Article pubs.acs.org/EF
Simple Functionalization of Asphaltene and Its Application for Efficient Asphaltene Removal Seonung Choi,† Wonbum Pyeon,† Jong-Duk Kim,*,† and Nam-sun Nho‡ †
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ‡ High Efficiency and Clean Energy Research Division, Korea Institute of Energy Research (KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon, 305-343, Republic of Korea S Supporting Information *
ABSTRACT: Asphaltene, the cheapest fraction of petroleum, was modified into a novel additive in order to facilitate a deasphalting process, such as paraffinic froth treatment. Asphaltene powder was oxidized by ozone, which is more powerful and less harmful to the environment than other oxidants. The ozonized asphaltene was characterized, and the reaction kinetics of ozonation was interpreted by the shrinking core model. Ozonized asphaltene was added to a water/n-pentane/bitumen emulsion to enhance the precipitation of asphaltene. Control of the properties of the precipitate was allowed by adjusting the ozonation degree and dosage of ozonized asphaltene. The removal of asphaltene was enhanced from 40% to a maximum of 70% by adding ozonized asphaltene under the same conditions. The boiling point distribution of deasphaltened oil indicates that a large amount of residue was removed using ozonized asphaltene. The dispersion behavior was checked by measuring the aggregate size in toluene and alkane solution. It was confirmed that asphaltene and ozonized asphaltene can interact with each other with high affinity.
1. INTRODUCTION Bitumen is one of the unconventional oils recovered from oil sands by steam-assisted gravity drainage (SAGD) or mining.1−4 When mined oil sands are mixed with water, bitumen froth is generated and cleaned by the froth treatment process, a separation process that removes water and sand particles from bitumen froth.5 In general, two main froth treatment processes are in operation: naphthenic froth treatment (NFT) and paraffinic froth treatment (PFT). In naphthenic froth treatment, naphtha is used as a diluent to reduce viscosity and density and can achieve a high yield of recovery (aproximately 99%); however, the produced bitumen contains water and solids. Conversely, paraffinic froth treatment, which is a relatively new process, uses paraffin solvent as a diluent and produces a higher-quality bitumen with low concentrations of water, solids, and asphaltene. Moreover, it consumes less energy than naphthenic froth treatment. However, one drawback of paraffinic froth treatment is the loss of hydrocarbons and a higher ratio of solvent/bitumen than seen with naphthenic froth treatment.6 In some cases, bitumen is required to be transported long distances, such as to Shell’s Albian Sands project; thus, it is necessary to remove asphaltene during paraffinic froth treatment.7 Often, partial deasphalting can be conducted by paraffinic froth treatment on-site at the mine to remove the majority of asphaltene from bitumen.8 Recent research has examined certain factors that have an effect on froth treatment. For instance, a temperature change from 80 to 50 °C resulted in a great decrease in recovery and an increase in the optimum paraffin/bitumen ratio in paraffinic froth treatment, while the temperature decrease had little impact on naphthenic froth treatment. Additionally, paraffinic © 2016 American Chemical Society
froth treatment has been shown to be more sensitive to the conditions of bitumen extraction.6,9−12 Unlike conventional oil, bitumen contains a high amount of asphaltene, which is insoluble in n-pentane or n-heptane but soluble in toluene.13 Moreover, asphaltene contains several aromatic rings and heteroatoms (N, S, and O). Thus, asphaltene has surface activity and polarity14−17 In industrial processes, asphaltene causes catalyst deactivation, coke formation, and plugging of the pipeline during refinement and transportation.18,19 Asphaltene is dispersed by resin-like surfactant in crude oil,20 which can interact with asphaltene via several intermolecular forces, such as van der Waals force, π−π stacking, acid−base interaction, and hydrogen-bonding, electrostatic interactions.21,22 The dispersion or aggregation can be controlled by adjusting the amount or species of surfactant, resin, or functional group in resin/asphaltene.23,24 On the basis of this fact, in the present paper, we studied an innovative method to facilitate the aggregation of asphaltene during paraffinic froth treatment. It was assumed that oxidized asphaltene can encourage stronger interaction with asphaltene due to the increased proportion of hydrophilic groups.25 Among the various oxidants, ozone is a great candidate for the oxidation of asphaltene, since the ozonation process is not only simple but also leaves a smaller number of byproduct than other oxidants. In industrial processes, ozone is usually used for the treatment of water and intermediate preparation of plasticizer and lubricant synthesis and in the food industry and during pharmaceutical production. Further, ozone has been Received: May 17, 2016 Revised: July 26, 2016 Published: August 23, 2016 6991
DOI: 10.1021/acs.energyfuels.6b01184 Energy Fuels 2016, 30, 6991−7000
