Energy Fuels 2010, 24, 1640–1645 Published on Web 02/04/2010
: DOI:10.1021/ef901470j
Comparative Kinetics and Thermal Behavior: The Study of Crude Oils Derived from Fosterton and Neilburg Fields of Saskatchewan Nader Mahinpey,* Pulikesi Murugan, and Thilakavathi Mani Department of Chemical and Petroleum Engineering, Schulich School of Engineering, The University of Calgary, Calgary, Alberta T2N 1N4, Canada Received December 2, 2009. Revised Manuscript Received January 22, 2010
Pyrolysis and combustion characteristics of two different crude oil samples obtained from Fosterton (medium oil) and Neilburg (heavy oil) fields in Saskatchewan were studied and compared using the results of thermogravimetry (TG) and differential thermogravimetry (DTG) analyses. In addition, the properties of whole oil and asphaltene were determined by means of proximate and ultimate analyses. The analyses indicate that asphaltene from both Fosterton and Neilburg fields has a lower volatile matter and ash content as well as higher fixed carbon values when compared to the values of the respective whole oil. From the elemental analysis, it was determined that the H/C ratio is approximately the same for both reservoirs whole oil and asphaltenes. The reaction region, peak, and burnout temperatures of the samples were also determined. The Arrhenius equation provides kinetic data: activation energy, pre-exponential factor, and order of the reaction. The kinetic analysis showed similar activation energy for the combustion of coke produced from Neilburg and Fosterton oils, as 129.5 and 127 kJ/mol, respectively. The activation energy for Neilburg and Fosterton asphaltenes were 117.7 and 93.46 kJ/mol, respectively.
to 11 points. High oil recoveries were achieved for all runs and ranged from approximately 53 to 74% original oil-in-place. Crude oil is a complex mixture of hundreds of different chemical species consisting mostly of hydrocarbons. The ISC process involves a variety of chemical reactions in the presence of oxygen. Among them, low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO) are the dominant ones. Dependent upon the type of the oil, the nature of these reactions varies. LTO reaction yields water and partially oxygenated compounds, while HTO produces carbon oxides and water. The crude oil sample is separated into smaller fractions, with each fraction having a different composition and different molecular-weight species. Each fraction consists of four solubility classes referred to collectively as saturates, aromatics, resins, and asphaltene (SARA). Karacan and Kok3 studied the pyrolysis behavior of SARA fractions to determine the effect of each constituent on the overall pyrolysis behavior of oils. Asphaltene is usually defined as the pentane-soluble and benzene-insoluble fraction of crude oil. Asphaltene is the strongest fraction present in the oil, which gives the maximum amount of energy during pyrolysis and combustion of crude oil. Thermogravimetric techniques have considerable significance in the determination of the changes in properties, such as composition, decomposition characteristics, calorific effects, kinetics, and proximate analysis. Thermogravimetric analysis (TGA) measures the weight change as a function of time and temperature, while the substance is subjected to a controlled temperature program.4,5 The review of TG analysis
1. Introduction According to the Canadian Association of Petroleum Products (CAPP), Canada is the third largest producer of natural gas, the fifth largest energy producer, and the seventh largest producer of crude oil in the world. The Canadian oil industry produces over 2.6 million barrels of oil per day and is a major player in the global crude oil market.1 Conventional crude oils are classified into light, medium, or heavy according to their measured American Petroleum Institute (API) gravity. Heavy oil is often defined as anything less than 22° API gravity and refers to oil with a thick uniformity that does not flow easily. Light oil can flow naturally to the surface and is one of the world’s