Effect of Alkyl Chain Length of Ionic Surfactants on Selective Removal

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Effect of alkyl chain length of ionic surfactants on selective removal of asphaltene from oil sand bitumen Eun Hee Kwon, Kang Seok Go, Nam-Sun Nho, and Kwang Ho Kim Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01933 • Publication Date (Web): 17 Aug 2018 Downloaded from http://pubs.acs.org on August 17, 2018

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Effect of alkyl chain length of ionic surfactants on selective removal of asphaltene from oil sand bitumen

Eun Hee Kwon1, Kang Seok Go1*, Nam Sun Nho*, Kwang Ho Kim

Climate Change Research Division, Korea Institute of Energy Research (KIER), 152 Gajeongro, Yuseong-gu, Daejeon 305-343, Republic of Korea

*Corresponding Author (Kang Seok Go) Tel.: 82-42-860-3738, Fax: 82-42-860-3739, E-mail: [email protected] *Corresponding Author (Nam Sun Nho) Tel.: 82-42-860-3631, Fax: 82-42-860-3739, E-mail: [email protected] 1

Both authors contributed equally to this work.

Keywords : bitumen, froth treatment, selective asphaltene removal, ionic surfactants

Abstract In an attempt to find a more effective way to separate asphaltene from bitumen froth or bitumen emulsion by utilizing solvents we added four different types of cationic (pyridinium series) and anionic (sulfate series) surfactants having different alkyl chain lengths and then compared the results. The data of the experiments showed that at given conditions (n-heptane at 50°C, solvent-to-bitumen ratio of 3, 20% water) and based on 1

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feedstock treated with 0.4mmol of surfactant, asphaltene-resin particles (colloid) with an initial negative charge showed different characteristics of adsorption of surfactants and aggregation of asphaltenes depending on the charge of the surfactants (cationic or anionic) and the alkyl-chain length. Ultimately, the results showed that when methyl-pyridinium chloride (which is cationic and has the shortest alkyl-chain) is added that the colloidal instability of the asphaltene became the highest so that the asphaltene removal increased by up to about 10% compared to treatments without surfactants. From this study, it was found that using those surfactants during the froth treatment can improve the quality of the derived bitumen.

1. Introduction Interest in oil sand bitumen has been increasing as an alternative to help meet the ever growing demand for oil and as a result many studies have been conducted to find ways to upgrade oil extracted from the sands to be lighter. When bitumen is produced from oil sands, water and mineral solids contained within must be removed before mixing with condensate (diluent) so that it can be pumped through a pipeline[1-3]. The process whereby water and mineral solids are separated from the bitumen emulsion or bitumen froth (produced from the steam-assisted gravity-drainage or in-situ mining with a hydrocarbon-based gravity separation) is known as the froth treatment. Depending on the type of solvents used, froth treatment is classified into either naphthenic froth treatment (NFT) or paraffinic froth treatment (PFT)[4]. NFT uses naphtha as a solvent because bitumen recovery yield is high and the amount of solvent-to-bitumen ratio is relatively low (0.6~0.75w/w) due to the high 2


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solubility of naphtha in bitumen. However, the diluted bitumen still contains about 1~2wt.% of water and 0.5wt.% of mineral solids[5]. And due to the fraction of asphaltene that remains, NFT also often results in low API gravity and high viscosity. As a result, they cannot meet the requirements for transportation through a pipeline. Normally, pipelines require API gravity to be over 19, viscosity below 350cSt, and sediment and water below 0.5wt.%[4]. On the other hand, using PFT results in much lower water and mineral solids in the separated bitumen because it uses a lighter and more paraffinic solvent such as normal pentane than does NFT. However, PFT has the disadvantage of resulting in a higher solvent-to-bitumen ratio and lower bitumen recovery due to its inability to effectively dissolve heavy fractions like resin or asphaltene[5, 6]. As a result, the concentration of contamination in the products is lower but the bitumen recovery yield is decreased. Based on the above comparison between NFT and PFT, we can see that there are limitations and trade-offs between the amount of bitumen recovery and its quality with only a change of solvent types. Therefore, it is required to improve the conventional technologies for higher bitumen recovery and better selective separation of impurities including water, minerals and asphaltene at the same time. In this respect, the selective asphaltene removal of PFT can be an important factor to compensate for its disadvantages. In order to find a better way, studies on the behavior of asphaltene dispersion using various surfactants to reduce asphaltene precipitation can be a good motivation for improving the technical limits of the conventional forth treatment processes. In their research, Chang and Fogler[7] used about 14 types of amphiphile surfactants to examine the adsorption of asphaltene and the changes in the stability of asphaltene depending on 3


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the functional groups of the surfactants and lengths of the alkyl chains. They added surfactants having a similar number of alkyl chains (i.e. 9~12) and different head groups to a fraction containing asphaltene, then measured the degree of adsorption of asphaltene and surfactant using FT-IR. Their experiments confirmed that the degree of adsorption of asphaltene increased in the order of p-(n-Dodecyl) benzene sulfonic acid (DBSA, sulfonic acid group) was greater than p-(n-Nonyl) phenol (NP, phenol group) which was greater than p-[(hydroxyethoxy)ethoxy]-n-nonylbenzene (NBDO, ethoxy group) which was greater than nonyl benzene (NB, without a polar group). The adsorption trends of the surfactant on the asphaltene surface are similar to the results of the experiment conducted by Peramanu et al.[8]. That research group mixed the bitumen and the solvents (toluene, n-heptane) in a vessel and injected nonyl phenol (NP) and dodecylbenzenesulfonic acid (DDBSA) surfactants to observe the changes of the onset points of the asphaltene. Through their study they explained that the stability of the asphaltene in oil increases as the head (aromatic ring) of the surfactant and the heteroatom of the asphaltene are combined, and revealed that DDBSA with the sulfonic acid group is more stable than the NP with the phenol group. As for the influence of changes induced by the length of the alkyl chain, Chang & Fogler[7] reported that when they fixed the head group with phenol and changed the lengths of the tails that the stability of the asphaltene increased as the length of the tail increased, and when there were 6 or more tails, the dispersion stability of the asphaltene remained constant. Meanwhile, Goual et al.[9] used octyl-phenol (OP) and dodecyl-phenol (DP) to observe the changes in the efficiency of the dispersant upon the asphaltene through the asphaltene precipitation onset time and changes in the aggregate size. As a result, the increase in the length of the surfactant’s alkyl-chain (OP to DP) did not affect the precipitation onset time but rather reduced the asphaltene 4


