Water Nanoemulsions: Activity at the WaterâOil Interface and

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OIL/WATER NANOEMULSIONS: ACTIVITY AT THE WATER/OIL INTERFACE AND EVALUATION ON THE ASPHALTENES AGGREGATES Veronica Bomfim Souza, and Claudia R.E. Mansur Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01996 • Publication Date (Web): 30 Nov 2015 Downloaded from http://pubs.acs.org on December 2, 2015

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OIL/WATER NANOEMULSIONS: ACTIVITY AT THE WATER/OIL INTERFACE AND EVALUATION ON THE ASPHALTENES AGGREGATES

Verônica B. Souza and Claudia R. E. Mansur* Institute of Macromolecules/Rio de Janeiro Federal University– IMA/UFRJ, Cidade Universitária, Centro de Tecnologia, Bl. J, Ilha do Fundão – Rio de Janeiro – Brazil, CEP: 21945-970. E-mail: [email protected]; [email protected];

ABSTRACT Oil-in-water (O/W) nanoemulsions based on nonionic ethoxylated polymeric surfactants were prepared and evaluated for demulsification of water/oil emulsions and model asphaltene emulsions. The nanoemulsions were prepared using two nonionic ethoxylated polymeric surfactants with different numbers of ethylene-oxide (EO) units in their chains and the solvents xylene and Solbrax as the oil phase, in different concentrations. The interfacial properties of the different systems applied in the demulsification process were evaluated in model emulsions and were correlated with their ability and/or speed of diffusion to the interface. Tests of asphaltene dispersion/flocculation were performed to evaluate whether the nanoemulsions change the aggregation state of asphaltenes during the demulsification process. The results of gravitational separation tests showed that the new nanoemulsion formulations studied can be applied to demulsify water/oil emulsions. Both the type of polymeric surfactant used and the type and content of the oil phase in the nanoemulsions had a significant influence on the efficiency and speed of breaking down emulsions. The efficiency was related to surfactant hydrophilicity and the solubility parameter of the oil phase, which also affected the size of the asphaltene aggregates.

Keywords:

Demulsification,

nanoemulsions,

oil

surfactants, asphaltenes.

ACS Paragon Plus Environment

emulsions,

nonionic

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INTRODUCTION

Nanoemulsions are dispersions in which the dispersed droplets have nanoscale size, normally defined as in the range between 1 and 100 nanometers in diameter.

1

However, some authors consider as 500 nm a

maximum limit of size of dispersed droplets. 2,3 Nanoemulsions do not form spontaneously. They need an energy source, which can be supplied by mechanical devices.

4

These generate

mechanical energy by high shear force, such as in high-pressure homogenizers or microfluidizers, or by application of ultrasound. 5 The high mechanical energy imposed on the system generates forces that deform and break up the droplets of the internal phase into smaller (nanometric) particles by overcoming the Laplace pressure.

6

The surfactants play important roles in the formation of

nanoemulsions: by reducing the interfacial tension, the internal pressure is reduced and thus the force required to break a drop is also reduced. 4 Our research group has developed oil-in-water (O/W) nanoemulsions with different compositions for application in the pharmaceutical or petroleum sectors.

7,8

In the latter sector, we have studied their application as alternatives

in the process of separating the water and oil phases. 9-11 Extracted crude oil generally is accompanied by water, called produced water, normally having high salt content, along with gas, sediments and/or other contaminants. The pretreatment of crude oil requires removing the produced water and other pollutants because they can cause problems along the entire production chain. Hence there is a need for destabilization of water-in-oil emulsions to allow separation of the phases, to avoid problems associated with corrosion and the cost of transporting excessive volumes of water. 12,13


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Crude oil is composed of a series of compounds, including natural surfactants (asphaltenes and resins) that can stabilize emulsions by migrating to the oil-water interface. 14,15 The asphaltenes are a group of polar molecules, as are resins, but with higher molar mass. Due to the complexity of their composition, the definition of different asphaltene fractions is based on their precipitation in light alkanes, such as n-pentane, hexane or heptane. Besides this, the precipitate is soluble in aromatic solvents such as toluene and benzene.16 Asphaltic macromolecules tend to interact chemically, forming molecular aggregates. After formation of the emulsion, these stabilizing agents tend to concentrate at the water-oil interface due to their affinity for both phases, forming a mechanically resistant elastic film.17 The breakdown of water/oil emulsions is a complex process that generally requires use of physical treatments (gravitational, thermal and/or electrostatic) and chemical treatments as well.

18

Among these, the addition of

chemical demulsifiers followed by heating the emulsion is one of the most effective mechanisms.

19-21

These demulsifiers are normally formed by

polymers, such as poly(ethylene oxide)-b-poly(propylene oxide) (PEO-PPO) block

copolymers,

ethoxylated

phenols,

alcohols,

ethoxylated

amines,

ethoxylated resins, ethoxylated nonylphenols and sulfonic acid salts. These additives are added to solutions containing 30 to 40% of active material, normally using solvents such as toluene or xylene / ethanol mixtures. 9,21-23 Among the desired properties of demulsifiers are adsorption at the water/oil interface, displacement of natural emulsifiers that stabilize emulsions and formation of thin and fragile films at the interface. 17,24


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In a previous work

10

, nanoemulsions were prepared using two types of

ethoxylated nonionic surfactants (nonylphenol and lauryl ether) along with the solvent xylene as the oil phase, at different concentrations. The results of the demulsification tests showed that the nanoemulsions developed are a viable alternative to break down petroleum emulsions, with efficiency ranging from 90 to 95%. Also, the greater the xylene concentration in the nanoemulsion, the faster the demulsification process was. The development of nanoemulsions mainly aims to reduce the concentration of additives and solvents in the formulations used as demulsifiers, with the twin benefit of reducing costs and environmental impact. These nanoemulsions contain surfactant concentrations (active material) of about 12wt% of the mixture. The amount of oil used in the preparation of nanoemulsions is also low (5 to 10wt%), with the remainder being composed of water (about 78 to 83wt% of the formulation). This permits producing large volumes of emulsions without the need for large amounts of active materials, because nanoemulsions maintain their particle size even under substantial dilution. 10,11,25,26 This article reports the results of follow-on studies to those cited above, here with O/W nanoemulsions based on ethoxylated nonionic surfactants (nonylphenol or lauryl ether), using either xylene or Solbrax as the oil phase, at different concentrations. The purpose of the experiments was to evaluate the activity of these nanoemulsions at the water/oil interface and assess their direct action on the asphaltene aggregates present in crude oil.


