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Effect of Surfactant on Asphaltene Deposition on Stainless Steel and Glass Surfaces Abdulaziz Al Sultan, Mohsen Zirrahi, Hassan Hassanzadeh, and Jalal Abedi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00215 • Publication Date (Web): 25 Mar 2018 Downloaded from http://pubs.acs.org on March 25, 2018
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Effect of Surfactant on Asphaltene Deposition on Stainless Steel and Glass Surfaces
2
Abdulaziz Al Sultan1, Mohsen Zirrahi2, Hassan Hassanzadeh2*, Jalal Abedi2
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1
Saudi Aramco, Dhahran, Saudi Arabia
4
2
Department of Chemical & Petroleum Engineering, Schulich School of Engineering, University
5
of Calgary, Calgary, AB, Canada T2N 1N4
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Abstract
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Surfactant dispersants have been introduced as a proper candidate to mitigate the problems
8
caused by asphaltene precipitation such as clogging wells, flowlines, and surface facilities in oil
9
industry. In this work, we study the effects of Dodecylbenzenesulfonic acid (DBSA) as a
10
surfactant on asphaltene deposition on the stainless steel and glass surfaces. Experiments were
11
conducted to measure the asphaltene precipitation in bulk system, asphaltene deposition on the
12
stainless steel and glass surfaces. Results revealed that the surfactant delays the asphaltene onset
13
in the bulk system. However, asphaltene deposition on the stainless steel surface was increased at
14
all measured concentrations of the surfactant while the deposition rate on glass surface decreased
15
by increasing the surfactant concentration. Affinity of the surfactant molecules to the stainless
16
steel surface was verified in asphaltene deposition and removal tests. The results revealed that
17
the DBSA surfactant is able to remove the deposited asphaltene on glass surfaces at high
18
concentrations. This study reveals the importance of surface properties when the surfactant is
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used as asphaltene dispersant.
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Keywords: Asphaltene dispersant; onset; surfactant; Dodecylbenzenesulfonic acid (DBSA)
*
Corresponding Author, E-mail:
[email protected] 1 ACS Paragon Plus Environment
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1. Introduction
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Asphaltene deposition is known to cause clogging of oil wells, flowlines, and surface facilities.
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Asphaltene deposition costs operators millions of dollars due to issues such as maintenance,
4
replacement or loss of production.1 Finding an effective way to control asphaltene dispersion in
5
petroleum fluid is still a demanding area of research. The past literature on asphaltene mitigation
6
was mainly focused on either prevention or delay of asphaltene precipitation/aggregation.2-5
7
Prevention and delay of asphaltene can be achieved through injection of aromatic solvents,
8
taking benefit from natural inhibitor in crude oil or finally by using dispersants/inhibitors. The
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latter is the most efficient way to delay or prevent asphaltene problems economically and
10
environmentally, which can lead to stabilizing asphaltene and preventing precipitation or
11
deposition.2 An increasing number of studies are being published related to surfactant
12
dispersants, but until now, these studies are mostly far from practical use and still under the
13
laboratory studies.3-5
14
As an iconic reference in asphaltene dispersion area, Chang and Fogler 5 studied the effect
15
chemical structure of several amphiphiles on stabilization of asphaltene flocs. Asphaltene
16
powder was analyzed for its properties to be used for the onset detection experiments. The
17
adsorption of some amphiphile head group was studied using Fourier Transform Infrared (FTIR)
18
spectrophotometer. Four different amphiphile head groups were compared with respect to the
19
stabilized asphaltene weight and asphaltene adsorption with amphiphiles. Sulfonic acid group
20
(DBSA) showed a desirable result as an effective asphaltene stabilizer. Then, the effect of tail
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length of amphiphile was studied; concluding that longer tail accounted to better asphaltene
22
stability at the expense of losing some affinity to asphaltene. Afterward, the effect of different
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amphiphile side groups was studied by adding a polar group (i.e. hydroxyl group) to amphiphile.
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The results showed increase of asphaltene stability. However, the addition of side group has
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some negative side effect on asphaltene dispersion in solution when it joins the amphiphile at the
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tail. Lastly, n-alkane solvent type was varied to investigate asphaltene stability. Chang and
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Fogler 5 concluded that having more volatile solvent lowered asphaltene stability for weak
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amphiphiles. However, no effect was observed when using strong amphiphiles like DBSA.
