Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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Effect of the Surfactant on Asphaltene Deposition on Stainless-Steel and Glass Surfaces Abdulaziz Al Sultan,† Mohsen Zirrahi,‡ Hassan Hassanzadeh,*,‡ and Jalal Abedi‡ †
Saudi Aramco, Dhahran 31311, Saudi Arabia Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada
‡
ABSTRACT: Surfactant dispersants have been introduced as a proper candidate to mitigate the problems caused by asphaltene precipitation, such as clogging wells, flowlines, and surface facilities in oil industry. In this work, we study the effects of dodecylbenzenesulfonic acid (DBSA) as a surfactant on asphaltene deposition on stainless-steel and glass surfaces. Experiments were conducted to measure asphaltene precipitation in the bulk system and asphaltene deposition on the stainless-steel and glass surfaces. Results revealed that the surfactant delays the asphaltene onset in the bulk system. However, asphaltene deposition on the stainless-steel surface was increased at all measured concentrations of the surfactant, while the deposition rate on the glass surface decreased by increasing the surfactant concentration. Affinity of the surfactant molecules to the stainless-steel surface was verified in asphaltene deposition and removal tests. The results revealed that the DBSA surfactant is able to remove deposited asphaltene on glass surfaces at high concentrations. This study reveals the importance of surface properties when the surfactant is used as an asphaltene dispersant.
1. INTRODUCTION Asphaltene deposition is known to cause clogging of oil wells, flowlines, and surface facilities. Asphaltene deposition costs operators millions of dollars as a result of issues such as maintenance, replacement, or loss of production.1 Finding an effective way to control asphaltene dispersion in petroleum fluid is still a demanding area of research. The past literature on asphaltene mitigation was mainly focused on either prevention or delay of asphaltene precipitation/aggregation.2−5 Prevention and delay of asphaltene can be achieved through injection of aromatic solvents, taking benefit from a natural inhibitor in crude oil or finally using dispersants/inhibitors. The latter is the most efficient way to delay or prevent asphaltene problems economically and environmentally, which can lead to stabilizing asphaltene and preventing precipitation or deposition.2 An increasing number of studies are being published related to surfactant dispersants, but until now, these studies are mostly far from practical use and still under laboratory studies.3−5 As an iconic reference in the asphaltene dispersion area, Chang and Fogler5 studied the effect of the chemical structure of several amphiphiles on stabilization of asphaltene flocs. Asphaltene powder was analyzed for its properties to be used for the onset detection experiments. The adsorption of some amphiphile headgroups was studied using a Fourier transform infrared (FTIR) spectrophotometer. Four different amphiphile headgroups were compared with respect to the stabilized asphaltene weight and asphaltene adsorption with amphiphiles. The sulfonic acid group [dodecylbenzenesulfonic acid (DBSA)] showed a desirable result as an effective asphaltene stabilizer. Then, the effect of the tail length of the amphiphile was studied, concluding that a longer tail accounted for better asphaltene stability at the expense of losing some affinity to asphaltene. Afterward, the effect of different amphiphile side groups was studied by adding a polar group (i.e., hydroxyl © XXXX American Chemical Society