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EXPERIMENTAL SECTION

MATERIALS The oil-in-water nanoemulsions were prepared using two commercial lines of nonionic polymer surfactants with different hydrophilic- lipophilic balance (HLB) values: surfactants containing ethoxylated nonylphenol – Ultranex line Ultranex NP80 (8 ethylene oxide (EO) units - HLB 12.3) and Ultranex NP150 (15 EO units - HLB 15.0); and surfactants containing ethoxylated lauryl ether – Ultrol line - Ultrol L70 (7 EO units - HLB 11.50) and Ultrol L100 (10 EO units HLB 13.90). These surfactants were acquired from Oxiteno do Brasil (São Paulo, Brazil) and were used as received. The oil phases (solvents) used to prepare the nanoemulsions were: xylene PA, from Vetec, and Solbrax ECO 175/235, made by Petrobras through catalytic hydrogenation at high pressure of petroleum distillates and characterized by low concentration of aromatic compounds, olefins and sulfur. This solvent (SOBRAX) was characterized in previous work

11

. The aqueous

phase was distilled deionized water. The synthetic emulsions were prepared using a crude oil sample donated by the Petrobras Research Center (CENPES), in Rio de Janeiro, Brazil, with the following composition: water = 0.6wt%; saturates = 58.4wt%; aromatics = 26.2wt%; resins = 14.6wt%; and asphaltenes = 0.7wt%, with density (oAPI) = 29.9. To prepare the model emulsions we used asphaltenes extracted from asphaltic residue samples from the Duque de Caxias Refinery (REDUC), also donated by CENPES.


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The aqueous phase used to prepare the synthetic emulsions and model emulsions was brine, composed of 55,000 ppm of salts (NaCl:CaCl2 ratio of 10:1), prepared according to the method described in the literature.11 The sodium chloride (NaCl) and calcium chloride (CaCl2) were acquired from Vetec, Rio de Janeiro.

METHODS Preparation and characterization of the O/W nanoemulsions The nanoemulsions were prepared in an EmulsiFlex C5 high-pressure homogenizer (HPH) using pressure of 15.000 psi and 4 cycles. We prepared different nanoemulsions containing surfactants of the same line, but varying the type and content of the oil phase used. Table 1 shows all the dispersions used to prepare the O/W nanoemulsions and the concentrations of each component. Table 1.

The size and size distribution of the droplets in the nanoemulsions, as well as their stability, were determined in a Zetasizer Nano ZS particle size analyzer, which works on the principle of dynamic light scattering (DLS). The stability of the nanoemulsions was evaluated by monitoring the size and size distribution of the particles over time, at the following intervals: end of preparation (time 0), and at 1, 2, 24, 48, 72 hours and so on successively, until visual observation of total separation of the phases. All the analyses were carried out in triplicate and the results are presented as curves of the mean values obtained, with the respective standard deviations.


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Preparation and characterization of the synthetic emulsions made from crude oil and the model asphaltene emulsions The synthetic petroleum emulsions were obtained by first adding the brine (55,000 ppm of salts, NaCl:CaCl2 ratio of 10:1) in the crude oil, under manual stirring until complete incorporation of the water in the oil phase, resulting in the formation of synthetic emulsions with an oil:water ratio of 50:50. These dispersions were then submitted to shear force in an Ultra-Turrax homogenizer, at rotation of 11,000 rpm for three minutes, with steady circulation of the entire emulsion around the device’s shaft. The model asphaltene emulsions were prepared from the extracted asphaltene samples by dispersion in mixtures of the solvents n-heptane and toluene (heptol), which composed each emulsion’s oil phase. The asphaltenes were extracted from the asphaltic residue sample by precipitation induced by addition of n-heptane as flocculant in a Soxhlet, extractor, as described by Honse et al.22 Their composition was the same as characterized in a previous study

23

regarding the concentrations of total

carbon, aromatic carbon, oxygen, nitrogen and hydrogen. The model emulsions were prepared by slowly adding brine to the dispersion of asphaltenes (composed of 0.25% w/v of asphaltenes in a 35/65 ratio with heptol) under shear action in a Polytron PT 3100D homogenizer at a speed of 8,000 rpm until complete incorporation of the water in the organic phase. The concentration of this saltwater phase in the emulsion was 50%. After addition of all the brine, the system was stirred for another 3 minutes. The water content in the synthetic oil emulsion and model emulsion was determined by the potentiometric titration method employing Karl-Fischer (KF)


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reagent. This technique directly provides the percentage of water in the sample, only requiring supplying the mass of the sample in the titration flask in the calculation formula.

Evaluation of the demulsification performance of the nanoemulsions The O/W nanoemulsions with different water/surfactant/oil compositions (type of surfactant and oil phase content) were assessed for their efficiency in demulsifying the recently prepared model emulsions by the bottle test (gravitational separation), carried out in a thermostatically controlled water bath at 45°C. This efficiency was assessed using nanoemulsion samples of 25.0 and 50.0µL, corresponding to surfactant concentrations of 30.0 and 60.0 ppm and oil phase concentrations of 12.5 and 25.0 ppm, respectively. The water separated out was quantified during 65 minutes (at 5, 10, 15, 20, 25, 35, 45, 55 and 65 minutes). Before each observation, the sample was swirled for 1 minute. The efficiency of each formulation used in these tests was calculated by Equation 1:

EFWO = (VWS/VWT) x 100

(Equation 1)

Where, EFWO = water-oil gravitational separation efficiency, % by volume; VWS = volume of water separated during the test, mL; VWT = total volume of water present in the test tube, mL.