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aggregate size. This result was caused by the hydrogen bonding between the nitrogen containing asphaltene and the hydroxyl group of the DP through molecular simulation. This phenomenon is thought to have appeared as this interaction occurs at the periphery of the asphaltene, and the steric repulsion between the aliphatic tails of the DP increased. Examining the result of applying ionic surfactant, Li et al.[10] used Lungu atmospheric residue to mix n-heptane and toluene at the ratio of 1:1, sealed the mix for 48 hours, and observed the changes in the SARA and ξ-potential of the precipitates as well as the size of the colloid particles when they added sodium dodecyl sulfonate (SDS), coconut amine (CA) and oleic acid (OA) to the mix. As a result, their analysis of the precipitates explained that as the amount of surfactant increased, the asphaltene content of the SDS and CA rapidly decreased to 0.7wt.% and 0.5wt.% respectively, and as the repulsion between asphaltenes increased, the stability of the asphaltene increased. With regard to changes in the stability of the asphaltene through the ξ-potential, Salmón-Vega et al.[11] also used n-heptane to extract the asphaltene, put it in a 1.0mmol NaNO3 aqueous solution, added cetylpyridinium chloride (CPCl), dodecylamine hydrochloride (DHA) and sodium dodecyl sulfonate (SDS), and observed the changes in the stability of the asphaltene. As a result, they found that if 1.0mmol or more of SDS is injected, the ξpotential of the asphaltene in the given pH section remained negative. They concluded that this was due to the interaction of the hydrophobic surface site of the asphaltene and the hydrocarbon chain of the surfactants. Also, when CPCI and DHA cationic surfactants were added, they explained that the positive ξ-potential was shown at 1.0mM or higher due to electrostatic attraction as well as the hydrophobic interaction with the asphaltene. In particular, as CPCI has a longer alkyl chain than DHA, they argued that the asphaltene adsorption increased, and resultantly the dispersion characteristic of the asphaltene is 5


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greater. A comparison of the research mentioned above is summarized in Table 1. Based on the previous studies related to the dispersion effect of surfactants, we can see that if the type of head and length of alkyl chain of the surfactants is appropriately adjusted we can expect that it will be possible to effectively aggregate and separate the asphaltene selectively in the froth treatment. Accordingly, this study used bitumen as the feedstock and n-heptane as the solvent, and then tried to explain the mechanisms that caused changes in the aggregation characteristics of the asphaltene as they correlated with the corresponding length of the alkyl chain of the surfactants having similar head groups. In addition, this study also investigated the effect of surfactants on the change of yield and properties of deasphalted oil (DAO) in terms of bitumen recovery and its qualities. To do this, we used three different types of anionic and four different types of cationic surfactants which have a sulfate group and pyridinium group respectively, and different lengths of alkyl chains as well. We then confirmed the changes in the adsorption characteristic of the surfactants on the asphaltene-resin colloids through X-ray Photoelectron Spectroscopy (XPS), and the changes in the dispersion or aggregation characteristics of the asphaltene based on the extent of asphaltene removal and its ξpotential.

2. Experiments 2.1. Materials The feedstock used in this study was bitumen from Athabasca (Alberta, Canada) oil sand. The basic properties of the bitumen are shown in Table 2. The solvent used was a 6


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reagent-grade product from Sigma Aldrich (USA) and the surfactants were reagent grades from Sigma Aldrich and TCI America. Details are shown in Table 3.

2.2. Deasphalting experiment The procedure for deasphalting with surfactants is shown in Figure 1. First, 5ml of bitumen was placed in an Erlenmeyer flask with a side arm and then a mixture of 0.4mmol of surfactant, 20% of water and three times the bitumen volume’s n-Heptane were added. The solution was agitated for 5 minutes at room temperature and then about 30 minutes at 50°C in the water bath then let stand for an hour to form a precipitate (surfactant-asphaltene-resin mixture). The precipitate was then passed through a 0.45㎛ filter, dried at 107°C for about 2 hours, and then weighed. For DAO mixed with solvent, n-Heptane and water were evaporated at 40°C then centrifugally evaporated at 80mbar and then dried at 107°C for about 24 hours. The weight was then divided by the weight of the feedstock to get the DAO yield and precipitate. We conducted the experiment four times and used the mean. This study designated the precipitate as pitch with the asphaltene content in the pitch measured three times according to ASTM D3279[17] with the mean being used. We used the definition of weight percentage of asphaltene removal in the deasphalting process as the indicator for changes in the asphaltene aggregation characteristic shown in Eq. (1).

