Impact of Asphaltene Surface Energy on Stability of Asphaltene

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Impact of Asphaltene Surface Energy on Stability of Asphaltene-Toluene System: A Parametric Study mahshid nategh, Hojjat Mahdiyar, Mohammad Reza Malayeri, and Mojtaba Binazadeh Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b02566 • Publication Date (Web): 09 Oct 2018 Downloaded from http://pubs.acs.org on October 9, 2018

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Graphical Abstract 315x263mm (96 x 96 DPI)

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Impact of Asphaltene Surface Energy on Stability of AsphalteneToluene System: A Parametric Study Mahshid Nategh1, Hojjat Mahdiyar2*, Mohammad Reza Malayeri2,3, Mojtaba Binazadeh1 1 Department

of Chemical Engineering, School of Chemical, Petroleum, and Gas Engineering, Shiraz University, Mollasadra Street 71345, Shiraz, Fars, Iran 2 Department of Petroleum Engineering, School of Chemical, Petroleum, and Gas Engineering, Shiraz University, Mollasadra Street 71345, Shiraz, Fars, Iran 3 Institute of Process Engineering and Environmental Technology, Technical University of Dresden, George-Bähr Street 3b 01069, Dresden, Saxony, Germany

Abstract Asphaltene is a complex macromolecule whose abundance strongly affects physical and interfacial properties of crude oil. Asphaltene molecules may precipitate during crude oil production/transportation which may lead to plugging/clogging of wellbores, pipelines, and equipment. In this study, the solubility of asphaltene in toluene has been investigated by calculation of non-covalent interaction energies between asphaltenes in toluene medium. The results of this study revealed that the main interactions in the asphaltene-toluene system are Lifshitz-van der Waals and Lewis acid-base interactions; while the Electrostatic double layer is of lower comparative order of significance specifically at lower separation distances and lower zeta potentials. However, the repulsive Electrostatic double layer interactions may assist in stabilizing the asphaltene-toluene system based on the comparative values of Lifshitz-van der Waals, Lewis acid-base, and Electrostatic double layer interactions. This is the case especially at higher separation distances and/or higher temperatures where asphaltene particles have greater values of zeta potential. Furthermore, it is illustrated that when asphaltene has lower electron donor parameter i.e. lower basicity than toluene, then Lewis acid-base interactions between asphaltenes in toluene are repulsive. This repulsive Lewis acid-base interaction may compensate for the

Corresponding author: Email: [email protected] *

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attractive van der Waals interactions between asphaltene particles at low asphaltene basicity. Finally the electron donor/acceptor component of surface energy strongly determines the fate of asphaltene in crude oil colloidal system. Introduction Asphaltene, as the most complex and problematic fraction of crude oil, is typically present in the suspended state and its presence strongly affects physical and interfacial properties of crude oil.1–3 Asphaltene is generally defined as a solubility fraction of crude oil which is soluble in aromatics (e.g. toluene and benzene) and insoluble in low molecular weight normal paraffin (e.g. pentane and heptane).4–6 Asphaltene chemical structure is not well defined; however, it may be composed of poly-condensed aromatic sheets and aliphatic chains, heteroatoms (O, N, S), and metals (V, Ni, Fe), which have polar functional groups such as hydroxyl, carboxyl, and carbonyl. Asphaltenes are also known as part of N-S-O fractions of crude oil.7–9 Clearly asphaltenes are amphiphilic components and their physical and chemical properties depends on the physical and maturation conditions of reservoir.10 Asphaltenes tend to precipitate during the production/transportation of crude oil due to the changes in equilibrium conditions e.g. temperature, pressure, and composition.11 Asphaltene precipitation is promoted by aggregation of asphaltene molecules and flocculation of small aggregates to form the larger ones. Asphaltene aggregation may lead to formation of stable emulsions, wettability alteration of the rocks, and plugging/clogging of wellbores, pipelines and the equipment.12–14 Asphaltene aggregation and its underlying mechanisms has been extensively studied. Two approaches have been reported for the stability of asphaltenes in oil, based on the chemical and structural properties of asphaltene molecules: 1) the colloidal approach in which asphaltene particles form micelles and stay dispersed in crude oil. These micelles form when resins act as a protective layer between asphaltene particles and crude oil, and 2) the thermodynamic approach in which asphaltenes are considered to be stabilized in crude oil as separate dissolved particles.7,15–18 In each of the mentioned approaches, the behavior of asphaltenes in crude oil depends largely on the oil composition, physical condition, and the asphaltene-asphaltene and asphaltene-oil molecular interactions. Hence, in order to illustrate the asphaltenes stability, it is required to study the possible molecular interactions.


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Interactions between asphaltene molecules/aggregates in different solvents has been previously investigated to determine the stability and/or solubility of asphaltenes.13,14,19–22 Wang et al.13,14,19 reported that asphaltenes are stable in toluene due to the steric repulsion between asphaltene surfaces. In their studies though, some parts of asphaltene molecules are anchored to a hydrophilic surface and hence are excluded from any interactions. Thus, the conclusion of these studies may not be generic for all cases of asphaltene-asphaltene as well as asphaltene-toluene interactions in toluene.13 Siffert et al.22 correlated the magnitude of the asphaltene-solvent and asphaltene-asphaltene interaction parameters with the solvent’s ability to stabilize asphaltenes. Population balance technique has been used to determine asphaltenes stability.23,24 Painter et al.21 used Hildebrand solubility parameters or cohesion parameter to determine solvency behavior of asphaltene. They reported that toluene with solubility parameter of 18.2 MPa0.5 can only dissolve asphaltenes with solubility parameters less than a certain value of 21.7 MPa0.5 in concentrated solutions. They also reported that toluene can dissolve components with higher solubility parameters in dilute solutions, which is the condition at which many experimental studies are performed and asphaltene solubility is reported.21 Thus, the asphaltene-toluene system is called ‘stable’ due to the absence of a visible precipitate in spite of the fact that there may be a complex mixture of dissolved nano-aggregates and a dispersed phase in toluene.25–27 Other researchers have utilized force measurement techniques such as Atomic Force Microscopy (AFM) and Surface Force Apparatus (SFA) to quantify the interactions between asphaltene particles in different solvents.13,14,19 In spite of numerous studies on the stability of asphaltene-toluene system, the exact status of asphaltenes in toluene is a matter of much debate and there is no clear consensus on the state of asphaltenes in the asphaltene-toluene system and/or on the major reasons for stability of this system in terms of interaction energies. Previous studies have only considered specific interactions between asphaltenes and solvent.19 Additionally, all of the interaction energies have not been quantified and only a qualitative investigation has been carried out in the related studies. Moreover, the chemistry of asphaltenes has not been directly related to the stability of asphaltene-toluene system through its influence on different interaction energies. Thorough understanding of Asphaltenes behavior in crude oil lies on the interactions between asphaltene molecules/aggregates in an organic solvent. Hence, it is imperative to meticulously study these interactions and the impact of asphaltene structure on each of the interactions, which 3 ACS Paragon Plus Environment