group) to the amphiphile. The results showed an increase of asphaltene stability. However, the addition of a side group has some negative side effects on asphaltene dispersion in solution when it joins the amphiphile at the tail. Lastly, the n-alkane solvent type was varied to investigate asphaltene stability. Chang and Fogler5 concluded that having more volatile solvent lowered asphaltene stability for weak amphiphiles. However, no effect was observed when using strong amphiphiles, such as DBSA. Wang et al.6 studied the ability of different ionic and nonionic liquids and their structural differences on asphaltene dispersion. The impendance analysis method was used and confirmed the results of the refractometry method. Then, highresolution transmission electron microscopy was used to study the structure of asphaltene dispersion and also to confirm the results of the previous methods. The author concluded that ionic surfactant DBSA is the most effective dispersant among those studied, followed by the non-ionic liquid 4-octylphenol (OP). Aslan and Firoozabadi7 studied the effect of brine and deionized (DI) water on asphaltene deposition using a pipeflow setup. Asphaltene deposition was simulated using the pipeflow setup where water, oil, and heptane from separate lines were mixed in one junction with a specified concentration. The mixture was then sent through a metal pipe, while a pressure transducer was used to measure the pressure difference in the system. Pressure versus the injected volume was used for analysis. They concluded that addition of water to the system noticeably delayed the asphaltene deposition. Received: January 17, 2018 Revised: March 23, 2018 Published: March 25, 2018 A
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Subramanian and Firoozabadi2 went further to study the effect of two different ionic surfactants (ionic “DBSA” and nonionic “BA”) on asphaltene precipitation and deposition, introducing water and brine to the system. Sedimentation tests were carried out to study the effect of mixing of different water/brines with multiple surfactant concentrations on asphaltene precipitation on Falcon tubes. Although a previous study7 concluded that the presence of water or brine delays asphaltene deposition, the study of Subramanian and Firoozabadi2 showed that the butyl acrylate (BA) surfactant was not affected by water or brine addition because water would make the solution more polar by inducing negative charge on the surface of the asphaltene aggregate. On the other hand, DBSA showed poor dispersion in the presence of water or brine and associates with the asphaltene, which weakens the electrostatic interaction between DBSA and asphaltene, resulting in more unstable asphaltene and inefficient dispersion. Loureiro et al.9 examined the influence of two asphaltene stabilizers or inhibitors (DDBSA and CAAS) using two different destabilizing conditions, one with n-heptane and the other with CO2. Different concentrations of inhibitor were added to study the change in the onset point of precipitation. The results showed that the inhibitors were system-selective, meaning that each condition (CO2 or n-heptane) responded differently. They delayed asphaltene precipitation in systems containing n-heptane, while no significant effect was observed for CO2-containing systems. Several investigations have been conducted to study the effect of surfactants on the decrease and/or delay of the asphaltene precipitation and deposition.2−9 These studies suggested injection of the surfactants into streams susceptible to asphaltene precipitation and deposition. However, there is a lack of information on the effect of the surfactant on deposition of asphaltene particles on surfaces, such as stainless-steel (SS) and glass. In this work, we study the effect of DBSA as an ionic surfactant on asphaltene deposition on SS and glass surfaces. SS can be a representative of the pipeline surface, while glass beads can be a representative of porous media. Moreover, the capability of the surfactant to dissolve deposited asphaltene on a surface is evaluated. The rest of this paper is organized as follows: First, we present the experimental details consisting of material, apparatus, and procedure. Then, experimental results are presented, followed by conclusions.
