Energy Fuels 2009, 23, 4431–4437 Published on Web 08/12/2009
: DOI:10.1021/ef900309j
On Asphaltene and Resin Association in Athabasca Bitumen and Maya Crude Oil Bei Zhao,† M. Becerra, and J. M. Shaw* Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada. † Current address: Natural Resources Canada, CanmetENERGY, Devon, Alberta T9G 1A8, Canada. Received April 7, 2009. Revised Manuscript Received July 14, 2009
The mass fraction of resins in asphaltene-rich aggregates, present in crude oils, and the physics and chemistry associated with them are poorly defined because of the variability of the definitions of asphaltenes and resins but remain a subject of significant interest to practitioners who model asphaltene behavior in hydrocarbon resources. In this contribution, the mass fraction of resins in pentaneasphaltene-rich aggregates in nanofiltered Athabasca bitumen and Maya crude oil samples is evaluated using a mass balance model and data regression fits to saturates, aromatics, resins, and asphaltenes (SARA) analyses of permeate and retentate samples obtained by filtering these hydrocarbon resources directly through 5, 10, 20, 50, 100, and 200 nm filters. Solvents are not employed in the filtration experiments. At 473 K, the mass fraction of resins in pentane-asphaltene-rich aggregates and the fraction of resins present in aggregates are both found to be at or below the threshold for resin mass fraction measurement error. The aggregates present in both of these hydrocarbon resources may be treated as resins and pentane-free asphaltenes at this temperature. Nanofiltration measurements with Maya crude oil at lower temperatures, namely, 338-373 K, suggest that ∼16% of resins comprise ∼10 wt % of pentaneasphaltene-rich aggregates. Even at lower temperatures, the resins content of pentane-asphaltene-rich aggregates appears to be limited to a small fraction of resins that comprise a small fraction of asphaltenerich aggregates. On a heptane asphaltene basis, aggregates would comprise a minimum of 20 wt % resins. Because the definitions of asphaltenes and resins are fungible, these results provide directional and qualitative guidance with respect to asphaltene modeling and highlight limitations in terminology and ambiguity in analytic approaches used in this field.
been reported,4 and for a heptane asphaltenes, resin, and heptane mixture, a resin/asphaltene mass ratio of 1:7 has been reported.5 For both examples, the mass fraction of the resins is significant. Diverse definitions for asphaltenes complicate quantitative analysis. It is well-known that small variations in the separations procedure (timing, temperature, filter size, etc.) affect the mass fraction of a sample reported as resins or asphaltenes.6,7 Pentane and heptane asphaltenes have separate American Society for Testing and Materials (ASTM) standards and variants, and these lead to differing perceptions of sample compositions, as illustrated in Table 1, for Athabasca bitumen and Maya crude oil. The heptane asphaltenes and aromatics fractions are smaller, while the mass fraction of the resins is correspondingly larger than for the corresponding pentane asphaltene cases. Consequently, perceptions of the extent and importance of resin and asphaltene association may be colored by the definitions employed. Here, we analyze nanofiltration data reported previously,1 with a focus on defining the limits they impose, through mass balance constraints, on the possible range of mass fractions of the resins in resins and pentane-asphaltene-rich aggregates in Maya crude and Athabasca bitumen at 473 K. We also present new nanofiltration data for Maya crude oil obtained at 338, 353, and 373 K, where Maya crude maltenes (resins,
Introduction In a recent paper, we asserted that pentane-asphaltenes and resins do not associate preferentially in pentane-asphaltene-rich aggregates present in Maya crude oil and Athabasca bitumen, on a mass basis, at 473 K.1 This finding contrasts with prevalent views in the literature regarding resin and asphaltene association.2,3 Cartoons consistent with the prevalent view concerning the nature of coherent asphaltene-rich aggregates vary in detail but show asphaltene centers surrounded by resins. Such images are ubiquitous. One does not obtain a clear sense from the literature of what the mass ratio of resins to asphaltenes is in these aggregates, but from cartoons one has the impression that it is significant. Experimental work with model mixtures would appear to support this view. For example, for a mixture of heptane asphaltenes, resins, and toluene, a resin/asphaltene mass ratio of 2:1 has *To whom correspondence should be addressed. Telephone: 780-4928236. E-mail:
[email protected]. (1) Zhao, B.; Shaw, J. M. Composition and size distribution of coherent nanostructures in Athabasca bitumen and Maya crude oil. Energy Fuels 2007, 21 (5), 2795–2804. (2) Wiehe, I. A.; Liang, K. S. Asphaltenes, resins, and other petroleum macromolecules. Fluid Phase Equilib. 1996, 117 (1-2), 201–210. (3) Yarranton, H. W. Asphaltene self-association. J. Dispersion Sci. Technol. 2005, 26 (1), 5–8. (4) Merino-Garcia, D.; Andersen, S. I. Thermodynamic characterization of asphaltene-resin interaction by microcalorimetry. Langmuir 2004, 20 (11), 4559–4565. (5) Leon, O.; Contreras, E.; Rogel, E.; Dambakli, G.; Acevedo, S.; Carbognani, L.; Espidel, J. Adsorption of native resins on asphaltene particles: A correlation between adsorption and activity. Langmuir 2002, 18 (13), 5106–5112. r 2009 American Chemical Society
(6) Szewczyk, V.; Behar, E. Compositional model for predicting asphaltenes flocculation. Fluid Phase Equilib. 1999, 158-160, 459–469. (7) Alboudwarej, H.; Beck, J.; Svrcek, W. Y.; Yarranton, H. W.; Akbarzadeh, K. Sensitivity of asphaltene properties to separation techniques. Energy Fuels 2002, 16 (2), 462–469.
