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Energy & Fuels 2005, 19, 2014-2020
Viscosities of Heavy Oils in Toluene and Partially Deasphalted Heavy Oils in Heptol in a Study of Asphaltenes Self-Interactions Chandra W. Angle,*,† Leo Lue,‡ Tadeusz Dabros,† and Hassan A. Hamza† Natural Resources Canada, CANMET Energy Technology Centre Devon, Advanced Separations Technologies, #1 Oil Patch Drive, Devon, Alberta, Canada, T9G 1A8, School of Chemical Engineering and Analytical Science, The University of Manchester, P.O. Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom Received January 20, 2005
Interparticle interactions of the soluble asphaltenes in partially deasphalted heavy oils in toluene-heptane (heptol) mixtures are compared to those of several heavy oils diluted in toluene only. Viscosity-volume fraction (η-Φ) relationships for the heavy oils and bitumen in toluene were almost identical. However, the asphaltenes in toluene associated and scaled differently from its source oil. Four classical viscosity models were used to describe the data, and scaling was interpreted on the basis of asphaltenes association, as in macromolecular interactions. The PalRhodes model showed deviation from sphericity with solvation constants for heavy oils in toluene and C-5 asphaltenes in toluene, at 1.4-1.6 and 3.7, respectively. The Krieger-Dougherty (KH) model indicated high interparticle interaction factors, and maximum packing factors of ∼1 suggested polydispersity. Neither models fit the data for deasphalted oils. The Leighton-Acrivos model showed that (i) the maximum packing fraction (Φmax) for all oils was similar, (ii) the asphaltenes alone in toluene had the highest self-associations, and (iii) the deasphalted oils showed Φmax values close to the theoretical values (0.58). From the Einstein equations, intrinsic viscosities [η] of deasphalted oils in heptol gave aspect ratios (length to radius, L/R) of the asphaltenes at 10 (i.e., rodlike molecules). The K-H model gave [η] of ∼4 and L/R ≈ 3.5 for heavy oils in toluene; however, for asphaltenes in toluene, the model gave [η] ≈ 10.6 and L/R ≈ 5.8 (i.e., less-rodlike molecules).
1. Introduction Asphaltene precipitation and aggregation in various organic nonsolvents have been studied extensively for crude oils, heavy oils, and bitumen, using a variety of analytical techniques.1-3 The instability of these solubility classes of materials found in crude oils has raised concerns in catalyst fouling, emulsions stability, and in pipeline transportation of heavy oils. The high concentrations of these high-molecular-weight organic structures in heavy oils make significant contributions to the high viscosity of heavy oils. Thus, in the pursuit of understanding the behaviors of these materials in the crude oils, researchers have invoked thermodynamic arguments that include the regular solution approach, as well as macromolecular arguments,4-22 as are discussed in proteins, colloidal, or nanoparticle dispersions. In heavy oil processing, the viscosity of the oil diluted * Author to whom correspondence should be addressed. Telephone: 780-987-8621. Fax: 780-987-8676. E-mail address:
[email protected]. † Natural Resources Canada, CANMET Energy Technology Centre Devon, Advanced Separations Technologies. ‡ School of Chemical Engineering and Analytical Science, The University of Manchester. (1) Tanaka, R.; Sato, E.; Hunt, J. E.; Winans, R. E.; Sato, S.; Takanohashi, T. Energy Fuels 2004, 18, 1118-1125. (2) Espinat, D.; Fenistein, D.; Barre´, L.; Frot, D.; Briolant, Y. Energy Fuels 2004, 18, 1243-1249. (3) Angle, C. W.; Long, Y.; Hamza, H. A.; Lue, L. Submitted to Fuel, 2005.