largest petroleum resources. The recovery of heavy oil remains a key technical challenge because of the extremely high viscosity. The most common way to overcome this challenge is via in situ combustion (ISC). ISC, sometimes called “fireflood”, is a thermal-enhanced oil recovery technique, in which heat is generated and propagated along the reservoir. Heat is generated in the reservoir by igniting a part of the original oil-in-place (OOIP) to reduce the oil viscosity, thereby improving the flow of the unburnt region. In this process, the residual oil undergoes significant physical and chemical changes, forming a solid or semi-liquid type of material called “coke”. Abuhesa et al.2 compared the conventional and catalytic ISC process for oil recovery and found that the presence of a catalyst advanced the combustion reactions and the resultant oil was upgraded by up *To whom correspondence should be addressed: Department of Chemical and Petroleum Engineering, Schulich School of Engineering, The University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada. Telephone: (403) 210-6503. Fax: (403) 284-4852. E-mail:
[email protected]. (1) http://www.capp.ca/canadaIndustry/oil/Pages/default.aspx. (2) Abuhesa, M. B.; Hughes, R. Comparison of conventional and catalytic in situ combustion processes for oil recovery. Energy Fuels 2009, 23, 186–192. r 2010 American Chemical Society
(3) Karacan, O.; Kok, M. V. Pyrolysis of crude oils and their fractions. Energy Fuels 1997, 11, 385–391. (4) Murugan, P.; Mahinpey, N.; Mani, T. Pyrolysis and combustion kinetics of Fosterton oil using thermogravimetric analysis. Fuel 2009, 88, 1708–1713. (5) Murugan, P.; Mahinpey, N.; Mani, T. Thermal cracking and combustion kinetics of asphaltenes derived from Fosterton oil. Fuel Process. Technol. 2009, 90, 1286–1291.
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: DOI:10.1021/ef901470j
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Table 1. Physical Properties of Fosterton and Neilburg Oils reservoir name oil description 3
density (kg/m at 15 °C) viscosity at 20 °C (mPa s) saturates aromatics resins asphaltenes unrecovered
Fosterton
Neilburg
Swift current medium
Lloydminster heavy 959.5 (15.8° API) 1700
930.2 (20.5° API) 197 SARA Analysis (wt %) 39.8 30.2 8.8 12.8 8.4
40.3 29.0 19.2 9.5 3.8
for fuel characteristics and kinetics concluded that thermal methods were important not only theoretically but also from a practical point of view.6 The oil from each field is different. The origin of the oil reservoir might make some influence on the coke behavior. Therefore, the comparison of the Fosterton field (medium oil) with the Neilburg field (heavy oil) was made based on the kinetic analysis performed. In this process, both oils were converted into coke and subsequently compared for their quantity. In addition, the comparison of crude oil and its asphaltenes was studied on the basis of TGA data. This kinetic analysis data will be used in designing the in situ combustion process.
Figure 1. Schematic diagram of the TGA apparatus.
Varian digital gas flow meter was used to measure the flow rate of nitrogen and air supplied to the TGA. The schematic diagram of the apparatus used for the study is shown in Figure 1. 2.3. Experiments for Proximate and Ultimate Analyses. Proximate analysis for the whole oil and asphaltene samples was conducted using TGA.9,10 All experiments consisted of three different steps: drying, devolatilization in a nitrogen atmosphere, and combustion with oxygen. Initially, about 10 mg of samples was kept at 25 °C for 4 min in a nitrogen atmosphere and then continued heating. The moisture content was considered as the mass loss when the sample was heated at 85 °C/min until 110 °C, with a nitrogen flow rate of 45 mL/min. The same temperature was maintained for 5 min. The devolatilization step started at 110 °C, with a heating rate of 80 °C/min up to 900 °C, and was held for 5 min at 900 °C. Once a constant weight loss was reached, the final temperature was held constant for 7 min in an air atmosphere to allow for the complete combustion of the remaining char. Ultimate analysis was carried out using a Perkin-Elmer 2400 CHNS/O analyzer. 