ARTICLE pubs.acs.org/EF
Understanding Asphaltene Dispersants for Paraffinic Solvent-Based Bitumen Froth Treatment Xianhua Feng and Sanyi Wang* Baker Hughes, 7020 45th Street, Leduc, Alberta, Canada T9E 7E7 ABSTRACT: Asphaltene dispersants are used in the paraffinic solvent-based bitumen froth treatment process to increase the fluidity of underflow that is made of precipitated asphaltene aggregates, water, and mineral solids. In this work, the yield stress of the underflow was used to define the fluidity of underflow and to evaluate the performance of asphaltene dispersants. The performance of asphaltene dispersants was also examined using microscope, tensiometer, and DeanStark composition analysis. Results show that asphaltene dispersants prevent asphaltene particles from forming large aggregates by modifying their surface properties. Application of an effective asphaltene dispersant not only results in much lower yield stress of the underflow, but also brings more mineral solids and asphaltenes from rag layer to the underflow.
’ INTRODUCTION In oil sands extraction process, bitumen is liberated from oil sands by warm water under slightly alkaline condition and is floated to the top of the processing vessel under aeration, forming bitumen froth which contains approximately 60% bitumen, 30% water, and 10% solids. Clean bitumen is obtained in froth treatment where bitumen froth is mixed with solvents to remove impurities such as water and mineral solids. In the paraffinic solvent-based froth treatment process,1 a portion of total asphaltenes in bitumen form aggregates with solids and water. The aggregates precipitate out and constitute part of the underflow along with mineral solids and water. While asphaltene agglomeration helps clean bitumen froth, the aggregates may decrease the fluidity of the underflow and thus create high torque for settler rakes and underflow pumping problems. The aggregates may also contribute to the rag layer between diluted bitumen and underflow, which presents a barrier preventing solvent from rising and water/solids from settling, leading to a higher solvent carryover to the underflow. Asphaltene dispersant could be used to solve the aforementioned problems in paraffinic solvent-based froth treatment process. Figure 1 is a schematic representation of the three-stage countercurrent decantation paraffinic solvent-based froth treatment process currently employed in industry.2 The bitumen froth enters the first stage settler, and the tailings stream exits from the third stage settler. The paraffinic solvent is introduced into the third stage settler and the diluted bitumen product is released from the first stage settler. The solvent-to-bitumen ratio increases from the first stage settler to the third stage settler. In this process, the asphaltene dispersant may be added to the froth before it enters the first stage settler or other locations as desired. The formation and structure of asphaltene aggregates in the paraffinic solvent-diluted bitumen has been studied by Long et al.3,4 It was found that precipitated asphaltene forms aggregates with water droplets and solids. The size and density of the aggregates vary with solvents, solvent-to-bitumen ratio, and temperature. For example, at hexane-to-bitumen ratio of 1.5 2.0 and at 4050 °C, the size of aggregates is about 100 μm and the density of the aggregates is about 1.0 g/mL.3,4 r 2011 American Chemical Society
Asphaltene aggregation can be effectively controlled by asphaltene dispersants. It has been found that low-molecularweight amphiphiles, e.g., alkyl phenols5,6 and benzenesulfonic acid6,7 can prevent flocculation of asphltene in apolar alkane solvents. Polymeric dispersants are able to stabilize asphaltene8 or disperse asphaltene aggregates9 in heptane. In conventional crude oil with >0.1% asphaltene, asphaltenes form micelles and therefore asphaltenes are present in the form of colloid.10 The colloidal asphaltenes have a size of 0.11 μm. Upon dilution with alkane solvents, the colloidal particles aggregate and form flocculated asphaltene particles of 130 μm.11 Addition of asphaltene dispersants can prevent asphaltenes from flocculating in alkane-diluted oils and allows them to remain in the colloidal form, thus enhancing the compatibility of incompatible crude oil mixtures.12 Asphaltene dispersants were also found to prevent asphaltene precipitation in reservoir rocks and wellbore tubing.13 Although the effect of asphaltene dispersants on the aggregation of asphaltenes in crude oils has been extensively investigated,11,14,15 studies of asphaltene aggregates in the paraffinic solvent-diluted bitumen in the presence of asphaltene dispersants have never been reported. To effectively control asphaltene agglomeration in the paraffinic froth treatment, quantitative evaluation of the performance of asphaltene dispersants is required. Moreover, understanding how asphaltene dispersants control asphaltene agglomeration is important for asphaltene dispersant product development. The objective of this study is to understand the mechanism of asphaltene dispersants in controlling asphaltene agglomeration in the paraffinic solvent-based froth treatment and to correlate structure of asphaltene dispersants with their performance. In this study, the underflow of the first stage settler was created in the laboratory to simulate the commercial settler operations for the purpose of research. Rheological test, interfacial tension examination, quantitative composition analysis, microscopic observation, and settling tests
Received: March 4, 2011 Revised: May 17, 2011 Published: May 17, 2011 2601
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Figure 2. Illustration of settling zones.