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PVDF syringe filter, the ethanol was evaporated, and the weight of the ethanol-soluble part was measured. 2.4.3. Precipitation Enhancement with Ozonized Asphaltene. A 10−50 mg portion of ozonized asphaltene was dispersed in 5−15 mL of DI water in a 125-mL Erlenmeyer flask with sonication for 30 min. Three grams of bitumen and 9−50 mL of n-pentane were added. The bitumen emulsion was stirred magnetically at 200 rpm and room temperature for 30 min. Following agitation, the emulsion was filtered with filter paper (F2141 grade, CHMLAB Group). To completely eliminate n-pentane and water, the flask and filter were dried at 105 °C for 4 h. The dried precipitate was weighed and dissolved in dichloromethane (DCM) to collect all the precipitate. DCM was evaporated at 50 °C for further analysis of the precipitate. Moreover, deasphaltened oil (DAO) was separated from n-pentane and water using a vacuum rotary evaporator, and DAO was then evaporated in an oven at 120 °C for further analysis. 2.4.4. Asphaltene Aggregate Size Measurement. The asphaltene/ ozonized asphaltene mixtures in various proportions were dispersed in solvent at 0.5 g/L with ultrasonication for 30 min. Ozonized asphaltene, which was ozonized for 1 h, was used for size measurement. The solvent was mixed with various ratios of toluene and alkane (n-pentane, n-hexane, and n-heptane). Particle size distribution was measured using the dynamic light scattering (DLS) method within 10 min of sonication. 2.5. Instrument and Measurement. The particle size distribution of ground asphaltene was measured using a laser scattering particle size analyzer (HELOS), which can detect in the range of 0.1− 8750 μm. Element composition (C, H, O, N, S) was confirmed using the FlashEA 1112 (Thermo Finnigan) and FLASH 2000 series (Thermo Scientific) instruments. In addition, the chemical state data of each sample was obtained by X-ray photoelectron spectroscopy (XPS) using a MultiLab 2000. SARA (saturate, aromatic, resin, and asphaltene) analysis results were obtained using a TLC/FID analyzer (IATROSCAN MK-6s Mitsubishi Kagaku Iatron). The thermostability of samples was studied using a thermogravimetry analyzer (TGA) (TG 209 F3, NETZSCH). TGA was performed under a nitrogen atmosphere (100 mL/min), and the temperature was increased to 1000 °C at a rate of 10 °C/min. Simulated distillation (SIMDIS) analysis was performed to measure the boiling point distribution of DAO using a 6890N instrument from Agilent Technologies. Helium gas (99.999% purity) was used as the carrier gas. Samples were diluted in carbon disulfide (CS2) to 10%. The boiling point range was from 200 to 750 °C, and the analysis method was based on ASTM D750012. The functional groups of the oxidized asphaltene were analyzed using Fourier transform infrared (FT-IR) spectroscopy (Alpha-p). Dynamic light scattering (DLS) measurement was conducted to determine the size distribution in solvent using a Zetasizer Nano ZSP (Malvern) equipped with a laser diode.
used to produce azelaic acid and pelargonic acids from oleic acids by Emery Oleochemicals, Inc.26 The generally accepted mechanism of ozonation is the Criegee mechanism, proposed by Rudolf Criegee,27−29 in which ozone attacks the CC bond in alkenes and forms primary ozonide (−COOOC−). The primary ozonide then rapidly decomposes into the Criegee intermediate, which is an unstable molecule and reacts to produce a more stable molecule. Following formation, the Criegee intermediate undergoes unimolecular decomposition, rearrangement, or bimolecular reaction. Ketones, ethers, and carboxyl acids, or various gases (H2O, SO2, or NO3) are produced by reaction with trace gas. Even though the structure of asphaltene is ambiguous, and the reaction kinetics of the ozonation of asphaltene are inscrutable, it is assumed to generally follow these mechanisms. The ozonation product of asphaltene has been reported to contain various molecules.30 In the present research, the ozonation of asphaltene was conducted without solvent. As a result, the reaction begins on the surface of the asphaltene particles and heterogeneous reactions continue until all carbon has been exhausted. The shrinking core model can be applied to this case, because it is generally used for nonporous solid reactants that reacts with fluid.31 In the present paper, the ozonation of asphaltene and the characteristics of ozonized asphaltene were studied. Further, ozonized asphaltene was added to a water/n-pentane/bitumen emulsion as a novel additive to enhance the efficiency of asphaltene precipitation. The effect of ozonized asphaltene was investigated for pretreatment in the solvent deasphalting (SDA) process.
2. EXPERIMENTAL SECTION 2.1. Materials and Chemicals. Bitumen from Athabasca, Canada, was used. Solvents used in the experiment (n-C5H12, n-C6H14, nC7H16, ethanol, methanol, toluene, 1% phenolphthalein solution, sodium hydroxide, and dichloromethane) were purchased from SigmaAldrich. Water was deionized before use. 2.2. Asphaltene Preparation. Asphaltene was extracted from bitumen with an excess amount of n-pentane solvent. One gram of bitumen was added to 100 mL of n-pentane with stirring for 1 h at room temperature. After blending, the solution was filtered with a 0.45 μm membrane filter and dried to remove residual solvent. Completely dry asphaltene was ground and strained through a 100 μm mesh sieve. 2.3. Ozonation of Asphaltene. A 200 mg portion of ground asphaltene was placed in an SUS316 reactor, and oxygen gas passing through the ozone generator (1KNT-24, Enaly) was flowed into the reactor. The concentration of ozone in gas was 1.06 v/v%, and the flow rate was 1.5 L/min. The temperature and pressure were maintained at 40 °C and 1 bar, respectively. The reactor volume was 276.6 cm3. The ozonized asphaltene (OA) yield was measured immediately after the end of the reaction and stored in a desiccator until use, in order to prevent the absorption of water. 2.4. Characterization and Evaluation of Ozonized Asphaltene. 2.4.1. Neutralization Titration of Oxidized Asphaltene. The acidity of oxidized asphaltene was measured using neutralization titration. Thirty milligrams of oxidized asphaltene was dispersed in 15 mL of DI water for 30 min using bath sonication. Subsequently, 100 μL of phenolphthalein (1% in ethanol) solution was added, followed by the repeated addition of 20 μL of 0.1 N NaOH solution until the solution turned a red wine color. The total amount of added NaOH was then calculated. 2.4.2. Estimation of Ozonized Asphaltene Conversion. Conversion of ozonized asphaltene was measured by dispersion in ethanol. Ozonized asphaltene was dissolved in ethanol at 1 g/L using bath sonication. The undissolved fraction was filtered using a 0.45 μm