Measurement of the interfacial tension values of the model systems in the presence of the nanoemulsions The interfacial tensions of the model emulsions in the presence of the different systems assessed for demulsification efficiency were measured to


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assess these systems’ ability to reduce this tension in function of time and subsequently relate these values with the ability and/or speed of diffusion to the interface. These measurements were performed with a Kruss K100 tensiometer using the Wilhelmy plate method, at the interfaces: water/heptol or water/asphaltenes dispersion (containing or not aqueous surfactant solutions or nanoemulsions). The tests were carried out during 1 hour, to enable monitoring the variation of the interfacial tension values in function of time and to obtain these values after equilibrium of the system, i.e., after conclusion of the diffusion, adsorption, reorganization at the interface, desorption, and mass transfer of molecules to the other phase.

Evaluation of the nanoemulsions as asphaltene dispersants or flocculants The tests of dispersion/flocculation of the asphaltenes were carried out directly with the asphaltene dispersions used to prepare the model emulsions, through the asphaltene precipitation test.27 This test is based on inducing destabilization of the asphaltenes dispersed in a mixture of solvents (here heptol). When quantities of n-heptane are added to the model system, some of the previously stabilized asphaltenes precipitate out of the solution. The concentration of the remaining asphaltenes in solution is obtained by measuring the absorbances in an ultraviolet-visible spectrometer, with comparison against a standard curve. These tests, on the system of 0.25% (w/v) asphaltenes in the heptol mixture, were carried out to determine the concentration of asphaltenes dispersed in function of varied percentages of n-heptane added (0, 10, 20, 30, 40, 50, 60, 70, 80 and 90%).


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Since the objective was to ascertain whether the nanoemulsion promotes flocculation/dispersion of the asphaltenes, two tests were applied: a blank test (without adding the nanoemulsion) and another test after adding 10 µL of the selected O/W nanoemulsions (same formulations as used in the demulsification tests) to 10 mL of 0.25% (w/v) asphaltenes in the heptol mixture system. Besides these assays, to check the influence of the oil phase present in the

nanoemulsions

during

the

dispersion/flocculation

process

of

the

asphaltenes, we also performed precipitation tests using the following solvents as precipitation agent: the pure oil phases used in preparing the dispersions (xylene or Solbrax) or xylene/toluene or Solbrax/toluene mixtures. These dispersions were left at rest for 24 hours and then centrifuged at 3,000 rpm for 30 minutes. The measurements were performed with a Varian Cary 50 ultraviolet spectrometer equipped with a quartz cuvette, using a 2-mm optical path. The concentrations of asphaltenes in solution were read at a wavelength of 850 nm, at which there is absorption by the asphaltenes but not of the additives used.

Characterization of the size of the asphaltene aggregates in the presence of nanoemulsions To assess the influence of the direct action of the composition of the nanoemulsions on the size of the asphaltene aggregates, the dispersions of these compounds were investigated at the molecular level by atomic force microscopy (AFM). These analyses were carried out with dispersions of 0.25% (w/v) of asphaltenes in heptol (40:60 ratio) in the presence of some of the nanoemulsion systems evaluated in the previous tests as petroleum


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demulsifiers. This same analysis was also performed with the dispersions containing 0.25% (w/v) of asphaltenes in the presence of pure toluene and mixtures of toluene/heptane, toluene/xylene and toluene/Solbrax. All the dispersions were left at rest for 24 hours and then centrifuged at 3,000 rpm for 30 minutes. Then clean and cleaved mica sheets were placed in the supernatant to allow the sample containing asphaltenes to adhere to the surface and form a thin film. These pieces were then dried at room temperature before being examined with a JPK Nano Wizard atomic force microscope and Nanoworld NCSTR-50 rod, with resonance frequency of 160 KHz and spring constant of 7.4 N/m. The images (10 x 10 µm and 20 x 20 µm) of the surface of all the samples were captured by intermittent contact mode at room temperature.

RESULTS AND DISCUSSION Preparation of oil/water nanoemulsions in the high-pressure homogenizer The nanoemulsions were prepared in the presence of the pure commercial surfactants (ethoxylated lauryl ether or ethoxylated nonylphenol) with different oil phase types and concentrations (Table 1). The results obtained for the nanoemulsions containing the surfactants Ultrol L100 and Ultranex NP150 and with the oil phase composed of xylene were reported in a previous study.10 These results showed the formation of nanoemulsions with monomodal droplet size distribution (a single size range, between 5 and 20 nm) for all the systems in the presence of both surfactants, which was independent of the oil phase concentration used. However, the nanoemulsions with lower oil phase


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concentrations (5 and 7wt%) were more stable (longer than 12 weeks) than those formed with an oil phase concentration of 10wt%, which presented an increase in the average droplet size seven days after preparation and completely separated ten days after preparation. The results obtained for the systems in the presence of the surfactants L70 (Figure 1) or NP80 and containing Solbrax as the oil phase indicated, as observed previously

10

, that there was initial formation of O/W nanoemulsions

with monomodal size distribution (the same single size range between 5 and 20 nm). Figure 1

However, this behavior was not observed for the system in the presence of the surfactant L100 containing Solbrax as the oil phase, in which the droplet size distribution was heterogeneous (with wide size distribution in the range: 10 to 3000 nm) . This can attributed to the low affinity of L100 and Solbrax, resulting from the hydrophilic nature of the surfactant in contrast with the lipophilic nature of the oil phase. Solbrax was characterized in a previous article 11

, as being a mixture of very similar structures composed of hydrocarbons with

linear or branched chains, such as monocyclic alkanes (from C3H6 to C10H20). The presence of other compounds, such as alkenes, heteroatoms or aromatics, was not observed. In all the systems analyzed, the nanoemulsions with lowest oil phase concentrations (5 and 7wt%) were more stable (longer than 5 months) than those prepared with 10wt% oil phase, which in most cases showed an increase in the average droplet size 7 days after preparation and separated completely 10 days after preparation.


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In general, the results show that to obtain stable O/W nanoemulsions in the presence of the nonionic surfactants used in this study, two factors are important: the steric stability promoted by the polar part of the surfactant molecule and the interfacial tension values. In light of these observations, it can be assumed that the destabilization of the nanoemulsions containing 10wt% oil phase occurred due to the lower surfactant/oil ratio of the system. In other words, the higher oil phase content in the nanoemulsion impairs the system’s steric stability; since there is not enough surfactant to keep the droplets dispersed (prevent them from coalescing).