2.4. Non-isothermal Pyrolysis and Combustion. About 40 mg of sample F1 was pyrolyzed in a nitrogen atmosphere. The nonisothermal pyrolysis runs were performed at a heating rate of 10 °C/min up to the final temperature of 425, 500, 550, and 600 °C. The final temperature was maintained for 30 min to facilitate coke formation. Coke produced from pyrolysis was used for subsequent oxidation runs. In a non-isothermal oxidation run, coke produced from pyrolysis was heated to 800 °C in an air atmosphere at 10 °C/min and the final temperature was maintained for 30 min to ensure completion of the oxidation reaction. The weight loss versus temperature data for each of the experiments were saved for further analysis. Similar experiments were conducted for samples F2, N1, and N2. 2.5. Isothermal Pyrolysis and Combustion. In isothermal pyrolysis, sample F1 was placed in a nitrogen atmosphere and held at 425 °C, at which the production of coke yield was maximized and subsequent rate measurements were the most accurate. Isothermal experiments were conducted at 25 °C intervals from 375 to 500 °C on the coke from asphaltenes. At higher temperatures, the reaction was too rapid, and below 375 °C, the combustion rate became prohibitively slow for TGA tests. Similar experiments were conducted for samples F2, N1, and N2. Thermogravimetry (TG) and differential thermogravimetry (DTG) curves were continuously recorded and presented as a
2. Experimental Section 2.1. Materials. The crude oils used in this study were obtained from the Fosterton field, Swift current region, and Neilburg field, Lloydminster region, of Saskatchewan, Canada. Fosterton oil is medium oil, and Neilburg oil is heavy oil. The main physical properties of both of the oils are listed in Table 1. Fosterton (medium) oil has an API gravity of 20.5° (930.2 kg/ m3), and Neilburg (heavy) oil an API gravity of 15.8° (959.5 kg/ m3). The content of saturates and aromatics for both of the crude oils had approximately the same values. The asphaltene fractions were recovered from the oil by ultrasonic dispersion in 40 volumes of n-pentane, overnight flocculation, and vacuum filtration through 0.8 μm filter paper.7 It is to be noted that Fosterton asphaltene (12.8 wt %) content was higher than the Neilburg asphaltene (9.5 wt %). Because reservoir sand has shown significant catalytic activity during ISC,8 the oil and its asphaltene fractions were uniformly premixed with clean sand obtained from the core of the same reservoir in the ratio of 1:4. The samples were designated as sample F1 for Fosterton asphaltene plus sand, F2 for Fosterton whole oil plus sand, N1 for Neilburg asphaltene plus sand, and N2 for Neilburg whole oil plus sand. To remove the effect of sand concentration differences, the TGA results were normalized to 1 mg of pure original sample. 2.2. Equipment. A thermogravimetric analyzer DuPont Instruments 951 TGA-Thermal Analyzer 2100 was used to conduct isothermal and non-isothermal thermogravimetric experiments on the crude oil and its asphaltene. This instrument is capable of directly measuring and recording the weight loss of whole oil, asphaltene, and their products during experiments. A (6) Kok, M. V. Recent developments in the application of thermal analysis techniques in fossil fuels. J. Therm. Anal. Calorim. 2008, 91 (3), 763–773. (7) Freitag, N. P.; Exelby, D. R. A SARA-based model for simulating the pyrolysis reactions that occur in high-temperature EOR processes. J. Can. Pet. Technol. 2006, 45 (3), 38–44. (8) Ranjbar, M. Influence of reservoir rock composition on crude oil pyrolysis and combustion. J. Anal. Appl. Pyrolysis 1993, 27, 87–95.
(9) Beamish, B. B. Proximate analysis of New Zealand and Australian coal by thermogravimetry. N. Z. J Geol. Geophys. 1999, 37, 387–392. (10) Mayoral, M. C.; Izquierdo, M. T.; Andres, J. M.; Rubio, B. Different approaches to proximate analysis by thermogravemitry analysis. Thermochim. Acta 2001, 370, 91–97.
