Energy & Fuels 2004, 18, 1087-1092
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Bitumen Solubility Model Using Hansen Solubility Parameter Per Redelius* Nynas Bitumen, S-149 82, Nyna¨ shamn, Sweden Received January 6, 2004. Revised Manuscript Received April 26, 2004
The Hansen solubility parameter (HSP) for bitumen was determined using solubility data of bitumen in a set of 48 solvents with known solubility parameters. A computer program was used to calculate the best estimate of the solubility parameter of Venezuelan bitumen as well as a pseudo sphere around the HSP. The program also permitted plotting of the spheres in a 3D diagram. The solubility parameter of the asphaltenes and maltenes was determined and compared to the HSP of the bitumen. It was found that the asphaltenes may be dissolved in the maltenes rather than dispersed, indicating that no asphaltene micelles can exist. The HSP of bitumen was also compared with HSP of three different polymers to demonstrate how to predict the compatibility of polymers with bitumen. The HSP of one crude oil from the North Sea was also determined. The determination of the Hansen Solubility Sphere is proposed as a method to estimate internal stability of bitumen, crude oils, and residues as well as compatibility with added materials.
Introduction Bitumen is a semisolid material, which can be produced from certain crude oils by distillation. It can also be found in nature as “natural asphalt”. It consists of a mixture of hydrocarbons of different molecular sizes containing heteroatoms such as sulfur, nitrogen, and oxygen as well as traces of metals such as vanadium and nickel. The true nature of bitumen is not completely known. Most books and papers on bitumen chemistry teach that bitumen is a colloidal dispersion of asphaltenes in maltenes. The dispersion is stabilized with resins. This statement is based on the well-known fact that when bitumen is diluted with certain hydrocarbon liquids, a precipitate appears. If the hydrocarbon liquid is an n-alkane such as n-heptane or n-pentane, the precipitate is called “asphaltenes”. It has been proposed that the “asphaltenes” are present in the bitumen in the form of micelles. The first one to introduce this concept was Nelensteyn, 1924.1 The model was later refined by Pfeiffer and Saal.2 There have also been proposed bitumen models, which question the existence of micelles, for example by Park and Mansoori3 and later as a result of the SHRP development program in the United States.4 Recently it has been shown that the stability of bitumen can be described as a thermody-
namic mixture of hydrocarbons which are kept in solution by their mutual solubility.5 The chemistry of bitumen has mainly been investigated by different separation procedures of which the currently most popular is the SARA separation, which divides bitumen into four generic groups: saturates, aromatics, resins, and asphaltenes.6 This separation might have been misleading when trying to understand the chemistry of bitumen, since it has sometimes been perceived as a separation into four chemically different groups of molecules. In reality, the SARA separation is based on differences in polarity, and the separation is in principle three cuts through a continuous range of very similar molecules having different polarities. Other approaches to the separation of bitumen make use of differences in size (gel permeation chromatography) or charge (ion-exchange chromatography) as proposed in the SHRP program. Historically, several other separation procedures based on reactivity7 or solubility8, for example, have been proposed. One possible tool for prediction of properties of bitumen is solubility parameters or other cohesion parameters.9 Most solubility parameters are, however, developed to predict miscibility and compatibility between single component materials. Bitumen consists of a very complex mixture of millions of molecules and it is thus
* E-mail:
[email protected]. (1) Nellensteyn, F. J. Relation of the micelle to the medium in asphalt. Inst. Pet. Technol 1928, 14, 134-138. (2) Pfeiffer, J. P.; Saal, R. N. J. Asphaltic bitumen as colloidal system. Phys. Chem. 1940, 44, 139-149. (3) Park, S. J.; Mansoori, G. A. Aggregation and deposition of heavy organics in petroleum crudes. Energy Sources 1988, 10, 109-125. (4) Petersen, J. C.; Robertson, R. E.; Branthaver, J. F.; Harnsberger, P. M.; Duvall, J. J.; Kim, S. S.; Anderson, D. A.; Christiansen, D. W.; Bahia, H. U.; Binder characterisation and evaluation, Vol 1: physical characterisation. Strategic Highway Research Program SHRP-A-367. Washington, DC, 1993.