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Wang 6 studied ability of different ionic and non-ionic liquids and their structural differences on
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asphaltene dispersion. Impendance analysis method was used and confirmed the results of
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refractometry method. Then, high-resolution transmission electron microscope was utilized to
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study the structure of asphaltene dispersion and also to confirm the results of the previous
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methods. The author concluded that ionic surfactant 4-Dodecylbenzensulfonic Acid (DBSA) is
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the most effective dispersant among those studied followed by the non-ionic liquid 4-
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Octylphenol (OP).
14
Aslan and Firoozabadi 7 studied the effect of brine and deionised (DI) water on asphaltene
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deposition using pipe-flow setup. Asphaltene deposition was simulated using the pipe-flow setup
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where water, oil, and heptane from separate lines were mixed in one junction with a specified
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concentration. The mixture was then sent through a metal pipe while a pressure transducer was
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used to measure the pressure difference in the system. Pressure versus the injected volume was
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used for analysis. They concluded that addition of water to the system noticeably delayed the
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asphaltene deposition.
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Subramanian and Firoozabadi 8 went further to study the effect of two different ionic surfactants
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(ionic “DBSA” and non-ionic “BA”) on asphaltene precipitation and deposition introducing 3 ACS Paragon Plus Environment
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water and brine to the system. Sedimentation tests were carried out to study the effect of mixing
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of different water/brines with multiple surfactant concentrations on asphaltene precipitation on
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Falcon tubes. Although a previous study7 concluded that the presence of water or brine delays
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asphaltene deposition, study of Subramanian and Firoozabadi 9 showed that BA surfactant was
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not affected by water or brine addition because water would make the solution more polar by
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inducing negative charge on the surface of the asphaltene aggregate. On the other hand, DBSA
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showed poor dispersion in the presence of water or brine and associates with the asphaltene,
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which weakens the electrostatic interaction between DBSA and asphaltene, resulting in more
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unstable asphaltene and inefficient dispersion.
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10
Loureiro et al. 10 examined the influence of two asphaltene stabilizers or inhibitors (DDBSA and
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CAAS) using two different destabilizing conditions, one with n-heptane and the other one with
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CO2. Different concentrations of inhibitor were added to study the change in the onset point of
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precipitation. The results showed that the inhibitors were system-selective, meaning that each
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condition (CO2 or n-heptane) responded differently. They delayed asphaltene precipitation in
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systems containing n-heptane while no significant effect was observed for CO2 containing
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systems.
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Several investigations have been conducted to study the effect of surfactants on decrease and/or
18
delay of the asphaltene precipitation and deposition.3-10 These studies suggested injection of the
19
surfactants into streams susceptible to the asphaltene precipitation and deposition. However,
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there is a lack of information on the effect of surfactant on deposition of asphaltene particles on
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surfaces such as stainless steel and glass. In this work, we study the effect of dodecyl benzene
22
sulfonic acid (DBSA) as an ionic surfactant on asphaltene deposition on stainless steel and glass
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surfaces. Stainless steel can be a representative of pipeline surface while glass beads can be
2
representative of porous media. Moreover, capability of surfactant to dissolve the deposited
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asphaltene on a surface is evaluated. The rest of this paper is organized as follows: First, we
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present the experimental details consisting of material, apparatus and procedure. Then,
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experimental results are presented followed by conclusions.
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2. Experimental Details
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Chemicals and Materials
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The experiments were conducted using Athabasca bitumen to study the asphaltene deposition.
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Bitumen properties are listed in Table 1.
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Table 1. Bitumen source and properties.11, 12 SARA Fractions (wt.%) Saturates 12.26
Aromatics
Resins
Asphaltene
40.08
36.53
11.13
Density (g/cc)
API gravity
1.004
10.0
11
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Ionic surfactant 4-Dodecylbenzenesulfonic Acid (DBSA) was purchased from Sigma Aldrich
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with purity higher than 95%. The chemical structure of the DBSA is shown in Figure 1.
MW: 326.5 g/mol Density: 1.0 g/cm3 (at 25°C) Purity: ≥95% 14
Figure 1: 4-dodecylbenzene-1-sulfonic acid (DBSA) chemical structure and properties.