4431
pubs.acs.org/EF
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
Table 1. SARA Analyses for Athabasca Bitumen and Maya Crude Oil (wt %) Maya crude oil 1
heptane
pentane saturates aromatics resins asphaltenes
Athabasca bitumen 11
31.6 42.5 10.2 15.7
12.4
pentane1
heptane12
16.1 48.5 16.8 18.6
16.3 39.8 28.5 14.7
saturates, and aromatics) are liquid and Maya pentane asphaltenes exhibit solid-phase behavior.8 In contrast, pentane asphaltenes are more than 65 wt % liquid at 473 K. Filtration is a physical process. Permeates are enriched in constituents that pass freely through filters. Retentates are enriched in constituents that are partially or wholly retained by filters. The mass ratio of constituents that are retained to those that pass freely through filters (Y) is a key variable. In the development of the model, we presume that saturates, aromatics, and part of the resins, resins I, pass freely through the filters and that part of the resins, resins II, and the asphaltenes are partially retained. For simplicity, the composition of the asphaltene-rich aggregates is assumed to be independent of the mixture composition. With these assumptions, the saturates, aromatics, resins, and asphaltenes (SARA) compositions of all retentate and permeate samples are defined by eqs 1-4 Xsaturates ¼
X1 ½1þðY -1ÞðX4 þX5 Þ
ð1Þ
Xaromatics ¼
X2 ½1þðY -1ÞðX4 þX5 Þ
ð2Þ
Xresins
½X3 þYX4 ¼ ½1þðY -1ÞðX4 þX5 Þ
Xasphaltenes ¼
YX5 ½1þðY -1ÞðX4 þX5 Þ
Figure 1. (a) Mass balance constraint for saturates, aromatics, resins I, and resins II, where there is no association with asphaltenes, (b) mass balance constraint for saturates, aromatics, and resins I, where resins II is associated with asphaltenes, and (c) mass balance constraint for resins II, where it associates with asphaltenes.
