Thermal Behavior and Kinetic Triplets of Heavy Crude Oil and Its

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Thermal behavior and kinetic triplet of heavy crude oil and its SARA fractions during combustion by high pressure differential scanning calorimetry Shuai Zhao, Wanfen Pu, Chengdong Yuan, Xiaoqiang Peng, Jizhou Zhang, Liangliang Wang, and Dmitrii A. Emelianov Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b00399 • Publication Date (Web): 04 Mar 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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Thermal behavior and kinetic triplet of heavy crude oil and its SARA fractions during combustion by high pressure differential scanning calorimetry Shuai Zhao,† Wanfen Pu,*, †, ‡ Chengdong Yuan,*, †, ‡ Xiaoqiang Peng,§ Jizhou Zhang,§ Liangliang Wang,† Dmitrii A. Emelianov‡ †State

Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University,

Chengdu, 610500, People’s Republic of China ‡Department §Research

of Physical Chemistry, Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russia

Institute of Experimental and Detection, Petrochina Xinjiang Oilfield Company, Karamay, Xinjiang

834000, People’s Republic of China

ABSTRACT: In-situ combustion (ISC) has been regarded as an efficient technique concerning the exploitation of heavy oil reserves. In this work, the thermal behavoir of one heavy crude oil and its SARA fractions during combustion was thoroughly investigated using high pressure differential scanning calorimetry (HP-DSC). Two typical isoconversional methods were adopted to determine the variation of activation energy (E) and frequency factor (Ar) vs. conversion degree in the course of reaction, followed by the evaluation of reaction model, f(α), via master plot method. The results indicated that the heavy oil encountered larger thermal release caused by low temperature oxidation (LTO) reactions rather than high temperature oxidation (HTO) reactions, suggesting that appreciable heat could be available within the low temperature range. Saturates showed a notably apparent heat release in the LTO reactions. For aromatics, the exothermic effect at the LTO stage was apparently higher than that at the HTO stage, in contrary to the results detected at atmospheric pressure. Saturates and asphaltenes gave the highest cumulative heat release in the LTO and HTO regions, respectively. The variation of kinetic parameters (E and Ar) vs. conversion degree during combustion

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was quite different for the heavy oil and its SARA fractions, implying their varying reaction mechanisms and pathways. Saturates exhibited the lowest average value of E at the LTO stage, while aromatics and resins gave the lowest average value of E at the HTO stage. The most probable f(α) of LTO interval for the oil and its SARA fractions followed power law reaction models P-0.6, P-0.3, P0.1, P0.05 and P0.2, respectively. The appropriate f(α) for the HTO interval of the oil, saturates and aromatics were chemical process or mechanism non-invoking equations F2.1, F0.8 and F0.6, respectively. Sestak Berggren reaction model SB(0.5, 0.9) and Avrami-Erofeev reaction model A2 were regarded as the rational f(α) for the HTO region of resins. These observations could provide some guidance with regard to the numerical modeling of SARA fractions to simulate the ISC process.

1. INTRODUCTION In recent decades, the heavy oil has become an increasingly significant energy resource due to a declining oil production of conventional oil reserves as well as the rapid rise of global energy demand.1,

2

Thermal recovery techniques, involving in-situ combustion (ISC), supercritical water,

steam injection, binary mixtures, etc., turn out to be extremely promising in terms of the exploitation of (extra) heavy crude oils. ISC is now regarded as the most profitable oil recovery process compared to other thermal recovery methods, which was reported to be roughly two to four times higher energy efficient than steam drive.3 However, ISC is a notably complicated process including multiphase flow, mass transfer, heat transfer and a set of chemical reactions in the reservoir, which allows for combining the advantages of steam injection, flue gas flooding and hot water injection to attain a quite high oil recovery factor.4,

5

Nevertheless, approximately 80% of the ISC projects were

economic and technological failures, predominantly due to a poor understanding of thermal behavior


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and kinetics of heavy oils.6 As agreed by most peers, the reactivity of crude oil, which largely depends on their compositions, mostly determines the thermal behavior and kinetics. Basically, crude oils were split into four compositions, namely, saturates, aromatics, resins and asphaltenes (SARA).7-9 Over the past decades, substantial works had been implemented using thermogravimetry (TG) and differential scanning calorimetry (DSC) to analyze the combustion behavior of crude oils and their SARA fractions.10-13 For instance, the thermal characteristics of two Turkish crude oils and their SARA fractions were investigated by TG.13 The results indicated that for the two crude oils and their SARA fractions, the distillation and low temperature oxidation (LTO) reactions took place at the first reaction stage, and high temperature oxidation (HTO) reactions occurred at the second one. Light fractions (saturates) and heavy fractions (asphaltenes) were susceptible to severe weight loss in the first and second reaction intervals, respectively. The heat release during combustion of the crude oils and their SARA fractions was examined by Kuppe et al.11 using DSC. It was claimed that the cumulative thermal release of resins and asphaltenes was far higher than that of saturates and resins. However, TG and DSC merely operate at ambient pressure, and a high-pressure condition is required for ISC process in reservoirs. To simulate the combustion behavior of crude oils or oil components under the pressure close to reservoir condition, more emphasis should and has been paid to utilize accelerating rate calorimetry (ARC) and high pressure differential scanning calorimetry (HP-DSC) that can provide the high-pressure condition.4, 5, 14, 15 Li et al.5 concluded that an increase in pressure led to higher heat release from combustion reactions, and the chemical structure of hydrocarbons played a consequential role in their exothermic characteristics. Recently, a series of HP-DSC tests to examine


