Upgrading of a Petroleum Residue. Kinetics of Conradson Carbon

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Ind. Eng. Chem. Res. 1999, 38, 938-943

Upgrading of a Petroleum Residue. Kinetics of Conradson Carbon Residue Conversion Susana Trasobares, Marı´a A. Callejas, Ana M. Benito, and Marı´a T. Martı´nez* Instituto de Carboquı´mica CSIC, P.O. Box 589, 50080 Zaragoza. Spain

Dieter Severin and Ludwig Brouwer Institut fu¨ r Erdo¨ l Erdgas-Forschung, 38678 Clausthal-Zellerfeld, Germany

A pretreated petroleum residue was hydroprocessed in a continuous hydroprocessing unit provided with a continuous stirred tank reactor. In this paper, the kinetic study of Conradson carbon residue (CCR) conversion is reported. The range of CCR conversion is 5.6-62.4%. The data of CCR conversion fit first-order kinetics, and the activation energy is 36.3 kcal/mol. No m pressure dependence of the rate constants as defined by the equation K ) K *PH was observed. 2 The structural analysis of the feed and products indicated that hydroprocessing produces an increase in the saturated fraction and a decrease in the polar fraction. The higher content of saturated fraction in the products obtained at 400 °C than in those obtained at 415 °C together with the increase in aromatic carbon and decrease in molecular weight in the products processed at 415 °C seem to indicate that cyclization reactions plus aromatization of the formed rings are being produced at this temperature. The asphaltene content was linearly related with the CCR content, and the gas yield and 525+ °C fraction conversion were linearly related with the CCR conversion. Introduction The increasing use of heavy oils as refinery feedstock is now widely recognized, and it is further recognized that heavy crude oil will be available in much larger quantities as the supplies of light crude oil are gradually disminished.1 Various industrial processes have been developed to convert heavy crude oils into transport fuels, and the methods used vary from refinery to refinery.1-3 The problems of refining heavy feedstocks may be summarized very succinctly as being due to increased aromaticity, higher molecular weights, and higher heteroatom, asphaltene, and Conradson carbon residue (CCR) contents. This leads to higher coke yields and poorer quality products. The coke is usually deposited on the reactor as well as on the catalyst surface and causes both operability and catalyst deactivation problems. In addition, the product stability is also affected. The problem becomes particularly more important at high temperatures. Residue hydroprocessing was first developed to produce low sulfur fuel oil. The earliest commercial application took place in Japan.2 Currently this process is an integral part of the overall crude oil upgrading scheme. This process may operate independently or in combination with another refinery conversion unit, depending on the particular feedstock and product demand.4,5 Hydroprocessing allows metals to be removed to reduce aromatics in the feed in order to increase the liquid yield, to decrease the coke formation, and to remove CCR. This last point is important since it also allows higher liquid yield and lower coke formation. * Author for correspondence. Fax: 34976733318. E-mail: [email protected].

Bitumens, heavy oils, and residues are characterized by a large amount of asphaltenes, which consist of large molecules of condensed polyaromatic rings with a high percentage of heteroatoms and coke precursors.2 Asphaltenes have molecular weights ranging from 1000 to 2000 and generally possess a boiling point > 500 °C. The limitations of processing heavy oils and residues depend, to a large extent, on the amount of asphaltenes present in the feedstock,6 which are responsible for a high yield of thermal and catalytic coke. Asphaltenes possess many difficulties in heavy oil processing such as hydrocracking and hydrorefining. At high temperatures, asphaltenes polymerize and cause pluggings of the catalyst bed and the downstream lines and equipment. Kirchen et al.7 found a linear relationship between coke make and microcarbon residue value, MCR, during the coking of several feedstocks derived from Athabasca bitumen. The CCR and MCR numerical values are obtained by different experimental techniques, but the values are equivalent.8 This suggests that in order to improve the liquid yield and to avoid the deactivation problems, it is necessary to reduce the CCR in the feed. In this paper, a kinetic study of the CCR conversion reactions and a study of the possible relationship between CCR and some residue characteristics will be carried out. Experimental Section A Maya residue previously hydrotreated9 through a Topsoe TK-711 catalyst guard bed was submitted to further upgrading in a continuous hydroprocessing unit provided with a continuous stirred tank reactor. Some feed characteristics are indicated in Table 1. A commercial catalyst, Topsoe TK-751, was used in the hydroprocessing experiments. This catalyst has the

