Article pubs.acs.org/EF
Influence of the Architecture of Additives on the Stabilization of Asphaltene and Water-in-Oil Emulsion Separation Silas Rodrigues Ferreira,† Heloisa Ferreira Louzada,† Rocio Macarena Moyano Dip,† Gaspar González,† and Elizabete Fernandes Lucas*,†,‡ †
Laboratory of Macromolecules and Colloids for the Petroleum Industry, Institute of Macromolecules, Federal University of Rio de Janeiro, Avenida Horácio Macedo, 2030, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-598, Brazil ‡ COPPE, Program of Metallurgy and Materials Engineering, Federal University of Rio de Janeiro, Avenida Horácio Macedo, 2030, Block F, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-598, Brazil ABSTRACT: Amphiphilic chemical additives are widely used to prevent the formation of asphaltene deposits and to promote demulsification of crude oil. Although it is known that the efficiency of these additives is mainly related to their structure and molar mass, this correlation is still not well established, because it is also related to the type of petroleum to be treated. In this work, C10I asphaltenes extracted from two different types of asphaltic residues were used to prepare model systems containing 1 wt % asphaltenes in toluene. Amphiphilic macromolecules, obtained from polymerization of cardanol by polyaddition and polycondensation, were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), and size-exclusion chromatography (SEC) and evaluated regarding their influence on the variation of asphaltene precipitation onset of model systems and the variation of volume and separation kinetics of water in model water-in-oil emulsions. The results show that the structure of polycardanol obtained by polyaddition favors its action as a dispersant of asphaltenes, which can be related to the fact that its phenol groups are relatively free to interact with the sites of the asphaltene molecules, as opposed to polymers obtained by polycondensation, in which the polymerization reaction occurs in the aromatic ring. Besides this, the demulsification results indicate a close relation of the dispersant action of this type of additive with its performance in water−toluene separation, so that the separation kinetics is mainly related to the molar mass of the additive in determining the final performance. The results highlight potential asphaltene dispersants derived from renewable sources.
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INTRODUCTION Crude oil is a mixture composed mainly of linear chain hydrocarbons, with 1−100 carbon atoms. The processing or refining of petroleum requires a complex series of operations to promote its fractioning, with the main operation being distillation. Among the fractions normally distilled during refining, the asphaltenic fraction is the heaviest. Its constituents can be separated by crystallization, thermal diffusion, and methods based on difference in molar mass or solubility in relation to a solvent.1 Concerns over the heavy fractions of crude oil produced during refining have increased in recent years. This question is particularly important in Brazil because most of the oil in the country is heavy, requiring high investments to develop technologies to extract higher quantities of valuable derivatives. Heavy fractions, such as paraffins with high molar mass and asphaltenes, tend to form deposits during processing, causing problems, such as reduced flow or total blockage of lines. In particular, asphaltenes, even at low concentrations, have a tendency to aggregate and precipitate, generating problems during both extraction and refining.2−9 Another possible problem is the adsorption of asphaltenes on the surfaces of reservoirs, thus altering the wettability and reducing the potential to recover petroleum.10,11 Besides this, asphaltenes are also one of the main causes of stabilization of the water-inoil emulsions generated during extraction of crude oil, acting as a surfactant. These emulsions need to be submitted to a demulsification process because the water present in petroleum © 2015 American Chemical Society
is responsible for altering its viscosity as well as for causing corrosion of equipment and reducing the yield of refined products.12−17 With the growing demand for more efficient oil recovery, research into the behavior of asphaltenes in crude oil is relevant. A better understanding of the physical−chemical properties is fundamental to formulate new production programs and to develop stabilizers/flocculants to minimize the damages caused by the presence of asphaltenes in petroleum. Stabilizing additives has the purpose of keeping the asphaltenes dispersed in the oil, while flocculant additives are applied in deasphalting oil.18−22 The stabilization of asphaltenes can be promoted by the action of surfactant molecules. Of these, alkylphenols are the most widely studied. The efficiency of an additive mainly depends upon the polarity of the headgroup and length of the hydrocarbon chain linked to the aromatic ring. Besides these aspects, an additional polar side group can increase the ability of an amphiphilic compound to stabilize asphaltenes. This stabilization capacity will be higher the stronger the acid−base interactions are between the two species.18,23,24 Cardanol is a phenolic compound with an aliphatic C15 chain in the meta position. Because of its similarity with the chemical structure of the alkylphenols used as asphaltene stabilizers, it has also been studied for this purpose.19,20 Received: October 5, 2015 Published: November 3, 2015 7213