Figure 1. Schematic representation of counter current decantation paraffinic froth treatment.
Table 1. Relative Solubility Number (RSN) of Asphaltene Dispersants PAO1 PAO2 PAO3 PAO4 PAO5 PAO6 PAO7 PAO8 RSN
13.0
13.3
14.5
14.8
15.1
15.8
16.2
16.7
are used collectively to achieve a better understanding of asphaltene dispersants in the paraffinic bitumen froth treatment.
’ MATERIALS AND METHODS Materials. Bitumen froth obtained from industry contained 55.4 ( 3.4% bitumen, 9.7 ( 0.3% solids, and 34.9 ( 3.1% water. Asphaltene dispersants were synthesized by Baker Hughes research center in Houston, Texas. Their relative solubility numbers (RSN) were measured in tolueneethylene glycol dimethyl ether (EGDE) solvent system (2.6% toluene and 97.4% EGDE by volume) as shown in Table 1. The RSN is defined as the amount of water in milliliters required to produce persistent turbidity in a tolueneEGDE solvent system consisting of 1-g surfactant sample and 30-mL solvent.16 A higher RSN of an asphaltene dispersant in a chemical series means that chemical possesses a relatively higher hydrophilicity. Vacuum distillation feed bitumen was obtained from Syncrude Canada Ltd. Certified ACS toluene, pentane, and hexane were purchased from Fisher Scientific. Underflow Preparation. To ensure repeatability of the testing results, bitumen froth was homogenized prior to use for generating underflow. Homogenization was carried out by mechanically stirring the froth at 850 rpm and 80 °C for 1 h in a baffled stainless beaker with a water jacket. The homogenized froth was collected from the bottom of the beaker to a number of jars. The collected froth sample was mixed at 30 °C with 1:1 (v/v) pentane/hexane solvent at solvent/bitumen mass ratio of 2.4. After mixing at 700 rpm for 15 min, the mixture was transferred into a settling column. The settling was performed at 30 °C for 1 h. To avoid disturbance of underflow structure, the underflow was collected directly in a measuring cup which was connected to the bottom of the settling column. After 1-h settling, the diluted bitumen supernatant was discharged and then the measuring cup was disconnected from the settling column. Yield Stress Measurement. Yield stress was measured with an Anton Paar MCR101 rheometer with vane geometry. The vane geometry is used as its disturbance to the tested sample is
negligible and there is no wall slip effect.17 All yield stress tests were performed at 30 °C. Blank tests were performed for underflow samples without asphaltene dispersant addition as a control. The reported yield stress was the average of three repeats. To ensure reliability, the three repeats were performed with underflow samples collected from different locations in the same batch of homogenized froth. Composition Analysis. Composition analysis was performed with DeanStark extraction method. The bitumen froth or underflow sample was placed in a thimble and underwent repeated extraction by toluene under reflux. Finally, bitumen was dissolved in toluene, solids remained in the thimble, and water was brought to a solvent trap. Once the absolute amounts of bitumen, water, and solids were determined, the solvent content was calculated based on mass balance. Microscopic Observation. The size of asphaltene aggregates was estimated with an Olympus BX51 microscope under fluorescence. The samples were taken from the fresh precipitated asphaltenes-rich layer after settling and examined immediately after sampling. The observation was performed at room temperature of 20 ( 1 °C. Settling Test. The froth sample was mixed at 30 °C with 1:1 (v/v) pentane/hexane solvent at the solvent/bitumen mass ratio of 2.4. After mixing at 700 rpm for 15 min, the diluted froth was transferred to a graduated cylinder which was sealed immediately with aluminum foil after the transfer. The cylinder was placed in a glass tank filled with water. The water temperature was maintained at 30 °C with a circulator. The level of the upper interface between diluted bitumen and rag layer was recorded against the settling time with the aid of a laser illuminator. Interfacial Tension Measurement. The interfacial tension was determined with Fisher Surface Tensiomat Model 21 equipped with a Pt-Ir ring. The testing samples were made of 29.4% bitumen in the 25/25/50 (v/v/v) pentane/hexane/toluene mixed solvent with or without asphaltene dispersant. The solvent/ bitumen mass ratio was set at 2.4 as in the underflow preparation. Toluene was used for stabilizing asphaltenes in the mixed solvent and de-ionized (DI) water was used as aqueous phase. All tests were carried out at room temperature of 20 ( 1 °C.