in toluene would indicate limits for viscous resistance to turbulent deformation stresses by the droplet in water. In this case, viscosity provides the criteria for the oils in the investigation of droplet breakup behavior. (4) Ferworn, K. A. Thermodynamics and Kinetic Modelling of Asphaltene Precipitation from Heavy Oils and Bitumens, University of Calgary, Calgary, Alberta, Canada, Thesis/Dissertation, 1995, pp 1-236. (5) Mitchell, D. L.; Speight, J. G. Fuel 1973, 52, 149-153. (6) Ravey, J. C.; Ducouret, G.; Espinat, D. Fuel 1988, 67, 15601567. (7) Sheu, E. Y.; Storm, D. A.; De Tar, M. M. J. Non-Cryst. Solids 1991, 131-133 (Part 1), 341-347. (8) Sheu, E. Y.; De Tar, M.; Storm, D.; De Canio, S. Fuel 1992, 71, 299-302. (9) Cimino, R.; Correra, S.; del Bianco, A.; Lockhart, T. P. Solubility and phase behaviour of asphaltenes in hydrocarbon media. In AsphaltenessFundamentals and Applications; Plenum Press: New York, 1993; pp 97-130. (10) Sheu, E. Y.; Storm, D. A. Colloidal properties of asphaltenes in organic solvents. In AsphaltenessFundamentals and Applications; Plenum: New York, 1993; pp 1-52. (11) Storm, D. A.; Sheu, E. Y. Colloidal nature of petroleum asphaltenes. In Asphaltenes and Asphalts 1; Elsevier: Amsterdam, 1994; pp 125-157. (12) Rogel, E. Energy Fuels 1997, 11 (4), 920-925. (13) Escobedo, J.; Mansoori, G. A. SPE Prod. Facil. 1997, 12, 116122. (14) Werner, A.; Behar, F.; de Hemptinne, J. C.; Behar, E. Fluid Phase Equilib. 1998, 147, 343-356. (15) Schabron, J. F.; Speight, J. G. Pet. Sci. Technol. 1998, 16, 361375. (16) Baltus, R. E. Characterization of asphaltenes and heavy oils using hydrodynamic property measurements. In Structures and Dynamics of Asphaltenes; Plenum Press: New York, 1998; pp 303-335.
10.1021/ef0500235 CCC: $30.25 © 2005 American Chemical Society Published on Web 07/29/2005
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Table 1. Sources of Heavy Oils and Their Properties
a
source of heavy oil
Primrosea
Cold Lakeb
Athabascab
°API saturates content (wt %) aromatics content (wt %) resins (polars) content (wt %) asphaltenes content (wt %) molecular weight, MWtc (g/mol) density @ 22 °C (g/mL) viscosity @ 24 °C ( mPa s)
10-11 23 21.1 38.8 17.1 534 1.003 >10 000
11 21 19 44 16 585 1.0035 17 600-20 000
8.2-9.1 16.9 18.3 44.8 17.2 532 1.019 >300 000
Data from this work. b From ref 29. c As determined using gel permeation chromatography.4
For a colloidal suspension or macromolecular solution, the relationship between volume fractions and viscosity provides some insight into the interparticle interactions and the interactions with the continuous phase (e.g., asphaltenes-with-resins for increased heavy oils in diluents). Information on the viscosity of residual solutions of partially deasphalted heavy oils is sparse.13 Viscosity could provide insight on the state of aggregation of residual destabilized solutions after treatment with n-heptane. Others researchers have recognized that aggregation details for asphaltenes in heavy oils are still lacking.23 After systematic additions of n-heptane to various diluted heavy oils in toluene, it was previously found that low concentrations of residual asphaltenes remained in solution after equilibration in the mixtures of toluene and n-heptane (solvent and nonsolvent).3,24 At CANMET, the development of new instrumentation made it possible to measure low concentrations of asphaltenes undisturbed in solution after the partial removal of asphaltenes by successive precipitation with a nonsolvent. Thus, the viscosity-concentration relationships of residual oil from diluted heavy-oil-intoluene systems after n-heptane additions are reported in this paper. For the present paper, after asphaltenes in toluenediluted heavy oils were precipitated by n-heptane, the viscosities of partially deasphalted heavy oils in heptol (n-heptane + toluene) are compared with toluenediluted heavy oils and bitumens and their asphaltenes in toluene. The viscosities of the heavy oils in toluene and the residual heavy oil in heptol were measured. Established semi-theoretical-empirical models that have been used to investigate interparticle interactions and colloidal suspension behavior are used to describe the data. For the data analysis, we make the assumption that the mixtures are less than colloidal or are near colloidal for particles 2 min, as in the neat crude oils), the method of measurements was changed to a low-shear magnetically driven falling-ball viscometer designed by Cambridge Applied Systems, Inc., USA. This instrument consists of a sample holding chamber, a piston inside the chamber, and a control/monitoring unit. An alternating magnetic field causes the low-mass piston suspended in the fluid within the sample chamber to move up and down in the fluid. The time to move a fixed distance (0.508 cm) is correlated with the viscosity of the oil. For determining higher viscosities, the appropriately calibrated piston (five were supplied) is chosen for the viscosity range desired. Temperature was regulated by recirculating water around the chamber from a bath that was supplied by Julabo, USA.