3. RESULT AND DISCUSSION 3.1. Ozonation of Asphaltene. Particle size distribution of ground asphaltene (sieved using a 100-μm mesh) was measured by the laser diffraction method. For ground asphaltene particles, the x10, x50, and x90 were 1.45, 3.75, and 23.91 μm, respectively, where xn denotes the particle dimension corresponding to n% of the cumulative undersize distribution. Following ozonation of ground asphaltene, the product weight and element composition were estimated as shown in Figure 1. In the first 15 min of the reaction, the oxygen content in ozonized asphaltene was radically increased from 1% to 19% (Figure 1). However, after 15 min, the rate of the increase in oxygen content was conspicuously low, and the O/C atomic ratio showed a similar trend. Moreover, the yield of ozonized asphaltene showed a rapid increase in the early stage of the reaction; however, when the reaction time reached 2 h, the yield converged to 120%, and the oxygen content increased [Figure S1, Supporting Information (SI)]. This indicates that 6992
DOI: 10.1021/acs.energyfuels.6b01184 Energy Fuels 2016, 30, 6991−7000
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(2)
where X is the conversion, t is the reaction time, and τ is the characteristic time. Here, τr and τd denote the characteristic time for the surface reaction dominant case and the internal diffusion-limited case, respectively. These characteristic times indicate the time required to complete the reaction. Moreover, τr and τd can be obtained from the following equations
ρR kC
(3)
τd =
ρR2 6DC
(4)
where ρ is the density of solid particle, R is the radius of particle, C is the concentration of fluid, k is the reaction rate constant, and D is diffusion coefficient. To investigate the conversion kinetics of ozonized asphaltene, the ethanol-soluble proportion was measured. We assumed that all ozonized asphaltene was soluble in ethanol, and that asphaltene was insoluble. As ozonation proceeded, the ethanol-soluble fraction increased, but the conversion rate decreased (Figure 3). The solid line indicates ideal kinetics of
Figure 1. Oxygen content and O/C ratio of ozonized asphaltene at various ozonation times.
loss of ozonized asphaltene occurs during ozonation. The total weight of oxygen and carbon in the ozonized asphaltene was also calculated, as shown in Figure S2 (SI). The initial weight of asphaltene, carbon, and oxygen was 200, 162, and 2 mg, respectively. The weight of carbon decreased by 14 mg in the first 15 min of the reaction, and oxygen increased by 41 mg. Therefore, at the beginning of ozonation, the addition of oxygen is preferred, while the removal of carbon also occurs. As the ozonation reaction progressed, the rate of oxygen addition and carbon removal decreased. Ozone would react immediately after contact with the surface of asphaltene particles, since ozone is very reactive and can oxidize asphaltene. Thus, the ozonation of asphaltene can be thought of as occurring at the surface of asphaltene particles. Once the entire surface of the ground asphaltene is oxidized by ozone, ozone will penetrate into the core of unoxidized asphaltene. The unoxidized asphaltene core will then diminish gradually, and the oxidized asphaltene shell will thicken. This concept is called the “shrinking core model” and can be applied to heterogeneous reactions. Here, ground asphaltene particles were assumed to be spherical. Figure 2 shows the conception of ozonation on a spherical asphaltene particle and the effect of grinding during ozonation. While the coverage on the surface of asphaltene particles by ozonized asphaltene is very fast, the infiltration of ozone into the unoxidized asphaltene core is slow. Prior to the surface being completely covered by ozonized asphaltene, the total reaction is mainly controlled by the reaction on the surface. However, when ozone infiltrates toward the core, the reaction at the core zone is limited by the internal diffusion of ozone into the unoxidized core. On the basis of the shrinking core model of spherical particles,31,32 the relationship between time and conversion can be expressed as t = τr[1 − (1 − X )1/3 ]
τr =
Figure 3. Conversion of reaction time and its curve fitting to the shrinking core model (ideal surface reaction curve and ideal internal diffusion curve).
the shrinking core model for surface reaction dominant and internal diffusion dominant cases. In particular, there was an upsurge in conversion during the early stage of the reaction, similar to the results seen with oxygen content. The difference in conversion with the fitting model after 8 h can be considered as a loss by the reaction of ozonized asphaltene, and this is consistent with the convergence of yield. In particular, there was an upsurge in conversion during the early stage of the reaction, similar to the results seen with oxygen content. The
(1)
Figure 2. Schematic design of ozonation on asphaltene powder particle based on the shrinking core model. 6993
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Figure 4. Dispersion of ozonized asphaltene in a toluene/water emulsion.