’ RESULTS AND DISCUSSION After bitumen froth was mixed with paraffinic solvents at solvent/bitumen mass ratio of 2.4:1 and allowed to settle for 1 h, three settling zones were observed as shown in Figure 2. The top zone is diluted bitumen, the middle zone is rich in asphaltenes, and the bottom zone is mainly water and solids. For the sake of simplicity, the asphaltenes-rich middle layer is loosely defined as rag layer in this study, and these two terms (i.e., rag layer and asphaltenes-rich layer) are used interchangeably hereafter. If settling is allowed to proceed for a prolonged period of time, 2602
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Figure 3. Shear stress as a function of shear strain for underflow with and without asphaltene dispersant application. The dosage of asphaltene dispersants is 100 ppm based on the mass of froth.
Figure 4. Relationship between yield stress reduction and relative solubility number of asphaltene dispersants. The dosage of asphaltene dispersants is 100 ppm.
most of the rag layer will eventually fall into the bottom water/ solids zone. The middle and bottom zones, i.e., rag layer and water/solids, are collectively called underflow for rheological tests. It should be pointed out that the underflow generated from laboratory may not represent exactly the underflow produced in the industrial operation. However, rag layer does exist in the industrial production. The rheological tests for the underflow generated in the laboratory may mimic the fluidity of the underflow in the industrial operation. One of the key performance indicators of asphaltene dispersants is their ability to improve the fluidity of the underflow by reducing the yield stress of the underflow. Yield stress is the level of stress at which substantial deformation suddenly takes place.18 In the case of underflow, yield stress may be defined as the stress at which the structure of the aggregated particles is broken and the underflow is free to flow. There are many methods for the determination of yield stress.19 For the underflow system, the shear stress vs shear strain method was adopted. In this method, the yield stress is defined as the equilibrium stress in shear stress vs shear strain curve.17 In the two-plates model, the shear stress is defined as the shear force divided by the shear area, and the shear strain is defined as the length of deflection divided by the distance between the two plates.20 Figure 3 shows shear stress as a function of shear strain for the underflow in the absence and presence of asphaltene dispersants. The dosage of asphaltene dispersants is 100 ppm based on the mass of froth. To evaluate the performance of asphaltene dispersants, the percentage of yield stress reduction for each asphaltene dispersant was calculated using the following equation:
Figure 5. Yield stress reduction as a function of dosage of PAO4.
