Article pubs.acs.org/EF
Effect of Ionic Surfactants on Improving Deasphalting Selectivity in a Nonpolar System Kang Seok Go,*,†,‡ Eun Hee Kwon,†,‡,§ Kwang Ho Kim,‡ Nam Sun Nho,*,‡ and Ki Bong Lee*,§ ‡
Climate Change Research Division, Korea Institute of Energy Research (KIER), 152 Gajeongro, Yuseong-gu, Daejeon 305-343, Republic of Korea § Department of Chemical and Biological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea ABSTRACT: To reduce the amount of solvent used in the solvent deasphalting process, this study investigated the possibility of improving deasphalting selectivity at a low solvent/oil ratio (SOR) by modifying the stability of the asphaltene colloidal dispersion with ionic surfactants. To do this, an experiment was conducted by changing the solvent types (n-pentane and nheptane), temperature (35−90 °C), SOR (3−20, vol/vol), surfactants, and surfactant concentration (0.5−2.0 wt % of the feedstock). As a result, the ζ potential with sodium dodecyl sulfonate (SDS) was shown to decrease, while the ζ potential of pitch with cetylpyridinium chloride (CPCl) rose, as compared to those without surfactant. Also, the difference is bigger at a low SOR than at a high SOR. Finally, it was confirmed that, for SDS, the asphaltene content rose about 6% for the incremental 3% rise of pitch yield, while for CPCI, the asphaltene content rose 9−10% for the incremental 1.8% rise of the pitch yield, at the same time. The different movement of ζ potential and asphaltene content between SDS and CPCl can be explained by the adsorption mechanism.
1. INTRODUCTION As global demand for energy has been continuously increasing and causing ever faster depletion of existing conventional crude oil resources, there has been increased attention given to the upgrading of technologies applied for low-quality inexpensive crude oils, such as extra-heavy oils and oil sand bitumen. However, practical usage of these heavy oils in terms of production, transportation, supply, and upgrading are very limited as a result of the tough physical properties that they present, such as their high density, high viscosity, high sulfur content, and high content of various metals.1 In particular, extra-heavy oils, such as bitumen, that include about 15−20% of asphaltene incur higher operating costs as a result of the need to add diluents during processing to decrease viscosity to the extent that the diluents can comprise up to 30% of the volume. To further complicate matters, Conradson carbon residue (CCR) and heavy metals (nickel and vanadium) can suddenly occur, which deactivate the catalysts in an upgrading plant, such as a fluid catalytic cracker or hydrocracker used for producing light fraction oil. Therefore, it is necessary to remove asphaltene for stable operation of upgrading units before the feedstock is introduced.2 In general, crude oil composes four pseudo-components, which are saturate, aromatic, resin, and asphaltene, by its polarity. Particularly, asphaltene is defined as insoluble in a nalkane, such as n-pentane and n-heptane, but soluble in aromatics, such as benzene and toluene.3 As distinguishing asphaltene, the mixture of the remaining three components is called “maltene”. It is well-known that asphaltene is surrounded by resins and aromatics that act as peptizing agents that stabilize it in the form of a colloid in the oil phase.4−6 Heteroatoms, such as oxygen, nitrogen, and sulfur, included in asphaltene confer its polar characteristics in the oil phase. © XXXX American Chemical Society
If asphaltene is separated from resin or aromatics under certain temperatures, pressures, and compositions, they behave as colloid particles in the oil phase. The stability of the dispersion of asphaltenes can change variously when interacting with other asphaltenes as a result of charge transfer between donor and acceptor molecules (acid−base interaction), electrostatic (Coulombic) interaction by charge distribution, van der Waals interaction, etc.7 In general, the stability of a colloid in a solution is well-known to be identified by its ζ potential. If a colloid has high ζ potential, colloid particles can maintain a distance beyond the van der Waals force and disperse stably in a solution as a result of the repulsion force between them. However, if low ζ-potential colloid particles can come into collisions by Brownian motion, then they become unstable by aggregation.8 There is a lot of literature of previous studies conducted on ζ potential to explain the stability of asphaltene dispersion in a solution. Parra-Barraza et al. used n-heptane in aqueous suspensions to demonstrate the electrokintetic behavior of asphaltenes and explain why a charge forms on the surface.9 It was mentioned that the isoelectric point (IEP) was dependent upon the amount of resin in the asphaltene. The ζ potential of asphaltene has been reported in a lot of literature; mostly they suggest that it is negative above about pH 4.9−12 The reason for that was presented by dissociation of acidic surface groups, such as carboxylic, which have pKa values of ≤4, whereas the protonation of these acid groups may lead to a positive mobility in highly acidic solutions.13 Some authors showed the effect of co-solvents, such as ethylene glycol, which can modify the Received: December 7, 2015 Revised: February 4, 2016
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DOI: 10.1021/acs.energyfuels.5b02860 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 1. Physical Properties of Athabasca Oil Sand Bitumen analysis item
result
elemental analysis (wt %) boiling point distribution (°C) MCR content (wt %) metal content (wt ppm) viscosity (mPa s) API specific gravity (deg) SARA analysis (wt %)
C, 82.5; H, 11.7; N, 0.3; S, 5.5 206−745 14.48 Ni, 105; V, 195 240−46400 8.18 saturates/aromatics/resins/asphaltenes, 8.2/52.8/21.4/17.6
remark ASTM D7213 ASTM D4530 temperature range (35−100 °C) ASTM D287
Figure 1. Experimental procedure.