10.1021/ie980285c CCC: $18.00 © 1999 American Chemical Society Published on Web 01/28/1999

Ind. Eng. Chem. Res., Vol. 38, No. 3, 1999 939 Table 1. Characteristics of the Feedstock and Catalyst Feedstock carbon, wt % hydrogen, wt % sulfur, wt % nitrogen, wt % atomic ratio H/C nickel, ppm vanadium, ppm asphaltenes, wt % IBP - 540 °C, vol % bp > 540 °C cut properties asphaltenes, wt % ramsbottom C residue, wt % sulfur, wt % nickel, ppm vanadium, ppm

84.1 12 2.25 0.27 1.71 30.26 121.27 5.6 66.5 12.8 28.3 3.82 120 574

Catalyst NiO, wt % MoO3, wt % surface area, m2/g pore vol, cm3/g pore diameter, Å bulk density, kg/L sock loaded, 1/20-in. three lobes

2.3 9.8 170 0.58 130 0.58

Table 2. Experimental Conditions of the Kinetic Experiments and CCR Content and Conversion in the Products run

temp, °C

pressure, MPa

liq flow, g/h

CCR, wt %

liq yield, %

CCR convsn, %

feed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

375 375 375 375 375 375 375 345 375 400 400 400 415 415 415

10.0 10.0 10.0 12.5 12.5 12.5 15.0 15.0 15.0 12.5 12.5 12.5 12.5 12.5 12.5

21.21 42.43 58.66 19.12 37.71 60.23 13.36 37.45 48.71 17.55 37.97 59.71 16.24 35.88 54.21

8.5 7.3 7.9 8.1 6.7 7.7 7.7 6.6 7.2 7.7 4.6 6.2 7.0 3.3 5.0 6.4

99.34 99.60 99.68 99.27 99.56 99.59 99.13 99.63 99.60 97.48 98.49 98.75 95.40 97.20 98.31

14.4 7.4 5.6 22.1 10.4 9.5 23.1 15.6 10.2 47.1 28.5 18.2 62.4 43.2 25.8

function of desulfurization, demetalation, and reduction of asphaltenes and Conradson carbon residue. Topsoe TK-751 is also recommended for the second-stage catalyst in composite fillings. It is a Ni/Mo-type catalyst, the characteristics of which are indicated in Table 1. The kinetic study of CCR conversion was performed in a continuous stirred tank reactor (CSTR) which has 1000 cm3 of capacity provided with a “kinetic basket” for 185 cm3 of catalyst. The experimental setup was described elsewere.10 Interphase gradients were investigated by varying the stirring speed and gas/liquid ratio, and the study was carried out at 10 000 std ft3/bbl gas/liquid ratio and 3500 rpm stirring speed. To avoid intraparticle gradients, the kinetic runs were carried out with the catalyst crushed at a range of particle size between 53 and 530 µm. Twenty-seven grams of sulfided Topsoe TK-751 catalyst was placed inside bags of metallic mesh of 35-µm sieve aperture in order to avoid misleading results through losses of catalyst by attrition and by plugging the reactor output. After 180 h of running the hydroprocessing unit, steady-state conditions for the catalyst were reached, and the runs indicated in Table 2 had been started. The hydroprocessing experiments were carried out under the conditions of temperature, pressure, and