Asphaltene removal, wt% =

(%) !" #"" " (%) $ !" #"" " %(%)

7


(1)

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2.3. The zeta potential of the pitch To check the colloidal stability of the pitch, we used a Zetasizer Nano ZS (Malvern, UK) to measure the ξ-potential. The ξ-potential refers to the electric potential, which, more specifically, is the electrical characteristic of the surface of the colloid particles floating in the liquid. This study analyzed the ξ-potential in the same way as ParraBarraza et al.[15]. First, we collected 25mg of pitch, added 3.7ml of ethanol, then subjected the mixture to ultrasonic waves for 15 minutes. We then collected about 0.4ml of the supernatant liquid in which the pitch was well dispersed and put it in 50ml of a 0.001mol NaNO3 solution to fix the ionic strength. We then used a magnetic agitator to agitate the mixture for 20 minutes, and then put 1~2ml in the ξ cell while making sure that there would be no bubbles and conducted our analysis. We repeated the process six times and used the mean. The measurement of zeta potential of asphaltene or pitch in many prior studies was conducted in the aqueous solution according to its measuring principle. Since the environmental state for zeta potential measurement is different from the froth treatment or solvent deasphalting environment, the measured zeta potential for the same asphaltene or pitch may be different. Similarly, the zeta potential value at Iso-Electric Point (IEP=0mV), where the aggregation of the colloid (asphaltene-resin) maximizes, will be changed depending on the type of solution. To avoid this confusion, IEP was determined to be -18mV, which is the point at which the most unstable conditions of asphaltene were obtained from the extraction with the n-heptane-to-oil volumetric ratio being 100 according to ASTM D3279 (this data is not presented in this article). Therefore, all the zeta potential data used in this study was shifted up +18mV from the original measured value. 8


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2.4. Analysis of surfactant adsorption on the asphaltene-resin colloids (at the surface) The adsorption of surfactants on the asphaltene-resin colloids can be confirmed by the number of ξ-potential peaks. That is, the various peaks indicate the existence of different particles such as asphaltene and surfactant micelles not being adsorbed. To check the adsorption amount of the colloids by the surfactants on the surface, we conducted an XPS analysis (Axis Nova, Kratos, UK). We used monochromatic Al-Kα (hν=15KeV), collected about 0.5g of the pitch sample, and conducted an analysis. We repeated the analysis twice and used the mean value. Table 4 shows the amount of surfactant adsorbed on asphaltene-resin colloid.

2.5. Properties of the DAO Some of the important properties of the DAO, such as viscosity, metal content and API specific gravity, were measured. A Haake viscometer (RheoStress 6000) was used to measure the viscosity. To do this we took about 1ml of a DAO sample at a temperature ranging between 40~90°C. An XRF (X-Supreme 8000, ASTM D 4294) was used to measure the heavy metal content. To do this we collected about 12ml of the DAO sample. Finally, an API (Anton paar, ASTM D 287) was used to measure API gravity. To do this we collected about 2ml of the DAO sample at 15°C.

3. Results 3.1. Aggregation characteristic of asphaltenes depending on the changes in the lengths of the 9


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alkyl chains of the sulfate types (anions) of the surfactants Figure 2 shows the changes in the percentage of asphaltene removal depending on the length of the alkyl chain when sulfate-type surfactants are used. When sulfate surfactants were used, the asphaltene removal declined as the length of the chains increased from 1 to 12. It was confirmed that SMS (length of alkyl-chain: 1) had the highest asphaltene removal of 60% while SDS (length of alkyl-chain: 12) had the lowest asphaltene removal of 49%. Compared to the case of no surfactant, if an SMS with a short chain was used then the asphaltene removal increased by about 3%, whereas if an SDS with the longest chain was used then the asphaltene removal decreased by about 7%. To interpret this result, the amount of sulfate surfactants adsorbed onto the colloids was analyzed by XPS. Figure 3(a) shows the result of a sample of pitch not treated by any surfactant, while Figure 3(b) shows the XPS result of a sample of pitch treated with surfactants injected during the extraction process. When sulfate surfactants were injected, a sulfate group was detected in all surfactants at 168.7eV as shown in Figure 3(b)[18]. Based on this result, we compared the changes in the adsorption and ξ-potential of the asphaltene-resin colloids and surfactants resulting from using surfactants with varying lengths of alkyl chains (see Fig. 4). In Figure 4, in examining the relative areas of the sulfates as they correlate to the lengths of the alkyl chains, it can be confirmed that the adsorption of sulfate increases as the length of the alkyl chain increases. To check the electric characteristics of the pitch, when sulfate is added during the extraction process the ξ-potential was measured with the results also shown in Figure 4. Pitch for the case without surfactant shows a negative electric potential. As surfactant is injected and the alkyl chain increases, the negative 10


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electric potential value also increases. This phenomenon is attributed to the fact that as the length of the alkyl-chain increases (see Fig. 4) the adsorption of the surfactant also increases, therefore the net charge of the pitch increases as a negative value. After all, this increase in the electric potential creates a mutual repulsion between the asphalteneresin colloids so that it suppresses the aggregation of the asphaltenes in the deasphalting process (see Fig. 2). As the head group of the surfactant has a negative electrical charge that is the same as the one with the asphaltene-resin colloid they develop a repulsive force. In this regard, it can be considered that the bonding between the hydrocarbon tail of the surfactant and the hydrophobic site of the asphaltene-resin colloid serves as the main adsorptive force. Similar to the study conducted by Salmón-Vega et al.[11] in which sodium dodecyl sulfate (SDS) was used, it was also found in this study that as the length of the alkyl chain of the surfactant increases, the hydrophobic interaction also increases and, as seen in Figure 4, the adsorption of the surfactant onto the asphaltene-resin colloid surface increases as well. Accordingly, the ξ-potential of the pitch further increases as a negative value suppressing the aggregation of the asphaltenes.

