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Energy & Fuels 1996, 10, 474-481
Heavy Oil Hydroprocessing with the Addition of Hydrogen-Donating Hydrocarbons Derived from Petroleum† Junichi Kubo* Central Technical Research Laboratory, Nippon Oil Company, Ltd., Chidori-cho 8, Naka-ku, Yokohama, 231 Japan
Hidehiro Higashi, Yoshiharu Ohmoto, and Hiroki Arao Catalyst Research Institute, Catalysts & Chemicals Industries Co., Ltd., Kitaminato-machi 13-2, Wakamatsu-ku, Kitakyushu-shi, 808 Japan Received July 10, 1995X
The effects of the addition of hydrogen-donating hydrocarbons derived from petroleum were tested in a pilot plant (0.01 bbl/day) equipped with a downflow fixed bed reactor for the hydroprocessing of atmospheric residues, and the following results were obtained: (1) HHAP (partly hydrogenated product of a highly aromatic heavy fraction from petroleum) and HAP (highly aromatic heavy fraction prior to the hydrogenation to produce HHAP) were effective to reduce coke formation and hydrogen consumption. (2) A particular and effective mechanism resulting from the configurations of the additives was found to be initiated by the addition of these additives. (3) This mechanism was substantiated by detailed analyses of the products.
Introduction In heavy oil upgrading, coke formation is the most serious problem. It is well-known that the addition of hydrogen-donating hydrocarbons is an effective way to reduce coke formation, and they have also been applied to heavy oil hydroprocessing.2,3 It was already reported that hydrogen-donating hydrocarbons can be produced from petroleum.4,5 However, from the practical viewpoint, the problem seems to be that the radical-scavenging abilities of the hydrogen-donating hydrocarbons are not high enough to reduce coke formation satisfactorily, and a large amount of the additives is required to attain the desired effects. Recently, it was reported by us that hydrogendonating hydrocarbons which have high radical-scavenging abilities can be produced from petroleum.6 The high radical-scavenging abilities of these materials were already confirmed in the reactions with 2,2-diphenyl1-picrylhydrazyl (DPPH),6,7 and they were also confirmed by practical tests for the thermal, oxidative, and radiation-induced oxidative degradation of petroleum products,8-10 rubbers,8,11 plastics,8,12,13 and thermoplastic elastomers.14 * To whom correspondence should be addressed. † Presented at 208th ACS National Meeting, Division of Petroleum Chemistry, Washington, D.C., August 21-25, 19941. X Abstract published in Advance ACS Abstracts, January 15, 1996. (1) Kubo, J.; Higashi, H.; Ohmoto, Y.; Arao, H. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1994, 39, 416-421. (2) Aaarts, J. J. B.; Ternan, M.; Parsons, B. I. Fuel 1978, 57, 473478. (3) Doyle, G. Prepr. Pap.sAm. Chem. Soc., Div. Pet. Chem. 1975, 21, 165-172. (4) Fisher, I. P.; Southrada, F.; Wood, H. J. Prepr. Pap.sAm. Chem. Soc., Div. Pet. Chem. 1982, 27, 838-848. (5) Baksi, A. S.; Lutz, L. H. Oil Gas J. 1987, July 13, 84-87. (6) Kubo, J. Ind. Eng. Chem. Res. 1992, 31, 2587-2593. (7) Kubo, J.; Miyagawa, R.; Takahashi, S. Energy Fuels 1994, 8, 804-805.