Figure 1. DBSA chemical structure and properties. with the glass cover for microscope slides purchased from Canlab/ Baxter (24 × 25 mm). 2.2. Experimental Procedure. In this work, we studied the effect of DBSA on asphaltene precipitation in a system of a toluene− asphaltene mixture and also deposition of asphaltene on SS and glass surfaces. To study the effect of the surfactant on asphaltene precipitation, we measured the amount of precipitated asphaltene in different concentrations of precipitant and surfactant. 2.2.1. Asphaltene Fractional Yield Tests. The asphaltene solubility test or fractional yield test was conducted to generate solubility curves, which result in the percentage of precipitated asphaltene versus volume fraction of n-heptane in a toluene−heptane mixture. These experiments were conducted in the presence and absence of the surfactant. The procedure reported by Sadeghi Yamchi12 was adopted and slightly modified to fit our purpose. Asphaltene was precipitated using n-heptane from Athabasca bitumen as described by Azinfar et al.13 A total of 300 mg of solid-free asphaltene was added to a 25 mL vial. Toluene was added to asphaltene and then put in an ultrasonic bath for 20 min until all asphaltene was dissolved. A predetermined amount of toluene was added to the vial to reach the asphaltene concentration of 20 kg/m3 in the solution. Then, n-heptane was added to the mixture to obtain the desired heptane volume percent in toluene (60, 70, 80, and 90 vol %). For the samples containing the surfactant (DBSA), first, a certain amount of surfactant was added to n-heptane and then sonicated for 5 min. Next, the surfactant−heptane mixture was added to the mixture of the dissolved asphaltene in toluene to achieve the desired heptane/toluene volume percent. The concentration of the surfactant (ppm) in the mixture was calculated using msur surfactant (ppm) = × 106 mtoluene + mC7 + msur (1) where msur, mC7, and mtoluene are masses of surfactant, heptane, and toluene, respectively. The mixture was then put in an ultrasonic bath for 45 min and then left to settle for 1 h. Each vial was then centrifuged at 4000 rpm for 5 min to separate the precipitated asphaltene. Supernatant was then decanted; the vial is placed in a vacuum oven at 70 °C for 24 h; and then each vial was weighted to determine the asphaltene yield. The same experiments were also conducted in the absence of the surfactant, and the asphaltene yields at different n-heptane concentrations were measured. 2.2.2. Asphalting Deposition Experiments. The asphaltene deposition experiments were conducted using Athabasca bitumen. We prepared and tested the n-heptane/bitumen mixtures based on the mass fraction basis to avoid errors as a result of volume change during the mixing of n-heptane and bitumen. First, we prepared a solution of 40 wt % n-heptane in bitumen. The sample was then sonicated for 90 min and left for 72 h. This mixture was used to prepare the samples with a higher n-heptane concentration. This mixture was checked under a microscope to detect possible asphaltene aggregates. No asphaltene precipitation was detected for the mixture of 40 wt % nheptane in bitumen. To prepare the samples with higher concentrations of n-heptane, a small amount (20−30 g) of the prepared n-heptane−bitumen mixture (40 wt %) was put into a 250 mL beaker. Afterward, while mixing, a predetermined weight of nheptane was added to the mixture to achieve the desired n-heptane concentration. The sample was stirred for 2−10 min. Then, a microscope image was taken before being placed into the deposition apparatus to study the asphaltene aggregate. To prepare the mixture containing the surfactant, the concentration (ppm) of the surfactant in solution was calculated by
2. EXPERIMENTAL SECTION 2.1. Chemicals and Materials. The experiments were conducted using Athabasca bitumen to study the asphaltene deposition. Bitumen properties are listed in Table 1.
Table 1. Bitumen Source and Properties10,11 SARA fraction (wt %) saturate
aromatic
resin
asphaltene
density (g/cm3)
API gravity (deg)
12.26
40.08
36.53
11.13
1.004
10.0
Ionic surfactant DBSA was purchased from Sigma-Aldrich with purity higher than 95%. The chemical structure of DBSA is shown in Figure 1. n-Heptane and toluene were purchased from BDH VWR Analytical, while chloroform was provided by Anachemia. Two types of beads were used: (1) SS beads with 3.95 mm diameter and (2) borosilicate glass beads with 4 mm diameter from Chemglass, Inc. The microscope slides were purchased from VWR VistaVision (3 in. × 4 in. × 1.2 mm) B
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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Figure 2. Asphaltene deposition apparatus used in experiments.