ð3Þ
ð4Þ
loci for constituents that pass freely through filters, e.g., saturates and aromatics (Figure 1b), intersect the asphaltenes axis at the asphaltene mass fraction present in the asphaltene-rich aggregates, Xaas, and intersect the vertical axis at mass fractions exceeding values present in the asphaltene-free feed. In contrast, the resins composition locus (Figure 1c) terminates at the resins II composition in the asphaltene-rich aggregate, Xras. Dependent upon the magnitude of the resins II fraction in the aggregates, the slope of the resins versus asphaltenes composition locus can be either negative or positive. A negative slope is depicted in Figure 1c. The resins composition locus intersects the vertical axis at a composition less than the asphaltene-free feed composition. Because the slopes and intercepts of the composition loci are interrelated, the range of possible values for resins II composition in the feed, X4, is constrained by compositions of the permeate and retentate samples and their trends with global composition. For SARA analysis, measurement errors are significant, as shown in Table 1. Use of feed compositions as anchors for the model can lead to biased fits to experimental data. An empirical least-squares fit, exploiting the principles of the mass balance constraints (linear relationships, interpretation of asphaltene, and asphaltene-free axis intercepts), provides a second window into the composition of the asphaltene-rich
where the composition of the feed is defined as saturates (X1), aromatics (X2), resins I (X3), resins II (X4), and asphaltenes (X5). These compositions sum to unity. The variable Y ranges from 0 for aggregate-free samples (aromatics, saturates, and resins I samples) to 1 (the feed) to infinity for asphaltene-rich aggregates that are free of other feed constituents (asphaltenes and resins II samples). Y defines the locus of possible compositions, for any given resins II fraction, X4, in the feed. The resins II fraction, X4, cannot be measured directly and is the only fitting parameter in the model. These constraints impose linear relationships between the mass fractions of constituents, such as saturates, aromatics, and resins, and the mass fraction of asphaltenes. Possible loci are illustrated in Figure 1. If the resins II fraction is negligible (Figure 1a), composition loci pass through the feed composition, intersect the asphaltene axis at Xasphaltenes =1, and intersect the vertical axis at asphaltene-free compositions in the feed. The slope of the locus is negative. If the resins II fraction in the feed, X4, is significant, (8) Fulem, M.; Becerra, M.; Hasan, M. D. A.; Zhao, B.; Shaw, J. M. Phase behaviour of Maya crude oil based on calorimetry and rheometry. Fluid Phase Equilib. 2008, 272 (1-2), 32–41.
4432
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
Table 2. SARA Analysis Method and Errora test
method
concentration range (wt %)
saturates aromatics ASTM D2007
5
ASTM D3279 (pentane asphaltenes)
4.0-29.0 4.0-29.0
resins asphaltenes a
repeatability
reproducibility
2.1 2.3 0.24 0.81 1.2 standard deviation 0.53%xb 0.93%xc
4.0 3.3 0.4 1.3 1.8 acceptable range of two results 1.51%xb 2.78%xc
x is the mean value in weight percentage. b Single operator. c Multilaboratory.
Table 3. Low-Temperature Nanofiltration Results for Maya Crude Oil permeates temperature (K) filter size (nm) filter composition
338 200 Al2O3
353 50 zirconia
C H N S O
80.5 11.3 0.6 2.8 1.4
80.6 11.3 0.6 2.9 1.4
saturates aromatics resins asphaltenes (C5)
29.8 55.1 13.3 1.9
40.1 44.6 13.4 2.0
Maya crude oil 373 100 zirconia
353 50 zirconia
373 100 zirconia
Elemental Analysis (wt %) 80.5 84.5 10.6 11.3 0.7 0.3 3.4 3.3 1.4 1.2
82.6 8.8 0.9 5.8 1.4
82.6 9.2 0.8 5.6 1.4
81.9 9.5 0.6 5.1 1.4
SARA Analysis (wt %) 30.8 31.6 44.5 42.5 12.3 10.2 12.4 15.7
9.7 26.8 9.9 53.5
12.4 28.1 11.6 47.9
16.6 29.2 12.7 41.5
aggregates. Equations 5-8 comprise the simplest basis for a linear least-squares fit to sample composition data Xaromaticsþsaturates ¼ aaromaticsþsaturates Xasphaltenes þbaromaticsþsaturates Xresins ¼ aresins Xasphaltenes þbresins
the feed stocks, Athabasca bitumen and Maya Crude oil, were heated to 473 K under nitrogen and passed through commercially available zirconia and alumina filters with nominal pore diameters: zirconia, 20, 50, and 100 nm; and alumina, 5, 10, and 200 nm. The solvent was not added to the feed stocks. Filtration experiments were halted once approximately 50 g of permeate was collected. The duration of individual filtration experiments, at 473 K, was approximately 6 weeks. The filtration apparatus was then disassembled, and retentate samples, primarily filter cake combined with fresh feed, were obtained. Permeate, feed, and retentate samples were analyzed using a number of techniques. SARA analysis is the relevant measure here. The pentane SARA composition for Athabasca bitumen and Maya crude oil is shown in Table 1. All analysis methods and associated errors are reported in Table 2. Detailed composition data for Maya crude oil and Maya crude oil samples filtered at lower temperatures are presented in Table 3. It was not possible to conduct lower temperature filtration experiments with Athabasca bitumen. Permeates were not produced. SARA analysis data reported in all figures in this contribution have been assigned single-operator repeatability errors because most of the analyses were preformed by a single technician using the same apparatus. To avoid clutter in the figures, the symbol size is set to be larger than the error for the asphaltene weight percentage measurements. It is also important to note that pentane asphaltene analysis is not welldefined, according to the ASTM standards, for mixtures containing more than 30 wt % asphaltenes. Some of the retentate samples have up to 70 wt % asphaltenes.