0887-0624/96/2510-0474$12.00/0
Based on these facts, the additive effects of these hydrocarbons (called HHAP) were tested in heavy oil hydroprocessing in order to reduce coke formation. As a result, it was found that the steric effects are deeply related in this case and that the coke formation, the hydrogen consumption, and the properties of the products were distinctly changed by the addition of these hydrocarbons. That is, from the results obtained in the pilot plant, it was revealed that a very particular and effective mechanism appears due to the steric effects. Detailed analyses of the products and extensive data from the supplemental tests support this mechanism. The test results from a 0.01 bbl/day pilot plant and the detailed analytical results to elucidate the mechanism are reported in this paper. Experimental Section The tests were conducted in a pilot plant (0.01 bbl/day) equipped with a downflow fixed bed reactor (i.d. 19.4 mm, length 1200 mm, catalyst volume 400 mL). The simplified process flow of the pilot plant is illustrated in Figure 1. A series of tests to investigate the effects of additives in detail were conducted. The properties of the feedstock used in these tests are shown in Table 1. The main operating conditions are shown in Table 2. A commercial desulfurization catalyst (Ni-Co-Mo/Al2O3) was used in this series of tests. The conclusions obtained from these tests were confirmed by other tests on other feedstocks and catalysts, but detailed analyses were not carried out in the latter cases. (8) Kubo, J. Erdol Kohle Erdgas Petrochem. 1993, 46, 360-365. (9) Kubo, J. Fuel Process. Technol. 1991, 27, 263-277. (10) Kubo, J. Ind. Eng. Chem. Res. 1993, 32, 1754-1759. (11) Kubo, J. J. Appl. Polym. Sci. 1993, 47, 925-936. (12) Kubo, J. J. Appl. Polym. Sci. 1992, 45, 51-60. (13) Kubo, J.; Otsuhata, K. Radiat. Phys. Chem. 1992, 40, 477483. (14) Kubo, J.; Onzuka, H.; Akiba, M. Polym. Degr. Stab. 1994, 45, 27-37.
© 1996 American Chemical Society
Heavy Oil Hydroprocessing
Energy & Fuels, Vol. 10, No. 2, 1996 475 Table 3. Properties of HHAP density at 15 °C (g/cm3) viscosity at 100 °C (cSt) softening point (°C) composition (wt %) saturates aromatics resins asphaltenes av mol wt distillation (°C) BP/5% 10/30 50/70 90/EP
Figure 1. Simplified process flow of the pilot plant (0.01 bbl/ day). Table 1. Properties of the Feedstock (A/H Atm. Resid.) feedstock
A/H atm resid
density at 15 °C (g/cm3) viscosity at 50 °C (cSt) carbon residue (wt %) elemental analysis (wt %) C H N S metals (wppm) Ni V distillation (°C) IBP/5% 10/20 30/40 composition (wt %) saturates aromatics resins asphaltenes
0.9999 4157 (0.0416 m2 s-1) 15.5 84.3 10.6 0.24 4.42 37 95 276/387 419/453 491/536 14.0 67.7 7.9 10.4
Table 2. Main Operating Conditions in the Pilot Plant reactor temperature (°C) pressure (kg/cm2) LHSV (h-1) H2/feed (L(STP)/L) catalyst
383-395 150 (14.72 MPa) 0.2 700 Mo, Ni, Co/Al2O3
The additive (HHAP, heavy hydroaromatics from petroleum) is a mixture of hydrocarbons produced by the hydrogenation of a highly aromatic heavy fraction from petroleum with a commercial desulfurization catalyst (Co-Mo/Al2O3) under the following conditions: temperature 330-360 °C, H2 pressure 100-150 kg/cm2 (9.8-14.7 MPa), and LHSV 0.2-0.5 h-1. HHAP contains many components (more than 300 detected by gas chromatography) and it is difficult to define the individual ones; the properties as a mixture are shown in Table 3. Most of the components include the partially hydrogenated products of condensed aromatic rings. Hence, HHAP exhibits radical-scavenging ability based on its hydrogen-donating property. The high radical-scavenging abilities of HHAPs were confirmed6,7 in the reactions with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and by many practical tests for various hydrocarbon products.8-14 The highly aromatic heavy fraction from petroleum (this is called HAP) prior to the hydrogenation to produce HHAP was also tested (details will be described later).