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Table 2. Proximate (wt % Dry Basis) and Ultimate (wt % Wet Basis) Analyses of the Samples Fosterton oil asphaltenes
whole oil
Neilburg oil asphaltenes
Fosterton oil
Neilburg oil
whole oil
coking temperature (°C)
coke from asphaltene (wt %)
coke from whole oil (wt %)
coke from asphaltene (wt %)
coke from whole oil (wt %)
425 500 550 600
64.35 56.7 50.4 47.35
40.76 39.65 38.45 33
61.49 48.53 39.29 26.68
21.79 15.52 7.53 6.03
volatile matter fixed carbon ash
Proximate Analysis (wt %) 23.9 89.9 61.5 75.1 9.7 38.1 0.88 0.37 0.39
91.1 8.7 0.19
C H N S Oa H/C ratio
Ultimate Analysis (wt %) 55.4 73.6 82.6 5.2 9.2 7.8 0.5 0 1.1 1.7 2.8 6.5 37.2 14.4 2 1.1 1.5 1.1
85.1 11.2 0.2 2.3 1.2 1.6
a
Table 3. Quantity of Coke Produced by Pyrolysis from Different Sources
from asphaltenes than from the whole oil. The reason may be due to the light components present in the oil, which lead to more distillation.10 For both Fosterton and Neilburg asphaltenes, nearly the same amount of coke was produced at the coking temperature of 425 °C. However, for the whole oil, the Fosterton field produced more coke than the Neilburg field at the same coking temperature. The asphaltene constituent generally produces coke yields varying from almost 25 wt % to more than 60 wt %, and the value is matched with the results shown in Table 3. During the thermal decomposition of asphaltene, the majority of the organic nitrogen, sulfur, and metallic constituents originally present in the asphaltene invariably concentrate in the nonvolatile coke, even acting as chemical initiators to coke formation. Thus, the initial step in the formation of coke from asphaltene is the formation of volatile hydrocarbon fragments and non-volatile heteroatom-containing systems. The latter products are undoubtedly insoluble in the surrounding hydrocarbon medium, and the next step is gradual carbonization of such entities to form coke.12 3.3. Non-isothermal Coke Oxidation. Non-isothermal oxidation progression for cokes obtained from asphaltenes and whole oil from the Fosterton and Neilburg fields at 425 °C are shown in Figure 2. Coke samples from both whole oil and asphaltene of the Fosterton field started oxidation at approximately the same temperature. However, once the reaction proceeds, the Fosterton whole oil oxidized at a faster rate than the asphaltenes. This trend was contradictory with the Neilburg oil, for which both the coke samples followed the same pattern for oxidation at almost all times (Figure 2b).13 In addition, for both Fosterton and Neilburg, the coke derived from whole oil displayed a maximum oxidation rate at a slightly lower temperature than that from asphaltenes. From Table 4, it was observed that, as the coking temperature increased, the temperature corresponding to the maximum oxidation rate also increased. Fosterton oil showed a higher oxidation rate than the Neilburg oil because of the presence of a higher amount of asphaltene content. In the non-isothermal oxidation run, three distinct reaction regions were observed in crude oils and asphaltenes (Table 5). The first region occurred between 90 and 360 °C, which represented LTO. The second region FD was found in the range of 360-480 °C in Fosterton oil and was not observed in the Neilburg oil. The final region of crude oil inferred from the TG/DTG curves takes place between 480 and 580 °C and is identified as HTO. The burnout temperature represents the temperature at which the oxidation
By difference.
percentage of the initial sample weight. All experiments were performed twice to establish reproducibility.