3.2. Aggregation characteristic of asphaltenes as they correlate to changes in the lengths of the alkyl chains of pyridinium types (cationic) of surfactants Figure 5 shows the asphaltene removal as it correlates to the length of the alkyl chain of the surfactants when pyridinium types of cationic surfactants were injected during the deasphalting process. As with the sulfate types of surfactants it can be confirmed that the pyridinium types also had the highest asphaltene removal when a surfactant with a short 11


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chain was used. The highest asphaltene removal of 64% was measured when MPCI (length of chain: 1) was used whereas CPCI (length of chain: 16) had the lowest at 55%. Compared with no surfactant, it was determined that if an MPCI with a short chain was used, the asphaltene removal increased by up to about 8%. If a CPCI with the longest chain was used, however, asphaltene removal decreased by about 3%. Similar to the sulfate surfactants, when pyridinium surfactants were used, as the length of the alkylchain increased, the stability of the pitch increased and the asphaltene removal decreased. The contents of the pyridinium surfactants adsorbed onto the asphaltene-resin colloid were able to be checked through XPS analysis. Figure 6(a) shows the result of the asphaltene-resin colloid with no surfactants, while Figure 6(b) shows the result of the asphaltene-resin colloid with the surfactants injected during the extraction process. As shown in the figure, a new peak was found at 401.3eV for all surfactants as shown in Figure 6, which was confirmed to be pyridinium in previously published literature[19]. From these results, it can be explained that a pyridinium surfactant is adsorbed onto the asphaltene-resin colloid surface. Figure 7 illustrates the changes in the relative area of pyridinium and ξ-potential in the asphaltene-resin colloid depending on the length of the alkyl chain of the pyridinium surfactants. The relative area of the pyridinium of an MPCI with a short alkyl chain is shown to be about 18%, i.e. the lowest level of adsorption, whereas that of a CPCI with the longest chain is shown to be about 55%, i.e. the highest level of adsorption. That is, if the length of the alkyl-chain increases, the pyridinium content also increases as with sulfate. To check the electrical characteristics of the pitch when pyridinium surfactants were 12


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injected during the extraction process, the ξ-potential was measured as shown in Figure 7. The results showed that compared to the case where no surfactants were used, the ξpotential increased in the positive direction in all conditions. This can be attributed to the fact that cationic surfactants neutralized the electric potential of the anionic asphalteneresin colloid[20] and then gains a positive charge potential.

3.3. Comparison of the adsorption mechanism and pitch aggregation characteristics with alkyl chain lengths of anionic and cationic surfactants Previous studies that had examined the effect of ionic surfactants in a deasphalting condition explained that the adsorption of ionic surfactants (sodium dodecyl sulfate, cetyl pyridinium chloride) onto the asphaltene-resin colloid occurs through the acid-base interaction between the head group of the surfactants and the asphaltene-resin colloid surface causing the asphaltene-resin colloids to coagulate more due to the hydrophobic interaction between the hydrocarbon chains of the surfactants[21]. However, this study confirmed that there is a difference regarding the mechanism of adsorption of the surfactants on the asphaltene-resin colloid, and based on the results described in Sections 3.2 and 3.3, the mechanisms are newly explained (see Fig. 8). First, when the surfactants were not used, the pitch sample showed that the asphaltene and resin content were 56.79wt.% and 42.18wt.% respectively, and confirmed that they have a negative charge of approximately -20mV. (I) Adsorption of anionic surfactants and the aggregation mechanism of asphaltene-resin colloids (Fig. 8, top). 13


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In a deasphalting environment, anionic surfactants have an electric potential of the same polarity as the asphaltene-resin colloids, so as electrostatic repulsion is applied adsorption occurs due to the hydrophobic interaction (mostly by the Van der Waals force induced from dipole moments) between the hydrocarbon chain of the anionic surfactant and the hydrophobic sites of the asphaltene-resin colloid. As the length of the alkyl-chain of the anionic surfactants decreases, the repulsion between charges gets stronger (as described at the top of the figure) and the adsorption of surfactant decreases as shown in Figure 4. Resultantly, colloids with short alkyl-chain surfactant end up having a ξ-potential whose absolute value is smaller than that of the surfactants with a longer alkyl-chain (that is, the dispersion stability of the colloid decreases). On the other hand, as the adsorption of the surfactants increases with a longer alkyl-chain, the ξ-potential increases to a higher negative value and the dispersion stability of the colloid ends up increased. Finally, it is concluded that surfactants with a short alkyl-chain cause a lowering of the ξ-potential so that aggregation of asphaltene is promoted. (II) Adsorption of cationic surfactants and the aggregation mechanism of the asphalteneresin colloids (see Fig. 8, bottom) Unlike the anionic surfactants described in (I) above, as the cationic surfactants have an electric potential that is opposite that of the asphaltene-resin colloid, electrostatic attraction goes to work. Figure 7 shows that the adsorption amount of cationic surfactants increase as the chain length increase just as it does with anionic surfactants. Considering the above common adsorption behavior for both anionic and cationic surfactants, it can be confirmed that the dominant mechanism for the adsorption of surfactant is the 14


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hydrophobic interaction between the asphaltene-resin colloid and alkyl chain of the surfactant rather than the electrostatic forces. As the adsorption of pyridinium surfactants increases with longer alkyl chains, the ξ-potential of the colloid also increases to the direction of a positive value. Ultimately, the best way to use ionic surfactants to improve asphaltene removal selectively can be summarized as shown in Figure 9. As the ξ-potential of the asphalteneresin is a negative value, as illustrated in Figure 9(b), cationic surfactants are more helpful for improving asphaltene removal than anionic surfactants due to the opposing polarity. And as the length of the alkyl chain decreased, asphatlene removal increased by at most 8% compared to no surfactant. This difference is attributed to the characteristics of adsorption of the anionic and cationic surfactants onto the asphaltene-resin colloid and the change of ξ-potentials, as explained above.

