Conversion of Heavy Tar Sands with Asphaltene Chemical Structures

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Conversion of Heavy Tar Sands with Asphaltene Chemical Structures via Catalytic Coking using MoS2 catalytic material R. R. Chianelli, David Rendina, Edward G. Hauptmann, Peter J. Lucchesi, and Brenda Torres Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 29 Oct 2013 Downloaded from http://pubs.acs.org on November 2, 2013

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Energy & Fuels 2013 Conversion of Heavy Tar Sands with Asphaltene Chemical Structures via Catalytic Coking using MoS2 catalytic material R. R. Chianelli1, D. Rendina2, E. G. Hauptmann2, P. J. Lucchesi3 and B Torres1 1. Materials Research and Technology Institute, University of Texas at El Paso, El Paso, TX. U.S.A. 2. Lightyear Technologies Inc. #119-980 W. 1st St. N. Vancouver BC, Canada V7P 3N4 3. International Technology Services, Princeton, New Jersey. Received March 2013

Abstract: A basic understanding of Cataytic Micro-Reversibility described below has led to the further develpopment of the concept of Catalytic Coking. In this concept a catalyst, such as MoS2, which under high hydrogen pressure and temperature puts extensive amount of hydrogen in to petroleum molecues, under low pressure of hydrogen the catalyst redistributes the hydrogen, thus rejecting asphaltenes and other heavy molecules as coke. This results in a clean liquid product as the heavy molecules are rejected. MoS2 is a layrered Transition Metal Sulfide Catalytic material well know in the refining industry as described by O. Weisser & S. Landa., 1973. Upgrading tests on samples of Cold Lake Bitumen were carried out using Transition Metal Sulfide (TMS) nanoparticle catalysts in a special–purpose batch reactor as described below (R. Chianelli et al., 2009). The tests covered a range of process temperatures and catalyst concentrations in order to explore the broad effects of catalyst performance. Typical reactor process conditions were 400 – 450oC for periods of up to one hour, with catalyst weight concentrations ranging from approximately 0.2% to just under 1.0%. All tests were conducted at ambient pressure in a hydrogen atmosphere. Results show an upgrading of approximately 80 wt.% of the bitumen to a liquid product typically in the range of 21 API, (American Petroleum Institute viscosity index as described in reference 3 having viscosity of around 7 - 9 c Stokes, using as little as 0.23 wt.% catalyst (J. Speight, 2002). The remaining solid coke product is largely carbon, with the addition of most of the original trace heavy metals, and the catalyst. Keywords: Bitumen, Catalytic Coking, Upgrading Introduction: The concept of Catalytic Coking, though recent, had it origins in the work done by Exxon in the 80’s. Roby Bearden and his co-workers developed the Microcat hydroconversion process. This process related to the Exxon Coal Liquefaction process. This process is a high-pressure hydrogen process (> than 1500 psig H2) that dominated heavy feed processing during this period. A dilute molybdenum based catalyst (< 2000 ppm) was added to the feedstock, thus the process was named Microcat. During this period Exxon also developed another process called Flexicoking (Exxon Mobile). Flexicoking was a continuous low pressure coking process that was commercialized by Exxon. This period introduced a competitive attitude between research in 1 ACS Paragon Plus Environment

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Hydroconversion processing at high pressure and Coking processing at low pressure. This was termed Hydrogen Addition vs. Carbon Rejection (R. Chianelli, 2013). Results from the early experiments using MoS2 catalysts are shown in Figure 1. This research led to work on the effect of hydrogen pressure on various reactions. Approximate pressures for common reactions with catalysts are: Hydroconversion - > 1500 psig, Hydrocracking – 1000 – 1500 psig, HDS/HDN – 500 – 1000 psig. It is also noted that at 5000 psig a catalyst is not required, the metals contained in the feed are sufficient. Research led to the concept of “Catalytic Micro-Reversibility” as applied to the Transition Metal Sulfide (TMS) catalysts and described below.

