Article pubs.acs.org/EF
Influence of Commercial Anti-agglomerants and Ammonium Quaternary Compounds on the Stability of Waxy Crude Oil Emulsion R. M. Charin,† G. Salathe,‡ M. Nele,†,‡ and F. W. Tavares*,†,‡ †
Programa de Engenharia Química, Instituto Alberto Luiz Coimbra de Pós-Graduaçaõ e Pesquisa em Engenharia (COPPE), Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21945-970, Brazil ‡ Escola de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21949-900, Brazil ABSTRACT: Understanding the anti-agglomerant (AA) contributions to the physicochemical properties of waxy petroleum emulsions can provide improvements on handling problems caused by hydrates during petroleum production. This work evaluated the stability of a reference water-in-oil (W/O) emulsion perturbed by the presence of commercial hydrate AAs and ammonium quaternary compounds. The results showed that emulsion mean droplet size was not sensitive to the presence of these chemicals. Both W/O emulsions, with and without AA addition, were stable under a gravitational field. The amount of water separated during the stability experiments (bottle test under a centrifugal field) increased for emulsions containing a higher content of AA/quaternary ammonium compound. In a specific concentration of AA, stable W/O emulsion can no longer be obtained and an unstable liquid dispersion was formed, resembling emulsions near the transitional inversion point. In a dynamic experiment, monitored by in situ near-infrared spectroscopy (NIR), a transitional emulsion inversion was performed by adding quaternary ammonium compound to the emulsion.
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INTRODUCTION
The relevant engineering aspects of hydrate formation in high water cut systems are poorly understood. The main interests of the literature on slurry flow behavior are blockage prevention10 and rheological properties.11 During the oil production, high shear flow provides the condition for emulsion formation; therefore, emulsion properties contribute to define the flow behavior in the pipeline; in particular, emulsion stability12 and emulsion morphology13 are identified as key factors for the prevention of hydrate agglomeration. Emulsion properties are especially important at high water cuts. The action of AA should also influence the physicochemical variables governing emulsion properties, which is obviously relevant because the hydrate formation can happen in an emulsified substructure. Zerpa et al.14 and Salager and Forgarini15 have recently reviewed some aspects of emulsion formulation engineering that should encompass flow assurance issues. The petroleum and aqueous phase usually have the potential to form water-in-oil (W/O) emulsion in pipeline conditions. The formulation of petroleum systems corresponds to negative hydrophilic−lipophilic deviation (HLD)16 (HLD < 0) (the meaning of “emulsion formulation” follows the approach presented by Zerpa et al.14 and Salager and Forgarini,15 and the emulsion formulation variables are those that affect the HLD of the system). Several papers17−20 show that, when hydrophilic surfactants are added to a W/O crude oil emulsion, the maximum demulsification (i.e., the minimum stability) occurs when the system is neither “hydrophilic” (O/ W emulsion formation tendency) nor “lipophilic” (W/O emulsion formation tendency). This occurs at the transitional
During offshore petroleum production, high-pressure and lowtemperature conditions favor hydrate formation that can induce large pressure drops and even pipeline flow blockage. The traditional way to overcome this adversity is to inject thermodynamic hydrate inhibitors (THIs) as methanol and monoethylene glycol. The THI makes the pressure−volume− temperature (PVT) of hydrate envelope move far from the pipeline conditions. Sometimes, the THI remediation is impracticable mainly because of the direct proportionality between water cut and the injected amount of THI. Hydrate formation at high water cuts would require large amounts of THI injection. Therefore, lowdosage hydrate inhibitors (LDHIs) are desired.1 LDHIs are distinguished into two groups according to the inhibition mechanism: the kinetic inhibitor (KHI) and the antiagglomerant (AA). The kinetic inhibitor slows the hydrate formation, providing enough time for the oil to be pumped through the pipeline. The AA2 acts on the interface, inhibiting particle agglomeration and, therefore, allowing hydrates to be carried along with other phases without plug risk. The mechanism of anti-agglomeration is a complex interfacial phenomena, and its study should consider interactions between different variables.3 Some quaternary ammonium compounds (QAs) can be used as a dispersant of particulates, and they are widely used as an active chemical in AA formulations.1 In general, the AA active molecule contains a hydrophobic part that is believed to prevent the agglomeration of particles and a hydrophilic part that interacts with the surface of the hydrate particle.4,5 QAs are the most cited active chemical in AA formulation, but other types of chemicals4,6−9 have been suggested to be effective AAs able to prevent hydrate plug formation. © XXXX American Chemical Society
