Energy 153 Fuels 1995,9, 641-647
641
Solvent Deasphalting Effects on Whole Cold Lake Bitumen Glen Brons" Corporate Research, Exxon Research and Engineering Company, Route 22 East, Clinton Township, Annandale, New Jersey 08801-0998
Jimmy M. Yut Imperial Oil Research Limited, Research Centre, 3535 Research Road NW, Calgary, Alberta, Canada T2L 2K8 Received November 1, 1994. Revised Manuscript Received April 20, 1995@
Cold Lake bitumen was separated using light hydrocarbon solvents (n-pentane, n-butane, isobutane, and propane) into deasphalted oil (DAO) and asphaltene fractions. The resulting range of deasphalting was from 20 to 50 wt % of the whole bitumen. An extensive study of the fractions, as a function of yield, has shown how and to what extent volatiles, aromatics, sulfur, and metals are distributed between the fractions. A study of how the asphaltenes affect viscosity and overall molecular weight revealed that the heaviest-end fractions of asphaltenes have the most impact on the viscous nature of such heavy oils, suggesting that even low levels of deasphalting can have a dramatic impact in reducing viscosity. In addition, thiophenic sulfur was found to be more concentrated in the asphaltenes. It is also suggested that sulfides acting as cross-links between large structures may be responsible for the largest molecular weight fractions of the asphaltenes.
Introduction Heavy oils, including bitumen, are one of the world's largest resources. Estimates of known reserves suggest that nearly 4.0 trillion barrels of these crudes exist.l This is significantly more than the estimated 2.5 trillion barrels of worldwide conventional oil reserves.l Heavy crudes are, however, an underutilized resource because of their inherent poor qualities. Heavy oils are so named because they have larger densities than conventional light oils. They are also highly viscous in nature and contain large molecular weight fractions. In addition, the quality of heavy oils suffers because they contain significantly more heteroatoms and metals, both of which are costly to handle for most conversion processes and unacceptable in clean refinery products for environmental reasons. The heavy-end fractions of these crude oils contain large concentrations of heteroatoms, metals, and aromatics. The presence of these fractions is also responsible for the whole crude's large molecular weight and viscosity. While much of the heavy-end materials can be upgraded, conversion processes suffer high costs due t o the need for large amounts of hydrogen t o do the upgrading. As an alternative to using only hydroconversion techniques, an approach to improve the properties of these heavy crudes might be t o remove the fractions most responsible for their poor quality prior to conver+ Current address: Esso Singapore Private Limited, Lubes Process Technology,Pulau Ayer Chawan, Juron Town, P.O. Box 23, Singapore 9161. @Abstractpublished in Advance ACS Abstracts, June 1, 1995. (1) Tissot, B. P.;Welte, D. H. Petroleum Formation and Occurrence, 2nd ed.; Springer-Verlag: Berlin, 1984; pp 480-482.
0887-0624/95/2509-0641$09.00/0
sion. The more valuable fractions of the crude can be isolated by removing the heavy-end fractions by solvent separation. Such a separation would require a recoverable solvent capable of removing those fractions which contain significantly concentrated levels of heteroatoms, metals, and aromatics. The effects of such a separation approach on the quality of bitumen have been studied. Whole bitumen from the Cold Lake region of Alberta, Canada, was separated by solvent extraction. The solvents used were n-pentane, n-butane, isobutane, and propane. The products were the soluble, deasphalted oil (DAO) and the insoluble, heavy-end fraction (asphaltenes). The degree of deasphalting covered a broad range of 20-50 wt % of the whole oil. The effects of deasphalting on many of the oil properties are discussed as well as some relationships between these properties.
Experimental Section Solvent Deasphalting. The asphaltenes from n-pentane were isolated in the laboratory at ambient temperatures and pressures. The asphaltene and DAO fractions from the lighter solvents were isolated via the ROSE process by Kerr McGee Corp.2 n-PentaneAsphaltene Preparation. Whole, dewatered, demineralized bitumen (50.0 g) was charged into a mediumfritted Biichner funnel containing 20:l(vh) of n-pentane under a nitrogen atmosphere. Due to the slow filtration through the fritted disk in the absence of vacuum, the mixture was stirred well in the funnel and allowed to stand at room temperature for about 30 min. By vacuum filtration, the n-pentane soluble fraction was removed. The insoluble fraction (asphaltenes) was washed with additional n-pentane until the filtrates were (2) Gearhart, J. A,; Garwin, L. Hydrocarbon Process. 1970,55, 5 , 125.