Catalytic Coking

Hydroconversion

Figure 1: Effect of Catalyst on Coking and Hydroconversion Reference: R. Chianelli & R. Chianelli et al., 2006 Catalytic Micro-Reversibility: Catalytic Micro-Reversibility is a fundamental property of all catalysts. In the case of the catalyst MoS2, the catalyst facilitates hydrogen addition (hydrogenation) so the catalyst will also facilitate hydrogen removal from an organic molecule (dehydrogenation) and the reaction shown in Figure 2 is an example (O. Weisser & S. Landa, 1973). Tetralin is hydrogenated and Naphthalene is dehydrogenated by the MoS2 catalyst. The direction of the reaction is determined by thermodynamics and therefore, the H2 pressure and temperature.

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Tetralin

Naphthalene H222 MoS2

Figure 2: Catalytic Hydrogenation/Dehydrogenation When applied to heavy bitumen and tars in a coking environment the principle of MicroReversibility predicts increased coke production because the dehydrogenation is accelerated by the presences of the catalyst. This is the first explanation for the coke increase as a function of increase in catalyst concentration shown in Figure 1. There follows a demonstration of this concept on real petroleum crude oils. Asphaltenes: In order to understand the concept of Catalytic Coking, it is necessary to review the current understanding of Ashphaltenes and their structure. Asphaltenes are defined as a solubility class in petroleum. Compounds in petroleum are defined in the SARA scheme: Saturates, Aromatics, Resins and Asphaltenes. When the petroleum is dissolved in a light hydrocarbon, in a prescribed manner, the asphaltenes are insoluble and separated from the rest of the petroleum (J. Speight, 2002). Commonly, three hydrocarbons are used heptane, hexane and pentane. The amount of asphaltene recovered increases slight as the precipitating hydrocarbon decrease in molecular weight. Accordingly, “heptane insolubles” from a given petroleum weight less than “pentane insolubles”. Both heptane asphaltenes and pentane asphaltenes are frequently encountered in the literature on petroleum analysis (J. Speight, 2002). The difference in the amount of asphaltenes measured is to due to the properties of the asphaltenes and the petroleum as suspended in the petroleum. Today the Yen model originally proposed in the early sixties is used to describe asphaltenes and the dispersion in petroleum (T. Yen, 1975). The Yen model shows that asphaltenes have aromatic cores stacked together. X-ray diffraction measures the number of stacks as generally varying between 3 and 6 stacks with the condensed aromatic sheets averaging 7 cores. Asphaltenes vary greatly in molecular weight and they contain the metals such as V and Ni. These metals are contained in porphyrin rings within the asphaltene cores. The asphaltene cores are suspended in the petroleum by paraffinic chains that interact with the resins and other components in the petroleum. The asphaltenes are further aggregate into “particles” that are 3-4 nm in diameter. These asphaltene particles are further aggregated into larger particles. Converting these asphaltene aggregates is a prime challenge in upgrading heavy petroleum feedstocks. Asphaltene Model Compounds: Model compounds for asphaltenes have been developed to simplify understanding the structure and chemistry of natural asphaltenes. In the work a discotic compound, such as TOCP (tetra octyl carboxylate perylene), has a five member aromatic ring is attached to four C18 paraffin chains through ester linkages, 3 ACS Paragon Plus Environment

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and is pyrolyzed under coking conditions. The structure of the model compound is shown in Figure 3 (R. Chianell et al., 2006). Upon pyrolysis, CO2 is released from the ester group leaving a “sea of radicals” which reassemble in a material that is remarkable in its resemblance to natural asphaltenes. The radicals contain the aromatic cores and paraffinic chains. Both may undergo further reactions to form gases, liquids and coke as indicated in Figure 4. All physical properties of natural asphaltenes are replicated as seen by comparing the IR spectra of an Heavy Arab Vacuum Resid (HAVR) with the synthetic asphaltenes as shown in Figure 5. The properties of the synthetic asphaltens are very similar to those of the HAVR and they can be made closer to any natural asphaltene by adjusting the core size and/or the paraffin chain length. It is the reassembling of the components under coking conditions combined with the principle of Micro-Reversibility that leads to the theory of Catalytic Coking. This process is visualized in a simulation that is available on request (A. Adair, 2006).