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the thermal behavior of eight C20-C54 n-alkanes was conducted.4 The results revealed that the thermal release of linear alkanes was not dependent on their carbon number, and linear alkanes contributed little to the HTO reactions of crude oils. However, HP-DSC was seldom used to analyze the thermal behavior of combustion of SARA fractions. Combustion kinetics of crude oil has been extensively researched using TG, DSC, HP-DSC, ARC, and ramped temperature oxidation (RTO) instruments.13, 16-19 Generally, kinetics calculation involves model-fitting methods with a single heating rate and model-free methods with multiple heating rates. With respect to the model-fitting method, prior to estimation of the kinetic parameters, frequency factor (Ar) and activation energy (E), the reaction model should be assumed. For example, the reaction model of widely-used Arrhenius method is identified as αn (α represents the conversion degree).20 In 2011, the International Confederation of Thermal Analysis and Calorimetry (ICTAC) strongly recommends employing model-free methods that have some specific advantages relative to model-fitting methods. First, model-free methods can reflect the relation of kinetic parameters vs. conversion degree to disclose the intricate reaction process. Second, they are able to determine the kinetic parameters without the selection of reaction model, which avoids the so-called compensation effect.21, 22 Recently, an advanced master plot method proposed by Shahcheraghi et al.23 was adopted to evaluate the reaction model on the basis of E and Ar. Karimian et al.17 selected two appropriate reaction models for the HTO region of heavy crude oil mixed with limestone matrix using this method. Once the kinetic triplet is determined, the elementary kinetic equation will be readily deconvolved. Nevertheless, the reaction models in the LTO and HTO regions for SARA fractions were rarely investigated.


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In this study, the thermal behavior of one heavy oil and its SARA fractions during combustion was comprehensively studied by HP-DSC technique. The relation of E and Ar vs. conversion degree was determined by two typical model-free methods. At last, the reaction models in the LTO and HTO intervals for the heavy oil and its SARA fractions were obtained referring to an advanced master plot method. The obtained data should be highly valuable for using SARA fractions to model the ISC process.

2. EXPERIMENTAL 2.1. Materials The crude oil sample was derived from Hongqian block in Xinjiang oilfield, China. Some typical properties of the heavy crude oil are listed in Table 1. The SARA fractions were split from this heavy oil referring to the industrial standard of China Petroleum NB/SH/T 0509-2010. All the chemicals (ethanol, heptane, toluene, hydrochloric acid, etc.) were obtained from Chengdu Kelong Chemical Co., China, and employed as received. The components of aromatics used herein were measured by the high performance liquid chromatograph UltiMate 3000 (Thermo Scientific), and pertinent experimental procedures had been described in detail in our recent publication.24 The primary components of aromatics contain 49% of triaromatics and 35% of diaromatics. 2.2. DSC and HP-DSC Analyses In this work, the HP-DSC tests were performed from 30 to 600 oC at 5 MPa by NETZSCH DSC 204 HP Phoenix, and the DSC tests were carried out from 30 to 700 oC using NETZSCH STA 449 F3 Jupiter. Before each test, the thermal analysis system was calibrated as the method stated previously.24 The procedures encompassed placing sample (~0.5 mg), setting constant air flow rate


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(30 ml/min) and heating rates (5, 10 and 15 oC/min), then initiating the experiment. All the runs were carried out at least twice to ensure the accuracy and repeatability of experimental data, and the tests exhibited good consistency with standard errors of ±1 oC. 2.3. Kinetic Triplet Analysis 2.3.1. Methodology of Determining Activation Energy and Frequency Factor Given a series of advantages of model-free methods in comparison with model-fitting methods as described in section 1.1, two typical model-free methods known as distributed activation energy model (DAEM) and Friedman were adopted to evaluate E and Ar. The DAEM (integral isoconversional method) proposed by Vand25 assumes that numerous irreversible first-order parallel reactions with varying rate coefficients take place simultaneously with varying activation energies. The initial form of DAEM can be expressed as:26  t   E 1     exp   Ar  exp   0 0  RT 

 



0 tf

0



t



0

Hdt

   dt  f  E  dE  

(1)

(2)

Hdt

f  E  dE  1

(3)

A more simplified DAEM form (see Eq. 4) was deduced by Miura and Maki.27, 28

E    AR ln  2   ln  r   0.6075  RT T   E 

(4)

The basic equation of Friedman method (differential isoconversional method)21 is expressed as:

ln   i (d / dT ) ,i   ln Ar  ln f ( ) 

E RT ,i

(5)

where α is the conversion degree, E is the activation energy, Ar is the frequency factor, T is the


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absolute temperature, β is the heating rate, R is the universal gas constant, f(E) is the activation energy distribution curve, and H is the heat flow measured by HP-DSC. The E can be evaluated by the slope of the regression lines of ln(β/T2) vs. 1/T for DAEM and ln(β/(dα/dT)) vs. 1/T for Friedman. The Ar can be determined by the intercept of the regression lines of ln(β/T2) vs. 1/T for DAEM. 2.3.2. Methodology of Determining Reaction Model Shahcheraghi et al.23 put forward an innovative and advanced master plot method to evaluate the reaction model. The total variation in the reaction rate as reaction proceeds can be written as:

d  E   A exp     f   dt  RT 

(6)