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molecule can be polymerized by both addition and condensation. We obtained polycardanol by both of these routes, producing macromolecules with distinct architectures. Besides this, we also adjusted the reaction conditions to obtain samples with varying molar masses. To obtain the addition polymer, cardanol was polymerized in bulk by cationic initiation using BF3·O(C2H5)2 at varied concentrations, in a Schlenk tube at 140 °C for 4 h.20 The reaction was stopped by placing the tube in an ice water bath. To obtain the condensation polymer, cardanol was polymerized at different molar ratios of cardanol/formaldehyde with the addition of oxalic acid as a catalyst. The reaction mixture was left under reflux for ∼4 h and was stopped by the addition of distilled water. The polymers obtained were used without purification. Characterization of Polycardanol Samples. The molar masses of the polymer samples were measured with Viscotek GBC Max VC 2001 size-exclusion chromatography (SEC), with Shodex series KF806 M columns and viscometric and light-scattering detectors. The qualitative analysis of the structures was conducted by Fourier transform infrared (FTIR) spectroscopy in a Varian 3100 spectrometer coupled to a germanium attenuated total reflectance (ATR) element. The spectrum was varied from 4000 to 400 cm−1 with resolution of 16 cm−1. Proton nuclear magnetic resonance (1H NMR) was also applied to confirm the structures resulting from polyaddition and polycondensation, employing a Varian Mercury VX300 spectrometer, at 300 MHz, at 40 °C, using deutered chloroform as the solvent. Determination of the Asphaltene Precipitation Onset. This step consisted of assessing the ability of the synthesized polymers in displacing the asphaltene precipitation onset, because this experiment is susceptible to the presence of a particle. The tests were performed on model systems of asphaltenes in toluene at 1 wt %/vol, using nearinfrared (NIR) spectrometry to measure the absorbance as a function of the volume of n-heptane added to the medium. The asphaltene precipitation onset was determined using a NIR spectrophotometer equipped with an external probe with a 5 mm optical path inserted in a flask containing the model system. A high-performance liquid chromatography (HPLC) pump was used to titrate the flocculant, nheptane, into the flask containing the model system, at a flow of 2 mL/ min. The start of flocculation was determined by monitoring the absorbance versus flocculant volume, at a wavelength of 1600 nm.36 From this method, the start of precipitation is taken to occur at the minimum absorbance value. In this test, we used 10 mL of the model system; therefore, we divided the volume of the flocculant solvent (nheptane) related to the lowest absorbance value by 10 to express the asphaltene precipitation onset in terms of milliliters of flocculant per milliliter of the model system. Demulsification Tests. We first prepared water-in-oil model emulsions with synthetic brine as the aqueous phase containing 55 000 mg/L of salts (NaCl/CaCl2 mass ratio of 10:1). For the oil phase, we prepared 500 mL of stock solution at 1 wt %/vol containing asphaltenes dissolved in dry toluene. These oily dispersions were submitted to magnetic stirring for 24 h and then diluted according to the three asphaltene concentrations analyzed (1, 0.5, and 0.25 wt %/vol). The model emulsions were prepared in a water/oil ratio of 50:50 (%, v/v). For this purpose, 50 mL of the oil phase was placed in a 250 mL beaker and then the fluid was subjected to shear in a Kinematica Polytron PT 3100D homogenizer with a PT-DA 3020/2T mixing tool, under rotation of 8000 rpm, with slow addition of 50 mL of the aqueous phase. After all of the brine was added, the system was left under stirring for 3 min at room temperature. The gravitational water/oil separation was measured by the bottle test.14 The synthetic emulsions (100 mL) were placed in graduated tubes. Each tube was manually swirled vigorously for 1 min and then placed in a water bath at 25 °C. The volume of water separated out was measured at 5 min intervals for 65 min. Before the observation at each time interval, the tube was gently swirled for 1 min. The results were expressed in terms of volume of water (mL) separated as a function of time (min).
