Article pubs.acs.org/EF
Process for Solvent Extraction of Bitumen from Oil Sand Jiangying Wu* and Tadeusz Dabros CanmetENERGY, Natural Resources Canada, One Oil Patch Drive, Devon, AB T9G 1A8 ABSTRACT: Water-based bitumen extraction technology from mineable oil sands faces major challenges of high water usage and tailings disposal. In the present study, a process for solvent extraction of bitumen from Athabasca oil sands was investigated. In this process, oil sand is mixed with light hydrocarbon solvents, and the solvent−bitumen solution is separated from the mineral solids by centrifugal filtration or regular pressure filtration. The solvent left in the filtration cake is recovered by evaporation under vacuum at room temperature. The results show that, for both high-grade and low-grade ores, using appropriate solvent, the bitumen recovery and product quality are comparable to those from the currently used hot water extraction followed by naphtha froth treatment. The recovery of light hydrocarbon solvent is relatively easy, so this novel process has great potential to reduce solvent losses compared to existing technologies.
1. INTRODUCTION Alberta has total oil reserves of about 171 billion barrels, nearly all of which are contained in the Athabasca oil sands deposit. These reserves can provide reliable energy supply for North America. The Clark hot water extraction (CHWE) process has been used for commercial bitumen extraction from the Athabasca oil sands for over 40 years. This water-based technology now faces many challenges. First, the process has high water consumption: 3 to 4 barrels of water are required for every barrel of bitumen produced. Second, huge tailing ponds are generated that have serious, long-term environmental impacts. Third, if naphthenic froth treatment is utilized, bitumen product quality is low; if paraffinic froth treatment process is utilized, the asphaltenes rejection is high.1,2 Last, the high thermal capacity of water results in high energy consumption and high greenhouse gas (GHG) emissions. Therefore, advanced technologies that can make the oil sands a clean energy resource are urgently needed. Nonaqueous bitumen extraction is being investigated as an alternative to the CHWE process. By eliminating water use in bitumen extraction, all water-related issues would be resolved. For example, elimination of the fresh water draw from the Athabasca River would help preserve the ecology. The need for wet tailing ponds would be eliminated; instead, dry tailings suitable for continuous backfilling of the open pit would make it possible to reclaim the mined-out area in a much shorter period of time than is currently feasible. The nonaqueous process also has the potential to greatly improve energy efficiency and reduce GHG emissions. Nonaqueous bitumen extraction technologies have been explored, mainly in the United States. The oil sands deposits in some areas of the United States are not amenable to water extraction because the nature of minerals associated with the oil. The two types of nonaqueous bitumen recovery processes investigated were pyrolysis and solvent extraction. In pyrolysis processes, such as the AOSTRA Taciuk process, the oil sand is heated by mixing it with hot recycled sand.3 The bitumen is cracked into light hydrocarbons, vaporized, and separated from the mineral solids by cyclone. The coke left on the mineral solids can be burned to generate heat needed for Published 2011 by the American Chemical Society
the pyrolysis reaction. One drawback of the pyrolysis process is the high operating temperatures required. Several solvent extraction processes have been investigated. Graham et al. investigated a conceptual solvent extraction process using heptane,4 in which the bitumen and solvent are separated from the coarse minerals by hydrocyclones and from the fines by pentane deasphalting. The solvent is recovered from the mineral solids by centrifugation, filtration, and rotary kiln steam stripping. Rosenbloom used light oil to recover bitumen from tar sand.5 The solvent vapors are stripped from the mineral solids by flowing inert gas through the mineral solids in a multihearth solvent recovery furnace. Hanson and Sherk used toluene to recover bitumen from tar sand.6 Farcasiu and Whitehurst disclosed a method whereby the extraction of bitumen from tar sand is performed with a light naphtha/ methanol solvent system.7 The most desirable, nonpolar components of the extract are recovered from the naphtha phase; more-polar soluble components are recovered from the methanol phase, and most of the less-desirable asphaltenes remain insoluble but are separated from the mineral solids and are found at the interface of the two solvents. Meadus and Sparks from National Research Council of Canada in Ottawa developed the first solvent extraction process intended specifically