Application of the O/W nanoemulsions for water/oil demulsification The oil-in-water nanoemulsions were evaluated for their efficiency in demulsification of the synthetic emulsions of crude oil and recently prepared model asphaltene emulsions. The influence of the surfactant type and oil phase concentration was assessed to learn more about the mechanism by which the nanoemulsions function as demulsifiers. The efficiency results of the nanoemulsions in destabilizing the water/oil emulsions in the presence of the surfactants L100 and containing Solbrax as the oil phase are shown in Figures 2. The results of the nanoemulsions prepared with xylene (surfactants L100 and NP150) were presented in a previous article.10 Figure 2

These results and for the systems composed of the surfactants NP80 and L70, prepared with Solbrax as the oil phase, show the same behavior: that all the nanoemulsions were efficient in water/oil separation of the emulsions.


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Also, as expected, the separation speed was faster when using the largest nanoemulsion volume (50 µL). In previous work

10

was showed that the nanoemulsions containing

xylene as the oil phase initially presented faster demulsification and more efficient gravitational separation than the nanoemulsions containing Solbrax (results present in Figure 3). Furthermore, the nanoemulsions containing 10%m xylene (the highest oil phase concentration) were the most efficient in demulsification, regardless of the surfactant type or volume of volume of nanoemulsion utilized. 10 Another previous study

21

showed that the performance of surfactants as

demulsifiers is influenced by the solvent medium in which they are prepared. The greater the affinity of this solvent with the petroleum (which is the continuous phase of water/oil emulsions), the better the diffusion of the surfactant molecules is, resulting in faster phase separation. Based on the results obtained, it can be concluded that the participation of the oil phase (xylene or Solbrax) in the migration of the surfactant molecules to the water/oil interface is influenced by its affinity/solubility in crude oil. This can be explained in terms of the solubility parameters of the petroleum and solvents used as oil phase. In a previous study

23

it was observed that for crude oil samples

containing lower asphaltene concentrations, the solubility parameter range was 16-21 MPa¹/². Of the solvents used as the oil phase in this study, the solubility parameter of xylene is 18.0 MPa¹/²

28

, which is within the above range. In the

case of Solbrax, which is a mixture of hydrocarbon compounds, the solubility parameter can also be expressed based on the solubility parameters of


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hydrocarbon compounds available in the literature

28

. According to these, its

solubility is below 16 MPa¹/². Examples of these solubility parameters are: hexane (14.9 MPa¹/²); hexene (15.1 MPa¹/²); heptane (15.1 MPa¹/²), octane (15.6 MPa¹/²), decane (13.5 MPa¹/²) and dodecane (16.2 MPa¹/²). Therefore, the slower breakdown of the water/oil emulsions by the nanoemulsions containing Solbrax can be explained by the fact that this solvent improves the diffusion of the surfactant molecules, and hence helps their migration to the water/oil interface.

Application of the O/W nanoemulsions for water/oil demulsification of model emulsions containing asphaltenes To gain more insight into the action mechanism of the nanoemulsions in breaking down water/oil emulsions, we performed tests with the model asphaltene emulsions to evaluate the direct action of the nanoemulsions (with different surfactants and oil phase types and concentrations) on aggregation of asphaltenes (Figure 3). Figure 3

All these nanoemulsions presented fast demulsification rate. However, as observed in the water/oil demulsification tests, the nanoemulsions containing Solbrax were less efficient in separating the asphaltene emulsions compared to the nanoemulsions containing xylene. Furthermore, the

nanoemulsions

containing the

highest

Solbrax

concentration (10wt%) were the least efficient demulsifiers. This behavior can be related to the size of the asphaltene aggregates, which depending on the


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aromaticity of the dispersant medium can increase or decrease in size, hence influencing the efficiency of separating water/oil emulsions. 29 Based on these results, we can suggest that Solbrax, which contains low concentrations

of

aromatic

compounds

and

high

levels

of

aliphatic

hydrocarbons, works to increase the size of the asphaltene aggregates, so the gravitational separation efficiency decreased when the concentration of this oil phase increased from 5wt% to 10wt%.

Evaluation of the water/asphaltene dispersion interface in the presence of the nanoemulsions To ascertain the influence of the composition of the nanoemulsions and their performance in demulsification through direct action on the asphaltene aggregates present at the water/oil interface, the nanoemulsions’ ability to migrate, occupy the water-oil interface and reduce the interfacial tension was studied. These tests were performed first to determine the interfacial tensions of the 35:65 water:heptol mixture in the absence and presence of the different nanoemulsion systems shown in Table 1, containing 5 or 10wt% oil phase. In this case, the interfacial layer was composed only of the surfactants present in the nanoemulsion Then we determined the interfacial tensions of the water:asphaltene dispersion in heptol (1.0% w/v of asphaltenes dissolved in the 35:65 heptol mixture), also in the absence and presence of the different nanoemulsion systems, containing 5 or 10wt% oil phase. All these tests were performed using 250 ppm of the systems, corresponding to the surfactant and oil phase concentrations present in 25 µL of


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the nanoemulsions utilized in the water/asphaltene separation tests. The measures for the systems composed of the surfactants NP150, prepared with Xylene as the oil phase are shown in Figure 4. The curves of the other systems studied show the same behavior and the results obtained are shown in Table 2, where the initial and final values of interfacial tension of the system are presented.

