Catalytic Aquathermolysis of Heavy Crude Oil Using Surface-Modified

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Catalytic Aquathermolysis of Heavy Crude Oil using Surface-Modified Hematite Nanoparticles Munawar Khalil, Ning Liu, and Robert L. Lee Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00468 • Publication Date (Web): 03 Apr 2017 Downloaded from http://pubs.acs.org on April 4, 2017

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Industrial & Engineering Chemistry Research

Catalytic Aquathermolysis of Heavy Crude Oil using Surface-Modified Hematite Nanoparticles Munawar Khalila,*, Ning Liub, Robert L. Leec. a

Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of

Indonesia, Kampus UI Depok, 16424 Depok, Indonesia. b

Department of Petroleum Engineering, University of Louisiana at Lafayette, 70504 Louisiana,

USA. c

Petroleum Recovery Research Center (PRRC), New Mexico Institute of Mining and

Technology, 801 Leroy Place, 87801 Socorro, NM, USA.

*Corresponding author: Tel: +6221 7270027; Fax: +6221 7863432; e-mail: [email protected]

ABSTRACT The ability of both bare and surface-modified hematite nanoparticles to reduce the viscosity and upgrade the quality of heavy crude oil via aquathermolysis reaction was investigated in this study. The surface of hematite nanoparticles was modified using oleic acid to improve its hydrophobicity. First, a desulfurization study of thiophene was carried out to study the effect of hydrophobicity on the catalytic activity of the nanoparticles. Results showed that the catalytic activity could be improved by changing hydrophobicity of the nanoparticles from hydrophilic to slightly more hydrophobic. However, reduction of catalytic activity was observed when more oleic acids were attached due to blockage of the catalytic sites. In such a relatively mild aquathermolysis reaction, both untreated and surface-modified hematite nanoparticles were able

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to effectively reduce the viscosity of heavy crude oil by 61.52% and 74.33%. Additionally, the amount of large hydrocarbon molecules such as asphaltene and resin fractions were significantly reduced to form light oil which is proven by the increment of saturated and aromatic fractions.

KEYWORDS: Aquathermolysis, heavy oil, hematite, oleic acid, hydrophobicity

1. INTRODUCTION Growing demand for petroleum products in response to the rapid increment of global automotive and industrial needs and the shortage of conventional oil reserves has induced the exploration and production of the alternative unconventional resources. It is reported that unconventional resources are accounted for about 70% of total world oil reserves and more than half of them are being heavy and extra heavy oils1. Therefore, researches on maximizing the production of heavy and heavy crude oils have recently become one of the hot topics in petroleum industry. Nevertheless, exploration and production of unconventional heavy oil are considered more challenging than conventional light oils due to its high amount of heteroatoms components such as resins and asphaltene2. Heavy oil has a very high viscosity and low API gravity value which makes it hard to produce, transport and process. In general, optimization of heavy oil production can be done using several recovery techniques such as thermal, chemical, and biochemical recovery3-10. Among these recovery techniques, thermal recovery via catalytic aquathermolysis process is by far considered as the simplest and most effective method to extract heavy oil11. In aquathermolysis, degradation of large hydrocarbon molecules and heteroatom compounds has been known as one of the major factors responsible for the viscosity reduction and quality improvement of heavy crude oil11-14.