there being more asphaltene remaining in the DAO phase. Therefore, a minimum ratio is required to guarantee that hydrocarbons are completely solubilized in the solvent and reach equilibrium at the operating condition.18 In this study, ways to improve deasphalting by adding surfactants to change ζ potential as opposed to studying dispersion effects (as was performed in most previous studies) were investigated. In other words, we tried to find the effect that the ζ potential of pitch has on surfactants on deasphalting characteristics. In addition, we studied whether the use of surfactants can improve for deasphalting in a low solvent/feed ratio condition. To do this, we used n-pentane and n-heptane with ionic surfactants and checked the extraction yield and asphaltene content in pitch as the SOR was varied.
electrical charge and potential distribution of the asphaltene surface as a result of a change of viscosity.14,15 The effect of surfactants on the ζ potential of asphaltene in aqueous solutions has been amply reported. Poteau et al. made asphaltenes, dispersed them in water, added an ion surfactant, and checked the stability of the asphaltene depending upon the contents using the ζ potential and also studied the effects that injecting sodium dodecyl sulfonate (SDS), coconut amine (CA), and oleic acid (OA) surfactants among the asphaltene particles had on the ζ potential, amount of electric charge, and repulsive force.16 Parra-Barraza et al. explained that these ionic surfactants can modify the ζ potential of an asphaltene by adsorption. They also suggested that SDS and cetylpyridinium chloride (CPCl) were potential candidates that can be used controlling the stability of crude oil dispersion.9 The objectives of those studies were mainly to find ways to prevent the precipitation of asphaltene in the upstream processes of oil recovery from wells and transportation through a pipeline. That is, they were focused on improving asphaltene dispersion in the system. However, many processes for upgrading heavy oils in the downstream are limited in dealing with the feedstock as well because various impurities included in the asphaltene can severely affect catalysts in the upgrading reactor. To address this problem, solvent deasphalting (SDA) technology was developed and has been used to remove the asphaltene fraction from feedstock in the refineries. The SDA process, of which KBR and UOP/Foster-Wheeler are known to be the main licensors, uses normal paraffin solvents with carbon numbers of 3−6, so that saturate, aromatic, and resin fractions can be extracted from the oil, while a fraction of asphaltene remains. In a SDA process, two streams, one of deasphalted oil (DAO) at the top and one of pitch at the bottom of the extraction column, are produced. DAO is in a maltene-rich state, while pitch is in an asphaltene-rich state. On the basis of extraction with normal paraffin, it is reported that there is a trade-off between the DAO yield and its quality.17 This is because a large portion of impurities belong to the heavy fractions, such as asphaltene. If the solvent/oil ratio (SOR) is low, the separation efficiency between resin and asphaltene will also be low, so that an inferior DAO quality results as a result of
2. EXPERIMENTAL SECTION 2.1. Materials. The physical properties of the Athabasca bitumen used as feedstock in this study are shown in Table 1. All solvents and surfactants used in this study were reagent-grade materials (SigmaAldrich). Normal pentane and heptane as extracting solvents, five different ionic surfactants, and two agents to adjust pH were used. 2.2. Experimental Procedure. The scheme of the experimental procedure is shown in Figure 1. Pitch was prepared using a solvent extractor with n-pentane and n-heptane as the solvents. The manufacturing method was as follows: 5 mL of bitumen was prepared and mixed with solvent in a side arm Erlenmeyer flask at a ratio of 3:20. The temperature was set at each condition, and the mixture was stirred with an agitator for 30 min, after which it was allowed to settle for 1 h. The pitch was then dried on 0.45 μm filter paper at 107 °C for about 2 h. The weight of the dried pitch was then measured, and the yield was calculated. Also, the filtered solvent was evaporated to recover the DAO, which was then dried at 107 °C for about 2 h. Each experiment was repeated 4 times. If surfactants were used, they were put in a side arm Erlenmeyer flask at a surfactant/feed ratio of 0.5−2.0 wt %. At this time, water of 20% of the feedstock was added to the mixture, so that the surfactants could become ionized. The rest of the experiment was the same as previous experiments and repeated 4 times. 2.3. Sample Analysis. 2.3.1. Physical Properties of the Feedstock and Products. To measure heavy metals (Ni and V), we used a X-ray fluorescence (XRF) spectrometer (X-Supreme 8000, Oxford Instruments), and to analyze the components of saturates, aromatics, resins, B