surfactant (ppm) =
mbit
msur × 106 + mC7 + msur
Table 2. Range of n-Heptane and DBSA Concentrations in the Asphaltene Yield and Deposition Tests
(2)
where msur, mC7, and mbit are masses of surfactant, n-heptane, and bitumen, respectively. To prepare a sample with a certain amount (ppm) of surfactant, we made a predetermined mixture of the surfactant and n-heptane. Then, the mixture was added slowly to the solution of 40 wt % n-heptane in bitumen while stirring to reach the desired n-heptane and surfactant concentrations in the solution. After, the solution was stirred for 2−10 min, several drops were studied under the microscope to study the asphaltene aggregate and the rest of the mixture was put into the apparatus to conduct the asphaltene deposition experiments. It is worth mentioning that the time for asphaltene destabilization and aggregation for the mixtures with higher than 63 wt % n-heptane in bitumen was less than the preparation and settling time (∼1 h). The apparatus for asphaltene deposition experiments was designed similar to that used by Vilas Bôas Fávero et al.14 The setup shown in Figure 2 consists of a pump (Eyela, ceramic pump VSP-2200) that injects the mixture sample to a glass column (15.3 cm length and 10 mm inner diameter). The glass column was filled with SS beads (3.95 mm of diameter) or glass beads (4 mm of diameter). The total bed length in both SS and glass bead experiments was 13.5 cm, with a total of 152 beads for the SS bed and 132 beads for the glass beads. The packed bed column effluent was then returned to the mixture sample to form a closed loop. The sample was kept stirring during the entire period of the experiments. When a prepared sample was placed in the apparatus, it was pumped at 0.6 mL/min for a 24 h period. Then, the sample was drained slowly at a rate of 0.1 mL/min to prevent removal of any deposits from the packed bed. After the packed bed column was drained, it was then rinsed with chloroform and the mixture was collected in a vial. The vial was put in a vacuum oven at 75 °C for 24 h until all chloroform was evaporated. Following the study by Vilas Bôas Fávero et al.,14 the retaining material in the packed bed column consists of the deposited material and the trapped fluid. The trapped fluid was determined by performing the deposition experiments with a run time of 1 min. This time is assumed small enough for any depositions to occur.14 In these experiments, after circulation of the n-heptane−bitumen mixture for 1 min, the amount of trapped fluid in the packed bed was measured, which is the liquid trapped between the beads. We also used the microscope (AmScope microscope) to check the size of the aggregates before and after putting the sample in the apparatus. Self-association of asphaltene along with aggregate shape and size is examined using the microscope. Each sample was tested twice. First, the sample was tested 5 min after preparation, and the second test was conducted after 24 h of the sample being stirred and circulated in the deposition apparatus. All microscope image scales were kept the same for comparison purposes. Table 2 shows the range of n-heptane and surfactant in the conducted experiments in this work.
asphaltene yield experiments asphaltene deposition experiments
surfactant concentration (ppm)
n-heptane concentration
0−25000 0−50000
60−90 vol % 40−70 wt %
3. RESULTS AND DISCUSSION 3.1. Effect of the DBSA Surfactant on the Asphaltene Yield. Yield and solubility curves have been widely studied in the literature.11,13 The fractional yield is defined as the ratio of the precipitated asphaltene to the initial mass of asphaltene in the mixture. The effect of DBSA on asphaltene precipitation was studied in the bulk system using the asphaltene yield test. To obtain insight into the DBSA and asphaltene interaction in the absence of other factors, such as surface adsorption and other impurities/components in bitumen, solid-free asphaltene from the Athabasca bitumen was used to study the asphaltene solubility and determine how DBSA alters the yield.15 In this study, four n-heptane volumetric fractions (0.6, 0.7, 0.8, and 0.9) in toluene/asphaltene mixtures were studied to track the changes after adding DBSA to the mixture. These volumetric fractions of n-heptane allow us to focus on the region with asphaltene precipitation higher than the onset point. The results of the asphaltene yield in different n-heptane and DBSA concentrations are shown in Figure 3. It can be found that a higher n-heptane concentration results in higher precipitated asphaltene. Also, increasing the DBSA concentration decreases the asphaltene yield. However, n-heptane volume fractions of 0.8 and 0.9 show a slight increase in the fractional yield by the addition of DBSA at low DBSA concentrations. The measured fractional yield greater than 100 at 90 vol % n-heptane and 5000 ppm of DBSA can be attributed to precipitation of DBSA with asphaltene. This shows that the added surfactant sticks to asphaltene molecules. As the surfactant concentration is increased, the asphaltene precipitation was not observed. For instance, at 15 000 ppm of DBSA, asphaltene precipitation was not observed in the mixtures with 0.6, 0.7, and 0.8 n-heptane volumetric fractions. A 0.9 volumetric fraction of n-heptane and 15 000 ppm concentration of surfactant results in a fractional yield of 0.56. These observations suggest that the surfactant delays the onset and also decreases the asphaltene yield. All curves in this figure were measured at a settling time of 1 h. C
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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Figure 3. Fractional yield curve for solid-free asphaltene measured at different DBSA concentrations (0, 5000, 10 000, 15 000, and 25 000 ppm) for various volumetric fractions of heptane (0.6, 0.7, 0.8, and 0.9).