Cardanol is obtained from cashew nutshell liquid (CNSL), which is classified into two types (solvent-extracted and technical CNSL) based on the method of extracting the liquid. Technical CNSL mainly contains cardanol (60−65%), cardol (15−20%), and polymeric material (10%), along with traces of methylcardol. The solvent-extracted liquid contains anacardic acid (60−65%), cardol (15−20%), cardanol (10%), and traces of methylcardol. The cardanol fraction, in turn, is composed of triolefins (29%), diolefins (16%), monoolefins (50%), and saturates (5%).25,26 In comparison to similar phenolic derivatives, cardanol presents peculiarities in its chemical and physical−chemical characteristics, especially regarding the position of the double bond, which permits many functionalizations, besides the usual functionalizations of the phenolic ring, and characteristics specific to its derivatives (antioxidant, flameresistant, and hydrophobic properties). Cardanol has a weak smell, low volatilization, and higher boiling point than other phenolic compounds derived from petroleum, making it easier to work with and less aggressive to the environment.27 Therefore, derivatives of cardanol can be used in many industries, with the advantages of being biodegradable, renewable, and plentiful in regions where cashew fruit is grown.24 Some applications of cardanol and its derivatives that have been mentioned in the literature are to make varnishes, inks, stabilizers, plasticizers, ion-exchange resins, pesticides, and surface treatment agents.27−29 Because of the presence of a phenolic group and the double bond in the hydrocarbon chain, cardanol can be polymerized both by condensation (with electrophiles) and addition.20,26,31−33 Products of polyaddition of cardanol were first evaluated in processes to stabilize asphaltenes,19−21,34 and it has been suggested that the stabilizing/flocculant of an additive depends upon not only its concentration but also its molar mass. Studies with sulfonated polystyrene have indicated that, besides the molar mass and concentration, the content of sulfonic groups determines whether the additive will have a stabilizing or flocculating action on asphaltenes. However, these relations are still not well established, posing a problem because the action of an additive must be as specific as possible to leave not margin for antagonistic actions in function of small structural differences of the additive and/or in the environment where the additive will be used, such as the temperature, crude oil composition, and asphaltene structure. The aim of this study was to assess the relation between the architecture of an additive based on cardanol and its interaction with asphaltenes in terms of the variation of the asphaltene precipitation onset and destabilization of water−oil emulsions, using model systems of asphaltenes dispersed in toluene.
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EXPERIMENTAL SECTION
Materials. Oxalic acid (95−99%), formaldehyde P.A., and ń heptane (99.5%) were supplied by Vetec Quimica Fina (Xerém, Rio de Janeiro, Brazil) and used as received. Toluene, also obtained from ́ Vetec Quimica Fina, was used after distillation and drying in alumina. Cardanol, acquired from Satya Cashew Chemicals (Tamil Nadu, India), deuterated chloroform, obtained from Cambridge Isotopic Laboratory (CIL, Tewksbury, U.K.), and boron trifluoride diethyl ether [BF3·O(C2H5)2] (99%), obtained from Aldrich (São Paulo, Brazil), were used as received. C10I asphaltene fractions were extracted from two different asphaltic residues (AR1 and AR2), as described in previous papers.8,35 Synthesis of Polycardanol. The structure of cardanol contains a phenol group and a hydrocarbon chain that can contain up to three unsaturations, positioned closer to the end of the chain. Therefore, this 7214