ð5Þ ð6Þ
where from the asphaltene-free axis mass balance constraint bresins ¼ 1 -baromaticsþsaturates ð7Þ and from the asphaltene axis intercept baromaticsþsaturates Xaas ¼ aaromaticsþsaturates
retentates 338 200 Al2O3
ð8Þ
By lumping the saturates and aromatics fractions, there are three independent parameters in the linear least-squares fit. These comprise the slopes of the aromatics þ saturates and resins fractions versus the asphaltenes fraction (aaromaticsþsaturates and aresins) and the intercept of aromatics þ saturates fraction versus asphaltenes fraction (baromaticsþsaturates). The mass fraction of resins II in the feed (X4) can be obtained as long as the asphaltene mass fraction in the feed (X5) is known or assumed ð9Þ X4 ¼ ð1 -Xaas ÞX5 If SARA analysis was error-free, both approaches would be equivalent. Because this is not the case, the least-squares fit and the mass balance models are both applied to the experimental data. The least-squares fit can also be used to test the key underlying assumption in the model, i.e., concerning the global composition invariance of pentane-asphaltene-rich aggregate composition.
Results and Discussion Saturates, aromatics, and resins compositions and saturates and aromatics composition versus asphaltenes composition for permeates, feeds, and retentates derived from Athabasca bitumen and Maya crude oil at 473 K are shown in panels a-d of Figures 2 and 3, respectively. Low-temperature nanofiltration data obtained from Maya crude oil are reported in panels a-d of Figure 4. The thick solid lines, in panels c and d of Figures 2, 3, and 4, correspond to the linear least-squares
Experimental Section Nanofiltration experimental details and permeate and retentate composition data obtained at 473 K were presented previously.1 Key points are rehearsed here. Approximately 200 g of 4433
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
Figure 2. Composition data, least-squares fit, and mass balance model for nanofiltered Athabasca bitumen samples at 473 K: (a) saturates, (b) aromatics, (c) resins, and (d) saturates and aromatics. Mass fraction of resin II in the feed, X4, is a parameter. Values are 0, 0.01, 0.02, and 0.05.
fits for experimental resins and the sum of saturates and aromatics composition values (eqs 5 and 6). The thin lines correspond to the mass balance model (eqs 1-4). Experimentally measured feed compositions and the values of the mass fraction of resins II (X4), a parameter in the plots, define these lines. Mass Balance Model Evaluation. Qualitative Measures. From a qualitative perspective, composition data presented in Figures 2-4 follow the linear relationships anticipated by the mass balance model (eqs 1-4) within experimental error. The data do not justify more complex treatment, such as allowing for variation of asphaltene-rich aggregate composition with global composition or aggregate size. The experimentally measured resins compositions (X3 þX4) exhibit the greatest scatter but also impose the tightest constraints on the possible ranges for the mass fraction of resins II, because its variation with the asphaltene mass fraction is the most sensitive to the extent of resin-asphaltene association. For example, if the mass fraction of resins II, X4, exceeds 0.037 and 0.017 for Athabasca bitumen and Maya crude, respectively, the slopes of the resins composition loci (Figures 2c, 3c, and 4c) become positive, a result at qualitative variance with the trends in the resins composition data. Thus, the mass fraction of resins in pentane-asphaltene-rich aggregates at 473 K is limited to a small fraction of resins comprising a small fraction of the aggregates, with a fixed composition. Quantitative Measures. Least-squares fits for saturates and aromatics versus asphaltene compositions (Figures 2d
and 3d) yield asphaltene axis intercepts of 95.1 and 99.1 wt % asphaltenes, respectively, for Athabasca bitumen and Maya crude oil at 473 K. The resins content of the aggregates is ∼5 and ∼1 wt %, respectively. These compositions correspond to mass fractions of resins II in the corresponding feeds of 0.009 and 0.0014. The resins composition data (Figures 2c and 3c) are somewhat scattered but not independent and yield similar values; i.e., the resins II composition is less than or equal to the resins measurement error (repeatability), shown in Table 2. A least-squares fit to the saturates and aromatics data for the low-temperature Maya crude nanofiltration data (Figure 4d) yields an asphaltene axis intercept of 90.3 wt % asphaltenes (∼10 wt % resins), which corresponds to a mass fraction of resins II of 0.015. This value is an order of magnitude greater than the value at 473 K, but the value remains a small fraction of the resins and the Maya crude overall. According to the mass balance model (eqs 1-4), the maximum range for the resins II fraction is 0 < X4 < 0.025 for Athabasca bitumen at 473 K (panels a-d of Figure 2) and the resins content of pentane-asphaltene-rich aggregates is less than 10%. The centroids are comparable to the leastsquares fits. For Maya crude oil (panels a-d of Figure 3), use of the measured feed composition introduces a bias relative to the other SARA measurements. Even so, the possible range for the resins II fraction is narrow, 0 < X4 < 0.005, and the resins content of the aggregates is less than 2 wt %. Again, the centroids are comparable to the least-squares fits. Nanofiltration results for Maya crude oil filtered at 4434
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
Figure 3. Composition data, least-squares fit, and mass balance model for nanofiltered Maya crude oil samples at 473 K: (a) saturates, (b) aromatics, (c) resins, and (d) saturates and aromatics. Mass fraction of resin II in the feed, X4, is a parameter. Values are 0, 0.005, 0.01, and 0.02.