yield stress reduction, % ¼ ðy0 y1 Þ=y0 100
ð1Þ
where y0 is the yield stress of underflow without asphaltene dispersant application and y1 is the yield stress of underflow in the presence of asphaltene dispersant. A higher percentage of yield stress reduction would indicate a higher efficiency of asphaltene dispersion. The performance of asphaltene dispersants is shown in Figure 4 as a function of relative solubility number (RSN) of the dispersants. The results in Figure 4 show that the effectiveness of asphaltene dispersants decreases with an increase in the RSN of the chemicals. When RSN exceeds a specific value, e.g., 16.7, the asphaltene dispersant (i.e., PAO8) becomes ineffective. Besides RSN, performance of an asphaltene dispersant also depends on its dosage. Figure 5 shows the yield stress reduction as a function of dosage of PAO4. The yield stress decreased with
increasing asphaltene dispersant. However, when dispersant dosage was further increased beyond 50 ppm, the yield stress was reduced less significantly. This observation supports that the initial 50 ppm of asphaltene dispersant had a considerable impact on asphaltene dispersion. Increased chemical treatment beyond 50 ppm had a lesser effect on measured yield stress values. The effect of asphaltene dispersants on the paraffinic froth treatment was further evaluated by determining the water content and the density of the supernatant diluted bitumen and analyzing the composition of the underflow for all samples with and without application of asphaltene dispersants. The results were given in Table 2. In this paper, the organic component in underflow is simply called bitumen instead of asphaltene because it would contain asphaltenes and some maltenes which were dissolved in the solvent (i.e., the pentane/hexane mixture). It should be noted that the results in Table 2 and Figure 3 were obtained from the same batch of testing samples. As can be seen in Table 2, the water content of the supernatant diluted bitumen is about 180 ppm and the density of the supernatant is about 732 kg/m3 for all the supernatants with and without application of asphaltene dispersants. These results suggest that application of asphaltene dispersants has negligible effect on dewatering of bitumen froth in paraffinic froth treatment and the solubility of bitumen in the paraffinic solvents. As a result, the composition of underflow remains almost the same regardless of whether or which asphaltene dispersant is introduced. To reveal the influence of asphaltene dispersants on the formation of underflow, the distribution of the precipitated 2603
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Table 2. Water Content and Density of Supernatants and Composition of Underflows Generated with and without Application of Asphaltene Dispersants underflow chemical
bitumen, %
solids, %
supernatant solvent, %
water, %
water, ppm
density 20 °C, kg/m3
blank
16.5 ( 2.3
11.8 ( 1.3
14.8 ( 5.1
57.0 ( 6.5
227 ( 35
734
PAO1
15.8 ( 1.9
11.5 ( 0.3
18.2 ( 2.6
54.5 ( 1.9
216 ( 39
730
PAO2 PAO3
15.4 ( 1.0 16.3 ( 0.7
11.2 ( 0.4 12.1 ( 0.2
16.7 ( 5.0 14.1 ( 2.4
56.7 ( 5.8 57.5 ( 3.2
182 ( 15 183 ( 5
732 733
PAO4
16.5 ( 0.5
12.2 ( 0.3
13.0 ( 1.5
58.3 ( 1.7
161 ( 26
732
PAO5
16.1 ( 0.7
12.4 ( 0.2
14.1 ( 1.6
57.4 ( 2.4
159 ( 7
733
PAO6
16.1 ( 0.5
12.8 ( 0.4
13.6 ( 1.9
57.4 ( 2.0
165 ( 9
732
PAO7
16.7 ( 1.1
12.2 ( 0.6
16.0 ( 1.8
55.2 ( 2.4
168 ( 11
733
PAO8
16.3 ( 0.8
11.0 ( 0.2
15.8 ( 2.1
56.9 ( 2.7
197 ( 26
732
Table 3. Composition of the Rag Layer and the Bottom Water and Solids Phase in the Absence and Presence of Asphaltene Dispersants bitumen, %
rag layer solids, % water, %
solvent, %
blank
21.3 ( 1.6
7.8 ( 1.0
37.0 ( 8.3
33.9 ( 8.9
PAO3
22.9 ( 0.1
6.0 ( 0.3
42.9 ( 0.7
28.3 ( 0.9
PAO4 PAO5
24.2 ( 1.4 21.7 ( 0.8
6.8 ( 0.1 6.5 ( 0.8
40.1 ( 1.3 39.9 ( 2.9
28.9 ( 0.1 32.1 ( 2.9
PAO8
21.7 ( 0.4
7.4 ( 0.5
41.7 ( 2.3
29.4 ( 2.2
bitumen, % blank PAO3
2.9 ( 0.1 2.8 ( 0.1
bottom water and solids phase solids, % water, % 21.8 ( 0.1 21.7 ( 0.8
71.8 ( 0.4 72.3 ( 2.1
solvent, %
Figure 6. Percentage of rag layer in underflow in the absence and presence of 100 ppm asphaltene dispersants.
