418
I n d . Eng. Chem. Res. 1989, 28, 418-421
Joint Symp. on Dry SO2 and Simul. SO,/NO, Control Technol. 1, EPA-600/9-86-029a (NTIS PB87-1204653, Oct 1986, p 8-1. Lange, H. B. Experimental Study of Gas Use to Improve the Limestone Injection Process for SOz Control on Utility Boilers. Gas Research Institute Contract No. 5086-251-1232, 1987. McCarthy, J. M.; Chen, S. L.; Kramlich, J. C.; Seeker, W. R.; Pershing, D. W. Reactivity of Atmospheric and Pressure Hydrated Sorbents for SOz Control. Proc. 1986 Joint Symp. on Dry SOz and Simul. SOz/NO, Control Technol. 1, EPA-600/9-86-029a (NTIS PB87-120465), Oct 1986, p 10-1. Muzio, L. J.; Boni, A. A.; Offen, G. R.; Beittel, R. The Effectiveness of Additives for Enhancing SO2 Removal with Calcium Based Sorbents. Proc. 1986 Joint Symp. on Dry SOz and Simul. SOz/ NO, Control Technol. 1, EPA-600/9-86-029a (NTIS PB87120465), Oct 1986, p 13-1. Newton, G. H.; Harrison, D. J.; Silcox, G. D.; Pershing, D. W. Control of SO, Emissions by In-Furnace Sorbent Injection: Carbonates vs. Hydrates. AIChE Annual Meeting, Chicago, IL, Nov 1985. Overmoe, B. J.; Chen, S. L.; Ho., L.; Seeker, W. R.; Heap, M. P.; Pershing, D. W. Boiler Simulator Studies on Sorbent Utilization for SOz Control. Proc. First Joint Symp. on Dry SOz/NO, Control
Technol. 1, EPA-600/9-85-020a (NTIS PB85-2323533, July 1985, p 15-1. Simons, G. A. Parameters Limiting Sulfation by CaO. AZChE J . 1988, 34, 167. Slaughter, D. M.; Silcox, G. D.; Lemieux, P. M.; Newton, G. H.; Pershing, D. W. Bench Scale Evaluation of Sulfur Sorbent Reactions. Proc. First Joint Symp. on Dry SO2 and Simul. SOz/NO, Control Technol. 1, EPA-600/9-85-020a (NTIS PB85-2323533, July 1985, p 11-1. Slaughter, D. M.; Chen, S. L.; Seeker, W. R. Enhanced Sulfur Capture by Promoted Calcium-Based Sorbents. Proc. 1986 Joint Symp. on Dry SOz and Simul. SOz/NO, Control Technol. 1, EPA-600/9-86-029a (NTIS PB87-1204653, Oct 1986, p 12-1. Ulerich, N. H.; O'Neill, E. P.; Keairns, D. L. A Thermogravimetric Study of the Effect of Pore Volume-Pore Size Distribution on the Sulfation of Calcined Limestone. Thernochim. Acta 1978,26, 269.