Differentiating Eq. 6 in terms of α and utilizing chain rule yields:

 d 2   2    dt   1 dA  1 dE  E dT  f       2 2 f     d   A d RT d RT d    dt 

(7)

Combination of Eqs. 1 and 2, we obtain: A 

 E  E  exp    2 RCT  RT 

(8)

Substituting Eq. 8 into Eq. 7 and employing chain rule of differentiation gives:   1 f     Sh      f   d  dt

2     d      dt 2   1 dE d  2         d   E d dt  T     dt  

(9)

Theoretical Sh(α) in the left side of Eq. 9 was estimated using mathematical expressions of some classical reaction models listed in Table 3.17, 21, 23 According to the right side of Eq. 9, experimental Sh(α) was calculated by HP-DSC data. Comparison between theoretical and experimental Sh(α)


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facilitated to select the rational reaction model. Additionally, if the discrepancy between the minimum and maximum values of E is no greater than 20-30% of the average E, Eq. 9 can be further simplified as:   1 f     Sh     d f     dt

 2    d    2    dt  2      d   T            dt   

(10)

where f(α) is the reaction model, and C represents a constant value.

3. RESULTS AND DISCUSSION 3.1. Thermal Behavior of Heavy Crude Oil Characterized by HP-DSC Technique The HP-DSC profiles for the heavy oil at three heating rates (5, 10 and 15 oC/min) and 5 MPa are presented in Figure 1. Consistent with previous results measured by DSC and HP-DSC,5, 13, 24, 29 two distinctive exothermic regions, so-called LTO and HTO, were observed in the course of heating. In addition, the peak and ending temperatures of LTO and HTO intervals were all shifted to higher temperature ranges with the elevated heating rate because of thermal lag at a higher heating rate.30 The data at the heating rate of 10 oC/min were utilized as a reference in the following analysis including HP-DSC basic parameters such as heat flow, peak temperature, etc. The LTO and HTO reactions took place from 30 to 373 oC and from 373 to 494 oC, respectively, as listed in Table 2. For the LTO interval, the oxygen addition reactions to yield hydroperoxides at the initial stage coupled with the isomerization and decomposition reactions of these hydroperoxides at the late stage were considered as the dominating reaction pathways based on the classical free radicals theory.31-33 The oxygen addition reactions could occur at ambient conditions.31, 32 As is widely accepted, the thermal release at the HTO stage is mainly caused by the combustion of coke formed at fuel decomposition


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(FD) stage that is commonly detected by TG/DTG profiles.34-36 To better illustrate the thermal behavior at the high-pressure condition for heavy oil, the DSC profile was compared with HP-DSC one at 10 oC/min as shown in Figure 2. The heat flow in the LTO and HTO intervals under 5 MPa peaked at 251 and 465 oC with a value of 67.6 and 12.5 mW/mg, respectively, whereas that under atmospheric pressure peaked at 380 and 529 oC with a value of 1.9 and 3.88 mW/mg, respectively. The heat enthalpy at the LTO and HTO stages under 5 MPa was 19.7 and 5.4 kJ/g, respectively, much higher than that under atmospheric pressure (1.3 and 2.6 kJ/g). The facts verified that an increment in pressure intensified exothermic oxidative reactions, which was predominantly due to two aspects. First, the increased pressure resulted in the weaker evaporation effect, which accordingly kept a higher amount of crude oil in the sample holder. Besides, the acquirable oxygen for oxidation reactions in both vaporized phase and liquid phase was amplified with the elevated pressure.4, 5 In addition, it was interesting that the heavy crude oil was susceptible to larger thermal release caused by LTO reactions rather than HTO reactions under high oxygen partial pressure, which was in contrast to the phenomenon observed from DSC curves (given in Figure 2). This observation manifested that a considerable amount of heat could be obtained in the LTO temperature range under the high-pressure condition, which was a positive signal in terms of facilitating the sustainability and propagation of combustion front. 3.2. Thermal Behavior of SARA Fractions Characterized by HP-DSC Technique Figure 3 exhibits the HP-DSC profiles of SARA fractions separated from the heavy oil at three heating rates (5, 10 and 15 oC/min) and 5 MPa. Being identical to the heavy crude oil, the whole reaction process of SARA fractions was classified into two intervals, i.e. LTO and HTO. For


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saturates, only one notably exothermic peak was detected with a value of 63.8 mW/mg at 206 oC in the LTO interval (from 30 to 375 oC), accompanied by a weak peak with a value of 6 mW/mg at 456 oC

in the HTO interval (from 375 to 480 oC). The result elucidated that saturates almost completely

reacted with oxygen at the LTO stage, and thus little fuel was deposited to contribute to the HTO reaction, which was in line with the phenomenon observed from DSC curves.13,

