Energy Fuels 2010, 24, 5038–5047 Published on Web 08/11/2010
: DOI:10.1021/ef100396m
Solventless Deasphalting: Selective Sulfonation Chemistry of Petroleum Asphaltenes and Resids M. A. Francisco,* M. Siskin, S. R. Kelemen, D. J. Moser, J. S. Szobota, K. E. Edwards, and J. S. Lyng ExxonMobil Research and Engineering Company, 1545 Route 22 East, Clinton Township, Annandale, New Jersey 08801 Received June 3, 2010. Revised Manuscript Received July 27, 2010
Asphaltenes are the lowest value component of petroleum. They are found in a variety of crude oils and in higher concentrations in resids and bitumens. Petroleum resid is the non-volatile fraction of crude oil or bitumen after distillation. Current disposition of the asphaltenes is high-temperature thermal chemistry to form higher value liquids and coke or as feedstock for asphalt. Asphaltenes are separated from a resid by a commercial process called solvent deasphalting. Deasphalting is accomplished by treating a resid with a hydrocarbon solvent (propane or butane commercially and pentane-heptane in the lab), and the asphaltenes precipitate out of solution. The rest of the resid is soluble, and this is called the deasphalted oil (DAO). The DAO is recovered by evaporation of the solvent. The DAO is higher value than the original resid, and it is used as residual sulfur fuel oil (RSFO) and, in some cases, as a feedstock for fluid catalytic cracking (FCC) to form higher value liquids. Asphaltenes are composed of highly polar molecules that are soluble to sparingly soluble in the resid. Deasphalting takes advantage of this by diluting the resid with a nonpolar solvent and making the surrounding medium less polar. The asphaltenes are no longer soluble, and they precipitate out of the mixture of resid and solvent. Recovery of the solvent from the DAO and solvent losses are major costs of deasphalting. The solvents are not as selective as would be desired, causing non-asphaltenic molecules to co-precipitate with the asphaltenes and some asphaltenic molecules to remain with the DAO fraction, making it less valuable. This paper summarizes initial research to replace solvent deasphalting with a selective chemical treatment. Initial studies focused on sulfonation. The chemistry relies on the selectivity of sulfur trioxide (SO3) to react with the larger polycyclic aromatics and heteroaromatics found in asphaltenes to form asphaltene sulfonic acids. The addition of a sulfonic acid function to the asphaltene molecule significantly increases its polarity and decreases its solubility, causing the sulfonated asphaltene to precipitate from the resid without the use of solvent. The value of this approach is in avoiding the use of liquid solvents, which are difficult to use and recover efficiently on a commercial scale.
asphaltenes. Deasphalting is accomplished by treating a resid with a light, nonpolar hydrocarbon solvent, such as propane or butane, or by treatment with supercritical fluids.11,12 The heavy, polar asphaltenes are insoluble in the nonpolar solvent environment and precipitate out.1314 The soluble portion of the resid, after deasphalting, is called the deasphalted oil (DAO). The DAO is recovered by evaporation of the solvent. The DAO has a higher value than the resid, and it is used as RSFO and, in some cases, as a feedstock for fluid catalytic cracking (FCC) to form higher value liquids. Recovery of the solvent from the DAO and solvent losses are major costs14 of deasphalting. The solvents are not very selective and thereby cause non-asphaltenic molecules to coprecipitate with the asphaltenes and some asphaltenic molecules to remain with the DAO fraction. This paper summarizes initial research to replace solvent deasphalting with a selective chemical treatment. Initial studies focused on sulfonation.15 The chemistry relies on the
Introduction 1
Asphaltenes are the lowest value components of petroleum because they contain large paraffins, naphthenes, and aromatics (PNAs), metals, and N and S heteroatoms. They are found in a variety of crude oils and bitumens and in higher concentrations in resids.2 Petroleum resid is the non-volatile portion of crude oil or bitumen after atmospheric or vacuum distillation. Asphaltenes can be separated from a crude oil or resid by a commercial process called solvent deasphalting.1-4 Alternatively, resid can be visbroken,5-7 coked,8 or used for residual sulfur fuel oil (RSFO)9 or asphalt10 without removal of the *To whom correspondence should be addressed. E-mail: manuel.a.
[email protected]. (1) Ditman, J. G. Proc.;Am. Pet. Inst., Div. Refin. 1973, 53, 713–723. (2) Hassan, A. Pet. Sci. Technol. 2002, 20, 751–762. (3) Wiehe, I. A. Proceedings of the AIChE Spring National Meeting; Atlanta, GA, April 10-14, 2005. (4) Dang, G. S.; Rawat, B. S. J. Sci. Ind. Res. 1990, 49, 184–189. (5) Gareev, R. G. Chem. Technol. Fuels Oils 2005, 41, 329–336. (6) Leprince, P. Pet. Refin. 2001, 3, 365–379. (7) Murphy, J. R.; Whittington, E. L.; Chang, C. P. Hydrocarbon Process. 1979, 58, 119–122. (8) Belinko, K.; Denis, J. M. CANMET Rep. 1976, 77-43, 13. (9) Whitehead, E. V. Dev. Pet. Sci. 1994, 40A (Asphaltenes and Asphalts 1), 95–110. (10) Lesueur, D.; Gerard, J.-F.; Claudy, P.; Letoffe, J.-M.; Planche, J.-P.; Martin, D. J. Rheol. (Melville, NY, U.S.) 1996, 40, 813–836. r 2010 American Chemical Society
(11) Tiwari, K. K. Chem. Ind. Dig. 2007, 20 (3), 78–85. (12) Low, J. Y.; Hood, R. L.; Lynch, K. Z. Prepr.;Am. Chem. Soc., Div. Pet. Chem. 1995, 40 (4), 780–784. (13) Long, J.; Zu, D.; Roberts, M. C. Proc. World Pet. Congr. 2000, 3, 243–247. (14) Herod, A. A.; Kandiyoti, R.; Bartle, K. D. Fuel 2006, 85, 1950– 1951. (15) Singh, G.; Kapoor, I. P. S.; Jain, M. Roum. Chem. Q. Rev. 2000, 7, 201–212.
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Table 1. Summary of Experimental Results for Heavy Canadian Vacuum Resid (HCVR) and European Vacuum Resid (EVR) experiment number 1 2 3 4 5 6 7 8
sample
time (h) starting toluene toluene oleum, 20% (mL) (temperature, °C) material (g) insolubles (g) solubles (g)
HCVR heptane asphaltenes 2.50 HCVR heptane asphaltenes 2.50 HCVR heptane asphaltenes 1.00 HCVR heptane asphaltenes 0.50 HCVR 0.50 HCVR heptane asphaltenes 150 EVR 3.00 (liquid SO3) EVR 1.00 (liquid SO3)
24 (ambient) 2 (ambient) 2 (ambient) 0.25 (ambient) 4 (ambient) 0.25 (ambient) 1 (165) 1 (ambient)
selectivity of sulfur trioxide (SO3) to react with the larger polycyclic aromatics and heteroaromatics16-18 found in asphaltenes to form asphaltene sulfonic acids. The addition of a sulfonic acid function to the asphaltene molecule significantly increases its polarity and decreases its solubility, causing the sulfonated asphaltene to precipitate from the resid without the use of solvent. The value of this approach is in avoiding the use of liquid solvents, which are difficult to use and recover efficiently on a commercial scale.
1.00 1.00 1.04 1.00 2.26 300.78 96.13 99.79
1.94 1.68 1.97 1.11 1.05 396.84 4.43 not isolated
total yield (% yield)
0.05 1.99 (199.00) 0.02 1.70 (170.00) 0.15 2.12 (203.80) 0.11 1.22 (122.00) 2.26 3.31 (146.50) 43.90 440.74 (147.00) 97.02 101.45 (105.5) not isolated 100.65 (100.9)
1.5 drops/s) was added slowly by syringe to the asphaltene solution at 0 °C. An exotherm was observed as the temperature of the asphaltene solution rose to 7 °C. The reaction mixture was warmed to room temperature and allowed to stir for 0.25 h. A precipitate formed early during the addition of oleum. When the reaction time was complete, the entire reaction mixture was suction-filtered through a fritted glass filter. The filtered precipitate (TIs) was washed with distilled water (900 mL), air-dried, and then dried to a constant weight in a vacuum oven at 120 °C. The water layer was submitted for acid titration. The yield of sulfonated asphaltenes is shown in Table 1. The filtrate, “toluene solubles” (TSs), was washed in a separatory funnel with water (3 L) 3 times. The filtrate was dried over anhydrous sodium sulfate overnight, suction-filtered, and evaporated to dryness. The yield is shown in Table 1. TIs and TSs from these experiments were subjected to the following series of tests and analyses. Reaction of European Vacuum Resid with Sulfur Trioxide. The resid (96.13 g) was heated to 160 °C in a 500 mL three-necked flask, equipped with a mechanical stirrer, under a nitrogen atmosphere. The resid was fluid enough to stir at 165 °C. Sulfur trioxide (5.76 g, 0.072 mol, 3 mL) was slowly added to the hot, stirring resid under nitrogen. When the addition of the sulfur trioxide was complete, the reaction mixture was stirred at 160 °C for an additional hour. The reaction mixture was cooled to room temperature, and toluene (700 mL) was added. The mixture was allowed to sit overnight. It was then suction-filtered, and the filtered solids were washed with toluene. The solids were dried in a vacuum oven at 110 °C overnight to yield (4.43 g) of TIs. The toluene filtrates were evaporated to dryness, using a rotary evaporator, and dried in a vacuum oven to constant weight to yield 97.02 g of TSs. The total yield was 101.45 g (106% yield based on starting resid). Ambient Temperature Reaction of European Vacuum Resid in Methylene Chloride with Sulfur Trioxide. The resid (99.79 g) was dissolved in dry methylene chloride (100 mL) and poured into a 500 mL three-necked flask under a nitrogen atomosphere at ambient temperature. The flask was equipped with a mechanical stirrer. Sulfur trioxide (1.92 g, 0.024 mol, 1 mL) was slowly added to the stirring resid at room temperature. When the addition of the sulfur trioxide was complete, the reaction mixture was allowed to stir at room temperature for 1 h under a nitrogen atmosphere. The reaction mixture was evaporated to dryness, using a rotary evaporator, and dried in a vacuum oven to a constant weight to yield 100.65 g of product (101% yield based on starting resid). The products of these experimental procedures were subjected to some or all of the following tests and analyses: (1) Penetration point (PP, D5/DIS) and softening point (SP, D36/ DIS) determine asphalt quality. (2) Thermogravimetric analysis (TGA) was used with Perkin-Elmer Pyris 1. The temperature was increased from 30 to 800 °C at 10 °C/min with a flow (20 mL/min) of nitrogen. The temperature was then held for 20 min at 800 °C, and then the nitrogen was switched to air at a flow rate of 50 mL/min. (3) The weight percentage of C, H, N, and S was calculated (Atlantic Microlabs, Norcross, GA). (4) All infrared spectra were obtained using a Nicolet Nexus 670
Experimental Section Reaction of Heavy Canadian Vacuum Resid Heptane Asphaltenes in Toluene with Oleum (20%). Asphaltenes (1.0 g) were dissolved in toluene (25 mL) and stirred at room temperature under nitrogen. Oleum (20%; 2.5, 1.0, or 0.5 mL) was added slowly by syringe to the asphaltene solution at 0 °C. The reaction mixture was warmed to room temperature and allowed to stir for 24, 2, or 0.25 h. A precipitate formed early during the addition of the oleum. When the reaction time was complete, water (10 mL) was added and the entire reaction mixture was suction-filtered through a fritted glass filter. The filtered precipitate, “toluene-insoluble asphaltenes” (TIs) (Note that the derivatized asphaltenes are now toluene-insoluble, but they are not coke. Traditionally, coke is defined as a toluene-insoluble fraction.), was air-dried and then dried to a constant weight in a vacuum oven at 120 °C. The yield of sulfonated asphaltenes is shown in Table 1. The filtrate was washed with water 3 times in a separatory funnel. The filtrate (toluene solubles) was dried over anhydrous sodium sulfate overnight, suction-filtered, and evaporated to dryness. The yield is shown in Table 1. Reaction of Heavy Canadian Vacuum Resid in Toluene with Oleum (20%). Heavy Canadian vacuum resid (2.26 g) was dissolved in toluene (25 mL) and stirred at room temperature under nitrogen. Oleum (20%; 0.5 mL) was added slowly by syringe to the resid solution at 0 °C. The reaction mixture was warmed to room temperature and allowed to stir for 2 or 4 h. A precipitate formed early during the addition of the oleum. When the reaction time was complete, water (10 mL) was added and the entire reaction mixture was suction-filtered through a fritted glass filter. The filtered precipitate (TIs) was air-dried and then dried to a constant weight in a vacuum oven at 120 °C. The yield of sulfonated asphaltenes is shown in Table 1. The filtrate (toluene solubles) was washed with water 3 times in a separatory funnel. The filtrate was dried over anhydrous sodium sulfate overnight, suction-filtered, and evaporated to dryness. The yield is shown in Table 1. Large-Scale Sulfonation of Heavy Canadian Vacuum Resid Heptane Asphaltenes in Toluene with Oleum (20%). Asphaltenes (300.78 g) was dissolved in toluene (6 L) and stirred at room temperature under nitrogen. Oleum (20%; 150 mL at a rate of (16) Gilbert, E. E. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed.; John Wiley and Sons: New York, 1969; Vol. 19, pp 280-310. (17) Cerfontain, H. Recl. Trav. Chim. Pays-Bas 1985, 104, 153–165. (18) Singh, G.; Kapoor, I. P. S.; Jain, M. Roum. Chem. Q. Rev. 2000, 7, 201–212.
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from 30 to 325 °C at 10 °C/min. The components are eluted directly to the MS source, where they undergo 70 eV electron impact, which fragments the molecules into characteristic spectra. These spectra are compared to a library, where the best fit is determined. (9) Thermal desorption GC/MS is performed. The sample is heated at a constant rate (10-50 °C/min) to the desired temperature of 250 °C, using a Pyran system (made by Ruska Laboratories, ∼1995, Ruska Pyran Thermal Desorption/Pyrolysis unit HP GC 5890 series II, HP MS engine 5989B). The sample size can be as much as 50 mg. Helium flows through the sample from below as it is being heated at 30 cm3/min. The volatiles are carried via a heated transfer line (325 °C) to the head of a GC column (60 m DB-1, 0.25 mm, 1 μm), maintained at -60 °C for the entire desorption time. Once desorption is complete, the GC oven is heated at a constant rate (10 °C/min) to elute the components to the mass spectrometer for detection. The GC carrier gas is helium (constant flow; 2 cm3/min). The weight loss of the sample is also measured, similar to TGA.
Fourier transform infrared (FTIR) spectrometer equipped with a “Golden Gate” single-bounce Diamond on KRS-5 attenuated total reflectance (ATR) accessory (2 cm-1 resolution and 100 scans for both background and sample). This ATR accessory is ideally suited for analysis of these types of samples because the thin layer of Diamond on top of the KRS-5 ATR crystal is impervious to the sulfonating reagants used. (5) X-ray photoelectron spectroscopy (XPS) was used to quantify the amount of carbon, sulfur, nitrogen, and oxygen. Data acquisition and analysis was accomplished using a Kratos Axis Ultra instrument and Vision 2.0 analysis software. Elemental concentrations are reported relative to carbon from the areas of the XPS peaks after correction for differences in atomic sensitivity. XPS is surfacesensitive with, ∼90% of the signal coming from the first 50 A˚ of the sample. A comparison of XPS and elemental analysis data is needed to determine if the surface composition is comparable to the bulk. XPS is sensitive to the chemical forms of carbon, nitrogen, sulfur, and oxygen species, and in this study, it is used to directly quantify the concentration of SO3 groups introduced during sulfonation reactions of resid. (6) Acid leaching (D974) is performed with asphaltenes (1.00 g) suspended in 5 mL of distilled water. The mixture was stirred at room temperature overnight and then suction-filtered. The asphaltenes were airdried and weighed to determine if there was a weight loss. The water was titrated for acid content. (7) Selected DAOs were submitted for the following analyses: Oil compatibility tests19 [AM-S 1999-011 (Sbn/In)] and metal analyses [inductively coupled plasma emission spectroscopy (ICPES)]. The oil compatibility tests are as follows: (a) The heptane dilution test uses n-heptane added to the sample until insoluble asphaltenes are detected. The results are reported as the volume of n-heptane, in milliliters, added to 5 mL of oil at the point just before insoluble asphaltenes first appear. The range of the heptane dilution is from 0 to 25 mL. If no insolubles are detected at a heptane dilution of 25 mL, the oil is declared heptane-soluble and either the solvent oil equivalence or the non-solvent oil dilution test needs to be used to measure the solubility blending number of the oil (Sbn). (b) The toluene equivalence test uses a series of samples of oil dissolved in standard solutions of n-heptane containing successively increasing concentrations of toluene. Drops of each standard sample solution are spotted onto filter paper, and the formation of rings and patterns is closely observed. The toluene equivalence point is reported as the average of the volume percentages of toluene in two sample solutions. The first solution is the one that produces a spot with a ring pattern that is essentially no different from the ring pattern of the sample solution that has the next higher concentration of toluene. The second solution is the one with the next lower concentration of toluene. (c) The solvent oil equivalence test uses a series of samples of a test oil dissolved in standard solutions of n-heptane containing successively increasing concentrations of a solvent oil. The proportion of solvent oil to nheptane is varied and mixed with the test oil in the ratio of 10 mL of solvent oil-heptane mixture per 2 g of test oil. The minimum volume percent solvent in the solvent oil-heptane mixture needed to keep the asphaltenes in solutions is the solvent oil equivalence. It is used when dealing with heptane-soluble oils that do not have any heptane insolubles present when mixed with a standard test oil. (8) Pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS) is conducted with a CDS Pyroprobe directly connected to the inlet of a HP 5890 series II GC and a HP 5989B MS engine. Microgram quantities of sample are placed in a quartz tube at the tip of a probe. The probe is heated in helium from room temperature to 800 °C in less than 1 s and held at that temperature for approximately 10 s. The volatiles are transferred directly to the heated inlet of the GC (325 °C), where they are separated on a 60 m, DB-1 column (0.25 mm inner diameter, 1 μm film), temperature-programmed
Results and Discussion Selectivity of Sulfonation Chemistry. The selectivity of sulfonation has been demonstrated in previous research with model compounds and a comprehensive review of the literature.20 Room-temperature reactions demonstrate that pyrrolic nitrogen containing polycyclic heteroaromatics tend to react faster than polycyclic aromatics and sulfur containing heteroaromatics with SO3. Sulfonation of mono-, di-, tri-, and tetracyclic aromatics tend to favor the reaction of the larger ring systems. The asphaltenes contain both the polycyclic aromatic and polycyclic heteroaromatics, and therefore, the asphaltenes should react selectively versus the rest of the resid to form asphaltene sulfonic acids. Comprehensive literature searches on reactions of petroleum resid, asphaltenes, and bitumens indicate that reactions of oleum and sulfur trioxide have been tried on petroleum resids, asphaltenes, and bitumens to produce a variety of products ranging from surfactants,21 ion-exchange resins,22 metal extractors,23 water-insoluble sulfonates,24 watersoluble asphaltenes,25 and polymer-modified asphalts,26-32 but there is no indication of selectivity.33,34 Sulfonation of heavy (20) Francisco, M. A.; Siskin, M.; Katritzky, A. R.; Widyan, K.; Kim, M. S. Tetrahedron 2009, 65, 1111–1114. (21) Ozum, B. WO Patent 2006060917 A1 20060615, 2006. (22) Herlem, M.; Mathieu, C.; Herlem, D. Fuel 2004, 83, 1665–1668. (23) Kukes, S. G.; Smith, C. E. U.S. Patent 4802920 A 19890207, 1989. (24) Hardas, P. P.; Gurjar, V. G.; Patwardhan, S. R. Chem. Ind. Dev. 1977, 11, 21–23. (25) Moschopedis, S. E.; Speight, J. G. Fuel 1971, 50, 34–40. (26) (a) Gorbaty, M. L.; Bardet, J. G.; Nahas, N. C. U.S. Patent 5,248,407, 1993. (b) Gorbaty, M. L.; Peiffer, D. G. U.S. Patent 5,288,773, 1994. (27) Gorbaty, M. L.; Nahas, N. C., U.S. Patent 5,336,705, 1994. (28) Gorbaty, M. L.; Peiffer, D. G.; McHugh, D. J., U.S. Patent 5,348,994, 1994. (29) (a) Gorbaty, M. L.; Puzic, O.; Evers, L. J.; Williamson, K. E.; Nahas, N. C. U.S. Patent 5,549,744, 1996. (b) Gorbaty, M. L.; Peiffer, D. G.; Nahas, N. C.; Lenoble, C. G. U.S. Patent 5,627,225, 1997. (30) Gorbaty, M. L.; Puzic, O.; Evers, L. J.; Williamson, K. E.; Nahas, N. C.; Lenack, A. U.S. Patent 5,637,141, 1996. (31) Moschopedis, S. E.; Speight, J. G. Chemical Modification of Bitumen Heavy Ends and Their Non-Fuel Uses; American Chemical Society: Washington, D.C., 1976; Shale Oil, Tar Sands, and Related Fuel Sources, Chapter 12, Advances in Chemistry, Vol. 151, pp 144-152. (32) Speight, J. G.; Moschopedis, S. E. Oil sands. Proceedings of the 27th Canadian Chemical Engineering Conference; Canadian Society for Chemical Engineers (CSChE), Chemical Institute of Canada (CIC): Ottawa, Ontario, Canada, 1977; pp 176-190. (33) Siskin, M.; Kelemen, S. R.; Gorbaty, M. L.; Ferrughelli, D. T.; Brown, L. D.; Eppig, C. P.; Kennedy, R. J. Energy Fuels 2006, 20, 2117– 2124. (34) Ogbuneke, K. U.; Snape, C. E.; Andresen, J. M.; Crozier, S.; Sharpe, R. Prepr.;Am. Chem. Soc., Div. Pet. Chem. 2006, 51, 229–230.
(19) Wiehe, I. A.; Kennedy, R. J. Energy Fuels 2000, 14, 56–59.
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Figure 1. TGA analyses of heavy Canadian vacuum resid heptane asphaltenes.
Canadian vacuum resid demonstrates the selectivity of this chemistry for asphaltenes and is discussed below. Sulfonation Reactions of Asphaltenes. The sulfonation of the heptane asphaltenes from heavy Canadian vacuum resid in toluene at ambient temperature (see experiments 1-4 in Table 1) demonstrates that the asphaltenes react with SO3 in oleum at ambient temperature. The results also demonstrate that the sulfonated asphaltenes are insoluble in toluene, which indicates that they are not soluble in the resid. The sulfonated asphaltenes are similar to the unreacted asphaltenes, as illustrated by TGAs in Figure 1. The TGA analysis records the volatile and non-volatile fractions of the asphaltene sample as a function of the temperature.35 As the temperature is increased (∼200 °C), volatile material is lost and the sample weight begins to decline. The most significant weight loss occurs between 200 and 525 °C, where the asphaltenes begin to crack (>350 °C) and fragment thermally,36,37 losing more volatiles and weight. By 525 °C, coke remains.38,39 Further weight loss after 525 °C is minimal and is the result of further cracking and dehydrogenation reactions in the coke. The unreacted asphaltenes (red line in Figure 1) from solvent separation are similar to the sulfonated asphaltenes generated by different reaction conditions in the general form of the weight versus temperature curve. The unreacted asphaltenes differ from the other samples in two ways. One is that the evolution of volatiles occurs at a much lower temperature for the sulfonated asphaltenes, and the amount of coke formed at 525 °C is higher. The sulfonic acid groups in the sulfonated asphaltenes are thermally labile39 and may be responsible for some of the lower temperature weight loss. Other options include oleum salt formation, occlusion of oleum, and reaction and incorporation of residual toluene into the sulfonated asphaltenes.
Sulfonation may also be causing reactions other than the addition of sulfonic acid groups to the asphaltenes. It is possible that sulfonation causes some condensation and dehydrogenation,40 thereby increasing the size and number of coke-forming polycyclic aromatics. The first four reactions in Table 1 indicate that about 10% of the sulfonated asphaltenes are still soluble in toluene. This suggests that some of the asphaltenes may have fewer sulfonic acid functions added, which would be an indication of selectivity. The other option is that the toluene-soluble asphaltenes are sulfonated to the same degree as the insoluble product, but this is not adequate to make them insoluble in toluene. Sulfonation Reactions of Resid. The sulfonation of heavy Canadian vacuum resid (see experiment 5 in Table 1) demonstrates two points. The first point is that the asphaltenes react with oleum in the presence of the rest of the resid molecules and the added toluene solvent at ambient temperature. The second point is that the sulfonated asphaltenes are insoluble in the resid and toluene mixture. This also indicates that sulfonated asphaltenes should be insoluble in the resid in the absence or presence of toluene solvent. This observation will extend the definition of asphaltenes, a heptane-insoluble, toluene-soluble, solubility class. Table 2 shows the composition of sulfonated resid and asphaltene products via elemental analysis. Oxygen was determined by difference. The numbers of SO3H groups were calculated by subtracting the amount of sulfur in the heavy Canadian vacuum resid from the total amount of sulfur in each product sample. Numbers in parentheses are XPS data. SO3H is directly observed by XPS and quantified from curve resolution of the sulfur (2p) signal. For all but one sample, the XPS results for SO3H are close to those derived from the increase in total sulfur amount. This indicates that most of the sulfur is being added as SO3 groups. In all cases, the total increase in oxygen is greater than the amount of oxygen added as SO3H groups (roughly double the amount of oxygen). XPS results indicate that most of the additional oxygen is associated with oxidation products of organic
(35) Dong, X.-G.; Lei, Q.-F.; Fang, W.-J.; Yu, Q.-S. Thermochim. Acta 2005, 427, 149–153. (36) Kok, M. V.; Karacan, O. J. Therm. Anal. Calorim. 1998, 52, 781– 788. (37) Schabron, J. F.; Pauli, A. T.; Rovani, J. F. Fuel 2002, 81, 2227– 2240. (38) Abu-Khamsin, S. A.; Brigham, W. E.; Ramey, H. J., Jr. SPE Reservoir Eng. 1988, 3, 1308–1316. (39) Vogel, C.; Meier-Haack, J.; Taeger, A.; Lehmann, D. Fuel Cells (Weinheim, Ger.) 2004, 4, 320–327.
(40) Antonishin, V. I.; Grinenko, B. S. Izv. Vyssh. Uchebn. Zaved., Neft Gaz 1965, 8, 47–49.
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Table 2. C, H, N, S, and SO3 in Sulfonated Resid and Asphaltene Products from Elemental Analysis and XPS in Parentheses per 100 carbon sample description
hydrogen
nitrogen (XPS)
sulfur (XPS)
oxygen (XPS)
MW
SO3 (XPS)
heavy Canadian vacuum resid NHIa TIs from 1.0 g of heavy Canadian vacuum resid NHI and 2.5 mL of oleum (20%) at room temperature for 24 h TIs from 1.0 g of heavy Canadian vacuum resid NHI and 2.5 mL of oleum (20%) at room temperature for 2 h TIs from heavy Canadian vacuum resid and 0.5 mL of oleum (20%) at room temperature for 4 h TIs from 1 g of heavy Canadian vacuum resid NHI and 1 mL of oleum at room temperature for 2 h TIs from 1.0 g of heavy Canadian vacuum resid NHI and 0.5 mL of oleum (20%) at room temperature for 15 min TIs from 300 g of heavy Canadian vacuum resid NHI and oleum (20%) in toluene at room temperature for 15 min
116.99 116.40
1.22 0.85 (2.5)
3.14 7.49 (8.0)
0.83 35.24 (30.1)
1448 2132
0.00 4.35 (4.8)
105.14
0.80 (1.5)
7.69 (6.5)
31.70 (19.3)
2070
4.55 (3.7)
111.33
1.17
5.63
17.99
1796
2.49
99.03
1.02 (1.3)
6.30 (5.4)
20.79
1848
3.16 (2.4)
107.30
1.07 (1.9)
6.37 (5.7)
27.67
1969
3.23 (2.8)
117.86
1.26 (1.4)
5.32 (2.9)
18.19 (2.7)
1797
2.18 (0.1)
a
NHI = n-heptane insoluble.
carbon. Some organic sulfur was oxidized to sulfones. The presence of a significant number of SO3 groups is indicated by elemental analysis for TIs from 300 g of heavy Canadian vacuum resid þ oleum (20%) þ toluene at ambient temperature, for 15 min, but not by XPS. Oxidation products of organic carbon were not found in abundance for this sample by XPS. The surface of this sample may be depleted in sulfonation reaction products. The yields of the sulfonated asphaltenes suggest that the number of sulfonic acid groups added per average asphaltene molecule (average molecular weight of 1500 amu) ranged from 4 (4 -SO3H/ average asphaltene molecule) to 20 (20 -SO3H/average asphaltene molecule), depending upon the amount of oleum used and the reaction time. The amount of available SO3 calculated was sufficient to add the number of sulfonic acid groups calculated from the yield in all but one reaction. The sulfonation of heavy Canadian vacuum resid heptane asphaltenes in toluene with 1.0 mL and oleum (20%) at ambient temperature for 2 h is an exception. The amount of available SO3 is far less (7 mol/average asphaltene molecule) than the number of sulfonic acid groups (20 -SO3H/average asphaltene molecule) added to the average asphaltene molecule. Again, this number of 20 SO3H groups is calculated from the yield of sulfonated asphaltenes. The C, H, N, and S atomic composition analysis indicates that the number of sulfonic acid groups added range from 2 to 4.6 per 100 carbon atoms [Table 2, average molecular weight (MW) ∼1847]. Corrected to MW ∼ 1500 amu, the range changes from 1.8 to 3.8 per average asphaltene molecule. There are significantly fewer added sulfonic acid groups than the yield data suggests. The data indicate that perhaps the increase in yield is due to the occlusion of oleum with the product or more likely the formation of ammonium and sulfonium salts and organic oxidation products and not exclusively because of the addition of sulfonic acid groups. There is, however, a consistency in the chemical makeup of TIs isolated from the sulfonation reaction whether one starts with the resid or the asphaltenes. XPS indicates that the number of sulfonic acid groups ranges from 2 to 6, which is more consistent with the weight percentage of C, H, N, and S data than with the yield data. Quarternary ammonium salts of the nitrogen species were also observed. The range of salt formation goes from 17 to 63% of the total nitrogen species. These would be quaternary ammonium salts formed by the reaction of sulfuric acid
(H2SO4) from oleum with basic-type nitrogen species, e.g., pyridines, quinolines, etc. MW was calculated on a 100 carbon atom basis. FCC and RSFO Quality of DAO. The TSs from the sulfonation of heavy Canadian vacuum resid were compared to the heptane DAO of the unreacted heavy Canadian vacuum resid. The TSs are very similar in quality to the DAO. The number of atoms per 100 carbon atoms (100 C) was calculated from the weight percentage of C, H, N, and S analysis of a heptane DAO from an unreacted heavy Canadian vacuum resid and the TSs from the sulfonation of heavy Canadian vacuum resid (Table 3). Oxygen content was calculated by the difference. The data in Table 3 illustrate how similar these two materials are in H/C ratio and nitrogen, sulfur, and oxygen contents. Apparently, there are, essentially, no molecules in the TSs that contain added sulfonic acid groups (-SO3H). This indicates that the sulfonation reaction was highly selective. The TGA analysis (Figure 2) further demonstrates the similarity in the quality of the DAO and TSs. The coke formed at 525 °C is 8.8 wt % for each. This is significantly lower than the value for the whole unreacted resid (17.5 wt %). The catalytic cracking behavior of the TSs, however, does appear to be different from the DAO of unreacted heavy Canadian vacuum resid (see Table 4). The metal contents of the TSs are compared to the DAO from the heptane deasphalting of heavy Canadian vacuum resid in Table 4. The TSs from the sulfonation reaction have somewhat higher concentrations of metals than the DAO from heptane deasphalting of heavy Canadian vacuum resid. Sbn of unreacted heavy Canadian vacuum resid DAO is 143, and In = 0. Sbn of TSs from the sulfonation of heavy Canadian vacuum resid with oleum is 146, and In =39. The solubility properties of these two samples, as illustrated by the Sbn values, are very similar. Sulfonation adds asphaltenes to the product DAO but not sulfonic acid (-SO3H) groups. Separation of Insoluble Asphaltene Sulfonic Acids from Resid. The use of oleum was anticipated to result in difficulties of separating the spent oleum and sulfuric acid from the product. Therefore, liquid SO3 was used instead, because there would be no need to recover sulfuric acid or deal with water formed. A European vacuum resid was also substituted for heavy Canadian vacuum resid because it was identified as a poor feed stock for asphalt. The rationale was to take a non-asphalt resid, treat it chemically with liquid SO3, and produce a good asphalt feedstock. More value was 5042
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Table 3. Comparison of DAOs from Raw and Sulfonated Heavy Canadian Vacuum Residsa per 100 carbon sample description
hydrogen
nitrogen (XPS)
sulfur (XPS)
oxygen (XPS)
MW
SO3 (XPS)
heavy Canadian vacuum resid DAO from heptane deasphalting of heavy Canadian vacuum resid TS from heavy Canadian vacuum resid and 0.5 mL of oleum (20%) in toluene at RT for 15 min
142.54 146.35 145.69
0.72 0.59 (0.4) 0.56
2.33 2.16 (1.6) 2.25
0.43 0.82 (1.0) 0.83
1434 1437 1439
0 0 (0) 0.09
a
Atoms per 100 C calculated from the weight percentage of C, H, N, and S. XPS data appear in parentheses.