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Energy & Fuels and asphaltenes, we used a thin-layer chromatography with flame ionization detection (TLC/FID) analyzer (Iatroscan MK-6s). 2.3.2. ζ Potential and Fourier Transform Infrared Spectroscopy (FTIR). To check the electrical behavior of the pitch, we used a Malvern Zetasizer Nano ZS. ζ potential refers to the surface electrical properties of the colloidal particles floating in the liquid. To measure the ζ potential, an experiment was conducted using the same method as the manufacturing method used by Parra-Barraza et al., whereby 7.5 mL of ethanol was put in 50 mg of pitch and then agitated with ultrasonic waves for 15 min.9 The materials obtained at that time are deemed suspended solids. To collect 0.75 mL of suspended solids and fixate the ionic strength, they were put in 50 mL of a 0.001 M NaNO3 solution. Then, a magnet was used to stir them for 20 min, and 1−2 mL was injected into a cell exclusively for ζ in such a way that there are no bubbles. Then, the experiment was conducted. To check the adsorption of the surfactants, a FTIR (Bruker Alpha) analysis was performed to see if the surfactants adhered to the pitch. The wave range was 500−4000 cm−1, and about 0.5 g of pitch was sampled for analysis.
3. RESULTS AND DISCUSSION 3.1. Effect of Normal Paraffin Solvent on the Pitch Yield and Physical Properties. The effect of normal paraffin
Figure 3. Effect of the pitch yield on the (a) asphaltene content and (b) metal content in pitch according to variation of the SOR (at n-C7 extraction).
Figure 2. Effect of the SOR on the pitch yield according to variation of the extraction temperature and solvent type.
pentane with a low carbon number had a higher yield of 1−5 wt % than n-heptane. Because the solubility of n-pentane is 14.4 MPa1/2 and that of n-heptane is 15.2 MPa1/2, the solubility of npentane is lower and, thus, the yield of the pitch is higher.20 Figure 3 (within an experimental error of ±10%) shows how the asphaltene and metal (Ni and V) contents in pitch change with a change of the pitch yield when n-heptane was used. As illustrated in this figure, both contents decrease with an increasing pitch yield. This is because the maltene (saturate, aromatic, and resin) fraction, which has a relatively low amount of impurities in the oil, increases in the pitch. This is also wellunderstood to have a trade-off relation between the yield and quality.17 However, asphaltene and metal contents increase with an increasing SOR at a similar pitch yield. This is explained to be an improvement of selectivity for saturate and aromatic fractions of an extraction system, as Alain-Yves presented,18 and it means that the removal efficiency of impurities improves with the increasing quantity of solvent in terms of the SDA process.
solvents on the pitch yield and physical properties was investigated first without adding any surfactant. As shown in Figure 2 (within an experimental error of ±4%), the pitch yield increases as the SOR is increased. This is because resins dissolve in the solvent as the SOR increases, so that the asphaltene is separated from the resin, aggregated between them, and then precipitated, unlike its initial dispersed state. In particular, the pitch yield over a certain SOR (about 8) is shown to be nearly flat. The explanation for this is that the solvents fully dissolve the resin to approach the equilibrium state. At the same SOR, it was observed that the pitch yield increases with the temperature. This result is attributed to both the solubility change of the solvent, which decreases resin solubility, and the stronger interaction between resin and asphaltene. Similarly, Chandio and Mukhtar reported that the change of these two values depending upon the temperature was explained in terms of peptizability parameters and peptizing power.19 In comparison to the difference of solvent types, nC
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Figure 4. Effect of pH in solution on the ζ potential according to variation of SOR at 35 °C.