(5) Redelius, P. G. Solubility parameters and bitumen. Fuel 2000, 79, 27-35. (6) Altgelt, K. H.; Jewell, D. M.; Latham, D. R.; Selucky, M. L. In Chromatographic science series; Altgelt, K. H., ed.; New York: Marcel Dekker: 1979; pp 194-196. (7) Rostler, F. S.; White, R. M. Proc. Assoc. Asphalt Paving Technol. 1962, 31, 35-89. (8) Hoiberg, A. J.; Garris, W. E., Jr. Ind. Eng. Chem., Anal. Ed. 1944, 16, 294-302. (9) Barton, A. F. M. Handbook of Solubility Parameters and Other Cohesion Parameters; CRC Press: Boca Raton, FL, 1991; ISBN 0-84930176-9.
10.1021/ef0400058 CCC: $27.50 © 2004 American Chemical Society Published on Web 06/11/2004
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not completely evident that solubility parameters are appropriate for describing the stability and compatibility of bitumen. Attempts have been made to use Hildebrands solubility parameter for prediction of solubility of bitumen in different solvents with limited success.10 If polar interactions and/or hydrogen bonding are important, the use of the Hansen solubility parameter usually provides a better approximation. In a previous paper,5 the solubility and internal stability of bitumen have successfully been expressed in terms of Hansen solubility parameters (HSP). The HSP takes three types of molecular interactions into consideration: dispersive, polar, and hydrogen bonding. If each of the interactions is considered as one dimension in a coordinate system, they could be considered as three-dimensional (3D) solubility parameters. A 3D diagram may illustrate the solubility parameter as a point surrounded by a body showing the extension of the solubility (sphere). The position of the body for bitumen was estimated by turbidimetric titrations using three carefully selected nonsolvents representing each of three types of molecular interactions: dispersive, polar, and hydrogen bonding. The titrations give information about the internal stability and compatibility of bitumen and have been used, for example, to estimate compatibility between fresh and aged binder in recycling of asphalt.11 The 3D titrations, however, do not permit the calculation of the solubility parameter of the bitumen or the full extent of the solubility body. The HSP of the mixture of solvent and titrant at the precipitation point may be considered to be one point on the surface of the solubility body. The three titrations thus give three points on the surface of the body. Even if we assume the body to be a sphere, it is not possible to calculate the shape or position of the sphere knowing only these three points. In this paper we will also show how the size and extension of the solubility body can be estimated by including information from solubility testing. Methods Solubility Parameters. A solubility parameter is a kind of cohesion parameter, which describes the interactions between molecules in condensed materials. It could be expressed as the difference between the internal energy of the condensed material and that of an ideal gas of the same material at the same temperature. The solubility parameter as defined by Hildebrand9 is also called the Hildebrand parameter and is defined by
δ ) xc )
x-UV ≈ x
∆lfgU V
(1)
eters with more than one component were introduced. An example is Hansen et al.,12,13 who introduced a threecomponent solubility parameter to account for the dispersive forces, the polar interactions and hydrogen bonding. The use of Hansen solubility parameters (HSP) has proven suitable for describing bitumen.5 Determination of the Hansen Solubility Parameter. The determination of solubility parameters in complicated mixtures such as bitumen is more difficult than for pure substances. It is not possible to measure the HSP directly on such materials. There is, however, an indirect route to determine the solubility parameters of complex compounds by measuring the interaction of the compound with liquids with a known solubility parameter. It makes use of the well-known fact that a solvent with a solubility parameter similar to that of the material is a good solvent while a solvent with a different solubility parameter is a poor solvent. The standard procedure is to select a set of liquids with a known and reasonable range of solubility parameters and then to test the solubility with each of them. A large number of solvents are needed because apart from the solubility parameter the molecular volume of the solvent also has an influence on the solvent power, but is not taken into consideration in the HSP. Usually 40-50 solvents with different molecular volume will give a reasonably good precision for the determination of HSP. If the solubility parameter of the material under investigation is completely unknown, the selection of solvents should vary in HSP as much as possible. But if an approximate solubility parameter is known, the selection of solvents could be designed to give the best resolution. This is achieved by selecting solvents close to the estimated surface of the solubility body. The selection of solvents for bitumen is further discussed in the Experimental Section. In reference 13 is given eq 2 for calculation of the solubility sphere assuming that the body in the 3D Hansen space is a sphere after transformation of the δd with a factor of 4. The factor “4” have been empirically found by Hansen as a practical tool to convert the spheroid plots of δD with any of the other components to a spherical one.
(RA)2
RED )
[
RM2
)
]
(δP2 - δP1)2 (δH2 - δH1)2 + (δD2 - δD1) + 4 4 (2) 2 RM 2
where c ) cohesive energy density, U ) molar internal energy, V ) molar volume, and ∆lfgU ) heat of vaporization. The Hildebrand parameter was intended for nonpolar, nonassociating systems. To take also other types of interactions such as polar interactions and hydrogen bonding into consideration, solubility param-
RA is the modified difference between the solubility parameters of two substances of which one might be bitumen and the other a solvent. RM is the maximum solubility parameter difference, which still allows the bitumen to be dissolved in the solvent. This can also be imagined as the radius of the solubility sphere. From this follows that the relative distance RED ) 0 when the solvent and the bitumen have the same solubility
(10) Rahimian, I.; Zenke, G. Zum Verhalten organisher Lo¨semittel gegenu¨ber Bitumen. Bitumen 1986, 1, 2-8. (11) Karlsson, R.; Isacsson, U. Bitumen Structural Stability Characterisation Using Turbidimetric Titration. Energy Fuels 2003, 17 (6), 1407-1415.
(12) Hansen, C. M.; Skaarup, K. The three-dimensional parameter - key to paint component affinities. III. Independent calculation of the parameter componenets. J. Paint Technol. 1967, 39, 511. (13) Hansen, C. M. Hansen Solubility Parameters: a user’s handbook. CRC Press: Boca Raton, FL, 2000; ISBN 0-8493-1525-5.
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Table 1. Comparison of the HSP of Asphaltenes and Maltenes and Bitumen new set of solvents with their parameters solvent
D
P
H
mol vol
RED bitu
RED asph
RED malt
2-butanol 2-butyl octanol butyraldehyde caprolactone (epsilon) 1-chloropentane chloroform cyclohexanol cyclohexanone cyclohexylamine cyclopentanone cis-decahydronaphthalene 1,4-dichlorobutane dichloromethyl methyl ether 1,1-diethoxy ethanol (acetal) diethylene glycol monoethyl ether acetate diisopropylamine 1,2-dimethoxybenzene ethyl acetate ethyl benzene ethyl lactate 2-ethyl-hexanol ethylene glycol dibutyl ether hexadecane hexyl acetate isopropyl acetate lauryl alcohol mesityl oxide methyl acetate methyl benzoate methyl ethyl ketone 1-methyl naphthalene methyl oleate 3-methyl-2-butanol methylene dichloride nitrobenzene oleyl alcohol pyrrolidine salicylaldehyde tetrahydrofuran tetrahydronaphthalene 1,2,3,5-tetramethylbenzene toluene 2-toluidine 1,1,2-trichloroethane tricresyl phosphate 1,2,4-trimethylbenzene 2,2,4-trimethylpentane o-xylene
15.8 16.1 15.6 19.7 16.0 17.8 17.4 17.8 17.2 17.9 18.8 18.3 17.1 15.2 16.2 14.8 19.2 15.8 17.8 16.0 15.9 15.7 16.3 15.8 14.9 17.2 16.4 15.5 17.0 16.0 20.6 14.5 15.6 18.2 20.0 14.3 17.9 19.4 16.8 19.6 18.6 18.0 19.4 18.2 19.0 18.0 14.1 17.8
5.7 3.6 10.1 15.0 6.9 3.1 4.1 6.3 3.1 11.9 0.0 7.7 12.9 5.4 5.1 1.7 4.4 5.3 0.6 7.6 3.3 4.5 0.0 2.9 4.5 3.8 6.1 7.2 8.2 9.0 0.8 3.9 5.2 6.3 8.6 2.6 6.5 10.7 5.7 2.0 0.5 1.4 5.8 5.3 12.3 1.0 0.0 1.0
14.5 9.3 6.2 7.4 1.9 5.7 13.5 5.1 6.5 5.2 0.0 2.8 6.5 5.3 9.2 3.5 9.4 7.2 1.4 12.5 11.8 4.2 0.0 5.9 8.2 9.3 6.1 7.6 4.7 5.1 4.7 3.7 13.4 6.1 4.1 8.0 7.4 14.7 8.0 2.9 0.5 2.0 9.4 6.8 4.5 1.0 0.0 3.1