Figure 4 Table 2

The results demonstrated the interfacial activity of the asphaltenes: the water/heptol tension values declined from 28.0 mNm-1 to 22.0 mNm-1 when the asphaltenes were added to this system. All the nanoemulsion systems evaluated showed a strong tendency for migration and adsorption at the water/oil interface, and consequently reduced the tension for both interfaces evaluated: water/heptol and water/asphaltene dispersion in heptol. Besides this, all the nanoemulsion systems analyzed showed stronger interfacial activity than the asphaltenes, since the reduction of the water/heptol interfacial tension values was more pronounced in the presence of the nanoemulsions. This superior interfacial activity explains the effectiveness of these nanoemulsion

systems

in

water/oil

demulsification,

by

allowing

the

displacement of the natural emulsifiers of petroleum (asphaltenes) from the water/oil interface and destabilizing the emulsions. With respect to the relative effectiveness of the nanoemulsions in displacing the asphaltenes from the water/oil interface, those containing the surfactants NP150 and L100, in the presence of xylene as the oil phase, were


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able to displace all the asphaltenes from the interface, since the water/heptol interfacial tension measures of the nanoemulsions declined to values only slightly higher than those of the water/asphaltene dispersion in heptol. Contrary behavior was observed for the water/oil tension values in the presence of the nanoemulsions containing Solbrax: the water/asphaltene dispersion interfacial tension values were slightly lower than the water/heptol tension values in the presence of these compounds, indicating that the nanoemulsions containing Solbrax do not effectively displace the asphaltenes from the interface. We believe this behavior occurred because these nanoemulsion systems promote rearrangement of the asphaltene molecules at the interface, enabling a more substantial reduction of the water/asphaltene dispersion tension. The occurrence of this molecular rearrangement of the asphaltenes can explain the less efficient water/oil demulsification obtained for the nanoemulsion systems containing L70 and NP80 in the presence of Solbrax.

Evaluation of the nanoemulsions as asphaltene dispersants/flocculants The asphaltene precipitation tests were performed in the presence of the O/W nanoemulsions and the aqueous surfactant solutions, along with a blank test (without additives) for use as reference. The results of these tests were used to plot the graphs of dispersed asphaltene

concentration

(percentage

of

non-precipitated

asphaltenes

dispersed in the solvent medium) versus the heptane concentration (%v/v) in the heptol mixture, shown in Figures 5 to 7. Figures 5 to 7


Page 19 of 38

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Energy & Fuels

All the graphs showed a typical solubility curve of asphaltenes in mixtures of toluene/heptane, with a decline of asphaltene concentration dispersed in the solvent medium starting from a determined proportion of heptane added to the asphaltenes/toluene/heptane mixture. Based on the asphaltene precipitation test (blank, without addition of nanoemulsions), within the concentrations analyzed, precipitation started at a 50/50 toluene/heptane ratio. However, the nanoemulsions caused a significant change in the aggregation of the asphaltenes in solution: the concentrations of asphaltenes dispersed in the solvent medium at the precipitation point (50/50 toluene/heptane ratio) were smaller than the concentrations measured in the blank test. The addition of the nanoemulsions containing Solbrax promoted more pronounced changes in the aggregation of asphaltenes in the dispersions, increasing the quantity of asphaltenes precipitated for all the toluene/heptane ratios after the precipitation point. Furthermore, the nanoemulsions in the presence of the surfactants L70 and NP80 containing Solbrax, besides increasing the quantity of asphaltenes precipitated, also reduced the quantity of heptane necessary to reach the precipitation point, to toluene/heptane ratios of 70/30 and 60/40, respectively. These results, which show the modification in the aggregation state of the asphaltenes promoted by the addition of the nanoemulsions, mainly where Solbrax was the oil phase, suggest that this type of oil phase influences the size of the asphaltene aggregates, facilitating flocculation and consequently favoring precipitation of the asphaltenes even more.


Energy & Fuels

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Page 20 of 38

For the purpose of assessing the influence of the oil phases present in the nanoemulsions on the stabilization/flocculation process of the asphaltenes, we also performed asphaltene precipitation test using xylene or Solbrax as the precipitating

agent

instead

of

n-heptane,

such

as

xylene/toluene

or

Solbrax/toluene mixtures. Figure 7c shows the results of the asphaltene precipitation test of the solutions containing 0.25% (w/v) of asphaltenes in different proportions of the xylene/toluene or Solbrax/toluene mixtures. The results show that only Solbrax at high proportions helps precipitation of the asphaltenes, since there was a smaller asphaltene concentration remaining in the asphaltene/toluene/Solbrax system. With respect to the xylene/toluene mixture, regardless of the proportions of toluene and xylene, no asphaltene precipitation occurred. This can be explained by the fact that asphaltenes are highly soluble in aromatic solvents and hence are more dispersed in media containing this solvent type.

Characterization of the size of the asphaltene aggregates in the presence of nanoemulsions Because the oil phase used in preparing the nanoemulsions influenced the aggregation state of the asphaltenes, as observed in the results of the precipitation tests, we decided to investigate the influence of these oil phases on the size of the aggregates, using the AFM technique. Figure 8 shows the AFM micrographs obtained for the dispersions with asphaltene concentration of 0.25% (w/v) in the presence of pure toluene and mixtures of toluene/heptane, toluene/xylene and toluene/Solbrax. Table 3 reports the average size of the asphaltene aggregates, measured by height.


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Energy & Fuels

Figure 8

Table 3

In general it can be observed that the average sizes of the aggregates varied with the nature of the solvent. Examining Figure 8a first, it can be seen that the asphaltenes are relatively dispersed in the medium, explained by the fact that toluene is a good solvent of asphaltenes. Particles with size around 15 to 30 nm can be seen, a finding that is in accordance with the results of previous studies using light scattering. 30 The same behavior can be noted in Figure 8b, which shows that the addition of xylene (toluene/xylene mixture) did not significantly change the size of the asphaltene aggregates. This can be related this solvent’s aromaticity. On the other hand, Figure 8c shows that the addition of heptane (toluene/heptane mixture), because it is not a good asphaltene solvent, promoted a sharp increase in the size of the aggregates of these fractions, as expected. Finally, Figure 8d shows the AFM images of the asphaltene dispersions with the toluene/Solbrax mixture. It can be seen that Solbrax also substantially increased the size of the asphaltene aggregates, resulting in particles measuring 82.0 ± 20 mn. This increase can be explained by the lower aromaticity of the medium resulting form the addition of Solbrax, which promoted a reduction of the solvation of the dispersant medium, thus increasing the interactions between the asphaltene molecules, as also observed with addition of heptane. The micrographs of these systems also show particles still dispersed in the medium with small sizes, explained by the fact that Solbrax is a mixture of compounds, so it can have some affinity for asphaltenes.


Energy & Fuels

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

In the analyses carried out in the presence of the nanoemulsions (Figure 9), we used the following systems: nanoemulsions containing L100 and 5wt% xylene and nanoemulsions containing L100 and 5wt% Solbrax, as well as an aqueous solution of the surfactant L100. The average size distributions of the asphaltene aggregates are reported in Table 4.