liquid flow indicated in Table 2. The CCR was determined by the D189-81 ASTM11 on products from the kinetic runs from hydroprocessing. Structural analysis of the feed and products was carried out by chromatographic group-type separation into saturates, aromatics, and polars and by characterization by 1H and 13C NMR. The separation into saturates, aromatics, and polars was performed by thinlayer chromatography with a flame ionization detector (TLC/FID). A solution of the sample in toluene (2 wt %) was applied on an alumina-powder-coated glass rod (Chromarod-A Iatroscan). Then, the elution with nheptane of the saturated hydrocarbons was carried out until the front moved 10 cm from the starting point (time of elution: 33 min). After the rod was dried in an oven at 75 °C for 5 min, the aromatic hydrocarbon fraction was eluted with toluene (6 cm in 15 min). After this step, the rod was again dried (75 °C for 5 min). Using this method, the fraction of polar compounds remains at the starting point, and the rod is then quantitatively analyzed by moving it linearly through the flame. The ion current was recorded and integrated, and the relative areas were taken as a measure for the content of the saturate, aromatic, and polar compounds of the sample. 1H NMR was performed in a Unity 300 Varian at 293 K, with a resonance frequency of 299.863 MHz, an acquisition time of 3.7 s, a pulse angle of 45°, and spectral width of 40 000 Hz. The samples were dissolved in CDCl3 to a concentration of 5 wt %.13C NMR spectra were recorded with a Fourier transform Varian NMR spectrometer. The resonance frequency for 13C was 75.405 MHz. For each spectrum, 1500 scans were accumulated with a relaxation delay of 10 s. Broad-band decoupling WALTZ was gated during data acquisition. The samples were dissolved in CDCl3 (99% D), with a ratio of 50/50 by weight. Cr(AcAc)3 (0.7 wt %) was added to the sample as a paramagnetic relaxation agent. Results The results from the CCR determination and percentages of CCR conversion are indicated in Table 2. The CCR conversion ranged from 5.6 to 62.4%. Sanford12 obtained conversions from 20.7 to 74.6% in the hydrocracking of Athabasca bitumen in a batch stirred tank reactor and a wide range of experimental conditions and with Co/Mo- and Ni/Mo-type catalysts. Furthermore, in previous studies in our laboratory,10 conversions ranging from 21.1 to 98.2% were obtained in the hydroprocessing of the raw Maya residue with Topsoe TK-711 catalyst. In our experimental study, for a heterogeneous perfectly mixed system working continuously and after steady-state conditions have been reached, the rate equation, assuming constant density, is

C0 - C 1 ) -r LHSV

(1)

where C0 and C are the inlet and outlet concentrations of the Conradson carbon residue, respectively, LHSV is the liquid hourly space velocity, and -r is the CCR removal rate, which can be expressed by m n C -r ) K*PH 2

(2)

where K* is the intrinsic rate constant, m is the kinetic

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Figure 1. First-order kinetic plot for CCR conversion reactions at 12.5 MPa of hydrogen pressure. Table 3. Rate Constants and Activation Energy for the CCR Removal Reactions and, in Parentheses, the Standard Errors of the Estimated Coefficients 375 °C K10MPa, L/(h‚gcat) corr coeff std err of estn K12.5MPa, L/(h‚gcat) corr coeff std err of estn K15MPa, L/(h‚gcat) corr coeff std err of estn ln K0 -Ea/R corr coeff std err of estn Ea, kcal/mol

0.14(0.003) 0.99 4.7 × 10-3 0.2(0.02) 0.98 0.03 0.17(0.036) 0.81 0.077 26.46(1.2) -18 182(805.3) 1.00 0.052 36.3

400 °C

415 °C

0.6(0.032) 0.99 0.053

1.01(0.078) 0.99 0.143

m K*CnPH 2

LHSV

(3)

To obtain the kinetic order n, the process was carried out at constant pressure, 12.5 MPa, and a pseudokinetic rate constant (K) was defined: m K ) K*PH 2

(4)

Then eq 3 can be rewritten as

C0 - C )

KCn LHSV

(5)

For calculating m from expression 4, a series of experiments at 375 °C and different pressures and liquid flows, Table 2, were carried out. A logarithmiclogarithmic plot of K versus hydrogen pressure would have a slope m and ln K* as the intersection with the ordinate axis. The data of CCR conversion, Table 2, fit first-order kinetics, the first-order rate equation being

C0 - C K ) C LHSV

This result coincides with our previous observations.10 However, Beaton and Bertolacini13 found that the reaction of Ramsbottom carbon conversion is roughly first order with respect to hydrogen partial pressure for hydroprocessing of a typical vacuum residue in a commercial plant with three trains of three backmixed reactors in series with Co/Mo-type catalyst. The influence of temperature was assumed to follow the Arrhenius equation

K ) K0e-Ea/RT

order on H2 pressure, n is the kinetic order on CCR concentration, and PH2 is the hydrogen pressure. From eqs 1 and 2,

C0 - C )

Figure 2. Arrhenius plot for the first-order rate constants of CCR conversion reactions at 12.5 MPa of hydrogen pressure.