3. TheorysViscosity Models Earlier workers identified ∼96 empirical models that described the viscosity versus the fractions of dispersed phase for Newtonian mixtures and suspensions.17 These were condensed37 and reordered by further manipulation38 into one final general equation.39,40 Brief descriptions of the basic models that are applied to this work are as follows: (35) Shaw, D. J. Introduction to Colloid and Surface Chemistry; Butterworth: London, 1980; pp 213-231. (36) Ferguson, J.; Kemblowski, Z. Applied Fluid Rheology; Elsevier Applied Science: New York, 1991; pp 1-323. (37) Rutgers, I. R. Rheologica Acta 1962, 2, 305-348. (38) Rutgers, I. R. Rheologica Acta 1962, 2, 202-210. (39) Sudduth, R. D. J. Appl. Polym. Sci. 1993, 48, 25-36. (40) Sudduth, R. D. J. Appl. Polym. Sci. 1993, 50, 123-147.
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The Einstein model (eq 1.3) assumes that the fluid is a continuum that contains discrete noninteracting particles:41
ηr )
η ) 1 + 2.5Φ + o(Φ2) η0
(1.3)
where ηr is the relative viscosity, η0 the solvent viscosity, η the suspension viscosity, and o is a numerical coefficient specific for a system. The Einstein equation is only applicable in very dilute, noninteracting dispersions (Φ < 0.1). The intrinsic viscosity [η] is defined as
ηr - 1 Φf0 Φ
[η] ) lim
(1.4)
From the Einstein equation, [η] ) 2.5 for “solutions” of spherical particles (regardless of size); deviations from 2.5 occur if solvation of the solute occurs and the predicted size of solvated solute is larger than that of the dry mass. Therefore, a solvated sphere has a larger intrinsic viscosity. Other possible reasons for deviation are solute nonsphericity and polydispersity. The Pal-Rhodes model42 for suspensions extends the Einstein model to volume fractions of >0.1:
ηr )
η ) (1 - ksΦ)-2.5 η0
(1.5)
Mooney43 introduced the crowding factor of [1 - (Φ/ Φmax)]2 to account for the free space available from the crowding of particles at a volume fraction of Φ when a second fraction of particles is added.
η ) η0 exp
{[
( )] }
2.5Φ Φ 1 - kp Φmax
2
(1.8)
In this case, kp is a polydispersity factor and is equal to 1 for monodispersed spheres. The Eiler model44 (used for bitumen dispersions) can be used to determine the intrinsic viscosity if it fits the data.
(
[η]Φ/2 η ) 1+ η0 1 - (Φ/Φmax)
)
2
(1.9)
It is a two-parameter model: [η] and Φmax. Eiler’s model assumes that particles pack to a critical volume fraction Φmax. Rearranging eq 1.9 yields
η1/2 [η] r - 1 1 ) + (η1/2 - 1) Φ 2 Φmax r
(1.10)
Krieger and Dougherty45 developed a predictive viscosity model for suspensions of uncharged spheres that was applicable to volume fractions of >0.1 and accounted for the maximum packing fraction.
(
Φ Φmax
)
-[η]Φmax
where ks indicates the solvation of the suspended particles. If ks ) 1, there is no solvation (surrounding solvent dragged along) of the particles. Values of ks that are greater than unity suggest deviation from spheres.10,17 The exponent of 2.5 (taken from the Einstein equation (eq 1.3)) denotes hydrodynamic sphericity. Although the Pal-Rhodes model was derived for emulsion studies, Sheu10 determined that it was very suitable for asphaltenes in organic solvents and we followed suit. Taking the derivative of the Einstein equation and setting the solvent viscosity equal to the suspension viscosity gives
When [η]Φmax ) 2, the Krieger-Dougherty equation (eq 1.11) is the same as eq 1.9. A modified form of the Krieger-Dougherty model was introduced by Frankel and Acrivos46 and refined by Leighton and Acrivos47 for studying concentrated suspensions.
dη ) 2.5dΦ η
The Leighton-Acrivos47 model is a slight variation of eq 1.8. For suspensions, Leighton and Acrivos suggested values of Φmax ) 0.58 and n ) 2.
