Ind. Eng. Chem. Process Des. Dev. 1983, 22, 242-248
242
Table 111. Properties of Khafji VR and ABC/HDS Treated Oil Khafji VR C5+yield, wt % properties specific gravity, dI5, viscosity, at 50 "C, CP sulfur, wt % nitrogen, wt % CCR, wt % vanadium, wt ppm nickel, wt ppm distillation C,-375 OF, V O ~% 375-450 OF,V O ~7% 450-650 O F , VOI % 650-1050 OF, V O ~% 1050 "F +, vol % chemical hydrogen consumption, scf/bbl
combined ABC/HDS process compared with HDS to be expected are summarized as follows: longer catalyst life; higher qualities on metals in the product oil; more distillate in the product oil due to ABC reaction effect. (It is possible in the HDS section t~ operate at higher temperature.) In view of effective uses of petroleum resources and a long-range stable supply of primary energy, ABC technology seems to be extremely adequate for the upgrading of tar sand bitumen and Orinoco belt crude, because these represent a kind of oils which contain asphaltenes and metals in high concentrations and are of high residue yields.
ABC/HDS treated oil 94.9
1.023 5.1 X l o 5 4.96 0.40 21.2 130 41
27.5 72.5
0.9470 153 0.97 0.29 9.8 13 12
Acknowledgment
2 3 9.5 49.5 36 1000
Grateful appreciation is expressed to the memory of Dr. Akiyoshi Tamaki, the former president of Chiyoda Chemical Engineering Construction Co., Ltd.,deceased in June 1981. We are indebted to him for his leadership and assistance on the present work.
Literature Cited
uum residue, and the combination of ABC and HDS catalysts for some heavy residual oils will make it possible to produce feedstock for residual catalytic cracking. Figure 20 shows the results of ABC followed by HDS test during 5000 h, and some typical properties of the product oil therefrom are shown in Table 111. The effects of the
Fukui, Y.; Shhoto, Y.; Ando, M.;Homma, Y.; U.S. Patent 4 1 9 1 636, 1 9 8 0 . Dlckle, J. P.; Yen, T. F. Anal. Cbem. 1987 39, 1 8 4 7 .
Received for review March 12, 1982 Revised manuscript received August 26, 1982 Accepted September 20, 1982
Asphaltene Cracking in Catalytic Hydrotreating of Heavy Oils. 2.' Study of Changes in Asphaltene Structure during Catalytic Hydroprocessing Sachlo Asaoka,' SMnkhl Nrkata, Yoshiml Shlroto, and Chbato Takeuchl Chiyo& Chemical Engineering & Constructlon Co., LM.,3-13, Mor&a-cho, Kanagawa-ku, Yokohama 221, Japan
Characteristics in catalytic conversion of aspheltenes in petroleum heavy residues were studii in the hydrotreating process. A Boscan crude, an Athabasca bitumen, and a Khafji vacuum residue were tested as typical feedstocks. Various analyses were made to obtain the properties of asphaltenes before and aftsr the reaction, e.g., changes of heteroatoms such as sulfur and metals, and decreases of molecular weight. The characteristic changes of asphattene molecules were also investlgated by electron spin resonance (E=) and X-ray analyses. The association and coordination of vanadyl in asphaltenes were studied by the temperature dependence on the ESR spectra, and the sizes of the stacked crystallites and the aggregated asphaltene mlcelles were measured with X-ray diffraction and smalkngle scattering. In the asphaltene cracking mechanism, it was clarified that the main reactions were the destruction of asphaltene micelles caused by vanadium removal and the depolymerization of asphaltene molecules by removal of heteroatoms such as sulfur.