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N-heptane and toluene were purchased from BDH VWR ANALYTICAL, while Chloroform was
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provided by Anachemia. Two types of beads were used: 1) stainless steel beads with 3.95 mm
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diameter, 2) Borosilicate glass beads with 4 mm diameter from Chemglass Inc. The microscope
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slides were purchased from VWR VistaVision (3”×4”×1.2mm) with glass cover for microscope
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slides purchased from Canlab – Baxter (24 mm × 25 mm).
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Experimental Procedure
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In this work, we studied the effect of DBSA on asphaltene precipitation in a system of toluene-
8
asphaltene mixture and also deposition of asphaltene on stainless steel and glass surfaces. To
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study the effect of surfactant on asphaltene precipitation, we measured the amount of precipitated
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asphaltene in different concentrations of precipitant and surfactant.
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Asphaltene fractional yield tests: Asphaltene solubility test or fractional yield test was
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conducted to generate solubility curves, which results the percentage of the precipitated
13
asphaltene versus volume fraction of n-heptane in toluene-heptane mixture. These experiments
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were conducted in the presence and absence of surfactant. The procedure reported by Sadeghi 13
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was adopted and slightly modified to fit our purpose. Asphaltene was precipitated using n-
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heptane from Athabasca bitumen as described in Azinfar et al.14 . A 300 mg of solid-free
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asphaltene was added to a 25 ml vial. Toluene was added to the asphaltene then put in ultrasonic
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bath for 20 min till all asphaltene was dissolved. A predetermined amount of toluene was added
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to the vial to reach the asphaltene concentration of 20 kg/m3 in the solution. Then, n-heptane was
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added to the mixture to obtain the desired heptane volume percents in toluene (60, 70, 80, and 90
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vol.%). For the samples containing the surfactant (DBSA), first, a certain amount of surfactant
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was added to n-heptane and then sonicated for 5 min. Next, the surfactant-heptane mixture was 6 ACS Paragon Plus Environment
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added to the mixture of the dissolved asphaltene in toluene to achieve the desired
2
heptane/toluene volume percent. The concentration of the surfactant (ppm) in the mixture was
3
calculated using:
4
ppm =
msur ×106 mtoluene + mC 7 + msur
(1)
5
where msur, mC7, and mtoluene are mass of surfactant, heptane, and toluene, respectively.
6
The mixture was then put in ultrasonic bath for 45 min then left to settle for 1 hr. Each vial was
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then centrifuged at 4000 rpm for 5 minutes to separate the precipitated asphaltene. Supernatant
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was then decanted and the vial is placed in vacuum oven at 70 °C for 24 hr then each vial was
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weighted to determine the asphaltene yield. The same experiments were also conducted in the
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absence of surfactant and the asphaltene yields at different n-heptane concentrations were
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measured.
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Asphalting deposition experiments: The asphaltene deposition experiments were conducted
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using Athabasca bitumen. We prepared and tested the n-heptane/bitumen mixtures based on the
14
mass fraction basis to avoid errors due to volume change during the mixing of n-heptane and
15
bitumen. First, we prepared a solution of 40 wt.% n-heptane in bitumen. The sample was then
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sonicated for 90 min and left for 72 hr. This mixture was used to prepare the samples with higher
17
n-heptane concentration. This mixture was checked under microscope to detect possible
18
asphaltene aggregates. No asphaltene precipitation was detected for the mixture of 40 wt% of n-
19
heptane in bitumen. To prepare the samples with higher concentrations of n-heptane, small
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amount (20-30 g) of the prepared n-heptane-bitumen mixture (40 wt.%) was put into a 250 ml
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beaker. Afterward, while mixing, a predetermined weight of n-heptane was added to the mixture 7 ACS Paragon Plus Environment
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to achieve the desired n-heptane concentration. The sample was stirred for 2-10 min. Then, a
2
microscope image was taken before being placed into the deposition apparatus to study the
3
asphaltene aggregate.
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To prepare the mixture containing the surfactant, the concentration (ppm) of the surfactant in
5
solution was calculated by:
6
ppm =
msur × 106 mbit + mC 7 + msur
(2)
7
where msur, mC7, and mbit are mass of surfactant, n-heptane, and bitumen, respectively.