Received: December 16, 2014 Revised: March 24, 2015
A
DOI: 10.1021/ef502815x Energy Fuels XXXX, XXX, XXX−XXX
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ensure homogeneous samples. Here, the oil container (5 L) was placed in an oven for a few hours at a temperature of 80 °C. It was periodically shaken during this process. Therefore, the volumes were quartered forming homogeneous samples (100 mL) to ensure the experimental reproducibility. Three commercial hydrate AAs from different brands were tested. They are labeled as AA1, AA2, and AA3. In addition, two ordinary ammonium quaternary compounds (with known molecular formulas) were used to compare results to commercial hydrate AAs (AA1, AA2, and AA3). Ammonium quaternary compounds are Hesterquat 16-29 (cetyltrimethylammonium chloride, 29% of active material, labeled as QA1) and Hesterquat BKC-50 (alkyl dimethyl benzyl ammonium chloride, 50% of active material, labeled as QA2). Figure 1 shows the molecular formulas of these ammonium quaternary salts.
phase inversion locus (HLD close to zero). If more hydrophilic surfactant is added, the emulsion formulation turns to HLD > 0. In this case, the opposite trend is observed, and O/W emulsions are usually formed. This inversion affinity can also be achieved using solid particles.21 In addition to demulsification, studies about the hydrophilic−lipophilic nature of systems containing petroleum are useful to improve oil recovery.22,23 Studies of oil/water/gas systems with hydrate formation in high water cuts have received some attention from the literature. Greaves et al.24 investigated the features of hydrate formation and dissociation in high water cut crude oil emulsion systems using a high-pressure vessel through conductivity and in situ particle size analysis [particle vision and measurement (PVM) and focused-beam reflectance measurement (FBRM)]. They suggested that hydrate dissociation could invert the emulsion from W/O emulsion to oil-in-water (O/W) emulsion. Moradpour et al.13 studied the phase inversion in emulsions with and without hydrates. They observed that the water cut and the type of emulsion prior to hydrate formation are important factors to determine the water/oil/hydrate morphology. Gao3 performed experiments at various water cuts using a rocking cell apparatus with AAs in formulation. At high water cuts, the anti-agglomeration process strongly depends upon the brine salinity. Sun and Firoozabadi4 proposed a new surfactant for anti-agglomeration claiming to be effective for a very large range of water cuts even for systems without oil. Reported results are related to methane hydrate formation in model water or brine (NaCl)/n-octane systems. Recently, the authors25 revisited the AA formulation to cover processes with natural gas containing CO2. The emulsions formed during petroleum production are stabilized by different mechanisms.26 On that basis, satisfactory knowledge of the anti-agglomeration process depends upon emulsion formulation properties. Issues related to wax precipitation and hydrate formation particularly pose one of the main concerns in Brazilian deep offshore flow assurance.27,28 Nowadays, there is an important class of waxy crude oil produced in Brazil that presents the tendency to form high stable emulsions.29−31 The action of AAs should affect emulsion properties because they are mostly composed by hydrophilic surfactants. Because hydrate formation can occur in an emulsified matrix, the emulsion properties are important. Therefore, the present work studies the influence of commercial AAs and QAs in waxy crude oil emulsion stability. A transitional phase inversion from W/O emulsion to O/W emulsion was also performed by the increase of QA content. In addition, a procedure to investigate emulsion inversion in systems containing petroleum by in situ nearinfrared spectroscopy (NIR) is presented.