The authors of this work have previously reported a hydrotreating process (Asphaltenic Bottom Cracking (ABC) process) (Takeuchi et al., 1979a,b) with the focus on the conversion of asphaltenes. A catalyst employed shows a high activity for the decomposition of asphaltenes, in which molecular weight reduction proceeds with low hydrogen consumption and without any excessive hydrocracking reaction. Therefore, the characteristics of the catalytic conversion of asphaltenes during the processing were investigated based on the physical and chemical properties of asphaltenes. A Boscan crude, an Athabasca bitumen, and a Khafji vacuum residue were chosen as typical asphaltenic feedstocks for this study, since they contain many asphaltenes as well as sulfur, and their metal
Introduction Some heavy oils contain a large amount of asphaltenes formed by association of molecules, including condensed polyaromatic rings. Since the asphaltenes make catalytic hydrotreating very difficult, a better understanding of the properties and these changes is important for the development of upgrading technology for asphaltene-containing heavy oils. This work was presented a t the 181st National Meeting of the American Chemical Society, Division of Petroleum Chemistry, Symposium on Residuum Upgrading and Coking, Atlanta, Apr 1, 1981. 0198-4305/83/1722-0242$07.50/0
0
1983 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 243
Table I. Typical Inspections of Asphaltenes in Feed and Product Boscan crude feed product yield, wt % 11.9 4.8 carbon, wt % 81.30 85.96 hydrogen, wt % 7.85 6.79 sulfur, wt % 6.76 3.55 nitrogen, wt % 1.60 2.20 vanadium, wt ppm 5390 1730 nickel, wt ppm 466 47 8
Oil
contents are considerably different from one another. Any changes on these asphaltenes caused by metals and sulfur removal should, therefore, be observed more easily than on other asphaltenes similar to one another. Various measurements reported here are mainly for the asphaltenes isolated from these feedstocks and from their product oils. Further, the model of the asphaltene cracking mechanism is proposed from these results and is discussed in correspondence with the activities and selectivities among demetallation, desulfurization, and asphaltene cracking. Background The question as to how and why asphaltenes are converted or cracked to oils during the ABC process had arisen and remained unknown. In a previous investigation (Nakamura et al., 1980) on the properties of feedstocks and the whole product oils, demetallation and desulfurization were supposed to be two main reactions closely related to asphaltene cracking and to the decrease, and a shift of distribution in molecular weight of whole oil by gel permeation chromatography was observed during the asphaltene cracking reaction. In this work, characteristic analyses of the asphaltenes before and after the reaction were carried out with respect to demetallation and desulfurization from asphaltenes, decreases of molecular weight, and changes in the size or other structural characteristics of asphaltenes. This work aims to show that the differences of asphaltene properties between feedstock and product oil can clarify the conversion of asphaltenes to oils. For these reasons, the characteristics of asphaltenes were studied from the following viewpoints: atomic ratios of elements, average and distributions of molecular weights, unit weight, and number, macrostructure, particle size, and association and coordination of vanadyl. Experimental Section Asphaltene Cracking Reaction. The equipment for asphaltene cracking reactions was described in a previous paper (Takeuchi et al., 1979a) in which details can be found. The reactions were carried out under the following conditions: pressure, 90 to 180 kg/cm2; temperature, 360 to 430 OC; LHSV, 0.2 to 1.5 h-l; and hydrogen to liquid ratio in volume, 600 to 1000 NL/L. Separation of Asphaltenes. Asphaltenes were obtained by n-heptane precipitation from either feedstocks or product oils using typical deasphaltening procedures; i.e., one part of the sample oil was stirred at 400 rpm for 2 h and stood for 2 h with 10 parts of n-heptane in a double-walled 4-L glass container kept at 80 "C with circulated hot water. The mixture was then filtered through a 1-pm membrane filter and insoluble asphaltenes were washed several times with a total of 1L of n-heptane at 80 "C and dried in vacuo at 80 "C for 2 h. Analyses. VPO (Vapor Pressure Osmometry). Number average molecular weights were determined by VPO (Hitachi-Corona 117) in pyridine solvent at 60 "C. GPC (Gel Permeation Chromatography). Analytical gel permeation chromatograms were obtained by means