Figure 3: Discotic Compound (TOCP) (oxygen is red) that thermally produces asphaltenes8. Reference: R. Chianelli et al., 2006


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R02

CO2 Synthetic gases and liquids Synthetic Asphaltenes Synthetic Coke

+ R02

CO2

4R of TOCP producing synthetic asphaltenes8. Figure 4: Thermal Decomposition Reference: R. Chianelli et al., 2006

Figure 5: IR of Discotic compound, synthetic asphaltene and HAVR5. Reference: R. Chianelli, Asphaltene Coking Models: Conventional coking consists of a series of thermal reactions governed by the temperature and time at which the coking occurs. It maybe understood by referring to Scenario 1 that is presented in a way that is analogous to the thermal pyrolysis of the Discotic compound previously discussed.


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As the thermal reactions occur the aromatic cores are separated from the asphaltene and are generally excluded by forming coke through polymerization of the cores. As the temperature increases the coke would tend to become more graphitic. The paraffins are cracking and reassembling forming gas and liquids. A key point is that most of the coke forming compounds Conradson or Micro-carbon are contained in the aromatic cores and as they are excluded in the coke, there is a reduction in Conradson Carbon (CC) in the liquids. There was an 84% of liquid product in the case shown above for Jobo Crude (R. Chainelli et al., 2006). By contrast, the same Jobo crude under hydroconversion conditions (2000 psig H2) produce less coke and poorer liquids because under high pressure many of the cores excluded in the coking reaction are healed with the H2 remaining in the liquids. As a result, the CC materials are returned to the liquid product making them lower in quality. This process yields less coke and poorer liquids the CC reduction being only 56% as compared to 84% in the coking case. These facts are indicated in Scenario 2 seen below. In the previous coking case the experiment was run at the same temperature but with 2000 psig just so the only change in the experiment is the presence of high pressure H2. In the Catalytic Coking (Scenario 3), the presence of the catalyst redistributes the hydrogen pulling it from the cores and CC forming molecules and adding it to the paraffins. This makes a clean separation of the cores and the paraffins resulting in better liquids and reduction of CC molecules and coke precursors in the liquids.


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Experimental: An overall schematic of the reactor set-up is shown in Figure 2. The reactor shell and ancillary piping is ASME rated at 450oC and 1500 psig. The reactor was made of heavy walled stainless steel. However, only atmospheric pressure tests were carried out. The off-gases were passed through the tube side of a double-pipe condenser and collected at atmospheric pressure and temperature. An overpressure valve, set at 7 ACS Paragon Plus Environment

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approx. 6.7 psig was incorporated into the design to ensure safe venting in case of an exothermic overpressure condition. Heating was provided by a furnace with feedback control capable of holding a set temperature at its inner surface, so that input power varied through the course of a test. Three separate heating zones allowed for temperature profiling along the vertical axis of the sample however, all tests were carried out with all zones having equal set points. The 1.5 kg (nominal) sample filled about 24 inches of the reactor central section, and a thermocouple was inserted nominally at the sample center. A set of semi-porous screens retained the sample in position during tests, while allowing passage of hydrogen (or purge argon). The entire reactor/furnace assembly could be rotated into a horizontal position for ease of loading, unloading and cleaning. Temperature in the vapor space of the collection vessel was monitored and condenser coolant flow manually adjusted in order to ensure the off-gas was cooled to room temperature. Off-gas was collected in 100L sample bags, with 0.7L samples extracted both periodically while tests were proceeding, and from the total mixed gas sample at the end of a test. Following a test, the liquid sample in the collection vessel was removed, weighed and kept under an inert gas blanket prior to shipment for analysis. The reactor was the emptied and cleaned of all solid residue, which was also carefully weighed and analyzed. A detailed description may be found in reference (E. Hauptmann, 2008). A range of nanoparticle-based catalysts suitable for upgrading heavy crude oil were tested as described below. Preliminary tests on small batch samples of Cold Lake Bitumen were initially encouraging and thus, larger sample tests were undertaken. In a tyical experiment, a sample of least 1.5 kg was to be heated to 350oC while continuously passing 6 SCFH of hydrogen through the sample. Following this, the sample was to be heated quickly to either 420, 450 or 500oC, either at atmospheric pressure, or in one case, while held at 1500 psig. Catalyst concentrations of either 0.1% to1.0% were to be tested. Test # Catalyst % Final T0C Hours