3.2. Effect of the DBSA Surfactant on Asphaltene Deposition on a Packed Bed. 3.2.1. SS Beads. In the first step, the amount of the trapped fluid between the SS and glass beads was measured. Trapped fluid measurements were conducted using bitumen with different n-heptane and DBSA concentrations. These measurements were conducted with SS beads and then with glass beads in the packed bed column. The results of 11 repeated experiments showed that the measured values of the trapped fluid do not vary with the n-heptane or surfactant concentration. Instead, they are scattered closely to a mean value of 0.2061 g for SS beads in the packed bed, with a standard deviation of 0.0422. For glass beads in the packed bed, a similar pattern is observed, with a mean value of 0.1377 g and a standard deviation of 0.0112. Figure 4 shows how the trapped fluid appears in the packed bed surrounding some beads adjacent to the glass walls.
heptane. To avoid of this problem, we mixed bitumen with nheptane at a temperature higher than room temperature, where bitumen can be mixed with n-heptane (70−80 °C). To ignore the errors induced by evaporation of the solvent, we report the experiments in this section based on the weight fraction of nheptane in bitumen. Asphaltene deposition weight after a run time of 1 day was measured and is shown in Figure 5. The amount of asphaltene
Figure 5. Asphaltene deposition rate for Athabasca bitumen versus nheptane concentration. Figure 4. Trapped fluid as it appears in the packed bed column using glass beads.
deposition was converted to the specific deposition rate by dividing the mass of deposited asphaltene to time and surface area. We calculated the surface area by the number of beads, diameter of the beads, and inner diameter of the tube. This figure shows that the onset occurs between 55 and 58 wt % nheptane and the deposition shows an increasing trend reaching about 0.009 g cm−2 day−1 at 70 wt % n-heptane. To study the effect of the surfactant, DBSA was added and the specific deposition rate was measured. Starting with 1000 ppm of DBSA (Figure 6), deposition rates were not altered or shifted significantly and a similar trend was observed. A
We study the flow of diluted bitumen through a packed bed of SS beads. Destabilization of asphaltene in the diluted bitumen results in deposition on the SS packed bed. In this section, we report the n-heptane concentrations based on the weight fraction. Bitumen is a very viscous fluid at room temperature. Therefore, it cannot be agitated and mixed with nheptane perfectly. There is always the possibility of formation of a region in the mixture with a high local concentration of nD
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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asphaltene aggregates deposit in the space between the beads at low DBSA concentrations. Most of the beads in the sides can be seen clearly with no deposit on their surface. In contrast, at the concentrations higher than 25 000 ppm of DBSA, as seen in the right picture, the deposits are sticking as a film layer on all bead surfaces in addition to the deposits between the beads. To understand the effects of the surface, SS beads was replaced by glass beads and the same experiment was repeated. 3.2.2. Glass Beads. Depositional studies on glass beads have been reported in the literature. For example, an experiment was performed to study deposition of latex spheres on glass beads in the packed bed.16 Figure 9 shows that deposition on glass beads
Figure 6. Specific asphaltene deposition rate on the stainless-steel (SS) beads using Athabasca bitumen with different n-heptane concentrations and different DBSA surfactant concentrations. The dashed line shows the deposition trend in the absence of the surfactant.
surfactant concentration of 10 000 ppm results in a higher deposition rate at higher n-heptane mass fractions. The trend shown by the dashed line shows the asphaltene deposition in the absence of the surfactant. This trend reveals that deposition rates are higher in the presence of the surfactant. It was observed that the surface of SS beads has been altered from being shiny and reflective type to a dull, gray, and non-shiny surface when exposed to the DBSA concentration greater than 25 000 ppm, as shown in Figure 7. Figure 9. Specific asphaltene deposition rate in glass beads using Athabasca bitumen with different n-heptane concentrations and different DBSA surfactant concentrations.
