Energy & Fuels 1992, 6, 160-165
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Fractionation and Characterization of Whiterocks Tar Sands Bitumen K.Bukka,**tF. V. Hanson,t J. D. Miller,+and A. G. Obladi Department of Metallurgical Engineering and Department of Fuels Engineering, University of Utah, Salt Lake City, Utah 84112 Received August 23, 1991. Revised Manuscript Received December 4, 1991 Tar sand samples from the Whiterocks deposit, located in the Uinta basin of Utah, were obtained from three different locations. Bitumen separation from each of these samples was accomplished by the Dean-Stark toluene extraction method and the physical and chemical properties of the resulting bitumens were determined. Further, each bitumen sample was fractionated by the modified Saturates, Aromatics, Resins, and Asphaltenes method, and the separated fractions from one of the bitumens were characterized by Fourier transform infrared transmission and specular reflectance techniques. The results show that there are very small differences among them and that they contain relatively low amounts of asphaltenes. The low asphaltenes content of the Whiterocks bitumen is considered to be an advantageousfeature for the development of subsequent upgrading process strategies. Finally, properties of the Whiterocks bitumen were compared to the bitumens extracted from the other deposits of the Uinta basin, viz., Asphalt Ridge and Sunnyside. Introduction The tar sand deposits in the United States, though relatively small when compared to the Canadian deposits, are nonetheless a significant hydrocarbon resource. The estimated resource has the potential to supplement other known hydrocarbon resources to satisfy future energy requirements. It was estimated earlier that 90-95% of the known tar sand deposits were situated in Utah.'V2 However, since then several other tar sand deposits have been located in other parts of the United States and revised estimates are given in recent reporh3v4 In spite of these new estimates, the total Utah tar sand deposits still constitute a major portion of the U.S. tar sands. The Utah tar sands were estimated to contain 24-29 billion barrels of in-place bitumen, distributed among 9 major and 13 minor d e p o ~ i t s . ~The minor deposits are estimated to contain less than 4% of the known bitumen and as such are not considered to be of economic importance. The bitumen in the nine major deposits is unevenly distributed ranging from 0.06 to 4.4billion barrels of in-place bitumen. Optimal utilization of the bitumen recovered from any tar sand requires the determination of its chemical composition. A knowledge of the precise chemical composition of bitumen is neither possible nor an absolute requirement for the development of downstream processing strategies. However, chemical description based on the classification of compound types is very useful for the development of process models related to the upgrading steps. Earlier studies, conducted on bitumens derived from several of the major Utah tar sand deposits, indicated that their physical and chemical properties were very different.6 In a recent study,' Whiterocks tar sand bitumen was subjected to vacuum distillation. The 400-650 and 650-850 O F boiling range fractions and the residue were collected, and characterized by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC-MS). The physical and chemical characteristics of the fractions led to the conclusion that the lighter fraction (400-650 OF) possessed properties
* Author to whom correspondence should be addressed.
'Department of Metallurgical Engineering.
*Department of Fuels Engineering.
0887-0624/92/2506-0160$03.00/0
similar to high-density jet fuels, and the other fraction (650-850 O F ) met the specifications for AC-10 asphalt cements. In this paper the properties of bitumen extracted from the same Whiterocks tar sands are presented. In addition, FTIR spectroscopicanalyses of fractions obtained from a modified SARA (saturates, aromatics, resins, and asphaltenes) fractionation are also presented. Experimental Section The tar sand samples used in this study were obtained from three different sites at the Whiterocks deposit. The samples were obtained from an actively mined pit on the western flank outcrop (Section 18 and 19, Township 2 North, and Range 1East). Drum quantity (4-55gallon drums) samples were mined from the floor of the pit after removing 4-6 f t of the bitumen-impregnated sandstone from each of the three sites. At the time of the mining operation the floor of the pit was approximately 50 ft below the overburden-ore body interface. The overburden was approximately 80-100 ft at the face of the cut in the region of the pit, and the pit was 700-800 ft wide (south-to-north). The locations of the sample sites are indicated by their positions and indicated as northwest, west central, and southwest. A map of