Catalytic Aquathermolysis of Heavy Oil with Iron Tris(acetylacetonate

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Catalytic Aquathermolysis of Heavy Oil with Iron Tris(acetylacetonate): Changes of Heavy Oil Composition and in Situ Formation of Magnetic Nanoparticles Andrey V. Galukhin,* Anton A. Erokhin, Yuri N. Osin, and Danis K. Nurgaliev Kazan Federal University, 18 Kremlevskaya Street, Kazan 420008, Russia S Supporting Information *

ABSTRACT: We investigated the influence of catalytic aquathermolysis on the composition changes of Ashal’cha heavy oil. The synergetic effect of organic solvent and an oil-soluble catalyst leads to deep conversion of resins into light components. Composition changes of resins and asphaltenes before and after aquathermolysis were investigated by proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), and elemental analysis. It was shown that iron(III) tris(acetylacetonate) forms magnetic nanoparticles (MNPs) during aquathermolysis of heavy oil without any addition of surfactants. Composition of MNPs was determined as a mixture of hematite, magnetite, and maghemite. It turns out that obtained MNPs possess superparamagnetic properties of single-domain nanoparticles.

1. INTRODUCTION With the increasing demand of energy resources and the shortage of conventional hydrocarbon reserves, the exploitation and usage of heavy oil reservoirs have attracted more attention from oil companies. To advance in heavy oil production, development of enhanced oil recovery (EOR) methods is required. Among all EOR approaches, the thermal methods of heavy oil recovery, especially based on steam injection, play a crucial role because of their high displacement efficiency.1−3 Unfortunately, the steam injection leads to temporal decreasing of heavy oil viscosity by heating, and for deep conversion, the presence of various chemical processes (cracking, removal of heteroatoms, etc.) is required. Hyne et al. proposed the following chemical reaction on the assumption that viscosity of the heavy crude oil decreases because of C−S bond cleavage:4

catalysts. Various iron-based compounds, such as iron(II) sulfate, 1 0 iro n(II) naph th enat e, 1 0 iron(III) t ris(acetylacetonate),11 and iron(III) dodecylbenzenesulfonate, have been successfully used in aquathermolysis.12 Moreover, catalysts based on iron oxide nanoparticles have been successfully used in refining of petroleum residual oil and coal liquefaction.13,14 Despite plenty of investigations conducted in this area,6−12 the final form of the oil-soluble catalyst precursors in which they are converted during aquathermolysis has never been studied. Meanwhile, this information is important to understand the mechanism of the catalytic process and for further improvement of the effectiveness of catalysts. In this study, we examined the nature of the catalytic nanoparticles that are formed from an oil-soluble catalyst precursor during the aquathermolysis process. Their influence on changes of heavy oil composition during the process was also investigated.

RCH 2CH 2SCH3 + 2H 2O → RCH3 + CO2 + H 2 + H 2S + CH4

2. EXPERIMENTAL SECTION

Hydrogen released during the aquathermolysis can participate in further oil-improving processes. One of the most promising ways for deep conversion of crude oil during the steam injection process is applying various catalysts that can effectively participate in an aquathermolysis reaction. The catalysts used for aquathermolysis can be roughly divided into four categories: mineral, water-soluble catalysts, oil-soluble catalysts, and dispersed catalysts.5 Oil-soluble catalysts have a great advantage compared to the other types of catalysts; they can spread in heavy oil deposits and effectively catalyze the aquathermolysis process.6 At the moment, various oil-soluble derivatives of Fe, Co, Ni, Mo, and W were examined as catalysts.5 Carboxylates and sulfonates are usually used as a lipophilic ligands.6−8 The performance of some of them was tested in laboratory and field experiments.9 Iron derivatives take special place among other metals because of their low costs compared to other metals used as © XXXX American Chemical Society

2.1. Materials. Crude oil samples used in this research were obtained from the Ashal’cha field (Volga-Ural basin, Republic of Tatarstan, Russia). Organic solvents, such as toluene, n-heptane, dichloromethane, methanol, and cyclohexane, as well as inorganic salts were purchased from Sigma-Aldrich and used without additional purification. 2.2. Iron(III) Tris(acetylacetonate) Preparation. Iron(III) tris(acetylacetonate), used as a catalyst, was prepared as follows: The solution of 2.1 g (7.8 mmol) of FeCl3·6H2O in 15 mL of distilled water was added to the solution of 2.4 mL (23.4 mmol) of acetylacetone in 15 mL of methanol under stirring. After 15 min, the solution of 5.31 g (39 mmol) of sodium acetate trihydrate in 9 mL of distilled water was added and the mixture was heated at 80 °C for Received: March 19, 2015 Revised: June 19, 2015