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To prepare a sample with certain amount (ppm) of surfactant, we made a pre-determined mixture
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of surfactant and n-heptane. Then, the mixture was added slowly to the solution of 40 wt.% of n-
10
heptane in bitumen while stirring to reach the desired n-heptane and surfactant concentrations in
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the solution. After, the solution was stirred for 2-10 min, several drops were studied under the
12
microscope to study the asphaltene aggregate and the rest of the mixture was put into the
13
apparatus to conduct the asphaltene deposition experiments. It is worth to mention that the time
14
for asphaltene destabilization and aggregation for the mixtures with higher than 63 wt.% of n-
15
heptane in bitumen was less than the preparation and settling time (~ 1 hr).
16
The apparatus for asphaltene deposition experiments was designed similar to the one used by
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Fávero et al.15. The setup shown in Figure 2 consists of a pump (EYELA – CERAMIC PUMP
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VSP-2200) that injects mixture sample to a glass column (15.3 cm length and 10 mm inner
19
diameter). The glass column was filled with stainless steel (SS) beads (3.95 mm of diameter) or
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glass beads (4mm of diameter). The total bed length in both SS and glass bead experiments was
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13.5 cm with a total of 152 beads for the SS bed, and 132 beads for the glass beads. The packed 8 ACS Paragon Plus Environment
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bed column effluent was then returned to the mixture sample to form a closed loop. The sample
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was kept stirred during the entire period of the experiments.
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When a prepared sample was placed into the apparatus, it was pumped at 0.6 ml/min for a 24-
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hour period. Then, the sample was drained slowly at a rate of 0.1 ml/min to prevent removal of
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any deposits from the packed bed. After draining the packed bed column, it was then rinsed with
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chloroform and the mixture was collected in a vial. The vial was put in a vacuum oven at 75 °C
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for 24 hr till all chloroform was evaporated. Following the Fávero et al.15 , the retained material
8
in the packed bed column consists of the deposited material and the trapped fluid. The trapped
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fluid was determined by performing the deposition experiments with run-time of 1 min. This
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time is assumed small enough for any depositions to occur.15 In these experiments, after
11
circulation of the heptane-bitumen mixture for 1 minute, the amount of the trapped fluid in the
12
packed bed was measured, which is the liquid trapped between the beads.
13 14
Figure 2: Asphaltene deposition apparatus used in experiments.
15
We also utilized the microscope (AmScope Microscope) to check the size of the aggregates
16
before and after putting the sample in the apparatus. Self-association of asphaltene along with
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aggregate shape and size are examined using the microscope. Each sample was tested twice.
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First, the sample was tested 5 min after preparation and the second test was conducted after 24 hr
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of the sample being stirred and circulated in the deposition apparatus. All microscope images
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scale was kept the same for comparison purposes. Table 2 shows the range of n-heptane and
5
surfactant in the conducted experiments in this work.
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Table 2. Range of n-heptane and DBSA concentration in the asphaltene yield and deposition
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tests. Surfactant concentration
n-heptane concentration
Asphaltene yield experiments
0 to 25,000 ppm
60 to 90 vol. %
Asphaltene deposition experiments
0 to 50,000 ppm
40 to 70 wt.%
8
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3. Results and Discussion
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Effect of DBSA Surfactant on Asphaltene Yield
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Yield and solubility curves have been widely studied in the literature. 12, 14 The fractional yield is
12
defined as ratio of the precipitated asphaltene to the initial mass of asphaltene in the mixture.
13
Effect of DBSA on asphaltene precipitation was studied in bulk system using asphaltene yield
14
test. To get insight into DBSA and asphaltene interaction in the absence of other factors like
15
surface adsorption and other impurities/components in bitumen, solid-free asphaltene from the
16
Athabasca bitumen was used to study the asphaltene solubility and to determine how the DBSA
17
alters the yield.
18
In this study, four n-heptane volumetric fractions (0.6, 0.7, 0.8, and 0.9) in toluene/asphaltene
19
mixtures were studied to track the changes after adding DBSA to the mixture. These volumetric 10 ACS Paragon Plus Environment
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fractions of n-heptane allow to focus on the region with asphaltene precipitation higher than the
2
onset point. The results of asphaltene yield in different n-heptane and DBSA concentrations are
3
shown in Figure 3. It can be found that higher n-heptane concentration results in higher
4
precipitated asphaltene. Also, increasing DBSA concentration decreases the asphaltene yield.