Figure 6. Preliminary selection of candidate surfactants.
Figure 5. Effect of the ζ potential on the asphaltene content in pitch according to variation of the extraction temperature at pH 6. Color of symbols: (white) SOR of 3, (gray) SOR of 5, and (black) SOR of 8.
In the SDA extraction system, it was found that pH existed in the range of 5−6 during all of the experimental conditions. In this regard, the experiments to observe the change of ζ potential under various conditions were carried out at a fixed pH of 5−6. Figure 5 presents the effect of the ζ potential on the asphaltene content in pitch in temperature variations of 35−90 °C and SOR values of 3−8 at pH 6. As seen in this figure, asphaltene content in pitch increases by 2−2.5% as the absolute value of the ζ potential decreases at all extraction temperatures. In addition, the higher the SOR condition, the larger the asphaltene content. This indicates that pitch having a low ζ potential is likely to aggregate among the pitch because of increasing instability in the solution; as a result, asphaltene can be separated more selectively from the oil. In particular, it was found that a large amount of solvent for oil can dissolve more resin, so that the largest asphaltene content is presented. 3.3. Effect of Surfactants on the Deasphalting Performance. In the previous section, in the experiment conducted only with normal paraffin, it can be seen that low SOR decreases asphaltene and metal selectivity in the pitch phase as a result of a higher negative ζ potential. Therefore, a preliminary test was carried out to roughly find the candidate surfactants that can improve deasphalting selectivity (Figure 6). For five ionic surfactants (benzyldimetyhyl ammonium chloride, benzalkonium chloride, OA, CPCl, and SDS), the asphaltene/pitch yield ratio was compared at a given condition (30 °C, n-heptane, SOR of 4, and surfactant addition of 1 wt % of the feed). As a result, SDS and CPCl were selected because those have the highest value. For SDS and CPCl, the effect of the surfactant on deasphalting was investigated at different SORs and temperatures with n-heptane, of which the effects are expected to be large. 3.3.1. SDS. The adsorption of ionized SDS surfactant on pitch (or asphaltene) was examined by a FTIR analysis. The result is shown in Figure 7. As seen, the double bond (SO) between S and O was clearly confirmed at the wavelengths of 1100 and 1200 cm−1 on the sample with added SDS.21 This fact was also confirmed by the study from Hashmi et al., in which dodecyl benzenesulfonic acid (DBSA) as a similar molecular structure of SDS was used to find the mechanism facilitating
3.2. ζ Potential of Pitch Particles without Surfactant. Figure 4 (within an experimental error of ±10%) shows the effect that pH in a solution has on the ζ potential of pitch as the SOR varies for each of the pitch samples extracted at fixed temperature conditions. As seen in this figure, the IEP was found to be in the pH range of 2 and ζ potential decreases as pH increases from 2 to 8. This result can be explained by the degree of dissociation of the functional group in asphaltene with the change of pKa. A previous study reported that, in aqueous solutions with pKa being 2 or less, the basic functional groups of asphaltene, such as amine, amide, and pyridine, are ionized and asphaltene have a positive electric charge. On the other hand, if pKa is 4 or more, acidic functional groups, such as the carboxyl group, are dissociated and the electric potential of asphaltene will have a negative electric charge.13 Therefore, it can be confirmed from this study that ζ potential has a tendency similar to that of the study conducted by ParraBarraza et al.9 D
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Figure 7. Adsorption of ionized SDS on pitch (SO bonding near 1100 and 1200 cm−1).
Figure 8. Effect of the asphaltene content on ζ potential according to variation of the extraction temperature and SDS concentration at (a) SOR of 3 and (b) SOR of 5. Surfactant concentration: (white) 0.5 wt %, (gray) 1.0 wt %, and (black) 2.0 wt %.