for Athabasca oil sands. The naphtha-based process was termed SESA for solvent extraction spherical agglomeration.8,9 The major problem with the above solvent extraction processes is that they require large amounts of solvent to form a slurry with the oil sand feed, and high-boiling-point solvents make it difficult to recover the solvent from the large volumes of sand. Some combined solvent-and-water extraction processes have also been investigated. Graham disclosed a process of slurrying organic solvent with tar sand at mass ratio of about 0.5 to 4, then adding at least 50% water by mass and separating a bitumen-rich solvent phase.10 Wolff proposed a method in which solvent is added to water−oil sand slurry to form an emulsion from which Received: September 26, 2011 Revised: December 15, 2011 Published: December 20, 2011 1002
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the bitumen is recovered by breaking up the emulsion.11 It should be noted, however, that once water is introduced into the extraction process so are most of the problems associated with conventional water-based extraction. US patent 4347118 describes a process using a low-boiling hydrocarbon solvent in which bitumen and inorganic fines are separated from the extracted mineral solids at a low solvent-tobitumen ratio in an extraction zone containing a classifier and a countercurrent column.12 Solvent is recovered from the postextraction tar sand in a fluidized-bed drying zone. Since the liquid flow in the countercurrent column is hard to control, it is difficult to achieve a high bitumen recovery rate. In the present study, a new process for solvent extraction of bitumen from Athabasca oil sands was investigated. The objectives were to obtain bitumen recovery of more than 90 wt % and to limit solvent losses to less than 4 bbl of solvent per 1000 bbl of extracted bitumen. Low-boiling-point solvents were used to facilitate recovery; five different solvents were investigated at relatively low solvent-to-bitumen ratios (S/B), which is on mass basis. Centrifugal filtration and regular pressure filtration were used to separate solvent−bitumen solution from the solids. The bitumen recovery and the quality of the recovered bitumen were evaluated. Solvent remaining in the filtration cake was recovered by vacuum evaporation at room temperature and subsequent passage of the solvent vapor through a condenser.
on top of the screen such that the pore size of the middle divider can be controlled by selecting the appropriate filter paper. The entire vessel can be fitted in a commercial laboratory centrifuge so that controlled g-force can be applied to separate the solvent−bitumen solution from solids. The vessel is well sealed to prevent solvent loss. A valve at the bottom of the vessel can be used to add solvent and withdraw solvent−bitumen solution. Pressure can also be applied via a valve on the lid. A wrist-action shaker (model 75) manufactured by Burrell Scientific was used to mix solvent and oil sand. An Avanti J-30I centrifuge manufactured by Beckman Coulter Centrifuge was used to apply g-force on the vessel. The viscosity of the solvent−bitumen solution was monitored using viscometer manufactured by Cambridge Applied Systems Incorporated. A Karl Fischer titrator (Mettler DL18) was used to determine the water content of the solvent−bitumen solution. An NIR probe was used to determine the asphaltene content in bitumen. A gas chromatograph (Agilent 6890) was used to determine the residual solvent content in the extracted mineral solids after solvent recovery. The residual bitumen content in the extracted mineral solids and ash content in the bitumen product were determined by thermogravimetric analysis using a TGA/SDTA851 e instrument manufactured by Mettler Toledo. 2.3. Experimental Procedures. The experimental procedure is shown schematically in Figure 2. A filter paper was secured to the top of the middle screen of the vessel. About 50 g of oil sand was loaded into the upper part of the vessel. The vessel was capped and inverted. Solvent was injected into the vessel through the bottom valve using a syringe. The amount of solvent was calculated on the basis of the target S/B. A couple of minutes were allowed for the solvent to flow through the divider and enter the oil sand matrix. The vessel was then placed on the wrist-action shaker and agitated for about 1 h to make sure the solvent and oil sand matrix were thoroughly mixed. After mixing, the vessel was placed in the centrifuge and spun for 10 min at a known g-force. The solvent−bitumen solution passed through the filter paper and into the lower part of the vessel. It was then withdrawn using a syringe, and the weight was recorded. Water content in the first-stage solvent−bitumen solution was immediately measured by Karl Fischer titration. The solvent was then removed