Figure 9 Table 4

These analyses were performed with dispersions containing 0.25% (w/v) asphaltenes in mixtures of heptol (4/6 proportion), which explains the large size of the aggregates. We decided to examine these asphaltene dispersions with AFM to directly compare the results with those obtained in the precipitation tests of the asphaltenes in the presence of the nanoemulsions. The results indicate that the size of the asphaltene aggregates is influenced directly by the type of oil phase of the nanoemulsions. The sizes were larger for the dispersions containing the nanoemulsion with Solbrax, but there were no significant changes in aggregate size for the dispersions containing the aqueous solution of L100 in the presence of the nanoemulsion L100 and 5wt% xylene. As can be seen from the AFM results shown in Table 4, the asphaltene aggregates’ average sizes were 78 ± 24 nm and 99.4 ± 30 nm in the images obtained for asphaltene dispersions in the presence of the aqueous solution of L100 and the nanoemulsion containing xylene, respectively. In turn, there was an increase in the size of these aggregates on the order of 1 µm for the same asphaltene dispersions in the presence of the nanoemulsion containing Solbrax as the oil phase.


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Energy & Fuels

Considerations on the demulsification mechanism in the presence of the O/W nanoemulsions In a previous paper

29

, it was proposed a mechanism that has been

accepted regarding the chemical demulsification of crude oil emulsions that correlates the water/oil separation efficiency with the voids left between the asphaltene aggregates adsorbed at this interface. The smaller the aggregates are, the easier it is for the surfactant molecules to be adsorbed at this interface and displace the natural emulsifiers. Based on this mechanism, we observed in the present study that depending on the properties of the oil phase present in the nanoemulsion, such as aromaticity and solubility parameter, this phase, besides promoting diffusion of the surfactant molecules to the water-oil interface, can modify the aggregation state/degree of the asphaltenes adsorbed at the water/oil interface. Solbrax, because it is not a good solvent of asphaltenes, causes an increase in the size of the aggregates, so the interface is more completely filled with their molecules, making it harder to break up these emulsions. On the other hand, the nanoemulsion containing xylene as the oil phase does not cause a significant change in the size of the asphaltene aggregates, so it is very efficient in breaking up the emulsions. Figure 10 contains a diagram of the adsorption at the water/oil interface of the polymeric surfactants containing xylene and Solbrax as the oil phase.

Figure 10


Energy & Fuels

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

CONCLUSIONS The O/W nanoemulsion systems evaluated showed water/oil separation efficiencies by gravitation of 65 to 95%, depending on the composition of the nanoemulsion, so these systems can be a new alternative as demulsifiers in the petroleum industry. The hydrophilicity of the type of surfactant and the concentration of the oil phase present in the nanoemulsions evaluated as demulsifiers had a significant influence on the efficiency and speed of demulsification. In all the water/oil demulsification tests conducted with synthetic emulsions of crude oil and model emulsions of asphaltenes, the smallest efficiency values and slowest speed of the demulsification process were obtained when applying the nanoemulsion systems containing the solvent Solbrax as the oil phase. The presence of this product in the O/W nanoemulsion had a significant influence on the size of the asphaltene aggregates, favoring increased size, which hampered the demulsification action of the surfactants contained in the systems. In turn, xylene favored the dispersion of the asphaltenes in the medium, facilitating the demulsification process for the nanoemulsion systems containing this type of oil phase.

ACKNOWLEDGMENTS We thank CNPq, CAPES and PETROBRAS for the financial support.


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Energy & Fuels

REFERENCES 1- Solans, C.; Izquierdo, P.; Nolla, J.; Azemar, N.; Garcia-Celma M.J. Curr. Opin. Colloid Interface Sci. 2005, 10, 102 -110. 2- Wulff-Pérez, M.; Torcello-Gómez, A.; Gálvez-Ruíz, M. J.; Martín-Rodríguez, A. Food Hydrocolloids 2009, 23, 1096-1102. 3- Constantinides, P. P.; Chaubal, M. V.; Shorr, R. Advanced Drug Delivery Reviews 2008, 60, 757–767. 4- Tadros, T.; Izquierdo, P.; Esquena , J.; Solans, C. Adv. Colloid Interface Sci. 2004, 108-109, 303-318. 5- Abismail, B.; Canselier, J.P.; Wilhelm, A.M.; Delmas, H.; Gourdon, C. Ultrason. Sonochem. 1999, 6, 75–83. 6- Porras, M.; Solans, C.; González, C.; Martínez, A.; Guinart, A.; Gutiérrez, J.M. Colloids Surf., A 2004, 249, 115–118,. 7- Campos, V. E. B.; Mansur, C. R. E.; Ricci-Júnior, E. J. Nanosci Nanotechnol. 2012, 12, 2881-2890. 8- Fraga, A. K. ; Souza, L. F. I. ; Magalhães, J. R. ; Mansur, C. R. E. J. Appl. Polym. Sci, 2014, 131, DOI: 10.1002/app.40889. 9- Oliveira, P. F.; Oliveira, T. M.; SpinellI, L. S. ; Mansur, C. R. E. J. Nanomaterials 2014, 2014, 1-8. 10- Souza, V. B.; Neto, J. S. G.; Spinelli, L. S.; Mansur, C. R. E. Sep. Sci. Technol. 2013, 48, 1159-1166. 11- Costa, J. A. ; Queiroz, Y. G. C. ; Lucas, E. F. ; Mansur, C. R. E. Colloids Surf., A 2012, 415, 112-118. 12- Solovyev, A.; Zhang, l. Y.; Xu, Z.; Masliyah, J. H. Energy Fuels 2006, 20, 1572−1578. 13- Zhang, L. Y.; Xu, Z.; Masliyah, J. H. Langmuir 2003, 19, 9730−9741. 14- Gafona, O. V.; Yarranton, H. J. Colloid Interface Sci. 2001, 241, 469-478. 15- Feng, X.; Mussone, P.; Gao, S.; Wang, S.; Wu, S.; Xu, J. H. M. A. Langmuir 2010, 26 (5), 3050–3057. 16- Kokal, S. Soc. Petrol. Eng. 2005, 20 (1), 5-13. 17- Pereira, J. C.; Delgado-Linares, J; Scorzza, C.; Rondón, M.;Rodríguez, S.; Salager, J.L. Energy Fuels 2011, 25 (3), 1045–1050.