24

Comparison

between DSC and HP-DSC profiles evidenced that saturates contributed most to the LTO reactions regarding the thermal release, independent of pressure. Aromatics presented a significant exothermic effect both in the LTO (30-364 oC) and HTO intervals (364-511 oC). The peak heat flow and heat enthalpy of LTO (51.4 mW/mg and 16.1 kJ/g) were obviously higher than those of HTO (23.5 mW/mg and 12.9 kJ/g), which was inconsistent with the results reported by Li et al.5 It was believed that varying results were mostly in connection with the difference in the molecular structure of aromatics used. In their work, 7,12-dimethylbenzanthracene (C20H16) was tested by HP-DSC at 4.136 MPa, while aromatics used herein consists of 49% of triaromatics and 35% of diaromatics as mentioned in section 2.1. It was shown that aromatics with more benzene rings encountered higher thermal release at the HTO stage relative to LTO stage.5, 24 Besides the molecular structure of aromatics, we assumed that pressure also played an important role in the exothermic behavior of aromatics, like the crude oil case (given in section 3.1). To further confirm this assumption, the DSC test of aromatics was implemented to compare to HP-DSC one as shown in Figure 4. Unlike the HP-DSC profile, the accumulated heat release at the LTO stage was less than that at the HTO stage in the DSC profile. The fact unravelled that high oxygen partial pressure accelerated the thermal release of aromatics in the low temperature range.


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With respect to resins, the peak heat flow and heat enthalpy of the HTO region were 40.7 mW/mg and 16.9 kJ/g, respectively, which were approximately 1 and 1.77 times higher than those in the LTO interval (20.3 mW/mg and 6.1 kJ/g). Similar results were also obtained by DSC,12, 13 elucidating that resins released more heat in the HTO region compared to LTO region, independent of pressure. As seen from Figure 3 and Table 2, for asphaltenes, the LTO and HTO reactions took place at 30-344 oC and 344-536 oC, respectively. Asphaltenes gave higher cumulative thermal release in the HTO region in comparison with the LTO region, in accordance with the results determined by DSC.12, 24 Nevertheless, it should be noted that there were two apparent exothermic peaks in the HTO interval being observed, which was rarely detected at atmospheric pressure, suggesting that the heat release of asphaltenes at the HTO stage was more complicated and fiercer under high oxygen partial pressure. Within the HTO temperature range, the second peak heat flow (48.7 mw/mg) was clearly higher than the first one (22.7 mW/mg), which can be presumably explained as follows. The first exothermic region fell into the temperature range of 344-440 oC where part of LTO residue of asphaltenes (oxidized products and their condensation mixtures) could promote fuel deposition through polycondensation reactions (exothermic effect). However, a declining trend of heat flow appeared as temperature was increased from 407 to 440 oC, predominantly caused by the negative effects of endothermic reactions such as thermal cracking (destruction of intermolecular associations and chemical bonds, C-H, C-S, C-C, etc.) that commonly took place in this temperature interval.37, 38 The second exothermic region (440-536 oC) was believed to be the combustion of formed coke. Therefore, it was evident that the heat release of the second exothermic region was more drastic than the first one.


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3.3. Comparative Analysis of Thermal Behavior for Heavy Crude Oil and Its SARA Fractions Figure 5 presents HP-DSC profiles for the oil and its SARA fractions at 5 MPa and heating rate of 10 oC/min.

It was obvious that the thermal behavior of the heavy crude oil and its SARA fractions was

different. In the case of the LTO region, the heat enthalpy of the samples researched was ranked in this order: saturates (22.3 kJ/g) > oil (19.7 kJ/g) > aromatics (16.1 kJ/g) > asphaltenes (15.5 kJ/g) > resins (6.1 kJ/g). The heavy oil sample used herein includes 50.69% of saturates and 30.58% of aromatics (see Table 1), and thus its accumulative heat liberated in the LTO region lays between saturates and aromatics. Asphaltenes experienced higher thermal release at low temperatures than resins. This can be attributed to the special condensed structure of asphaltenes. As is widely acknowledged, asphaltenes is composed of condensed aromatics rings that are connected with rich fatty structural units. Therefore, it has a higher degree of aromatization that makes the molecular structure embody the stronger polarity and enables it more facilely to react with the oxygen compared with resins.39, 40 For the HTO stage, a rising order of the heat enthalpy of the used samples was in turn: saturates (3.9 kJ/g) < oil (5.4 kJ/g) < aromatics (12.9 kJ/g) asphaltenes (167±9 kJ/mol)> oil (140±12 kJ/mol) > aromatics (100±10 kJ/mol) ≈ resins (103±8 kJ/mol). As we mentioned before, the only pronounced reaction in the HTO interval was the combustion of coke. Hence, the value of E primarily hinged on the quality of the coke formed by the thermo-oxidative cracking reactions of the LTO residue.31 This gave a hint that the coke formed from aromatics and resins might own the most superior quality among the oil and its SARA fractions. Using the DAEM method, the variation of Ar with α for the LTO and HTO regions could be calculated as shown in Figure 11. The variation trend of Ar with α was almost identical to that of E with α, validating that the E correlated with Ar positively. The finding was consistent with that reported by Fan et al.28


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3.4.2 Reaction Model To obtain the appropriate theoretical function f(α), the experimental Sh(α) was compared to various theoretical Sh(α) listed in Table 3. Figures 12-16 present the experimental and best fitting theoretical Sh(α) profiles at the heating rate of 10 oC/min for the heavy crude oil and its SARA fractions, respectively. The experimental Sh(α) curves in the LTO interval for the oil and its SARA fractions followed the power law reaction models P-0.6, P-0.3, P0.1, P0.05 and P0.2, respectively. Chemical process or mechanism non-invoking equations F2.1, F0.8 and F0.6 were well fitted to the experimental Sh(α) profiles for the HTO stage of the oil, saturates and aromatics, respectively. Regarding the HTO region of resins, the appropriate mechanism functions were considered as the Sestak Berggren reaction model SB(0.5, 0.9) and Avrami–Erofeev reaction model A2. The suitable reaction model for the HTO region of asphaltenes was not obtained owing to the existence of two distinctive exothermic peaks in this stage, which still needed to be further investigated. Once the kinetic triplet is determined, the elementary kinetic equation will be readily deconvolved, which should be of much significance in consideration of employing SARA fractions to model the ISC process.