3.4 DAO yield and properties of products For the MPCI and SMS that had shown the best results, their DAO yields and properties were also examined. From Figure 10(a), the highest DAO yield can be seen for MPCI with an increase of about 1wt.% compared to the one with no surfactant. Notably, the asphaltene content in the DAO was the most important factor in this study as shown in Figure 10(b). From previously published literature, it has been reported that there is a trade-off between DAO yield and DAO quality due to the concentration of impurities in the heavily polarized aromatic fraction as mentioned in section 1[22]. In this respect, it seems that surfactants can break the trade-off as shown in Figure 10(b), and that this can be attributed to the improved selectivity of asphaltene removal afforded 15


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with the addition of select surfactants. In this regard, more selective removal of asphaltene in the deasphalting environment can result in a better quality of DAO as well as DAO yield at the same time. For example, changes in API gravity and viscosity (important factors for transporting bitumen through a pipeline) as a result of using surfactants can be compared in Figures 10(c) and 10(d) respectively. Similar to the results of DAO yield with MPCI, it can be found that API gravity increased by 1.5 at 40°C and viscosity decreased about 6 times lower than that without surfactants.

4. Conclusion Cationic and anionic surfactants with different alkyl-chain lengths were used in an attempt to improve asphaltene removal during a conventional oil sand bitumen froth treatment process. The results of the experiment showed that surfactants are adsorbed onto the negatively charged asphaltene-resin colloids at different ratios depending on the type of surfactant used and length of alkyl chains, and that those different adsorption mechanisms effected the interaction between the asphaltene-resin colloids so that their colloidal stability was changed. Finally, it was found that using cationic surfactants (MPCI) with a short alkyl chain is the best way to maximize the efficiency of asphaltene removal. Compared to cases in which surfactants were not used, DAO yield increased 1wt.%, API increased to 1.5, and viscosity decreased 6 times respectively. Based on this study, it was found that cationic surfactants with a short alkyl-chain can improve bitumen recovery and its quality at the same time.

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Acknowledgement We would like to acknowledge the financial support from the R&D Convergence Program of NST (National Research Council of Science & Technology) of Republic of Korea (Grant B551179-12-07-00).

References (1) Peramanu, S.; Pruden B. B.; Rahimi, P. Molecular Weight and Specific Gravity Distributions for Athabasca and Cold Lake Bitumens and Their Saturate, Aromatic, Resin, and Asphaltene Fractions. Ind. Eng. Chem. Res. 1999, 38 (8), p. 3121-3130. (2) Groenzin, H.; Mullins O. C. Molecular Size and Structure of Asphaltenes from Various Sources. Energy Fuels. 2000, 14 (3), 677-684. (3) Mullins, O.C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G. Asphaltenes, Heavy Oils, and Petroleomics. Springer, New York, 2007, 511-547. (4) http://www.oilsandsmagazine.com/technical/mining/froth-treatment/paraffinic. (5) Rao, F.; Liu, Q. Froth Treatment in Athabasca Oil Sands Bitumen Recovery Process: A Review. Energy Fuels. 2013. 27 (12), 7199-7207.

(6) http://canmetenergy.nrcan.gc.ca/oil-sands/404. (7) Chang, C. L.; Fogler, H. S. Stabilization of Asphaltenes in Aliphatic Solvents Using Alkylbenzene-Derived Amphiphiles. 1. Effect of the Chemical Structure of Amphiphiles on Asphaltene Stabilization. Langmuir. 1994, 10, 1749-1757. (8) Peramanu , S.; Clarke, P. F.; Pruden, B. B. Flow loop apparatus to study the effect of 17


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

Page 18 of 40

solvent, temperature and additives on asphaltene precipitation. J Pet Sci Eng. 1999, 23, 133143. (9) Goual, L.; Sedghi, M.; Wang, X.; Zhu, Z. Asphaltene Aggregation and Impact of Alkylphenols. Langmuir. 2014, 30, 5394-5403. (10) Li, C.; Wang, J. Q.; Deng, W. A.; Zhang, L. I.; Que, G. H. Effects of active additives on Zeta potential of Lungu atmospheric residue. J Fuel Chem. Technol. 2008, 36, 55-59. (11) Salmón-Vega, S.; Urbina-Herrera, R.; Galeana-Lira, C.; Valdez, M. A. The Effect of Ionic Surfactants on the Electrokinetic Behavior of Asphaltene from a Maya Mexican Oil. Pet Sci Technol. 2012, 30, 986-992. (12) Al-Sahhaf, T. A.; Fahim, M. A. Elkilani, A. S. Retardation of asphaltene precipitation by addition of toluene, resins, deasphalted oil and surfactants. Fluid Phase Equilib. 2002,194– 197,1045-1057. (13) 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, 87788785. (14) Goual, L; Sedghi, M. Role of ion-pair interactions on asphaltene stabilization by alkylbenzenesulfonic acids. J Colloid Interface Sci. 2015, 440, 23-31. (15) Parra-Barraza, H.; Herna´ndez-Montiel,

D.; Lizardi, J.; Herna´ndez, J.; Urbina, R. H.;

Valdez, M. A. The zeta potential and surface properties of asphaltenes obtained with different crude oil/n-heptane proportions. Fuel. 2003, 82, 869-874. (16) Salmón-Vega, S.; Urbina-Herrera, R.; Valdez, M. A.; Galeana-Lira, C. Effect of the concentration of ionic surfactants on the electrokinetic behavior of asphaltene precipitated from a maya mexican crude oil. Revista mexicana de ingeniería química. 18


2010, 9, 343-357.