3. Results and Discussion 3.1. Proximate and Ultimate Analyses. Proximate and ultimate analyses of whole oil and asphaltenes are given in Table 2. The volatile matter of the sample corresponds to the weight loss occurred between 110 and 900 °C under a N2 atmosphere as a consequence of thermal decomposition. Fosterton samples contain a lower percentage of volatile matter and a higher amount of fixed carbon than Neilburg samples. The fixed carbon is directly measured by observing the weight loss that takes place from the volatile free weight to the ash content. Because Fosterton asphaltene contains a highest percentage of fixed carbon, more coke yield was expected from Fosterton asphaltene compared to the Neilburg samples. The results from the table indicate that the ash content of all samples was less than 1%. The results of the ultimate analysis and H/C ratio are also shown in Table 2. The carbon and hydrogen contents of the asphaltene were lower than whole oil, because of the release of volatile components, including CO, CO2, and light alkanes. Asphaltenes are rich in heteroatoms, nitrogen, sulfur, and especially oxygen compared to whole oil. From the elemental analysis, it can be determined that the H/C ratio is lower for asphaltene of both reservoirs compared to the whole oil. The decrease in the H/C ratio for asphaltene indicates hydrogen transfer from heavier structures to lighter ones and carbon rejection from lighter components to heavier ones to produce coke. Savage and Klein explained that, in the absence of an external hydrogen donor, asphaltenederived free radicals could abstract hydrogen only from the asphaltene, making the remaining asphaltenic core increasingly refractory and hydrogen-deficient. These reactions could transform the core from being soluble in toluene to being insoluble, and hence, it would appear as coke in the solvent extraction procedure.11 3.2. Coke Formation. The quantity of coke produced at different coking temperatures for the four samples is compared in Table 3. As usual, the amount of residual fuel decreased as the coking temperature increased. At similar coking temperatures, higher amounts of coke were obtained
(12) Speight, J. G. The effect of asphaltenes and resin constituents on recovery and refining processes. Oil Gas Sci. Technol. Rev. IFP 2004, 59, 479–488. (13) Ren, Y.; Mahinpey, N.; Freitag, N. Kinetic model for the combustion of coke derived at different coking temperatures. Energy Fuels 2007, 21, 82–87.
(11) Martı´ nez, M. T.; Benito, A. M.; Callejas, M. A. Thermal cracking of coal residues: Kinetics of asphaltene decomposition. Fuel 1997, 76, 871–877.
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Figure 2. Non-isothermal oxidation of coke derived from 425 °C for (a) Fosterton and (b) Neilburg samples.
Figure 3. Comparison of combustion curves of coke prepared from different sources: (a) Fosterton asphaltene and whole oil and (b) Neilburg asphaltene and whole oil at 375 and 400 °C.
Table 4. Comparison of Temperatures at Maximum Oxidation Rates Fosterton oil
Neilburg oil
coking temperature (°C)
coke from asphaltene (°C)
coke from whole oil (°C)
coke from asphaltene (°C)
coke from whole oil (°C)
425 500 550 600
580 583 587 600
540 560 560 560
482 491 499 503
480 488 490 497
Table 5. Reaction Intervals and Burnout Temperatures of Whole Oil and Asphaltene sample
LTO (°C)
FD (°C)
HTO (°C)
burnout (°C)
Fosterton oil Fosterton asphaltene Neilburg oil Neilburg asphaltene
90-360 below 400
360-480 410-470
480-580 470-560
580 560
90-370 below 400
400-480
370-560 480-560
560 560
completed, and these have also been indicated in Table 5 for the crude oils and asphaltenes. Results showed that the heavy oil (Neilburg) exhibits a lower burnout temperature of 560 °C compared to the medium oil (Fosterton), which coincides with the results of Kok and Keskin.14 For asphaltenes derived from both fields, all three regions (LTO, FD, and HTO) were observed at approximately the same temperature range. LTO is observed below 400 °C with the minimum weight loss because of the fact that asphaltene molecules are so heavy and resistant that oxygen does not affect this fraction until very high temperatures are reached.15 3.4. Comparison of Isothermal Combustion Rates. A comparison plot of the coke combustion for Neilburg and
Figure 4. Comparison of combustion curves of coke prepared from different sources: (a) Fosterton asphaltene and whole oil and (b) Neilburg asphaltene and whole oil at 475 and 500 °C.
(14) K€ ok, M. V.; Keskin, C. Comparative combustion kinetics for in situ combustion process. Thermochim. Acta 2001, 369, 143–147. (15) Kok, M. V.; Karacan, C. O. Behavior and effect of SARA fractions of oil during combustion. SPE Reservoir Eval. Eng. 2000, 3 (5), 380–385.