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has remained a gap in the literature. Toluene, a solvent that defines asphaltene identity, is widely used for studying the molecular interactions of asphaltene particles. Therefore, the current study aims to clarify the state of asphaltenes in asphaltene-toluene system. This goal can be fulfilled by quantifying the different interaction energies between asphaltene surfaces in toluene as well as finding a relationship between asphaltene chemistry and its stability in toluene. In this study, the investigation of the stability of asphaltene-toluene system and the impact of asphaltene chemistry on the stability of this system is carried out using the approach of van Oss.28 From this perspective, the main interaction energies between particles in a medium are divided into four distinct classes of primary interactions including Lifshitz-van der Waals (LW), Lewis acid-base (AB), Electrostatic double layer (EL), as well as D (Br). Each of these interactions may play a role in the stability of the system based on their relative values. The total interaction energy of the system can illustrate the state of the system i.e. stability or instability. Theory Surface energy components The molecules on the surface of a material possess higher energy than the molecules present in the bulk, which is defined as surface energy. In another definition, the work required to increase the area of the surface is called the surface energy. Contact angle measurement is applied as an indirect method for determining the surface energy. Young29 proposed the following equation to relate the contact angle to the surface energy:

 sv   sl   lv cos 

(1)

Where subscripts sv, lv, and sl are the solid/vapor, liquid/vapor and solid/liquid surfaces energies, respectively, and θ is the contact angle between a liquid and a solid surface. Contact angle measurements using different sample liquids of known surface tension values can lead to the determination of a solid surface energy. However, the resulting surface energies depends, to a large extent, on the theoretical approach that has been followed. Some of these approaches are Zisman approach, Fowkes approach, Owens, Wendt or geometric mean approach, Wu or harmonic mean approach, equation of state approach, and Lewis acid-base approach.30 In this study, van Oss’s Lewis acid-base approach was employed, which includes three surface energy components: Lifshitz-van der Waals component (γLW), acidic or electron acceptor component (γ+), and basic or 4 ACS Paragon Plus Environment

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electron donor component (γ-) for solid asphaltene particles.31 The combination of two acidic and basic components leads to Lewis acid-base surface energy component (γAB). Based on this approach, the total surface energy is calculated using the following equations:  Total   LW   AB

(2)

 AB  2   

(3)

The determination of surface energy using contact angle measurements in combination with Lewis acid-base approach requires at least three liquids with known surface tensions. The following equation must be solved in order to obtain three surface energy components of the solid using contact angles and surface tension components of three probe liquids.32,33

 l Total (1  cos  )  2(  s LW  l LW   s  l    s  l  )

(4)

Interaction energies The stability of a system can be determined by its interaction energies. Lifshitz-van der Waals interactions ( E LW ), Electrostatic Double Layer interactions ( E EL ), Lewis acid-base interactions ( E AB ), and Diffusion interaction energy (Brownian motion) ( E Br ) are the primary non-covalent physical interactions which play a role in particulate or macromolecular interactions in the liquid media.34 Electrodynamic or Lifshitz-van der Waals interaction energy ( E LW ) van der Waals interaction energy is categorized in three groups: randomly orienting dipoledipole (or orientation) interactions, named after Keesom35–37; randomly orienting dipole-induced dipole (or induction) interactions, named after Debye38,39; and fluctuating dipole-induced dipole (or dispersion) interactions, named after London.40 Among these three interactions, van der WaalsLondon interactions have the highest contribution to the total van der Waals interactions. When the three van der Waals interactions are grouped together, they are called Lifshitz-van der Waals (LW) interaction energy.41,42 van der Waals interaction energy between two spheres of radius R in a liquid medium is formulated by the following equations: LW E ATA 

AATA R 12 H

(5) 5 ACS Paragon Plus Environment

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AATA  ( AAA  ATT ) 2

(6)

AAA  24 H 02 ALW & ATT  24 H 02 TLW

(7)

Where subscript A and T refer to asphaltene spherical particles and toluene. H is the separation distance between two asphaltene particles; R is radius of the particles; ATT, AAA, and AATA are the Hamaker constants of toluene, asphaltene, and composite Hamaker constant, respectively. 

LW A

and

 TLW are the LW component of surface energy for asphaltene and toluene, respectively. H0 is the

minimum equilibrium distance between the two bodies when they are in van der Waals contact. The value of H0 for asphaltene particles in toluene is assumed to be 0.165nm.41 Substituting equations (6) and (7) in equation (5) gives: LW E ATA 

2 H 02 R (  ALW   TLW ) 2 H

(8)

Electrostatic Double Layer interaction energy ( E EL ) When a charged particle is immersed in a solution containing dissolved ions, it tends to adsorb counter-ions (ions of opposite charge to that of the particle).43 The organic liquids with a low dielectric constant like toluene cannot form ionic species; however, ions and adsorbed films on the immersed particles’ surface due to proton transfer between the solvent and the ionizable groups of immersed particles are formed in this system.22,44 The electric double layer created in this situation is divided into two sub-layers: i) the immobile Stern or Helmholtz layer in which the ions are strongly bound to the charged surface, and ii) the diffuse layer consisting of free ions moving in the fluid.45 It should be noted that the net charge of each of these layers is opposite of the immersed particles’ surface charge; however, the charge density of the Stern layer is much higher than that of diffuse layer. The electrostatic interactions between the immersed surfaces can be repulsive or attractive depending on the electrical charge of the interactive surfaces.41 This type of interaction for two asphaltene spheres in toluene is expressed as: 34,46,47 EL E ATA  0.5 R 02 ln(1  exp(  H ))

(9)


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 0   0,1 0,2

(10)

D 0 r

(11)

 1 



In the above equations, ε and εr are the absolute and relative electrical permittivity of the medium, respectively. D is the diffusion coefficient in the solvent. κ-1 is characteristic length of the double layer i.e. Debye length.  0,1 and  0,2 are the electric surface potential of two interacting asphaltene surfaces, which are identical. Since the surface potential cannot be determined experimentally, it is usually approximated by the -potential.48 van der Waals attraction energy always exceeds the double-layer interaction energy at very short distances due to its power-law nature i.e. EATA  H ; LW