Figure 9. Effect of the asphaltene content on the ζ potential according to variation of the extraction temperature and CPCl concentration at (a) SOR of 3 and (b) SOR of 5. Surfactant concentration: (white) 0.5 wt %, (gray) 1.0 wt %, and (black) 2.0 wt %. E
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Figure 11. Change of deasphalting selectivity according to variation of the extraction temperature and CPCl concentration at (a) SOR of 3 and (b) SOR of 5. Surfactant concentration: (white) 0.5 wt %, (gray) 1.0 wt %, and (black) 2.0 wt %. Circles on data points indicate the same extraction temperature.
Figure 10. Change of deasphalting selectivity according to variation of the extraction temperature and SDS concentration at (a) SOR of 3 and (b) SOR of 5. Surfactant concentration: (white) 0.5 wt %, (gray) 1.0 wt %, and (black) 2.0 wt %. Circles on data points indicate the same extraction temperature.
3.3.2. CPCl. Unlike SDS, CPCl does not have different functional groups from those of resin or asphaltene, so that it was impossible to check its adsorption with FTIR. However, it is expected that CPCl can be ionized and have positive charges in water considering the literature reviewed in the previous section. That is, the carboxyl group on asphaltene formed by dissociation of protons at above pKa of 4 can be counterpart ions for CPCl ions. Figure 9 shows the effect of the asphaltene content (within an experimental error of ±20%) on the ζ potential (within an experimental error of ±10%) at various extraction temperatures and CPCl concentrations at SOR of 3 and 5. As definitely opposed to the result of SDS, it can be seen that almost all data lies above the reference data. Also, the asphaltene content stands out under certain conditions. In comparison to the reference, the asphaltene content at 50 °C and 1 wt % of CPCl from Figure 9a is shown to increase up to 7−8%, while it is rather decreased in Figure 9b, which is under the same conditions as Figure 9a. On the basis of those results, it is considered that the optimum condition to minimize the absolute ζ potential might depend upon its extraction conditions. Under the given experiment conditions, it is
the colloid to solution transition of asphlatene.22 They reported that heteroatoms, such as N, S, O, and amines, can accept an electron, so that they are able to adsorb the negative charge from an ionized DBSA onto those heteroatoms by acid−base interaction. In this way, they are expected to be similar to the case of SDS. Figure 8 shows the effect of the asphaltene content (within an experimental error of ±20%) on the ζ potential (within an experimental error of ±10%) at various extraction temperatures and SDS concentrations at SOR of 3 and 5. The “reference” shown in the legend of the figure means the data obtained from the experiment without surfactants. As seen in panels a and b of Figure 8, all of the data of ζ potential exists below the reference; that is, it presents a higher negative potential. The degree of ζ potential changed at about 5 mV at SOR of 5, which is bigger than that of SOR of 3. In Figure 8a, the ζ potential increases to a negative value when the concentration of the surfactant increases, while the relationship between the ζ potential and the concentration of the surfactant was not found at SOR of 5 in Figure 8b. F
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Figure 12. Hypothetical mechanism of enhancement of asphaltene aggregation with respect to (a) SDS and (b) CPCl at high and low SOR.
asphaltene stacking is hindered. Then, they disperse in the oil phase, causing DAO quality to degrade. (iii) When the surfactant is added at a low SOR, the head groups of cation and anion surfactants can be adsorbed on the different functional groups of heteroatoms of asphaltene by electrostatic or acid−base interactions.7,23,24 Then, negatively charged asphaltenes in our study, as confirmed in Figures 4 and 5, become more negative with adsorption of SDS, while the net charge of asphaltene moves toward positive with adsorption of cationic CPCl. Asphaltene-adsorbed surfactants form a reverse micelle structure. Particularly, cationic CPCl can be adsorbed more than anionic SDS because of the attraction force between asphaltene and the countercharge of CPCl ions and the chain− chain hydrophobic interaction among CPCls.24 (iv) Asphaltene aggregation can be enhanced by the hydrophobic interactions between surfactant tails uniformly exposed out of each asphaltene, despite some resin molecules remaining. Therefore, it is understood why the ζ potential of both SDA and CPCl moves in opposite directions and deasphalting selectivity is improved more in the case of CPCl.