Received for review May 20, 1988 Revised manuscript received November 17, 1988 Accepted December 14, 1988
Structure and Properties of Sludges Produced in the Catalytic Hydrocracking of Vacuum Residue I s a o Mochida,* Xing-zhe Zhao, and K i n y a S a k a n i s h i Institute of Advanced Material Study, Kyushyu University, Kasuga, Fukuoka 816, Japan
Shun-ichi Yamamoto, Hiro-aki T a k a s h i m a , a n d Sei-ichi U e m u r a T h e Central Research Institute, Nippon Oil Company Ltd., Yokohama 231, Japan
The structure and properties of sludge produced in the catalytic hydrocracking of atmospheric residue were investigated after the extractive fractionation of sludge-concentrated product. The product consisted of major HS (hexane-soluble: 86 % ) and minor HI-BS (hexane-insoluble-benzene-soluble: 7%), BI-THFS (benzene-insoluble-tetrahydrofuran-soluble: 2 % ), and T H F I (THF-insoluble: 5 % ) fractions. The HS fraction was essentially paraffinic, carrying some long-chain alkylbenzenes, while the hexane-insoluble fractions were aromatic and polar with a larger extent of aromaticity and polarity which decreased their solubility in spite of their rather similar molecular weight distributions. 'The H I fraction melted around 250 "C to give a homogeneous solution under hot-stage microscope, while the THFI showed a softening point as high as 360 "C, producing some coke particles. Addition of solvents such as 1-methylnaphthalene to the fraction provided a homogeneous solution above 80 "C. The brown flock substances and blue crystallines, which were sludge and wax, respectively, were observed in the 350+ "C product. T h e addition of 1-methylnaphthalene dissolved and dispersed the flock substance a t room temperature, leaving the crystallines unchanged, while ethanol dissolved the crystallines to form blue droplets. Catalytic hydrogenation around 350 "C removed the flocky substances, while the crystallines remained unchanged. Based on such results, the sludges are produced through the hydrocracking of resin and light asphaltene fractions and dealkylation of heavy asphaltene, which reduced their mutual solubility, leading to the sedimentation of the latter substances. Demand for clean distillate from the bottom of the barrel leads to severe hydrocracking of petroleum residues a t higher temperatures (Saito and Shimizu, 1985). The severe conditions cause problems of coke deposition on the catalyst and sludge formation in the product oil (Symoniak and Frost, 1971). Such troublemakers of both carbonaceous materials, of which formation may be intimately related, shorten the life of the catalyst, plug the transfer line, and deteriorate the quality of the products (Mckenna et al., 1964). Empirically, the dry sludge is believed to be produced when the conversion to the distillate is beyond a certain level (ca. 50%) regardless of the catalyst and feedstocks. However, its structure, properties, and mechanism of formation are not fully understood yet (Haensel and Addison, 1967). A better understanding of its structure related to its thermal behavior may lead to better catalysts 0888-5885/89/2628-0418$01.50/0
or schemes whichs can overcome the difficulty in the present hydrocracking process. Since the dry sludge is never a single species of a molecule, analyses of its fractions and their mutual interaction may be most important to define its properties, suggesting procedures for their removal. In the present study, dry sludge produced in a hydrocracked oil was analyzed chemically, and its solubility and fusibility were observed under a hot-stage microscope. Its reactivity was examined in the catalytic hydrogenation at a relatively lower temperature than those applied in the hydrocracking process. Experimental Section A vacuum residue of Arabian light oil (bp > 550 "C) was hydrocracked by Chiyoda Chemical Construction Co. under three different conditions (reaction temperatures: 395, 0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989 419 Table I. Solubility of the Concentrated Sludge Fraction extraction methods room temp Soxhlet
wt%
HS 72 86
HI-BS 14 7
BI-THFS 4 2
THFI 10 5
405, and 418 "C), which were the conditions for no formation, beginning of formation, and some formation of dry sludge, respectively, using a commercial Co-Mo/A1203 catalyst (Shokubai Kasei Co.) in the two-staged fixed-bed microreactors. The hydrocracked products were distilled, and the 350+ "C fraction was further separated by using a supercentrifuge (Hitachi-70P-72) to obtain the concentrated sludge fraction. Solubility of the centrifugated sludge fraction was examined by successive extractions with n-hexane, benzene, and tetrahydrofuran (THF) at room temperature or a t their boiling points using a Soxhlet apparatus. The original sludge and its solvent-fractionated components (HS, hexane soluble; HI-BS, hexane insoluble-benzene soluble; BI-THFS, benzene insoluble-THF soluble; and THFI, T H F insoluble) were analyzed by 'H NMR, elemental analysis, IR and GPC spectroscopies, and gas chromatography according to the properties and solubilities of the components. The 350+ "C fraction was observed under a transmission microscope with or without the existence of solvent (decaline, l-methylnaphthalene, or ethanol). Fusibility and solubilities of the HI and THFI in the concentrated sludge fraction were observed when heated a t a rate of 10 "C/min under hot-stage microscope with or without the solvent (1-methylnaphthalene). The hydrogenation of the 350+ "C fraction (10 g) was performed in a batch autoclave of 100-mL capacity (heating rate: 8 "C/min), under 100 atm of hydrogen pressure at 350 "C for 5 h using 1 g of commercial NiMo/A1203 catalyst (KF-840, Nippon Ketjen Co.). The catalyst was presulfided under 5% H2S/H2flow at 360 "C for 6 h using a flow reactor. Results Composition a n d S t r u c t u r a l Characteristic of t h e Centrifugated Sludge Fraction. Table I summarizes the solubility of the centrifugated sludge fraction. It was principally hexane soluble (HS) but carried some hexane-insoluble substance (HI), whose content was 14% a t the refluxing temperature of the solvent. The HI consists of HI-BS, BI-THFS, and THFI. Elemental analyses of the fractions are summarized in Table 11. The HS fraction exhibited a high H/C ratio of 1.59 with the least amount of heteroatoms. The insoluble fractions of HI-BS, BI-THFS, and THFI had much lower H/C ratios and higher contents of heteroatoms (N, S, and 0) than those of the HS fraction.