4. CONCLUSION The thermal behavior of heavy oil and its SARA fractions during combustion was thoroughly investigated by HP-DSC. Then, the relation of E and Ar vs. α was determined using two typical isoconversional methods (Friedman and DAEM), followed by the evaluation of reaction model via an advanced master plot method. The following conclusions are drawn from above work. (1) Being different from the results detected at atmospheric pressure, heavy crude oil obtained from Hongqian block was subjected to a larger thermal release caused by LTO reactions rather than HTO reactions under high oxygen partial pressure. An increment in oxygen partial pressure made more


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heat be released from the oxidation reactions for this crude oil, especially at the LTO stage, which promoted the sustainability and propagation of combustion front. (2) Saturates presented an extremely strong LTO region but a weak HTO region in terms of heat release. For aromatics, unlike the DSC test, the heat enthalpy at the LTO stage was apparently greater than that at the HTO stage in the HP-DSC tests. Resins and asphaltenes had a greater accumulated heat release in the HTO interval than LTO interval, especially asphaltenes. (3) Among the crude oil and its SARA fractions, saturates and asphaltenes gave the highest cumulative heat release at the LTO and HTO stages, respectively. Under high oxygen partial pressure, not only asphaltenes and resins but also aromatics could yield substantial coke for serving the HTO reactions. (4) The dependence of kinetic parameters (E and Ar) upon α during combustion was quite different for the oil and its SARA fractions, reflecting their varying reaction pathways and mechanisms. Saturates exhibited the lowest average value of E at the LTO stage, while aromatics and resins gave the lowest average value of E at the HTO stage. (5) In the case of LTO region, P-0.6, P-0.3, P0.1, P0.05 and P0.2 were considered as the appropriate reaction models of the heavy oil and its SARA fractions, respectively. The most probable reaction models for the HTO stage of crude oil, saturates and aromatics were F2.1, F0.8 and F0.6, respectively. SB(0.5, 0.9) and A2 were regarded as the rational reaction models for the HTO region of resins.

SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website at DOI: Activation energies of heavy crude oil and its SARA fractions under different conversion rates at the


Page 17 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

LTO stage (kJ/mol) (Table S1), and activation energies of heavy crude oil and its SARA fractions under different conversion rates at the HTO stage (kJ/mol) (Table S2).

AUTHOR INFORMATION Corresponding Author *Wanfen Pu, E-mail: [email protected]. *Chengdong Yuan, E-mail: [email protected]. ORCID Chengdong Yuan: 0000-0002-7327-8092 Notes The authors declare no competing ﬁnancial interest.

ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support of the Natural Science Foundation of Sichuan Province (2017JY0122). This work has been partly performed according to the Russian Government Program of Competitive Growth of Kazan Federal University.

REFERENCES (1) Li, C.; Chen, Y.; Hou, J.; Zhou, C. A mechanism study on the viscosity evolution of heavy oil upon peroxide oxidation and pyrolysis. Fuel 2018, 214, 123-126. (2) Hinkle, A.; Shin, E. J.; Liberatore, M. W.; Herring, A. M.; Batzle, M. Correlating the chemical and physical properties of a set of heavy oils from around the world. Fuel 2008, 87, 3065-3070. (3) Zhao, R. B.; Xia, X. T.; Luo, W. W.; Shi, Y. L.; Diao, C. J. The alteration of heavy oil properties under in-situ combustion: a field study. Energy Fuels 2015, 29 (10), 6839-6848. (4) Yuan, C. D.; Emelianov, D. A.; Varfolomeev, M. A.; Pu, W. F.; Ushakova, A. S. Oxidation behavior and kinetics of eight C20–C54 n-alkanes by high pressure differential scanning calorimetry (HP-DSC). Energy Fuels 2018, 32, 7933-7942. (5) Li, J.; Mehta, S.; Moore, R.; Zalewski, E.; Ursenbach, M.; Van Fraassen, K. Investigation of the oxidation behaviour of pure hydrocarbon components and crude oils utilizing PDSC thermal