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RESULTS AND DISCUSSION Synthesis and Characterization of Polycardanol. Polymers based on cardanol can be obtained by polycondensation or polyaddition. Addition polymers are obtained by opening one of the double bonds in the hydrocarbon chain.17 In turn, polycondensation occurs with the help of electrophiles (such as formaldehyde), along with the possible use of acid catalysts, such as oxalic acid, or with reactions of the hydroxyl group followed by oligomerization, to obtain functionalized prepolymers.37 Unlike the other resins obtained by polycondensation (high rigidity), those obtained from cardanol are more malleable and more soluble in organic solvents. Another interesting aspect is their hydrophobic character, which makes them resistant to bases and acids, resulting from the presence of an aliphatic chain of 15 carbon atoms in the meta position of the phenol ring. To evaluate the dispersant/flocculant power of the cardanolbased polymers, we used two forms of synthesis: polyaddition via cationic initiation and polycondensation. Polymerization of Cardanol by Polyaddition. Although the literature30−32 mentions different types of initiators and reaction conditions for polyaddition of cardanol, we chose to use BF3·O(C2H5)2 as the initiator.18−20,37 All of the reactions were conducted at 140 °C, which is defined as the optimal temperature for this reaction, because at lower temperatures, the conversion to polymer is reduced, while at higher temperatures, the polymer undergoes depolymerization, as happens with cationic polymerization of aliphatic olefins.37 As mentioned before, cardanol is composed of a mixture presenting different quantities of double bonds in the hydrocarbon chain (0, 1, 2, or 3). Because the structure containing one double bond (8′-monoene) is found in the largest proportion, we used it to represent the reaction by polyaddition of cardanol via cationic initiation (Figure 1).
dispersions obtained are presented in Table 1. As expected, the variation of the monomer/initiator ratio led to products with varied molar masses. The chains formed contained few repeated units, because the molar mass of cardanol (C21H32O) is 300 g/mol. The cardanol and polycardanol samples were characterized by FTIR spectrometry. The spectrum of cardanol presents the following absorption bands, with the respective deformations:19,38 3350 cm−1, O−H axial deformation; 3000 cm−1, C−H axial deformation of olefin; 2926−2854 cm−1, C−H axial deformation; 1650−2000 cm−1, meta-substituted aromatic ring; 1590 cm−1, axial deformation of CC bonds; 1487 and 1457 cm−1, axial deformation of CC bonds of the aromatic ring; 1350 cm−1, O−H out-of-plane deformation; 1265 cm−1, C−O axial deformation; 988 cm−1, CC; and 945 and 912 cm−1, CC at the end. The spectra of the polycardanol samples contain essentially the same bands as those observed for cardanol. The disappearance of the bands associated with the vinylic bond is absent, even though the polymerization reaction occurs by opening the double bond, because cardanol has more than one double bond in its structure,38 nor is there any variation of the intensity of the band associated with the vinylic bond in relation to the other bands. Therefore, to confirm the polyaddition reaction by opening of the vinylic double bond, we performed analyses by 1H NMR. Panels a and b of Figure 2 present the 1H NMR spectra of cardanol and polycardanol, respectively. The results confirm that the polymer was obtained by addition polymerization because the peak area related to CC has decreased when compared to peak areas related to the other groups. Polymerization of Cardanol by Polycondensation. The reactions to polymerize cardanol were also performed by polycondensation, with acid catalysis, to obtain non-crosslinked resins.25,28 Figure 3 presents a diagram of the polycondensation reaction of cardanol. Table 2 reports the reaction conditions used to obtain the polymer samples by polycondensation and the respective average molar masses and polydispersion. The samples obtained after varied reaction times had varied molar masses, as was our objective. The polycardanol samples obtained by polycondensation were also characterized by FTIR. The spectra of the polymers are essentially the same, with the same absorption bands observed for the unreacted cardanol sample. A slight difference between the spectra can be noted in the region from 2000 to 1650 cm−1, related to the meta substitution of the aromatic ring. This can be explained by the fact that the polycondensation reaction occurs directly from the aromatic ring, which becomes an ortho substitution, besides the meta substitution. Figure 4 presents the 1H NMR spectrum obtained for the sample PCC. The spectrum of unreacted cardanol is showed in Figure 2a. By comparison of the spectra of cardanol and polycardanol obtained by polycondensation, a peak around 3.8 ppm is observed, only for the polymer, related to the bond of the CH2−aromatic ring, which is formed because of polymerization at the ring.