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Figure 1. Chemical formulas of the ammonium quaternary compounds: QA1 and QA2. Deionized water and sodium chloride (Merck) were also used to prepare the emulsions. The water content of the oil sample is lower than 0.5 wt % (Karl Fisher, ASTM E-203). For the sake of simplicity, this content of brine was not taken into account during the calculations. Emulsion Preparation for the Stability Test. The emulsification was carried out using a high shear rate Polytron PT3100 mixer at 8000 rpm. An aqueous solution containing water, sodium chloride, and AA was added to the oil during stirring for 3 min, and the emulsion remained under agitation for an additional 2 min without any further addition. The volume of emulsion was 200 mL, and the emulsion temperature at the end of the process was approximately 45 °C. The volumetric ratios of water to oil (WOR) investigated were 0.428 and 1 [water volumetric fraction (f w) of 0.3 and 0.5], and the salinities tested here were 1 and 3 g of NaCl/100 g of H2O. The amount of commercial AA (AA1 or AA2) or QA (QA1 or QA2) used in each emulsion is described in Tables 1−3. Emulsion Stability Analysis. Because W/O emulsions were quite stable, they required long centrifugal testing to promote a measurable separation. Two types of emulsion instabilities characterized the systems resulting from centrifugal testing: sedimentation and separated water (Figure 2). The sedimentation is the result of the settlement of water droplets. This instability is reversible but its record can give further information about these emulsions. Other instabilities of emulsion come from coalescence, and it can be recorded by measuring the separation of water in the bottom of the tube. Therefore, two variables, sedimentation and separated water, were monitored over time by visual inspection in graduated tubes during centrifugal testing, as shown in Figure 2. To quantify these variables, the following equations were used: Percentage of oil separated by sedimentation (%) = [oil separated from original emulsion (mL) − dark phase/total oil in original emulsion (mL)] × 100. Percentage of water separated (%) = [water separated from original emulsion (mL)/total of water in original emulsion (mL)] × 100. The aim of the experiments was to evaluate the influence of interfacial agents. Therefore, a reference emulsion was always produced, i.e., a system without chemical addition. The reproducibility of experiments was evaluated by carrying out triplicates for each experimental condition. Samples were taken from the centrifuge for measurement every 30 min, 3 times. Therefore, the stability test took place in 90 min. The centrifugal rotation was 2000 rpm, and the temperature inside the centrifuge was set to 40 °C. The equipment used was a Novatecnica Centrifuge NT870.
EXPERIMENTAL SECTION
Materials. A crude oil [Petrobras Brazil, American Petroleum Institute (API) gravity of 27°] presenting a high content of wax [wax appearance temperature (WAT) defined by differential scanning calorimetry (DSC) of 37.5 °C] was used. The saturates, aromatics, resins, and asphaltenes (SARA) of this oil is the following: saturates, 37.72 ± 1.2%; aromatics, 44.39 ± 0.5%; resins, 14.35 ± 0.5%; and asphaltenes, 3.54 ± 0.2%. The oil samples were subjected to a quartering process to perform the sample homogenization. Petroleum comprises a variety of complex molecules of different molecular weights. Because of the thermodiffusion that occurs in oil fields, as a result of the imposed geothermal temperature gradients, samples of oil are different in terms of composition along the gravitational field direction. For handling petroleum, it is important to apply methods to B
DOI: 10.1021/ef502815x Energy Fuels XXXX, XXX, XXX−XXX
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Table 1. Composition Variables Investigated during the Experiments of Systems Containing Commercial AA (AA1 and AA2) for Experiments 1−5 [AA1] content (mLofAA/100mLofH2Ooremulsion)
a
[AA2] content (mLofAA/100mLofH2Ooremulsion)
experiment
H2O basis
emulsion basis
H2O basis
emulsion basisa
[NaCl] (g of NaCl/100 g of H2O)
WOR (water volume/oil volume)
1 2 3 4 5
0.10 0.20 0.05 0.10 0.10
0.050 0.100 0.025 0.050 0.030
0.10 0.20 0.05 0.10 0.10
0.050 0.100 0.025 0.050 0.030
1 1 1 3 1
1:1 1:1 1:1 1:1 0.428:1
The 100 mL of emulsion for this unity of measure corresponds to 50 mL of oil + 50 mL of brine containing AA.