A

DOI: 10.1021/acs.energyfuels.5b00587 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels 15 min. Then, the reaction mixture was cooled, and the residue was filtered off and dried in a vacuum dissicator. 2.3. Experimental Conditions. All of the experiments were carried out with 70 g of oil samples and 30 g of water (oil/water ratio = 7:3) in a Parr Instruments 4560 high-pressure reactor with a volume of 300 mL under a N2 atmosphere at 3 MPa. Data about the catalyst content in each experiment are grouped in Table 1. The reactions

such a kind of catalyst precursor is the ability to spread in a heavy oil reservoir that leads to more efficient conversion of heavy oil.8 We estimated iron tris(acetylacetonate) (Figure 1) performance by measuring the content of high-molecular-weight

Table 1. Experimental Conditions experiment number

catalyst content

1 2 3

without catalyst 0.10 g 0.10 g (in 5 mL of C6H12)

proceeded at the temperature of 250 °C for 6 h. During the reaction, the gas pressure would increase up to 6 MPa. After cooling, we separated water in a Dean−Stark apparatus with toluene and then removed volatile organic compounds from reaction mixtures with HeiVAP rotary evaporators (Heidolph) under reduced pressure (20 mbar and 80 °C). Obtained dry oil samples were used for further characterizations. 2.4. Oil Sample Analysis. Compositional analyses of petroleum samples [saturates, aromatics, resins, and asphaltenes (SARA) analysis] were conducted according to the common technique,15 which include asphaltene precipitation from heptane and further chromatographic separation of the non-asphaltic oil components through a column filled with alumina. Measurements of viscosity and American Petroleum Institute (API) gravity of oil samples were carried out on an Anton Paar SVM 3000 Stabinger viscometer at temperatures of 40, 60, and 80 °C. Mass spectra were recorded with the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) Dynamo Finnigan mass analyzer using trans-2-[3-(4-tert-butylphenyl)-2-methyl-2propenylidene]malononitrile as a matrix. CHNS elemental analysis of crude oils was carried out on a PerkinElmer 2400 Series II elemental analyzer. Proton nuclear magnetic resonance (1H NMR) spectra were recorded on a Bruker Avance 400 spectrometer (400.1 MHz) in CDCl3 as a solvent at ambient temperature. Infrared (IR) spectra were recorded on a Tensor Fourier spectrometer (Bruker) in thin films on KBr plates. 2.5. Obtaining Magnetic Nanoparticles and Characterization. Magnetic nanoparticles, formed during aquathermolysis, were isolated from heavy oil samples by their dilution with toluene and further centrifugation at 3000 rpm for 1 h. Collected powder was then washed with toluene and methanol and dried at room temperature under a flow of nitrogen. Scanning electron microscopy measurements were carried out using a field-emission high-resolution scanning electron microscope (Merlin Carl Zeiss). An observation photo of the morphology surface is applied at an accelerating voltage of incident electron of 15 kV and current probe of 300 pA to modify the sample minimally. X-ray diffraction (XRD) spectra were obtained using a D2 Phaser (Bruker) powder X-ray diffractometer. Thermomagnetic properties were studied using a homemade magnetic Curie balance.16 Magnetization was induced in a field of 1500 Oe and measured as a function of the temperature at a rate of 100 °C min−1, to prevent the oxidation of magnetic nanoparticles (MNPs), which would be obstructed at lower heating rates. The magnetic hysteresis loop of the sample was measured at 300 K using a homemade coercivity spectrometer.17 The sample were placed onto the non-magnetic paper sample holder, and the isothermal hysteresis loop was acquired at 25 °C.

Figure 1. Molecular structure of iron tris(acetylacetonate).

components (resins and asphaltenes) with SARA analysis. Table 2 shows the results of SARA analysis of the heavy oil Table 2. SARA Analysis of Oil before and after Aquathermolysis fraction (%) sample

saturates

aromatics

resins

asphaltenes

initial 1 2 3

24.2 23.8 24.7 25.8

43.0 40.5 43.6 51.3

28.8 31.6 27.4 18.6

4.0 4.1 4.3 4.3

before and after aquathermolysis. It can clearly be seen that only using a catalyst precursor dissolved in cyclohexane provides significant differences in composition of heavy oil. Catalyst reduces the resin content from 28.8 to 18.6 wt %. Apparently, the catalyst precursor dissolved in organic solvent evenly distributes in crude oil and more effectively catalyzes conversion of heavy oil. A slight increase of the asphaltene content can be explained by maltene to asphaltene conversion during the aquathermolysis process. It is interesting to compare viscosity of crude oil before and after aquathermolysis. Table 3 shows that viscosity and API Table 3. Viscosity and API Gravity of Oil before and after Aquathermolysis viscosity (mPa s) sample