from the bitumen by evaporation, and the dry bitumen was collected and weighed. The S/B was calculated from the weights of the solvent−bitumen solution and the dry bitumen. The n-pentane asphaltene content in the bitumen was measured using an NIR probe.13 Ash content in the bitumen was measured by TGA. Multistage extractions were conducted, if needed, following the same procedure. At the end of the extraction, the solvent vapor left over in the filtration cake was drawn out and passed through a condenser by connecting the bottom valve to a vacuum source. The weight change of the cake was monitored, and the final residual solvent content in the mineral solids was determined by extraction followed by GC-FID analysis. o-Xylene was used to extract the solvent from the mineral solids, and the extracts were directly analyzed by capillary column gas chromatography with FID detector. The bitumen content of the extracted mineral solids after drying was measured by TGA by monitoring the weight change during heating in the air environment. The reference sample used was the mineral solids obtained from Dean−Stark extraction.
2. EXPERIMENTAL SECTION 2.1. Materials. High-grade and low-grade oil sand ores from the Athabasca deposit were used. High-grade oil sand ores would normally have higher bitumen content and lower clay content. The n-pentane, toluene, and hexanes were ACS certified and supplied by Fisher. Cyclopentane (reagent grade) and octane (HPLC grade) were purchased from Sigma-Aldrich. All chemicals were used as purchased. 2.2. Apparatus. A vessel was designed and built that allowed us to mix solvent and oil sand and separate the solvent−bitumen solution from the minerals. A schematic of the vessel is shown in Figure 1. It is
3. RESULTS AND DISCUSSION 3.1. Properties of Oil Sands and Solvent. Two types of oil sand ore were used for the experiments: high-grade ore and low-grade ore. The compositions of the two ores are listed in Table 1. The high-grade ore contained 12.2 wt % bitumen and a small amount of water while the low-grade ore contained only 6.8 wt % bitumen and had a higher water content of 11.4 wt %. The particle size distributions of the solids in the two ores obtained by Dean−Stark extraction are shown in Figure 3. The sand-to-fines ratios are listed in Table 1. Fines are defined as
Figure 1. Schematic of the extraction vessel. divided into two chambers by a screen in the middle. The vessel is 12.5 cm high and has a diameter of 6 cm. A filter paper can be secured 1003
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Figure 2. Schematic of the extraction procedure.
Table 1. Composition of Oil Sand Ores Evaluated bitumen (wt %) water (wt %) solids (wt %) sand-to-fines ratio
high-grade ore
low-grade ore
12.2 1.1 86.7 36.9
6.8 11.4 81.8 3.0
Table 2. Properties of Extraction Solvents npentane hexanes cyclopentane boiling point(°C) density@25 °C (g/cm3)
36.1
68.7
49
0.621
0.66
0.745
mixture of npentane and cyclopentane
toluene 110.6
0.692
0.867
evaluate bitumen and solvent recoveries using the light hydrocarbon solvents. 3.2. Operating Conditions. To prevent passage of the small mineral solids into the solvent−bitumen solution, a filter paper with pore size of 40 μm was used. For the first-stage extraction, S/B varied from 1 to 4. The first-stage S/B is labeled as S1/B1. For the second- and third-stage extractions, half the amount of solvent used for the first stage was used. If continuous three-stage extraction is used, the solvent−bitumen solution from the second and the third stages can be recycled as the solvent for the first-stage extraction since the bitumen contents in those solutions are relatively low. In this case, the total amount of solvent used for the three-stage extraction equals that used in the first stage. However, in the batch tests conducted in the lab, fresh solvent was used for each stage of extraction. The impact of g-force on the separation of solvent−bitumen solution from the oil sand matrix was also investigated. The single-stage tests were conducted using cyclopentane and highgrade oil sand at S/B of about 3. The plot of bitumen recovery vs g-force is shown in Figure 4. As can be seen, bitumen recovery increased with increasing g-force from 100 to 500g; after the g-force reached 500g, bitumen recovery did not increase further. Considering that viscosity increases at low S/B, separation at 1000g for 10 min was selected for all of the tests. Since the oil sand samples used for each test were relatively small, it was very difficult to ensure their homogeneity. Therefore, the total weight of bitumen was not calculated on the basis of Dean−Stark results but rather by summing the bitumen collected at each stage plus the bitumen left over on the mineral solids. Bitumen recovery was calculated by dividing the bitumen collected by the total bitumen in the sample.