Wavelength (nm) Figure 1. UV spectra of dry sludge fractions: (a) HS; (b) HI-BS; (c) BI-THFS.
4000
30'00
2000
1000
Wave number (cm-1)
Figure 2. IR spectra of dry sludge fractions: (a) HS; (b) HI-BS; (c) BI-THFS; (d) THFI.
Table I1 also shows the hydrogen distributions of the fractions revealed by 'H NMR. The HS fraction showed a high content of aliphatic hydrogens, especially a t the /3 positions, suggesting long paraffinic chains. Many of them are not connected to the aromatic ring. In contrast, the HI-BS and BI-THFS fractions carried fairly high amounts of aromatic hydrogens to show fa (carbon aromaticity) values of 0.7-0.8. The aromatic hydrogen content increased significantly when the solubility decreased. The major aliphatic groups may be short and attached to the aromatic rings, since large Ha (a-hydrogen content) was observed. Figure 1 shows the UV spectra of the HS, HI-BS, and BI-THFS fractions. The HS fraction exhibited a shoulder peak around 280 nm, indicating some presence of the benzene ring. The other fractions showed much more intense absorption around 350 nm, suggesting that the
Table 11. Elemental and 'H NMR Analysesa of Extracts and Residue in the Sludge Fraction before and after the Hydrotreatment elemental anal., wt % hydrogen composition, ./, sampleb C H N o+s ash H/C Ha H" H R H, OR-1 88.2 10.6 0.36 0.84 1.44 9.2 12.9 54.6 23.3 HS 87.6 11.6 0.28 0.51 1.59 7.9 11.9 57.1 23.1 HI-BS 89.7 5.96 0.80 3.51 trace 0.80 31.1 19.3 37.8 11.8 BI-THFS 88.4 5.21 1.01 3.62 1.81 0.71 36.1 27.8 22.2 13.9 THFI 88.8 3.93 1.06 6.22 trace 0.53 OR-2 87.8 11.6 0.20 0.45 1.58 7.8 11.8 57.5 22.9 HT-OR2 87.7 11.8 0.16 0.34 1.62 5.5 10.5 60.1 23.9 ~~
~~
f. 0.40 0.33 0.74 0.79
0.33 0.30
'Ha, 6-9 ppm; H,, 2-4 ppm; Hp, 1.1-2 ppm; H,, 0.3-1.1 ppm; fa, carbon aromaticity. *OR-1, concentrated sludge fraction; OR-2, the fraction of bp >350 "C containing sludge; HT-ORB, hydrotreated OR-2 (reaction condition: 350 "C and 5 h).
420 Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989
. .I ./
.
3800
':! .
3600
3400
3200
wave number (crri')
!!
f j
Figure 5. IR spectrum of HI-BS fraction in the dry sludge (in dilute CS2solution): (a) 3610 cm-l (phenolic OH); (b) 3530 cm-l (carboxylic OH); (c) 3464 cm-I (pyrrolic NH).