1

while electrostatic double-layer interaction energy remains finite as H → 0. Lewis acid-base interaction energy ( E AB ) Based on Lewis definition, a Lewis acid is any substance that can accept a pair of non-bonding electrons. On the contrary, a Lewis base is any substance that can donate a pair of non-bonding electrons. A bipolar substance has therefore both electron donor and electron acceptor capacities; while a monopolar substance has only one of these capacities. When a bipolar or monopolar solid is immersed in a bipolar or monopolar liquid of the opposite sign, the electron donor-electron acceptor (acid-base) interactions will occur.31 This type of interaction energy has a polar character and can be either attractive or repulsive depending on the surface energy components of the interacting bodies and medium.34 Toluene is considered a monopolar liquid, having only the electron-donor properties (Lewis base) due to the presence of π electrons in their molecules. As pure monopolar substances cannot contribute to their own cohesion energy due to lack of complementary monopole of opposite sign to react with,32 toluene can only react strongly with a bipolar substance or with a monopole of the opposite sign. As a result, for the case of asphaltenetoluene system in the current study, the original acid-base interactions for sphere-sphere interactions in a liquid medium can be simplified to:

AB AB exp( E ATA   RE ATA , H0

H0  H



)

(12)


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AB E ATA  4  [  A T   A A ] , H0

(13)

From the above equation, one can perceive that the Lewis acid-base interaction energy of the asphaltene particles and toluene are influenced by electron donor (γ-) and electron acceptor (γ+) surface energy parameters. Equation (13) implies that the acid-base interactions in the asphaltenetoluene system comprise of 1) interaction between basic and acidic components of asphaltene particles and 2) interaction between basic component of toluene and acidic component of asphaltene. Diffusion interaction energy (Brownian motion) ( E Br ) Each molecule or particle in a liquid medium has a repulsive Brownian (Br) free energy of 1 k BT per degree of freedom where 2

k is the Boltzmann constant ( 1.3806 10 B

23

J .K 1 ) and T is the

absolute temperature. This type of interaction is always repulsive. A system of two spherical asphaltene particles with a fixed separation distance has two degrees of freedom. Thus, the diffusion interaction energy for such system is

k BT

.34

E Br   k BT

(14)

Total interaction energy ( E Total ) Assuming that all of the above-mentioned interactions are independent, the equation for the total interaction energy in asphaltene-toluene system is: Total LW EL AB E ATA  E ATA  E ATA  E ATA  E Br

(15)

The total interaction energy may be positive (repulsive) or negative (attractive) depending on the relative magnitude of the various contributions. van Oss’ approach was first used to calculate the interaction energies in the aqueous media. However, van Oss also investigated the application of his theory in organic solvent systems. For instance, he studied the phenomenon of polymer phase separation in apolar or partly polar organic solvents using combined LW and AB interactions.49 The key note while applying this approach in the organic media is that the system-specific


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parameters such as decay length, Debye length, etc., which must be calculated for each system. Table 1 tabulates the value/range of the parameters used for calculation of interaction energies. Table 1. The value/range of parameters used in calculation of interaction energies Parameter

Value/Range

Ref.

T

298.15K

-

R

12.15nm

-

H0

0.165nm

42

H

0.165-10nm

-

10.4-38.2mJ/m2

42

 A

0-3.5mJ/m2

42

 A

0-2.3mJ/m2

42

 TLW

28.5 mJ/m2*

50

 T

2.3mJ/m2*

50

λ

1.88nm**

51

ε

2.102 × 10-11C.V-1.m-1

52

0

10-60mV***

-

D

2.88 × 10-11m2/s****

53

σ

400pS/m

54

κ-1

1.23μm*****

-



LW A



*

Other values are also reported by other researchers55 (  T =28.3mJ/m2 and LW

 T =2.7mJ/m2), that results in a more

positive AB interaction. ** Obtained by extrapolation from the quadratic fitting of the data reported by Brown et al. 1992 (R-square=0.9831). *** A wider range than zeta potential of asphaltene in toluene/normal heptane solution at T=298.15K 24 was used in this study. The experimental data of zeta potential of asphaltene in toluene will be published in our future work. **** Recalculated for particles with R=12.15nm. ***** Calculated using Eq.11 and the input parameters in Table 1.

Results and discussion In this part, the effect of surface energy components, γLW, γ+, and γ-, on non-covalent interaction energies in asphaltene-toluene system is investigated and their influence on the interaction energies and asphaltene stability are discussed. The interaction energies were calculated using an in-house model in MATLAB based on the assumption of dilute asphaltene solutions in toluene. All of the interactions are calculated at 298.15K. The asphaltene particles are considered spheres with the radius of 12.15nm, which has been measured using Dynamic Light 9 ACS Paragon Plus Environment

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Scattering (DLS) apparatus. This value is so close to the value reported by Espinat et al. (23.4nm for diameter of asphaltene particles at room temperature).56 Also, the measured value is in accordance with values reported by other researchers such as Spieker et al. in the literature.57 Israelachvili noted that H0=0.165nm is an average value for the minimum equilibrium distance,41 which yields good accordance with experimental values for surface tension. Also, van Oss has listed the value of H0 for a wide range of materials and reported a mean value of H0=0.157nm for all the materials tested from liquid He to liquid Hg.28 The mean value of H0=0.165nm has been used previously for asphaltene as well as some organic liquids. It is worth mentioning that the error associated with using H0=0.165nm is in the range of 10–20%.42 According to Eq. (4), the asphaltene surface energy components (  ,  ,   A

 A

LW A

) can be obtained from contact angle

measurements with three probe liquids of known surface tension components (  ,  ,   l

 l

LW l

). In

other words, the contact angle of a drop of each of three liquids on the asphaltene surface is measured and using the known surface energy components of liquids, the asphaltene surface energy components are calculated. In this study, we adapted the surface energy components from Fotland and Askvik.42 Based on reported values in the literature, a meaningful range of different properties of asphaltenes were employed for calculation of interaction energies.22,44 As the calculation results revealed that diffusion interaction energy has the smallest order amongst all of the interactions, E Br  4.11 1021 J at 298.15 K, all of the interactions are divided by diffusion interaction energy in order to simplify the comparison of the interactions. Figure 1 illustrates the impact of 

LW A

and separation distance on E

LW ATA

/ k BT

. It can be deduced

from this figure and equations (5)-(8) that Lifshitz-van der Waals interaction energy is always attractive (negative) for two identical particles in a liquid medium and monotonically decreases by increasing the separation distances. More importantly, it can be inferred from Figure 1 that as the value of 

LW A

increases and gets closer to the 

LW T

=28.5mJ/m2, then the absolute value of LW

interaction energy decreases i.e. this interaction tends to be less attractive. Finally, at the point when these values are equal,

LW E ATA / k BT

becomes zero. In other words, when the dispersive, or

non-polar, part of asphaltene particles becomes more similar to that of toluene, the tendency of these parts to have van der Waals interactions is reduced and the interaction becomes less attractive. It can be concluded that the attractive van der Waals interaction energy between asphaltene particles in toluene is variable for different asphaltenes from various crude oil sources 10 ACS Paragon Plus Environment

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with varying dispersive parts. This is consistent with the results of Painter et al.21 who reported that pyridine with a solubility parameter of 21.8 MPa0.5 is a good solvent for asphaltenes, which is justified with the fact that the solubility of two materials is only possible when their intermolecular attractive forces are similar. In other words, when only the negative LW interaction energy is considered in the investigation of stability, as it approaches zero, the system tends to have less aggregation. According to Spieker57 and Wang58, π-π interaction between aromatic sheets is one of the most plausible mechanisms of asphaltene aggregation. π-π interaction between the polycyclic aromatic hydrocarbon moieties, θ-θ interaction between the long side chains, θ-π interaction between aliphatic side chains and aromatic rings, and are categorized as dispersion forces.57 In this study, the stability of asphaltene-toluene system has been investigated using the theoretical modelling LW based on van Oss’ approach. In this approach, E ATA represents all the above-mentioned dispersion

interactions.