Table 2. Composition Variables Investigated during the Experiments of Systems Containing QA1 for Experiment 6 [QA1] (mL of AA/100 mL of H2O or emulsion) experiment 6 a
emulsion basisa
H2O basis 0.050
0.020
0.010
0.025
0.010
0.005
[NaCl] (g of NaCl/100 g of H2O)
WOR (water volume/oil volume)
1
1:1
The 100 mL of emulsion for this unity of measure corresponds to 50 mL of oil + 50 mL of brine containing QA.
Table 3. Composition Variables Investigated during the Experiments of Systems Containing QA2 for Experiment 7 [QA2] (mL of AA/100 mL of H2O or emulsion) experiment 7 a
emulsion basisa
H2O basis 0.015
0.010
0.005
0.0075
0.0050
0.0025
[NaCl] (g of NaCl/100 g of H2O)
WOR (water volume/oil volume)
1
1:1
The 100 mL of emulsion for this unity of measure corresponds to 50 mL of oil + 50 mL of brine containing QA.
Figure 2. Typical test tube after centrifugation. The brown−black interface indicates the oil separated by sedimentation, while the water separated in the bottle of the tube indicates separated water caused by the coalescence of water droplets. The result presented in this photo corresponds to the conditions of experiment 1 (Table 1) for AA1 during the third view of centrifugal testing.
Figure 3. Inversion route. The emulsion formulation was selected to initiate an emulsion inversion by continuous addition of brine containing AA. This graph contains the approximate lines of emulsion inversion according to WOR map formalization. Figure 4 presents the experimental setup of the emulsion inversion. The solution that was pumped into the mixing vessel contains a fixed concentration of AA and sodium chloride. As the water cut increases at a constant flow rate, the AA concentration also increases in the emulsified system, changing the emulsion formulation. The production of the initial emulsion in the mixing vessel followed the same protocol used for the stability experiments. A circulating bath was used to keep the temperature at 40 °C during the whole experiment because this was the temperature of centrifugal testing, which was used as a reference. The conductivity and NIR probes were positioned inside the mixing vessel. The stirrer (Ika Eurostar, 700 rpm, four flat blade stirrer), spectrophotometer NIR (ABB FTLA-154), conductivity data collection (Gehaka, CG2000 coupled with a modified probe), and the pumping (Watson Marlon 120s) were started to monitor the dynamic emulsion inversion route (Figure 3).
The water droplets were observed in a microscope Zeiss (Axiovert 40 MAT, 100×) with the dilution of the sample in the spindle (1 mL of spindle/1 pipet drop of the emulsion), and 200 drops were captured for each measurement. Dynamic Emulsion Inversion. It was observed during the stability experiments that emulsions reached a pronounced instability condition at a certain concentration of each AA tested. Then, an inversion route in a WOR map was proposed,32 as shown in Figure 3. For the approach developed here, the concentration of AA in emulsion was the formulation variable. Hence, AA is supposed to be hydrophilic and to combine with natural hydrophobic surfactants of oil to attain the HLD = 0, a situation where the emulsion breaks. If so, an increasing AA concentration should go down according to the usual direction or more hydrophilic formulation. C
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comparing different AA contents. In Table 1, each experiment was performed with regard to AAs from different brands. Figure 5 shows the experimental triplicates of oil separated by droplet sedimentation observed in experiments 3 and 7. It is possible to notice that the results are inside the same error range. This tendency was observed in all experiments that sedimentation was evaluated. In the same way, the microscopy results do not show measurable differences between mean drop sizes of the emulsions with and without AAs. The mean droplet diameter ranged from ∼3.2 to 3.6 μm. Results of separated water during centrifugation are shown in Figure 6. It was found that emulsions