1 0.0 420 1.0

2 0.23 400 1.5

3 0.96 420 1.0

4 0.85 420-480 1.0 – 0.5

Table 1. Summary of test conditions. Table 1 shows the designated Test #, measured catalyst concentration, actual final temperature and time held. The raw Cold Lake Bitumen (from of Western Oil Sands Inc.) sample was analyzed for composition and properties. Analysis of the solids was by standard practice in the petroeluming refining industry (J. Speight, 2002).


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Figure 6 Schematic diagram of reactor set-up.

Results for Catalytic Coking of Cold Lake Bitumen: Several examples will now be discussed showing the Catalytic Coking model described below that fits the observed real feed data. We concentrate on the resulting asphaltene destruction and coking precursor destruction as predicted by the model. It should be remembered that the model predicts only hydrogen redistribution will occur in thermodynamic allowed cases. Hydrogen will be redistributed from asphaltene core to saturated molecules that split off from the cores as the free radicals formed are healed by the hydrogen transfer process. Saturates and liquids that are stable at coking temperatures will be unaffected unless cracking conditions are reached. Table 2 shows the significant results of the first three coking runs. The experiments were performed under 1 atm of H2. The hydrogen pressure remains a variable to be optimized. Test 2 shows a significant (more than 50%) reduction in both the asphaltenes and coking precursors as predicted. This reduction of the “bad actors” is accompanied by an expected increase in API, rendering the synthetic crude ready to “pipeline”. Coke also increases as the model predicts. A significant reduction in sulfur is also noted.


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Test

Tmax °C

API

CC

Bitumen Test 1 (no cat) Test 2 (0.206gm) Test 3 (0.955gm) Test 4 (0.845gm)

420 420 420 450

12.4 14.0 21.0 20.2 22.4

7.59 8.14 3.65 4.20 1.38

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Asphaltenes C5 10.89 6.21 3.02 2.47 1.14

Coke%

S

11.3 20.0 15.5 14.5

4.30 3.98 2.98 3.29 2.95

Table 2 Results of Catalytic Coking of Cold Lake Bitumen Table 2 shows the Test #, catalyst concentration, final temperature and time held (as in Table 1) with the additional summary of a few key results.

Test # Liquid % Solid % Gas % Test # API Viscosity cSt. Bromine # Asphaltene %

1 82.1 11.8

1 14.7 99.9 18 5.2

Test # Carbon wt.% Vanadium Sulfur

1 61 13 4

Test # Hydrogen %

1 0

Mass Distribution 2 79.9 27.0 Liquid Characteristics 2 3 21.0 20.2 7.1 9.4 22 28 3.1 3.6 Solid Sample Characteristics 2 56 16 3 Gas Characteristics 2 0