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combustion of crude oil in the presence of limestone matrix. Fuel 2017, 209, 203-210. (18) Murugan, P.; Mahinpey, N.; Mani, T.; Freitag, N. Pyrolysis and combustion kinetics of Fosterton oil using thermogravimetric analysis. Fuel 2009, 88 (9), 1708-1713. (19) Kok, M. V.; Varfolomeev, M. A.; Nurgaliev, D. K. Crude oil characterization using TGA-DTA, TGA-FTIR and TGA-MS techniques. J. Pet. Sci. Eng. 2017, 154, 537-542. (20) Pu, W. F.; Liu, P. G.; Li, Y. B.; Jin, F. Y.; Liu, Z. Z. Thermal characteristics and combustion kinetics analysis of heavy crude oil catalyzed by metallic additives. Ind. Eng. Chem. Res. 2015, 54, 11525-11533. (21) Vyazovkin, S.; Burnham, A. K.; Criado, J. M.; Pérez-Maqueda, L. A.; Popescu, C.; Sbirrazzuoli, N. ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data. Thermochim. Acta 2011, 520 (1), 1-19. (22) Opfermann, J. R.; Kaisersberger, E. Flammersheim, H. J. Model-free analysis of thermoanalytical data-advantages and limitations. Thermochim. Acta 2002, 39, 119-127. (23) Shahcheraghi, S. H.; Khayati, G. R.; Ranjbar, M. An advanced reaction model determination methodology in solid-state kinetics based on Arrhenius parameters variation. J. Therm. Anal. Calorim. 2016, 123, 221-229. (24) Yuan, C. D.; Varfolomeev, M. A.; Emelianov, D. A.; Eskin, A. A.; Nagrimanov, R. N.; Kok, M. V.; Afanasiev, I. S.; Fedorchenko, G. D.; Kopylova, E. V. Oxidation behavior of light crude oil and its SARA fractions characterized by TG and DSC techniques: differences and connections. Energy Fuels 2018, 32, 801-808. (25) Vand, V. A theory of the irreversible electrical resistance changes of metallic films evaporated in vacuum. Proceedings of the Physical Society 1943, 55, 222–246. (26) Burnham, A. K.; Braun, R. L. Global kinetic analysis of complex materials. Energy Fuels 1999, 13, 1-22. (27) Miura, K.; Maki, T. A simple method for estimating f(E) and k0(E) in the distributed activation energy model. Energy Fuels 1998, 12, 864-869. (28) Fan, C.; Zan, C.; Zhang, Q.; Ma, D.; Chu, Y.; Jiang, H.; Shi, L.; Wei, F. The oxidation of heavy oil: Thermogravimetric analysis and non-isothermal kinetics using the distributed activation energy


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model. Fuel Process. Technol. 2014, 119 (1), 146-150. (29) Varfolomeev, M. A.; Nurgaliev, D. K.; Kok, M. V. Calorimetric study approach for crude oil combustion in the presence of clay as catalyst. Pet. Sci. Technol. 2016, 34 (19), 1624-1630. (30) Mothé, C. G.; Miranda, I. C. D. Study of kinetic parameters of thermal decomposition of bagasse and sugarcane straw using Friedman and Ozawa–Flynn–Wall isoconversional methods. J. Therm. Anal. Calorim. 2013, 113 (2), 497-505. (31) Yuan, C. D.; Emelianov, D.; Varfolomeev, M. A. Oxidation behaviour and kinetics of light, medium and heavy crude oils characterized by thermogravimetry coupled with fourier-transform infrared spectroscopy (TG-FTIR). Energy Fuels 2018, 32 (4), 5571-5581. (32) Freitag, N. P. Chemical reaction mechanisms that govern oxidation rates during in-situ combustion and high-pressure air injection. SPE Reserv. Eval. Eng. 2016, 4, 645-654. (33) Ushakova, A.; Zatsepin, V.; Varfolomeev, M. A.; Emelyanov, D. Study of the radical chain mechanism of hydrocarbon oxidation for in situ combustion process. J. Combust. 2017, 11, 1-11. (34) Zhao, S.; Pu, W. F.; Varfolomeev, M. A.; Yuan, C. D.; Pan, J. J.; Wang, R. Y.; Chen, L.; Kan, N. Low-temperature oxidation of light and heavy oils via thermal analysis: kinetic analysis and temperature zone division. J. Pet. Sci. Eng. 2018, 168, 246-255. (35) Zhao, S.; Pu, W. F.; Varfolomeev, M. A.; Yuan, C. D.; Zhang, J. Z.; Han, X. Q.; Yang, Y.; Peng, X. Q.; Wu, J. X. Comprehensive investigations into low temperature oxidation of heavy crude oil. J. Pet. Sci. Eng. 2018, 171, 835-842. (36) Pu, W. F.; Yuan, C. D.; Jin, F. Y.; Wang, L.; Qian, Z.; Li, Y. B.; Li, D.; Chen, Y. F. Low-temperature oxidation and characterization of heavy oil via thermal analysis. Energy Fuels 2015, 29 (2), 1151-1159. (37) Wei, B.; Zou, P.; Zhang, X.; Xu, X. G.; Wood, C; Li, Y. B. Investigations of structure-property-thermal degradation kinetics alterations of Tahe asphaltenes caused by low temperature oxidation. Energy Fuels 2018, 32, 1506-1514. (38) Alvarez, E.; Marroquín, G.; Trejo, F.; Centeno, G.; Ancheyta, J.; Díaz, J. AI. Pyrolysis kinetics of atmospheric residue and its SARA fractions. Fuel 2011, 90, 3602-3607. (39) Jia, H.; Liu, P. G.; Pu, W. F.; Ma, X. P.; Zhang, J. In situ catalytic upgrading of heavy crude oil


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through low-temperature oxidation. Pet. Sci. 2016, 13 (3), 476-488. (40) Castro, L.V.; Vazquez, F. Fractionation and characterization of mexican crude oils. J. Eur. Ceram. Soc. 2009, 27 (13), 4417-4420. (41) Zhao, S.; Pu, W. F.; Sun, B. S.; Gu, F.; Wang, L. L. Comparative evaluation on the thermal behaviors and kinetics of combustion of heavy crude oil and its SARA fractions. Fuel 2019, 239, 117-125.