without AA did not present any free water in the end of centrifugal testing. The emulsions with AA1 and AA2 presented an increase in the separation of water over time, as shown by experiment 1 in Figure 6. When the AA concentration was doubled (comparing experiment 2 to experiment 1), the AA2 sample did not form a stable emulsion. This means that the emulsion formulation of the sample containing AA2 in experiment 2 does not correspond to a stable W/O emulsion. This occurs because the formulation of the system is near the optimum formulation. The result for AA1 in experiment 2 was the emulsion breaking during the centrifugal testing. In this case, in comparison to experiment 1, the water separations were more pronounced for the first and second half hours. The emulsion with AA1 was completely broken during the third data recording. In the experiment 3, the AA concentrations were decreased by half in comparison to experiment 1. Emulsions of experiment 3 presented the same stability behavior as the emulsions of experiment 1. This means that the AAs presented the same effect on emulsion stability far from the optimum formulation. In the experiment 4, we tested a higher salinity in comparison to experiment 1. The stability decreases as indicated by the emulsion containing AA2, which separated completely during the centrifugal testing. However, some assist experiences showed that, when salinity was increased, the systems became less hydrophilic for the same content of AA. In other words, more AA was needed to balance the HLD (HLD ∼0). The electrolytes decrease at the same time as the hydrophilic action of the cationic surfactant and the W/O emulsion stability. In terms of emulsion formulation, more AA means lower HLD and more salt means higher HLD.
Figure 4. Experimental setup. The thermostatic bath was set to 40 °C, and the stirring rate was 700 rpm. The pumping of the AA aqueous solution makes the emulsion follow the prescribed inversion route. The pump flow rate was set to 12.56 mL/min. The inversion process was performed slowly to provide enough time for NIR spectra collection in a small composition change range. With regard to NIR, the resolution was 4 cm−1, the optical paths by transflectance (Solvias) were 2 × 0.5 (1 mm), and 64 scans were collected for each final spectra. GRAMS software was used to collect each spectrum during the inversion process. A total of 43 spectra were recorded during each experiment.
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RESULTS AND DISCUSSION Emulsion Stability Analysis. The emulsion stability experiments are organized in Tables 1−3. Table 1 presents the relative quantities of all substances including the commercial AAs. AA3 is not included in Table 1 because this product presented particular results that will be discussed latter. It is not our intention to compare the performance of different commercial AAs, but rather we would like to show general patterns of physicochemical behavior regarding emulsion formulation. The variables manipulated include WOR, salinity (g of NaCl/100 g of H2O), AA concentration, and AA type, as noticed in Table 1. Tables 2 and 3 contain information about experiments performed to evaluate the effect of known molecular formula QAs. Each experiment comprises the emulsion formulations evaluated at the same time during the centrifugal testing. For the cases described in Tables 2 and 3, the stability of emulsion for each experiment was performed
Figure 5. Results of oil separated by sedimentation. All data points are in the same error experimental range. The composition features of experiment 3 are presented in Table 1. Table 3 shows the composition of the emulsions containing QA2 (experiment 7). D
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Figure 6. Stability results in terms of separated water. Each experiment corresponds to determined composition providing a comparison between AA1 and AA2. Experiment 1 was the reference where each subsequent experiment tested a different perturbation (bold).