(6)

Figure 1 represents the first-order kinetic plot for CCR conversion. Table 3 indicates the kinetic constant values found at different pressures and shows that no pressure dependence of the rate constant, as defined by eq 4, was observed.

(7)

Figure 2 shows the Arrhenius plot of ln K versus 1/T. The values of the rate constants and activation energy are indicated in Table 3. The activation energy is lower than the value obtained in the hydroprocessing of the raw Maya crude with TK-711 catalyst.10 For this reason, the reactions of CCR removal in the hydroprocessing of a Maya crude with TK-711 are more sensitive to the temperature than the reactions of CCR removal in the hydroprocessing of a pretreated residue with TK-751 catalyst. Sanford12 proposed a mechanism for the conversion of a residue into distillate. This mechanism is centered around two classes of residue molecules, one of which forms residue in the test CCR, while the other, nonCCR residue, does not. In this scheme, the ratedetermining step is the thermal breaking of a carbonto-carbon bond to give an aliphatic radical and an aromatic radical. This first step is independent of whether hydrogen is present or not. The aliphatic radical can undergo rapid fragmentation to produce gases and distillates, whereas the aromatic radical can either undergo condensation reactions, leading to coke formation, or react with molecular hydrogen to produce a carbon-to-hydrogen bond and a hydrogen atom. The hydrogen atom can react with condensed aromatic centers, leading to the decomposition of these centers, again giving distillates and gases. The group-type separation of the samples in saturated, aromatic, and polar fractions is indicated in Table 4. In this table, it can be observed that the percentage of saturated fraction is lower in the feed than in the obtained products, the highest being those obtained at 400 °C, runs 10-12. Therefore, the hydroprocessing produced an increase of the saturated fraction and a decrease of the polar fraction. This decrease in the polar fraction indicates that heteroatoms are being removed

Ind. Eng. Chem. Res., Vol. 38, No. 3, 1999 941 Table 4. Group-Type Separation (wt %) Obtained by TLC/FID and Molecular Weight (MW) of Products from Hydroprocessing run

saturates

aromatics

polars

MW

feed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

31.6 36.6 35.2 32.3 39.0 32.8 33.4 35.0 39.9 34.5 41.6 37.3 40.7 39.5 39.7 37.0

36.0 41.7 43.3 37.0 34.7 37.7 37.2 39.6 39.7 38.9 29.2 38.8 34.5 35.2 34.5 35.0

32.4 20.9 21.0 30.3 25.5 29.0 28.7 24.5 19.9 26.2 26.6 22.4 23.6 20.7 23.0 26.3

350 318 335 342 316 329 334 311 331 337 337 291 314 198 248 280

Table 6. Distribution of Carbon Atom by 13C NMR of the Feed and of the Products from the Runs Performed at 12.5 MPa and Structural Parameters run

Caro, % (100-210)a

Csat, % (10-100)a

feed 4 5 6 10 11 12 13 14 15

20.75 19.82 20.72 21.61 18.68 20.56 21.83 21.93 24.53 20.79

79.25 80.18 79.28 78.39 81.32 79.44 78.17 78.07 75.47 79.21

fab

AGc

CLd

0.21 0.2 0.21 0.22 0.19 0.21 0.22

1.23 1.43 1.42 1.58 0.99 1.21 1.60

15.44 11.54 12.92 11.90 13.79 13.09 11.06

0.25 0.21

1.19 1.38

11.08 11.25

a Chemical shift, ppm. b fa, the fraction of aromatic carbon or aromaticity. c AG, the number of alkyl and hydroaromatic groups per molecule, AG ) HR/a (a ) 2.3). d CL, the average size or chain length of the alkyl and hydroaromatic groups.

Table 5. Distribution of Hydrogen Atom by 1H NMR of the Feed and of the Products from the Runs Performed at 12.5 MPa run