5
However, n-heptane volume fractions of 0.8 and 0.9 show a slight increase in the fractional yield
6
by addition of DBSA at low DBSA concentrations. The measured fractional yield greater than
7
100 at 90 vol.% n-heptane and 5,000 ppm of DBSA can be attributed to precipitation of DBSA
8
with asphaltene. This shows that the added surfactant sticks to asphaltene molecules. As the
9
surfactant concentration is increased asphaltene precipitation was not observed. For instance, at
10
15,000 ppm of DBSA asphaltene precipitation was not observed in the mixtures with 0.6, 0.7 and
11
0.8 n-heptane volumetric fractions. At 0.9 volumetric fraction of n-heptane and 15,000 ppm
12
concentration of surfactant results in a fractional yield of 0.56. These observations suggest that
13
surfactant delays the onset and also decreases the asphaltene yield. All curves in this figure were
14
measured at settling time of 1 hr.
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140
120
Fractional Yeild (%)
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60 vol% 70 vol% 80 vol% 90 vol%
100
80
60
40
20
0
0
1
5000
10000
15000
20000
25000
30000
Surfactant (DBSA) Concentration (ppm)
2
Figure 3: Fractional yield curve for solid-free asphaltene measured at different DBSA
3
concentration (0, 5000, 10000, 15000, and 25000 ppm) for various volumetric fractions of
4
heptane (0.6, 0.7, 0.8, and 0.9).
5 6
Effect of DBSA Surfactant on Asphaltene Deposition on Packed Bed
7
Stainless steel (SS) beads: In the first step, the amount of the trapped fluid between the stainless
8
steel (SS) and glass beads was measured. Trapped fluid measurements were conducted using
9
bitumen with different n-heptane and DBSA concentrations. These measurements were
10
conducted with SS beads and then glass beads packed bed column. The results of 11 repeated
11
experiments showed that the measured values of the trapped fluid do not vary with n-heptane or
12
surfactant concentrations. Instead, they are scattered closely to a mean value of 0.2061 g for
13
stainless steel beads packed bed with standard deviation of 0.0422. For glass beads packed,
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similar pattern is observed and a mean value of 0.1377 g with standard deviation of 0.0112.
2
Figure 4 shows how the trapped fluid appears in the packed bed surrounding some beads
3
adjacent to the glass walls.
4
5 6
Figure 4: Trapped fluid as it appears in the packed bed column using glass beads.
7
We study flow of diluted bitumen through a packed bed of stainless steel (SS) beads.
8
Destabilization of asphaltene in the diluted bitumen results in deposition on the stainless steel
9
packed bed. In this section, we report the n-heptane concentrations based on weight fraction.
10
Bitumen is a very viscous fluid at room temperature. Therefore, it cannot be agitated and mixed
11
with n-heptane perfectly. There is always possibility of formation of a region in the mixture with
12
high local concentration of n-heptane. To avoid of this problem, we mixed the bitumen with n-
13
heptane at a temperature higher than room temperature where the bitumen can be mixed with n-
14
heptane (70 to 80 ºC). To ignore the errors induced by evaporation of solvent, we report the
15
experiments in this section based on weight fraction of n-heptane in bitumen.
16
Asphaltene deposition weight after run-time of one day was measured and is shown in Figure 5.
17
Amount of asphaltene deposition was converted to specific deposition rate by dividing the mass
18
of the deposited asphaltene to time and surface area. We calculated the surface area by having 13 ACS Paragon Plus Environment
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the number of the beads, diameter of the beads, and the inner diameter of the tube. This figure
2
shows that the onset occurs between 55-58 wt.% of n-heptane and the deposition shows an
3
increasing trend reaching about 0.009 g/cm2/day at 70 wt.% of n-heptane. 0.010 Specific Deposition Rate (gr/cm2/day)
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0.008
0.006
0.004
0.002
0.000 0.4
4
0.5
0.6
0.7
0.8
Heptane Mass Fraction
5
Figure 5: Asphaltene deposition rate for Athabasca bitumen versus n-heptane concentration.