of a Japan Anal. Ind. LC-08 chromatograph, equipped with four columns of 600 mm length and 20 mm diameter in series, filled with Shodex A-802x1, A-803x2 and A-804x1, respectively. Molecular weight distributions were calibrated by the use of polystyrene. NMR (Nuclear Magnetic Resonance). High-resolution 'H NMR spectra were obtained using a Pulsed and Fourier Transform NMR spectrometer (Japan Electron Optics Laboratory, JNM-FX6O FT NMR) at a frequency of 15.02 MHz. All measurements were carried out in a 0.5% solution in carbon disulfide and tetramethylsilane was used as the internal reference. The unit weight, M(u.s.) and the unit number, n, were calculated according to Haley (1971). X-ray Diffraction. The X-ray diffraction techniques used in this study are those of Yen et al. (1961) and Shiraishi et al. (1976) in studies of pitches, asphaltenes, and heat-treated pitches. Sample asphaltenes in powder were packed into aluminum holders, each of which was mounted in a goniometer; the X-rays from a Cu target were diffracted at the sample; and the X-ray intensities were measured over the range 28 = 4 to 100" by a Rigaku X-ray diffractometer. The intensities of diffracted and highly monochromated X-rays were measured with continuous scanning over 28 = 4 to 35O, y and (002) X-ray band region and with step scanning over 28 = 60 to looo, (11)-band region. Small Angle X-ray Scattering. A Rigaku small-angle X-ray scattering unit has an BO-pm entrance slit and a sample-to-detector distance of 250 mm. Monochromatization of the X-rays from a Cu target was achieved using an Ni filter. The liquid samples were held in glass capillary tubes 0.7 mm in diameter. The X-ray scattering intensity was measured with a scintillation counter with a receiving slit opened to 100 pm. The scattering experiments were performed with the sample of feedstocks and product oils. Subsequently,the scattering intensity of the deasphaltened oil from the sample was measured. The net intensity as the difference of these intensities is the scattering from the asphaltene colloids, because the sample can be considered as a solution of asphaltenes in the deasphaltened oil. A detailed description of this procedure can be referred to in the articles by Pollack et al. (1970) and Kim et al. (1979). ESR (Electron Spin Resonance). ESR spectra were observed using a JEOL EF-1 spectrometer operating at X-band frequency (9.2 GHz) with 100 kHz field modulation. The microwave cavity for measurements at high temperature was equipped with a hot-air blower. The ESR spectra were obtained at temperatures between 20 and 270 "C. The ESR techniques and analytical procedures used in this study were according to Tynan et al. (1969).
Athabasca bitumen feed product 7.7 81.00 7.68 8.31 1.51 933 3 59
1.9 83.85 7.39 5.27 1.28 554 264
Khafji vacuum residue feed product 11.8 82.13 7.38 10.57 1.16 615 201
5.4 86.77 6.56 3.92 1.53 182 173
Results and Discussion Elemental Composition. The inspections of the typical asphaltenes analyzed in this work are shown in Table I. To compare elemental contents of product asphaltenes
244
Id.Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 Sorcan Cruds
"IC
\
E
Crude
Athobosm Bitumen
Khafji Vocuum Residue
0
20 40 60 80 Conversion of Arpholtene i%)
I,/& ,\ \ , I
100
,
Figure 1. H/C, V/C, and S/C atomic ratio of asphaltene. 102
103
,
10.
Equivolent Molecular Weight (Calibrated by polystyrene 1
Figure 3. Molecular weight distribution of asphaltenes from products and feeds (by gel permeation chromatograpy).
.-
20
Conversion
40 of
60 Asphaltenc
82
loo
l%i
Figure 2. Molecular weight of asphaltene (by vapor pressure osmometry).