Figure 1. Scheme of the cardanol reaction by polyaddition via a cationic mechanism.
We carried out two reactions under different conditions to obtain polymers with distinct molar masses. The reaction conditions and respective average molar masses and poly-
Table 1. Molar Masses of Polycardanol Obtained by Polyaddition with Cationic Initiation product
temperature (°C)
molar ratio (monomer/initiatior)
time (h)
M̅ n (g/mol)
M̅ w (g/mol)
M̅ w/M̅ n
PCA01 PCA02
140
120 130
4 4
1353 8347
3691 17611
2.73 2.11
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Figure 2. 1H NMR spectra of (a) cardanol and (b) polycardanol synthesized by polyaddition.
of a flocculant solvent, such as n-heptane. The asphaltene precipitation onset determined by the addition of a flocculent solvent can be related to the potential for precipitation of asphaltenes in petroleum.9,36,39,40 The asphaltene precipitation onset determined by NIR for the model systems of asphaltenes in toluene refers to the volume (mL) of solvent (n-heptane) necessary to start the precipitation of asphaltenes present in 1 mL of the model solution.9,35
Figure 3. Scheme of the cardanol reaction by polycondensation.
Evaluation of Cardanol/Polycardanol for Dispersion/ Flocculation of Asphaltenes in Toluene Model Systems. The precipitation of asphaltenes can be induced by the addition
Table 2. Reaction Conditions To Obtain Polycardanol by Polycondensation and the Respective Average Molar Masses and Polydispersivities of Samples product
temperature (°C)
molar ratio (cardanol/formaldehyde)
time (h)
M̅ n (g/mol)
M̅ w (g/mol)
M̅ w/M̅ n
PCC01 PCC02 PCC03
90
1:0.8
1.0 1.5 2.0
15570 9250 13320
30990 14880 25480
1.99 1.61 1.91
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Figure 4. 1H NMR spectra of polycardanol synthesized by polycondensation.
phenol groups of polycardanol obtained by polyaddition are relatively free to interact with the sites of the asphaltene molecules. In contrast, the phenol groups of polycardanol obtained by polycondensation are linked to each other, restricting their interaction with the sites of the asphaltene molecules. In this case, the interaction sites of the molecules must be positioned to favor interaction, which can occur in different ways for the two groups of asphaltene molecules with the same solubility behavior but different chemical structures.35 Effect of Cardanol/Polycardanol in the Stabilization of Water-in-Oil Model Emulsions. The water-in-oil gravitational separation tests were carried out by the bottle method with water/oil model emulsions (50:50, v/v), in which the aqueous phase consisted of brine and the oil phase was C10I asphaltenes extracted from AR02 dispersed in toluene. We first evaluated the stability of the emulsions containing 0.25 and 0.5 wt %/vol of asphaltenes without an additive (Figure 5). As expected,14 the stability of the emulsion increased with an increased concentration of asphaltenes in the oil phase, observed by the separation kinetics and the total quantity of water separated after analysis for 65 min. The water started separating after 10 and 20 min, respectively, for the emulsions containing 0.25 and 0.5 wt %/vol of asphaltenes. Of the 50 mL of water contained in the systems, the total volumes of water that separated out reached 15 and 10 mL for the emulsions containing 0.25 and 0.5 wt %/vol of asphaltenes, respectively. To assess the influence of the additives on the stability of the emulsions, we selected the asphaltene concentration of 0.5 wt %/vol because it was the most stable. None of the additives tested was able to cause 100% water separation (50 mL), which was not totally unexpected, because the commercial demulsification formulations are composed of