1.056 84.00 (8.4 × 10-5 m2 s-1) 24.0 12.1 74.4 8.1 5.4 360 235/297 349/401 432/464 511/593
The effects of the additives on the inhibition of coke formation were mainly evaluated by dry sludge (ASTM D4870) and toluene insolubles (JPI-5S-18-80) along with stability tests of the storage of the products (ASTM D4740, modified by Nippon Oil Co., Ltd.) and microscopic photographs. In addition, more detailed analyses of the products together with the feedstock were conducted. That is, as shown in Figure 2, two desulfurized samples, one without additives and the other with 3 wt %/feed HHAP added, were analyzed along with the feedstock. The three samples were divided into asphaltenes and maltenes by n-heptane, and the maltenes were divided into the fractions by changing the solvents in elutionadsorption chromatography with the silica gel/alumina gel dual packed column. The individual fractions were analyzed by elemental analysis and 1H NMR. Furthermore, the asphaltenes were analyzed in detail, and the structural parameters are demonstrated.
Results and Discussion First, the effects of HHAP on coke formation in the series of detailed tests are shown in Table 4. From this table, it is quite obvious that the dry sludge and toluene insolubles were inhibited by the addition of HHAP (3 wt %). The results from the stability tests are illustrated in Figure 3. Without the addition of HHAP, the stability of the products deteriorates above 385 °C at the reaction temperature. However, with the addition of 3 wt % HHAP to the feed, coke deposition on filter paper appeared at higher temperatures. From these results, it is obvious that the addition of HHAP in small amounts (3 wt %/feed) is effective for the inhibition of coke formation. This is attributable, first of all, to the high radical-scavenging ability of HHAP mentioned before. However, considering that a much greater quantity of HHAP is required to get distinct effects in the thermal cracking of heavy oils (not reported yet) and that the hydrogenation conditions to produce HHAP from HAP are similar to those of the hydroprocessing, it can be deduced that the following types of reactions occur in the reactor along with the desulfurization reactions (tetralin is taken as the example for the explanation): –4H +4H H2 in vapor phase and catalyst
That is, aromatics are regenerated to hydroaromatics by the hydrogen in the vapor phase in the presence of catalysts. In other words, hydroaromatics (or aromatics) function as the hydrogen transfer medium from the vapor phase to the oil.
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Figure 2. Separation procedures for maltenes from products and feedstock. Table 4. Test Results in the Pilot Plant (Additive Effects of HHAP) expt 1a additive
none
dry sludge (wt %) ASTM D4870 toluene insolubles (wt %) reaction temp (°C) density (g/cm3) carbon residue (wt %) desulfurization (%) denitrogenation (%) demetallization (%) conversion of asphaltenes (%)
0.79 0.11 383 0.9224 4.7 94.8 54.4 86.6 74.8
a
expt 2a HHAP 3 wt %/feed 0.05 0.05 383 0.9317 5.0 91.3 49.8 88.2 76.7
expt 3 none 0.65 0.17 389 0.9246 5.2 91.6 66.5 79.5 61.5
expt 4 HHAP 3 wt %/feed 0.04 0.04 390 0.9296 5.3 90.9 64.7 85.6 69.2
expt 5 none 0.95 0.10 395 0.9184 4.8 93.9 70.2 87.1 65.4
expt 6 HHAP 3 wt %/feed 0.13 0.03 395 0.9222 5.1 93.3 67.8 87.1 75.0
Feedstock was slightly different from other tests.
Figure 3. Additive effects of HHAP on the stabilities of the products.
To confirm this concept, HAP was added (5 wt %) instead of HHAP. The results are shown in Table 5. From these results, it can be clearly seen that the addition of HAP is as effective as that of HHAP. These data confirm that the above deduction is correct. This means that HHAP (or HAP) functions as a hydrogen transfer medium from the vapor phase to the oil in the reactor.