the deposit on which the sample locations are identified is presented in Figure 1. A representative tar sand sample for each location was obtained by taking a 20-lb sample from a well-mixed 1600-lb sample of the crushed ore. Bitumens from these samples were separated from sand and water by the Dean-Stark toluene extraction method. The toluene was removed from the extracts by distillation on a rotary evaporator. The residual toluene left in the bitumen sample was determined by gas chromatography and found to be less than 0.2 wt % bitumen for each sample. The physical properties of the extracted bitumens were determined by standard ASTM methods. Included in these were the specific gravity, API gravity, Conradson carbon, ash, and heat (1) Oblad, A. G.; Seader, J. D.; Miller, J. D.; Bunger, J. W. AIChE. Symp. Ser. 1976, 72, No.155, 69. (2)Ritzma, H.R. 'Oil Impregnated Rock Deposita of Utah'', Map 47. Utah Geological and Mineralogical Survey, 1979; 2 sheets. (3)Major tar and and heavy oil deposits of the United States; Kuuskraa, V. V., Hammershaimb, V. A., Eds.; The Interstate Oil Compact Commission: Oklahoma City, OK, 1984. (4)Dana,G. F.;Oliver, R. L.; Elliot, J. R. Geology and resources of the Tar Sand Triangle, Southeastern Utah. WRI-DOE Tar Sand Symp., Paper 2-4,Vail, Colorado. June 26-29, 1984. (5) Oblad, A. G.; Bunger, J. W.; Hanson, F. V.; Miller, J. D.; Ritzma, H.; Seader, J. D. Annu. Rev. Energy 1987,12, 283. Thomas, K. P.; Dorrence, S. M. Fuel 1979,58, 183. (6)Bunger, J. W.; (7)Taai, C. H.;Deo, M. D.; Hanson, F. V.; Oblad, A. G. Fuel Sci. Technol. Int. 1991, 9(10),1259.
0 1992 American Chemical Society
Whiterocks Tar Sands Bitumen
Energy & Fuels, Vol. 6, No. 2, 1992 161
Sample Coated
M4
Aluminum Strip
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Figure 3. Schematic of the FTIR-specularreflectance accessory.
Figure 1. Map indicating the major tar sand deposits of Utah. Whiterocks deposit and its sample locations are shown in the expanded version of the region.
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= 40: 1 I d .
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Figure 2. Bitumen fractionation scheme. of combustion. The viscosity measurements were made on a Brookefield Viscometer with a cone and plate assembly (3O cone). Viscosities for the three bitumens were measured in the temperature range 30-90 O C . All three samples of bitumen were subjected to the fractionation scheme illustrated in Figure 2. This scheme is essentially based on the solubility and polarity differences among the compounds present in the bitumen. There have been several fractionation techniques based on compound-typeseparation methods described in the literature.*'* These techniques vary in the use of adsorbent (8) Jewell, D. M.; Weber, J. H.; Bunger, J. W.; Plancher, H.; Latham, D. R. Anal. Chem. 1972,44,1391.
materials (i.e., attapulgus clay, silica gel, alumina, and both anionand cation-exchange resins) and eluting solvent sequences. In the present study Fuller's earth (calcium montmorillonite) was used as adsorbent.12J3 The experimental details of the fractionation scheme are described eleeWhere.l4 The only modification in the present scheme is that the aromatic fraction was subdivided into three fractions; designated as aromatics-I, aromatics-11, and aromatics-111, which progressively increase in their polarities. In view of the apparent similarity in the physical properties of the three bitumens, only the west central bitumen sample and its fractions were chosen for elemental analysis and molecular weight determinations. Elemental analyses consisted of quantitative determination of carbon, hydrogen, nitrogen, and sulfur contents. These analyses were performed on the LECO-600 and LECO-SC132 analyzers. The oxygen content of the fractions was determined by difference. Molecular weights were determined at a commercial laboratory (GalbraithLabs.,Knoxville, TN) using a vapor phase osmometer. These determinations were made at three different concentrations using toluene as the solvent, and at an operating temperature of 60 "C. A standard solution of benzil was used to obtain the instrument calibration factor. Infrared spectra of the Whiterocks tar sand bitumen (west central) and its fractions were determined with a Digilab FTS-40 spectrometer fitted with a liquid nitrogen cooled MCT (HgCd-Te) detedor. Transmission spectrum of the saturate fraction was obtained by applying the sample uniformly on circular KBr windows (25 X 5 mm). However, as the bitumen and some of ita fractions were highly viscous materials, reliable transmission spectra could not be obtained using the same technique. Until recently such samples were dissolved in a suitable solvent and the differential spectrum of the sample was obtained by using a solution cell accessory of known path length.16J6 FTIR spectra were obtained using a recently developed