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18- Abdurahman, H. N.; Hassan, M. A. A.; Yunus, R. M. J. Appl. Polym. Sci. 2007, 7 (10), 1437-1441. 19- Borges, B.; Rondon, M.; Sereno, O.; Asuaje, J. Energy Fuels 2009, 23, 1568-1574. 20- Bouriat, P.; Rondon, M.; Lachaise, J.; Salager, J. L. Energy Fuels 2009, 23, 3998–4002. 21- Pacheco, V. F.; Spinelli, L. S.; Lucas, E. F. Energy Fuels 2011, 25 (4), 1659-1666. 22- Honse, O. S.; Mansur, C. R. E.; Lucas, E. F. J. Braz. Chem. Soc. 2012, 23 (12) 2204-2210. 23- Aguiar, J. I. S.; Garreto, M. S. E.; González, G.; Lucas, E. F.; Mansur, C. R. E. Energy Fuels 2014, 28 (1), 409-416. 24- Wu, I.; Xu, Y.; Dabros, T.; Hamza, H. Energy Fuels 2003, 17 (6), 15541559. 25- Souza, V.B.; Almeida, S. M.; Spinelli, L. S.; Mansur, C.R.E.; Gonzalez, G. Nanosci Nanotechnol. 2011, 11 (3), 2237-2243. 26- Kourniatis, L. R. ; Spinelli, L. S. ; Piombini, C. R. ; Mansur, C. R. E. Colloid j. Russ. Acad. Sci. 2010, 72, 396-402. 27- Lima, A. F.; Mansur, C. R. E.; Lucas, E. F.; Gonzalez, G. Energy Fuels 2010, 24, 2369-2375. 28- Brandrup, J., Immergut, E. H., Grulke, E. A. Polymer Handbook, 4.ed. New York: Jonh Wiley & Sons, 1999. 29- RAMALHO, J. B. V. S. Ph.D. Quim. Nova 2010, 33, 1664-1670. 30- Mansur, C. R. E.; Melo, A. R.; Lucas, E. F. Energy Fuels 2012, 26 (8) 49884994.


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Energy & Fuels

Table 1. Composition of oil/surfactant/water dispersions Surfactant line

Lauryl ether

Nonylphenol

Lauryl ether

Nonylphenol

(a)

Surfactant (a)

Ultrol L70

Ultranex-NP 80

Ultrol L100

Ultranex-NP 150

HLB

Water content (wt%)

Oil content (wt%)

83

5

81

7

78

10

83

5

81

7

78

10

83

5

81

7

78

10

83

5

81

7

78

10

11.50

Solbrax

12.30

Solbrax

13.90

15.00

Surfactant content = 12%wt


Xylene and Solbrax

Xylene

Energy & Fuels

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

Page 28 of 38

Table 2. Interfacial tension of water/heptol or water/asphaltenes dispersions containing or not aqueous surfactants solutions or nanoemulsions Aqueous solution or Nanoemulsion (a) --Aqueous NP150 solution NP150 and 5wt% xylene NP150 and 10wt% xylene Aqueous L100 solution L100 and 5wt% xylene L100 and 10wt% xylene Aqueous NP80 solution NP80 and 5wt% solbrax NP80 and 10wt% solbrax Aqueous L70 solution L70 and 5wt% solbrax L70 and 10wt% solbrax (a) (b)

System Water/heptol Water/asphaltenes dispersion Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion Water/heptol Water/asphaltenes dispersion

Initial interfacial tension (mN/m) (b) 32.5 24.2

Final interfacial tension (mN/m) (b) 27.0 20.8

16.0

14.3

14.5 14.8

12.5 12.8

12.4 12.6

11.0 11.0

21.0

18.8

19.0 19.4

16.5 16.9

17.5 17.8

15.8 16.0

21.2

20.2

20.8 18.6

18.9 17.0

20.6 19.4

18.8 17.5

22.0

20.0

21.3 19.6

19.5 18.0

21.3 20.4

19.5 18.5

Aqueous surfactant solutions or nanoemulsions added to system (water/heptol or water/asphaltenes dispersion); Error = ±0.1 mN/m.


Page 29 of 38

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

Table 3. Average size of the asphaltenes aggregates in the presence of different solvents Average size of the asphaltenes aggregates *

Solvents 10x10 µm;

20x20 µm

Toluene

19.27 nm ± 9.2

30.37 nm ± 7.4

Toluene/xylene

19.0 nm ± 5.5

24.5 nm ± 7.1

211.7 nm ± 45.6 115.8 nm ± 53.0 Toluene/heptane Toluene/solbrax 82.0 nm ± 20.0 98.3 nm ± 28.0 * Determined from the height of the asphaltenes aggregates obtained in AFM images

Table 4. Average size of the asphaltenes aggregates in the presence of different systems Average size of the asphaltenes aggregates

Systems

* 10x10 µm;

20x20 µm

Aqueous solution of L100

78.0 nm ± 24.0

61.2 nm ± 11.0

Nanoemulsion: L100 and 5wt% xylene

99.4 nm ± 30.0

86.0 nm ± 35.0

1.216 µm 718 nm Nanoemulsion: L100 and 5wt% solbrax * Determined from the height of the asphaltenes aggregates obtained in AFM images


Energy & Fuels

30

(a) t=0 t=1 week t= 1 month t= 5 months

25

Volume( %)

20

15

10

5

0 1

10

100

1000

10000

Size (nm) 30

(b) t=0 t= 1 week t= 1 month t= 4 months

25

Volume (%)

20

15

10

5

0 1

10

100

1000

10000

Size (nm) 30

(c) t=0 t=1 week t= 3 weeks

25

20

Volume( %)

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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15

10

5

0 1

10

100

1000

10000

Size (nm)

Figure 1. Droplet size distribution of the solbrax/water nanoemulsions in function of time since preparation, utilizing 12wt% of the surfactant L70 in aqueous phase and different solbrax concentrations: (a) 5wt%; (b) 7wt%; (c) 10wt%