difference in conversion with the fitting model after 8 h can be considered as a loss by the reaction of ozonized asphaltene, and this is consistent with the convergence of yield. D (5.22 × 10−10 m2/h) and k (4.82 × 10−2 m/h) were calculated by fitting to the model. The diffusion coefficient of ozone to asphaltene is about 1/6-fold of the diffusion coefficient of free ozone in air.33 Furthermore, this k value is relatively large for the oxidation of pyrite (k = 3.07 × 10−6 m/h) with air, which can be considered as a slower reaction.34 This is reasonable in view of the fact that ozone is very reactive. Asphaltene is insoluble in n-pentane or n-heptane but soluble in toluene; however, the solubility of asphaltene can be altered by ozonation. To visualize the hydrophilicity of ozonized asphaltene, asphaltene and asphaltene ozonized for various times were dispersed in a water/toluene emulsion (Figure 4). After 30 min of ozonation, a portion of ozonized asphaltene could be dispersed in water, while the oxygen content increased slightly relative to the sample that was ozonized for 15 min. On the other hand, no visible change could be observed thereafter, even though the oxygen proportion in ozonized asphaltene was highly increased after 15 min. We suppose that some of the ozonized asphaltene coheres to asphaltene when dispersed in toluene. Excessive ozonized asphaltene may then be dissolved in water, when the proportion of ozonized asphaltene exceeds the coherence with asphaltene. A detailed argument will be discussed in section 3.3. As the ozonation time increased, a larger fraction of the sample was dissolved in water, indicating higher hydrophilicity. In particular, after 18 h of ozonation, the toluene solution of ozonized asphaltene became almost transparent. As mentioned earlier, ozonation can give asphaltene an acidic fraction. The total amount of acidic fraction in ozonized asphaltene can be quantified using neutralization titration. As shown in Figure 5, an increasing trend in acidity presented a similar change in the shape of the O/C atomic ratio by ozonation. Moreover, the linear relationship between acidity and the O/C atomic ratio was confirmed by plotting the O/C atomic ratio vs the acidity. Thus, it can be said that the ozonation of asphaltene causes the acidification of asphaltene, which can be controlled by reaction time. The increase in hydrophilic groups upon ozonation was also identified using FT-IR spectroscopy, as seen in Figure 6. There was a remarkable increase in the peak of O−H stretching (3400 cm−1), CO stretching (1625−1800 cm−1), and C−O stretching (1000−1260 cm−1). On the other hand, the intensity of the aromatic C−H peak (2850−2950 cm−1), a pair of aromatic CC peaks (1475 and 1600 cm−1), and the −CH2/− CH3 asymmetric deformation peak (1456 cm−1) were abated by ozonation.35 In summary, the hydrophilic parts, such as carboxyl, alcohol, ketone, and aldehyde groups, in asphaltene
Figure 5. Acidity change in ozonized asphaltene measured by neutralization titration and the relationship between O/C ratio and acidity (inset).
Figure 6. FT-IR spectrum of asphaltene and ozonized asphaltene.
were increased by ozonation, while the hydrophobic parts were decreased. On the basis of the shrinking core model, the chemical state of the surface of asphaltene particles should be unchanged following consumption of all molecules that can react with ozone. Using XPS analysis, the chemical state of carbon (C 1s) on the surface was measured (Figure 7). The spectra were deconvoluted to four main peaks. The binding energy of unoxidized carbon was calibrated to 284.7 eV. C−O (ether, hydroxyl), CO (ketone), and O−CO (ester, carboxyl) were fitted to 286.0, 287.1, and 288.9 eV, respectively.36 The 6994
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Figure 8. Removal efficiency of SARA without ozonized asphaltene at various water and n-pentane volumes.
Figure 7. Chemical state of carbon (C 1s) on the surface of ozonized asphaltene measured by XPS.
The removal efficiency of asphaltene was mainly influenced by the amount of n-pentane solvent. When 15 mL of n-pentane was used, approximately 40% asphaltene and 20% resin were filtered. At the same time, little saturates or aromatics were involved in the precipitate. The increased amount of water from 5 to 15 mL caused little increase in asphaltene precipitation. When the amount of n-alkane solvent used is low, the presence of emulsified water increases the asphaltene precipitation. Asphaltene absorbs at the interface of the water droplet and is removed with water at a yield below precipitation onset.37 Ozonized asphaltene was added to enhance the precipitation of asphaltene, as shown in Figure 9. The effects of the amount, degree of oxidation, and solvent of ozonized asphaltene on precipitation were investigated. When ozonized asphaltene O19% (oxygen content 19 wt %) was added, the effect on precipitation was not significant, even when 50 mg (1.7% to bitumen) of ozonized asphaltene was added. For ozonized asphaltene O24%, the addition of ozonized asphaltene resulted in a gradual increase in asphaltene removal efficiency. However, the higher the amount of ozonized asphaltene added, the more saturates and aromatics were removed. Furthermore, the use of ozonized asphaltene O32% showed a notable effect on asphaltene removal. For instance, the addition of 20 mg of ozonized asphaltene caused the maximum improvement of 25% on precipitation efficiency. This result indicates that precipitation can be