3 80.3 15.7

4 74.9 15.9 4.7 4 022.4 6.5 18 1.1

Crude 12.4 199.0 20 10.8

3 73 21 7

4 75 31 8

3 0

4 80

Table 3 Summary of key results. (API Gravity @ 60 0F, Viscosity, cStokes @ 122 0F, Asphaltenes, wt.%) The summary of results in Table 3 shows significant upgrading of the raw bitumen sample can result even with modest amounts of catalyst. As an example, Test 3 ( 0.96% catalyst) yielded over 80% liquid having an API gravity of 20.2 (raw sample API of 12.4), a viscosity of 9.4 cStokes (raw sample 199.0) and a Bromine # (an improved Bromine# is related to an increase in oxidative stability) of 28 (raw sample 20) (J. Speight, 2002). Test 2, with only 0.23% catalyst also yielded nearly 80% liquid having 21 API, a viscosity of 7.1 cStokes, and a Bromine # of 22! Test 4, with 0.85 % catalyst, but with a holding temperature of 450oC, produced a similar high quality liquid product, but with slightly lower liquid yield (nearly 75%). Taken together, the results indicate the nanoparticle catalyst is highly efficient as an upgrader for bitumen, and shows great 10 ACS Paragon Plus Environment

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promise for integration into SAGD wellhead installations, as well as more traditional refinery upgrading processes. The observed API increase from 12.4 to 20.2 makes the product suitable for pipelining replacing the currently used “Dilbit” technology in which the crude is diluted with a lighter oil (Dilbit, 2013).

Figure 7 Viscosity vs. temperature for Test 2 Figure 7 Viscosity vs. temperature for Test 2: 0.23% catalyst (by assuming a Viscosity Index similar to SAE 5W oil), and for Test 1, no catalyst. The viscosity at 7.5 oC (45.5 0F) is an important variable for pumping and field collection from a SAGD site. Figure 12 shows a projected viscosity in the range of 60 cStokes at 45.5 0F for bitumen upgraded with a nanoparticle catalyst, based on data from Test #2 (at 122 0F). Figures 8, 9, 10, and 11 shows in graphic form the product properties for API gravity, Sulfur and C/H ration for test 1, 2, 3 and 4. Table 2 previously showed the large increase in overall sample API gravity when processed with RSC catalyst. Figures 7, 8, 9, and 10 show that this improvement occurs largely with products in the 400 - 975 0F range. Test 4 (0.85% catalyst) also showed significant improvement in API for products distilled above 975 0F. These figures also show that carbon/hydrogen ratio is higher at higher temperatures, consistent with destruction of asphaltenes in the original sample.


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Figure 7 Test 1

Figure 8 Test 2 12 ACS Paragon Plus Environment

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Figure 9 Test 3

Figure 10 Test 4


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Discussion Conventional Coking: Catalytic Coking Asphaltene Reduction: The above theory predicts that addition of catalyst to the coking process will redistribute the hydrogen to the paraffins leading to an increase in coke and a reduction in coke forming entities (CC), and asphaltenes. This result is a “separation” of carbon in useful and clean liquids and carbon that is hydrogen poor, contains impurities and is not useful for liquid fuels. In addition, the heavy bitumen now becomes a synthetic crude that is suitable for a pipeline and requires less upgrading in the refinery. According to the above theory the ultimate fate of the asphaltenes can be predicted. Asphaltenes are typically 33 – 45 % aromatic carbon and 55 – 65% aliphatic carbon. As indicated in Figure 11, the final separation between aromatic and aliphatic carbon can be predicted from the carbon to hydrogen of the starting crude. For example the HAVR previously discussed has a starting C/H ratio of 1.10. This predicts if the catalytic separation is complete a 45% aromatic/55% aliphatic will result. The saturates will be added to the liquid product and the aromatic carbon rejected as coke. Of course the above theory is dependent on several factors: simplified thermodynamics that predicts under low pressure the following is true, Methane is the stable product and excess carbon tends to graphite. It is also tassumes that Catalytic Micro – Reversibility is operating:

C + H2

Low Pressure

CH4

In real processes complex kinetics will take place and time and temperature will become crucial for accurate predictions. It should also be noted that thermal cracking needs to be considered and for optimum product quality lower temperatures are preferred. In addition it should be noted that liquid products are already in equilibrium and will not be further modified by the hydrogen redistribution method described above.