To study the influence of the additives on its performance, we used the C10I asphaltenes, obtained from both residues (AR01 and AR02).8,35 We chose this fraction because it is more susceptible to precipitation;8 that is, this fraction is more critical for evaluation of stabilizing additives and less critical for flocculant additives. The results obtained with the samples of the addition of polycardanol (PCA series) and condensation of polycardanol (PCC series) are shown in Table 3. For the additives PCA01 and PCC02, the addition of 0.05 mass % did not cause a significant variation in the precipitation onset values of the model systems prepared with the asphaltenes extracted from the two types of asphaltic residues (AR01 and AR02). At 0.10 mass %, in general, there was an increase on the precipitation onset, indicating that the additive has stabilizing action. Increasing the additive concentration to 1.00 mass % did not result in better efficiency, because the values were similar to or even less than those obtained with 0.10% concentration. Because that this concentration appeared to be the best, we also evaluated unreacted cardanol at 0.10%. The polymers had a better stabilizing effect than cardanol, providing evidence of the efficiency of polymerization to obtain an additive with better performance in stabilizing asphaltenes. In turn, the performance of the samples of PCC (Table 3) varied depending upon the type of residue from which they were obtained: for the C10I fraction from AR01 at the concentration of 0.10%, the additive had a stabilizing effect, while for the same fraction obtained from AR02, the additive did not have a stabilizing effect. In this last case, the additives showed a slight effect in inducing the particle formation. The results obtained for the two types of chemical structures (PCA series and PCC series) show that polymerization of cardanol can enhance its performance as a stabilizer. However, this behavior depends upon the polymer structure formed. The 7217
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Table 3. Asphaltene Precipitation Onset Obtained by NIR for Model Systems Containing 1% Asphaltenes (C10I−AR01 or C10I−AR02) in Toluene as a Function of the Addition of PCA (Addition of Polycardanol) Samples or PCC (Condensation of Polycardanol) Samples at Different Concentrations asphaltene fraction
additive
C10I (AR01) PCA01
PCA02
cardanol PCC01 PCC02 PCC03 C10I (AR02) PCA01
PCA02
cardanol PCC01 PCC02 PCC03
additive concentration (mass %)
asphaltene precipitation onset (mL of heptane/mL of the model system) (±0.05)
0.00 0.05 0.10 1.00 0.05 0.10 1.00 0.10 0.05 0.10 0.05 0.10 0.05 0.10 0.00 0.05 0.10 1.00 0.05 0.10 1.00 0.10 0.05 0.10 0.05 0.10 0.05 0.10
1.00 1.06 1.38 1.20 0.96 1.48 1.42 1.08 0.10 1.40 1.04 1.12 1.04 1.14 1.04 1.02 1.28 1.24 0.98 1.26 1.26 1.10 0.92 1.02 1.00 0.84 1.00 0.82
Figure 6. Stability of water-in-oil model emulsions (50:50) containing 0.5 wt %/vol of asphaltene C10I (AR02) in the oil phase and PCA01 at different concentrations.
Figure 5. Stability of water-in-oil model emulsions (50:50) containing 0.25 and 0.5 wt %/vol of asphaltene C10I (AR02) in the oil phase.