Figure 3. Particle size distribution of the solids from the oil sand samples.
weight percent of mineral solids smaller than 44 μm. It can been seen that the high-grade ore contained less than 2 wt % fines while the low-grade ore contained about 25 wt % fines. The sand-to-fines ratio of the high-grade ore was 36.9 and for the low-grade ore was 3.0. The properties of the ores show that the high-grade ore was an average good-quality ore and the low-grade ore was a very poor quality ore. The ideal solvent for a solvent extraction process is one that has strong bitumen solubility and a low boiling point, which allows easy solvent recovery. Five solvents were investigated, and their properties are listed in Table 2. The tested mixture comprises n-pentane and cyclopentane at a ratio of 3:7 (w/w). As can be seen, the boiling points of the selected solvents are lower than 70 °C. Toluene was used as a reference solvent to 1004
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Figure 4. Effect of g-force on bitumen recovery.
3.3. Solvent Extraction of High-Grade Ore. 3.3.1. Bitumen Recovery of High-Grade Ore. Toluene is known as a good solvent for dissolving bitumen; however, it has a relatively high boiling point, which makes solvent recovery more difficult. In this work, toluene was used as a reference for comparison. A set of single-stage extraction tests using toluene were conducted with S1/B1 varied from 1 to 4. The bitumen recovery at various S1/B1s is shown in Figure 5. As can be
Figure 6. Bitumen recoveries of the multistage extractions using toluene.
Figure 5. Bitumen recovery of single-stage extraction using toluene.
Figure 7. Bitumen recoveries of multistage extractions using hexanes.
first-stage S/B could be between 2 and 3; however, if first-stage S/B is greater than 4, only single-stage extraction is needed. The bitumen recoveries at various S/Bs using hexanes and n-pentane are shown in Figures 7 and 8. For hexanes, the
seen, bitumen recovery increased with increasing S1/B1 until S1/B1 reached around 3; the recovery then leveled off. At S1/B1 of 3.8, bitumen recovery of a single-stage extraction can reach around 90 wt %. Multistage extraction tests using toluene were also conducted. As described in the Experimental Procedures, the amounts of solvent used for the second and the third stages were half of that used for the first-stage extraction. The cumulative bitumen recovery at various S/Bs is shown in Figure 6. There are three points on each curve; from left to right, the three points represent singlestage, two-stage, and three-stage extractions. S/B is the averaged value. For example, for the two-stage extraction, S/B is the total solvent in the first- and second-stage solvent−bitumen solutions divided by the total bitumen recovered from the first- and secondstage extractions. The recovery is the sum of the recoveries of the current stage plus the former stages. For instance, the recovery for the third point is the total recovery from all three stages. Given a target recovery of more than 90 wt % bitumen, it can be seen that, if three-stage extraction was adopted, the first-stage S/B could be as low as 1. If two-stage extraction was used, the
Figure 8. Bitumen recoveries of multistage extractions using n-pentane.