with those of feedstock asphaltenes, the contents of sulfur and vanadium decrease clearly, but those of nitrogen and nickel change only a little. Therefore, sulfur and vanadium are considered to play more important roles than nitrogen and nickel. Atomic Ratio. Figure 1 shows the changes of the atomic ratios of asphaltenes in H/C,V/C, and S/C, against asphaltenes conversion. During asphaltene cracking, H/C of asphaltenes does not change considerably but V/C and S/C of asphaltenes change remarkably. This fact suggests that asphaltene cracking cannot occur independently of the removal of vanadium and sulfur from asphaltenes. Molecular Weight. As shown in Figure 2, the molecular weight of asphaltenes measured by VPO decreases with the progress of asphaltene cracking. As for Boscan crude and Khafji vacuum residue, the molecular weight of the remaining asphaltenes decreases remarkably with asphaltene cracking until about 40% conversion of asphaltenes; at the region of the asphdtene conversion higher than about 40%, the molecular weight remains a t about 1100 instead of decreasing. About 1100 is noted as the boundary molecular weight between asphaltenes and nonasphaltenes. On the other hand, for Athabasca bitumen the molecular weight of the remaining asphaltenes decreases gradually and does not reach a certain constant value. Probably, the asphaltene cracking in Athabasca bitumen is slightly different from those of the other two feedstocks. Molecular Weight Distribution. The observation on the average molecular weight by VPO can be applied on the molecular weight distribution by GPC, as shown in Figure 3: (1) The molecular weight distribution of asphaltenes from product oils becomes lower than that of
asphaltenes from feedstocks. (2) The degree of shift in Athabasca bitumen is less than those in Boscan crude and Khafji vacuum residue. Unit Weight and Number. The study was made by 'H NMR to clarify where in the molecular structure the decrease of molecular weight of asphaltenes mentioned above occurs and is shown in Figure 4, in which the results in Figure 2 are also shown as a reference. The molecular structure of asphaltene comprises some unit sheets polymerized with linkages interconnecting. Figure 4 shows that unit weight does not change in spite of the decrease of molecular weight. Therefore, the unit numbers change and, except for Athabasca bitumen, finally approach a certain value. To summarize the results above, it is considered that the decrease of asphaltene molecular weight during asphaltene cracking is caused by depolymerization, which leads eventually to unit sheets. However, for Boscan crude and Khafji vacuum residue, destruction of micelles as well as the depolymerization occurs as shown by rapid decrease of the molecular weight even at a low conversion. Macrostructure. As has been said, the asphaltenes not only consist of huge molecules of condensed polyaromatic rings but also are associated with each other in a state of micelles. Consequently, the change in the macrostructure of asphaltene is one of the items of this work. The cross-sectional view of the asphaltene model shown in Table I1 was reported by Yen et al. (1961). The structural parameters in the model can be obtained by a powder X-ray diffraction; e.g., the percentage of stacking, P,,the aromaticity value, fa, the interlayer distance, dM and so forth were obtained from the y- and (002) X-ray bands after necessary corrections were applied. The weight percentage of stacking structures in the asphaltenes, P,, is calculated on the assumptions that the asphaltene consists only of organized and disorganized carbons and the stacking structure comprises more than two parallel layers of carbon according to the work by Shiraishi et al. (1976). The results of the X-ray diffraction are illustrated in Figure 5. As the X-ray diffraction can give the information only on the crystallized materials, the values in
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 245
Table 11. Macrostructure of Asphaltene by X-ray Diffraction
Boscan crude
Athabasca bitumen
Khafji vacuum residue
structural parameters
feed
product
feed
product
feed
product
(aromaticity) d M , A (interlayer distance) d, A (interchain distance) L,,A (cluster diameter) La, A (layer diameter) Me (effective stacking layers) P, (percentage of stacking)
0.44 3.55 5.9 19.6 11.7 6.5 0.19
0.61 3.54 5.9 19.9 14.4 6.6 0.31
0.45 3.58 5.7 16.8 15.0 5.7 0.19
0.55 3.55 5.5
0.56 3.56 6.0 19.1 15.6 6.4 0.22
0.58 3.55 5.9 20.8 13.0 6.9 0.25
fa
Boscan Crude
17.7 13.3 6.0 0.26
Khofji Vacuum Residue
Athabasca Bitumen
I
I
Conversion of Asphaltene 171 .
I
"
Conversion of Asphaltene (%I
I
,
Conversion of Asphaltcne IW
Figure 4. Molecular weight, unit weight, and unit number of asphaltenes (by 'H NMR). -
Boscan Crude Athabasm Bitumen Khafil Vacuum Residue
.
I Feed !
P
0
.
~
e
A
Athabasca Bitumn
I
Khafji Vacuum Residue Feed Product
i\
-'
05
IO
20
I5
28
24
i.1
Figure 6. X-ray scattering pattern of some petroleum asphaltenes.
28 1.1
2 8 1.1
Figure 5. X-ray diffraction patterns of some petroleum asphaltenes.