6
To study the effect of surfactant, DBSA was added and the specific deposition rate was
7
measured. Starting with 1000 ppm of DBSA (Figure 6), deposition rates were not altered or
8
shifted significantly and a similar trend was observed. A surfactant concentration of 10,000 ppm
9
results in higher deposition rate at higher n-heptane mass fractions. The trend shown by the
10
dashed line shows the asphaltene deposition in the absence of surfactant. This trend reveals that
11
deposition rates are higher in the presence of the surfactant. It was observed that surface of SS
12
beads has altered from being shinny and reflective type to dull, grey, and non-shiny surface when
13
exposed to DBSA concentration greater than 25,000 ppm as shown in Figure 7.
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0.012
2
Specific Deposition Rate (gr/cm /day)
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
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0 ppm 1,000 ppm 10,000 ppm 25,000 ppm
0.010
0.008
0.006
0.004
0.002
0.000 0.4
1
0.5
0.6
0.7
0.8
Heptane Mass Fraction
2
Figure 6: Specific asphaltene deposition rate on the stainless steel (SS) beads using Athabasca
3
bitumen with different n-heptane concentrations and different DBSA surfactant concentrations.
4
The dashed line shows deposition trend in the absence of surfactant.
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6 7
Figure 7: Stainless steel (SS) bead surface appearance before (right) and after (left) exposure to
8
n-heptane/bitumen with DBSA concentrations of 25,000 ppm and above. 15 ACS Paragon Plus Environment
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Page 16 of 25
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Figure 8 shows how the deposition mechanism is altered at high concentrations of DBSA. As
2
shown in the left picture, the asphaltene aggregates deposit in the space between the beads at low
3
DBSA concentrations. The most of the beads in the sides can be seen clearly with no deposit on
4
their surface. In contrast, at the concentrations higher than 25,000 ppm DBSA as seen in the right
5
picture, the deposits are sticking as a film layer on all beads surface in addition to the deposits
6
between the beads. To understand the effects of the surface, stainless steel beads was replaced by
7
glass beads and the same experiment was repeated.
8 9
Figure 8: Asphaltene deposition on stainless steel, (left) with no DBSA where the deposition
10
occurs between beads, and (right) stainless steel beads surface after running the experiments at
11
DBSA concentrations higher 25,000 ppm with asphaltene surrounding all beads surface area.
12
Glass beads: Depositional studies on glass beads have been reported in the literature. For
13
example, an experiment was done to study deposition of latex spheres on glass beads packed
14
bed. 17 Figure 9 shows that deposition on glass beads for bitumen/n-heptane mixture without
15
DBSA is similar to the one with stainless steel beads. The specific deposition rate is 2
16
mg/cm2/day at 60 wt.% of n-heptane and approaches 8 mg/cm2/day at 70 wt.% of n-heptane.
17
Addition of 10,000 ppm DBSA caused reduced deposition rate at 60 wt. % and 65 wt. %
18
compared to the results in the absence of surfactant. However, at higher n-heptane concentration
19
(e.g. 70 wt.%) the presence of the surfactant results in higher deposition rate, which may be
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Page 17 of 25
1
attributed to experimental error. The results show that further addition of DBSA (25,000 ppm) at
2
all three weigh fractions of n-heptane decreases the asphaltene deposition on the glass bead
3
surface.
4
0.012 Specific Deposition Rate (gr/cm2/day)
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
0.010 0 ppm 10,000 ppm 25,000 ppm
0.008
0.006
0.004
0.002
0.000 0.4
5
0.5
0.6
0.7
0.8
Heptane Mass Fraction
6
Figure 9: Specific asphaltene deposition rate in glass beads using Athabasca bitumen with
7
different n-heptane concentrations and different DBSA surfactant concentrations.
8
9
Figure 10 shows two examples of asphaltene deposits on glass beads packed bed. The picture on
10
the right (65 wt.% n-heptane and no DBSA) shows asphaltene depositing on around of the glass
11
beads. The left picture displays glass beads after 24 hr of run-time of experiments with 25,000
12
ppm of DBSA. As can be seen, there is significantly less asphaltene deposits on the system. It
13
can be concluded that surfactant has decreased the asphaltene deposition on glass surface.
17 ACS Paragon Plus Environment
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1
Similarly, in the bulk system surfactant decreases the asphaltene precipitation (see Figure 3).
2
However, the surfactant increased the asphaltene deposition on stainless steel surface. The
3
surfactant molecule acts as a bridge between asphaltene molecules and stainless steel surface.
4
Therefore, DBSA is not recommended for flow assurance in steel pipelines.