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In literatures, different types of iron-based catalysts such as FeSO4, Fe-naphthenate, Fe(CH3COCHCOCH3)3, iron (III) dodecylbenzene sulfonate, and iron-based ionic liquid have been widely used in aquathermolysis process2,15-18. The formation of strong interaction between iron and heavy oil molecules (asphaltene and heteroatom compounds) has been considered as the key factors for the high catalytic activity of iron-based catalysts. Strong interaction between iron and model asphaltene molecules both in the presence of water and electron-donor additives has been proven in a theoretical modelling study19. Based on this study, Rosales and co-workers reported that iron forms a strong interaction directly with N and S on the heteroatoms compounds. As a result, bond energy (bond activation) of C-C, C-N, and C-S bonds on the heteroatoms molecules decreases which give rises to the activation of these bonds for scission and ultimately lead to the degradation of asphaltene molecules. In other studies, oil-soluble and amphiphilic catalysts are reported to exhibit better catalytic activity than water-soluble catalysts20-22. This is due to their ability to penetrate into hydrocarbon phase and thus have a maximum contact with heavy oil. For instance, Yufeng and co-workers compared four different types of iron- and nickel-based catalysts as both as water soluble- and oil-soluble in aquathermolysis reaction of Liaohe heavy crude oil22. Based on the results, the performance of oil-soluble catalysts was significantly superior than water-soluble catalysts. The catalytic activities of these catalysts could be arrange according to: no catalyst < NiSO4 < FeSO4 < Ninaphthenate < Fe-naphthenate. Recently, the application of hematite nanoparticles as catalyst has attracted many attentions due to their advantages as the most stable, nontoxic, inexpensive and naturally abundant phase of iron oxide23-30. According to literatures, one of the most common catalytic applications of hematite is for the catalytic steam hydrocracking of petroleum residual oil31-33. In our recent


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work, hematite nanoparticles were found to be catalytically active to oxidatively decompose thiophene via desulphurization reaction34. Because of this good catalytic desulfurization activity, hematite nanoparticles can potentially be used in aquathermolysis reaction of heavy crude oil. Nevertheless, because of the high surface charge of hematite’s oxygen rich surface, the nanoparticles can only be dispersed in polar phases such as water or alcohol, making it less favorable for aquathermolysis reaction. Therefore, surface modification is necessary to change the surface property of hematite nanoparticles from hydrophilic to hydrophobic. In the past few years, various types of modifiers have been used for modification of hematite surface35-40. However, most of these surface modifications were carried out in an aqueous suspension. As a result, both adsorption density and rate of adsorption are significantly affected by the pH of the solution. Recently, we have successfully developed a non-aqueous method to modify the surface hydrophobicity of hematite nanoparticles using oleic acid41. It is observed that hydrophobicity of the nanoparticles could be changed from hydrophilic to hydrophobic by simply forming a monodentate interaction between oleic acid and hematite surface. The degree of hydrophobicity could also be adjusted by simply controlling the amount of oleic acid used for modification. In this paper, the catalytic activity of both bare and surface-modified hematite nanoparticles in catalytic aquathermolysis of heavy crude oil were investigated. To study the effect of surface modification, nanoparticles with different degree of hydrophobicity were firstly used in desulphurization reaction of thiophene. The effect of hydrophobicity on the performance of hematite nanoparticles in aquathermolysis was also investigated in terms of viscosity reduction and quality improvement of the heavy crude oil. Moreover, the possible catalytic mechanism of heavy crude oil on hematite nanoparticles with different degree of hydrophobicity was also investigated in this study.


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2. EXPERIMENTAL SECTION 2.1. Materials For the synthesis of hematite nanoparticles, iron (III) chloride hexahydrate was purchased from Alfa Aesar® and used as the iron source. Ammonium hydroxide and ethanol were purchased from Sigma-Aldrich® and used in the synthesis of nanoparticles. Oleic acid and methanol were purchased from Fisher Scientific® and used in surface modification. For the aquathermolysis reaction, thiophene and hexane were purchased from Sigma-Aldrich®. Meanwhile, for SARA analysis, mobile phases such as n-heptane, petroleum ether, toluene were purchased from Sigma-Aldrich® and activated aluminum oxide (Sigma-Aldrich®) was used as the stationary phase. 2.2. Synthesis of Hematite Nanoparticles Hematite nanoparticles were synthesized via hydrothermal method according to our previous work [42]. In this method, a mixture of aqueous iron (III) chloride and ammonium hydroxide solution was prepared and heated at 120oC for 24 h in a Teflon-lined autoclave. The reaction products were then centrifuged and washed with distillated water and ethanol three times, and finally dried under vacuum at 70oC for 12 hours. The as-synthesized hematite nanoparticles were then characterized using XRD, Raman spectroscopy and HR-TEM. X-ray diffraction study was carried out using a PANalytical X'Pert Pro diffractometer equipped with PIXcel detector (PANalytical B.V., Almelo, Netherlands). The measurements were performed on zerobackground silicon plates with the diffraction angle from 6o to 70o using Cu Kα radiation. Data were collected using X'Pert Data Collector software and processed using X'Pert HighScore Plus (PANalytical B.V.). Raman active bands were obtained using a LabRAM ARAMIS Raman