Table I1 are due to the crystallized part of asphaltenes. In the comparison with the asphaltenes from feedstocks, Table I1 shows that the structural features of the asphaltenes from product oils are as follows: (1)increase of the percentage of stacking, P,; (2) increase of the aromaticity, f a (in agreement with the values obtained by
NMR technique); (3) no major changes of the structural parameters of stacking, dM,d,, L,, and Me; (4) no significant change of the layer diameter, La. These facts suggest that during the asphaltenes cracking the stacking part of asphaltene is not converted, but the other irregular part of asphaltenes (Le., the part containing vanadium, weak link sulfur, etc.) receives major changes. Together with the measurements obtained by NMR, the facts stated above suggest that the stacking parts consist of the unit sheets mentioned in the preceding section. Particle Size. Kim et al. (1979) said that the radii of gyration of asphaltenes obtained by small angle X-ray
248
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983
Table 111. Radii of Gyration of Asphaltenes by Small Angle X-ray Scatteringa
Product
Feed
1
,in
radius of gyration, A Boscan crude Athabasca bitumen Khafji vacuum residue a
feed
product
11 18 15
13 22 18
Note: measured in deasphaltened oil. Anisotropic
6 50°C
Figure 8. Temperature dependence study of Boscan asphaltenes (by ESR of vanadyl). Asphaltenes, 5 W T %
1 Boscun Crude Athabaxa Bitumen Khafll vacuum Residue
Isotropic
1
DPM !Product 0 a
in
Feed
A
A cI
,
B 210°C 9.2002
e
100 gauss
Figure 7. Typical ESR spectra of vanadyl in asphaltene.
scattering appeared to reflect the particle sizes of the asphaltenes. The scattering data from asphaltenes are shown in Figure 6, from which the radii of gyration of asphaltenes shown in Table 111were obtained with Guinier plots. The values of the radii are considered to be the sizes of unit sheet including the nonaromatic portion, because the stacking does not change the radii, according to Kim et al., and the radii are considerably larger than half of La obtained by X-ray diffraction. As shown in Table 111, the particle sizes of the asphaltenes from product oils are a little larger than those of the asphaltenes from feedstocks. The result above means that asphaltene cracking does not occur in the unit sheets shown as the gyration radii, but the portions having larger gyration radii show lower reactivity to be concentrated into remaining asphaltenes. The asphaltene cracking, therefore, proceeds in the portions which interconnect unit sheets. These portions of asphaltene exist as associations of metal-aromatic sheets, alkyl-aromatic bonds and the alkyl chains containing weak links such as thioether. Association and Coordination of Vanadyl in Asphaltene. In general, petroleum asphaltenes exhibit two types of signals when examined by ESR techniques. One is the 16-line, anisotropic, or 8-line, isotropic, vanadyl (V=02+) resonance; the other arises from free radicals existing in the relatively stable state. The vanadyls in the asphaltenes were examined by ESR at elevated temperatures from 20 OC. No attempt was made to observe the behavior of the free-radical line. The vanadyls in the asphaltenes give anisotropic spectra at a low temperature
20
22
24 26 28 I,OOO/T l*K-’l
30
Figure 9. Temperature dependence study for asphaltenes in untreated and ABC-treated heavy oils (Arrhenius plot).
and isotropic spectra at a high temperature. The typical
ESR spectra of the vanadyl (i.e., in Boscan crude asphaltenes) are illustrated in Figure 7. The smooth transition of the spectrum of asphaltenes was observed in diphenylmethane solvent from an anisotropic to an isotropic type in temperature rise from 20 to 210 “C. For example, Figure 8 shows the transitional spectra of asphaltenes from Boscan crude and its product oil. As Tynan et al. (1969) said, no. 5 is0 and no. 6 aniso lines represent the best compromise between two desirable characteristics because of freedom from extreme overlap with other lines and reasonable “intensity” (peak-to-peak height). In Figure 9, the ratios no. 5 iso/no. 6 aniso for asphaltenes from three feedstocks and their product oils are plotted against the reciprocal of absolute temperature (Arrhenius plot). The ratios of isotropic to anisotropic vanadyl spectra observed at any temperature are different between the asphaltenes of product oils and those of the feedstocks and also among the asphaltenes from different feedstocks. As anisotropic and isotropic vanadyl spectra are due to “bound” and “free” vanadyls, the ratio of isotropic to anisotropic indicates the relative degree of “freedom” of associated micelles and molecules. Vanadyl with an anisotropic spectrum is likely to exist in a more rigidly stacked structure. Therefore, the vanadyls in the asphaltenes separated from product oils are less “free” than those from
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983
Table IV. Activation Energy of Association for Vanadyl in Asphaltenes by ESR Temperature Dependence Study dissoc energy, kcal/mol deg Boscan crude Athasbasca bitumen Khafji vacuum residue a
feed
product
16.5 16.4 15.1
9.9 9.8 8.9
-M-
w
247
Metal (Vanadium) Aromatic Sheet Aliphatic Weak Link (Sulfur)
Note: measured a t 5 wt % in diphenylmethane. -Aspha 1t enes Boscan Crude Atho bosca Bitumen Khofji Vacuum Residue
ModelComplexes
By I
-
Figure 11. Proposed mechanism of asphaltene cracking.
