). Make-up gas was used employing a low dead volume tee iniet (SGE, Inc., Austin, Texas). Gas Chromatography -Mass Spectrometry. A HitachiPerkin-Elmer RMU-6L single focusing mass spectrometer operating at ionlzing voltages of 70 or 15 eV was employed. It was interfaced to a Perkin-Elmer 990 gas chromatograph through a jet separator (SGE, Inc., Melbourne, Australia). Vapor Phase Subtraction System. Branched and cyclic alkanes and alkenes were isolated by vapor phase subtraction employing 100-200 mesh Molecular Sieve 5A (MS5A) (Analabs, North Haven, Conn.). The system has been described previously
EXPERIMENTAL
l
Present address: Mobil Research/Development Corp., Pauls-
boro. N.J. 08066.
0003-2700/80/0352-0906$01 .O@/O
(16).
RESULTS AND DISCUSSION The general fractionation procedure was carried out in four steps. These consisted of an initial cleanup on Florisil to separate nonpolar compounds from polar compounds and asphaltenes; a silica separation to resolve alkanes and alkenes C 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52,NO. 6, MAY 1980
naphthalene were fully resolved. However, a TOSCO I1 shale oil hydrocarbon mixture obtained from Step 1, showed only a slight indication of resolution of alkane and alkene groups. Thus the alkane/alkene fraction was collected a3. one and then resolved on a silver nitrate column (Step 3) t o give much improved resolution. A detailed GC analysis of the combined alkane/alkene fraction on an 18-m OV 101 SCOT column is shown in Figure 1. Double peaks are clear in homologous series, the first peak in each pair corresponding to the 1-alkene and the second to the n-alkane; alkane/alkene resolution is complete t o around C-26 on this column. Analysis on a packed 2 % Dexsil 300 GC column indicated alkanes and alkenes to greater than C-35 to be eluted in Step 2. Preliminary studies on detection of this fraction by a vapor phase UV detector sensitive at 210 nm to aromatic rings indicates a minimal proportion of the unresolved envelope to be due to aromatic compounds (11). The capillary gas chromatogram of the pentane eluted aromatic components is shown in Figure 2. Systems of up to three rings can be eluted with pentane; the higher ring systems may be eluted with a more polar solvent, e.g., methylene chloride. Further analysis of this latter fraction is presently underway by HPLC (11);GC/MS has revealed the presence of isomers with a t least five carbon alkyl substitutions for single ring aromatics and a t least three carbon alkyl substitutions for naphthalenes. Apart from the very low molecular weight components eluting before 4-5 min which may result in part from solvent impurities, no peaks resolved above the base envelope correspond to components similarly resolved in the alkane/alkene fraction (Figure 1). Separation of Alkanes from Alkenes (Step 3). A 20% silver nitrate impregnated silica column gave improved resolution of alkanes from alkenes. Standard alkanes and alkenes were fully resolved as were these groups from the TOSCO I1 shale oil fraction from Step 2. A single Woelrn silica silver nitrate column showed no detectable loss of resolution during a t least two months of use; the use of a nonpolar solvent such as pentane, does not lead to any detectable leaching out of the silver nitrate. A 30 cm X 11 mm i.d. silver nitrate column has a sample capacity of approximately 100 mg of a shale oil alkane/alkene mixture as obtained in Step 2. For resolution of the original shale oil sample this required replicate injections.
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0
12
36
24
48
64
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MiN Figure 1. Gas chromatogram of alkanedalkenes eluted from 32-63 Fm silica (Step 2). Column: 18 m X 0.4 mm i.d. glass SCOT OV 101 programmed 30-225 O C at 4 OC/min; carrier gas: helium, 4 mL/min
from aromatics; the separation of alkanes from alkenes on silver nitrate loaded silica; and resolution of branched and cyclic alkanes and alkenes from straight chain species by vapor phase molecular sieve subtraction. Sample Cleanup (Step 1 ) . For the clean-up step on Florisil, 0.5-0.7 g of TOSCO I1 shale oil (TOSCO, T h e Oil Shale Corporation, Denver, Colo.) was placed on a 40 cm X 17 m m i.d. glass column and was eluted with pentane. As monitored by refractive index detection, almost all hydrocarbons eluted within 10 min although collection was usually continued for a further 10 min to ensure a high recovery of the larger aromatic hydrocarbon ring systems. Gas chromatographic analysis on Dexsil 300 GC indicated that hydrocarbons of carbon numbers to above C-35 were eluted. Analytical H P L C indicated polynuclear aromatics up to a t least 4-ring systems also to be eluted. Separation of Paraffins and Olefins from Aromatic Hydrocarbons (Step 2). Hydrocarbon class separation of shale oil has been difficult because of the high concentration of olefins present. Poulson et al. ( 3 )have recently observed t h a t even a very efficient H P L C silica column yielded only a n inflection point in the resolution envelopes between the two classes of alkanes and alkenes although standards were readily resolved. T h e results in this present study were similar, standards consisting of 3-methylheptane, 1-dodecene, ethylbenzene, and
0
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32
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907
40
44 48 52
56
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64 68 72