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-2

0

-4

LW

EATA/k B T

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-5 -6 -10

-8 -10

-15 40 10

30 LW A

2

(mJ/m )

-12

5

20

H (nm)

10 0

Figure 1. Lifshitz-van der Waals interaction energy between Asphaltenes in toluene (  TLW  28.5 mJ/m2 at T=298.15K) as a function of separation distance and Asphaltene LW component of surface energy (  ALW )

Some researchers have questioned the presence of electrostatic stabilization in non-aqueous solutions since the low dielectric constant of medium leads to much weaker repulsion between charged particles.59 However, some studies have reported asphaltene coagulation in organic solvents under influence of an electrical field, which supports the presence of surface charge on asphaltene particles.23,44,60 On the other hand, other researchers have reported that the zeta potential of a surface is not directly related to its acid-base component of surface energy.33 In this study, a range of zeta potentials from│10-60│mV, based on our unpublished experimental data, were utilized for calculation of electrostatic double layer interaction energy. The absolute values have been reported because the measured values of zeta potential were negative. The Dilute asphaltene in toluene solutions were prepared and Malvern zeta potential apparatus were used to measure the zeta potential of asphaltene particles in toluene. Results revealed that the zeta potentials recorded for asphaltene in toluene are negative. The measured zeta potential is different for asphaltenes with 12 ACS Paragon Plus Environment

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different sources, which is due to their chemistry and structure. The net charge recorded for soluble asphaltenes might be due to the size distribution of asphaltenes in toluene, as also reported by Pinter et al. and various studies in the literature.21 According to Painter et al., asphaltene solutions in toluene is a complex mixture of a dispersed phase and dissolved nanoaggregates. The considered range can cover the zeta potentials for different asphaltene types. Additionally, the data on zeta potentials of asphaltene in toluene/normal heptane system have been reported previously by Torkaman et al.23 Also, the Debye length, was calculated using Equation (11). The variation of electrostatic interaction energy with zeta potential, and separation distance for the calculated Debye length from Equation (11) is depicted in Figure 2. This figure demonstrates that the electrostatic interaction energy increases and becomes more repulsive with increasing zeta potential. A comparison between Figure 1 and Figure 2 reveals that the value of electrostatic interaction energy is of lower order compared with LW interaction energy in spite of the high value of Debye length. Wang et al.13 also reported that the electrostatic interaction energy is negligible in toluene at room temperature. However, according to the studies on asphaltene stability in organic media, the zeta potential as well as the electrostatic double layer repulsion of asphaltene particles in organic solutions e.g. toluene/normal heptane mixture increase with temperature.23 This may assist in stabilizing the asphaltenes in organic solution at higher temperatures regarding the relative value of electrostatic interaction energy compared to other interaction energies present in the system. On the other hand, at higher separation distances between asphaltenes in toluene, the attractive LW interactions become less negative (see Figure 1) and its absolute value might be comparable to the repulsive EL interactions. Hence, the repulsive EL can help prevention of asphaltene aggregation in toluene at higher separation distances.


Page 14 of 32

Page 15 of 32

0.2

0.25 0.2

EL

EATA/k B T

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

Langmuir

0.15

0.15 0.1

0.1

0.05 0 60 10

40  A (mV)

0.05

5

20

H (nm)

0 0

Figure 2. Electrostatic interaction energy between asphaltenes in toluene (at T=298.15K) as a function of zeta potential and separation distance

Figure 3 illustrates the DLVO interaction energies i.e. sum of Lifshitz-van der Waals and Electrostatic double layer energies as a function of asphaltene zeta potential and separation distance for different values of asphaltene LW component of surface energy. This figure also reveals that if only DLVO interactions were present in the asphaltene-toluene system, the value to LWEL interaction energy would be negative even for high zeta potential of asphaltene particles in toluene. This can occur in the case of asphaltene types having LW component of surface energy not near the value of LW component of surface energy of toluene (Equations (5)-(7)). In other words, as much as the value of



LW A

 

LW T

becomes higher, the LW interaction energy becomes

larger. Thus, in some asphaltene cases, the DLVO interaction energies might be insufficient for determination of the stability of asphaltene-toluene system and another interaction energy must compensate for the defect of DLVO theory in this case. However, EL interaction energy can aid other present repulsive interaction energies in order to stabilize the system.


Langmuir

0 -2

5

-4

0 DLVO

EATA /k B T

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 16 of 32

-6

-5 LW 2  A =29.86mJ/m

-10

-8

LW 2  A =38.2mJ/m LW 2  A =18.74mJ/m

-15 60

-10

LW 2  A =10.4mJ/m

40

10

-12

5

20  A (mV)

H (nm)

0 0

Figure 3. DLVO interaction energy between asphaltenes in toluene (  TLW  28.5 mJ/m2 at T=298.15K) as a function of asphaltene zeta potential and separation distance for different values of asphaltene LW component of surface energy

Figure 4a represents the acid-base interaction energies between asphaltene particles in toluene as a function  of  and at different separation distances. It is worth mentioning that in  A

 A

spite of the lower range of electron donor and electron acceptor components of surface energy of asphaltene compared with its non-polar Lifshitz-van der Waals component, they have a high degree of contribution to the interactions between asphaltenes in toluene (Equations (12)-(13) and Figure 4a). Figure 4a demonstrates that acid-base interaction energy approaches to zero as H increases. This observation is consistent with the fact that acid-base interaction energy is a shortrange energy operating at a distance less than 0.3nm.43 In order to better illustrate the data in Figure 4a, plots of acid-base interaction energy vs.  and  at the minimum equilibrium distance are  A

 A

shown in Figure 4b & Figure 4c, respectively. Figure 4b reveals that the AB interaction energy decreases monotonically by increasing 

 A

for all values of  . However, for higher values of  , the slope of curve has a higher magnitude.  A