Dickson et al. I
(1972) I
I
110
‘1
1.0
v)
a 0
,” 100
a
VON4
90
:r
In
vos202
0
1
Asphaltene Cracking ,Vanadium Removal Desulfurization
0.4
0.2
BO
1.965
1.970
1.975
1.980
$
1.985
0
Boscan
go
Figure 10. Characterization for vanadyl in asphaltenes.
the feedstocks and the relative degrees of the “freedom” in the association of vanadyl to asphaltene are ranked, both among feedstocks and among product oils, as follows: Khafji vacuum residue < Boscan crude IAthabasca bitumen. From the slopes in Figure 9, the dissociation energies are obtained, as shown in Table IV. The dissociation energies of the vanadyl are 15-17 kcal/mol in the asphakenes from feedstocks are 9-10 kcal/mol in the asphaltenes from product oils. These energy values are considered as characterizing the association between the porphyrin or porphyrin-like vanadium(1V) complex and stacked aromatic sheets of asphaltene. It is interesting to note the energy values below cited by %an et al. (1969): 14 kcal/mol in dimerization of formic acid, 23 kcal/mol in association of ethanol tetramer, 1kcal/mol in association of armomatic layers in asphaltene, and 2-8 kcal/mol in intermolecular or intramolecular attraction due to hydrogen bonding. On the other hand, as shown in Figure 10, it was reported by Dickson et al. (1972) that a plot of A. (the isotropic coupling constant) vs. go (the isotropic g value) for a variety of vanadyl square-planar complexes, which includes both porphyrin and nonporphyrin, is useful to characterize the particular types of ligands. The data for the asphaltenes of this work included in the plot were obtained at elevated temperatures. As these six points are located relatively near the region of the four-nitrogen donor system (VON4),all of these vanadyls are almost certainly identified with the VON4type. If examined in detail, due to the relative location of these data, part of the ligands may be S in Boscan crude and 0 in Athabasca bitumen. As the difference of the location between the feed and product is very small, it seems that the reactivity of vanadyls in ,a certain feed asphaltene is determined primarily by the association (i.e., macrostructure) and not by the nature of ligands. Proposed Mechanism of Asphaltene Cracking. In summary, the macrostructure of asphaltene molecules
Crude
Athobasca Khofji Bitumen Vacuum Residue
Figure 12. Reactivities of asphaltenes on cracking, demetallation, and desulfurization. Bascan Crude Athabasca Bitumen Khafji Vacuum Residue 100
r-
201
6
0
0 2 0 4 0 6 0 8 0 1 0 0 Asphaltenes Conversion, WT %
Figure 13. Selectivityof asphaltenes on demetallation and desulfurization at cracking.
previously postulated by Dickie et al. (1967) and the consequent mechanism of the reaction as shown in Figure 11have been confirmed. In this model, the destruction of asphaltene micelles, if they contain vanadium, by the removal of vanadium, and the depolymerization of asphaltene molecules by the removal of heteroatoms such as sulfur (i.e., the rupture of bonds called weak links) are the main reactions. Reactivities and Selectivities. To compare the mechanism of asphaltene cracking proposed above with the information from the reactions for asphaltene cracking and the removal of vanadium and sulfur from asphaltenes, the relative reactivities and the selectivities for three feedstocks are shown in Figure 12 and 13. Athabasca bitumen and Khafji vacuum residue are less reactive toward the removal of vanadium and sulfur from asphaltene as well as cracking than Boscan crude. The low reactivities of asphaltene cracking for the two feedstocks seem to be
248
Ind. Eng. Chem. Process Des. Dev. 1903, 22, 248-257
due to the difficulties of vanadium and sulfur removal from asphaltenes. Figure 13 shows that the degree of the contribution of the two removal reactions to the cracking relates to the mechanism of the reaction; i.e., each of three feedstocks has a respective type of asphaltene cracking as follows: Boscan crude is mainly related to vanadium removal (because conversions are ranked in order: cracking < desulfurization < vanadium removal); Athabasca bitumen is equally related to the removal of vanadium and sulfur; and Khafji vacuum residue is mainly related to desulfurizationat low conversion and to vanadium removal at higher conversion.