Hγ,a % (0.5-1)f

Hβ,b % (1-1.6)f

HR,c % (1.9-3.3)f

HF,d % (3.3-4.5)f

Haro,e % (7.2-8.5)f

feed 4 5 6 10 11 12 13 14 15

19.81 23.33 22.92 22.94 23.66 23.53 21.21 20.18 21.81 22.17

56.16 56.69 56.23 56.69 56.44 56.15 57.15 56.05 56.29 56.34

10.53 9.26 9.01 9.59 8.83 8.85 10.30 11.46 10.01 10.03

0.21 0.16 0.14 0.04 0.02 0.00 0.14 0.71 0.49 0.47

5.32 5.55 5.62 5.55 5.80 5.73 5.13 5.45 5.93 5.52

a H , CH γ or further from an aromatic ring. b H , β-(CH , CH ) γ 3 β 3 2 and CH γ or further from an aromatic ring. c HR, CH3, CH2, and d CH R to an aromatic ring. HF, ring joining methylene ArCH2Ar. e H , aromatic hydrogen. f Chemical shift, ppm. aro

during the hydroprocessing. In fact, we observed a decrease in the heteroatoms content with the hydrotreatment.14 This heteroatom removal would imply an increase in the aromatic fraction. However, it is necessary to take into account that in the hydrocracking conditions, the radicals produced could be stabilized by hydrogen to produce saturated compound and gases or by condensation reactions to form compounds that would remain in the aromatic fraction to produce coke. In Table 4, it can be observed that the aromatic fraction does not have a clear increasing tendency. This suggests that both saturation and condensation reactions were taking place simultaneously. The molecular weight, hydrogen atom distribution, and carbon atom distribution are indicated in Tables 4, 5, and 6 respectively, and the structural parameters were calculated from the values given in them according to the scheme reported by Snape et al.15 Table 5 shows that the lowest aromatic hydrogen content corresponds to the feed, and this value increases by hydroprocessing, the highest value being that corresponding to the product obtained in run 14. On the other hand, the molecular weight, Table 4, is higher in the feed than in the processed products and decreases when the LHSV decreases and the temperature increases. The lowest value was obtained at the most severe conditions. The decrease in the molecular weight indicates that cracking reactions were produced during the processing. The decrease in CL, the average chain length size of the alkyl and hydroaromatic groups, Table

Figure 3. CCR content versus aromatic carbon content at 12.5 MPa of hydrogen pressure.

6, also suggests that with cracking of the alkyl side chains, reactions are being produced. In Table 6, it can be observed that the aromatic carbon hardly changed in the products obtained at 375 and 400 °C; however, it increased at 415 °C. This increase may suggest that condensation reactions were carried out at high temperatures. Nevertheless, the increase in aromatic hydrogen and the decrease in molecular weight with temperature do not indicate an increase in condensation degree, so it suggests that cyclization reactions plus aromatization of the formed rings are being produced during the processing at 415 °C. The decrease in AG, the number of alkyl and hydroaromatic groups per molecule, fits with this supposition since a cyclization plus aromatization process would decrease the number of alkyl groups in the aromatic rings, would increase the aromatic carbon, and would not increase the molecular weight. This also fits with the decrease of the saturated fraction, Table 4, from 400 to 415 °C. In addition to the cyclization plus aromatization reactions, a decrease in hydrogenation could occur. The hydrogenation of the aromatic rings is exothermic and equilibrium limited16,17 and could be thermodynamically disfavored at 415 °C. Sanford12 and Gray et al.18 showed that the CCR content of a residue can be correlated with the aromatic fraction in the 525+ °C cut. In our study, the relationship between the CCR content and the aromatic carbon content in the whole sample was studied, Figure 3. A linear relationship was found in the obtained products

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at 375 and 400 °C, but this relationship was not found in the obtained products at 415 °C. The equations found were

Caro ) 11.56 + 1.22CCR (r ) 0.97) at 375 °C Caro ) 12.71 + 1.28CCR (r ) 0.99) at 400 °C As in a previous study,10 it could be said that there is not a general correlation between aromatic carbon and CCR in the hydroprocessing products when they are considered all together. The correlation between CCR and the aromatic carbon fraction for the 525+ °C data reported by other authors18 is not fulfilled for products with aromatic fractions of low molecular weight that could not be coke precursors. Although asphaltenes produce high thermal coke yields,19 little is known of the actual chemistry of coke formation. In a more general scheme, the chemistry of asphaltene coking has been suggested to involve the thermolysis20 of bonds to form reactive species, which then react with each other (condensation) to form coke. Since the asphaltenes make catalytic hydrotreating very difficult, a better understanding of the properties and changes during the processing is important for the development of upgrading technology for asphaltenecontaining heavy feedstocks:

Figure 4. Linear relationship between CCR content and asphaltene content.