first-stage S/B varied from 1 to 3; even for three-stage extraction, the total recovery would be less than 90 wt %. Lower 1005
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A mixture of cyclopentane and n-pentane was also investigated since n-pentane is a commonly used light solvent and could be cheaper than cyclopentane. Multistage bitumen recovery using a mixture of n-pentane and cyclopentane at a mass ratio of 3:7 is shown in Figure 10. It can be seen that the
first-stage S/B resulted in slightly higher total bitumen recoveries. This is because some of the asphaltenes precipitate at high S/B. For n-pentane at a first-stage S/B of 1.03, the three-stage extraction can achieve 85 wt % bitumen recovery; however, if the first-stage S/B is high, for example, 3.16, the total bitumen recovery is less than 80 wt %. Considering presence of around 20 wt % asphaltenes in the original bitumen from the ore, at high S/B, most of the asphaltenes precipitate during the extraction process and cannot be recovered by npentane extraction. The results show that the investigated paraffinic solvent with low boiling point cannot achieve overall bitumen recovery over 90 wt % using the investigated process. Cyclopentane, which has boiling point of 49 °C, was investigated. The bitumen recovery of multistage extraction is shown in Figure 9. It can be seen that cyclopentane has very
Figure 10. Bitumen recoveries of multistage extractions using a mixture of n-pentane and cyclopentane.
bitumen recovery using the mixture is not as good as that using pure cyclopentane. To reach 90 wt % bitumen recovery, twostage extraction is needed with a first-stage S/B greater than 2, but using three-stage extraction, the total bitumen recovery can be over 95 wt %. Therefore, using the mixture could also be a good option, considering the operating cost of the bitumen extraction process. Comparing the single-stage solvent extraction abilities of toluene, cyclopentane, and the mixture of cyclopentane and n-pentane as shown in Figure 11, cyclopentane has better bitumen
Figure 9. Bitumen recoveries of multistage extractions using cyclopentane.
good bitumen extraction ability: 90 wt % of the bitumen can be recovered by single-stage extraction using S/B greater than 4. If two-stage extraction is applied, the first-stage S/B can be as low as 1 to obtain 90 wt % bitumen recovery. Using three-stage extraction, over 95 wt % of the bitumen can be recovered. The potential recovery of bitumen using cyclopentane is even higher than that using toluene. The viscosities of the solvent−bitumen solutions of cyclopentane and toluene at various S/Bs were measured and are given in Table 3. The viscosities were measured at 25 °C. Comparing Table 3. Viscosities of Solvent−Bitumen Solutions for Cyclopentane and Toluene at 25°C viscosity (mPa·s) S/B of solvent−bitumen solution
cyclopentane
toluene
1 2 3 4
6.78 1.90 1.15 0.94
6.97 2.47 1.63 1.55
Figure 11. Comparison of bitumen recoveries of single stage extractions.
extraction ability than toluene, while the mixture has a slightly poorer ability than toluene. 3.3.2. Quality of Extracted Bitumen Product. The quality and the properties of the extracted bitumen product are listed in Table 4. The water content in the first-stage solvent− bitumen solution is in the range of 0.01 to 0.2 wt %. From the mass balance calculation, it can be estimated that less than 3 wt % of the total water in the oil sand goes into the solvent− bitumen solution. Most of the water remained in the extracted mineral solids.