Conclusion The features of asphaltene cracking are summarized as follows: (1)the removal of vanadium and sulfur from asphaltenes; (2) the decrease of molecular weight of remaining asphaltene; (3) the decrease of unit number and no change of unit sheet weight; (4)no change of asphaltene macrostructure in the stacking portion (cracking occurring at the nonstacked portion); ( 5 ) no major change of asphaltene particle size, (6) the change of vanadyl association type in remaining asphaltenes from “free” to “bound” state and the decrease of the dissociation energy of the vanadyl. According to these features, the model of asphaltene ciacking previously proposed was confirmed, where the main reactions are the destruction of asphaltene micelles caused by vanadium removal and the depolymerization of asphaltene molecules by removal of heteroatoms such as
sulfur. By comparing the model with the reactivities and selectivities, it is shown that the contribution of the two reactions in the model for asphaltene cracking depends on the kinds of feedstocks. Acknowledgment We would like to thank Dr. T. Tatsumi and Professor H. Tominaga of Tokyo University for their assistance in the ESR measurement. Grateful appreciation is expressed to the memory of Dr. Akiyoshi Tamaki, the former president of Chiyoda Chemical Engineering & Construction Co., La., deceased in June 1981. We are indebted to him for his leadership and assistance in the present work. Registry No. Vanadium, 7440-62-2. Literature Cited Dlckie, J. P.; Yen, T. F. Anal. Chem. 1987, 39, 1847. Dlckson, F. E.; Kunnesh, C. J.; McGlnnls, E. L.; Petrakls, L. Anal. Chem. 1972, 44, 978. Haiey, G. A. Anal. Chem. IS71 43, 371. Kim, ti.; Long, R. B. Id.Eng. Chem. Fundam. 1979, 18, 60. Nakamura, M.; Shiroto, Y.; Takahashi, H. Nlppon Kagaku Kabhi 1980, 1037. Pollack, S. A.; Yen, T. F. Anal. Chem. 1970, 42, 623. Shiralshl, M.; Sanada. Y. hvppon Kagaku Kaishi. 1978, 153. Takeuchl, C.; Nakamura, M.; Shlroto Y. ACS/CSJ Joint Meeting, Prepr. Div. Pet. CY”.,Am. Chem. Soc. 1979a 24. 666. Takeuchl. C.; Nakamura, M.; Shiroto, Y. Paper presented at 62nd Canadian Chemical Conference 8 Exhlbltlon, Sect. Novel Chem. Processes, Vancower, June 6, 1978b. Tynan, E. C.; Yen T. F. Fuel 1989, 43. 191. Yen, T. F.; Erdman, J. Q.: Pollack, S. S. Anal. Cbem. IS81 33, 1587.
Received for review March 12, 1982 Accepted August 26, 1982
Asphaltme Cracking in Catalytic Hydrotreating of Heavy Oils. 3.‘ Characterization of Products from Catalytic Hydroprocessing of KhafJiVacuum Residue Yoshbnl Shlroto,’ Shlnlchl Nakata, Yoshlo Fukul, and Chkato Takeuchl Chiyo& Chemical Engineering & Construction Co., LM., 313, Morlya-cho, Kanagawa-ku, Yokohama 221, Japan
Technologies for upgrading heavy residual oils for transportation fuels are becoming increasingly important. The asphattenic Bottom Cracking (ABC) process developed by Chiyoda is one of the new upgrading technologies. ABC is the process of asphaitenes converslon by catalytic hydrotreatingfor petroleum heavy ends. The combination of ABC and solvent deasphalting (SDA) is the effective route for the complete conversion of asphaitenic bottoms. This report presents the characterlzatlons of various products from Khafji vacuum residue by the pilot plant test of ABC combined with an SDA. One typlcal feature of product oils is to show good qualities (gravity: >20° API; metals:
