Chemical Approach to Control Morphology of Coke ... - ACS Publications

Energy & Fuels 2006, 20, 2117-2124

2117

Chemical Approach to Control Morphology of Coke Produced in Delayed Coking M. Siskin,* S. R. Kelemen, M. L. Gorbaty, D. T. Ferrughelli, L. D. Brown, C. P. Eppig, and R. J. Kennedy ExxonMobil Research and Engineering Company, Corporate Strategic Research Laboratories, 1545 Route 22 East, Clinton Township, Annandale, New Jersey 08801 ReceiVed June 7, 2006. ReVised Manuscript ReceiVed June 23, 2006

Air oxidation of vacuum resid delayed coker feeds promotes the formation of anisotropic shot coke. The combination of the microcarbon residue test (MCRT) on a feed to the delayed coker followed by crosspolarized light optical microscopy on the coke produced in the MCRT is a predictive test for the morphology of the coke formed in delayed cokers. Sponge-coke-forming feeds produce cokes with highly anisotropic (ordered) 10-60 µm flow domains, whereas shot-coke-forming feeds produce cokes with a less anisotropic mosaic structure of 1-10 µm. Air oxidation increases both the asphaltene content and the polarity of the asphaltenes by increasing the organic oxygen heteroatom content of the asphaltenes in vacuum resid feeds. The higher solubility parameter of the oxidized asphaltenes favors phase separation from the hydrocarbon matrix and leads to shot coke formation. Another possible explanation is that the oxygen incorporated in the asphaltene structures leads to more rapid coke formation, thus favoring shot coke. Our experiments do not allow a distinction to be made between these two possible explanations for the increased shot coke formation tendency following oxidation of the resid.

I. Introduction Delayed coking involves the thermal decomposition of petroleum residua (resids) to produce gas, liquid streams of various boiling ranges, and coke. Delayed coking of lowerquality resids from the increasing quantity of heavy and heavy sour (high sulfur) crude oils is carried out primarily as a means of disposing of these low-value resids by converting part of the resids to more valuable liquid and gaseous products and leaving a solid coke product residue. Although the resulting coke product is generally thought of as a low-value byproduct, it may have some value, depending on its grade, as a fuel (fuel-grade coke), electrodes for aluminum manufacture (anode-grade coke), and so forth. In addition, the economic value can be offset if the morphology of the coke produced is controlled to increase process capacity, for example, by the formation of free-flowing shot coke. The feedstock in a delayed coking process is rapidly heated in a fired heater or tubular furnace at about 500 °C to allow some thermal conversion, but not to the point where an appreciable amount of coke is formed. The heated feedstock, wherein coke formation is “delayed”, is then passed to a large steel vessel, commonly known as a coke drum, that is maintained at conditions under which coking occurs, generally at temperatures above about 400 °C under super-atmospheric pressures (15-80 psig). The heated residuum feed in the coke drum results in volatile components that are removed overhead and passed to a fractionator, leaving coke behind. When the coke drum is full of coke, the heated feed is switched to a “sister” drum, and hydrocarbon vapors are purged from the full drum with steam. The drum is then quenched, first by flowing steam and then by filling it with water, to lower the temperature * To whom correspondence [email protected].

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to less than about 100 °C, after which the water is drained. When the cooling and draining steps are complete, the drum is opened and the coke is removed after drilling or cutting using highvelocity water jets. Cutting is typically accomplished by boring a hole through the center of the coke bed using water jet nozzles located on a boring tool. The morphology of the coke in the drum is typically described in simplified terms such as sponge coke, shot coke, transition coke, and so forth. Sponge coke, as the name suggests, has a spongelike appearance with various sized pores and bubbles “frozen into” a solid coke matrix. One key attribute of sponge coke produced by routine coker operating conditions is that the coke is self-supporting and typically will not fall out of the bottom of the coke drum, which typically has a diameter of about 6 ft, when it is opened. Shot coke is a distinctive type of coke. It is comprised of individual particles that look like BBs. These individual particles range from substantially spherical to slightly ellipsoidal with average diameters of about 1-4 mm. While shot coke has a lower economic value than sponge coke, it is the desired product coke because its ease of removal from the coker drum results in effectively increasing the process capacity, which more than offsets its reduced economic valve. At times, there appears to be a binder material present between the individual shot coke particles, and such a coke is sometimes referred to as “bonded shot”. Depending upon the degree of bonding in the bed of shot coke, the bed may not be self-supporting and can flow out of the drum in an uncontrolled manner when the drum is opened. The term “transition coke” refers to coke that has a morphology between that of sponge coke and shot coke. For example, coke that has a mostly spongelike physical appearance but with evidence of small shot spheres that are just beginning to form as discrete particles is one type of transition coke.

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2118 Energy & Fuels, Vol. 20, No. 5, 2006

Coke beds are not necessarily comprised of all of one type of coke morphology. For example, the bottom of a coke drum can contain large aggregates of shot, transitioning into a section of loose shot coke, and finally have a layer of sponge-rich coke at the top of the bed of coke. Factors that affect coke morphology in the coke drum are complex and inter-related and include such things as the particular coker feedstock, coker operating conditions, and coke drum hydrodynamics. The judicious choice of feedstocks and operating severity can push the production of sponge coke to transition coke or from transition coke to shot coke. Higher temperatures and lower pressures favor the removal of volatile liquids and the formation of shot coke. The amount of asphaltenes present in a vacuum resid feed is believed to be one of the major properties responsible for shot coke versus sponge coke formation in delayed cokers.1-4 However, the quantity of asphaltenes and the asphaltene/ concarbon ratio are not reliable predictive indicators of coke morphology. The detailed structural characterization of asphaltenes from several shot-coke- versus nonshot-coke-producing vacuum resid feeds indicates that the average asphaltene ring sizes of both is about four.5 With an average of about one heteroatom or less per average four-ring aromatic cluster, the lower solubility parameter favors sponge coke formation. We have found that, when the sum of the unreactive (i.e., heterocyclic aromatic) N, S, and O atoms in the average four-ring aromatic cluster is about two, the solubility parameter of the asphaltenes is about 0.5-1.5 unit [(cal/cm3)1/2] higher than in asphaltenes from feeds making sponge coke.5 The higher solubility parameter of the asphaltenes, and therefore the larger difference in the solubility parameter between the asphaltenes and the hydrocarbon matrix, appears to be a factor governing coke morphology. In addition, more rapid coking or carbonization rates also favor the formation of shot coke.6,7 Because higher-solubility-parameter asphaltenes in the vacuum resid feeds are believed to be the major contributor to shot coke formation, we hypothesized that increasing the solubility parameter by increasing both the concentration of asphaltenes and their polarity by increasing the amount of organic oxygen in the asphaltenes should help to increase shot coke formation.8 We found that the asphaltene and organic oxygen contents of vacuum resid feeds to delayed cokers can both be increased by air oxidation of those feeds. Air oxidation (185-225 °C) directionally increases the oxygen heteroatom content of asphaltenes and thereby brings the solubility parameter into the range where shot coke formation would be favored. This is analogous to the air blowing of asphalt.9,10 Optical microscopy (1) Marsh, H.; Calvert, C.; Bacha, J. J. Mater. Sci. 1985, 20, 289-302. (2) Ellis, P. J.; Paul, C. A. Tutorial: Delayed Coking Fundamentals; Great Lakes Carbon Corporation: New York, 1998; pp 151-169. (3) Rodrigues-Reinoso, F.; Santana, P.; Palazon, E. R.; Diez, M.-A.; Marsh, H. Carbon 1963, 1, 105-116. (4) Elliott, J. D. Chem. Eng. World 1999, 6, 83-90. (5) Siskin, M.; Kelemen, S. R.; Eppig, C. P.; Brown, L. D.; Afeworki, M. Energy Fuels 2006, 20, 1220-1226. (6) Eser, S.; Jenkins, R. G.; Malladi, M.; Derbyshire, F. J. Proceedings of the 17th Biennial Conference on Carbon, Lexington, KY, 1985; pp 253254. See also Eser, S.; Jenkins, R. G.; Malladi, M.; Derbyshire, F. J. Carbon 1986, 24, 77-82. (7) Eser, S.; Karsner, G.; Derbyshire, F. Proceedings of the 4th International Carbon Conference, Baden-Baden, W. Germany, 1986; pp 99-100. See also Eser, S.; Karsner, G.; Derbyshire, F. Carbon 1987, 25, 53. (8) Siskin, M.; Ferrughelli, D. T.; Gorbaty, M. L.; Kelemen, S. R.; Brown, L. D. U.S. Patent 2003/0102250 A1. (9) Roberts, F. L.; Kandhal, P. S.; Brown, E. R.; Lee, D.-Y.; Kennedy, T. W. In Hot Mix Asphalt Materials, Mixture Design, and Construction; NAPA Education Foundation: Landham, MD, 1991; pp 14-15.

Siskin et al.

can distinguish between sponge and shot coke via the size of the domains in the formed cokes. In our experiments, microcarbon residue (MCR) tests on the vacuum resid feeds and airoxidized vacuum resid feeds were performed followed by crosspolarized light optical microscopy on the resultant cokes. The micrographs show a dramatic decrease in the domain size of the anisotropic coke produced from an air-oxidized sponge-cokeforming feed. This is comparable to the mosaic size of 2-10 µm in commercial shot cokes. Therefore, on the basis of smallscale testing, it appears that partial oxidation pretreatment of the vacuum resid can alter the resultant coke morphology from sponge to shot. It should be noted that a previous report11 described a delayed coking process wherein “isotropic” coke is the product of air blowing a petroleum resid feedstock. The process was run at a relatively high recycle ratio (200-500 vol %) and with large quantities of heavy aromatic diluent oil (up to 50 vol %), both of which favor the formation of a mesophase leading to sponge coke.11 II. Experimental Section A. Microcarbon Residue (MCR) Test. A sample of vacuum residuum (∼2 g) is heated from room temperature to 100 °C over 10 min under a nitrogen flow of 66 cm3/min. The temperature is then increased from 100 to 300 °C at the 66 mL/min flow rate and from 300 to 500 °C at a reduced nitrogen flow rate of 19.5 cm3/ min. The total heating time from 100 to 500 °C is 30 min. The sample is then held at 500 °C for 15 min at a 19.5 mL/min flow rate of nitrogen and finally is cooled to room temperature over 40 min while maintaining the 19.5 mL/min nitrogen flow rate. The residue is weighed and is expressed as a weight percent based on the weight of the starting sample. B. General Resid Oxidation Procedure. Approximately 180 g of resid was added to a 500 mL round-bottom flask equipped with a THERM-O-WATCH controller, a mechanical blade stirrer, and a condenser attached to a Dean-Stark trap to recover any light ends and water generated during the reaction. The resid was heated to 180 °C, at which time air was introduced into the hot feedstock under its surface by means of a sparge tube. The temperature was then raised and was controlled to between 220 and 230 °C, and the flow rate of air was controlled at 0.675 cubic feet/hour (5.3 cm3/sec) for 3 h or longer depending on the desired degree of oxidation. The sparge tube was removed after the desired time, and the flask was allowed to cool to room temperature. C. Resid Deasphalting Procedure. A mixture of fresh or oxidized coker feedstock and n-heptane was added to a 250 mL round-bottom flask in a ratio of one part of feedstock to eight parts of n-heptane and was allowed to stir for 16 h at room temperature. The mixture was then filtered through a coarse Buchner funnel to separate the precipitated asphaltenes. The solids were dried in a vacuum oven at 100 °C overnight. The heptane was evaporated from the oil/heptane mixture to recover the deasphalted oil. The amount of asphaltenes produced from the oxidized feed was compared to the amount generated from the starting resid under the same deasphalting procedure (Table 1). D. Polarized Light Optical Microscopy. The best method for identifying and characterizing the morphology of thermal coke is polarized light optical microscopy. The key indicator is the optical texture of the polished cross-section of the sample. In most cases, thermal coke consists of small regions of anisotroptic (ordered) carbon called mosaics (ranging in size from less than a micrometer to 10 µm) and larger regions called domains (greater than 10 µm). The larger the mosaic or domain size, the greater the degree of (10) Broome, D. C. In Modern Petroleum Technology, 4th ed.; Hobson, G. D., Pohl, W., Eds.; Applied Science Publishers Ltd.: Lomdon, Great Britain, 1975; pp 808-809. (11) Kegler, W. H.; Huyser, M. E. U.S. Patent 3,960,70, June 1, 1976.

Chemical Approach to Control Morphology of Coke

Energy & Fuels, Vol. 20, No. 5, 2006 2119

Figure 1. Example XPS nitrogen (1s) spectra and curve resolution results. Table 1. Properties of Petroleum Vacuum Resid and Oxidized Vacuum Resid asphaltenes wt %

MCR wt %

MCR domain size µm

vacuum resid oxidized vacuum resid

Mid-Continent U.S. 8.9 27.0

16.4 19.4

10-50 2-3


San Joaquin Valley 13.6 37.8

19.6 24.1

10-30 2-5


Maya 40.9 41.0

29.5 30.4

2-10 2-10


Heavy Canadian 19.4 23.8

21.9 23.8

10-20 2-15


Cerro Negro 20.4 32.7

19.5 22.4

LA Sweet 0 11.9 31.7

9.4 11.4 18.6

vacuum resid oxidized vacuum resid (3h) oxidized vacuum resid (6h)

20-60 2-5

order in the coke. The observed anisotropic structure in thermal coke is made possible by a liquid crystal precursor called mesophase, which begins to form from the liquid phase above 400 °C. The greater the opportunity for the mesophase to grow and coalesce in the liquid phase, the greater the degree of order in the thermal coke. Factors affecting mesophase growth include the properties of the pitch, the coking temperature, and the time spent at that temperature. Therefore, the observed anisotropic texture of a thermal coke can reveal qualitative information on the conditions in which the coke was formed. Isotropic coke, in contrast, is usually formed by the decomposition of polymeric material or another highly cross-linked structure that has not gone through the intermediate fluid phase. Optical microscope samples are prepared by embedding the coke sample in epoxy, followed by a series of standard grinding and polishing procedures. The highly polished cross-section of each sample is then examined under reflected cross-polarized light. To add color to the image, a λ retardation plate (full wave) is inserted between the cross polars. The resulting pink, blue, and yellow regions of the sample (mosaics and domains) are caused by different orientations of the anisotropic material with respect to the polarized light. Most observations were made with a 20× or 50× oil immersion objective in order to enhance the contrast. Observations to be made on the sample include the general morphology, particle

size, degree of anisotropy, reflectance, porosity, and inclusions (such as metal sulfides). E. X-ray Photoelectron Spectroscopy (XPS). XPS spectra were obtained on a Kratos Axis Ultra system using monochromatic Al KR radiation and automatic charge neutralization. The asphaltene samples were finely ground and mounted to a metallic sample nub using double-sided nonconducting tape. An energy correction was made to account for sample charging on the basis of the carbon (1s) peak at 284.8 eV. Elemental concentrations are reported relative to carbon from the area of the XPS peaks after correcting for differences in atomic sensitivity. The sensitivity factors were obtained from Kratos sensitivity tables and checked against experimental results from standard samples. The relative amount of aromatic carbon was determined from the calibrated intensity of the Π to Π* signal intensity.12 For nitrogen, the following was used to curve-resolve the nitrogen (1s) spectrum. In general, a mixed (30% Gaussian) Gaussian-Lorentzian line shape and a peak width at half-maximum of 1.4 (( 0.1) eV for each peak was used to curveresolve the carbon (1s) spectrum. During the curve resolution process, the peak shape and peak energy positions were fixed and only the amplitudes of the peaks were varied to obtain the best fit to the experimental XPS spectrum. The nitrogen (1s) spectrum from asphaltenes was curve-resolved using two peaks at energy positions characteristic of pyridinic (398.7 eV) and pyrrolic (400.2 eV) nitrogen.13 Figure 1 shows typical nitrogen (1s) spectra of asphaltenes from an oxidized resid and the curve-resolved spectra. The XPS sulfur 2p spectrum from a single species is made up of 2p3/2 and 2p1/2 components having a 2:1 relative intensity and separated in energy by 1.2 eV. The 2p3/2 and 2p1/2 peaks were linked by this relationship during the curve-resolution process. The energy position of the 2p3/2 component sets the energy position of the overall sulfur 2p peak. Each XPS sulfur 2p spectrum of an asphaltene sample could be curve-resolved using 2p3/2 peak positions at 163.4, 164.1, and 166.0 eV (( 0.1). These peaks correspond to nonaromatic, thiophenic, and sulfoxide forms, respectively.14 Figure 2 shows typical sulfur (2p) spectra of asphaltenes from oxidized resids and the curve-resolved spectra.

III. Results and Discussion Six vacuum resid feeds to delayed cokers and their airoxidized products were coked in the MCR test unit and examined by cross-polarized light optical microscopy. The (12) Kelemen, S. R.; Rose, K. D.; Kwiatek, P. J. Appl. Surf. Sci. 1993, 64, 167-173. (13) Kelemen, S. R.; Gorbaty, M. L.; Kwiatek, P. J. Energy Fuels 1994, 8, 896-906. (14) Kelemen, S. R.; George, G. N. Fuel 1990, 69, 939-944.


Siskin et al.

Figure 2. Example XPS sulfur (2p) spectra and curve resolution results.

vacuum resid delayed coker feeds used in this study were oxidized by air blowing for 3 h at 185-225 °C. The change in n-heptane asphaltene content was then measured. The cokes produced from the microcarbon residue of the oxidized versus the raw feeds were then examined by cross-polarized light optical microscopy to determine flow domain and mosaic sizes which are characteristic of the coke morphology. These results are summarized in Table 1, wherein the properties of the petroleum vacuum resid and the oxidized vacuum resid are compared. Oxidation results in a significant increase in the weight percent of asphaltenes for all vacuum resids except Maya. The values remained constant for the Maya feed that already contained about 40% asphaltenes and already produced largely free flowing shot coke in commercial units. In all cases, the amount of MCR increases upon oxidation of the vacuum resid.15 The domain size of the MCR was reduced following oxidation for all of the resids except Maya. Figure 3 shows a polished cross-section of the commercial shot coke sphere produced from (15) Mukherjee, S. K.; Mukherjee, D. K. Fuel Sci. Technol. 1985, 4, 61-72.

the Maya vacuum resid. The mosaic size of the anisotropic coke inside the sphere ranges typically from 2 to 10 µm. There is also evidence of a poorly defined layer structure within the shot coke sphere. The binding material for the shot coke (upper right) has a much coarser texture (10-20 µm domains). The viewing area is 425 × 340 µm under cross-polarized light. Figure 4A shows the polished cross-section of coke formed from the midcontinent U.S. vacuum resid, a sponge coke former, which has highly anisotropic flow domains ranging from 10 to 50 µm. In contrast, Figure 4B gives the cross-section of coke formed from the mid-continent U.S. vacuum resid after air oxidation, which shows a fine mosaic texture 2-3 µm in size. The viewing area for both photomicrographs is 170 × 136 µm under crosspolarized light. Domain sizes of anisotropic coke from the oxidized products decreased in each case except for the Maya vacuum resid. Flow domain sizes of 10-50 µm are indicative of sponge coke, whereas mosaic sizes of 2-10 µm indicate a shot coke morphology. The mosaic sizes in commercial shot cokes range from about 5 to 10 µm. The basic chemical composition of asphaltenes from petroleum resid and oxidized petroleum resid was determined from elemental analysis and XPS results. Table 2 shows the hydrogen,



Figure 3. Polished cross section of commercial shot coke sphere produced from Maya vacuum resid. Table 2. Hydrogen, Nitrogen, and Sulfur Elemental Data for Petroleum Vacuum Resid Asphaltenes and Oxidized Resid Asphaltenes Expressed Per 100 Carbon Atoms

Table 3. Aromatic Carbon, Nitrogen, Sulfur, and Oxygen Amounts from XPS Analysis for Petroleum Vacuum Resid Asphaltenes and Oxidized Resid Asphaltenes Expressed Per 100 Carbon Atoms

elemental analysis per 100 carbons asphaltene sample

hydrogen

per 100 carbons (XPS)

nitrogen

sulfur

aromatic carbon

asphaltene sample

nitrogen

sulfur

oxygen


Mid-Continent U.S. 122 118

1.0 1.0

1.7 1.6


Mid-Continent U.S. 36 0.7 43 1.0

1.1 1.3

1.4 3.3


San Joaquin Valley 118 119

2.6 2.3

1 0.9


San Joaquin Valley 43 2.4 40 2.0

1.0 0.9

2.0 3.0

1.2 1.4

3.1 2.1


1.3 1.3

2.7 2.9

1.6 1.7

Heavy Canadian 50 1.5 41 1.1

2.2 2.3

1.4 2.7

Maya 115 114

vacuum resid oxidized vacuum resid vacuum resid oxidized vacuum resid

Heavy Canadian 112 117

1.2 1.1

2 2.8



Cerro Negro 113 116

1.7 1.7

2.3 2.1


LA Sweet 120 115

0.9 1.0

0.5 0.6

oxidized vacuum resid (3h) oxidized vacuum resid (6h)


nitrogen, and sulfur elemental data for petroleum vacuum resid asphaltenes and oxidized vacuum resid asphaltenes expressed as the number of atoms per 100 carbon atoms. Table 3 shows the amount of aromatic carbon along with the results for nitrogen, sulfur and oxygen from XPS analysis expressed as number of atoms per 100 carbon atoms. Figure 5 shows a general relationship between the amount of hydrogen in asphaltenes and the amount of aromatic carbon determined by XPS for both resid asphaltenes and oxidized resid asphaltenes. In general, the H/C atomic ratio increases with the decreasing amount of aromatic carbon. XPS is a surface-sensitive spectroscopy, and the majority of the signal originates within the first 50 Å of the surface. It is

Maya 45 47

Cerro Negro 43 46

1.7 1.6

2.1 2.1

1.7 3.1

LA Sweet 43 43

0.9 1.0

0.4 0.4

3.9 5.0

possible to determine if the composition of nitrogen and sulfur species at the surface is significantly different than that in the bulk by comparing the total amount of nitrogen from an elemental analysis with XPS. Figure 6 contains a comparison of the amount of nitrogen per 100 carbons determined by elemental analysis and by XPS. For finely ground asphaltenes, the total nitrogen level determined by XPS corresponds closely with elemental analysis. XPS nitrogen (1s) curve resolution results for petroleum resid asphaltenes and oxidized vacuum resid asphaltenes are shown in Table 4. Each XPS nitrogen (1s) spectrum could be curve-resolved using two peaks located at 398.6 and 400.2 eV. The position of these peaks is consistent with pyridinic and pyrrolic nitrogen forms, respectively. Re-


Siskin et al.

Figure 6. Comparison of the amount of nitrogen per 100 carbons determined by elemental analysis and by XPS.

Figure 7. Comparison of the amount of sulfur per 100 carbons determined by elemental analysis and by XPS. Figure 4. (A) Polished cross section of coke formed from midcontinent U.S. vacuum resid, a sponge coke former. (B) Cross section of coke formed from mid-continent U.S. vacuum resid after air oxidation.

Table 4. XPS Nitrogen (1s) Curve Resolution Results for Petroleum Resid Asphaltenes and Oxidized Vacuum Resid Asphaltenes mole percent pyridinic (398.6 eV)

asphaltene sample

pyrrolic (400.2 eV)


Mid-Continent U.S. 28 30

72 70


San Joaquin Valley 28 26

72 74

Maya vacuum resid oxidized vacuum resid

30 33

70 67



74 72

Cerro Negro vacuum resid oxidized vacuum resid

33 35

67 65

26 29

74 71

LA Sweet oxidized vacuum resid (3h) oxidized vacuum resid (6h)

Figure 5. Relationship between the amount of hydrogen in asphaltenes and the amount of aromatic carbon determined by XPS.

markably, the relative amount of pyridinic and pyrrolic nitrogen is the same for petroleum resid asphaltenes and oxidized resid asphaltenes. While the total amount of nitrogen can vary significantly among asphaltenes, the relative amounts of pyridinic and pyrrolic nitrogen appear almost constant. Figure 7 shows a comparison between the amount of sulfur

per 100 carbons determined by elemental analysis and by XPS. The good agreement indicates that the amount of sulfur at the surface is comparable to the bulk. Table 5 shows the XPS sulfur (2p) curve-resolution results for petroleum resid asphaltenes and oxidized vacuum resid asphaltenes. For some oxidized resid asphaltenes, a signal appeared at an energy position expected for sulfoxide species. There was significant variation in the relative amount of aromatic and aliphatic sulfur among petro-



Figure 8. Modeled PNA core solubility parameter of asphaltenes plotted versus the ratio of aromatic carbon to the sum of nitrogen, sulfur, and oxygen (from ref 5). Table 5. XPS Sulfur (2p) Curve Resolution Results for Petroleum Resid Asphaltenes and Oxidized Vacuum Resid Asphaltenes mole percent aliphatic (163.3 eV)

asphaltene sample vacuum resid oxidized vacuum resid vacuum resid oxidized vacuum resid

Mid-Continent U.S. 16 20 San Joaquin Valley 37 38


Maya 32 27




Cerro Negro 25 20


LA Sweet 16 13

aromatic (164.1 eV) 84 80 63 56 68 73 70 67 75 76 77 84

sulfoxide (166.0 eV) 0 0 0 5 0 0 0 0 0 4 7 3

leum resids. In all cases, however, the relative amounts of aromatic and aliphatic sulfur are comparable for petroleum resid asphaltenes and oxidized resid asphaltenes. The detection limit, given the total amount of sulfur and signal-to-noise considerations, is 2 mol %. Sulfones (168.2 eV) and sulfonic acids (169.1 eV) were not needed to fully curve-resolve each spectrum. This indicates that these species, if present, correspond to less than 2 mol % of the total sulfur. Previous work has shown that the average asphaltene aromatic carbon per cluster size is between 14 and 22 carbon atoms, and this corresponds to three-to-five ring average clusters.5 When the atomic ratio of aromatic carbon to the nitrogen and sulfur in asphaltenes is

Chemical Approach to Control Morphology of Coke ... - ACS Publications

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