40 °C

60 °C

80 °C

API gravity (deg)

initial 1 2 3

668.82 804.42 814.70 1039.50

172.80 199.97 201.96 245.17

64.01 72.24 72.83 85.40

14.3 13.7 13.5 13.3

gravity of oil samples increase after aquathermolysis, especially the catalytic version. We explain it by features of oil sample preparation that includes removing of water from the samples by distillation with toluene in a Dean−Stark apparatus, followed by removing of volatile organic compounds under reduced pressure. On the other hand, data obtained from SARA analysis (Table 2) and IR spectroscopy (Figure 2) show that, during catalytic aquathermolysis of heavy crude oil, elimination of light saturated hydrocarbons and high-molecular-weight aromatic compounds from the resin core take place. It should also be mentioned that significant reducing of the average molecular mass of resins after aquathermolysis (from approximately 1400

3. RESULTS AND DISCUSSION Application of oil-soluble catalyst precursors based on Fe, Co, Ni, Mo, and W salts and complex compounds is a modern trend in the heavy oil recovery process. The main advantage of B

DOI: 10.1021/acs.energyfuels.5b00587 Energy Fuels XXXX, XXX, XXX−XXX

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Figure 3. 1H NMR spectrum of oil before and after aquthermolysis (sample: initial, black; 1, blue; 2, red; and 3, purple). Figure 2. Combined FTIR spectrum of resins before and after aquthermolysis (sample: initial, black; 1, blue; 2, red; and 3, purple).

Table 5. 1H NMR of Resins before and after Aquathermolysis

to approximately 1000; see the Supporting Information) shows that polymerization and polycondensation processes did not occur. Detailed analysis of the Fourier transform infrared spectroscopy (FTIR) spectrum (Figure 2) revealed decreasing of intensities of bands at 2922, 2851, 1457, and 1375 cm−1, which are the characteristic absorption peaks for methyl and methylene groups that indicate the dealkylation process. Increasing of the intensity of the characteristic absorption peaks at 857, 810, and 742 cm−1, corresponding to out-of-plane bending of aromatic C−H bonds, shows that transformation of polycyclic aromatic systems into mono- and bicyclic aromatic systems occurs. Table 4 shows that removing of light hydrocarbons that formed during the aquathermolysis by evaporation increases the content of carbon and heteroatoms in oil samples.

type of proton (%) (chemical shift range, ppm) sample

HA (6.0−9.0)

Hα (2.0−4.0)

Hβ (1.0−2.0)

Hγ (0.5−1.0)

initial 1 2 3

7.6 8.5 3.4 11.4

14.9 19.0 17.0 19.3

46.7 54.4 58.4 52.9

30.7 18.1 21.2 16.3

transforms into MNPs (Figure 4). It should be noted that usually the presence of surfactants that stabilize nanoparticles is

Table 4. CHNS Elemental Analysis of Oil before and after Aquathermolysis element (%) sample

C

H

N

S

initial 1 2 3

81.3 83.2 83.2 83.2

10.2 10.4 10.2 10.3

0.5 0.6 0.5 0.6

2.1 2.3 2.3 2.4

Figure 4. MNPs obtained from oil after the aquathermolysis experiment dispersed in methanol in the (left) absence and (right) presence of a magnet.

We applied 1H NMR spectroscopy to examine structure changes of resins that occur during aquthermolysis (Figure 3). Table 5 shows integrated area percentages based on the assignment of protons in the 1H NMR spectrum, which were the same as refs 18−20. We observe decreasing of Hγ protons, which provides evidence of removing hydrocarbon chains from the condensed core. At the same time, we observe increasing of aromatic protons that can be related with conversion of polyclic aromatic fragments into bi- and monocyclic aromatic fragments by hydrogen released during the aquathermolysis process. Organic derivatives of iron, including iron(III) acetylacetonate, are widely used for obtaining various nanoparticles based on iron oxides, such as magnetite and maghemite.21−24 Therefore, we tried to isolate iron-containing compounds formed from iron(III) acetylacetonate during aquathermolysis of the heavy crude oil. It turns out that iron(III) acetylacetonate