76
min Figure 2. Gas chromatogram of pentane eluted aromatic hydrocarbons (Step 2). GC conditions: as in Figure 1. Retention time of naphthalene
and anthracene is indicated
908
ANALYTICAL CHEMISTRY, VOL. 52, NO. 6,MAY 1980
pristane (2,6,10,14-tetramethylpentadecane) and phytane (2,6,10,14-tetramethylhexadecane), respectively, both of which are present in large amounts in the bitumen of oil shale (12). Packed column gas chromatography of the alkene fraction on Dexsil300 GC showed no envelope in the C-30 region as was seen for the alkane fraction corresponding to steranes and triterpanes. Low energy (15 eV) mass spectral data obtained on eluted peaks indicated slight alkane overlap above C-25. Of considerable interest is the large component “A’ between normal-C-17 and normal-C-18 in Figure 5. GC/MS (Figure 6) indicated a molecular weight of 266 for this component. The molecular ion was further confirmed by low energy mass spectrometry a t 15 eV. Presumably this is the same unidentified component previously reported by Gallegos during the pyrolytic studies on Green River kerogen (12-14). Recently, pyrolysis studies by Larter et al. (15) showed that this compound is probably prist-1 .ene. Based on the separation scheme employed t o isolate component “A” and on mass spectral data, this compound is certainly a CI9Hs8mono-alkene. T h e mass spectral fragmentation shows very strong evidence for “A” being prist-1-ene, most of the major fragmentation ions being accounted for. T h e major ion at m l e 56 is a strong indication of the terminal olefinic group of the type H2C=C(CHJ(R2) (16). Analytical HPLC of the alkene fraction isolated in Step 3 on a bonded pyrrolidone column (17 ) a t various wavelengths is shown in Figure 7. Various types of olefinic conjugation appear to be present. The large early eluted component band whose maximum response occurs a t 220 nm probably consists of species exhibiting a single olefinic double bond (mostly 1-alkenes)whereas the band eluting at higher elution volumes and showing a greater response a t higher wavelengths is probably due to multiconjugated olefins, e.g., diolefins. The existence of the latter in shale oil has previously been reported (18). Isolation of Branched Chain and Cyclic Alkanes a n d Alkenes (Step 4). The normal alkanes and alkenes were completely removed from their respective samples a t the analytical level by vapor phase subtraction employing Molecular Sieve 5A (MS5A). Figure 8 shows the nonsubstracted branched and cyclic alkanes with carbon numbers up to carbon 16 which appeared in the chromatogram when the reactor was heated to 220 “C. At this temperature n-alkanes up to C-6 were not subtracted. Operation of the reactor a t 140 “ C simplified the gas chromatogram a t lower retention volumes by subtracting n-alkanes below n-C-6. At this lower tem-
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PROGRAM
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BLANK
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Flgure 3. Gas chromatogram of TOSCO shale oil alkane fraction (Step 3). GC conditions: 6 foot X ‘ I 8 inch SS 2 % Dexsil 300 GC, 50-350 O C at 10 ‘C/min; carrier gas: helium at 20 mL/min
0
16
48
32
a0
64 Mir
96
132
124
Flgure 4. Gas chromatogram of TOSCO shale oil alkane fraction (Step 3). GC condions: as in Figure 1. z = sample spiked with ldodocene; E and F are pristane and phytane, respectively
Packed column gas chromatographic characterization of the alkane fraction eluted from a silver nitrate column (Figure 3) showed that alkanes to greater than C-30 were present. The small envelope at approximately C-30 is mostly due to steranes a n d triterpanes; many of these are found in the oil shale bitumen while others have been shown to be released during pyrolysis of kerogen (12, 13). T h e same alkane fraction gas chromatographed on the OV 101 SCOT column is shown in Figure 4. It is clear that the first component, i.e., t h e 1-alkene, of the homologous series of doublets is completely missing. Components E and F are 2
3
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Figure 5. Gas chromatogram of TOSCO shale oil alkene fraction (Step 3,. GC conditions. as in Fisure 1. Sample spiked wirh 1-dodocene
ANALYTICAL CHEMISTRY, VOL. 52, NO. 6, MAY 1 9 8 0
909
V" Flgure 6. Mass spectrum of component "A" in Figure 5 Figure 9, Gas chromatogram of nonsubtracted alkenes isolated by Molecular Sieve 5A subtraction at 220 O C ; GC conditions: as in Figure 8
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Flgure 7. High pressure liquid chromatogram of TOSCO alkenes from Step 3. Conditions: 25-cm analytical LC column packed with bonded pyrrolidone on silica; solvent: heptane, 1.O mL/min; detector: UV at indicated wavelengths
found in commercial shale oils. Alkenes not subtracted by the MS5A reactor are shown in Figure 9. The nonsubtracted alkene fingerprint is more complex than that for the corresponding cyclic and branched alkanes with the presence of a large envelope being noted. This envelope may be simplified by running the MS5A reactor first at a low temperature and then reheating the same reactor to a higher temperature. The complexity of this class requires extensive chromatographic manipulation. GC "heart cutting" of a narrow boiling point range and rechromatographing on a capillary of higher polarity may prove useful in the identification of these minor alkenes.