The obvious effects of HHAP and HAP are demonstrated in Figure 4. This figure shows the microscopic photos of the products without addition, with HHAP (3 wt %) added, and with HAP (5 wt %) added, all at 395 °C. The effects of HHAP and HAP are quite clear. The other important results obtained from these tests are the reduction of hydrogen consumption during the addition of HHAP and HAP. The changes in hydrogen consumption plotted against desulfurization are shown in Figure 5. It is manifested by this figure that hydrogen consumption was reduced by about 20% by the addition of HHAP or HAP. The reasons why the hydrogen consumption was reduced are elucidated in Table 6. From this table, the following observations can be made: (1) Saturates (eluted with n-hexane in TLC) are lower in the cases with HHAP or HAP. (2) Aromatics (not eluted with n-hexane/eluted with toluene) are higher in the cases with HHAP or HAP. (3) H/C (atomic ratios) are lower in the cases with HHAP or HAP. From these results, it is inferred that more aromatic rings are hydrogenated to naphthenes in the cases without additives. In contrast, fewer aromatic rings are hydrogenated in the presence of HHAP or HAP. Hence, it can be deduced that the reduction of hydrogen consumption is mainly due to the suppression of the hydrogenation of aromatic rings by the addition of HHAP or HAP. This is supported by the data described hereafter.
Heavy Oil Hydroprocessing
Energy & Fuels, Vol. 10, No. 2, 1996 477 Table 5. Test Results in the Pilot Plant (Additive Effects of HAP) expt 3
additive
none
dry sludge (wt %) ASTM D4870 toluene insolubles (wt %) reaction temp (°C) density (g/cm3) carbon residue (wt %) desulfurization (%) denitrogenation (%) demetallization (%) conversion of asphaltenes (%)
0.65 0.17 389 0.9246 5.2 91.6 66.5 79.5 61.5
expt 7 HAP 5 wt %/feed 0.05 0.04 390 0.9297 5.1 92.1 62.8 83.3 70.2
expt 5 none 0.95 0.10 395 0.9184 4.8 93.9 70.2 87.1 65.4
expt 8 HAP 5 wt %/feed 0.06 0.02 395 0.9248 5.1 93.3 65.3 87.9 71.2
Figure 5. Additive effects of HHAP and HAP on hydrogen consumption.
ation (%), 0.7 increase; H/C (atomic ratio), 0.02 decrease. Judged from these values, the effects of the addition itself are relatively small compared with the ones between the cases without and with the addition because the amounts of the additives are small and the differences in properties between the additives and the products are also small. In addition, in some items such as the conversion of asphaltenes, desulfurization, and denitrogenation, the opposite trends to the addition itself appear, as shown in Tables 4, 5, and 6. Thus, from these facts, the results derived from Tables 4, 5, and 6 can be deemed to be due to the chemical reactions and not to the addition itself. Nitrogen atoms exist substantially in aromatic rings and they are thought to be removed by the nuclear hydrogenation of aromatic rings.15-17 The distinct decreases in denitrogenation support the conclusion that the nuclear hydrogenation is suppressed by the addition of HHAP or HAP. This is a solid evidence to show the suppression of the nuclear hydrogenation. The increases in density also support this conclusion because aromatics have higher densities than other hydrocarbons at the same molecular weights. As to desulfurization, the results can be understood by the fact that sulfur atoms do not substantially exist in aromatic rings, and the active sites for desulfurization are different or separate from the ones for nuclear hydrogenation as many researchers have pointed out18-24 multipoint adsorption.18 Most of the metals exist outside the aromatic rings as porphyrins and other organometallic complexes, and fundamentally, more energy put into the system can be used for the removal of the metals instead of the nuclear hydrogenation as well as the removal of the side chains. The increases in carbon residues seem to mean that the aromatic contents are increased. In contrast, asphaltenes are markedly reduced by the addition of the additives. This seems to be consistent with the results