Energy & Fuels

120 0

5 C/min 0 10 C/min 0 15 C/min

Exo 100

DSC/(mW/mg)

80

60

40

20

0 100

200

300

400

500

600

o

Temperature/ C Figure 1. HP-DSC curves for heavy crude oil at the heating rates of 5, 10 and 15 oC/min and 5 MPa.

80

5

Exo

Exo

4

5 MPa 0.1 MPa

3

DSC/(mW/mg)

60

DSC/(mW/mg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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40

2

1

0

-1

100

200

300

400

500

600

700

o

Temperature/ C

20

0

100

200

300

400

500

o

Temperature/ C Figure 2. DSC and HP-DSC curves for heavy crude oil at the heating rate of 10 oC/min.


600

Page 23 of 29

Energy & Fuels 100

80 0


Exo 80

(a)

0


Exo 60

(b)

DSC/(mW/mg)

DSC/(mW/mg)

60

40

40

20

20

0

0

100

200

300

400

500

100

600

200

300

400

500

600

o

o

Temperature/ C

Temperature/ C 60

80

0


Exo

(c)

0


Exo 60

(d)

DSC/(mW/mg)

40

DSC/(mW/mg)

20

40

20

0

0

100

200

300

400

500

600

100

200

o

300

400

500

600

o

Temperature/ C

Temperature/ C

Figure 3. HP-DSC curves for SARA fractions at the heating rates of 5, 10 and 15 oC/min and 5 MPa: (a) saturates, (b) aromatics, (c) resins, (d) asphaltenes.

80

5

Exo

Exo

4

5 MPa 0.1 MPa

3

DSC/(mW/mg)

60

DSC/(mW/mg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2

1

40 0 100

200

300

400

500

600

700

o

Temperature/ C

20

0

100

200

300

400

500

600

o

Temperature/ C Figure 4. DSC and HP-DSC curves for aromatics at the heating rate of 10 oC/min. ACS Paragon Plus Environment

Energy & Fuels

80

Exo crude oil saturates aromatics resins asphaltenes

DSC/(mW/mg)

60

40

20

0

100

200

300

400

500

600

o

Temperature/ C Figure 5. HP-DSC curves for heavy crude oil and its SARA fractions at the heating rate of 10 oC/min and 5 MPa. 300

300

(a) 200

150

100

50

0 0.0

DAEM Friedman

250

Activation energy (kJ/mol)


(b)

DAEM Friedman

250

200

150

100

50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.0

1.0

0.1

0.2

0.3

Conversion degree

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Figure 6. Dependence of activation energy upon the conversion degree for heavy crude oil: (a) LTO stage, (b) HTO stage. 300

300

(a)

(b)

DAEM Friedman

200

150

100

200

150

100

50

50

0 0.0

DAEM Friedman

250


250


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 29

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Conversion degree

Figure 7. Dependence of activation energy upon the conversion degree for saturates: (a) LTO stage, (b) HTO stage. ACS Paragon Plus Environment

Page 25 of 29

300

300

(a)

DAEM Friedman

250



(b)

DAEM Friedman

250

200

150

100

200

150

100

50

50 0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0

1.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Conversion degree

Figure 8. Dependence of activation energy upon the conversion degree for aromatics: (a) LTO stage, (b) HTO stage.

300

300

(a) 200

150

100

50

0 0.0

DAEM Friedman

250



(b)

DAEM Friedman

250

200

150

100

50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.0

1.0

0.1

0.2

0.3

Conversion degree

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Figure 9. Dependence of activation energy upon the conversion degree for resins: (a) LTO stage, (b) HTO stage.

300

300

(a)

(b)

DAEM Friedman

200

150

100

50

0 0.0

DAEM Friedman

250


250


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

200

150

100

50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 0.0

0.1

Conversion degree

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Figure 10. Dependence of activation energy upon the conversion degree for asphaltenes: (a) LTO stage, (b) HTO stage.


Energy & Fuels

(a)

1E21

heavy crude oil saturates aromatics resins asphaltenes

1E17

(b)

1E21

1E13

1E9

100000

heavy crude oil saturates aromatics resins asphaltenes

1E17

Frequency factor (1/min)

Frequency factor (1/min)

1E13

1E9

100000

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0

0.1

0.2

0.3

Conversion degree

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Conversion degree

Figure 11. Dependence of frequency factor upon the conversion degree determined by DAEM method for heavy crude oil and its SARA fractions: (a) LTO stage, (b) HTO stage.

80

P-0.6 (LTO) Exp. Sh(α) (LTO) F2.1 (HTO)

40

Exp. Sh(α) (HTO)

Sh(α)

0

-40

-80

0.0

0.2

0.4

0.6

0.8

1.0

α

Figure 12. Experimental and theoretical Sh(α) curves at the heating rate of 10 oC/min for heavy crude oil.

Sh(α)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 29

60

P-0.3 (LTO)

40

Exp. Sh(α) (HTO)

Exp. Sh(α) (LTO) F0.8 (HTO)

20

0

-20

-40 0.0

0.2

0.4

0.6

0.8

1.0

α

Figure 13. Experimental and theoretical Sh(α) curves at the heating rate of 10 oC/min for saturates. ACS Paragon Plus Environment

Page 27 of 29

P0.1 (LTO)

40

Exp. Sh(α) (LTO) F0.6 (HTO) Exp. Sh(α) (HTO)

Sh(α)

20

0

-20

-40 0.0

0.2

0.4

0.6

0.8

1.0

α

Figure 14. Experimental and theoretical Sh(α) curves at the heating rate of 10 oC/min for aromatics.