HAVR C/H ratio 1.10

Figure11 Predicted % Aromatics/Aliphatics vs. C/H Ratio 14 ACS Paragon Plus Environment

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Conclusions: Test 3 tests the effect of increased catalyst. The results are similar to the previous test but not quite as dramatic. The asphaltene reduction is greater but the coke precursor number (CC) is not as high as Test 2. This result indicates the convoluting effect of H2. The MoS2 catalyst may be returning some of the “core radicals” to the feed as they are “healed” with hydrogen as in the hydroconversion scenario described above. This would be consistent with the lower sulfur reduction that is observed. The “healed cores” are returned to the liquids resulting in a lower quality, lower API and reduced coke as seen in Table 3. Test 4 is the best of the series with the lowest CC, asphaltene content and sulfur content. Test 4 was conducted at a higher temperature. The conclusion of these tests is that Catalytic Coking process developed by Refinery Science Corporation results in the destruction of asphaltenes and Conradson Carbon (coke precursors). This results in a lower viscosity and higher quality liquids. An examination of the liquid quality (reproduced elsewhere in this report) shows the largest increase in API occurs in the 975 °F+ fraction of the crude. This is also consistent with the destruction of the asphaltenes as predicted by the theory. A theoretical model has been developed for catalytic coking: that offers support for the results observed in the current series of tests. The model follows a stepwise development in the understanding of asphaltene structures and the processes that can affect their conversion. The model predicts addition of catalyst to the coking process will redistribute hydrogen to the paraffins, leading to an increase in coke, and a reduction in coke forming entities such as Conradson Carbon (CC) and asphaltenes. This result is a “separation” of carbon into useful clean liquids, and carbon that is hydrogen poor, contains impurities and is not useful for liquid fuels. In addition, the heavy bitumen now becomes a synthetic crude that is suitable for shipping by pipeline and requires less upgrading in the refinery. More needs to be done to optimize the process and further develop the theory: • Optimize and understand the effect of H2 pressure. • Optimize and understand the effect of catalyst. • Optimize and understand the effect of temperature. Based on the initial results it seems clear that the process can further be improved and optimized. Nevertheless, these results indicate that a new previously unrecognized process useful for upgrading heavy petroleum bitumens and tars has been discovered.

Acknowlegements: We would like to thank our collegues at Western Oil Sands, Alberta, Canada for their assistance and advice. They also provide us with the Cold Lake Bitumen.


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References: A. H. Adair. (2006) Asphaltene Simulation V1.2, Refinery Science Corporation. R. R. Chianelli, A. Mehata, J. Pople, L. Carbognani Ortega. (2006). Self Assembly of Asphaltene Micelles: Synchrotron, Simulation and Chemical Modeling Techniques Applied to Problems in the Structure and Reactivity pf Asphaltenes. Asphaltenes, Heavy Oils and Petroleomics. Chapter 15. Ed. OC Mullins, EY Sheu, AG Marshall, Springer Pub Co., New York. R. R. Chianelli, M. H. Siadati, M. Perez De la Rosa, G. Berhault, J. P. Wilcoxon, R. Bearden, Jr. and B. L. Abrams. (2006) Catalytic Properties of Single Layers of Transition Metal Sulfide Catalytic Materials, Catalysis Reviews, 48, 1-41. R. R. Chianelli, G. Berhault, & B. Torres. (2009) Unsupported Transition Metal Sulfide Catalysts: 100 years of Science and Application, Catalysis Today, 147, 275-286. R .R. Chianelli. (2013) Personal communication via electronic mail, unpublished work. Dilbit.

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http://en.wikipedia.org/wiki/Dilbit E. G. Hauptmann, (2008) Development of a Thermally-Intensive Reactor and a Process for Upgrading Heavy Crude Oil. Green Chemistry And Engineering, International Conference On Process Intensification And Nanotechnology. J. Speight. (2002) Handbook of Petroleum Product Analysis. John Wiley & Sons, Inc. O. Weisser & S. Landa. (1973) Sulfide Catalysts Their Properties and Applications, Pergamon Press, New York. T. F. Yen. (1975). The Role of Trace Metals in Petroleum. Ann Arbor Science, MI-USA.


Conversion of Heavy Tar Sands with Asphaltene Chemical Structures

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