controlled by adjusting the amount and oxidation degree of ozonized asphaltene. However, when 50 mg of O32% ozonized asphaltene was added, the eliminated saturates and aromatics were approximately 60% and 7%, respectively, which is an unwanted increase. It seems that saturates and aromatics are entangled in asphaltene aggregates due to an excessive quantity of ozonized asphaltene. Thus, an appropriate amount of ozonized asphaltene should be added to achieve effective precipitation. The volumes of water and n-pentane were changed to observe their effect on precipitation. Changing the water volume to 5 mL (C15 W5 O24%) hardly affected precipitation with the other conditions fixed. As discussed earlier, a larger volume of n-pentane (C25 W15 O24%) generally resulted in a greater amount of asphaltene removal than seen with the sample C15 W15 O24%. The increase in precipitation efficiency by a higher oxidation degree (C15 W15 O32%) exceeded the increase seen with the addition of npentane (C25 W15 O24%) under the same conditions. This indicates that the degree of ozonation is as influential a factor as
majority of the carbon (90%) in asphaltene (n-pentane insoluble) was unoxidized, while the amounts of C−O, C O, and O−CO were small. Following 1 h of ozonation, however, the proportion of carbon in the oxidized part remarkably increased to almost 60%, and the proportions of C−O, CO, and O−CO were highly increased to 10−15%. Nevertheless, there was no significant change in the spectrum when the ozonation time was longer than 1 h. While the oxygen content, acidity, and hydrophilicity increased continuously, the yield, conversion, and proportion of bonding between C and O converged. This supports the notion that the ozonation of asphaltene follows the shrinking core model and that some ozonized asphaltene can be lost by ozone flow during excessive reaction. That is, excessive ozonation causes loss of the ozonized asphaltene surface and a new ozonized asphaltene surface is exposed to ozone, resulting in the maintenance of the surface properties of ozonized asphaltene. 3.2. Enhancing Precipitation with Ozonized Asphaltene. SARA (saturate, aromatic, resin, and asphaltene) analysis of the precipitate was performed to evaluate the precipitation ability of ozonized asphaltene. By measuring the SARA ratio of the precipitate, the efficiency of elimination from bitumen was calculated using the following equations: asphaltene elimination% =
(mprecipitate × asphaltene%) − mOA (mbitumen × asphaltene%)
saturate, aromatic, resin elimination% (mprecipitate × content%) × 100% = (mbitumen × content%)
× 100%
(5)
(6)
Here, OA denotes the ozonized asphaltene, and m is the weight of each material. We assumed that all the ozonized asphaltene was included in the precipitate. Figure 8 shows the precipitation efficiency without ozonized asphaltene in a water/n-C5H12/bitumen emulsion. C and W denote the volume of n-pentane and water, respectively. Since asphaltene is insoluble in n-pentane, the amount of precipitate increased when a larger volume of n-pentane was used. For instance, in the case of C25 W15 and C50 W15, the elimination efficiency of asphaltene increased to 45% and 60%, respectively. 6995
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Figure 9. Removal efficiency using ozonized asphaltene: (a) C15 W15 O19%, (b) C15 W15 O24%, (c) C15 W15 O32%, (d) C15 W5 O32%, and (e) C25 W15 O24%.
bitumen (3 g), respectively] of ozonized asphaltene was added. As shown in Figure 10a, the addition of ozonized asphaltene to a bitumen/n-pentane/water emulsion resulted in a left-shift, which means a decrease in the overall boiling point of DAO. In particular, the highest boiling point in DAO decreased from 740 to 640 °C by the addition of 1.00 wt % ozonized asphaltene. Moreover, the proportion of residue decreased, while the proportion of vacuum gas oil (VGO) and gas oil in DAO increased (Figure 10b). Thus, a finer quality of deasphaltened oil was obtained by the successful facilitation of precipitation using ozonized asphaltene.
the quantity of alkane solvent; thus, it would be possible to contrive an efficient process of froth treatment with ozonized asphaltene. Oil can be cut on the basis of the boiling point: naphtha (540 °C).38 For evaluation of DAO, the distribution of boiling points was analyzed using a simulated distillation method (SIMDIS). SIMDIS is a standardized chromatographic method that simulates the distillation curve of hydrocarbons and translates the retention time to a boiling point. The proportion of oxygen in the ozonized asphaltene was 32%, when 10, 20, and 30 mg [0.33, 0.67, 1.00 wt % 6996
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nm), submicron cluster (0.1−1 μm), and micron-sized aggregate (1−10 μm). While asphaltene and ozonized asphaltene had an unimodal distribution, the mixture of asphaltene and ozonized asphaltene in toluene showed a bimodal distribution. If there were no interaction between asphaltene and ozonized asphaltene, the spectra c−f would be bimodal, which is just the total spectrum of asphaltene and ozonized asphaltene; i.e., only nanosized and submicron-sized particles exist. The existence of micron-sized particles indicates that there is an interaction between asphaltene and ozonized asphaltene. Thus, ozonized asphaltene would play the role of enhancer to condense asphaltene with high affinity to asphaltene. In the Asp:OA (c) 1:1 and (d) 5:1 samples, micron- and submicron-sized particles were observed. It can be thought that