 A


Page 17 of 32 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

Langmuir

It can be deduced from Equations (12) and (13) that the AB interaction energy is repulsive between asphaltene and toluene at  <  . At  =  , the AB interaction energy becomes zero. For  >  A

 T

 A

 T

 A

 T , the AB interaction energy is attractive. This means that when asphaltene has lower basicity

compared with toluene, the basic part of toluene interacts more repulsively with acidic part of asphaltene. Under such circumstances, the weak basic part of asphaltene has a low attractive interaction with acidic part of other asphaltene particles. The overall result of these interactions is the higher degree of partitioning of asphaltenes in toluene. In other words, the higher basicity of toluene inhibits asphaltene particles to attract each other by acid-base interactions. On the other hand, when asphaltene becomes a stronger base relative to toluene, it can develop attractive interactions with acidic parts of other asphaltene particles which may result in aggregation of asphaltenes and may lead the system to become unstable. This result is consistent with the findings of Siffert et al.22, who studied the stability of distillation residues in organic media. They related the surface potential of the solid particles to the electron transfer between solid particles and liquid and reported that the higher donor or acceptor numbers of liquid leads the solid-liquid system to be more stable. The donor (DN)/acceptor number (AN), which can be measured by NMR, defines the capacity of donating/accepting an electron pair from a standard accepting/donating molecule. They defined two interaction parameters: 1) IISL between the solid and the dispersion liquid (Eq. (16)) and 2) IISS between two solid particles (Eq. (17)). They reported that the dispersion is stable when IISL > IISS and is unstable when IISS >IISL. ΔII= IISL-IISS also specifies the degree of stability. II SL  ( AN 0 )( DN )  ( DN 0 )( AN )

(16)

II SS  2[( DN 0 )( AN 0 )]

(17)

Where AN and DN are the electron acceptor and donor numbers of asphaltene, respectively. AN 0

0

and DN are the electron acceptor and donor numbers of the liquid, respectively. Figure 4c shows the variation of acid-base interaction energy with  for different values of  A

 A . Two different trends can be observed in this figure:

1) For  <  i.e. weaker basicity of asphaltene compared with that of toluene, the increase  A

 T

in  (acidity) of asphaltene has a positive effect on the stability of the system. The reason  A

is that higher acidity of asphaltenes in these conditions results in higher repulsive 16 ACS Paragon Plus Environment

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Page 18 of 32

interactions between acidic part of asphaltene and basic part of toluene. The acid-base interaction present in the asphaltene-toluene system (Eq. 13) is sum of acid-base interactions between asphaltene-asphaltene and asphaltene-toluene. As toluene is monopolar, having just basic functional group, the basic parts of asphaltene and toluene compete to interact with the only acidic part present in the system i.e. acidic part of asphaltene. When asphaltene is a weaker base than toluene (  <  ), toluene has much  A

 T

more electron donor power than asphaltene to interact with electron acceptor part of asphaltene, which makes the net acid-base interaction energy repulsive. On the other hand, the higher electron acceptor power of asphaltene in this case can result in its higher tendency to accept electron pairs from electron donor part of toluene, which in turn leads to the stronger bonding between asphaltene and toluene. The stronger bonding between asphaltene and toluene results in more repulsive interaction energy. However, increasing the acidic power of asphaltene can simultaneously increase its contribution in acid-base interactions with other asphaltene particles. But as explained previously, toluene with higher electron donating power than asphaltene wins the competition to stabilize asphaltene with more powerful bonding. In other words, the higher electron accepting capacity of asphaltene helps stronger acid-base interactions with the stronger base present in the system i.e. toluene. 2) For  >  i.e. higher basicity of asphaltene compared with that of toluene, the increase in  A

 T

 A (acidity) of asphaltene has a negative effect on the stability of the system. The reason

is that higher acidity of asphaltene in these conditions leads to higher attractive interactions between acidic and basic parts of asphaltene based on the above explanations. The data for asphaltene components of surface energy used in this study has been adapted from Fotland et al. in which the maximum calculated value for asphaltene electron donor from contact angle measurements has been reported to be 2.3 mJ/m2 (same as  at the used  T

temperature). From the adapted data and the experimental data obtained by our research group for asphaltenes from various crude oil sources, it was concluded that ‘Lower basicity of asphaltene compared with that of toluene is widely observed for asphaltene samples from various crude oil sources.’ According to Eq. 13, the AB interaction energy becomes


Page 19 of 32

negative for  >  . In this case, if any is observed, EL interaction can help stabilizing  A

 T

asphaltenes in toluene.

180

(a)

200

160 140

150

AB

EATA/k B T

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

Langmuir

120 100

Increasing H

100 80

50

60

0 4 3

3 2

+

2

A (mJ/m )

2 1

1 0 0

-

2

A (mJ/m )


40 20 0

Langmuir

200 180

+

(b)

A=0mJ/m + +

2

+

2

A=2.1mJ/m

140

AB

2

A=1.05mJ/m

160

EATA/k B T

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 20 of 32

A=3.5mJ/m

2

120 100 80 60 40 20 0 0

-

0.5

1

-

2

1.5

A (mJ/m )


2

-

  A= T 

2.5

Page 21 of 32

200 180

-

(c)

A=0mJ/m -

2

-

2

A=1.15mJ/m

140

AB

2

A=0.23mJ/m

160

EATA/k B T

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

Langmuir

-

A=2.3mJ/m

2

120 100 80 60 40 20 0 0

0.5

1

1.5 + A

2 (mJ/m )

2.5

2

3

3.5

Figure 4. Acid-base interaction energy between asphaltenes in toluene (  T  2.3 mJ/m2 and  T  0 mJ/m2 at T=298.15K) as a function of: (a)  A and  A at different separation distances (H=0.165nm, H=1.1485nm, H=2.132nm, H=10nm); (b)  A for different  A at H=H0; (c)  A for different  A at H=H0

According to Figures 3 and 4a, the values of Br as well as EL interaction energies are small in comparison with both LW and AB interaction energies. Consequently, the total interaction energy can be approximated with the sum of LW and AB interaction energies. Lifshitz van der Waals and acid-base interaction energies are insignificant at high separation distance between the interactive bodies (Figures 1 and 4a). Thus, it is reasonable to study the resulting LW and AB interaction energies at H = H0. Figures 5a, 5b, and 5c illustrated the LWAB interaction energies of asphaltene particles in toluene as a function of 

LW A

,  , and  at H0.  A

 A


Langmuir

180

(a)

160

200 150

LWAB

EATA /k B T

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 22 of 32

140

+

Increasing A

120

100

100 50

80

0

60

-50 40

40 3

30 LW A

2

(mJ/m )

2

20

1 10 0

A

0 2

(mJ/m )