3.5 ( 0.9 3.3 ( 1.3
PAO4
3.2 ( 0.1
20.5 ( 1.1
71.8 ( 0.3
4.5 ( 0.7
PAO5
3.1 ( 1.1
21.5 ( 1.7
71.9 ( 0.3
3.5 ( 0.8
PAO8
2.1 ( 0.1
22.8 ( 0.6
70.6 ( 1.5
4.6 ( 0.8
bitumen, solids, water, and solvents in the asphaltene-rich layer and the bottom water and solids phase was examined. To this end, the underflow collected in the measuring cup was carefully divided into two fractions after 1 h of settling at 30 °C. The precipitated asphaltenes-rich layer at the top was first collected as the first fraction. When the rag layer was removed and water phase was first observed, the remaining water/solids phase was collected as the second fraction. The composition of these two fractions was analyzed and given in Table 3. Although the rag layer and the bottom water/solids layer both contain bitumen, solids, water, and solvent, the precipitated bitumen remains mainly in the rag layer and most of water and solids settle to the bottom water/solids phase. The effect of asphaltene dispersants on the rag layer and distribution of the asphaltenes and solids in the total underflow was investigated. The mass percentage of rag layer in the underflow is shown in Figure 6. It can be seen that the percentages of the rag layer are 67% and 51% in the underflow without asphaltene dispersant and with 100 ppm PAO4, respectively. This is a 23% reduction in the mass of rag layer by 100 ppm of PAO4 addition. In contrast, other asphaltene dispersants did not bring about the same amount of rag layer reduction. For example,
Figure 7. Distribution of bitumen in rag layer and water/solids phase 4of underflow in the absence and presence of 100 ppm asphaltene dispersants.
100 ppm PAO3 or PAO5 led to only 12% reduction, and 100 ppm PAO8 gave 4% reduction. Further examination of bitumen and solids content in the underflow revealed that compared to the blank, PAO4 was able to bring 4.9% more bitumen and 15.8% more solids from the rag layer to the bottom water/solids phase, whereas corresponding values were 1.6% bitumen and 13.2% solids for PAO3, and 3.2% bitumen and 11.7% solids for PAO5 (Figures 7 and 8). In addition, PAO8 did not bring any more bitumen but rather 4.9% more solids from the rag layer to the bottom water/solids phase. In the continuous paraffinic froth 2604
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Energy & Fuels treatment, a fraction of precipitated asphaltenes contributes to the formation of rag layer which inhibits solvent release. This leads to more solvent entrained in the underflow or ultimately a higher solvent loss to TSRU (Tailings Solvent Recovery Unit) feed. If a chemical can reduce the tendency of rag layer formation, it is reasonable to predict that solvent losses to tails may also be reduced. It should be noted that the reported solvent content here was calculated based on mass balance. The accurate determination of
Figure 8. Distribution of solids in rag layer and water/solids phase of underflow in the absence and presence of 100 ppm asphaltene dispersants.
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solvent amount in the underflow was not achieved in this work. The results of Figures 79 suggest that PAO4 is more effective than other asphaltene dispersants in dispersing asphaltenes and solids from the rag layer to the bottom water/solids phase. The action of asphaltene dispersants in the paraffinic froth treatment was also examined by microscope under fluorescence. Figure 9 shows micrographs of asphaltene aggregates in the rag layer with and without application of asphaltene dispersants. In the absence of asphaltene dispersants, the aggregates were about 100 μm in size. This result is consistent with the reports by Long et al.3,4 As pointed out earlier, the aggregates are composed of asphaltenes, solids, and water. Application of 100 ppm PAO3, PAO4, or PAO5 decreased the size to about 50 μm, whereas application of the same amount of PAO7 or PAO8 could only decrease the size slightly below 100 μm. These results indicate that asphaltene dispersants are able to either prevent asphaltenes from aggregating or reduce the size of asphaltene aggregates that have already existed. Furthermore, results of Figure 9 revealed that asphaltene dispersants causing greater reduction of aggregate size would lead to lower yield strength of the underflow (see Figure 4). Because the aggregate size is reduced with the addition of asphaltene dispersants, it is important to know if the application of asphaltene dispersants would hinder the settling of aggregates. For this purpose, settling experiments were performed. The settling results are shown in Figure 10 with the normalized upper
Figure 9. Micrographs of asphaltene aggregates in the absence and presence of 100 ppm asphaltene dispersants. The samples were taken from rag layer and viewed under fluorescence. The scale bar is 100 μm in all micrographs. 2605
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Figure 10. Effect of 100 ppm PAO4 on the settling rate of the aggregates.