aggregates in these hydrocarbon resources can be considered to be pentane asphaltenes. If the heptane asphaltenes definition was used instead of pentane asphaltenes, one would expect significant resins contents in the asphaltenes-rich aggregates. From the data presented in Table 1, a sample comprising 100% pentane asphaltenes would comprise less than 80 wt % heptane asphaltenes and more than 20 wt % heptane resins. Impact on Resin and Asphaltene Association Models. These results restrict the possible proportions of resins in pentaneasphaltene-rich aggregates, present in Athabasca bitumen and Maya crude oil, to a few percent at most at 473 K and perhaps 10% at 338 K. Numerous models have been proposed for asphaltene-rich aggregates. Dependent upon the asphaltene definitions employed, aggregates may be treated as essentially homogeneous or they may be conceived of as biplex with a core of asphaltenes surrounded by a shell of resins, where the shell can be of constant thickness or be a fixed volume fraction. Larger aggregates may comprise multiple smaller aggregates. Results reported here provide some insights with respect to these models. For example, pentane-asphaltene-rich aggregates in both Maya crude oil and Athabasca bitumen span a minimum of 2 orders of magnitude in size, from less than 5 nm to more than 100 nm, at 473 K.1 Moreover, the composition appears to be sizeinvariant as the composition data from all samples irrespective of filter size follow the composition invariant model. If the resin layer is of fixed thickness, the volume fraction
338-373 K, where the asphaltenes are largely solid (at 400 K, they are ∼67% solid by volume)8 (panels a-d of Figure 4), suggest that the mass fraction of resins in the pentaneasphaltene-rich aggregates is significant. The resins weight percentage is essentially invariant with respect to asphaltenes weight percentage. From eqs 1-4, this corresponds to a resins II fraction, X4, of ∼0.017. Again, the least-squares fit and the mass balance model are in agreement. Working with the data directly or imposing a mass balance model yields consistent and similar results. At 473 K, the resins II fraction for Athabasca bitumen, X4, is ∼0.01. That is to say, approximately 6% of Athabasca bitumen resins are present in pentane-asphaltenes-rich aggregates and resins comprise ∼5% of the aggregates. For Maya crude, at 473 K, X4 is ∼0.002; i.e., ∼3% of Maya resins are present in the pentane-asphaltene-rich aggregates, and resins comprise ∼1% of the aggregates. Given the measurement errors for resins composition (Table 2), the mass fractions of resins II are at the margins of significance for Athabasca bitumen and well within measurement noise for Maya crude oil at 473 K. The low-temperature nanofiltration results suggest that ∼16% of Maya resins are present in pentane-asphaltenerich aggregates and resins comprise ∼10% of the aggregates. Overall, the nanofiltration data support limited resin and pentane asphaltene association at low temperatures, where the asphaltenes are largely solid, and do not support significant association at 473 K, where the asphaltenes are largely liquid.8 To a first approximation, asphaltene-rich 4435
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
Figure 4. Low-temperature composition data, least-squares fit, and mass balance model for nanofiltered Maya Crude oil samples: (a) saturates, (b) aromatics, (c) resins, and (d) saturates and aromatics. Mass fraction of resin II in the feed, X4, is a parameter. Values are 0, 0.01, 0.016, and 0.028.