(1.6)
Sudduth39 generalized this equation to
∫
dη ) η
∫
ν dΦ Φ 1Φmax
(
)
n
η ) η0 1 -
[
η ) η0 1 +
1.5Φ 1 - (Φ/Φmax)
(1.11)
]
n
(1.12)
4. Results and Discussions
(1.7)
where n is the particle interaction coefficient or an indicator of the amount of particle interaction that is occurring in the system. The particle shape factor (v) is normally 2.5 for spheres. The packing factor (Φmax) accounts for polydispersity. Polydisperse systems pack more efficiently than monodisperse systems. Integrating eq 1.7 and substituting n ) 0, 1, or 2 gives other equations (n ) 1 for the Mooney model,43 and n ) 2 for the Krieger-Dougherty models) that describe viscosityconcentration relationships. (41) Einstein, A. Ann. Phys. 1906, 19, 289. (42) Pal, R.; Rhodes, E. J. Rheol. (N.Y.) 1989, 33, 1021-1045. (43) Mooney, M. J. Colloid Sci. 1951, 6, 162-170.
The Mooney and Eiler models did not adequately describe the data in regard to viscosity versus volume fraction of oils and, therefore, are not shown. The other four basic models were applied to the data to find some indication of the hydration of the particles and the maximum packing factors. In most models tested, the relative viscosity of the system should have a linear relationship with increasing volume fraction to a value of ∼0.1. Strong interparticle interactions appear as deviations from linearity. However, after evaluations, three of the suspension models (Pal-Rhodes, KriegerDougherty, and Leighton-Acrivos), seemed to be suitably fitted to the data for viscosity of heavy oils in (44) Eilers, H. J. J. Phys. Colloid Chem. 1948, 53, 1195-1211. (45) Krieger, I. M. Adv. Colloid Interface Sci. 1972, 3, 111-136. (46) Frankel, N. A.; Acrivos, A. Chem. Eng. Sci. 1967, 22, 847-853. (47) Leighton, D.; Acrivos, A. Chem. Eng. Sci. 1986, 41, 1377-1384.
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Angle et al.
Table 2. Parameters for the Krieger-Dougherty Model (eq 1.11) Fitted to the Viscosity Data of Heavy Oils and C-5 Asphaltenes in Toluene
a
sample
[η]
aspect ratioa
Φmax
Rcorr
number of data points
Primrose-1 Primrose-2 Cold Lake Athabasca-1 Athabasca-2 Athabasca-1-C-5 asphaltenes
3.91 ( 0.09 3.79 ( 0.08 3.81 ( 0.01 4.11 ( 0.15 3.92 ( 0.03 10.63 ( 0.25
3.5 3.5 3.5 3.6 3.5 5.8
0.93 ( 0.03 0.91 ( 0.02 0.99 ( 0.01 0.99 ( 0.02 0.99 ( 0.01 0.99 ( 0.01
0.98 1.0 1.0 0.99 0.99 0.99
12 9 11 6 11 12
The aspect ratio is calculated from [η] ) length2/(π × radius2).
Table 3. Parameters for the Pal-Rhodes Model (eq 1.5) Fitted to the Viscosity Data of Heavy Oils and C-5 Asphaltenes sample
intercept
solvation constant, ks
Rcorr
number of data points
Primrose-1 Primrose-2 Cold Lake Athabasca-1 Athabasca-2 Athabasca-1-C-5 asphaltenes
1.00 ( 0.01 1.02 ( 0.01 0.997 ( 0.00 1.00 ( 0.01 0.988 ( 0.00 0.996 ( 0.00
1.42 ( 0.02 1.54 ( 0.07 1.41 ( 0.02 1.57 ( 0.07 1.39 ( 0.02 3.71 ( 0.11
0.998 ( 0.01 0.994 ( 0.01 0.999 ( 0.01 0.996 ( 0.01 0.999 ( 0.01 0.998 ( 0.01
12 9 11 6 11 12
Table 4. Parameters for the Leighton-Acrivos Model (eq 1.12) Fitted to Viscosity Data of Heavy Oils and C-5 Asphaltenes in Toluenea
a
sample oil
Φmax
n
Rcorr
Primrose Cold Lake Athabasca-1 Athabasca-2 Athabasca-1-C-5 asphaltenes
0.724 ( 0.01 0.801 ( 0.02 0.458 ( 0.16 0.724 ( 0.03 0.234 ( 0.03
2.4 ( 0.04 2.5 ( 0.03 2.4 ( 0.23 2.5 ( 0.05 5.8 ( 0.26
1.0 1.0 0.991 1.0 0.995
number of points 11 11 6 11 12
Here, η0 is the viscosity of toluene at 22 °C (η0 ) 0.577 mPa‚s).
toluene, and only one of these (Leighton-Acrivos) fit both the heavy oils and bitumen in toluene, as well as deasphalted heavy oil in heptol. These models were chosen based on the assumptions that, if Φg 0.1, the particles will interact hydrodynamically and the basic Einstein model will not fit. However, we found that the Einstein model was useful to determine the intrinsic viscosity of asphaltenes in solution for the partially deasphalted oils. The summary of the parameters for the various heavy oils and asphaltenes fitted with the Krieger-Dougherty model appear in Table 2, those fitted with the PalRhodes model are given in Table 3, and, those fitted with the Leighton-Acrivos model are given in Table 4. The Φmax values obtained by fitting the KriegerDougherty model for heavy oils and bitumen in toluene are all ∼1. This suggests polydispersity, because, for monodispersed hard spheres, Φmax ) 0.74. The [η] values are similar for all oils except the C-5 asphaltenes, which have larger values than their source Athabasca bitumen-1 (by a factor of >2). The aspect ratios calculated from the intrinsic viscosity are the same for all oils except the asphaltenes. Other researchers have found the [η] values of asphaltenes in xylene to be 3.6 if extracted by pentane and 3.9 if extracted by nonane, whereas, in maltenes, the [η] values are 10.9 and 10.1, respectively.48 Our results are consistent with their published values in other solvents. Table 3 shows that the ks values for the Pal-Rhodes model fitted to the data are all similar for the heavy (48) He´naut, I.; Argillier, J.-F.; Couster, C.; Moan, M. Influence of asphaltenes and resins content on heavy oil rheology. In AIChE International Symposium of Characterization of Petroleum Macromolecules, AIChE Spring National Meeting, March 10-14, 2002, New Orleans, LA; pp 29-36.
oils and bitumen (ks ≈ 1.5), indicating a deviation from spheres. However, the ks value for C-5 asphaltenes is much larger than that for pure oils in toluene, which indicates more swelling and association of the particles. Figure 1 shows the curves for the Leighton-Acrivos model fitted to the data of viscosity versus volume fraction of oils in toluene for two heavy oils, two bitumens, and asphaltenes. Figure 3 shows the curves for the same model fitted to data of partially deasphalted heavy oils in heptol. Other viscosity models did not fit the data for the residual heavy oils in heptol very well. These residual oils were very diluted and exhibited behaviors that were more similar to the solvent mixtures initially, until a substantial quantity of oils was present. The responses differed from Primrose, which was the heavy-oil-in-toluene source. Figure 1 shows that all heavy oils and bitumen data except asphaltenes fell along the same curve and generally follow the same relationship described by the Leighton-Acrivos model. This model fitted the experimental η versus Φoil data for both toluene-diluted heavy oils and residual heavy oils in heptol with correlation coefficients of R2 > 0.99. The summaries of the parameters for this model are found in Table 4 for the heavy oils and bitumen in toluene, and Table 5 for partially deasphalted heavy oils in heptol. For the partially deasphalted heavy oils in heptol, the Leighton-Acrivos model, which does not require a value input for the pure solvent viscosity (i.e., the third parameter), was allowed to converge to the viscosity of the heptol solvent mixtures after several iterations of curve fitting. The converged viscosity values matched the measured solvent viscosities.