expected that the case of low SOR of 3.0 would have more influence on the deasphalting performance because of a larger change of the ζ potential and asphaltene content. 3.4. Change of Deasphalting Selectivity with Surfactants. Figures 10 and 11 show the change of deasphalting selectivity at various extraction temperatures and surfactant concentrations of SOR of 3 and 5. As explained in section 3.1, increasing the pitch yield causes the concentration of asphaltene in pitch to lower at the deasphalting condition with only normal paraffin solvent, in general. In other words, deasphalting selectivity declines with an increasing pitch yield. In contrast to the results without surfactants, SDS surfactant at SOR of 3, 50 °C, and SDS of 1.0 wt %, as seen in Figure 10a, shows that the asphaltene content (within an experimental error of ±20%) increases by about 6% for the rise of the pitch yield (within an experimental error of ±5%) of 3% at the same time. On the other hand, there seems to be a relatively minor improvement at SOR of 5 in Figure 10b. As for CPCl, enhanced deasphalting selectivity is observed at SOR of 3, 50 °C, and CPCl of 1.0 wt %, and the maximum value was found to be an incremental rise of the asphaltene content (within an experimental error of ±15%) of about 9−10% with the incremental rise of the pitch yield (within an experimental error of ±3%) of 1.8% at the same time. The above results can be interpreted as follows (with reference to Figure 12): (i) At a high SOR, the amount of resin that dissolves in the solvent increases. The approach between asphaltene molecules then becomes easy as a result of the reduced steric repulsion by the resins, so that asphaltene stacking can be incurred by van der Waals interaction.7,22 (ii) At a low SOR, some resins still remain in the asphaltene, so that
4. CONCLUSION Two types of ionic surfactants were used to enhance deasphalting selectivity by modifying asphaltene colloidal dispersion stability. To do this, experiments were carried out by varying the solvent type, temperature, SOR, surfactant type, and concentration of surfactant. For comparison, a test was conducted without surfactant, which showed that the IEP was found to be pH 2 and negative ζ potential was shown to be over pH 2. It was found that, as the extraction temperature G
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(5) Hunt, A. Uncertainties remain in predicting paraffin deposition. Oil Gas J. 1996, 96. (6) Spiecker, P. M.; Gawrys, K. L.; Kilpatrick, P. K. Aggregation and solubility behavior of asphaltenes and their subfractions. J. Colloid Interface Sci. 2003, 267 (1), 178−193. (7) Murgich, J. Intermolecular Forces in Aggregates of Asphaltenes and Resins. Pet. Sci. Technol. 2002, 20, 983−997. (8) Riddick, T. M. Control of Colloid Stability through Zeta Potential; Livingston: Wynnewood, PA, 1968. (9) Parra-Barraza, H.; Hernández-Montiel, D.; Lizardi, J.; Hernández, J.; Herrera Urbina, R.; Valdez, M. A. The zeta potential and surface properties of asphaltenes obtained with different crude oil/n-heptane proportions. Fuel 2003, 82 (8), 869−874. (10) Kokal, S.; Tang, T.; Schramm, L.; Sayegh, S. Electrokinetic and adsorption properties of asphaltenes. Colloids Surfaces A Physicochem. Colloids Surf., A 1995, 94, 253−265. (11) Abraham, T.; Christendat, D.; Karan, K.; Xu, Z.; Masliyah, J. Asphaltene−Silica Interactions in Aqueous Solutions: Direct Force Measurements Combined with Electrokinetic Studies. Ind. Eng. Chem. Res. 2002, 41, 2170−2177. (12) González, G.; Neves, G. B. M.; Saraiva, S. M.; Lucas, E. F.; dos Anjos de Sousa, M. Electrokinetic Characterization of Asphaltenes and the Asphaltenes−Resins Interaction. Energy Fuels 2003, 17, 879−886. (13) Jada, A.; Salou, M. Effects of the asphaltene and resin contents of the bitumens on the water−bitumen interface properties. J. Pet. Sci. Eng. 2002, 33, 185−193. (14) Weast, R. C.; Astle, M. J. CRC Handbook of Chemistry and Physics, 60th ed.; CRC Press, Inc.: Boca Raton, FL, 1981. (15) Vega, S. S.; Urbina, R. H.; Covarrubias, M. V.; Galeana, C. L. The zeta potential of solid asphaltene in aqueous solutions and in 50:50 water+ethylene glycol (v/v) mixtures containing ionic surfactants. J. Pet. Sci. Eng. 2009, 69, 174−180. (16) Poteau, S.; Argillier, J.