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microspectrometer (Horiba Jobin Yvon, Lille, France). The excitation laser source was a Ventus 532 nm mpc6000 laser (Laser Quantum, England). Spectral measurements were conducted in the range of 200-2500 cm-1 using Labspec5 software (Horiba Jobin Yvon, Lille, France). TEM images were collected using JEOL 2010 EX high-resolution transmission electron microscope (HR-TEM) with Oxford-Link EDS and a Gatan Digital Micrograph equipped with slow scan CCD camera, operated at 200 kV. 2.3. Surface Modification Surface modification of as-synthesized hematite nanoparticles was done via non-aqueous method according to our previous work41. In this method, a series of oleic acid solution in methanol were prepared at different concentration which was varied between 0.05 to 25 mM in methanol. Into the solution, 0.02 gram of as-synthesized hematite nanoparticles was added. The final mixtures were then incubated at room temperature for 1 hour using an IKA® KS 400 Incubating Shaker. The final mixture was then centrifuged and the precipitated particles collected and washed 3 times with methanol to remove the remaining unattached oleic acid residue. To study the attachment of oleic acid onto the surface of hematite nanoparticles, FTIR and hydrophobicity analyses were carried out. FTIR spectra of samples were obtained using with a Thermo Scientific Nicolet Avatar 370 DTGS FTIR Spectrometer at room temperature. Meanwhile, the degree of hydrophobicity was measured by determining the contact angle of thin film of hematite nanoparticles using OCA 20 (DataPhysics Instrument GmbH, Filderstadt, Germany). Furthermore, the hydrodynamic particle size of hematite nanoparticles was determined by Microtrac Zetatrac (Model NPA152-31A), a dynamic light scattering (DLS) analyzer. 2.4. Desulphurization of Thiophene


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Desulphurization of thiophene was carried out to investigate the effect of hydrophobicity on the catalytic activity of hematite nanoparticles. The reaction was done in a home-made Teflonline autoclave reactor. As the feedstock, some amount of thiophene in hexane solution with known initial concentration (1.2 M) was mixed with water at ratio of 3:7. The mixture was then transferred into the reactor along with 0.1% wt. of hematite nanoparticles as catalyst. The mixture was then heated up to 150oC for 48 hours. After the reaction, the reactor was cooled to room temperature. The catalytic performance of hematite nanocatalyst was determined by the percentage conversion of thiophene before and after the reaction. Here, Agilent 7890A Gas Chromatograph equipped with TCD as the detector and Agilent J&W HP-5 Column (Length: 30 m; ID: 0.32 mm; Film: 0.25 µm) was used to measure the concentration of thiophene. 2.5. Catalytic Aquathermolysis Reaction Catalytic aquathermolysis reaction was done to study the effect of surface modification on the performance of hematite nanoparticles in reducing the viscosity and improving the quality of heavy crude oil. In this study, aquathermolysis reaction was done in Teflon-line autoclave reactor where heavy crude oil sample was used instead of thiophene. The ratio between oil sample and water was 3:7. The mixture was then transferred into the reactor along with 0.1% wt. of catalyst and then heated up to 150oC for 48 hours. After the reaction, the reactor was naturally cooled to room temperature and the crude oil sample was collected for viscosity determination and SARA analysis. In this study, viscosity measurements were done using Physica MCR 301 rheometer (Anton Paar, GmbH) at room temperature (25oC). 2.6. Saturated, Aromatic, Resin, and Asphaltene (SARA) Analysis To further investigate the effect of hydrophobicity on the ability of hematite nanoparticles to improve the quality of heavy crude oil, the composition of saturated, aromatic, resin, and