Fosterton fields provides much information on the combustion pattern. The plots at temperatures of 375 and 400 °C and higher temperatures of 475 and 500 °C are shown in Figures 3 and 4, respectively. At lower combustion temperatures of 1643
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: DOI:10.1021/ef901470j
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Table 6. Comparison of Kinetic Parameters for Fosterton and Neilburg Oils Fosterton oil
Neilburg oil
kinetic parameters
asphaltene
whole oil
asphaltene
whole oil
activation energy, E (kJ/mol) pre-exponential factor, A (min-1) order of reaction, n
93.46 9.59 105 0.7-0.8
127 1.6 108 unity
117.7 0.44 108 0.4-0.9
129.5 2.69 108 0.5-0.7
375 and 400 °C, coke from Neilburg sources burns more slowly compared to the Fosterton field. Figure 3a (375 °C) shows that, during the first 150 min, the curves nearly coincided, representing a similar combustion pattern. After 150 min, the coke formed from asphaltenes showed a slightly higher rate of combustion. At higher temperatures, a different trend was observed for the combustion of coke from the Fosterton fields. The combustion of coke from Fosterton asphaltenes is less temperature-sensitive than coke from the whole oil at 475 and 500 °C. In contrast, the Neilburg oxidation rates are the same for coke from both oil and asphaltenes. The difference between the Neilburg and Forsterton samples becomes significant when the temperature increases.16 At 500 °C, the combustion curves of coke obtained from both samples overlapped in the first 4 min, showing a similar combustion pattern. After 4 min, the coke formed from asphaltenes oxidized faster than the coke from the whole oil. From Figure 4b, it was observed that the coke formed from asphaltenes combusted at a slower rate initially. The curve is convex-shaped at the beginning, indicating that there may be some reactions occurring at this temperature. This may be attributed to oxygen uptake. 3.5. Comparative Combustion Kinetics. Combustion of coke was performed with the coke samples produced from pyrolysis at 425 °C. It was observed that, in higher temperatures (>425 °C), much of the whole oil had evaporated, leaving behind much less oil to be pyrolyzed to coke. Conducting combustion runs on the coke obtained from such high temperatures were not possible, because it was difficult to collect reliable data points to determine the kinetics. The case was the same for coke formed from asphaltenes. To facilitate a direct comparison, the coking temperature was made the same for both the asphaltenes and the whole oil. An isothermal pyrolysis temperature of 425 °C was chosen for both the samples because, at this temperature, the production of coke was maximized. The Arrhenius theory was used for kinetic analysis of data generated by the TG/DTG experiments. The rate of the reaction is given by the following equation: dCA ð1Þ ¼ -kn CA dt kn ¼ Ae-E=RT
Figure 5. Rate constant versus temperature.