for the bitumen−n-heptane mixture without DBSA is similar to that with SS beads. The specific deposition rate is 2 mg cm−2 day−1 at 60 wt % n-heptane and approaches 8 mg cm−2 day−1 at 70 wt % n-heptane. The addition of 10 000 ppm of DBSA caused a reduced deposition rate at 60 and 65 wt % compared to the results in the absence of the surfactant. However, at a higher n-heptane concentration (e.g., 70 wt %), the presence of the surfactant results in a higher deposition rate, which may be attributed to experimental error. The results show that further addition of DBSA (25 000 ppm) at all three weight fractions of n-heptane decreases the asphaltene deposition on the glass bead surface. Figure 10 shows two examples of asphaltene deposits on glass beads in the packed bed. The picture on the right (65 wt % n-heptane and no DBSA) shows asphaltene depositing on/
Figure 7. Stainless-steel (SS) bead surface appearance before exposure (right) and after exposure (left) to n-heptane/bitumen, with DBSA concentrations of 25 000 ppm and above.
Figure 8 shows how the deposition mechanism is altered at high concentrations of DBSA. As shown in the left picture, the
Figure 8. (left) Asphaltene deposition on stainless-steel (SS) with no DBSA, where the deposition occurs between beads, and (right) stainless-steel (SS) bead surfaces after running the experiments at DBSA concentrations higher than 25 000 ppm with asphaltene surrounding all bead surface areas. E
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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Figure 10. Asphaltene deposition on glass beads: (left) glass beads with no deposition after running the experiment with 65 wt % n-heptane in bitumen and a concentration of 25 000 ppm of DBSA and (right) glass beads with deposited asphaltene on the surface of glass beads (no DBSA).
around the glass beads. The left picture displays glass beads after 24 h of run time of experiments with 25 000 ppm of DBSA. As seen, there is significantly less asphaltene deposits on the system. It can be concluded that the surfactant has decreased the asphaltene deposition on the glass surface. Similarly, in the bulk system, the surfactant decreases the asphaltene precipitation (see Figure 3). However, the surfactant increased the asphaltene deposition on the SS surface. The surfactant molecule acts as a bridge between asphaltene molecules and the SS surface. Therefore, DBSA is not recommended for flow assurance in steel pipelines. During the measurement of deposition rates of destabilized asphaltene from bitumen, each sample was studied under the microscope to evaluate behavior and size of the asphaltene aggregates. This was conducted to relate the size and shape of asphaltene particles with the deposition rate of the asphaltene. The smallest size seen in the microscope used in this experiment was 0.5 μm (500 nm). The difference in aggregate size and shape was compared between a sample stirred for about ∼24 h and another sample that was circulated in the apparatus for ∼24 h. Figure 11 shows the aggregate size for a fixed n-heptane concentration (63 wt %) after 2 min of stirring time (a), followed by about 24 h of stirring (b), and 25 h of circulation in the apparatus (c). The results showed that the stirred sample exhibits a relatively bigger size, reaching an average of 80 μm, while with a circulated sample asphaltene aggregate shows a mean size of about 40 μm. 3.3. Ability of the DBSA Surfactant To Dissolve Deposited Asphaltene. The ability of DBSA to dissolve deposited asphaltene was examined. First, asphaltene was deposited at a n-heptane concentration of 65 wt % and circulation run time of 24 h. Then, a new sample of 65 wt % nheptane concentration was prepared with a predetermined DBSA concentration and circulated with a run time of 24 h. These experiments were performed using both SS and glass beads. The results are shown in Figure 12. The solid lines show the baseline of the amount of asphaltene deposition on SS and glass beads in the absence of DBSA. Any points below these lines mean successful removal of asphaltene, and any points above these lines indicate additional asphaltene deposition, instead of removal. For SS beads, it can be seen that no successful removal is achieved, even with 50 000 ppm, which was thought to be enough to dissolve all asphaltene. In addition, data for SS show that deposition remains around 1 g, followed by a decline, as the concentration of DBSA is increased. On the other hand, the glass bead curve shows a maximum deposition at 10 000 ppm, followed by a sharp decline. The results show that deposited asphaltene has dropped below the baseline deposition in the absence of the
Figure 11. Microscope images of the n-heptane/bitumen mixture (63 wt % n-heptane): (a) 2 min of stirring after mixture preparation, (b) after 23.5 h of stirring without circulation in a packed bed column, and (c) after 23.5 h of circulation in a packed bed column.