maltenes f resins f asphaltenes f carbenes f coke The relationship between CCR content and asphaltene content was studied, Figure 4, and a linear relationship was observed with the equation and regression coefficient following:

Figure 5. Linear relationship between gas yield and CCR conversion.

asphaltenes ) 2.536 + 0.916CCR (r ) 0.97) This confirms the asphaltenic fraction as being a coke precursor, as was reported by Quann et al.2 The highest asphaltene and CCR values were obtained in the feed. The CCR content decreases as the asphaltene content decreases, the lowest value being obtained at 415 °C and the lowest liquid flow. Asphaltene conversion occurs through gas and oil formation, with the coke formation being strongly inhibited21-23 by hydrogen. A relationship between CCR conversion and gas yield was found, Figure 5. The equation and regression coefficient are

gas ) -0.3617 + 0.0712CCR (r ) 0.97) The highest CCR conversion and gas yield were obtained at 415 °C and the lowest liquid flow. Several studies had been done to show the relationship between CCR and 525+ °C residue content. Ternan and Kritz24 found that there was a correlation between pitch content and CCR in the feeds and products from hydrocracking reactions, both with hydrotreating catalysts and hydrogen-transfer additives in continuous pilot plant reactions. Sanford25 did not find a clearly linear relationship for batch catalytic hydrocracking, but a linear tendency was found. In our experimental conditions, a linear tendency with a poor correlation (r ) 0.73) between CCR content and 525+ °C residue content was

Figure 6. Linear relationship between residue conversion (T > 525 °C) and CCR conversion at 12.5 MPa of hydrogen pressure.

found (Figure 6). Nevertheless, a very good correlation (r ) 0.94) between the CCR and 525+ °C conversions was obtained. Conclusions The data of CCR conversion fit first-order kinetics, and the activation energy is 36.3 kcal/mol. No pressure dependence of the rate constants as defined by the m was observed. The range of CCR equation K ) K*PH 2 conversion is 5.6-62.4%.

Ind. Eng. Chem. Res., Vol. 38, No. 3, 1999 943

The percentages of the saturated fraction increase and the percentages of the polar fraction decrease by hydroprocessing. The decrease of the polar fraction is consistent with the heteroatoms removal. The decrease of the molecular weight and the increase of aromatic hydrogen with the increasing temperature indicate that cracking reactions predominate at the three temperatures used. The higher content of the saturated fraction in the products obtained at 400 °C than in those obtained at 415 °C together with the increase of the aromatic carbon and decrease of the molecular weight in the products processed at 415 °C seems to indicate that cyclization reactions plus aromatization of the formed rings are being produced at this temperature. A linear relationship between the CCR and aromatic carbon contents was found at 375 and 400 °C, but a general relationship between the CCR content and aromatic carbon content was not found. It was found that asphaltene content was linearly related with CCR content and CCR conversion with gas yields and 525+ °C fraction conversion. Acknowledgment We thank the European Community (Contract JOU2CT92-0206) and the DGICYT (AMB93-1137-CE) for financial support. Literature Cited (1) Speight, J. G. Fuel Science and Technology Handbook; Dekker: New York, 1990. (2) Quann, R. J.; Ware, R. A.; Hung, Ch. W.; Wei, J. Catalytic Hydrodemetalation of Petroleum. Adv. Chem. Eng. 1988, 14, 95259. (3) O’Connor, P.; Gerritsen, L. A.; Pearce, J. R.; Desai, P. H.; Yanik, S.; Humphries, A. Improve resid Processing. Hydrocarbon Process. 1991, 70, 76 et seq. (4) Howell, R. L.; Hung, C.; Gibson, K. R.; Chen, H. C. Catalyst Selection Important for Residuum Hydroprocessing. Oil Gas J. 1985, 83, 121-128. (5) Siewert, H. R.; Koenig, A. H.; Ring, T. A. Optimize Design for Heavy Crude. Hydrocarbon Process. 1985, 64, 61-66. (6) Speight, J. G. Catalyst on the Energy Science; Elsevier: Amsterdam, 1984. (7) Kirchen, R. P.; Sanford, E. C.; Gray, M. R.; George, Z. M. Coking of Athabasca Bitumen-Derived Feedstocks. AOSTRA J. Res. 1989, 5, 225-235. (8) Anonymous. Standard Test Method for Micro Carbon Residue of Petroleum Products. 1987 Annual Book of ASTM Standards: Section 5, Petroleum Products, Lubricants and Fossil Fuels; ASTM: Philadelphia, PA, 1987; Section 05.03, pp 585-590. (9) Martinez, M. T.; et al. Hydroprocessing of Heavy Petroleum Fractions. Final Report, 1996, Contract JOU2-CT92-0206.