Page 31 of 38

100 90

L100

80 70

Water removal (%)

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

60 50 40 Oil/water Solbrax (pure) Nanoemulsion content 5% solbrax (25 µL)

30

Nanoemulsion content 7% solbrax (25 µL) Nanoemulsion content 10% solbrax (25 µL) Nanoemulsion content 5% solbrax (50 µL) Nanoemulsion content 7% solbrax (50 µL) Nanoemulsion content 10% solbrax (50 µL)

20 10 0 10

20

30

40

50

60

70

Time (min) Figure 2. Tests

of the efficiency in demulsifying crude oil emulsions of the

nanoemulsion system containing 12wt% L100 and 5wt%; 7wt% and 10wt% of the oil phase (solbrax)


Energy & Fuels

100

a 90 80

Walter removal (%)

70 60 50 Oil /Water

40

Nanoemulsion 12% NP150 content 5% Xylene Nanoemulsion 12% L100 content 5% Xylene

30

Nanoemulsion 12% L100 content 5% Solbrax Nanoemulsion 12% L70 content 5% Solbrax

20

Nanoemulsion 12% NP80 content 5% Solbrax

10 0 10

20

30

40

50

60

70

Time (min)

100

b 90 80 70

Water removal (%)

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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60 50 40 Oil /Water

30

Nanoemulsion 12% NP150 content 10% Xylene Nanoemulsion 12% L100 content 10% Xylene

20

Nanoemulsion 12% L100 content 10% Solbrax Nanoemulsion 12% L70 content 10% Solbrax

10

Nanoemulsion 12% NP80 content 10% Solbrax

0 10

20

30

40

50

60

70

Time (min)

Figure 3. Tests

of the efficiency in demulsifying crude oil emulsions of the

nanoemulsion system containing: (a) 5 wt% and (b) 10 wt% of oil phase


Page 33 of 38

water/ heptol

water/ asphaltene dispersion + aqueous sol. NP150

water/ asphaltene dispersion

water/ asphaltene dispersion + nanoemulsion 5% xylene

water/ heptol + nanoemulsion 5% xylene

34 asphaltene dispersion + nanoemulsion 10% xylene water/

water/ heptol + nanoemulsion 10% xylene

32 30

Interfacial tension (mN/m)

28 26 24 22 20 18 16 14 12 10 0

10

20

30

40

50

60

Time (min) Figure 4. Water/oil interfacial tensions in the presence or not of nanoemulsions containing 12 wt% NP150 with 5 or 10 w% xylene.

0,200 0,175

Asphaltene in solution (% m/v)

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

0,150 0,125 0,100 0,075 White

0,050

Aqueous solution NP150

0,025

Nanoemulsion content 5% xylene Nanoemulsion content 10% xylene

0,000 0

20

40

60

80

100

n-heptane (% v / v) Figure 5. Asphaltenes concentration in dispersion versus n-heptane concentration in the precipitation test in toluene/heptane mixtures in presence or not of nanoemulsions containing 12 wt% of NP150 and 5 and10 wt% of xylene


Energy & Fuels

0,200

a

Asphaltene in solution (% m/v)

0,175 0,150 0,125 0,100 0,075

White

0,050

Aqueous solution L100 Nanoemulsion content 5% xylene

0,025

Nanoemulsion content 10% xylene 0,000 0

20

40

60

80

100

n-heptane (% v / v)

0,200

b 0,175

Asphaltene in solution (% m / v)

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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0,150 0,125 0,100 0,075

White

0,050

Aqueous solution L100 Nanoemulsion content 5% solbrax

0,025

Nanoemulsion content 10% solbrax 0,000 0

20

40

60

80

100

n-heptane (% v / v) Figure 6. Asphaltenes concentration in dispersion versus n-heptane concentration in the precipitation test in toluene/heptane mixtures in presence or not of nanoemulsions containing (a) 12 wt% of L100 and 10 wt% of xylene; (b) 12 wt% of L100 and 10 wt% of solbrax


Page 35 of 38

White 0,200

Aqueous solution NP80 Nanoemulsion content 5% solbrax

Asphaltene in solution(% m / v)

0,175

Nanoemulsion content 10% solbrax

0,150 0,125 0,100 0,075 0,050 0,025

a

0,000 0

20

40

60

80

100

n-heptane (% v / v) White 0,200

Aqueous solution L70 Nanoemulsion content 5% solbrax


0,175

Nanoemulsion content 10% solbrax

0,150 0,125 0,100 0,075 0,050 0,025

b

0,000 0

20

40

60

80

100

n-heptane (% v / v) 0,25

c 0,20


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

0,15

0,10

0,05

Toluene/xylene Toluene/solbrax 0,00 0

1

2

3

4

5

6

7

8

9

10

% xylene or solbrax (% v / v )

Figure 7. Tests of asphaltenes precipitation: (a) in toluene/heptane mixtures in presence or not of nanoemulsions containing NP80 and 5 and 10 wt% of solbrax; (b) in toluene/heptane mixtures in presence or not of nanoemulsions containing L70 and 5 and 10 wt% of solbrax; (c) in different proportions of toluene/heptane or solbrax/toluene mixtures


Energy & Fuels

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

(a)

(c)

Figure 8. Atomic

Page 36 of 38

(b)

(d)

force microscopy of 0.25% w / v of asphaltenes dispersions in the

presence of different solvents: (a) pure toluene, (b) toluene / xylene mixtures (c) toluene / heptanes mixtures and (d ) toluene / solbrax mixtures


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Energy & Fuels

(a)

(b)

(c)

Figure 9. Atomic

force microscopy of 0.25% w / v of asphaltenes dispersions in the

presence of different systems: (a) aqueous L100 solution; (b) nanoemulsion containing L100 and 5 wt% of xylene; (c) nanoemulsion containing L100 and 5 wt% of solbrax


Energy & Fuels

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Figure 10. Water /

oil interface: (a) in the absence of the nanoemulsions; (b) in the

presence of nanoemulsions containing xylene; (c) in the presence of nanoemulsions containing solbrax


Page 38 of 38

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