P(0.05) (LTO)

40

Exp. Sh(α) (LTO) A2 (HTO) SB(0.5, 0.9) (HTO)

Sh(α)

20

Exp. Sh(α) (HTO)

0

-20

-40 0.0

0.2

0.4

0.6

0.8

1.0

α

Figure 15. Experimental and theoretical Sh(α) curves at the heating rate of 10 oC/min for resins.

P(0.2) (LTO)

40

Exp. Sh(α) (LTO)

Sh(α)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

20

0

0.0

0.2

0.4

0.6

0.8

1.0

α

Figure 16. Experimental and theoretical Sh(α) curves at the heating rate of 10 oC/min for asphaltenes. ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Page 28 of 29

Table 1 Properties and SARA fractions of heavy crude oil. API (o)

Density (g/cm3, 20 oC)

Viscosity (mPa·s, 50 oC)

Saturates

Aromatics

Resins

Asphaltenes

C

H

O

N

S

HHVa (J/g)

19.81

0.9331

610

50.69

30.58

14.81

3.92

80.7

13.2

2.76

0.72

0.91

-43286.3 ± 27.1

SARA fractions (wt%)

Element analysis (wt%)

aHHV

represents higher heating value. Table 2 HP-DSC reaction regions, peak temperatures, peak heat flows and heat enthalpies of heavy crude oil and its SARA fractions at different heating rates. LTO

HTO

Sample

Heating rate (oC/min)

Region (oC)

Peak temperature (oC)

Peak heat flow (mW/mg)

Heat enthalpy (kJ/g)

Region (oC)

Peak temperature (oC)

Peak heat flow (mW/mg)

Heat enthalpy (kJ/g)

Oil

5

30-355

246

35.5

18.2

355-463

451

6.0

5.1

10

30-373

251

67.6

19.7

373-494

465

12.5

5.4

15

30-384

254

102.6

21.2

384-505

470

21.5

6.9

5

30-369

196

37.0

20.2

369-467

440

4.1

2.9

10

30-375

206

63.8

22.3

375-480

456

9.4

3.9

15

30-388

212

94.0

22.9

388-491

461

14.3

4.0

5

30-352

282

28.1

17.7

352-494

445

11.3

12.6

10

30-364

293

51.4

16.1

364-511

456

23.5

12.9

15

30-374

299

72.9

17.8

374-538

490

48.1

18.2

5

30-319

271

12.5

7.0

319-508

385

25.1

19.4

10

30-323

282

20.3

6.1

323-513

402

40.7

16.9

15

30-334

288

27.5

5.9

334-526

429

54.9

17.4

5

30-330

264

18.0

15.5

330-511

395/490

12.1/19.1

10.2/9.4

10

30-344

276

35.9

15.5

344-536

407/503

22.7/48.7

9.5/9.9

15

30-351

285

54.1

15.8

351-547

417/514

35.7/71.1

9.6/8.6

Saturates

Aromatics

Resins

Asphaltenes


Page 29 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Energy & Fuels

Table 3 Mathematical expressions of functions, f(α) and Sh(α), for different classical reaction models. No.1

Reaction model

Code

f(α)

Sh(α)

1

Power law (Acceleratory rate equations)

Pn (n≠1)

(1/n)α(1-n)

(1-n)/α

2

Avrami–Erofeev (Sigmoidal rate equations)

An

n(1-α)[-ln(1-α)](1-1/n)

[1-(1/n)+ln(1-α)][(α-1)ln(1-α)]-1

D1

(1/2)α-1

-1/α

D2

[-ln(1-α)]-1

[1/(1-α)]/ln(1-α)

D3

[(3/2)(1-α)2/3][1-(1-α)1/3]-1

-(2/3)(1-α)-1[1+(1/2)(1-α)1/3(1-(1-α)1/3)-1]

D4

(3/2)[(1-α)-1/3-1]-1

(1/3)(1-α)-4/3[(1-α)-1/3-1]-1

R1

Constant

0

R2

2(1-α)1/2

(1/2)(1-α)-1

R3

3(1-α)2/3

(2/3)(1-α)-1

Fn (n≠0, 1/2, 2/3, 1)

(1-α)n/|1-n|

-n/(1-α)

SB(m, n)

αm(1-α)n

(m/α)-(n/(1-α))

3

One-dimensional diffusion

4

Two-dimensional diffusion

5

Three-dimensional diffusion

6

Four-dimensional diffusion

7 8 9 10 11

(Deceleratory rate equations)

Phase boundary controlled reaction (Deceleratory rate equations) Chemical process or mechanism non-invoking equations Sestak Berggren

Table 4 Mean activation energy for crude oil only, saturates, aromatics, resins and asphaltenes (kJ/mol). Sample Stages DAEM Friedman LTO 134±17 142±11 Oil HTO 140±12 151±12 LTO 79±5 74±7 Saturates HTO 222±9 219±6 LTO 145±11 144±6 Aromatics HTO 100±10 98±10 LTO 150±7 139±5 Resins HTO 103±8 95±8 LTO 113±4 122±3 Asphaltenes HTO 167±9 170±10


Thermal Behavior and Kinetic Triplets of Heavy Crude Oil and Its

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