Page 18 of 25
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6 7
Figure 10: Asphaltene deposition on glass beads, (left) shows glass beads with no deposition
8
after using running the experiment with 65 wt.% of n-heptane in bitumen and concentration of
9
25,000 DBSA, (right) glass beads with deposited asphaltene on the surface of glass beads (no
10
DBSA).
11
During the measurement of deposition rates of the destabilized asphaltene from bitumen, each
12
sample was studied under the microscope to evaluate behaviour and size of the asphaltene
13
aggregates. This was conducted to relate the size and shape of asphaltene particles with the
14
deposition rate of the asphaltene. The smallest size can be seen in the microscope used in this
15
experiment was 0.5 µm (500 nm).
16
The difference in aggregate size and shape were compared between a sample stirred for about ~
17
24 hr and another sample that was circulated in the apparatus for ~24 hr. Figure 11 shows the
18
aggregate size for a fixed n-heptane concentration (63 wt.%) after 2 min stirring time (a) ,
19
followed by about 24 hr stirring (b) and 25 hr circulation in the apparatus (c). The results showed 18 ACS Paragon Plus Environment
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Energy & Fuels
1
that the stirred sample exhibits relatively bigger size reaching an average of 80 µm, while with
2
circulated sample asphaltene aggregate shows a mean size of about 40 µm.
3 4
Figure 11: Microscope images of n-heptane/bitumen mixture (63 wt. % of n-heptane) a) 2 min
5
of stirring after mixture preparation, b) after 23.5 hr of stirring without circulation in packed bed
6
column, c) after 23.5 hr of circulation in packed bed column.
7
Ability of DBSA surfactant to dissolve the deposited asphaltene
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Page 20 of 25
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The ability of DBSA to dissolve the deposited asphaltene was examined. First, asphaltene was
2
deposited at n-heptane concentration of 65 wt.% and circulation run-time of 24 hr. Then, a new
3
sample of 65 wt.% n-heptane concentration was prepared with a pre-determined DBSA
4
concentration and circulated with a run-time of 24 hr. These experiments were performed using
5
both stainless steel and glass beads. The results are shown in Figure 12. The solid lines show the
6
baseline of the amount of asphaltene deposition on stainless steel and glass beads in the absence
7
of DBSA. Any points below these lines mean successful removal of asphaltene and any points
8
above indicate additional asphaltene deposition instead of removal. For stainless steel beads, it
9
can be seen that no successful removal is achieved even with 50,000 ppm, which was thought to
10
be enough to dissolve all asphaltene. In addition, data for stainless steel show that deposition
11
remains around 1 g followed by a decline as the concentration of DBSA is increased. On the
12
other hand, glass-bead curve shows a maximum deposition at 10,000 ppm followed by a sharp
13
decline. The results show that the deposited asphaltene has dropped below the base line
14
deposition in the absence of surfactant. At surfactant concentration of 50,000 ppm all asphaltene
15
deposits on glass surface have been removed effectively, which agrees with literature data that
16
shows DBSA dissolve all deposited asphaltene at 5% (50,000 ppm).3
17
These experiments confirmed stainless steel beads surface property alteration observed during
18
deposition experiments. The surface alteration that occurred during deposition significantly
19
changed the removal process. Adsorption properties are suspected to have made sticking of
20
asphaltene and DBSA aggregate to wall more favourable. The results suggest that surface
21
properties should be taken into account carefully when the surfactant is considered as asphaltene
22
dispersant in oil and gas industries. As seen in the previous section, surfactant can act as link
23
between asphaltene molecules and stainless steel surface. Traditional solvents such as xylene and 20 ACS Paragon Plus Environment
Page 21 of 25
1
aromatic hydrocarbons solvents do not interact with surface while the surfactant molecules can
2
interact actively with the surface. Therefore, the surface properties are not very important when
3
the traditional solvents are used. However, as shown here the interaction of surface and
4
surfactant molecules is critical.
1.4
Weight of Asphaltene (gr/day)
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
Glass Bead
1.2 Stainless Steel 1.0 0.8 0.6
Glass bead with no surfactant
0.4579 0.4
0.4156 Stainless steel with no surfactant
0.2 0.0 0
10000
20000
30000
40000
50000
Concentration of DBSA (ppm)
5 6
Figure 12: Asphaltene deposited at 65 wt.% n-heptane flooded by a sample of asphaltene with
7
65 wt.% but with different DBSA concentration.