-F.; Langevin, D.; Pincet, F.; Perez, E. Influence of pH on Stability and Dynamic Properties of Asphalteness and Other Amphiphilic Molecules at the Oil−Water Interface. Energy Fuels 2005, 19 (4), 1337−1341. (17) Houde, E. J.; Mcgrath, M. J. When solvent deasphalting is the most appropriate technology for upgrading residue. Proceedings of the International Downstream Technology & Strategy (IDTC) Conference; London, U.K., Feb 15−16, 2006; pp 1−11. (18) Huc, A.-Y. Heavy Crude Oils: From Geology to Upgrading: An Overview; Technip: Paris, France, 2011. (19) Chandio, Z. A.; Ramasamy, M.; Mukhtar, H. B. Temperature effects on solubility of asphaltenes in crude oils. Chem. Eng. Res. Des. 2015, 94, 573−583. (20) Gonzalez, G.; Sousa, M. A.; Lucas, E. F. Asphaltene precipitation from crude oil and hydrocarbon media. Energy Fuels 2006, 20 (6), 2544−2551. (21) Chatterjee, S.; Salaün, F.; Campagne, C. The Influence of 1Butanol and Trisodium Citrate Ion on Morphology and Chemical Properties of Chitosan-Based Microcapsules during Rigidification by Alkali Treatment. Mar. Drugs 2014, 12 (12), 5801. (22) Anisimov, M. A.; Ganeeva, Y. M.; Gorodetskii, E. E.; Deshabo, V. A.; Kosov, V. I.; Kuryakov, V. N.; Yudin, D. I.; Yudin, I. K. Effects of Resins on Aggregation and Stability of Asphaltenes. Energy Fuels 2014, 28, 6200−6209. (23) Hashmi, S. M.; Zhong, K. X.; Firoozabadi, A. Acid−base chemistry enables reversible colloid-to-solution transition of asphaltenes in non-polar systems. Soft Matter 2012, 8, 8778. (24) Somasundaran, P.; Zhang, L. Adsorption of surfactants on minerals for wettability control in improved oil recovery processes. J. Pet. Sci. Eng. 2006, 52, 198−212.
rises, the pitch yield has a tendency to decrease in the range of 8−20 wt % and increases in the range of 55−61 wt % for the asphaltene content in pitch. Both the ζ potential and asphaltene content in pitch rise by increasing the SOR. At a given SDS extraction condition, the ζ potential was shown to fall for the reference and was not found to have any relationship with any variables. However, the ζ potential of pitch with CPCl was found to rise for the reference, and the difference for a low SOR is bigger than that for a high SOR. In contrast to the trade-off relationship of the conventional deasphalting process (without surfactants), it was found that both the pitch yield and asphaltene concentration in pitch increase at the same time when surfactants were added. In particular, the increment of the asphaltene content of about 6% was confirmed on the rise of the pitch yield of 3% for SDS, and the increment of the asphaltene content of 9−10% was confirmed on the rise of the pitch yield of 1.8% for CPCl. The reason for the different movements of ζ potential between SDS and CPCl was elucidated by the amount of adsorption as a result of the interaction between asphaltene and ionic surfactants. Finally, it was found that the adsorption of the surfactant on asphaltene could change asphaltene ζ potential, so that aggregation between asphaltenes improved to increase deasphalting selectivity. It was understood that the deasphalting selectivity with regard to variation of the surfactant is attributed to the different types of asphaltene aggregation according to the difference of hydrophobic interaction. However, the amount of adsorption for surfactants on asphaltene is necessary to be proven quantitatively by an analytical method in a further study.
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AUTHOR INFORMATION
Corresponding Authors
*Telephone: 82-42-860-3738. Fax: 82-42-860-3739. E-mail:
[email protected]. *Telephone: 82-42-860-3631. Fax: 82-42-860-3739. E-mail:
[email protected]. *Telephone: 82-02-3290-4851. Fax: 82-2-926-6102. E-mail:
[email protected]. Author Contributions †
Kang Seok Go and Eun Hee Kwon contributed equally to this work. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge the financial support from the R&D Convergence Program of the National Research Council of Science & Technology (NST) of Republic of Korea (Grant B551179-12-07-00).
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REFERENCES
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DOI: 10.1021/acs.energyfuels.5b02860 Energy Fuels XXXX, XXX, XXX−XXX