20

Page 23 of 32

180

(b)

LWAB

EATA /k B T

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

Langmuir

200

160

150

140 120

100

-

Increasing A

100

50

80

0

60

-50 40

40 30

LW A

2

(mJ/m )

20 10 0

1

2 +

3 2

A (mJ/m )


4

20 0

Langmuir

(c)

180 160

200 LW

A =38.2mJ/m

150

LWAB

EATA /k B T

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 24 of 32

140

2

120

100 50

100 LW

A =10.4mJ/m

2

80

0

60

-50 4

LW

A =24.3mJ/m

40

2

3

3 2

+ A

2

(mJ/m )

2 1

1

-

20 0

2

A (mJ/m )

0 0

Figure 5. Sum of LW and AB interaction energies between asphaltenes in toluene at H=H0 as a function of: (a)  ALW and  A , for  A = 0, 1.05, 2.1, and 3.5 mJ/m2; (b)  ALW and  A , for  A = 0, 0.23, 1.15, and 2.3 mJ/m2; and (c)  A and  A

As LW and AB interaction energies both decay with distance, Figures 6 presents the sum of these interactions at H=10nm in order to quantify the total interactions at higher distance. The results depicted in this figure reveal that sum of LW and AB interaction energies are smaller at higher separation distances between asphaltene particles. In these circumstances, the repulsive EL interaction energy between asphaltene particles in toluene can aid the stability of the system while sum of LW and AB interaction energies is negative (compare the orders of magnitude in Figure 2 and Figure 6). In this case, EL interaction energy can prevent further agglomeration of asphaltene particles. However, at lower separation distances (compare Figure 2 and Figure 5), EL interaction energy has a lower order of magnitude compared with two other interaction energies.


Page 25 of 32

1

(a) 1.5

LWAB

EATA /k B T

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

Langmuir

0.8

1

0.6

+

Increasing A

0.5

0.4

0 0.2 -0.5 40 3

30 LW A

2

(mJ/m )

0

2

20

1 10 0

-

2

A (mJ/m )


-0.2

Langmuir

1

LWAB

EATA /k B T

(b) 1.5

0.8

1

0.6

0.5

0.4

-

Increasing A

0

0.2

-0.5 40

0 4

30 LW A

2

(mJ/m )

2

20

-0.2

+

2

A (mJ/m )

10 0

1

(c) 0.8

1.5

LWAB

EATA /k B T

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 26 of 32

1

LW

A =38.2mJ/m

0.6

2

0.5

0.4

LW 2 A =10.4mJ/m

0

0.2 -0.5 4

LW

A =24.3mJ/m

2

3

3 2

+

2

A (mJ/m )

0

2 1

1 0 0

-

2

A (mJ/m )


-0.2

Page 27 of 32 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

Langmuir

Figure 6. Sum of LW and AB interaction energies between asphaltenes in toluene at H=10nm as a function of: (a)  ALW and  A , for  A = 0, 1.05, 2.1, and 3.5 mJ/m2; (b)  ALW and  A , for  A = 0, 0.23, 1.15, and 2.3 mJ/m2; and (c)  A and  A , for  ALW = 10.4, 24.3, and 38.2 mJ/m2

As can be deduced from Figure 5c and 6c, there is a plane on which the total interaction energy of the system becomes zero. The coordinates of this plane are 1) 

LW A

  TLW

and 2) 

 A

  T or  A  0 .

Reported data from surface energy characterization of different asphaltenes from various crude oil sources42 show that the electron donor parameter of surface energy is lower than that of toluene, the AB interaction energy is repulsive for asphaltene-toluene system. The experimental data of Asphaltene surface energy components from various crude oil sources will be reported in our future work. As a result, the stability of asphaltene-toluene system is mainly due to the stabilizing repulsive AB interactions between asphaltene particles in toluene. The Steric repulsion, which is placed in the category of the AB interactions60, might be the reason for the stability of the asphaltene-toluene system. This conclusion is consistant with previous studies13,14,19,20,61 who reported that the steric repulsion between asphaltene particles in toluene is the main reason for the stability of the system. It is worth mentioning that according to van Oss, who first included the acid-base interaction in the total interaction energy, several interactions including steric interaction are subsets of acid-base interaction. Additionally, according to van Oss, ‘Steric stabilization’, more appropriately ‘polymer-induced stabilization’, is due to the strong Acid-base (non-electrostatic) repulsion forces between polar components of polymer molecules present in the liquid. This strong AB interactions between polar entities overcome LW and EL interaction energies and elucidate the polymer contribution to the stability.60 The polymer-induced stabilization due to polar repulsion between polymer molecules has a subcomponent with a real “steric” influence. This component is the additional repulsive contribution due to the chain elasticity of the polymer strands at very short range. In our ongoing project, we are investigating the impact of other influenctial parameters on asphaltene aggregation such as tempearture, toluene/normal heptane ratio in a synthetic oil, asphaltene concentration, etc. Temperature affects the parameters including surface energy components of toluene as well as asphaltene, nano-aggregate radius, zeta potential, dielectric constant, and Debye length in the system.


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Page 28 of 32

Summary and Conclusions As asphaltene is defined by its solubility in toluene, investigating the stability of asphaltenetoluene system for a wide range of asphaltene properties can assist in understanding the behavior of this crude oil fraction. Investigation of the total interaction energy of asphaltene-toluene system, including E

LW ATA

EL AB , E ATA , E ATA , and E Br , is a useful tool for predicting the stability of this system.

The results of this study revealed that

EL E ATA

between asphaltene particles in toluene is of lower

order specifically at low separation distances due to the low value of dielectric constant of toluene. On the other hand, the attractive

LW E ATA

asphaltene precipitation. Additionally,

for asphaltene-toluene system is the main cause of

AB is E ATA

repulsive only if 

 A

  T i.e.

if asphaltene is less

basic than toluene. Lower basicity of asphaltene compared with that of toluene is widely observed for asphaltene samples from various crude oil sources. Hence, positive AB interactions counterbalances LW attractions and tend to stabilize the system. It is worth mentioning that according to the asphaltene type, i.e. the comparative values of various interaction energies, the repulsive E

EL ATA

can help to stabilize the asphaltene-toluene system, especially at higher

temperatures and/or higher separation distances. The results of this study provide additional insight about the underlying mechanisms of asphaltenes stability in organic solvents and could be useful for understanding the interactions between asphaltene particles in crude oils. The experimental data of surface energy components of asphaltene from various crude oil sources, as well as the stability of asphaltene/organic liquid systems will be reported in our future work. Nomenclature A E

Hamaker constant [J] AB ATA

E Br E

Lewis acid-base interaction energy [J]

Diffusion interaction energy (Brownian motion) [J]

DLVO ATA

DLVO interaction energy [J]