8
4. Summary and Conclusion
9
Asphaltene precipitation and deposition cause many problems such as clogging wells, flowlines,
10
and surface facilities in oil production operations, which cost companies millions of dollars due
11
to maintenance, replacement or loss of production issues. Recently, surfactant dispersants have
12
gained increasing interest. In this work, the effect of Dodecylbenzenesulfonic acid (DBSA) on
13
fractional yield of asphaltene in n-heptane/toluene mixture was studied. The results suggest that
21 ACS Paragon Plus Environment
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Page 22 of 25
1
DBSA surfactant decreases the asphaltene precipitation in the bulk system in the absence of a
2
surface, which is in agreement with the literature data. Moreover, the effects of DBSA as a
3
surfactant on asphaltene deposition on metal and glass surfaces have been studied.
4
In the presence of stainless steel surface, the surfactant increased the asphaltene deposition at
5
low surfactant concentrations. It was found that in this region, surfactants acted as a link between
6
asphaltene molecules and surface. The effect of surfactant on removal of deposited asphaltene
7
was studied. The results suggest that during the removal process asphaltene deposition increased
8
on both glass and stainless surfaces at low concentration of DBSA surfactant. The maximum
9
deposition rate for glass and stainless steel surfaces found to occur at 10,000 ppm and 20,000
10
ppm DBSA concentration, respectively. The results showed decline in deposition rate at higher
11
concentrations of DBSA. The decline in deposition rate is shown to be much faster for the glass
12
surface. At a DBSA concentration above 30000 ppm the deposited asphaltene on glass surface
13
starts to detach from the surface and the deposition rate reached below the originally deposition
14
base line. At a DBSA concentration of 50,000 ppm the whole deposited asphaltene was removed
15
from the glass surface. However, in case of stainless steel surface this was not possible and the
16
deposited asphaltene remained above the originally deposited level even at 50,000 ppm of DBSA
17
concentration. The results of this study highlights the importance of the surface properties when
18
a surfactant is used as asphaltene dispersant. In case of using aromatic solvents the role of
19
surface is not very important.
20
Acknowledgments
21
The authors would like to thank four anonymous referees for useful and constructive comments.
22
Abdulaziz Al Sultan would like to thank Saudi Aramco for financial support. The support of
22 ACS Paragon Plus Environment
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Energy & Fuels
1
NSERC IRC in Solvent Enhanced Recovery Processes and the Department of Chemical and
2
Petroleum Engineering and the Schulich School of Engineering at the University of Calgary is
3
also acknowledged.
4
References
5
1. Akbarzadeh, K.; Ahmed, H.; Dan, Z.; Stephan A.; Jefferson C.; Shah K.; Jamal A. J.;
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Alan G. M.; Ryan P. R.; Oliver C. M. Asphaltenes - problematic but rich in potential.
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2. Subramanian, D.; Firoozabadi, A. Effect of surfactants and water on inhibition of asphaltene precipitation. Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, UAE, 9-12 Nov. 2015. SPE-177669-MS. 3. Hashmi, S. M.; Firoozabadi, A. Effective removal of asphaltene deposition in metalcapillary tubes. SPE J. 2016, 21 (5), 1747-1754. 4. Fávero, V. B. C.; Maqbool, T.; Hoepfner, M.; Haji-Akbari, N.; Fogler, H. S. Revisiting
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11. Haddadnia, A.; Azinfar, B.; Zirrahi, M.: Hassanzadeh, H.; Abedi, J. Thermophysical
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12. Nourozieh, H.; Kariznovi, M.; Abedi, J. Experimental and modeling studies of phase
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behavior for propane/Athabasca bitumen mixtures. Fluid Phase Equilib. 2015, 397, 37-
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13. Sadeghi, H. Effect of refining on asphaltene property distributions. Thesis, University of Calgary. 2014 14. Azinfar, B.; Haddadnia, A.; Zirrahi, M.; Hassanzadeh, H.; Abedi, J. Effect of asphaltene
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asphaltenes. Fuel 2016, 178, 218-233.
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17. Elimeiech, M.; O’Melia, C. R. Kinetics of deposition of colloidal particles in porous media. Environ. Sci. Technol. 1990, 24 (10), 1528-1536.
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