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asphaltene (SARA) fractions were determined before and after the reaction. In this study, separation of SARA was done using column chromatography and composition of each fractions were determined gravimetrically. To separate asphaltene fraction, some amount of heavy crude oil sample was boiled in n-heptane (40 mL of n-heptane/g of oil sample) for an hour and then allowed to rest for 16 hours. The mixture was then vacuum filtered through a Büchner-style fritted glass funnel (60 mL, ASTM 10-15 µL medium porosity) to obtain the asphaltene fraction. The precipitate (asphaltene) was washed with n-heptane several times until no color was observed and then was vacuum dried for 5 hours. The de-asphaltene filtrate was concentrated and used for separation in column chromatography using activated aluminum oxide as stationary phase. To obtain the saturated, aromatic and resin fractions, the column was finally eluted with petroleum ether, toluene and toluene/methanol (30:70 v/v), respectively. Each eluate was then collected and the corresponding fractions could be obtained by concentrating them using rotary evaporator.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Surface Modification of Hematite Nanocatalyst In this study, a facile one step hydrothermal method was used to synthesize the nanoparticles42. Results from XRD and Raman spectroscopy analyses showed that pure crystalline phase of hematite crystal could be obtained with this method (see Supporting Information S-1). Microscopic images obtained from HR-TEM also showed that monodisperse polyhedron-shaped hematite nanoparticles with average particle size of around 100 nm were formed as the result of hydrothermal reaction (Figure 1a). To alter their hydrophobicity, the surface of as-synthesized hematite nanoparticles was modified using oleic acid via non-aqueous


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method. Figure 1b presents the FTIR spectra of the synthesized hematite nanoparticles, oleic acid, and oleic acid surface modified hematite nanoparticles. Based on the spectra, it is clear that oleic acid could successfully be anchored onto the surface of hematite nanoparticles since IR spectra of hematite nanoparticles after oleic acid modification resembles a combination between the spectra of pure hematite nanoparticles and pure oleic acid. This is confirmed by the appearance of both hematite and oleic acid specific peaks as the result of the strong interaction between hematite surface and oleic acid as they form a complex. In addition, it is also known that the amount of oleic acid grafted on hematite surface is proportionally correlated to the amount of oleic acid used for treatment (see Supporting Information S-2).

Figure 1. (a) TEM image of hematite nanoparticles and its corresponding FFT pattern, (b) FTIR spectra of hematite nanoparticles, oleic acid, and hematite nanoparticles after oleic acid modification.


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3.2. Hydrophobicity of Hematite Nanoparticles In this work, the degree of hydrophobicity of hematite nanoparticles prior and after surface modification was determined by measuring the contact angles of nanoparticles thin film. Figure 2 presents contact angles of as-synthesized hematite nanoparticles thin film treated with different concentrations of oleic acid. Based on the result, it is obvious that the contact angle of hematite thin film gradually increased with concentration of oleic acid. This indicates that the degree of hydrophobicity increases gradually as more oleic acid are attached onto the surface of hematite nanoparticles. In Figure 2a, untreated hematite nanoparticles had a very low contact angle (θ = 31.3o) indicating that the nanoparticles are very hydrophilic (θ < 90o). However, when the nanoparticles were treated with only 0.05 mmol/dm3 of oleic acid, an increase in contact angle was observed (θ = 73.7o) and the surface of nanoparticles became less hydrophilic (see Figure 2b). As expected, further increment in contact angle was observed when hematite nanoparticles were treated with larger concentration of oleic acid, and thus making the nanoparticles more hydrophobic (Figure 2c and d).


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Figure 2. Contact angle of synthesized hematite nanoparticles thin film treated with oleic acid at different concentration, (a) 0; (b) 0.05; (c) 0.4; (d) 25 mM.