surfactant. At a surfactant concentration of 50 000 ppm, all asphaltene deposits on the glass surface have been removed effectively, which agrees with literature data that show DBSA dissolve all deposited asphaltene at 5 wt % (50 000 ppm).3 These experiments confirmed SS bead surface property alteration observed during deposition experiments. The surface alteration that occurred during deposition significantly changed F
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
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and the deposition rate reached below the original deposition baseline. At a DBSA concentration of 50 000 ppm, whole deposited asphaltene was removed from the glass surface. However, in the case of the SS surface, this was not possible and deposited asphaltene remained above the originally deposited level, even at 50 000 ppm of the DBSA concentration. The results of this study highlight the importance of the surface properties when a surfactant is used as an asphaltene dispersant. In the case of using aromatic solvents, the role of the surface is not very important.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Hassan Hassanzadeh: 0000-0002-3029-6530 Jalal Abedi: 0000-0003-4211-9176
Figure 12. Asphaltene deposited at 65 wt % n-heptane flooded by a sample of asphaltene with 65 wt % but with different DBSA concentrations.
Notes
The authors declare no competing financial interest.
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the removal process. Adsorption properties are suspected to have made sticking of asphaltene and DBSA aggregate to the wall more favorable. The results suggest that surface properties should be taken into account carefully when the surfactant is considered as an asphaltene dispersant in oil and gas industries. As seen in the previous section, the surfactant can act as a link between asphaltene molecules and the SS surface. Traditional solvents, such as xylene and aromatic hydrocarbon solvents, do not interact with the surface, while the surfactant molecules can interact actively with the surface. Therefore, the surface properties are not very important when traditional solvents are used. However, as shown here, the interaction of the surface and surfactant molecules is critical.
ACKNOWLEDGMENTS The authors thank four anonymous reviewers for useful and constructive comments. Abdulaziz Al Sultan thanks Saudi Aramco for financial support. The support of the Natural Sciences and Engineering Research Council of Canada (NSERC) Industrial Research Chair (IRC) in Solvent Enhanced Recovery Processes and the Department of Chemical and Petroleum Engineering and the Schulich School of Engineering at the University of Calgary is also acknowledged.
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REFERENCES
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4. SUMMARY AND CONCLUSION Asphaltene precipitation and deposition cause many problems, such as clogging wells, flowlines, and surface facilities, in oil production operations, which cost companies millions of dollars as a result of maintenance, replacement, or loss of production issues. Recently, surfactant dispersants have gained increasing interest. In this work, the effect of DBSA on the fractional yield of asphaltene in a n-heptane−toluene mixture was studied. The results suggest that the DBSA surfactant decreases the asphaltene precipitation in the bulk system in the absence of a surface, which is in agreement with the literature data. Moreover, the effects of DBSA as a surfactant on asphaltene deposition on metal and glass surfaces have been studied. In the presence of the stainless-steel (SS) surface, the surfactant increased the asphaltene deposition at low surfactant concentrations. It was found that, in this region, surfactants acted as a link between asphaltene molecules and the surface. The effect of the surfactant on the removal of deposited asphaltene was studied. The results suggest that, during the removal process, asphaltene deposition increased on both glass and SS surfaces at a low concentration of the DBSA surfactant. The maximum deposition rate for glass and SS surfaces was found to occur at 10 000 and 20 000 ppm of the DBSA concentration, respectively. The results showed a decline in the deposition rate at higher concentrations of DBSA. The decline in the deposition rate is shown to be much faster for the glass surface. At a DBSA concentration above 30 000 ppm, deposited asphaltene on the glass surface starts to detach from the surface G
DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
Article
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DOI: 10.1021/acs.energyfuels.8b00215 Energy Fuels XXXX, XXX, XXX−XXX