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

Energy & Fuels

(17) ASTM. Standard test method for n-Heptane Insolubles. ASTM D 3279. West Conshohochen:ASTM international, 2001. (18) Zhou, G.; Paek, E.; Hwang, G. S.; Manthiram, A. Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphurcodoped graphene sponge. Nat Commun. 2015, 6, 7760. (19) Lezanska, M.; Pietrzyk, P.; Sojka, Z. Investigations into the Structure of NitrogenContaining CMK-3 and OCM-0.75 Carbon Replicas and the Nature of Surface Functional Groups by Spectroscopic and Sorption Techniques. J Phys Chem C. 2010, 114, 1208-1216. (20) Al-Mubarak, T.A.; Al-khaldi, M.H.; Al-Ibrahim, H.A.; Rafie, M.M.; Al-Dajani, O. Investigation of acid-induced emulsion and asphaltene precipitation in low permeability carbonate reservoirs. in SPE Saudi Arabia Section Annual Technical Symposium and Exhibition. Society of Petroleum Engineers. 2015, fall. (21) Go, K. S.; Kwon, E. H.; Kim, K. H.; Nho, N. S.; Lee, K. B. Effect of Ionic Surfactants on Improving Deasphalting Selectivity in a Nonpolar System. Energy Fuels. 2016, 30, 20762083. (22) Huc, A.Y. Heavy crude oils: from geology to upgrading: an overview; Technip: Paris, France, 2011.

19


Energy & Fuels

Graphical Abstract

1 Comparison of the adsorption mechanism and pitch aggregation characteristics with alkyl-chain 2 3  Short alkyl chain (I) Anionic surfactants 4 5 6 7 8 9 10 11 12 Head (sulfate group) 13 Tail (alkyl chain) 14 15Asphaltene (Asp,) 16 Resin 17 Low adsorption amount of surfactants Acting electrostatic 18 & negative-charged ξ-potential repulsive force 19 20 21 22  Short alkyl chain Acting electrostatic 23 attractive force 24 25 26 27 Head (Pyridinium group) 28 Tail (alkyl chain) 29 30 31 Negative-charged Asphaltene-Resin 32 colloid (-20 mV) 33 34 35 36 (II) Cationic surfactants 37 Low adsorption amount of surfactants 38 & Low negative or positive-charged ACS Paragon Plusξ-potential Environment 39 40 (the most unstable state of colloids) 41

Page 20 of 40

lengths of anionic and cationic surfactants  Long alkyl chain

CH3

CH3

CH3

CH3

CH3

+

H2S

O

+

NH

+

O

N

H3C

O

+

N

S

O

+

+

NH

O

+

O

N

CH3

-

O

O

+

+

H2S

O

O

+

NH

O

O

+

N

S

S

-

S

H3C

S

H3C

-

O

N

-

+

N

+

CH3

S

+

CH3

+

N

+

N

+

N

O

+

S

H3C

NH

O

+

+

N

O

+

+

N

CH3

H2S

O

H2S

-

S

CH3

CH3 +

O

+

O

CH3

-

O

O

+

-

O

+

+

N

H3C

O

-

O

H3C

H3C

+

H3C

H3C

H3C

H3C

H3C

High adsorption amount of surfactants & High negative-charged ξ-potential

CH3

CH3

+

H2S

O

+

NH

O

+

O

N

-

S

H3C

O

+

N

S

+

CH3

+

N

O

-

O

 Long alkyl chain

+

H3C

H3C

CH3

CH3

CH3

+

H2S

O

+

NH

CH3 CH3

O

+

O

N

-

S

H3C

O

CH3

+

N

S

+

+

H2S

CH3

O

+

NH

O

+

+

O

N

N

O

-

+

H3C

O CH3

CH3 CH3

-

+

H2S

O

S

+

CH3

O

-

O

+

O

+

O

-

H3C

S

O

+

N

S

+

O

+

NH

O

H3C O

+

N

S

+

N

+

CH3

-

O

O

+

H3C H3C H3C H3C

CH3

+

-

O

S

+

CH3

+

N

N

O

-

S

N

O

O

N

-

+

NHH3C O

+

N

+

H2S

O

S O

+

CH3

H2S

NH

O

H3C

+

N

H3C

H3C

+

+

N

+

N

H3C

O

+

S

+

H3C

H3C

High adsorption amount of surfactants & High positive-charged ξ-potential

-

O

+

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

Energy & Fuels

Figure 1. Experimental procedure for solvent deasphalting

Solvent Water+Surfactant Pitch (Drying 2 hr, 107 ℃)

400 rpm 50 ℃

bitumen

Stirring 5 min

Heating and stirring 30 min


0 rpm 50 ℃

Maintenance 1 hr

DAO (Evaporator, Drying 24 hr, 107 ℃)

Energy & Fuels

Figure 2. Percentage of asphaltene removal as a function of the alkyl chain length of the sulfate

75

70 Asphaltene removal (wt.%)

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

65

60

No surfactant

55

50

45 0

1

2 3 4 5 6 7 8 9 10 11 12 13 Length of alkyl chain of sulfate surfactants


Page 22 of 40

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

Energy & Fuels

Figure 3. XPS S-2p spectra for pitch obtained from deasphalting (a) without sulfate-surfactants (b) with sulfate-surfactants [18]

(a)

Sum

Sulfide (162.1 eV) S-S/S-C (163.7 eV)

160

162

164

166

168

Binding energy (eV)


170

172

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

Page 24 of 40

Figure 3. XPS S-2p spectra for pitch obtained from deasphalting (a) without sulfate-surfactants (b) with sulfate-surfactants [18]

(b) Sum

Sulfide (162.1 eV) S-S/S-C (163.7 eV) Sulfate (168.6 eV)

158

160

162

164

166

168

170

Binding energy (eV)