This hydrophobicity improvement is believed to be the result of oleic acid attachment on the surface of the nanoparticles. As the result, surface property of hematite nanoparticles is altered from hydrophilic to hydrophobic. Similar phenomenon has also been reported in a study reported by Hsiang and co-workers when nano-sized boehmite (γ-AlO(OH)) particles were coated with a perflurodecanoic acid (PFDA)43. They observed that water contact angles for PFDA-modifiedboehmite increases with PDFA concentration as the result the formation of a strong ionic bonding between PFDA and the surface of boehmite. In this work, it is believed that oleic acid was also forming a strong bonding interaction with the surface of hematite nanoparticles. Previously, we have reported that oleic acid can attach strongly to the surface of hematite surface by forming a chemical interaction41. The interaction between oleic acid and hematite surface was proven by the disappearance of C=O stretch (1716.16 cm-1) in the FTIR spectra of pure oleic acid and the appearance of two new peaks at 1646.32 cm-1 and 1413.76 cm-1, which correspond to the asymmetric νas(COO-) and the symmetric νs(COO-) (Figure 1b). According to literatures, these two new peaks could be used to predict the type of binding interaction between carboxylate head and iron oxide surface simply by calculating their wave number of separation (∆ν)41,44-45. Interaction between carboxylate head and iron oxide surface could form monodentate interaction (∆ν = 200-300 cm-1), chelating bidentate (∆ν < 110 cm-1) or bridging bidentate (∆ν = 140-190 cm-1). Here, since the calculated wave number of separation (∆ν) is 233.1 cm-1, therefore the type


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of interaction between oleic acid and hematite surface can be categorized as monodentate interaction. Moreover, it was also observed that surface modification not only renders hematite nanoparticles to be hydrophobic but also induces particle aggregation. This aggregation is proven by the hydrodynamic particle size distribution of the nanoparticles as presented in Figure 3. Based on the result, a very narrow particle size distribution with average particle size of about 100 nm were observed for untreated hematite nanoparticles. However, particle size distribution became wider and average hydrodynamic particle size became larger when the nanoparticles were treated with oleic acid. Figure 3 shows that a very wide particle distribution with average size as large as 838 nm were obtained when 25 mM of oleic acid was used to treat hematite nanoparticles. Similar aggregation due to oleic acid attachment has also been reported previously by Baalousha and co-workers46. In their study, severe aggregation of iron oxide nanoparticles was observed when the nanoparticles were coated with humic acid. This severe aggregation is believed due to charge neutralization as a result of the formation of oleic acid and hematite nanoparticles interaction.


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Figure 3. Hydrodynamic particle size of hematite nanoparticles treated with oleic acid at 0, 0.4, 5 and 25 mM.

3.3. Desulphurization of Thiophene In aquathermolysis, desulfurization has been considered as one of the most important reactions that responsible in reducing the viscosity of heavy oil. In this study, the effect of surface modification on the catalytic activity of hematite nanoparticles in desulfurization reaction was firstly carried out against thiophene. Figure 4 shows the catalytic activity of hematite nanoparticles treated with different concentration of oleic acid in desulfurization of thiophene. Based on the result, it is clear that untreated hydrophilic hematite nanoparticles exhibit a good catalytic activity by converting nearly half of the initial amount of thiophene. In our previous work, we report that thiophene undergoes oxidative desulphurization on the surface of oxygenrich hematite nanoparticles to produce maleic acid, SO2 and CO247. During desulfurization reaction, it is believed that the catalytic process involved a cyclic phase transformation between hematite and magnetite. As thiophene is oxidatively decomposed into its products, crystalline phase of some part of hematite surfaces are reduced into magnetite. However, in the presence of water as the source of the active oxygen, these magnetite surfaces can be re-oxidized back into hematite.


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An increase in thiophene conversion was observed when the hydrophobicity of hematite nanoparticles was altered using 0.05 mM of oleic acid. At this condition, the nanoparticles are slightly more hydrophobic (θ: 73.7o) due to the presence of oleic acid on its surface. As the result, surface-modified hematite nanoparticles were able to penetrate into the oil phase and have a maximum contact with thiophene and effectively increases thiophene conversion to 59.9%. However, further improvement on hydrophobicity resulted in a less thiophene conversion. Modification using 0.4 mM of oleic acid reduces thiophene conversion to 45.6%. Meanwhile, total surface modification using 25 mM of oleic acid resulted in further reduction on the nanoparticles catalytic activity (thiophene conversion: 41.2%).

Figure 4. Catalytic activities of hematite nanocatalysts treated with 0, 0.05, 0.4 and 25 mM oleic acid in desulfurization of thiophene.