required for this process. We suggest that some polar components of heavy-oil-containing polar groups (carboxylic, hydroxylic, amine, etc.) can act like surfactants and promote MNP formation. Scanning electron microscopy (SEM) image of the obtained MNPs shown in Figure 5. The average size of MNPs is 106 nm, and the standard deviation is 23 nm. For chemical characterization of the surface of the sample, we applied energydispersive X-ray spectroscopy (Figure 5). Energy dispersive Xray (EDX) analysis revealed (Figure 6) that the sample contains about 51 wt % iron, 39 wt % oxygen, and 9 wt % carbon (see the Supporting Information). We applied XRD analysis for phase identification of collected MNPs. Detailed analysis of obtained XRD patterns revealed the presence of three phases: magnetite (Fe3O4), maghemite (γFe2O3), and hematite (α-Fe2O3) (Figure 7). Deconvolution of C

DOI: 10.1021/acs.energyfuels.5b00587 Energy Fuels XXXX, XXX, XXX−XXX

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The isothermal magnetization properties of the MNPs are presented in Figure 8. We found that the saturation

Figure 5. SEM images of the MNPs obtained from oil after the aquathermolysis reaction.

Figure 8. Magnetization loop of the MNPs acquired at 25 °C.

magnetization (Ms) and saturation remanence magnetization (Mrs) were 15.96 and 0.84 emu g−1, respectively. The low value of Mrs indicates that the MNPs possess superparamagnetic properties. Further evidence of the superparamagnetic properties of the nanoparticles can be found from the relationship of the remanence magnetization value to the saturation magnetization value (Mrs/Ms = 0.053), which is characteristic of the superparamagnetic behavior of single-domain nanoparticles.26 Furthermore, taking into account the fact that the saturation magnetization for the obtained MNPs is 15.96 emu g−1, which is much lower than that of bulk magnetite (Ms = 92 emu g−1)27 and maghemite (Ms = 76 emu g−1),27 we conclude that the low magnetization value is caused by the presence of a low magnetic component (hematite; Ms = 0.02−2 emu g−1) and

Figure 6. EDX spectrum for MNPs collected from the heavy oil matrix.

the combined peak at 57.0−57.6° 2θ (Figure 7, inset) allows us to evaluate the magnetite/maghemite ratio as 65:35.25

Figure 7. XRD patterns of obtained MNPs: (∗) magnetite and maghemite and (▽) hematite. D

DOI: 10.1021/acs.energyfuels.5b00587 Energy Fuels XXXX, XXX, XXX−XXX

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on the ACS Publications website at DOI: 10.1021/ acs.energyfuels.5b00587.

some non-magnetic components in the total sample volume.28,29 The thermomagnetic properties of the MNPs were also studied. Existence of inflection points on the thermomagnetic curve (Figure 9) indicates the presence of two magnetically

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work is performed according to the Russian Government Program of Competitive Growth of Kazan Federal University.

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Figure 9. Thermomagnetic curve of the MNPs.

active phases with different Curie temperatures: 585 °C for magnetite30 and 640 °C for maghemite.31 Decreasing of magnetization in Figure 9 corresponds mostly to two temperature-induced processes: transformation of maghemite to hematite and decay of magnetite magnetization with an increasing temperature. Recent research on catalytic aquathermolysis of model organosulfur compounds with iron oxide nanoparticles describes a possible mechanism of this process as oxidation of a model compound (thiophene) by lattice oxygen in the hematite surface with simultaneous reduction of hematite to magnetite.32 Further oxidation of magnetite to hematite by water completes the catalytic cycle. This process leads to C−S and C−C bond cleavage that is a key aspect of decreasing the molecular mass of high-molecular-weight components of heavy crude oil. We think that this mechanism combined with the classical mechanism proposed by Hyne et al. in our case could take place.4

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CONCLUSION In summary, we investigated the influence of iron(III) tris(acetylacetonate) on the aquathermolysis of heavy oil. The study showed that applying an oil-soluble catalyst precursor dissolved in cyclohexane leads to significant changes in oil composition. It was demonstrated that iron(III) tris(acetylacetonate) forms nanosized MNPs during aquathermolysis of heavy oil without any addition of surfactants. Composition of MNP was determined as a mixture of hematite, magnetite, and maghemite. Studying of magnetic properties of obtained nanoparticles revealed their superparamagnetic properties. We suppose that the formation of such a kind of nanoparticle has great opportunities in terms of monitoring parameters of the steam injection process.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

MALDI TOF mass spectra and table of results of EDX analysis (PDF). The Supporting Information is available free of charge E

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DOI: 10.1021/acs.energyfuels.5b00587 Energy Fuels XXXX, XXX, XXX−XXX