the viscosities of cyclopentane−bitumen solution and toluene− bitumen solution at the same S/B, it can be seen that, at S/B of 1, the viscosities are similar. At S/B greater than 2, the viscosity of cyclopentane−bitumen solution is over 30% lower than that of toluene−bitumen solution. The lower viscosity of the cyclopentane−bitumen solution could be the reason for the higher bitumen recovery using cyclopentane rather than toluene. 1006
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Table 4. Quality and Properties of Solvent Extracted Bitumen Product for High-Grade Ore solvent
toluene
1st-stage S/B water content (wt %) ash content (wt %) n-C5 asphaltene content solvent 1st-stage S/B water content (wt %) ash content (wt) n-C5 asphaltene content
1.13 0.17 0.06 18.3 hexanes 1.09 0.12 0.13 11.5
2.05 0.02 0.3 7.3
2.01 0.19 1.15 18.3 3.10 0.01 0.2 5.88
cyclopentane
2.76 0.02 1.09 17.5 n-pentane 1.03 0.23 0.4 14.4
3.16 0.01 0.04 2.4
The ash content in the bitumen was in the range of 0.04 to 1.3 wt %. The high ash content in some cases may have resulted from leakage through the gap between the filter paper and the screen. The average ash content in the bitumen was 0.5 wt %. The n-C5 asphaltene content in the bitumen product varied depending on the type of solvent and the S/B. For toluene and cyclopentane, the n-C5 asphaltene content is around 18 wt %; all of the asphaltenes in the oil sand can be recovered. For hexanes and n-pentane, the n-C5 asphaltene contents in bitumen are less than 18 wt %, and the higher the first-stage S/B, the lower is n-C5 asphaltene content in the product. For n-pentane with a first-stage S/B of 4, the n-C5 asphaltene content in the bitumen is only 2.4 wt %. For the cyclopentane and n-C5 mixture, the n-C5 asphaltene content is slightly less than 18 wt %, which means that most of the heavy components, like asphaltenes, can be recovered from the oil sand. We compared the product quality for the current water-based extraction process using naphtha in froth treatment with that obtained for the solvent extraction process. The diluted bitumen product for water-based extraction typically contains about 3 wt % water and 0.5 wt % solids,1 so the quality of the product from the solvent extraction process for high-grade ore is comparable to that using the current water-based bitumen extraction technology. 3.3.3. Solvent Recovery from Extracted High-Grade Ore. After the three stages of bitumen extraction, the vessel was connected to a vacuum source to recover the solvent in the filtration cake at room temperature. This is not a very efficient solvent recovery procedure. The main purpose of the test was to compare the solvent recovery performance of toluene and the other light hydrocarbon solvents. The results are shown in Figure 12. The x-axis is the time connected with the vacuum source, and the y-axis is the calculated residual solvent in units of barrels of solvent lost per 1000 barrels of bitumen production. It can be seen that, for similar bitumen recoveries, cyclopentane is much easier to recover than toluene. Although the current adopted solvent recovery method is not very efficient, it is not difficult to confine the solvent losses in compliance with the currently stipulated value of less than 4 barrels of solvent lost per 1000 barrels of bitumen produced. 3.3.4. Solvent Extraction of High-Grade Ore Using Pressure Filtration. Regular pressure filtration was also used for separating solvent−bitumen solution from the oil sand matrix. The pressure of 100 kPa is applied on the extraction vessel via the valve on the lid. The bitumen recoveries at various S/Bs are shown in Figure 13. Comparing to the results using centrifugal filtration, it can be seen that, at first-stage S/B of about 1, the bitumen recovery is very low, and the recovery of the threestage extraction was less than 50 wt %. At higher first-stage S/B and using two- or three-stage extraction, bitumen recovery can exceed 90 wt %. The bitumen recovery is slightly lower than
3.73 0.04 0.9 18.5
1.03 1.87 2.97 0.02 0.02 0.04 0.85 1.3 0.62 19.1 18.8 18.3 mixture of cyclopentane and n-pentane 1.09 0.02 0.57 19.3
2.07 0.01 0.25 16.5
3.99 0.02 0.2 17.6 3.40 0.01 0.12 16.2
4.53 0.03 0.16 14.9
Figure 12. Residual solvent in the mineral solids in the solventrecovery process.