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This phenomenon could be explained by taking into account the availability of catalytic sites to accommodate the reaction. It is true that surface modification using oleic acid would render the nanoparticles to have a more hydrophobic surface. As the result, the particles would easily be transferred into non-polar phase and have an optimum contact with thiophene as the substrate. However, it is also important to note that the adsorption of oleic acid on the hematite surface would block the catalytic active sites. The higher the degree of hydrophobicity, the more oleic acid are attached on the surface and block the catalytic sites. Moreover, particle aggregation due to charge neutralization and interparticle hydrophobic interaction could also be another possible reason for the reduction of nanoparticles catalytic activity. As more oleic acid are attached on the surface of hematite nanoparticles, some nanoparticles could form particle clusters or possibly micelle-like aggregates which ultimately lead to the reduction of catalytic active site. Furthermore, FTIR analysis of the catalysts collected after the reaction also revealed that two peaks for the asymmetric and symmetric CH2 stretch and C–O stretch specific for oleic acid were still observed (Supporting Information S-3). This suggests that oleic acid was still intact on the surface of hematite nanoparticles and not easily desorbed or replaced by heavy oil molecules even though the catalyst had been subjected to high temperature. 3.4. Aquathermolysis of Heavy Crude Oil To further investigate the effect of surface modification on the ability of hematite nanoparticles to reduce the viscosity and upgrade the quality of heavy crude oil, aquathermolysis reactions were carried. The result of these investigations are presented in Table 1. Based on the result, it is clear that aquathermolysis reaction without the presence of catalyst did not significantly change physical properties and chemical composition of heavy crude oil. Viscosity of heavy crude oil remained unchanged, while the composition of aromatic and resin fractions


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was also unchanged. There is only a slight reduction of asphaltene because of the thermal degradation. However, when untreated hematite nanoparticles were used, significant reduction on the viscosity of heavy crude oil was observed. Based on Table 1, viscosity decreases by 61.52%; from 356 cP to 137 cP. This viscosity reduction is believed due to the degradation of large hydrocarbon molecules in asphaltene and resin fractions to become smaller saturated and aromatic hydrocarbon molecules. This is proven by the increment of saturated and aromatic fractions in correspond to the reduction of asphaltene and resin fractions. Further improvement on the catalytic activity was also observed when surface-modified hematite nanoparticles was used as catalyst. After aquathermolysis reaction using surface-modified hematite nanoparticles, viscosity of heavy crude oil was significantly dropped by nearly 75% from 356 cP to 137 cP. Additionally, greater reduction in asphaltene and resin composition and higher increment of saturated and aromatic fractions were also observed at this condition. Table 1. Effect of surface modification on hematite nanoparticles towards physical characteristic and chemical composition of heavy crude oil in aquathermolysis reaction.

Initial heavy crude oil

Catalyst

Untreated No Catalyst Hematite Nanoparticles Viscosity (cP)* 356.0 378.8 137.0 Asphaltene (%) 6.28 5.25 4.91 Saturated (%) 62.92 64.58 65.83 Aromatic (%) 17.52 16.61 18.02 Resin (%) 13.28 13.56 11.24 * o Viscosity was measured at 25 C (see Supporting Information, S-4 to S-7) + Treated with 0.05 mM of oleic acid Parameters

Surface-Modified Hematite Nanoparticles+ 91.4 4.17 66.55 19.89 9.39

In the literatures, there have been number of studies were reported related to the mechanism of aquathermolysis reaction. For instance, Wang and co-workers (2010) reported that there were