mixtures of surfactants.41,42 Despite this, behavior differences were observed as a function of the additive type and concentration, allowing for correlation between these factors. Furthermore, we also tried to establish a correlation between the emulsion stability results and the shift in the asphaltene precipitation onset. Figure 6 presents the results of water separation as a function of time for the model emulsion containing additive PCA01 at concentrations of 0.1, 0.25, and 0.5 wt %/vol. There was a variation in performance as a function of the concentration of the additive . At 0.5 wt %/vol (highest concentration), the separation profile was very similar to that of the system without
an additive, with the start of water separation after 20 min and total volume separated of 10 mL. For the lower concentrations (0.1 and 0.25 wt %/vol), the water separation started after only 10 min and the volume separated was larger (23 mL) with the use of only 0.1 wt %/vol of additive PCA01. This additive was tested at additive/asphaltene ratios of 1:1, 1:10, and 1:20 (Table 3) and presented stabilizing action at the 1:1 and 1:10 ratios. In fact, the highest concentration (1:1) did not improve the dispersant action (onset = 1.20 mL of heptane/mL of the model system) when compared to the effect observed at 1:10 (onset = 1.38 mL of heptane/mL of the model system). The 7218
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during the entire 65 min of the test, meaning that it increased the stability of the emulsion. This behavior is closely related to the behavior of this additive in the asphaltene precipitation onset test (Table 3). PCC02 did not have any influence on the onset when added at low concentrations, but as the concentration increased, it shifted the onset to lower values, meaning that it favored flocculation of the asphaltenes. The formation of asphaltene aggregates at the interface is believed to be responsible for the stabilization of water/oil emulsions.14 The water−oil separation results of the model emulsion obtained with the addition of 0.1% unreacted cardanol are presented in Figure 9. The behavior was closer to that of the
same behavior was observed for the model system prepared with C10I AR02. The overall results of the emulsion stability tests indicated that this overdosage (1:1) impairs the action of this additive in separating water from oil. We also compared the performance of PCA01 to that of PCA02 at the concentration of 0.1 wt %/vol (Figure 7), which
Figure 7. Stability of water-in-oil model emulsions (50:50) containing 0.5 wt %/vol of asphaltene C10I (AR02) in the oil phase and PCA01 or PCA02 at 0.1 wt %/vol.
presented a similar asphaltene dispersant action (Table 3). It is interesting to note that the performance of these two molecules was also similar regarding the volume of water separated (∼23 mL), but the separation kinetics were substantially different: while PCA01 started to cause separation of water at 10 min and reached a maximum separation at 65 min, PCA02 only took 15 min to reach maximum separation. Because the chemical structure of these two molecules is equal, this difference in separation kinetics is associated with the difference in the molar mass (Table 1). This can be related to the fact that molecules with a higher molar mass are less soluble in the medium and migrate faster to the water/oil interface.43 Figure 8 shows the water separation results for the model emulsion containing the additive PCC02 at concentrations of 0.1 and 0.25 wt %/vol. The demulsification results were not satisfactory: at the 0.1 wt %/vol concentration, the separation was very slow, while at 0.25 wt %/vol, there was no separation
Figure 9. Stability of water-in-oil model emulsions (50:50) containing 0.5 wt %/vol of asphaltene C10I (AR02) in the oil phase with and without the addition of unreacted cardanol at 0.1 wt %/vol.
polymers obtained by polyaddition than that of the polymers obtained by polycondensation. The total volume of water separated by adding cardanol unreacted was virtually the same as that observed for PCA01 and PCA02 at the same concentration, but the separation was slower. These results confirm that the increase of the molar mass, within the range tested, hastens the water−oil separation in the model emulsions studied.
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CONCLUSION The structure of polycardanol obtained by polyaddition favors its action as an asphaltene dispersant, which can be related to the fact that its phenol groups are relatively free to interact with the sites on the asphaltene molecules. The structure of polycardanol obtained by polycondensation contains interconnected rings in its phenol groups, constraining the interaction of these groups with the sites of the asphaltene molecules, so that its stabilization or flocculation action depends upon the structure of the asphaltene molecules. A single type of asphaltene fraction, i.e., isolated by the same solubility differential procedure, can present significantly different types and/or locations of its polar groups. The demulsifying action of an additive is closely related to its ability to disperse the asphaltenes: the stronger this dispersant ability, the better the additive will perform with respect to the total volume of water separated, although the separation kinetics are related to the molar mass of a determined structure. On the other hand, additives that act to flocculate asphaltenes tend to make the emulsion more stable.
Figure 8. Stability of water-in-oil model emulsions (50:50) containing 0.5 wt %/vol of asphaltene C10I (AR02) in the oil phase and PCC02 at 0.1 and 0.25 wt %/vol. 7219
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AUTHOR INFORMATION
Corresponding Author
*Telephone: 55-21-3938-7033. E-mail:
[email protected]. br. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank CNPq, CAPES, FAPERJ, Nalco Brasil Ltda., ANP, and Petrobras for financial support. REFERENCES
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DOI: 10.1021/acs.energyfuels.5b02337 Energy Fuels 2015, 29, 7213−7220