From Tables 4 and 5, the following tendencies can be observed by the addition of HHAP and HAP: (1) density, increase, (2) carbon residue, increase, (3) desulfurization, unchanged (slight decrease), (4) denitrogenation, decrease, (5) demetallization, increase, and (6) conversion of asphaltenes, increase. Here, we have to take the effects of the addition itself into consideration for the discussion hereafter. The effects of the addition itself on the individual items are estimated as follows assuming that HHAP is not converted at all: density (g/cm3), 0.007 increase; carbon residue (wt %), 0.24 increase; saturates (wt %), 1.21 decrease; aromatics (wt %), 0.78 increase; conversion of asphaltenes (%) 0.9 decrease; demetallization (%), 0.7 increase; desulfurization (%), 0.2 increase; denitrogen-
(15) Smith, H. A. In Catalysis; Emmett, P. H., Ed.; Reinhold Pub. Corp.: New York, 1954; Vol. 5, Chapter 4, pp 175-197. (16) Dzidic, I.; Balicki, M. D.; Peterson, H. A.; Nowlin, J. G.; Evans, W. E.; Siegel, H.; Hart, H. V. Energy Fuels 1991, 5, 382-386. (17) Girgis, M. J.; Gates, B. C. Ind. Eng. Chem. Res. 1991, 30, 20212058. (18) Kwart, H.; Schuit, G. C. A.; Gates, B. C. J. Catal. 1980, 61, 128-134. (19) Singhal, G. H.; Espino, R. L.; Sobel, J. E. J. Catal. 1981, 67, 446-456. (20) Gevert, B. S.; Otterstedt, J. E.; Massoth, F. E. Appl. Catal. 1987, 31, 119-131. (21) Moreau, C.; Aubert, C.; Durand, R.; Zmimita, N.; Geneste, P. Catal. Today 1988, 4, 117-131. (22) Geneste, P.; Amblard, P.; Bonnet, M.; Graffin, P. J. Catal. 1980, 61, 115-127. (23) Owens, P. J.; Amberg, C. H. Adv. Chem. Ser. 1961, 33, 182198. (24) Griffith, R. H.; Marsh, J. D. F.; Newling, W. B. S. Proc. R. Soc. (London) 1949, A197, 194-201.
Figure 4. Microscopic photos to show the effects of the additives; (A) without additive; (B) 3 wt % HHAP added; (C) 5 wt % HAP added.
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Table 6. Effects of the Additives on Composition and H/C of the Products (A/H Atmospheric Residue, Reaction Temperature: 390, 395 °C) expt no.
feedstock
expt 3
expt 4
expt 7
expt 5
expt 6
expt 8
389 none
390 HHAP 3 wt %/feed
390 HAP 5 wt %/feed
395 none
395 HHAP 3 wt %/feed
395 HAP 5 wt %/feed
14.0 67.7 7.9 10.4
33.8 60.5 1.7 4.0
32.2 62.6 2.0 3.2
28.4 66.4 2.1 3.1
36.2 58.8 1.4 3.6
33.9 61.6 1.9 2.6
30.7 64.3 2.0 3.0
83.3 10.63 1.531
87.04 12.41 1.711 172
87.48 12.25 1.680 129
87.59 12.19 1.670 143
87.05 12.64 1.742 198
87.45 12.47 1.711 156
87.31 12.29 1.689 161
reaction temp (°C) additive composition (wt %) saturates aromatics resins asphaltenes elemental analysis (wt %) C H H/C (atomic ratio) hydrogen consumption (m3(STP)/kL)
from the stability tests (Figure 3), and those for dry sludge and toluene insolubles (Tables 4 and 5). That is, free radicals are effectively stabilized by the hydrogen liberated from HHAP, and the formation of materials with higher molecular weights is inhibited. The cracking conversion or the formation of lighter fractions was not visually changed by the addition of the additives, as judged from the distillation data (they are not shown here), and the conclusions derived so far are not affected by this factor. This can be also understood from the fact that denitrogenation exhibits opposite trends to demetallization by the additives. In any case, as judged from these results, especially for saturates and aromatics, H/C (atomic ratio), denitrogenation, and density, the nuclear hydrogenation can be deemed to be suppressed by the addition of HHAP or HAP. The experimental results described so far are summarized as follows: (1) Coke formation is evidently inhibited by the addition of HHAP. (2) The addition of HAP results in the same effects as HHAP. (3) HAP (or HHAP) functions as a hydrogen transfer medium from the vapor phase to the oil. (4) Hydrogen consumption is reduced by the addition of HHAP or HAP. (5) The hydrogenation of aromatic rings is suppressed by the addition of HHAP or HAP. These conclusions seem to be reasonable and selfconsistent; however, they were also ascertained by detailed analyses of the products. Two desulfurized samples, one without additives and the other with 3 wt %/feed HHAP added, were analyzed