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Table 5. Leighton-Acrivos Model Correlation for Data on Residual Heavy Oils in Heptola Primrose-HvOi in toluene at start, before heptane 10 wt % 17 wt % 25 wt % 35 wt % δmix 15.6-15.79 MPa1/2 15.9-16.23 MPa1/2 16.21-16.62 MPa1/2 16.67-17.04 MPa1/2 a
η0
Φmax
n
Rcorr
0.417 ( 0.006 0.401 ( 0.006 0.401 ( 0.01 0.399 ( 0.006
0.19 ( 0.10 0.64 ( 0.22 0.64 ( 0.22 0.54 ( 0.07
3.27 ( 0.62 1.78 ( 0.04 2.07 ( 0.28 2.02 ( 0.15
0.993 0.999 0.997 0.998
0.436 ( 0.004 0.431 ( 0.02 0.441 ( 0.02 0.482 ( 0.44
0.21 ( 0.02 0.21 ( 0.0 0.42 ( 0.34 0.44 ( 0.46
1.47 ( 0.16 2.45 ( 0.95 2.68 ( 0.27 1.9 ( 0.0
0.997 0.57 0.972 0.906
Data are categorized by the starting toluene/HO ratio. b Here, η0 is the viscosity of the heptol solvents at 22 °C.
Figure 1. Viscosity (η) versus maximum packing fraction (Φoil) data and the fit to the Leighton-Acrivos model (denoted by the lines) for all heavy oils diluted in toluene (Primrose, Cold Lake, Athabasca-1, and Athabasca-2 bitumens, as well as C-5 asphaltenes from Athabasca-1.
Figure 2. Fits of the Leighton-Acrivos model (denoted by the lines) to the viscosity versus volume fraction of deasphalted heavy oils in heptol, categorized by original stock concentrations of heavy oil in toluene. The parameters are given in Table 5.
Figure 2 shows the fit of the Leighton-Acrivos model to the viscosity of partially deasphalted heavy oils in heptol versus their volume fractions (categorized by their starting concentration in toluene before heptane addition). All data from starting concentrations of >10 wt % almost fell on a single curve with an averaged Φmax value of 0.61, n ) 1.96 ( 0.1, and η0 ) 0.41 (that for n-heptane is 0.41 mPa‚s), as indicated in Table 5. Residual oils for samples from deasphalting of the 10 wt % heavy oil were dilute. The Φmax was low at 0.19, but n ) 3.27, which is a high value for this model, thus indicating larger solvated or noninteracting particles. When the viscosity data of the remaining partially
Figure 3. Summary of relative viscosity versus soluble asphaltenes volume fraction for all deasphalted heavy oils in heptol; the line shows the linear fit, and the intercept and slope are given in the graph legend inside the figure.
deasphalted heavy oil in heptol were categorized by solubility parameters δmix and fitted to the LeightonAcrivos model, there was a clear distinction between the less-soluble systems and more-soluble oils.3 Yet, all followed the same viscosity rise with an increased concentration of oil. At the same concentrations of oil in heptol, the higher solubility δmix gave higher viscosities. This suggests that there were some conformation differences in the structures associated with residual oils in heptol. However, this categorization did not produce consistent data. Figure 3 shows a linear correlation between the volume fraction of soluble asphaltenes measured in the partially deasphalted heavy oils and the corresponding measured relative viscosity. The slope of this line shows the intrinsic viscosity [η] to be 34.5 ( 1.3. If compared with an [η] value of 2.5 in the Einstein equation (eq 1.3), then the value [η] ) 34.5 ( 1.3 indicates that the asphaltenes aggregates are nonspherical. If we assume that the aggregates behave as rigid rods, as in macromolecules,49 then the aspect ratio (length/radius, L/R) is 10.4. This ratio is larger than that calculated for the heavy oils and the powdered C-5 asphaltenes dissolved in toluene, as shown in the third column of Table 2. This indicates that asphaltenes are important, per se, but not pivotal for the entire array of physical responses of the heavy oils. Thus, it follows that, in a droplet of heavy oil, the macromolecular materials should pack better and perhaps contribute to a more mobile surface when (49) Evans, D. F.; Wennerstro¨m, H. The Colloidal Domain-Where Physics, Chemistry, Biology, and Technology Meet; Wiley-VCH Publishers: New York, 2004; pp 1-631.