92.0 224.2 90.5 110.8 120.8 80.7 106.0 104.0 113.8 89.1 156.9 109.5 90.5 142.2 175.5 141.1 127.7 98.5 123.1 115.0 156.6 209.5 294.1 165.0 117.1 224.2 115.6 79.7 124.9 90.1 138.8 340.0 107.7 63.9 102.7 316.0 83.5 104.6 81.7 136.0 150.8 106.8 107.8 92.9 316.0 137.3 166.1 121.2
2.128 1.276 1.522 2.096 1.022 0.445 1.762 0.540 0.670 1.434 0.925 0.678
2.448 1.629 2.014 2.280 1.594 0.732 1.932 0.888 1.000 1.747 1.101 1.000 2.080 1.726 1.618 1.864 0.985 1.584 1.039 2.214 1.995 1.499 1.642 1.478 1.942
1.980 1.294 1.050 1.662 0.447 0.802 1.802 0.563 0.897 0.991 1.013 0.377 1.218 0.894 1.222 1.080 1.309 1.001 0.839 1.692 1.654 0.722 1.000 0.970 1.282
1.360 1.825 1.346 1.739 0.631 1.948 2.320 0.831 1.000 2.138 1.045 2.406 1.341 0.391 1.000 0.851 1.060 0.790 1.707 0.999 2.346 0.860
0.769 1.090 0.582 0.800 1.307 1.000 1.848 0.730 0.896 1.449 0.897 2.118 1.000 0.910 0.914 0.741 1.304 0.842 1.073 0.791 1.358 0.825
parameter. RED ) 1 when the solvent has a solubility on the surface of the solubility sphere, and RED > 1 when the liquid is a nonsolvent for bitumen. Experimental Section Selection of Solvents. A preliminary investigation of the solubility of bitumen in a standard set of solvents ( as suggested in ref 13) to cover the full range of solubility parameters has given a Hansen solubility parameter of δD ) 17.5 MPa0,5, δP ) 3.5 MPa0,5, and δH ) 3.9 MPa0,5. When testing different types of bitumens with this set of solvents, a rather small difference in HSP was found. The reason is that the selected solvents were designed to cover a large range of solubility parameters and thus most solvents were either “good solvents” or “poor solvents” for all the tested bitumens. Just two or three solvents were either good or bad solvents for bitumen and gave thus the whole variation in the calculations of HSP for the different bitumens. Knowing the approximate solubility parameter for bitumen, we decided to increase the precision of the solubility test and calculation of HSP by selecting a new set of solvents more
1.177 1.258 1.301 1.059 1.126 0.710 1.877 1.676 0.945 1.165 1.000 1.459 1.080 0.906 1.353 0.914 1.245 0.959 1.349 1.979 0.615 1.000 1.630 0.827 2.299 1.000 0.546 0.794 0.524 1.127 0.620 1.489 0.681 1.746 0.544
suitable for testing of bitumen. For this purpose we selected solvents with RED values close to 1 which is to say solvents with a HSP close to the surface of the solubility sphere. Another requirement on the solvents is to have as large a variation in each of the three components δD, δP, and δH as possible while still fulfilling the requirement of RED < 2. By setting the upper limit of RED to 2, we eliminate solvents known to always be “poor solvents” for bitumen but at the same time maintaining a reasonably large variation in HSP to permit testing of bitumen-related materials such as asphaltenes, maltenes, polymers, oils, resins, waxes, etc. The solvents should also be readily available and be reasonably