accessory, viz., variable angle specular reflectance (SR) device (Spectra-Tech Inc., Model No. 502). In this method the sample is dissolved in a very small volume of dichloromethane (5 mg/0.5 mL) and the solution is applied to a clean rectangular aluminum strip (2.5 X 5.0 cm) to cover half its area. The aluminum strip is allowed to dry in the fume hood and inserted into the accessory for FTIR spectroscopic examination. The background spectrum consisted of the same aluminum strip treated with dichloromethane. The schematic of the SR accessory is presented in the Figure 3. The infrared beam enters through the opening, falls on the mirror M1, and travels by reflection to a concave mirror M2, which is focused onto the mirror M3 and then onto the sample-coated aluminum strip. After interaction with the sample the resulting beam is reflected to the mirror M5 and then on to the detector. The angle between the aluminum strip (S) and mirror M3 is fixed, m "-)
(9)Sadeghi, K.M.; Sadeghi, M. A.;Wu, W.H.;Yen, T. F. Fuel 1989,
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7A9
(10)Middleton, W.R.Anal. Chem. 1967,39,1839. (11)Callen, R.B.; Bendoraitis, J. G.; Simpson, C. H.; Voltz, S.E. Znd. Eng. Chem., Prod. Res. Deu. 1976,15,22. (12)Syncrude analytical methods for oil sand and bitumen processing; Bulmer, J. T., Starr, J., Eds.;Alberta Oil Sand Technology and Research Authority: Edmonton, Alberta, 1979. (13)Speight, J. G.;Moschopedis, S.E. Prepr. Am. Chem. SOC.,Diu. Pet. Chem. 1981,26,907. (14)Bukka., K.;Miller, J. D.; Oblad, A. G.Energy Fuels 1991,5,333. (15)Beitchman, B. D. J. Res. Natl. Bur. Stand. 1959, 63A(2),189. (16)Peterson, J. C. Anal. Chem. 1975,47(1),112.
162 Energy & Fuels,
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Table I. Average Bitumen Saturations of Whiterocks Tar Sand Samples Taken from Three Different Locations (Obtained from 18 Extractions) northwest west central southwest 7.3 f 0.1 7.7 f 0.6 5.9 f 0.3 bitumen 4.9 1.0 water 1.2 89.5 91.5 solids 91.4 and the assembly is rotated as a unit. The M3/M4 assembly is rotated through different angles to obtain the best possible spectrum. Optimal spectra were obtained at an angle of 30'. The equivalence between the transmission spectrum (KBr pellet) and SR spectrum was verified in the case of the solid asphaltene fraction in which case both techniques could be used.
Results and Discussion The bitumen saturations of the Whiterocks tar sand samples are presented in Table I. The values reported are the average of 18 extractions. The bitumen saturation values for Whiterocks tar sands were significantly lower than those of the other Uinta basin deposits such as Asphalt Ridge (13.1%) and Sunnyside (9-lO%)." While the samples taken from northwest and southwest locations of the deposit have similar bitumen contents, the sample from the west central location has consistently shown lower amounts of bitumen and higher water content. This difference is perhaps attributable to the topology of the west central site, which is the low point of the mine. Thus the high water content reported for the west central sample is believed to be the result of gravitationally accumulated water. Although strong experimental evidence is lacking, all Utah tar sands are presumed to be oil-wet. Physical Properties. The physical properties of the bitumens from the three locations are listed in Table 11. Despite small differences in the specific gravity, API gravity, Conradson carbon residue, ash content, heat of combustion, and viscosity it was concluded that the bitumens were similar in nature and the deposit was uniform in the lateral (south-to-north) direction. This observation is consistent with the geological character of the reservoir/deposit. The saturated zones of the Navajo Sandstone are tilted upward at an angle of 65". Thus, lateral sampling across the south-to-north axis of the pit should provide samples from the same depositional zone, and the bitumens should be similar in physical and chemical character. In general, the measured values for properties listed in Table I1 agree well with those reported earlier,5Js except for the ash and Conradson carbon, both of which are lower in the present study. The observed differences in the properties among the three bitumen samples, as listed in Table I1 were very small and considered to be insignificant. Fractionation. The results of the bitumen fractionations are presented in Table 111. The method devised to separate the bitumen into various compound types is based mainly on differences in polarities. The separated fractions were designated as saturates, aromatics-I, aromatics-11, aromatics-111, resin-I, and resin-11, and asphaltenes. Distinctions among the aromatic fractions were made based on the polarity differences in the eluting solvents. The asphaltene fractions in all three cases were found to contain an insignificant amount of mineral matter (