(10) Trasobares, S.; Callejas, M. A.; Benito, A. M.; Martı´nez, M. T.; Severin, D.; Brouwer, L. Kinetics of Conradson Carbon Residue Conversion in the Catalytic Hydroprocessing of a Maya Residue. Ind. Eng. Chem. Res. 1998, 37, 11-17. (11) Anonymous. Standard Test Method for Conradson Carbon Residue of Petroleum Products. 1987 Annual Book of ASTM Standards: Section 5, Petroleum Products, Lubricants and Fossil Fuels; ASTM: Philadelphia, PA, 1987; Section 05.01, pp 137-143. (12) Sanford, E. C. Conradson Carbon Residue Conversion during Hydrocracking of Athabasca Bitumen. Catalyst Mechanism and Deactivation. Energy Fuels 1995, 9, 549-559. (13) Beaton, W. I.; Bertolacini, R. J. Resid Hydroprocessing at Amoco. Catal. Rev. Sci. Eng. 1991, 33, 281-317. (14) Martı´nez, M. T.; Callejas, M. A.; Carbo´, E.; Herna´ndez, A. Dynamic of Surfaces and Reaction Kinetics in Hetereogeneous Catalysis. Stud. Surf. Sci. Catal. 1997, 109, 565-570. (15) Snape, C. E.; Ladner, W. R.; Bartle, K. D. Coal Liquefaction Products; John Wiley and Sons: New York, 1983. (16) Girgis, M. J.; Gates B. C. Reactivities, Reaction Networks, and Kinetics in High-Pressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 1991, 30, 2021-2058. (17) Yui, S. M.; Sanford, E. C. Kinetics of Aromatics Hydrogenation of Bitumen-Derived Gas Oils. Can. J. Chem. Eng. 1991, 69, 1087-1095. (18) Gray, M. R.; Jokuty, P.; Yeniova, H.; Nazarewycz, L.; Wanke, S. E.; Achia, U.; Krzywicki, A.; Sanford, E. C.; Sy, O. K. Y. The Relationship between Chemical Structure and Reactivity of Alberta Bitumens and Heavy Oils. Can. J. Chem. Eng. 1991, 69 (9), 833-843. (19) Sheu, E. Y.; De Tar, M. M.; Storm, D. A.; De Canio, S. J. Aggregation and Kinetics of Asphaltenes in Organic-Solvents. Fuel 1992, 71, 299-302. (20) Levinter, M. E.; Medvedera, M. I.; Panchenkov, G. M.; Agapov, G. I.; Galiakbarov, M. F.; Galikeev, R. K. The Mutual Effect of Group Components During Coking. Khim. Tekhnol. Topl. Masel 1967, 4, 20-22. (21) Schucker, R. C.; Keweshan, C. F. The Reactivity of Cold Lake Asphaltenes. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1980, 25, 155-165. (22) Savage, P. E.; Klein, M. T.; Kukes, S. G. Asphaltene Reaction Pathways. 3. Effect of Reaction Environment. Energy Fuels 1988, 2, 619-628. (23) Martinez, M. T.; Benito, A. M.; Callejas, M. A. Kinetics of Asphaltene Hydroconversion. 1. Thermal Hydrocracking of a Coal Residue. Fuel 1997, 76, 899-905. (24) Ternan, M.; Kritz, J. F. +525 °C Pitch Content Versus Microcarbon Residue: A Correlation for Characterizing Reaction Products Obtained by Hydrocracking Bitumens, Heavy Oils, and Petroleum Residua. AOSTRA J. Res. 1990, 6, 65-70. (25) Sanford, E. C. The Mechanism of 524 °C+ Residuum Conversion: Pitch Content Versus CCR During Hydrocracking of Athabasca Bitumen. AOSTRA J. Res. 1991, 7, 163-168.

Received for review May 7, 1998 Revised manuscript received November 27, 1998 Accepted December 11, 1998 IE980285C