nontoxic. A list of solvents selected for the tests in this paper is presented in Table 1. Test Procedure. A set of test tubes is prepared with 5 mL of solvent in each tube. To each tube is added approximately 0.5 g of bitumen. The tubes are sealed with a suitable stopper to prevent evaporation of solvent. A storage time of 48 h at room temperature is maintained to permit time for complete dissolution. During storage, the tubes are carefully shaken a few times in such a way that no liquid touches the stopper. Initially the solubility is recorded and classified in three
1090 Energy & Fuels, Vol. 18, No. 4, 2004 levels: (1) completely soluble; (2) uncertain; (3) not soluble (big residue, lump, or sludge). Since the samples are black, it might sometimes be difficult to determine if we have a true solution or not. In such cases a drop of the solution is spotted on a filter paper. If a black spot is formed at the application of the sample, a precipitate is present. If the sample is wetting the filter paper with a ring of constant color, it is a true solution. Another test is to put a drop of the solution on a microscopy glass slide and cover it with another glass to make a very thin film. The film is viewed in the microscope to see if precipitate particles are visible. After these tests, also the uncertain samples are classified either as soluble or as nonsoluble. Calculations. The calculation is made with a computer program sp3D, which was developed in a joint project with Western Research Institute.14 The input to the program is the result of the solubility tests described in Test Procedure where each solvent is considered to be “good” if it completely dissolves bitumen without any residual precipitate. If the bitumen is incompletely dissolved or not dissolved at all, it is considered to be a “bad” solvent. The program then calculates a pseudo sphere with all “good” solvents inside the sphere and all “bad” solvents outside the sphere. For the calculations presented in this paper, we have used a factor of four for the dispersive component of the HSP as proposed by Hansen.13 There is, however, no reason to believe that this factor is constant for complicated mixtures such as bitumen. The sp3D program gives a number of options to fit the solubility data to shapes other than a sphere. The detailed description of the sp3D will be presented in a separate paper. The results from the sp3D program are printed as the HSP of the best fit; the radius of the assumed pseudo sphere is also indicted as well as the fit of the entered data followed by the list of the solvents that were used with their respective HSP values. In the list are also the RED values calculated, which indicate how far the HSP of the solvent is from the bitumen. A RED ) 0 indicates that the solvent has exactly the same solubility properties as the bitumen, a RED ) 1 indicates that the solvent has an HSP which is on the surface of the sphere, and an RED > 1 indicates that the solvent is not a good solvent for bitumen.
Results and Discussion Hansen Solubility Parameter of Bitumen. Plotting of the results from a solubility test of a Venezuelan bitumen in a 3D diagram is presented in Figure 1. It can be seen that the fit is rather good with Hfit ) 0.980 (Table 2). The solvency power of each solvent for dissolution of bitumen is estimated by the RED values listed in Table 1. Out of 48 solvents used, there are three outliers which means that three solvents did not fall on the correct side of the interface of the best fitted spheroid. The outliers are 1-chloropentane, which was found to be a good solvent in the test but had a RED value of 1.022 indicating a borderline solvent on the poor side. The other two outliers solvents were ethylene glycol dibutyl ether and mesityl oxide which were recorded as poor solvents in the test but which had RED values of 0.945 and 0.906, indicating good solvents. No simple explanation for this behavior has been found. The RED values close to 1 indicate that they are located very close to the interface of the sphere and some of these solutions may have been erroneously recorded as “soluble” or “nonsoluble” since it is very difficult to see small amounts of precipitate in the black bitumen (14) Turner, F.; Redelius, P. Computer program sp3D developed in a joint project Western Research Institute, Laramie, WY, and Nyna¨s Bitumen, Nyna¨shamn, Sweden.
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Figure 1. Plot of solubility sphere for Venezuelan bitumen and its solubility parameters. Table 2. An Improved Set of Solvents for Determination of HSP of Bitumena sample bitumen asphaltenes maltenes crude oil n-heptane
δP δH δD MPa0,5 MPa0,5 MPa0,5 radius 18.4 19.6 17.7 17.7 15.3
3.9 3.4 5.8 4.0 0
3.6 4.4 2.5 0.6 0
5.76 5.3 6.7 9.3
fit
outliers
0.980 0.940 0.850 0.936
3 5 7 3
a Also included are RED values for bitumen, asphaltenes, and maltenes.
solutions. Another explanation could be the different size of the solvent molecules which is known to have an influence on solubility, but which is not taken into consideration in the HSP. Solubility of Fractions from Bitumen. Venezuelan bitumen was separated into asphaltenes and maltenes using standard method IP 143-90. The two fractions were subjected to the solubility test as described in the Experimental Section. The results after calculating the solubility sphere are presented in Table 2 and plotted in Figure 2. The corresponding RED values for each solvent is listed in Table 1. The difference in HSP between the asphaltenes and maltenes is surprisingly small, and is in contradiction with the assumption that the asphaltenes are a very polar fraction in bitumen. A very common assumption is that the asphaltenes are dispersed in the maltenes. This requires, however, that the asphaltenes are not soluble in the maltenes. The finding in this test is that the difference in solubility parameters between asphaltenes and maltenes is not high enough to reach insolubility between the two fractions and thus suggests that the asphaltenes are in fact dissolved in the maltenes rather than dispersed. According to the preparation procedure for the asphaltenes, they should be insoluble in n-heptane and thus have RED g 1 in relation to n-heptane, while the maltenes should have RED < 1 in relation to n-heptane. An estimate of the difference calculated using eq 2 gives a RED value of 0.93 for the asphaltenes which is close to the expected value of RED g 1 showing non-solubility
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Figure 3. HSP of polyethersulfone, polyethylensulfide compared to HSP of Venezuelan bitumen. Figure 2. The solubility spheres of maltenes and asphaltenes separated from a Venezuelan bitumen.