Figure 11. Interfacial tension between water and bitumen diluted with 25/25/50 (v/v/v) pentane/hexane/toluene as a function of dosage of PAO4.
interface level as a function of settling time. It can be seen that the aggregates settled rapidly within the first 10 min and then started to slow down. Presence of asphaltene dispersants (such as PAO4) did not affect the settling of aggregates, although the aggregate size was reduced. Based on Stokes’ law, settling rate is proportional to the square of particle size and the density difference between dispersed particles and medium. This finding suggests that the aggregates in the presence of asphaltene dispersants may have a higher density than those in the absence of asphaltene dispersants. In fact, Rahmani et al.21 found that there is an inverse relationship between asphaltene aggregate size and its density. If this relationship still applies when asphaltene dispersants are used, the reduced aggregate size implies an increased aggregate density. Therefore the effect of reduced aggregate size was offset by the effect of increased aggregate density on its settling rate. In general, asphaltene dispersants are polymeric surfactants. In diluted bitumen and aqueous environment, they tend to adsorb at the bitumen/water interface. On the other hand, asphaltene molecules contain not only aromatic structure but also a variety of polar functional groups. These groups would interact with asphaltene dispersant molecules.6 When asphaltenes form aggregates, asphaltene dispersant molecules will adsorb onto the surface of asphaltene particles and change their surface properties, thereby preventing asphaltene particles from further coagulating to form larger aggregates. The fluidity of underflow is
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Figure 12. Interfacial tension between water and bitumen diluted with 25/25/50 (v/v/v) pentane/hexane/toluene in the presence of 100 ppm asphaltene dispersants.
therefore improved. To correlate the performance of asphaltene dispersants with their interfacial activity, the interfacial tension (IFT) between water and bitumen diluted with pentane/hexane/ toluene mixed solvent was measured in the absence and presence of asphaltene dispersants. Figure 11 shows the IFT as a function of dosage of PAO4 in the oil phase. It can be seen that the IFT between water and diluted bitumen decreased with increasing dosage of PAO4. For example, with 100 ppm of PAO4 addition, the IFT was lowered from 27 to 18 mN/m. Clearly, PAO4 changed the bitumen/water interfacial properties. The ability of asphaltene dispersants in changing interfacial properties was further compared at 100 ppm of dosage. As shown in Figure 12, in the presence of PAO1, PAO2, PAO3, or PAO4, the IFT was decreased to about 20 mN/m, whereas in the presence of PAO5, PAO6, PAO7, or PAO8, the IFT was only decreased to about 25 mN/m. The results of Figure 12 indicated that PAO1, PAO2, PAO3, and PAO4 are more interfacial active than other asphaltene dispersants. The stronger ability of PAO1, PAO2, PAO3, and PAO4 in decreasing the IFT corresponds well to their performance in decreasing the yield stress of underflow shown in Figure 4.