EL E ATA

electrostatic double layer interaction energy [J]

LW E ATA

Lifshitz-van der Waals interaction energy [J]

LWAB E ATA

Sum of Lifshitz-van der Waals and Acid-base interaction energies [J]

Total E ATA

H

Total interaction energy [J] Separation distance between the interacting bodies [m]


Page 29 of 32 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

Langmuir

H0

Minimum equilibrium distance between two particles [m]

I

Ionic strength [mole/m3]

II

Interaction parameter

kB

Boltzmann constant [J/K]

R

Particle radius [m]

T

Temperature [K]

Greek symbols 

Electron acceptor component of surface energy [J/m2]



Electron donor component of surface energy [J/m2]

 LW

Lifshitz-van der Waals surface energy [J/m2] Electrical permittivity of the solution [C/V.m]





Zeta (Electrokinetic) potential [V]



Electric surface potential [V]

κ-1

Debye length [m]

λ

Correlation length pertaining to water molecules [m]

Subscripts A

Asphaltene

L

Liquid

S

Solid

T

Toluene

References (1) (2) (3) (4) (5) (6)

Badre, S.; Carla Goncalves, C.; Norinaga, K.; Gustavson, G.; Mullins, O. C. Molecular Size and Weight of Asphaltene and Asphaltene Solubility Fractions from Coals, Crude Oils and Bitumen. Fuel 2006, 85 (1), 1–11. Chemistry of Asphaltenes, Bunger, J. W.; Li, N. C. Eds.; American Chemical Society: Washington, 1982; 195. Asphaltenes: Fundamentals and Applications, Mullins, O. C.; Sheu, E. Y.; Mullins, O. C., Eds.; Springer, 1995. Barré, L.; Simon, S.; Palermo, T. Solution Properties of Asphaltenes. Langmuir 2008, 24 (8), 3709–3717. Roux, J.-N.; Broseta, D.; Demé, B. SANS Study of Asphaltene Aggregation: Concentration and Solvent Quality Effects. Langmuir 2001, 17 (16), 5085–5092. Hashmi, S. M.; Firoozabadi, A. Controlling Nonpolar Colloidal Asphaltene Aggregation by 28 ACS Paragon Plus Environment

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(7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26)

Electrostatic Repulsion. Energy Fuels 2012, 26 (7), 4438–4444. Pedersen, K. S.; Christensen, P. L.; Azeem, S. J. Phase Behavior of Petroleum Reservoir Fluids, CRC Press, 2006. Speight, J. G. J. The Chemistry and Technology of Petroleum, Taylor & Francis, 2006. Asphaltenes, Heavy Oils, and Petroleomics. Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G., Ed.; Springer 2007. Lyon, L. A. Handbook of Applied Surface and Colloid Chemistry. Journal of the American Chemical Society 2002, 124 (50), 15143–15144. Hammami, A.; Phelps, C. H.; Monger-McClure, T.; Little, T. M. Asphaltene Precipitation from Live Oils: An Experimental Investigation of Onset Conditions and Reversibility. Energy Fuels 2000, 14 (1), 14–18. Wu, J.; Prausnitz, J. M.; Firoozabadi, A. Molecular-Thermodynamic Framework for Asphaltene-Oil Equilibria. AIChE J 1998, 44 (5), 1188–1199. Wang, S.; Liu, J.; Zhang, L.; Xu, Z.; Masliyah, J. Colloidal Interactions between Asphaltene Surfaces in Toluene. Energy Fuels 2009, 23 (2), 862–869. Wang, S.; Liu, J.; Zhang, L.; Masliyah, J.; Xu, Z. Interaction Forces between Asphaltene Surfaces in Organic Solvents. Langmuir 2010, 26 (1), 183–190. Merino-Garcia, D.; Andersen, S. I. Calorimetric Evidence about the Application of the Concept of CMC to Asphaltene Self-Association. J. Dispersion Sci. Technol. 2005, 26 (2), 217–225. Joshi Shilpi, N. B., Agarwal, A, H. M. Relate Crude Oil Fouling Research to Field Fouling Observations. International Conference On Heat Exchanger Fouling and Cleaning VIII. Schladming, Austria. 2009, 15–16. Long, J.; Xu, Z.; Masliyah, J. H. Single Molecule Force Spectroscopy of Asphaltene Aggregates. Langmuir 2007, 23 (11), 6182–6190. Mansoori, G. A. Modeling of Asphaltene and Other Heavy Organic Depositions. J. Pet. Sci. Eng. 1997, 17 (1–2), 101–111. Wang, J.; van der Tuuk Opedal, N.; Lu, Q.; Xu, Z.; Zeng, H.; Sjöblom, J. Probing Molecular Interactions of an Asphaltene Model Compound in Organic Solvents Using a Surface Forces Apparatus (SFA). Energy Fuels 2012, 26 (5), 2591–2599. Natarajan, A.; Xie, J.; Wang, S.; Liu, Q.; Masliyah, J.; Zeng, H.; Xu, Z. Understanding Molecular Interactions of Asphaltenes in Organic Solvents Using a Surface Force Apparatus. J. Phys. Chem. C. 2011, 115 (32), 16043–16051. Painter, P.; Veytsman, B.; Youtcheff, J. Guide to Asphaltene Solubility. Energy Fuels 2015, 29 (5), 2951–2961. Siffert, B.; Kuczinski, J.; Papirer, E. Relationship between Electrical Charge and Flocculation of Heavy Oil Distillation Residues in Organic Medium. J. Colloid Interface Sci. 1990, 135 (1), 107–117. Torkaman, M.; Bahrami, M.; Dehghani, M. Influence of Temperature on Aggregation and Stability of Asphaltenes. I. Perikinetic Aggregation. Energy Fuels 2017, 31 (10), 11169– 11180. Khoshandam, A.; Alamdari, A. Kinetics of Asphaltene Precipitation in a Heptane-Toluene Mixture. Energy Fuels 2010, 24 (3), 1917–1924. Andersen, S. I.; Birdi, K. S. Aggregation of Asphaltenes as Determined by Calorimetry. J. Colloid Interface Sci. 1991, 142 (2), 497–502. Andersen, S. I.; Speight, J. G. Observations on the Critical Micelle Concentration of 29 ACS Paragon Plus Environment

Page 30 of 32

Page 31 of 32 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

Langmuir

(27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48)