Elution vdume (ml 1
Figure 3. GPC spectra of dry sludge fractions: (- - -) original, (---) HS; HI-BS; BI-THFS. (-**e-)
(-a*-)
IC '
0
5
IO Retention
15
20
25
30
.u '
Figure 6. Micrographs of the 350+ "C fraction before and after addition of solvent: (a) original 350+ "C fraction; (b) after addition of decalin (10 wt %); (c) after addition of 1-methylnaphthalene (10 wt %); (d) after addition of ethanol (10 wt %).
Tim (mm )
Figure 4. Gas chromatogram of HS in the dry sludge.
fractions carry fairly large aromatic rings. Figure 2 shows FT-IR spectra of the fractions. The spectra indicate the higher aromaticity of the fractions with decreased solubility, as described above. It should be noted that THFI still carried some aliphatic CH, although the fraction was highly aromatic. GPC spectra of the fractions are shown in Figure 3, where a UV detector was applied. All the fractions were in similar ranges of molecular weight distribution, less than 600, although HI-BS and BI-THFS contained a smaller amount of larger molecules. It should be noted that HS, HI-BS, and BI-THFS showed larger intensities in the order given because of the aromaticity increase, being consistent with Figure 2. Some Detail Structures of the Fractions. Figure 4 shows a gas chromatogram of the HS fraction. The chromatogram indicates that the fraction consists essentially of paraffins ranging from Cll to C3* The majority of them were straight in their chains; minor amounts of isoparaffin also exist in the range Cl0-CzO. A broad peak around 15-min retention time (corresponding to Cz5)may correspond to alkyl aromatics. Figure 5 shows the IR spectra of the diluted HI-BS fraction in CS2. The absorption bands at 3610,3530, and 3454 cm-l indicated the presence of phenolic OH, carboxylic OH, and pyrrolic NH groups in the fraction. Considerable polarity is suggested. Microscopic Observation of the 350+ "C Fraction. A microphotograph of the 350+ "C fraction under a transmission microscope is shown in Figure 6a, where brown flocks and blue crystallines were clearly observable. Brown flocks are dry sludge, while the blue crystallines are wax.
Addition of decalin at room temperature did not bring any change in the appearance, as shown in Figure 6b. In contrast, 1-methylnaphthalenedecreased the amount and size of brown flocks, while nothing happened to the definite blue crystallines (Figure 6c). Ethanol dissolved the blue crystallines, forming blue droplets, and some of the brown flocks also formed brown droplets, while some of the others stayed unchanged (Figure 6d). Behavior of the Concentrated Sludge Fraction When Heated under a Hot-Stage Microscope. The HI fraction of the concentrated sludge fraction softened around 210 "C under a hot-stage microscope and became viscous liquid at 250 "C, no insoluble nor infusible portion being observable. The THFI fraction showed some softening at 360-370 "C. Further heating produced black particles like chars. Since such black particles were not observed in HI, the THFS fraction may dissolve THFI at elevated temperatures, suppressing the coke formation. HI was almost completely insoluble in molten paraffin; however, homogeneous liquid was observed at 150 "C. A major portion of the HI fraction should be dissolved in the molten paraffin. Decalin dissolved half of the HI fraction at room temperature and dissolved all of it at 120-130 "C. 1-Methylnaphthalene dissolved 70% of HI fraction at room temperature. At 150 "C, an orange solution was observed. The THFI fraction was not completely soluble in 1methylnaphthalene at room temperature, black particles of variable diameter being observed. At 1W120 "C, small particles started to be dissolved, and major particles, regardless of their diameters, were dissolved a t 160 "C, although a few black particles were still observable in the orange solution. The solvent started to evaporate a t 180 "C, black solids being to precipitate. Hydrogenation of the 350+ "C Fraction. Figure 7 shows photographs of the 350+ "C fraction before and
Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989 421