0 1995 American Chemical Society
Brons and Yu
642 Energy & Fuels, Vol. 9, No. 4, 1995
Table 1. Asphaltene Yields from Solvent Separations of Cold Lake Bitumen solvent solventlbitumen (Lkg) asphaltenes (wt %) 47.8 propane 8: 1 isobutane 8: 1 35.9 28.4 n-butane 4.5:1 27.2 n-butane 8: 1 20.6 n-pentane 20:l clear (typically, 2-3 additional washes of 100 mL were required). The asphaltenes were vacuum dried under a nitrogen blanket at room temperature for 1 h and recovered (10.25 g). The DAO fraction was recovered by removing the n-pentane by rotary evaporation (38.95 g). The DAO was not analyzed in this report. Thermal Gravimetric Analysis (TGA). TGA analyses of samples (10-20 mg) were carried out on a Perkin Elmer TGS-2 thermogravimetric analyzer with a Perkin Elmer System 4 thermal analyzer microprocessor controller. The data were collected on a Serrogor 210 recorder. A standard analysis increases the temperature of the sample from 30 to 800 "C at a rate of 10 "C/min under a 50 cm3/min flow of argon. At 800 "C, the gas is switched over to oxygen (10 cm3/min)for complete burn-off of volatiles and ash level determinations. The material requiring oxygen for burn off is termed fixed carbon. Viscosity Measurements. All viscosity measurements were carried out using a cone-plate, Brookefield digital viscometer (Model HBTDV-IICP, full scale torque was 57 496 dymcm). A cone spindle of radius 1.2 cm (no. CP-51) was used for measurements a t temperatures ranging from 13 t o 50 "C and a t shear rates from 1.92 to 192 s-l. Brookefield viscosity standards of 49 490 and 103 400 CPwere used for instrument calibration. Elemental Analyses. The compositional information for contents of carbon, hydrogen, nitrogen, sulfur, ash, and Karl Fischer water were determined according to established ASTM procedures for petroleum fractions by Galbraith Laboratories, Knoxville, TN. Average Molecular Weight Determinations. Numberaverage molecular weight (M,) measurements were carried out on a vapor pressure osmometer at Galbraith Laboratories, Knoxville, TN, according t o the standard test method ASTM D 2503-82 (reapproved 1987) for petroleum fractions. The measurements were carried out with toluene as the solvent at 60 "C.
Results and Discussion Bitumen recovered from the Cold Lake region of Alberta, Canada, was fractionated using solvent separations to yield insoluble fractions which are precipitated out as solids (at room temperature). These insoluble fractions of the whole bitumen will be termed asphaltenes. The soluble and/or extractable fractions will be termed the deasphalted oil (DAO) fractions. The a m o u n t s of solvent used for this study are reported in
Table 1.
Virtually all of the properties of the oil are altered as a result of removing the heavy-end fractions. These properties can be affected by both the amount of asphaltenes and the type of asphaltenes removed. The different solvents used in this study remove different amounts of asphaltenes and provide a set of samples to examine the changes in properties of the DAO as a function of the degree of deasphalting (removal of asphaltenes). In addition, these provide a set of insoluble samples that can also be studied. This paper is a report of how the level of deasphalting affects the DAO properties. This also offers a data base one can use to extrapolate other effects of similar deasphalting approaches. Solvent Separation. The levels of deasphalting from the solvent separations are reported in Table 1as wt % asphaltenes recovered. The data from the two n-butane separations suggests there is a little difference in using solvent to bitumen ratios of 4.5:lor 8:l. The data from the higher of the two treatment rates suggest that there is only a small increase in selectivity. While the data may also suggest that branching in the solvent increases the level of deasphalting, or that such crude oils are more soluble/extractable in the linear solvents, this is more likely due to the higher density of the linear solvents. In addition, solubility increases with chain length of n-alkyl solvent, or less asphaltenes are removed. Effects on Elemental Composition. Elemental analyses of each of the solvent fractions are reported in Table 2. The data show that relationships exist between the degree of deasphalting and the elemental variables. More specifically, as the degree of deasphalting increases, or as more heavy-end material is removed, the higher in quality the oil fraction becomes. For example, the hydrogen contents of the DAO fractions increase as more deasphalting occurs. The reverse is true for the asphaltenes, where the hydrogen contents decrease as these represent less of the whole bitumen. Sulfur contents follow the reverse trend to that observed for hydrogen. The sulfur contents of the DAO fractions decrease as more deasphalting occurs. The asphaltene fractions appear t o contain more concentrated levels of sulfur as less deasphalting occurs. This may be due to the types of sulfur present and how these are distributed in the bitumen. The forms of sulfur in Alberta bitumen are predominantly sulfides and thiophenes. Approximately 70% of the sulfur in Athabasca bitumen is reported to be thiophenic with the balance as sulfide^.^^^ The thiophenic sulfur may be concentrated in the heavier, more aromatic fractions of the bitumen (asphaltenes). This is suggested by the relationship illustrated in Figure 1. The asphaltenes are
Table 2. Analysis of Cold Lake Bitumen DAO and Asphaltene Fractions (in wt % as received) n-C4
n-C4
wt%
water ash carbon hydrogen nitrogen sulfur oxygen (dim TGA FC CCR
n-C3
i-C4
whole bitumen
n-Csasph
DAO
asph
DAO
asph
DAO
asph
DAO
asph
100 81.21 10.09 0.53 4.84 1.33 7.5 13.2
20.5 0.21 0.59 81.03 8.02 1.09 8.17 1.69 38.0 44.7
72.8
27.2 0.02