Figure 13. Bitumen recoveries of multistage pressure filtration extractions using cyclopentane.
that obtained using centrifugal filtration. Therefore, regular pressure filtration could also be used at higher first-stage S/Bs. 3.4. Solvent Extraction of Low-Grade Ore. For lowgrade ore, only cyclopentane and toluene were investigated for bitumen extraction. The bitumen recoveries for first-stage S/Bs around 2 and 3 are shown in Figure 14. It can be seen that cyclopentane can achieve higher bitumen recovery than 1007
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ACKNOWLEDGMENTS Financial support provided by the EcoETI and PERD programs is gratefully acknowledged.
Figure 14. Bitumen recoveries of multistage extractions of low-grade ore.
toluene. Using cyclopentane in three-stage extraction, bitumen recovery can reach 70 wt %. The quality of the bitumen product and solvent loss for the low-grade ore is given in Table 5. The ash content in the Table 5. Quality of Bitumen Product and Solvent Loss for Low-Grade Ore toluene 1st-stage S/B ash (wt %) qater content (wt %) solvent lost (bbl/1000bbl)
2.02 0.73 0.2 152.4
3 0.47 0.2 192.9
REFERENCES
(1) Tipman, R. N.; Shaw R. C. Our Petroleum Future Conference, Edmonton, April 4−7 1993. (2) Long, Y.; Dabros, T.; Hamza, H. Chem. Mater. Sci. 2007, 511− 547. (3) Taciuk, W.; Caple, R.; Goodwin, S.; Taciuk, G. U.S. Patent 5,366,596, 1994. (4) Graham, R. J.; Helstrom, J. J.; Mehlberg, R. L. Eastern OH Shale Symposium, Hyatt Regency, Lexington, Kentucky, Nov 18−20 1987; pp 93−99. (5) Rosenbloom, W. J. U.S. Patent 5,534,136, 1996. (6) Hanson, D. O.; Sherk, F. T. U.S. Patent 4,139,450, 1979. (7) Farcasiu, M.; Whitehurst, D. D. U.S. Patent 4,046,668, 1976. (8) Meadus, F. W.; Bassaw, B. P.; Sparks, B. D. Fuel Proc. Technol. 1982, 6, 289−300. (9) Meadus, F. W.; Sparks, B. D. Energy Process./Can. 1979, 72 (1), 55−61. (10) Graham, R. J.; Helstrom, J. J.; Peck, L. B.; Stone, R. A.; U.S. Patent 4,722,782, 1988. (11) Wolff, V. T. Canadian Patent 2,520,943, 2006. (12) Funk, E. W.; May, W. G.; Pirkle, J. C., Jr. U.S. 4,347,118, 1982. (13) Long, Y.; Dabros, T.; Hamza, H. Can. J. Chem. Eng. 2004, 82 (4), 776−781.
cyclopentane 2 0.44 0.3 58.4
2.89 0.58 0.3 80.0
bitumen is less than 1 wt %, and water content in the first-stage solvent−bitumen solution is less than 0.5 wt %. Solvent loss for the low-grade ore is high. However, if a better solvent recovery unit was used, it would be easier to obtain lower solvent loss for cyclopentane than toluene.
4. CONCLUSIONS (1) Cyclopentane is a good solvent for extracting bitumen from oil sand. Cyclopentane gives higher bitumen recovery than toluene. To reduce solvent cost, cyclopentane can be mixed with n-pentane. (2) For both high-grade and low-grade ores, bitumen recovery using the investigated solvent extraction process is comparable to that of the water-based bitumen extraction process. (3) The quality of solvent extracted bitumen is similar to that of bitumen from water-based extraction followed by naphtha froth treatment. (4) Centrifugal filtration has a higher efficiency than regular pressure filtration. However, if high S/B is used, regular pressure filtration can also achieve over 90 wt % bitumen recovery. (5) Owing to its higher bitumen recovery and low boiling point, cyclopentane is much easier to recover than toluene. For high-grade ore, solvent loss can be easily limited to less than 4 barrels per 1000 barrels of bitumen production; for low-grade ore, this could be achieved at slightly elevated temperatures.
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