Raman, with API gravities of 18.7° and 12.9°, respectively.17 The rate constants at different temperatures were determined and shown in Figure 5. As expected, the rate constant increases with the temperature. Asphaltene conversion has higher rate constants than whole oil. Figure 5 implies that the rate constants of the asphaltenes and whole oil from different fields follow a similar pattern. The order of the reaction n has been determined using the Wilson equation18 " # 1 CA0 n -1 - 1 ¼ τ for n 6¼ 1 ð3Þ CA ðn - 1Þkn ðCA0 Þn -1 where CA0 is the initial weight percent of the sample on the TGA pan, CA is the weight percent of the sample at time τ, n is the order of the reaction, and kn is the rate constant determined from the regression of the data. Equation 3 was used to determine the best fit for different values of n ranging from 0.5 to 1.5. However, for n = 1, eq 1 was implemented rather than eq 3. From the experimental data, it was observed that the order of the combustion reaction was unity for sample F2 and from 0.7 to 0.8 corresponding to the temperatures from 375 to 500 °C for sample F1. The order of reaction for N2 was found to be in the range of 0.5-0.7, while the order of the reaction was from 0.4 to 0.9 for sample N1 at 375-500 °C.16 Overall, a first-order reaction may be considered for the combustion of coke from whole oil and its asphaltenes. Results from the kinetic analysis of combustion reactions for asphaltene and whole oil show that the order of the reaction is almost the same for both fields and the activation energy is lower for asphaltenes compared to the whole oil. With similar information about coke oxidation from more reservoir fields, it may be possible to correlate a relationship for whole oil oxidation derived from the asphaltene oxidation process. Then, a reliable coke combustion model could be obtained on data based on only asphaltene pyrolysis, which can generally be conducted easily and more accurately than pyrolysis of the whole oil. Moreover, coke formed from
ð2Þ
Table 6 showed that the activation energies for Neilburg and Fosterton whole oils were in close agreement, whereas the activation energies for asphaltenes showed a greater discrepancy. The activation energy of asphaltenes increased as the API gravity of the crude oil decreased. Similar results were observed from the Turkish oil fields Raman and Bati (16) Ambalae, A.; Mahinpey, N.; Freitag, N. Thermogravimetric studies on pyrolysis and combustion behavior of a heavy oil and its asphaltenes. Energy Fuel 2006, 20, 560–565. (17) K€ ok, M. V. Use of thermal equipments to evaluate crude oils. Thermochim. Acta 1993, 214, 315–324.
(18) Wilson, J. W. Fluid Catalytic Cracking Technology and Operations; Penn Well Books: Tusla, OK, 1997.
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the asphaltene fraction of oil could be treated as a representative of coke formed from whole oil in ISC field projects. 3.6. Error Analysis. The error analysis of the experimental data for the Fosterton field was performed, and the errors have been presented in Figures 2-4. The weight loss data used in the present work was measured directly from the TG apparatus; hence, the small deviations observed may be due to the instrumental errors. Because the experimental curves of the Neilburg field were obtained from the literature, the error bars for those data was not included in the Neilburg TG curves.
oils, respectively. However, the activation energy for asphaltene combustion of Fosterton and Neilburg oils reveal a larger discrepancy. They are 93.4 and 117.7 kJ/mol, respectively. Asphaltene contains less volatile matter and more fixed carbon compared to whole oil, and that difference makes the asphaltene more suitable as a fuel source for combustion present in whole oil. As a result, asphaltene yields a higher amount of coke during pyrolysis. With asphaltene being the strong fraction present in crude oil, the combustion rate of the asphaltene was smaller to the whole oil. Therefore, the coke produced from the asphaltene burns for a longer period of time, releasing more energy compared to the whole oil. Moreover, for the Fosterton field, the activation energy for asphaltene combustion is less than the whole oil combustion, requiring less energy for the process to initiate. In comparison to the Neilburg asphaltene, the Fosterton asphaltene produced more coke under the same operating conditions.
4. Conclusion In this work, a comparative study has been conducted to investigate the thermal behavior of asphaltene and whole oil from two different reservoirs of Fosterton and Neilburg fields in Saskatchewan. The result of the proximate analysis showed that volatile matter and fixed carbon contents vary with the reservoir. In the combustion of crude oils, three distinct reaction regions were identified as LTO, FD, and HTO. It was found that the heavy oil (Neilburg) exhibits moderately lower burnout temperatures of 560 °C compared to the medium oil (Fosterton oil). The reaction regions were dissimilar for two reservoirs. The activation energy of whole oil combustion was approximately the same for both reservoirs. They are 127 and 129.5 kJ/mol for Fosterton and Neilburg
Acknowledgment. The authors express their appreciation for the financial support of the Petroleum Technology Research Centre (PTRC) and Natural Science and Engineering Research Council (NSERC-RTI). We thank the Saskatchewan Research Council (SRC) for providing an opportunity to work in their laboratory. The authors extend their thanks to Dr. Norman Freitag and Mr. Ray Exelby for their prompt help with the laboratory work.
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