172

Page 25 of 40

Figure 4. Effect of alkyl chain length of surfactants on the relative area of sulfate of asphaltene-resin and ξ-potential of pitch (● : relative area of sulfate, ○ : ξ-potential)

60

0

55

-5

50 -10 45 -15

40 35

No surfactant

-20

30 -25 25

-30

20 15

-35 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Length of alkyl chain of sulfate surfactants


ξ-potential (mV)

Relative area of sulfate (%)

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

Energy & Fuels

Energy & Fuels

Figure 5. Percentage of asphaltene removal as a function of alkyl chain length of pyridinium

80


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

70

65

60

55

No surfactant

50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Length of alkyl chain of pyridinium surfactants


Page 26 of 40

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

Energy & Fuels

Figure 6. XPS N-1s spectra for pitch obtained from deasphalting (a) without pyridinium-surfactant (b) with pyridiniumsurfactant [19]

(a) Sum Pyridine (398.6 eV)

396

398

400

402

404

Binding energy (eV)


406

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

Page 28 of 40

Figure 6. XPS N-1s spectra for pitch obtained from deasphalting (a) without pyridinium-surfactant (b) with pyridiniumsurfactant [19] (b) Sum Pyridine (398.6 eV) Pyridinium (401.2 eV)

396

398

400

402

Binding energy (eV)


404

406

Page 29 of 40

Figure 7. Effect of alkyl chain length of surfactants on the relative area of pyridinium of asphaltene-resin and ξ-potential of pitch (▲ : relative area of pyridinium, ∆ : ξ-potential)

65 45

60 55

35

50

25

45 15

40 35

5

30

-5

25

-15

20

No 15 -25 surfactant 0 1 2 3 4 5 6 7 8 9 1011121314151617

Length of alkyl chain of pyridinium surfactants


ξ-potential (mV)

Relative area of pyridinium (%)

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

Energy & Fuels

Energy & Fuels Figure 8. Comparison of the adsorption mechanism and pitch aggregation characteristics with alkyl-chain lengths of anionic and cationic surfactantsPage 30 of 40 1 2 3 (I) Anionic surfactants 4 5 6 7 8 9 10 11 12 Head (sulfate group) 13 Tail (alkyl chain) 14 15Asphaltene (Asp,) 16 Resin 17 Acting electrostatic 18 repulsive force 19 20 21 22 Acting electrostatic 23 attractive force 24 25 26 27 Head (Pyridinium group) 28 Tail (alkyl chain) 29 30 31 Negative-charged Asphaltene-Resin 32 colloid (-20 mV) 33 34 35 36 (II) Cationic surfactants 37 38 39 40 41 CH3

 Short alkyl chain


CH3

CH3

CH3

CH3

CH3 +

H2S

O

+

NH

+

H2S

O

N

+

N

S

O

+

+

NH

O

+

H2S

O

O

+

NH

O

O

O

-

H3C O S

-

S

+

N

S

O

N

-

S

H3C

O

+

N

CH3 H3C

-

NH

O

+

+

N

O

+

+

N

CH3 H2S

O

O

+

-

S

H3C

CH3

CH3 +

O

+

N

+

CH3

S

+

CH3

+

N

+

N

O

+

+

N

S

+

O

CH3

-

O

O

+

-

O

+

+

N H3C

O

-

O

H3C

H3C

+

H3C

H3C

H3C

H3C

H3C

High adsorption amount of surfactants & High negative-charged ξ-potential

Low adsorption amount of surfactants & negative-charged ξ-potential

CH3

+

H2S

O

+

NH

O

+

O

N

-

S

H3C

O

+

N

S

+

CH3

+

N

O

-

O

 Short alkyl chain

+


H3C

H3C

CH3

CH3 CH3 +

H2S

O

+

NH

CH3 CH3

O

+

O

N

-

S

H3C O

CH3

+

N

S

+

+

H2S

CH3

O

+

NH

O

+

+

O

-

+

CH3

-

+

H2S

O

O

N

O

S

+

CH3

O

+

O

+

O

O

O

-

O

N CH3

H3C

O

+

H3C

H3C

+

N

S

+

CH3

+

N

O

-

O

+

H3C

H3C

Low adsorption amount of surfactants & Low negative or positive-charged ACS Paragon Plusξ-potential Environment

(the most unstable state of colloids)

S

+

CH3

+

N

H3C O

-

+

+

H3C

-

S

O

N

NHH3C O

+

N

NH

O

H3C

S

+

CH3 +

+

S

+

N -

O N

-

S

H3C O

O

+

H2S

O

+

+

N H3C

H2S

NH

+

N

H3C

H3C

+

+

S

H3C

O CH3

CH3 O

N

N

High adsorption amount of surfactants & High positive-charged ξ-potential

-

O

+

Page 31 of 40

Figure 9. Effect of alkyl chain length of anionic (●) and cationic (▲) surfactants on (a) asphaltene removal and (b) ξ-potential

(a) 70


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

Energy & Fuels

60

55 No surfactant

50

45 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Length of alkyl chain


Energy & Fuels

Figure 9. Effect of alkyl chain length of anionic (○) and cationic (∆) surfactants on (a) asphaltene removal and (b) ξ-potential

(b)

50 40 30

cationic

20

ξ-potential (mV)

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

Page 32 of 40

10 0 -10 -20

No surfactant

-30

anionic

-40 -50 0

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17

Length of alkyl chain


Page 33 of 40

Figure 10. Comparison of (a) DAO yield, (b) asphaltene content with DAO yield, (c) API gravity of DAO, and (d) viscosity of DAO at different surfactants applied

(a) 86.2

86

85.8

DAO yield

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

Energy & Fuels

85.6

85.4

85.2

85

84.8

No surfactant

SMS


MPCl

Energy & Fuels


(b) 10 9 Asphaltene content in DAO (wt.%)