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diluted and, at high concentrations, become more rigid. Asphaltenes associated with the oil’s resins in a heptol droplet should dissipate more energy in motion and assume a packing configuration different from the original heavy oils. The viscosity of toluene-diluted heavy oils, bitumens, and asphaltenes, as described by the Pal-Rhodes model, suggest solvation and deviation from sphericity for dispersed particles. High correlations with the KriegerDougherty model indicated interparticle interactions that occur at higher concentrations, and, hence, maximum packing factors were determined to be close to unity, which is indicative of polydispersity. These values were all higher than those obtained with the LeightonAcrivos model, which showed Φmax values that were similar for all heavy oils except Athabasca-1 and its C-5 asphaltenes. Asphaltenes in the toluene associated more strongly than asphaltenes in the heavy oils and in the bitumens, and is indicated by the relatively high intrinsic viscosity value in Table 2. The viscosity dependence on the volume fraction of heavy oils and partially deasphalted heavy oils indicates that the asphaltenes in oils exist as macromolecular structures that associate to varied extents in the solvents. Associations of only asphaltenes in toluene seem to influence the viscosity more than the asphaltenes within the oils. However, their presence in heavy oils does not dominate the viscosity behavior of the oils. Other components in the heavy oils prevent strong asphaltenes association, thus creating a polydispersed macromolecular or colloidal system that contributed to the viscosity. If one should need heavy oil samples for fundamental emulsification study, these heavy oils in toluene show predictable viscosity behaviors. The partially deasphalted oils in heptol are prone to have many variables within one sample (heptol, as well as asphaltenes, changed in composition as n-heptane is added to the toluene-diluted oils). Removal of the heptol from the residual heavy oils in the heptol will simplify the system for comparison to the original oils and produce stock modified heavy oils. The results of this study indicated that asphaltenes alone in toluene associate strongly and are not a true representative of heavy oils for use in emulsion study that mimics heavy oils. The partially deasphalted heavy oils in heptol will also behave similar to macromolecules and show a high degree of selfassociation during a deasphalting process. Conclusions (1) The viscosity versus volume fraction relationships of heavy oils and bitumen in toluene were identical. Asphaltenes in toluene deviated from the source bitumen behavior. The increase in viscosity with increasing
Angle et al.
volume fraction oils indicated that interparticle interactions were significant above a volume fraction heavy oil in toluene of 0.15. Above a volume fraction of 0.25, the viscosities sharply increased. Three of five viscosity models tested fit the data. (2) Viscosity data on toluene-diluted heavy oils, bitumens, and asphaltenes were described by the PalRhodes model, which suggests solvation and deviation from sphericity for dispersed particles. The KriegerDougherty model indicated interparticle interactions that were occurring at higher concentrations. Maximum packing factors determined to be ∼1 for all, which was a sign of polydispersity. These values were all higher than those obtained with the Leighton-Acrivos model, which showed similar maximum packing fraction (Φmax) values for all heavy oils except the bitumen Athabasca-1 and its C-5 asphaltenes. Asphaltenes only in toluene associate more strongly than in the heavy oils, and in the bitumens, as shown by a relatively high intrinsic viscosity. (3) The relationships between viscosities of residual (partially deasphalted) heavy oils in heptol and volume fraction all followed the Leighton-Acrivos model that was developed for particle suspensions. Large deviations from source oil behaviors were observed for each of the diluted partially deasphalted heavy oils tested. The Φmax value for the partially deasphalted diluted oils (starting oils were 17, 25, and 35 wt % heavy oils before heptane) were 0.64, 0.64, and 0.54 and were similar to the theoretical value of 0.58 that was predicted by the model. The residual oils that remained after partially deasphalting the 10 wt % starting heavy oil gave a value of Φmax ) 0.19. The Φmax values were much lower for the deasphalted oils if they were categorized by solubility parameters. The Φmax value was the lowest for those with the lowest solubility parameter (δmix) and vice versa, and this observation might be indicative of swelling. (4) The increase in viscosity was lower for asphaltenes of heavy oils-in-toluene, compared to that for asphaltenes only in toluene. Components in the heavy oils prevent strong asphaltenes association. The asphaltenes, as colloids in toluene, deviated from sphericity. (5) In partially deasphalted heavy oils in heptol, the high intrinsic viscosity indicated that asphaltenes had high aspect ratios and suggested a rodlike configuration. Acknowledgment. This work was supported in part by Canadian Panel of Energy Research and Development. This study is a part of Dr. Angle’s Ph.D. dissertation at the Department of Chemical Engineering, UMIST, Manchester, U.K. C.W.A. thanks Edwina Ng for her help while performing some of the experiments. EF0500235