all the asphaltene was consumed to form micron-sized aggregates, while the residual ozonized asphaltene formed the submicron-sized clusters. The intensity of the micron-sized aggregates became greater as asphaltene was added. Eventually, the only micron-sized peak was detected in the 10:1 sample (e). In other words, it can be said that 1-h-ozonized asphaltene can interact with 10-fold asphaltene by weight. On the other hand, when more asphaltene was added to the 20:1 sample (f), the micron- and submicron-sized aggregates suddenly almost disappeared, which indicates nano-sized dispersion of ozonized asphaltene. On the basis of this result, we can infer that toluene permeates into asphaltene/ozonized asphaltene aggregates and collapses them into nano-sized clusters when more than 10-fold asphaltene is added. In addition, the sudden change in solubility in water for 30-min-ozonized asphaltene, as shown in Figure 4, can be attributed to the fact that the ratio of asphaltene and ozonized asphaltene exceeded a specific value to create residual ozonized asphaltene. Furthermore, it can be conjectured that the interaction between asphaltene and ozonized asphaltene is greater than the toluene−asphaltene interaction. Asphaltene and ozonized asphaltene interact not only via π−π stacking but also via acid−base and dipole interactions.22 Even though asphaltene molecules can have intermolecular acid−base and dipole interactions, they will happen more frequently in ozonized asphaltene due to the abundance of acidic parts. When asphaltene and ozonized asphaltene are dissolved in toluene, ozonized asphaltene will be hindered by asphaltene via acid−base interactions, and this phenomenon induces the formation of large aggregates. Toluene is a good solvent for asphaltene, while n-alkane is a poor solvent, resulting in the aggregation of asphaltene. The asphaltene cluster sizes at various ratios of n-heptane in toluene have been studied.24,44−46 In the present paper, the aggregate size increased with the addition of n-alkane and showed a similar trend (Figure 12). The aggregates started to grow when 30% n-heptane was added and suddenly increased near to 60% n-heptane content. The aggregate size at more than 80% nheptane in solution was unmeasurable due to the instability of asphaltene. Following the addition of ozonized asphaltene (1 h, Asp:OA = 10:1), large aggregates also formed and showed growth with an increase in alkane proportion. It can be thought that the aggregate profile was left-shifted by ozonized asphaltene. As the number of carbons in n-alkane decreases, the solvency of alkanes also decreases, which causes more aggregation of asphaltene. This fact also affected the growth of asphaltene/ozonized asphaltene aggregates with n-alkane solvent addition. However, the size of asphaltene/ozonized asphaltene aggregates with a high proportion of n-alkane was
Figure 10. (a) Effect of ozonized asphaltene (O32%) on the boiling point distribution of deasphaltened oil. (b) Change in the composition proportion based on boiling point cut.
3.3. Asphaltene/Ozonized Asphaltene Aggregate. Asphaltene has a critical concentration at which it starts to form a nanoaggregate structure similar to the critical micelle concentration (cmc) of surfactants, which is called the critical nanoaggregate concentration (cnc or cnac).39 Even though the characteristics of crude oil vary depending on the production site, and there is some controversy regarding the value of cnc, the cnc of asphaltene in the literature is 0.164 g/L in toluene.40 Thus, the asphaltene concentration selected in this study was 0.5 g/L, which is low enough, but higher than 0.164 g/L, to form nanoaggregates. At a dilute concentration, the radius of gyration of asphaltene aggregates in toluene was measured as 1−10 nm by several methods such as DLS and SANS.41−43 Moreover, the aggregate size of asphaltene in the present study was measured as 7.372 nm (Figure 11a) with unimodal distribution. A DLS spectrum of ozonized asphaltene in toluene was also obtained. Ozonized asphaltene in toluene tended to hide hydrophilic groups inside and form a much larger particle size (891.2 nm), as shown in Figure 11b. In addition, asphaltene and ozonized asphaltene were dispersed in toluene together at various ratios [asphaltene:ozonized asphaltene (Asp:OA) = 20:1, 10:1, 5:1, and 1:1 by weight]. By measuring particle sizes, three types of peak were confirmed; nanosized cluster (0.1−10 6997
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Figure 11. Size distribution of asphaltene aggregate: (a) asphaltene (Asp), (b) O24% ozonized asphaltene (OA), (c) Asp:OA = 1:1, (d) Asp:OA = 5:1, (e) Asp:OA = 10:1, and (f) Asp:OA = 20:1.
ozonation of asphaltene interpreted by the shrinking core model, and the product, was characterized by FT-IR, XPS, element analysis, and solubility. The increase in hydrophilic parts of ozonized asphaltene strengthened the interaction with asphaltene. The stronger interaction with asphaltene resulted in an aggregation of asphaltene. As a result, the micron-sized aggregation was detected, even in toluene solvent at a low concentration of asphaltene, due to ozonized asphaltene. Moreover, the ozonized asphaltene showed a significant effect on the agglomeration of asphaltene in water/n-pentane/bitumen, and a significantly larger amount of precipitate was obtained. Thus, it can be said that separating the unit load or alkane volume of
not measured, since the size of large aggregates was out of the detectable range.