decreased with increasing aromaticity and polarity, the molecular weight varying rather slightly among the fractions. Such a contrast in structural characteristics of the HS and HI fractions may not allow for mutual miscibility, precipitating or segregating the insoluble substances from the HS matrix at room temperature. In spite of the low solubilities of the sludge components at room temperature, they melt or are dissolved in the light component a t elevated temperatures above 80 "C, depending on the content of lighter fractions. Thus, the sludge may disappear at elevated temperatures such as the reaction temperature, although its limited solubility in the matrix may enhance its adsorption or longer residence on the catalyst surface, leading to the severe catalyst deactivation. An aromatic additive such as 1-methylnaphthalene accelerates the disappearance of sludge, especially on heating. Hence, the addition of suitable aromatic solvent can stabilize the hydrocracked product by dissolving the sludge fraction. Hydrogenation with a commercial Ni-Mo catalyst under rather mild conditions converted the sludge fraction miscible with the HS matrix. Reducing its aromaticity and removal of polar heteroatoms can increase its solubility. Sludge appears to be slightly adsorbed on the catalyst a t room temperature. In addition to brown flocks of the sludge, bluish crystallines, very probably long paraffinic waxes, were observable under the microscope. Hydrogenation at low temperatures cannot deal with such components. They should be handled at the hydrocracking stage. (b) Figure 7. Micrographs of the 350+ O C fraction after the addition of catalyst a t room temperature and the hydrotreatment a t 350 "C: (a) after the addition of catalyst a t room temperature; (b) after the hydrotreatment with the catalyst at 350 "C and 5 h.
after the hydrogenation at 350 "C with a Ni-Mo/AI2O3 catalyst. The catalyst did not do anything with brown flocks and blue crystallines at room temperature (Figure 7a). However, the hydrogenation at 350 "C removed almost completely the brown flocks, although some fine brown spots were still observed in high dispersion. In contrast, blue crystallines remained almost unchanged (Figure 7b). Table I1 summarizes the elemental and lH NMR analyses of the hydrogenated product. A slight increase of aliphatic hydrogens and decreases of aromatic hydrogen, nitrogen, and sulfur were noticed. A very small amount of the heavier fraction may be selectively hydrogenated. Discussion Solvent extraction of the sludge-concentrated fraction revealed that a significant amount of hexane-insoluble substance stayed in the major hexane-soluble product. About half of its content was insoluble in benzene, implying decreased solubility of a part of the asphaltene in the vacuum residue during the hydrocracking process, since no benzene-insoluble substance was present in the feedstock. Such an insoluble substance can be recognized as the dry sludge in the hydrocracked product. Structural analyses of the extracted fractions indicated that the HS fraction in the product consists essentially of long-chain paraffins and long-chain alkylbenzenes. In contrast, the insoluble substances are fairly aromatic with much less and shorter alkyl groups and are rather polar, carrying a considerable amount of heteroatoms. Solubility
Conclusions According to the above results and discussions, several proposals to reduce the sludge formation come to mind; (1)addition of aromatic solvent; (2) hydrogenation after the hydrocracking; (3) two-stage hydrotreatmentextensive hydrogenation of the aromatic rings and heterocycles in the asphaltene at a lower temperature and hydrocracking at a higher temperature. The first two proposals intend to dissolve the sludge after its formation. Hence, no increase of conversion is expected. However, the third one can provide higher conversion without sludge formation. Such a process requires a katalyst which can extensively hydrogenate the asphaltene before dealkylation. A preliminary result revealed that the two-stage hydrocracking was very effective for achieving higher cracking conversion without sludge formation. The details will be reported later. Acknowledgment The authors are very grateful for the financial support from the Ministry of International Trade and Industry through the Petroleum Institute of Japan. They also appreciate the Committee of the Institute for the Study of Heavy Oils for its cooperation in the present research. Literature Cited Haensel, V.; Saddison, G. E. Adu. Catal. Reforming, 7th World Pet. Congresss 1967, 4 , 113-119. Mckenna, W . L.; Owen, G. H.; Mettick, G. R. Oil Gas J. 1964,62(20), 106-111. Saito, K.; Shimizu, S. Petrotech (Tokyo) 1985, 8(1),54-60. Symoniak, M. F.; Frost, A. C. Oil Gas J. 1971, (March 15),76-81. Received for review May 13, 1988 Revised manuscript received November 9, 1988 Accepted December 11,1988