Figure 2. TGA of products from sulfonation of heavy Canadian vacuum resid. Table 4. Metal Contents in Parts Per Million (ppm) of Deasphalted Products metals concentration (ppm)
aluminum
calcium
iron
sodium
nickel
vanadium
zinc
TSs from sulfonation of heavy Canadian vacuum resid DAO from heptane deasphalting of heavy Canadian vacuum resid
7.9 not detected
17.5 0.55
137 0.94
56.6 1.92
38.2 53.2
132 113
4.15 0.123
anticipated from this approach than working on a resid that is already a good feedstock for asphalt production. The sulfonation reactions were also conducted at the melting point of the resid to determine if the reaction could be carried out without the use of solvent. One experiment was carried out by reacting liquid SO3 with European vacuum resid at its melt temperature (∼165 °C). The product was cooled to room temperature, and toluene was added. The toluene was stirred with the sulfonated product overnight and then suction-filtered to separate TSs and TIs. This reaction was difficult to run because of the reactivity of pure SO3 at 165 °C. Elemental analyses of the TIs from this experiment are summarized in Table 5 and compared to heptane asphaltenes from unreacted European vacuum resid. The TIs from this experiment and previous experiments with oleum (20%) were found to have quality issues, as discussed in the next section, on the quality of sulfonated asphaltenes. The reaction of European vacuum resid with SO3 at 165 °C was extremely exothermic. The yield of TIs was 4.2 wt %. The yield of heptane asphaltenes from unreacted European vacuum resid is 5.5 wt %. The yields are similar, and this indicates that only the asphaltenes in European vacuum resid are targeted by the sulfonation chemistry, even at 165 °C. The presence of SO3
groups and oxidation products of organic carbon were not found in abundance for this sample by XPS. The surface of this sample may be depleted in sulfonation reaction products, analogous to the hydrophobic affect.41 The TGA weight percentage of coke at 525 °C (Figure 3) values are almost identical at 50.3 and 50.4, respectively. The TIs evolve more volatiles early on in the TGA measurement but the ultimate weight percentage of coke is the same. This reinforces the elemental analysis data (Table 6) that it is the asphaltene fraction that is selectively sulfonated. The TSs from the sulfonation of European vacuum resid at 165 °C are also very similar in elemental analysis (Table 6) to the heptane DAO of the unreacted European vacuum resid. This is another indication of the selectivity of the sulfonation chemistry. Very little of the DAO reacts. One sees that about 0.17 -SO3H groups are added per 100 carbon atoms. The TGA data (Figure 4) support this. The thermal chemistries of both the heptane DAO and the TSs are very similar. The coke formation for the TIs is roughly double that of the DAO, but the TGA data are similar for both the TIs and the DAO. It was anticipated that a better asphalt feedstock would result from sulfonating a non-asphaltic, resid such as European vacuum resid, without removing the sulfonated asphaltenes. The experiment was repeated with liquid SO3 and European vacuum resid, but this time at room temperature in methylene chloride. The reaction appeared to be
(41) Kelemen, S. R.; Siskin, M.; Gorbaty, M. L.; Ferrughelli, D. T.; Kwiatek, P. J.; Brown, L. D.; Eppig, C. P.; Kennedy, R. J. Energy Fuels 2007, 21, 927–940.
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Table 5. Elemental Analyses and XPS Data of the European Vacuum Resid Asphaltenes and TIs per 100 carbon sample description
hydrogen
nitrogen (XPS)
sulfur (XPS)
oxygen (XPS)
MW
SO3 (XPS)
European vacuum resid C7 asphaltenes TIs from 96.13 g of European vacuum resid and 3 mL of liquid SO3 at 165 °C for 1 h
111.62 112
1.34 0.92 (0.4)
1.38 2.82 (0.6)
0.96 15.68 (0.7)
1375 1666
NA 1.44 (0.1)
Figure 3. TGA of European vacuum resid heptane asphaltenes and TIs. Table 6. Elemental Analyses of European Vacuum Resid Heptane DAO and TSs per 100 carbon sample description
hydrogen
nitrogen
sulfur
oxygen
-SO3H
European vacuum resid C7 DAO TSs from European vacuum resid and 3 mL of liquid SO3 at 165 °C for 1 h
153.14 153.31
0.53 0.61
0.79 0.96
0.16 0.46
NA 0.17
selective at 165 °C, and this was an attempt to obtain a sulfonated product without having to do the reaction at an elevated temperature. Methylene chloride was used in place of toluene to avoid ambiguities from sulfonating the toluene solvent. The elemental analysis of the product is compared to unreacted European vacuum resid in Table 7. The materials are similar, and one can see that about 0.2 -SO3H groups have been added per 100 carbon atoms. The quality issues are discussed in the next section. The TGA (Figure 5) indicates that the sulfonated European vacuum resid is not much different than the unreacted material. This is supported by the elemental analysis data (Table 7), which indicate that this reaction has added a lot fewer -SO3H groups than the reaction at 165 °C (Table 5 and Figure 5). Quality of Sulfonated Asphaltenes. Thermal Stability. Py-GC/MS qualitatively demonstrates the evolution of SO2, but the temperature at which this occurs is unclear (Figure 6). The results also suggest that salt formation or occlusion of oleum is not likely but that the reaction and incorporation of toluene is likely. The evolution of SO2 is obvious in all of the samples, except the unreacted asphaltenes. Sulfonic acid groups typically evolve SO 2 during pyrolysis.39 The results on a HCVR sample are for the asphaltenes that precipitate after sulfonation. Methylbenzene and benzene 2-methylthiol are indicative of reaction and incorporation of the toluene solvent during the sulfonation. These two chemical features do not appear in
the unreacted asphaltenes. It is difficult to say how much toluene reacts and incorporates into the asphaltenes because the results represent a percentage of the total volatile molecules identified in GC/MS. The same thing is true of SO2. Further experiments on the thermal stability of sulfonated asphaltenes were conducted by pyrolyzing the sulfonated asphaltenes at 250 °C for 1 h instead of flash pyrolysis. The volatiles were captured and analyzed by GC/MS. The results are shown in Figure 7. These data indicate the stability of the sulfonated asphaltenes. It is clear that the evolution of SO2 from the sulfonated asphaltenes is more than it is for the unreacted asphaltenes. The same analysis was performed on the sulfonation product of European vacuum resid. Figure 8 illustrates the results. Again the sulfonated product evolved more SO2 than the unreacted European vacuum resid. Summary of Thermal Stability Experimental Results. (1) Virgin Heavy Canadian vacuum resid heptane asphaltenes exhibited very little evolution of SO2 (0.44%) and no evolution of SO3. (2) Sulfonated Heavy Canadian vacuum resid heptane asphaltenes (TIs) showed some evolution of SO2 (14.42%) but no SO3. (3) Virgin European vacuum resid exhibited no evolution of SO2 or SO3. (4) Sulfonated European vacuum resid exhibited evolution of SO2 (11.46%) but not SO3. Acidity of Sulfonated Products. It was anticipated that sulfonated products may have residual or occluded sulfuric 5044
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Figure 4. European vacuum resid heptane DAO and TS TGA. Table 7. Elemental Analyses of European Vacuum Resid and Sulfonated European Vacuum Resid per 100 carbon description
hydrogen
nitrogen
sulfur
oxygen
MW
SO3
European vacuum resid European vacuum resid and 1 mL of liquid SO3 at room temperature for 1 h
153.5 150.85
0.65 0.60
0.85 1.05
0 1.06
1390 1401
NA 0.21
Figure 5. TGA of European vacuum resid and sulfonated European vacuum resid.