4. CONCLUSION The precipitation of asphaltene was facilitated by ozonized asphaltene as an additive for paraffinic froth treatment. Asphaltene was oxidized to give higher hydrophilicity using a simple method with ozone. Since the majority of asphaltene, which is generated from froth treatment, is buried in tailing ponds and causes environmental problems, the modification and application of asphaltene have a great value with respect to cost and the environment. Ground asphaltene was oxidized by ozone to achieve reaction kinetics and economical benefits. The 6998
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(4) Osacky, M.; Geramian, M.; Ivey, D. G.; Liu, Q.; Etsell, T. H. Influence of Nonswelling Clay Minerals (Illite, Kaolinite, and Chlorite) on Nonaqueous Solvent Extraction of Bitumen. Energy Fuels 2015, 29 (7), 4150−4159. (5) Chen, Q.; Stricek, I.; Cao, M.; Gray, M. R.; Liu, Q. Influence of hydrothermal treatment on filterability of fine solids in bitumen froth. Fuel 2016, 180, 314−323. (6) Rao, F.; Liu, Q. Froth treatment in Athabasca oil sands Bitumen recovery process: a review. Energy Fuels 2013, 27 (12), 7199−7207. (7) Moritis, G. Innovations push bitumen mining, economics; cut environmental effects. Oil Gas J. 2010, 108 (33), 88−97. (8) Shelfantook, W. E. A perspective on the selection of froth treatment processes. Can. J. Chem. Eng. 2004, 82 (4), 704−709. (9) Garner, W. N.; Madge, D. N.; Strand, W. L., Bituminous froth inclined plate separator and hydrocarbon cyclone treatment process. In Google Patents: 2008. (10) Romanova, U.; Valinasab, M.; Stasiuk, E.; Yarranton, H.; Schramm, L.; Shelfantook, W. The effect of oil sands bitumen extraction conditions on froth treatment performance. Journal of Canadian Petroleum Technology 2006, DOI: 10.2118/06-09-03. (11) Romanova, U.; Yarranton, H.; Schramm, L. Towards the improvement of the efficiency of oil sands froth treatment. In Canadian International Petroleum Conference 2003; Petroleum Society of Canada, 2003. (12) Romanova, U. G.; Yarranton, H. W.; Schramm, L. L.; Shelfantook, W. E. Investigation of oil sands froth treatment. Can. J. Chem. Eng. 2004, 82 (4), 710−721. (13) Yang, X.; Hamza, H.; Czarnecki, J. Investigation of subfractions of Athabasca asphaltenes and their role in emulsion stability. Energy Fuels 2004, 18 (3), 770−777. (14) Speight, J. Petroleum Asphaltenes-Part 1: Asphaltenes, resins and the structure of petroleum. Oil Gas Sci. Technol. 2004, 59 (5), 467−477. (15) Bouhadda, Y.; Bormann, D.; Sheu, E.; Bendedouch, D.; Krallafa, A.; Daaou, M. Characterization of Algerian Hassi-Messaoud asphaltene structure using Raman spectrometry and X-ray diffraction. Fuel 2007, 86 (12), 1855−1864. (16) Czarnecki, J.; Tchoukov, P.; Dabros, T. Possible role of asphaltenes in the stabilization of water-in-crude oil emulsions. Energy Fuels 2012, 26 (9), 5782−5786. (17) Yang, X.; Czarnecki, J. Tracing sodium naphthenate in asphaltenes precipitated from Athabasca bitumen. Energy Fuels 2005, 19 (6), 2455−2459. (18) Reynolds, J. Effects of asphaltene precipitation on the size of vanadium-, nickel- and sulfur-containing compounds in heavy crude oils and residua; Asphaltenes and asphalts, 1; Yen, T. F., Chilingarian, G. V., Eds.; Elsevier Science Press: New York, 1994. (19) Yen, T. Structure of petroleum asphaltene and its significance. Energy Sources 1974, 1 (4), 447−463. (20) Acevedo, S.; Escobar, G.; Gutiérrez, L. B.; Rivas, H.; Gutiérrez, X. Interfacial rheological studies of extra-heavy crude oils and asphaltenes: role of the dispersion effect of resins in the adsorption of asphaltenes at the interface of water-in-crude oil emulsions. Colloids Surf., A 1993, 71 (1), 65−71. (21) Chang, C.-L.; Fogler, H. S. Stabilization of asphaltenes in aliphatic solvents using alkylbenzene-derived amphiphiles. 2. Study of the asphaltene-amphiphile interactions and structures using Fourier transform infrared spectroscopy and small-angle X-ray scattering techniques. Langmuir 1994, 10 (6), 1758−1766. (22) Murgich, J. Intermolecular forces in aggregates of asphaltenes and resins. Pet. Sci. Technol. 2002, 20 (9−10), 983−997. (23) McLean, J. D.; Kilpatrick, P. K. Effects of asphaltene aggregation in model heptane−toluene mixtures on stability of water-in-oil emulsions. J. Colloid Interface Sci. 1997, 196 (1), 23−34. (24) Goual, L.; Sedghi, M.; Wang, X.; Zhu, Z. Asphaltene aggregation and impact of alkylphenols. Langmuir 2014, 30 (19), 5394−5403. (25) Choi, S.; Byun, D. H.; Lee, K.; Kim, J.-D.; Nho, N. S. Asphaltene precipitation with partially oxidized asphaltene from water/heavy crude oil emulsion. J. Pet. Sci. Eng. 2016, 146, 21−29.
Figure 12. Change in asphaltene/ozonized asphaltene aggregate size in toluene by the addition of alkane (n-C5H12, n-C6H14, and n-C7H16) and reference data24,44,45
paraffinic froth treatment can be reduced with ozonized asphaltene.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b01184. Figures summarizing the reaction yield for various ozonation times, the total weight of carbon and oxygen of ozonized asphaltene, the conversion X vs [1 − (1 − X)1/3] and regression curve, the conversion X vs [1 − 3(1 − X)2/3 + 2(1 − X)] and regression curve, and the XPS spectrum of ozonized asphaltene at various ozonation times (Figures S1−S5) (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Tel: +82 42 350 3921. Fax: +82 42 350 3910. E-mail: kjd@ kaist.ac.kr. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We would like to acknowledge the financial support of the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea and the R&D Convergence Program of MSIP (Ministry of Science, ICT and Future Planning) and ISTK (Korea Research Council for Industrial Science and Technology) of Republic of Korea (B551179-12-07-00).