ACKNOWLEDGMENT We are grateful to Mark T. Atwood of The Shale Oil Corporation (TOSCO) for providing samples of shale oil, and to Thomas H. Mourey for the use of the pyrrolidone liquid chromatographic column.
LITERATURE CITED
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2 %
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Flgure 8. Gas chromatogram of branched/cyclic alkanes isolated by Molecular Sieve 5 A subtraction a t 220 O C GC conditions. 18 m X 0.4 mm I d. OV 101 SCOT column, cryogenically condensed sample temperature programmed from 30-200 O C at 4 OC/min; carrier gas helium, 4 mL/min. Retention times of subtracted n-alkanes is indicated
perature, however, less of the higher boiling end were eluted, although the reactor may be reheated later to 220 "C to elute the other components up to C-16. The branched and cyclic alkane fraction up to C-16 is relatively simple as indicated by Figure 8, resolution being obtained for most of the major components. Results compare very favorably with those obtained with sulfuric acid/MS5A subtraction previously reported (10). Operation of the MS5A reactor a t 300 "C gave identical results to those a t 220 "C; temperatures above 300 "C were not investigated. However, branched and cyclic alkanes, including steranes and triterpanes, may be released by heating the reactor to over 450 "C or by refluxing the pure alkane fraction isolated in Step 3 in cyclohexane or isooctane over MS5A (19). This procedure should provide sufficient sample for a detailed study of most of the branched/cyclic alkanes
Dinneen, G. U.; Smith, J. R.; Van Meter, R. A.; Allbright, C. S.; Anthoney, W. R. Anal. Chem. 1955, 2 7 , 185. Dinneen. G. U.; Van Meter, R. A.; Smith, J. R.; Bailey, C. W.; Cook, C. L.; Allbright, C. S.; Ball, J. S. "Composition of Shale Oil Naphtha"; Bureau of Mines Bulletin, No. 593, 1961. POulSOn, R. E.; Jensen, H. B.; Duvall, J. J.; Harris, F. I-.;Morandi, J. R. Anal. Instrum., Instrum. SOC. of Am. Proc. 1972, 1 0 , 193. Jensen, H. B.; Morandi, J. R.; Cook, C. L. "Abstracts of Papers", 155th National Meeting of the American Chemical Society, San Francisco, Calif., April 2-5. 1968; F 98. Ruberto, R. G.; Jewell, D. M.; Jensen, R. K.; Cronaur, D. C. I n "Characterization of Synthetic Liquid Fuels-Shale Oil. Tar Sands, and Related Fuel Sources", Adv. Chem. Ser. 1976, 157. Jones, A. R.; Guerin. M. R.; Clark, 8. R. Anal. Chem. 1977, 49, 1766. Heath, R. R.; Tumllnson, J. H.; Doolittle, R. E.; Proveaux, A. T. J . Chromatogr. Sci. 1975, 13, 380. Cramers, C. A.; Vermeer. E. A.; Franken, J. J. Chromdtographia 1977, 10, 413. Bertsch, W.; Anderson, E.; Halger, G. J . Chromatogr. 1976, 126, 213. DiSanzo, F. P.; Uden, P. C.; Siggia, S.Anal. Chem. 1979, 57, 1531. Crowley. R.; Uden, P. C.; Siggia, S. University of Massachusetts, Arnherst, Mass., unpublished results. Scrima, D. A.; Yen, T. F.; Warren, P. L. Energy Sources 1974, 1 , 321. GallegOS, E. J. Anal. Chem. 1975, 4 7 , 1524. Gailegos, E. J. I n "Biological Fossil Hydrocarbons in Shale". Development in Future Energy Sources, Vol. 1, Yen, T. F., Chillinger. G. U., Eds.; Elsevier: Amsterdam, 1974. Larter, S. R.; Solli, H.; Douglas, A. G. J . Chromatogr. 1978, 167. 421. Mayer, K. K.; Djerassi, C. Org. Mass. Spectrom. 1971, 5 , 817. Mourey, T. H.;Siggla, S. Anal. Chem. 1979, 57, 763. Jackson, L. P.; Allbright, C. S.; Poulson, R. E. I n "Olefin Analysis in Shale Oil." Analytical Chemistry of Liquid Fuel Sources: Tar Sands, Oil Shale, Coal, and Petroleum, Adv. Chem. Ser. 1978, 170. Pym, J. G.: Ray, J. E.; Smith. G. W.; Whitehead, E. V, Anal. Chem. 1975, 4 7 . 1617.
RECEIVED for review November 8, 1979. Accepted February 2, 1980. The support of the National Science Foundation through Grant CHE74-15244 is acknowledged.