acid and/or SO3, which could be leached out by water during the preparation or use of asphalt. This section summarizes the results of acid-leaching experiments performed on sulfonated heavy Canadian vacuum resid heptane asphaltenes and virgin heavy Canadian vacuum resid heptane asphaltenes. The sulfonated heavy Canadian vacuum resid heptane asphaltenes were generated on a large scale by dissolving virgin heavy Canadian vacuum resid heptane asphaltenes in toluene and sulfonating them with oleum (20%) at room temperature. The solid that precipitated from the toluene during the reaction (TIs) was suction-filtered and washed with water (this is the first water wash). The sulfonation reaction described above yielded three products: the TIs (sulfonated heavy Canadian vacuum resid
heptane asphaltenes), toluene solubles (TSs), and first water wash. The first water wash was titrated for acid content. The TIs were submitted for a second water wash. The second water wash involved stirring the TIs with distilled water overnight, suction-filtering, and sending the second water wash for acid titration. Acid Leaching Results. (1) Pure, distilled water (base case) requires 0.100 31 mg of KOH/L to neutralize the acid content. (2) The second water wash with pure, unsulfonated heavy Canadian vacuum resid heptane asphaltenes requires 6.36 mg of KOH/L to neutralize the acid content. (3) The second water wash of the sulfonated heavy Canadian vacuum resid heptane asphaltenes (TIs) requires 6.49 mg of KOH/L to neutralize the acid content. (4) The first water wash of the sulfonated heavy Canadian vacuum resid 5045
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Figure 6. Flash Py-GC/MS up to 800 °C.
Figure 7. Heavy Canadian vacuum resid heptane asphaltenes (HCVRHAs) Py-GC/MS at 250 °C for 1 h.
Figure 8. European vacuum resid (EVR) Py-GC/MS at 250 °C for 1 h.
heptane asphaltenes (TIs) requires 156.8 mg of KOH/L to neutralize the acid content. (5) The first water wash indicates the difficulty of excluding residual or occluded sulfuric acid and/or SO3 from the sulfonated product. It is expected that there may be leaching of acid from sulfonated asphaltene or resid products. PP and SP. The TIs from the sulfonation of heavy Canadian vacuum resid heptane asphaltenes with oleum at room temperature in toluene would not melt or soften at the temperatures needed to conduct these two tests. The same was true of the TIs from the sulfonation of European vacuum resid at 165 °C with no toluene. Therefore, we conclude that these sulfonated products are not suitable feedstocks to make asphalt. The last experiment was to test the sulfonation product of European vacuum resid without removing the TIs. This experiment was performed at room temperature in methylene chloride to generate a sulfonated product and to avoid the drastic reaction conditions encountered at 165 °C (Table 7). The sulfonated product had PP and SP (98 MM/10 and 46.4 °C) different from the starting resid
Figure 9. IR of the TIs from sulfonated heavy Canadian vacuum resid heptane asphaltenes.
(92 MM/10 and 38 °C). The sulfonation chemistry appears to change the asphalt properties slightly and in the right direction to make asphalt. This indicates that a higher temperature 5046
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would sulfonate the European vacuum resid enough to move PP and SP into the asphalt range. Infrared (IR) Spectral Analysis of Sulfonation Products. The primary interest for IR analysis was to confirm the identity of any sulfones and sulfonic acids in the sulfonation products that were found by XPS. Artifacts of the sulfonation reaction might also be present, e.g., SO2, SO3, and H2SO4. Heavy Canadian vacuum resid heptane asphaltenes (1.00 g) and 20% oleum (2.50 mL) were stirred at room temperature for 2 h. The IR of the TIs is shown in Figure 9. The features observed were essentially the same as those observed in the other cases discussed above. Hydrated sulfonic acid functionalities predominate.
Summary and Conclusions (1) Asphaltenes can be selectively sulfonated and precipitated from resid in the absence of a solvent. (2) The worst asphaltenes are targeted. (3) The sulfonation reaction works with oleum (20%) or preferably with liquid sulfur trioxide. (4) Separation of the sulfonated asphaltenes from the resid product without solvent is possible. (5) The sulfonated asphaltenes are toluene-insoluble, indicating that they are more polar than heptane asphaltenes and, therefore, not good feedstocks for asphalt by themselves. (6) The resid sulfonation product minus the sulfonated asphaltenes is equivalent in quality to the DAO from heptane deasphalting of the resid.
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