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REFERENCES
(1) Banerjee, D. K. Oil Sands, Heavy Oil, & Bitumen: From Recovery to Refinery; PennWell Corp., 2012 (2) Noorjahan, A.; Tan, X.; Liu, Q.; Gray, M. R.; Choi, P. Study of Cyclohexane Diffusion in Athabasca Asphaltenes. Energy Fuels 2014, 28 (2), 1004−1011. (3) Pal, K.; Nogueira Branco, L. d. P.; Heintz, A.; Choi, P.; Liu, Q.; Seidl, P. R.; Gray, M. R. Performance of Solvent Mixtures for Nonaqueous Extraction of Alberta Oil Sands. Energy Fuels 2015, 29 (4), 2261−2267. 6999
DOI: 10.1021/acs.energyfuels.6b01184 Energy Fuels 2016, 30, 6991−7000
Article
Energy & Fuels (26) Cook, G. A. Industrial uses of ozone. J. Chem. Educ. 1982, 59 (5), 392. (27) Criegee, R. Mechanism of ozonolysis. Angew. Chem., Int. Ed. Engl. 1975, 14 (11), 745−752. (28) Novelli, A.; Vereecken, L.; Lelieveld, J.; Harder, H. Direct observation of OH formation from stabilised Criegee intermediates. Phys. Chem. Chem. Phys. 2014, 16 (37), 19941−19951. (29) Donahue, N. M.; Drozd, G. T.; Epstein, S. A.; Presto, A. A.; Kroll, J. H. Adventures in ozoneland: down the rabbit-hole. Phys. Chem. Chem. Phys. 2011, 13 (23), 10848−10857. (30) Platonov, V.; Kudrya, A.; Proskuryakov, S. Ozonolysis of asphaltenes from semicoking tar of G17 coal. Russ. J. Appl. Chem. 2003, 76 (1), 148−152. (31) Amiri, A.; Ingram, G. D.; Maynard, N. E.; Livk, I.; Bekker, A. V. An unreacted shrinking core model for calcination and similar solid-togas reactions. Chem. Eng. Commun. 2015, 202 (9), 1161−1175. (32) Yoshioka, T.; Motoki, T.; Okuwaki, A. Kinetics of hydrolysis of poly (ethylene terephthalate) powder in sulfuric acid by a modified shrinking-core model. Ind. Eng. Chem. Res. 2001, 40 (1), 75−79. (33) Nakayama, M.; Zhu, C.; Hirokawa, J.; Irino, T.; YoshikawaInoue, H. Ozone depletion in the interstitial air of the seasonal snowpack in northern Japan. Tellus, Ser. B 2015, 67, 24934. (34) Nicholson, R. V.; Gillham, R. W.; Reardon, E. J. Pyrite oxidation in carbonate-buffered solution: 2. Rate control by oxide coatings. Geochim. Cosmochim. Acta 1990, 54 (2), 395−402. (35) Wilt, B. K.; Welch, W. T.; Rankin, J. G. Determination of asphaltenes in petroleum crude oils by Fourier transform infrared spectroscopy. Energy Fuels 1998, 12 (5), 1008−1012. (36) Abdallah, W. A.; Taylor, S. D. Study of asphaltenes adsorption on metallic surface using XPS and TOF-SIMS. J. Phys. Chem. C 2008, 112 (48), 18963−18972. (37) Tharanivasan, A. K.; Yarranton, H. W.; Taylor, S. D. Asphaltene precipitation from crude oils in the presence of emulsified water. Energy Fuels 2012, 26 (11), 6869−6875. (38) King, D. Fluidized catalytic crackers: An engineering review. In Fluidization VII. Proceedings of the Seventh Engineering Foundation Conference on Fluidization; 1992; pp 15−26. (39) Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G. Asphaltenes, Heavy Oils, and Petroleomics; Springer-Verlag, 2007. (40) Andreatta, G.; Bostrom, N.; Mullins, O. C. High-Q ultrasonic determination of the critical nanoaggregate concentration of asphaltenes and the critical micelle concentration of standard surfactants. Langmuir 2005, 21 (7), 2728−2736. (41) Yarranton, H.; Ortiz, D.; Barrera, D.; Baydak, E.; Barre, L.; Frot, D.; Eyssautier, J.; Zeng, H.; Xu, Z.; Dechaine, G.; et al. On the size distribution of self-associated asphaltenes. Energy Fuels 2013, 27 (9), 5083−5106. (42) Fenistein, D.; Barre, L. Experimental measurement of the mass distribution of petroleum asphaltene aggregates using ultracentrifugation and small-angle X-ray scattering. Fuel 2001, 80 (2), 283−287. (43) Espinat, D.; Fenistein, D.; Barre, L.; Frot, D.; Briolant, Y. Effects of temperature and pressure on asphaltenes agglomeration in toluene. A light, X-ray, and neutron scattering investigation. Energy Fuels 2004, 18 (5), 1243−1249. (44) Ramalho, J. B. V.; Lechuga, F. C.; Lucas, E. F. Effect of the structure of commercial poly (ethylene oxide-b-propylene oxide) demulsifier bases on the demulsification of water-in-crude oil emulsions: elucidation of the demulsification mechanism. Quim. Nova 2010, 33 (8), 1664−1670. (45) Yudin, I. K.; Anisimov, M. A. Dynamic light scattering monitoring of asphaltene aggregation in crude oils and hydrocarbon solutions. In Asphaltenes, Heavy Oils, and Petroleomics; Springer-Verlag, 2007; pp 439−468. (46) Rajagopal, K.; Silva, S. An experimental study of asphaltene particle sizes in n-heptane-toluene mixtures by light scattering. Braz. J. Chem. Eng. 2004, 21 (4), 601−609.
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