together with the feedstock. First, the H/C atomic ratios of the maltenes, the asphaltenes, and the fractions from the maltenes are illustrated in Figure 6. For asphaltenes, the difference is relatively small, but a distinct difference can be observed for maltenes. In all of the fractions from maltenes, the H/C ratios are smaller in the case of the addition of HHAP, and these differences approximately correspond to a 20% reduction in hydrogen consumption. It cannot be denied that this substantiates the conclusions described before that the nuclear hydrogenation is suppressed by the additives; nevertheless, that the differences between the two cases are not big enough when the precision of the analyses is taken into account. Next, Ha/H (the ratios of aromatic hydrogen to the total hydrogen) for the individual fractions from the maltenes are shown in Figure 7. From this figure, the tendency that Ha/H is higher in the case with the additive in the heavier fractions can be observed. This means that more aromatic rings remain unhydro-
Figure 6. H/C atomic ratios of maltenes, asphaltenes, and the fractions from maltenes.
Figure 7. Ha (ratios of aromatic hydrogen to the total hydrogen) for the individual fractions from maltenes.
genated in the case with the additive. This is consistent with the H/C atomic ratios of the fractions from the maltenes described above. Figure 8 shows HR, Hβ, and Hγ from 1H NMR. It can be observed that Hγ is lower in the case of the addition. This means that the side chains are relatively short, and more side chains are removed in the case with the additive. From these figures, it can be understood that fewer aromatic rings are hydrogenated and more side chains are eliminated in the case with the additive, and this means that the hydrogenating function for aromatic rings is weakened by the addition of HHAP. The analytical results for the asphaltenes are shown in Table 7. The same tendencies as mentioned so far can be observed from this table; that is, the average molecular weight (by vapor pressure osmometry) is lower and Hγ is lower.
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Energy & Fuels, Vol. 10, No. 2, 1996 479
Figure 8. HR, Hβ, and Hγ for the individual fractions from maltenes. Table 7. Properties of Asphaltenes in Feed Oil and Products
elemental analysis C H H/C (atomic ratio) av mol wt 1H NMR (%) Ha HR Hβ Hγ
feed oil
without additive
HHAP 3 wt %/feed
82.2 7.4 1.080 3970
84.7 7.1 1.006 4350
85.0 7.1 1.002 4180
11.9 16.0 49.3 22.8
15.1 14.2 48.8 21.9
15.7 15.1 49.4 19.8
The structural parameters (by the Williams method) for asphaltenes in the desulfurized products at 390 and 395 °C are shown in Figure 9. The distinct differences can be seen in the average side chain carbon number (n). The figure shows that n is smaller in the case with the additive, and this is consistent with the analytical results of maltenes. When the errors in these data are considered, a definite description cannot be made; however, at least the tendencies appearing in these figures are quite consistent with the results described before. In conclusion, the detailed analytical results for maltenes and asphaltenes are well self-consistent, and they substantiate the conclusions derived from pilot plant tests even when the analytical errors are taken into consideration. So far, the experimental results from the series of tests whose data are summarized in Tables 4, 5, and 6 have been discussed in detail. Now, the results from other tests conducted in the same pilot plant will be reviewed. The test results are listed in Table 8. The different feedstocks and the catalysts from the previous tests were used in these tests, but detailed analyses were not conducted. From Table 8, the tendencies that denitrogenation decreased, demetallization increased, the H/C atomic ratio decreased, and the specific gravity increased due
to the additives can be seen. These tendencies are quite the same as the results in Tables 4, 5, and 6. However, in many of the tests in Table 8, the dry sludges and toluene insolubles in the cases without addition were very small (