decreases with the aggregate diameter to the third power. It is not possible to sustain a fixed volume fraction over such a broad size range, unless large aggregates comprise multiple smaller aggregates with a narrow size distribution, as discussed, for example, by Chianelli et al.9 and Betancourt et al.10 Given the size range of the pentane-asphaltene-rich aggregates, fixed average resin fractions consistent with the nanofiltration data correspond to monolayer or partial coverage by molecules in the biplex sphere model, at 473 K, and to at most a few molecular layers at lower temperatures for Maya crude oil, if the leading dimension of a benzene molecule, ∼0.7 nm, is used as a surrogate for monolayer thickness. Because resin molecules are much larger than benzene, surface coverage may remain partial on average even at low temperatures. A shift from partial surface coverage by resins to more full coverage at lower temperatures is consistent with both theory and measurements in cognate fields. Thus, the data reported here lend
support for large asphaltene-rich aggregates comprising multiple small aggregates, where the mass fraction of resins is small. However, because the definitions of asphaltenes and resins are fungible, results reported here can only be directional and qualitative in nature. Conclusions Asphaltene-rich aggregates present in Maya crude oil and Athabasca bitumen comprise pentane asphaltenes, to a first approximation. The nanofiltration data do not support significant interaction between resins and asphaltenes, on a mass basis, at 473 K, for both Athabasca bitumen and Maya crude oil, if asphaltenes are defined as “pentane” asphaltenes. Both the mass balance model and linear regression fits to experimental composition data are in agreement. At lower temperatures, namely, 338-373 K, resin and pentane asphaltene association is supported by the nanofiltration data for Maya crude, where approximately 16% of resins comprise approximately 10 wt % of aggregates. Because the asphaltenes present at low temperature are more than two-thirds solid and those
(9) Chianelli, R. R.; Siadati, M.; Mehta, A.; Pople, J.; Carbognani Ortega, L.; Chiang, L. Y. Self-assembly of asphaltene aggregates: Synchrotron, simulation and chemical modelling techniques applied to problems in the structure and reactivity of asphaltenes. In Asphaltenes, Heavy Oils, and Petroleomics; Mullins, O. C., Sheu, E. Y., Hammami, A., Marshall, A. G., Eds.; Springer Publishing: New York, 2007; pp 375-400. (10) Betancourt, S. S.; Ventura, G. T.; Pomerantz, A. E.; Viloria, O.; Dubost, F. X.; Zuo, J.; Monson, G.; Bustamante, D.; Purcell, J. M.; Nelson, R. K.; Rodgers, R. P.; Reddy, C. M.; Marshall, A. G.; Mullins, O. C. Nanoaggregates of asphaltenes in a reservoir crude oil and reservoir connectivity. Energy Fuels 2008, 23 (3), 1178–1188.
(11) Trejo, F.; Centeno, G.; Ancheyta, J. Precipitation, fractionation and characterization of asphaltenes from heavy and light crude oils. Fuel 2004, 83 (16), 2169–2175. (12) Akbarzadeh, K.; Alboudwarej, H.; Svrcek, W. Y.; Yarranton, H. W. A generalized regular solution model for asphaltene precipitation from n-alkane diluted heavy oils and bitumens. Fluid Phase Equilib. 2005, 232 (1-2), 159–170.
4436
Energy Fuels 2009, 23, 4431–4437
: DOI:10.1021/ef900309j
Zhao et al.
present at 473 K are two-thirds liquid, no statement can be made regarding the magnitude or sign of the enthalpy of association based on these nanofiltration data. If asphaltenes are defined on a heptane basis, the asphaltene-rich aggregates identified in Maya crude and Athabasca bitumen comprise at least 20 wt % resins, at 473 K, and more at lower temperatures. Thus, the impact of chemical analysis definitions employed by researchers on their perceptions of the extent, nature, and significance of the resin-asphaltene interaction in native crude oils points to limitations of terminology and
analysis methods related to the capture of the physics and chemistry of hydrocarbon resources. Acknowledgment. The authors thank the staff of the Natural Resources Canada analytical laboratory in Devon, Canada, for their careful analytical work and gratefully acknowledge financial support from the Alberta Energy Research Institute, ConocoPhillips, Inc., Imperial Oil Resources, Halliburton, Kellogg Brown and Root, NEXEN Inc., Shell Canada, Total E & P Canada, the Virtual Materials Group, and the Natural Science and Engineering Research Council of Canada (NSERC).
4437