Asphaltenes. Fuel 1993, 72 (9), 1343–1344. Sheu, E. Y.; De Tar, M. M.; Storm, D. A.; DeCanio, S. J. Aggregation and Kinetics of Asphaltenes in Organic Solvents. Fuel 1992, 71 (3), 299–302. van Oss, C. J. Interfacial Forces in Aqueous Media, Marcel Dekker: New York, 1994. Young, T. An Essay on the Cohesion of Fluids. Philos. Trans. R. Soc. London 1805, 95, 65–87. Al-Janabi, A. K. O. Convective Heat Transfer Fouling of Aqueous Solutions on Modified Surfaces, University of Stuttgart, Germany, Ph.D. Dissertation, 2011. Van Oss, C. J.; Good, R. J.; Chaudhury, M. K. The Role of van Der Waals Forces and Hydrogen Bonds in “hydrophobic Interactions” between Biopolymers and Low Energy Surfaces. J. Colloid Interface Sci. 1986, 111 (2), 378–390. van Oss, C. J.; Chaudhury, M. K.; Good, R. J. Monopolar Surfaces. Adv. Colloid Interface Sci. 1987, 28 (Supplement C), 35–64. van Oss, C. J.; Chaudhury, M. K.; Good, R. J. Interfacial Lifshitz—van Der Waals and Polar Interactions in Macroscopic Systems. Chem. Rev. 1988, 88 (6), 927–941. van Oss, C. J. Interfacial Forces in Aqueous Media, CRC Press, 2006. Keesom, W. H. The Second Viral Coefficient for Rigid Spherical Molecules, whose Mutual Attraction is Equivalent to that of a Quadruplet Placed at Their Centre. Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, 1915, 636–646. Keesom, W. H. The Quadrupole Moments of the Oxygen and Nitrogen and Nitrogen Molecules. Royal Netherlands Academy of Arts and Sciences (KNAW). 1920. Keesom, W. H. Die van Der Waalschen Kohäsionskräfte. Zeitschrift für Physik 1921, 22, 643-644. Debye, P. Die Van Der Waalschen Kohäsionskräfte. Zeitschrift für PhysikPhy 1920, 21, 178–187. Debye, P. Molekularkräfte Und Ihre Elektrische Deutung. Zeitschrift für Physik 1921, 22, 302–308. London, F. Zur Theorie Und Systematik Der Molekularkräfte. Zeitschrift für Physik 1930, 63 (3–4), 245–279. Israelachvili, J. N. Intermolecular and Surface Forces, 2nd Ed.; Elsevier: California, USA, 1991. Fotland, P.; Askvik, K. M. Determination of Hamaker Constants for Asphaltenes in a Mixture of Pentane and Benzene. Colloids Surf., A 2008, 324, 22–27. Oliveira, R. Understanding Adhesion: A Means for Preventing Fouling. Exp. Therm. Fluid Sci. 1997, 14 (4), 316–322. Fowkes, F. M.; Jinnai, H.; Mostafa, M. A.; Anderson, F. W.; Moore, R. J. Mechanism of Electric Charging of Particles in Nonaqueous Liquids. In Colloids and Surfaces in Reprographic Technology, American Chemical Society, 1982, Vol. 200., pp. 15–307. Dukhin, S. S.; Derjaguin, B. V. Electrokinetic Phenomena. In Surface and Colloid Science, Matievic, E., Ed.; John Willey and Sons: New York, 1974. Li, B.-R.; Chen, C.-C.; Kumar, U. R.; Chen, Y.-T. Advances in Nanowire Transistors for Biological Analysis and Cellular Investigation. Analyst 2014, 139 (7), 1589–1608. Demortière, A.; Snezhko, A.; Sapozhnikov, M. V; Becker, N.; Proslier, T.; Aranson, I. S. Self-Assembled Tunable Networks of Sticky Colloidal Particles. Nat. Commun. 2014, 5, 3117. Zhao, Q.; Muller-Steinhagen, H. Intermolecular and Adhesion Forces of Deposits on 30 ACS Paragon Plus Environment

Langmuir 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

(49) (50) (51) (52) (53) (54) (55) (56) (57) (58)

(59) (60) (61)

Modified Heat Transfer Surfaces. In Proceedings of the 4th International Conference on Heat Exchanger Fouling, Fundamental Approaches & Technical Solutions, MüllerSteinhagen, H.; Malayeri, M. R.; Watkinson, A. P., Eds.; Davos, 2001. van Oss, C. J. Interaction Forces betwben Biological and other Polar Entities in Water: How many Different Primary Forces are there?. J. Dispersion Sci. Technol. 1991, 12(2), 201219. Erbil, Y. Surface Energetics of Films of Poly (vinyl acetate-butyl acrylate) Emulsion Copolymers. Langmuir 1996, 37 (24), 5483-5491. Brown, W.; Mortensen, K.; Floudas, G. Screening Lengths in Concentrated Polystyrene Solutions in Toluene Determined using Small-Angle Neutron and Small Angle X-Ray Scattering. Macromolecules 1992, 25 (25), 6904–6908. Mardolcar, U.V.; Nieto de Castro, C.A.; Santos, F.J.V. Dielectric Constant Measurements of Toluene and Benzene. Fluid Phase Equilib. 1992, 79 (25), 255-264. Andrews, A. B.; Guerra, R. E.; Mullins, O. C.; Sen, P. N. Diffusivity of Asphaltene Molecules by Fluorescence Correlation Spectroscopy. J. Phys. Chem. A 2006, 110 (26), 8093–8097. Shell Chemicals Data Sheet for Toluene, Issued 19th October 2007. van Oss, C. J.; Chaundhury, M. R.; Good, R. J. The Mechanism of Phase Separation of Polymers in Organic Media-Apolar and Polar Systems. Sep. Sci. Technol. 1989, 24(1-2), 15-30. Espinat, D.; Ravey, J. C.; Guille, V.; Lambard, J.; Zemb, T.; Cotton, J. P. Colloidal Macrostructure of Crude Oil Studied by Neutron and X-Ray Small Angle Scattering Techniques. J. Phys. IV. 1993, 03(C8), C8-181-C8-184. Spiecker, P. M.; Gawrys, K. L.; Kilpatrick, P. K. Aggregation and Solubility Behavior of Asphaltenes and Their Subfractions. J. Colloid Interface Sci. 2003, 267, 178–193. Wang, H., Xu, H., Jia, W., Liu, J., and Ren, S. Revealing the Intermolecular Interactions of Asphaltene Dimers by Quantum Chemical Calculations. Energy Fuels. 2017 31 (3), 2488-2495 Barrett, K. E. J. Dispersion Polymerisation in Organic Media. Br. Polym. J. 1973, 5 (4), 259–271. van Oss, C. J. Acid-base interfacial interactions in aqueous media. Colloids Surf., A 1993, 78, 1-49 Natarajan, A.; Kuznicki, N.; Harbottle, D.; Masliyah, J.; Zeng, H.; Xu, Z. Understanding Mechanisms of Asphaltene Adsorption from Organic Solvent on Mica. Langmuir 2014, 30 (31), 9370–9377.


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Impact of Asphaltene Surface Energy on Stability of Asphaltene

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