’ CONCLUSIONS A key performance indicator of asphaltene dispersants in paraffinic solvent-based froth treatment is their ability to reduce the yield stress of the underflow and improve its fluidity. Through this work, an appropriate yield stress measurement method has been established to successfully evaluate asphaltene dispersant candidates. The performance of asphaltene dispersants was also evaluated by their effect on the particle size and composition of the rag layer. Results show that asphaltene dispersants modify surface properties of the asphaltene particles, whereby the size of asphaltene aggregates is significantly reduced and more solids and asphaltenes are drawn from the rag layer to the bottom water/solids phase, resulting in a much lower yield stress of the underflow. The relationship between product performance and structure of asphaltene dispersants has been established. It seems that an optimal hydrophilicity does exist to give the best performance of asphaltene dispersant. ’ AUTHOR INFORMATION Corresponding Author
*Phone: (780)980-5970. Fax: (780)980-5973. E-mail: sanyi.wang@ bakerhughes.com. 2606
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’ ACKNOWLEDGMENT Throughout this project, we have been supported by our colleagues in Sugar Land, Texas. In particular we appreciate the contributions from Bruce Horne and Dr. Patrick Breen. This work was generously funded by Alberta Innovates Technology Futures. We thank Alberta Innovates for its funding and Baker Hughes for the permission to publish this work. ’ REFERENCES (1) Tipman, R. N.; Long, Y. Solvent process for bitumen separation from oil sands froth. US patent 5876592, 1999. (2) Masliyah, J. H. Fundamentals of Oil Sands Extraction (CHE 534 text book); University of Alberta: Edmonton, Alberta, Canada, 2006. (3) Long, Y.; Dabros, T.; Hamza, H. Stability and settling characteristics of solvent-diluted bitumen emulsions. Fuel 2002, 81, 1945–1952. (4) Long, Y.; Dabros, T.; Hamza, H. Structure of water/solids/ asphaltenes aggregates and effect of mixing temperature on settling rate in solvent-diluted bitumen. Fuel 2004, 83, 823–832. (5) Gonzalez, G.; Middea, A. Peptization of asphaltene by various oil soluble amphiphiles. Colloids Surf. 1991, 52, 207–217. (6) Chang, C. L.; Fogler, H. S. Stabilization of asphaltenes in aliphatic solvents using alkylbenzene-derived amphiphiles. 1. Effect of the chemical structure of amphiphiles on asphaltene stabilization. Langmuir 1994, 10, 1749–1757. (7) Wiehe, I. A.; Varadaraj, R.; Jermansen, T. G.; Kennedy, R. J.; Brons, C. H. Branched alkyl-aromatic sulfonic acid dispersants for solublizing asphaltenes in petroleum oils. US patent 6048904, 2000. (8) Chang, C. L.; Fogler, H. S. Peptization and coagulation asphaltenes in apolar media using oil-soluble polymers. Sci. Technol. Int. 1996, 14, 75–100. (9) Hart, P. R.; Maharajh, E. M. Process for extracting bitumen. US patent 7357857 B2, 2008. (10) Mullins, O. C.; Sheu, E. Y. Structures and Dynamics of Asphaltenes; Plenum Press: New York, 1998. (11) Kraiwattanawong, K.; Fogler, H. S.; Gharfeh, S. G.; Singh, P.; Thomason, W. H.; Chavadej, S. Effect of asphaltene dispersants on aggregate size and distribution and growth. Energy Fuels 2009, 23, 1575–1582. (12) Wiehe, I. A.; Jermansen, T. G. Design of synthetic dispersants for asphaltenes. Pet. Sci. Technol. 2003, 21, 527–536. (13) Contreras, O. L. E.; Rogel, E.; Dambakli, G.; Espidel, J.; Acevedo, S. The influence of the adsorption of amphiphiles and resins in controlling asphaltene flocculation. Energy Fuels 2001, 15, 1028– 1032. (14) Abdel-Moghny, T.; Desouky, S. M.; Ramzi, M. Effect of surfactant on the growth of onset aggregation of some Egyptian crude oils. J. Dispersion Sci. Technol. 2008, 29, 397–405. (15) Barcenas, M.; Orea, P.; Buenrostro-Gonzalez, E.; ZamudioRivera, L. S.; Duda, Y. Study of medium effect on asphaltene agglomeration inhibitor efficiency. Energy Fuels 2008, 22, 1917–1922. (16) Wu, J.; Xu, Y.; Dabros, T.; Hamza, H. Development of a method for measurement of relative solubility of nonionic surfactants. Colloids Surf., A 2004, 232, 229–237. (17) Barnes, H. A.; Nguyen, Q. D. Rotating vane rheometry-a review. J. Non-Newtonian Fluid Mech. 2001, 98, 1–14. (18) Robinson, M., Ed. Chambers 21st Dictionary; W & R Chambers: Edinburgh, 1996. (19) Barnes, H. A. The yield stress-a review-everything flows? J Non-Newtonian Fluid Mech. 1999, 81, 133–178. (20) Mezger, T. G. The Rheology Handbook, 2nd ed.; Vincentz Network: Hanover, 2006. (21) Rahmani, N. H. G.; Dabros, T.; Masliyah, J. H. Settling properties of asphaltene aggregates. Energy Fuels 2005, 19, 1099–1108.
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