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at least nine types of reactions were observed during the reaction when Fe3+ and Mo6+ were used as catalysts48. These reactions are pyrolysis, depolymerization, hydrogenation, isomerization, ring opening, oxygenation, alcoholization, reconstruction and esterification. Recently, Li et al. (2013) has suggested that the major reaction that is responsible for viscosity reduction of heavy crude oil was due to the hydrodesulphurization of heavy components during the reaction1. It is reported that transition metals such as Fe, Cu, Ni, Cr, Mo and Co could form strong interactions with heavy oil components and serve as catalytic center during the reaction1,19. Additionally, theoretical study has also suggested that any aromatic system like benzene can interact strongly with hematite surface through π-bonding in the parallel adsorption geometries and weak hydrogen bonds in the vertical geometries49. These interactions can cause distortions in benzene ring where the hydrogen atom bound to the ring is slightly displaced upward. As the result, C-H bond and the C-C bond will be elongated and thus lead to the reduction of molecule stability. In this work, it is believed that large hydrocarbon molecules such as asphaltene and resins interact with hematite surface through π-bonding, Van der Waals, H-bonding, and Fe-heteroatoms interactions. As the result, some parts of these large hydrocarbon molecules were destabilized and finally decomposed into smaller light oil components due to complex reactions, thermal decompositions and/or oxidative reaction with lattice oxygen. Because of these decomposition, some area in the hematite surface undergo phase transformation to become magnetite. However, in the presence of water as the source of active oxygen during the reaction, the oxygen species could be used to reoxidize magnetite to hematite. The overall possible mechanism for catalytic aquathermolysis of heavy crude oil using surface-modified hematite nanoparticles can be expressed as shown in figure 5.


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Figure 5. Catalytic mechanism of aquathermolysis of heavy crude oil using surface-modified hematite nanoparticles. 4. CONCLUSION Investigation on catalytic aquathermolysis reaction of heavy crude oil to study the effect of surface modification of hematite nanocatalysts was presented in this work. Based on the results, it is observed that catalytic activity of hematite nanoparticles was significantly affected by the degree of particle hydrophobicity. The catalytic activity of hematite nanoparticles to oxidatively decompose thiophene could be improved by altering particles surface property from hydrophilic to slightly more hydrophobic. This can be done by modifying hematite nanoparticles with 0.05 mM of oleic acid. However, further improvement on hydrophobicity significantly decreases catalytic activity since more oleic acid are attached on the surface of nanoparticles and block the catalytic sites. Moreover, it is observed that hematite nanoparticles were able to significantly reduce the viscosity and upgrade the quality of heavy crude oil during aquathermolysis reaction. This viscosity reduction was due to degradation of large hydrocarbon molecules on asphaltene


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and resin fractions to produce smaller hydrocarbon molecules. This is proven by the increment of saturated and aromatic fractions as the result of the reduction of asphaltene and resin. Further improvement in aquathermolysis catalytic activity was also observed when surface-modified hematite nanoparticles was used as catalyst. It is believed that surface modification has allowed hematite nanoparticles to penetrate out of aqueous phase to have a maximum contact with heavy oil molecules as the substrate of the reaction. At this condition, viscosity of oil sample can be further reduced by nearly 75%.

ACKNOWLEDGEMENT We gratefully acknowledge the support of the Department of Energy through the National Energy Technology Laboratory under contract number DE-FE0005979. SUPPORTING INFORMATION Additional data on the characterization of as-synthesized hematite nanoparticles, i.e. XRD and Raman spectroscopy analysis (Figure S-1), FTIR spectra (Figure S-2 and S-3), and Rheology analyses (Figure S-4 to S-7).

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Graphical Abstract


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Figure 1. (a) TEM image of hematite nanoparticles and its corresponding FFT pattern, (b) FTIR spectra of hematite nanoparticles, oleic acid, and hematite nanoparticles after oleic acid modification. 250x166mm (96 x 96 DPI)


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Figure 2. Contact angle of synthesized hematite nanoparticles thin film treated with oleic acid at different concentration, (a) 0; (b) 0.05; (c) 0.4; (d) 25 mM. 203x185mm (96 x 96 DPI)



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Figure 3. Hydrodynamic particle size of hematite nanoparticles treated with oleic acid at 0, 0.4, 5 and 25 mM. 149x118mm (150 x 150 DPI)


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Figure 4. Catalytic activities of hematite nanocatalysts treated with 0, 0.05, 0.4 and 25 mM oleic acid in desulfurization of thiophene. 148x118mm (150 x 150 DPI)



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Figure 5. Catalytic mechanism of aquathermolysis of heavy crude oil using surface-modified hematite nanoparticles. 238x149mm (96 x 96 DPI)


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173x139mm (96 x 96 DPI)


Catalytic Aquathermolysis of Heavy Crude Oil Using Surface-Modified

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