in n-heptane. The corresponding value for the maltenes is RED ) 0.35 showing good solubility in n-heptane. It is also obvious from Table 2 that asphaltenes have a strong dispersive interaction and a strong hydrogen bonding interaction but a surprisingly low polarity. In fact the polarity is slightly lower than the average for bitumen. The high dispersive interaction of the asphaltenes is probably a result of the separation using n-heptane having low dispersive interaction and thus causing precipitation of the asphaltenes mainly by high dispersive interaction. It is also seen that maltenes have a remarkable high polarity. Compatibility between Bitumen and Polymers. Modification of bitumen with polymers is today a wellknown and common way of improving performance of bitumen for roads and bitumen membranes for water proofing. When blending polymer into bitumen it is important to know the compatibility or how well the polymer will mix with the bitumen. A polymer which is basically nonsoluble in bitumen will disperse and act more as a filler in the bitumen. At higher concentration of polymer, phase inversion may occur, resulting in bitumen being dispersed in the polymer. A polymer, which is soluble in bitumen, will dissolve completely and therefore just contribute to a limited extent for improving the physical properties. The most common types of polymers used for modification of bitumen are the socalled block copolymers of which SBS (styrene-butadiene block copolymer) is perhaps the most common type. If the HSP of the polymer is known, it is very easy to predict the compatibility with bitumen. An example is shown in Figure 3, where literature data13 for two polymersspolyethersulfone and polyethylensulfidesare plotted together with data for Venezuelan bitumen. It is very obvious that polyethersulfone is completely insoluble in bitumen while polyethylensulfide is completely soluble. In the case of SBS, the situation becomes more complicated since SBS consist of two different types of polymerssbutadiene and polystyreneswhich have different solubility. The data in Figure 4 are based on solubility testing of the SBS and thus give the sphere where both polymers are soluble. It is very clear that we have a partial solubility of the polymer in bitumen,
Figure 4. HSP of SBS compared to Venezuelan bitumen.
which is a requirement for the good effect also with addition of small amounts of SBS (1%-10%). Stability of Crude Oil and Bitumen. The solubility parameter of bitumen can be considered as a measure of the interaction strength between molecules in bitumen. The extension of the solubility body can be considered as a measure of the internal stability of the bitumen. We may speculate that this internal stability is dependent on the mutual solubility of all the millions of molecules constituting bitumen. A consequence is that the bitumen is dependent on a continuum of molecules with gradually different polarities to maintain internal stability. If a fraction of molecules with similar HSP located inside the sphere is removed, the continuum is broken and the remaining molecules are no longer completely soluble in each other. We might conclude that the removed fraction is needed and acts as a compatibilizer or a solubilizer. The surface of the solubility sphere gives the limit in terms of solubility parameters where we could expect full stability. By adding solvents, diluents, or polymers, which have solubility parameters outside the sphere, we might cause instability to the system and a precipitate may form. This is the proposed mechanism for precipitation of asphaltenes by adding n-heptane to bitumen. It is obvious from Figure 1 that adding n-heptane is just one way of causing instability since there are a large number of other solvents with HSP outside the solubility sphere, which thus could cause
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The knowledge of the solubility parameter and the 3D solubility body gives a very good tool to understand formation of precipitates during mixing and handling of crude oils. It is obvious that depending on the type of operation we could disturb the system in different ways and, by doing so, cause precipitation. The use of HSP gives a good tool for analyzing the reason for instability and makes it easier to find preventive tools for decreasing the sensitivity of the system. Conclusions
Figure 5. Solubility sphere of crude oil Leadon from the North Sea.
similar types of precipitate upon dilution of bitumen. Using these other types of solvents or combinations of solvents will result in precipitates with different chemical composition. The same discussion could be extended to crude oils. The HSP of crude oils can be determined in the same way as has been described for bitumen. For some very stable crude oils the set of solvents used for the test might have to be adjusted to have a reasonable ratio between “good solvents” and “poor solvents”. An example of the solubility body of the North Sea crude oil Leadon is presented in Figure 5 and in Table 2.
The Hansen solubility parameter for bitumen and crude oil could be determined by solubility testing with a large number (40-50) of solvents with known Hansen solubility parameter. The results permit calculation of the HSP as well as the solubility body by a computer program. The best estimate of the Hansen solubility parameter for Venezuelan bitumen is δD ) 18.4 (MPa)0,5, δP ) 3.9 (MPa)0,5, and δH ) 3.6 (MPa).0,5 Determination of the HSP of asphaltenes and maltenes from Venezuelan bitumen shows that the asphaltenes are soluble in the maltenes rather than dispersed. Compatibility between bitumen and solvents or polymers with known HSP could easily be calculated using eq 2. HSP is a tool for analyzing causes of instability and precipitation in bitumen and crude oils. EF0400058