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

Page 34 of 40

8 7 6 5 4 3 2

No surfactant SMS MPCl

1 0 75

80

85 DAO yield (wt.%)


90

95

Page 35 of 40


(c)

12

9.6

10 API Gravity at 15.6 ℃ (-)

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

Energy & Fuels

8.6

8.1 8

6

4

2

0 No surfactant

SMS


MPCl

Energy & Fuels


(d) 30000 No surfactant SMS MPCl

25000

Viscosity (mPa.s)

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

Page 36 of 40

20000

15000

10000

5000

0 40

50

60

70

Temperature (℃)


80

90

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

Energy & Fuels

Table 1. Summary of literature related to the study of asphaltene stability subjected to different types of surfactants Surfactant type Amphiphile

Surfactants Used

Adsorption interaction

Research group

Base-acid

Chang & Fogler [7]

H-bonding

Goual et al. [9]

14 amphiphile surfactants (C, EP, BP, SBP, OP, DP…)

The amount of adsorption between asphaltene and amphiphile surfactants was measured with different head lengths and tail lengths. The amount of adsorption became constant with six or more alkyl chains.

OP, DP

The size of asphaltene was measured with the surfactants in order to evaluate asphaltene stability. The longer the chain, the smaller the asphaltene became.

NP, DDBSA

Base-acid The stability of asphaltene was measured with different functional groups of surfactants. Asphaltene was found to stabilize best when subjected to the surfactant with an acid functional group.

Peramanu et al. [8]

DBSA, DR, NP, DO , R, T

The onset point of asphaltene was measured with six surfactants with different head groups in order to evaluate asphaltene stability. The surfactant with polarized and acid group stabilized asphaltene.

Base-acid

Al-Sahhaf TA et al. [12]

Bonding between asphaltene and surfactants was measured with UV-visible spectroscopy. surfactants with an acid group raised the stability of asphaltene.

Base-acid

Hashmi et al. [13]

The stability of asphaltene increased by surfactants was measured through HRTEM and Molecular dynamics. HRTEM revealed the structure of surfactants adsorbed onto asphaltene.

Base-acid

Goual & Sedghi [14]

SDS, CPCl

With surfactants applied to asphaltene extracted from crude oil/n-Heptane volume at ratios of 1:5, 1:15 or 1:40, asphaltene stability was measured for zeta potential. SDS 10-3 or CPCl 10-4 injected into the asphaltene which was extracted at the ratio of 1:15 kept its zeta potential across the entire pH section, maintaining asphaltene stability.

Hydrophobic

Parra-Barraza et al. [15]

SDS, CA, OA

Change of SARA, ξ potential and colloid particle size of the precipitates created by surfactants were measured in order to verify asphaltene stability. It was found that a certain amount of surfactant increases the repulsive power of asphaltene, increasing stability.

Base-acid

Li et al. [10]

SDS, DHA. CPCl

The stability of asphaltene increased by surfactants was measured through zeta potential. 0.1 mmol or more surfactant increased asphaltene stability.

Hydrophobic

Salmon-Vega et al. [16]

SDS, DHA. CPCl

The stability of asphaltene depending on concentration of surfactants was measured through zeta potential, and changes of interfacial tension caused by surfactants was checked. It was found that 1 mmol or more of each surfactant kept the zeta potential of asphaltene within the pH section, maintaining the stability of asphaltene.

Hydrophobic

Salmon Vega et al. [11]

DBSA

DBSA, OP Ionic

Significant findings/results


Table 2. Physical properties of feedstock 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Energy & Fuels

Page 38 of 40

Measured Item

Results

Elemental analysis (wt.%)

C: 83; H: 10.3; N: 0.5; S: 5.2; O:0.9

Boiling point distribution (mass %)

Naphtha ( 0 ~ 177 ℃ ): 0 Middle Distillate (177 ~ 343 ℃): 13.5 Vacuum Gas Oil (343 ~ 524 ℃): 39.03 Residue (524 ℃ +): 47.47

ASTM D 7169

MCR content (wt.%)

14.48

ASTM D 4530

Heavy metal content (ppm)

Ni: 105; V: 195

ASTM D 4294

Viscosity (mPa.s)

240-46,400

Temp. Range (35~100 ℃)

API specific gravity (deg)

8.18

ASTM D 287

SARA analysis (area %)

Saturates / Aromatics / Resins /Asphaltenes, 8.2 / 52.8 / 21.4 / 17.6

IP 469-01

C7 insoluble (wt.%)

14.36

ASTM D 3279


Remarks

Page 39 of 40

Energy & Fuels

Table 3. Chemical information of the anionic and cationic surfactants used in this study

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

Chemical structure

Anion

Name

Abbreviation

Alkyl chain length

Sodium methyl sulfate

SMS

1

Sodium octyl sulfate

SOS

8

Sodium dodecyl sulfate

SDS

12

1-Methyl pyridinium chloride

MPCl

1

Butyl pyridinium chloride

BPCl

4

Dodecyl pyridinium chloride

DPCl

12

Cetyl pyridinium chloride

CPCl

16

Cation


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 40 of 40

Table 4. . Effect of alkyl chain length of surfactants on the relative area of sulfate and pyridinium of asphaltene-resin

Sulfate (Anion)

Abbreviation

Relative area of surfactant (%)

Error

SMS

16.03

0.25

SOS

31.56

1.05

SDS

51.09

1.41

MPCl

17.72

0.42

BPCl

42.12

0.92

DPCl

54.02

0.06

CPCl

64.66

0.06

Pyridinium (Cation)


Effect of Alkyl Chain Length of Ionic Surfactants on Selective Removal

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