Figure 7. Stability results in terms of separated water for the QAs tested. Experiment 6 (Table 2) used QA1. Experiment 7 (Table 3) used QA2. QA2 presented a more hydrophilic behavior in terms of HLD. E
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water phase in the first data recording of the centrifugal test. In the second data point, this system was completely separated. As a consequence of this result, this formulation should be near balanced affinity (near HLD = 0). Because WOR slightly affects the formulation of emulsions (HLD), this configuration was brought to the water cut of 0.3 (WOR = 0.428), neglecting the contribution of the additional oil content. The inversion route (Figure 3) was prepared on the basis of this hypothesis. This new emulsion presents the same concentration on an emulsion basis in comparison to experiment 6 (0.025 mL of AA/100 mL of emulsion), but now the concentration of AA on an aqueous basis is 0.083 33 mL of AA/100 mL of H2O, instead of 0.05 mL of AA/100 mL of H2O. Pumping an aqueous solution with the same AA content (0.083 33 mL of AA/100 mL of H2O), the total concentration of AA in emulsion will increase, following the prescribed inversion route (Figure 3), and the transitional phase inversion will be achieved. The AA was always solubilized in the water phase. The unity is milliliters of AA/100 mL of H2O. Likewise, the water phase always contained sodium chloride. Thus, the water phase of emulsions was brine. The unit is grams of NaCl/100 mL of H2O. For this dynamic experiment (under agitation) of emulsion inversion, the water phase of emulsion contained a salinity of 1 g of NaCl/100 mL of H2O (formulation of Table 2, experiment 6). The AA concentration of the water phase is 0.083 33 mL of AA/100 mL of H2O, as explained in the previous paragraph. This concentration corresponds to the AA content on a water basis. When pumping is started, the concentration of the water phase in emulsion increases (modifying WOR) as well as the AA concentration on an emulsion basis (according to the inversion route; Figure 3). The transitional phase inversion is achieved because the HLD changes during this process. The application of NIR to perform in situ monitoring of the transitional emulsion inversion was recently suggested and tested.33 From the present work, it is shown now that the NIR is also useful for monitoring emulsion inversion in an emulsion containing crude oil (Figure 8). Particularly, three transitions during emulsion inversion were detected for the system studied herein. In the first transition, the initial W/O emulsion became an unstable liquid dispersion but the formulation was still more
In experiment 5, the concentration of AA on an aqueous basis (mL of AA/100 mL of H2O) is the same as the concentration of experiment 1, but the water cut is 30% instead of 50%. Therefore, the content of AA is globally lower if we consider the AA concentration on an emulsion basis (mL of AA/100 mL of emulsion). As a result, the emulsions became more stable because there is less AA in the mixture; thus, the optimum formulation is still far enough, and the separation does not take place. However, this comparison should take into account the same emulsification protocol performed on different WORs, which disturbs the comparison basis. Experiments 6 and 7 (Figure 7) were accomplished using two types of commercial QAs. QA2 showed more “hydrophilic” action in the formulation than QA1. For comparison to other commercial AAs investigated, AA3 does not form emulsion for the contents investigated, except at the conditions of experiment 3. However, even in that case, we could not observe separated water for AA3 because it formed foam between separated water and emulsion. This AA presented higher hydrophilic action than the others commercial AAs tested here. Therefore, it was not possible for the comparison in the same centrifugal testing experiment. AAs are mostly composed of hydrophilic surfactants. At a specific AA concentration, the emulsion breaks instantaneously as an unstable dispersion when the stirrer stops. This led to the formulation of unstable emulsions near the transitional phase inversion point. In such cases, when the system has HLD > 0, the tendency is the formation of W/O emulsion. As a hydrophilic surfactant compound, the AA should induce the system to change its HLD in the opposite way, i.e., toward HLD = 0. After this point, if more chemical is added, the system changes to HLD < 0. The HLD near zero corresponds to unstable emulsion. When HLD becomes negative (HLD < 0), the system tends to form O/W emulsion. The trend of pronounced emulsion instability at a certain AA concentration was similar for both commercial AAs and QAs. The formation of O/W emulsions was evaluated for higher contents of AA and QA. The emulsification protocol described in the Experimental Section did not favor O/W emulsion; however, when the protocol was inverted with regard to the phase addition, it was possible to form O/W emulsions. These O/W emulsions were not stable; however, they were less “unstable” than emulsions near balanced affinity of formulation (HLD = 0). Hydrate formation takes place at high-pressure conditions, where oil with a high content of lighter fractions influences emulsion formulation. Even though data reported here are only qualitative because of this, the behaviors observed are useful to recognize important patterns, mainly related to the AA impact on emulsion formulation. Dynamic Emulsion Inversion. According to the experiment 6 (Figure 7), considering the QA1 concentration of 0.025 mL of AA/100 mL of emulsion, this system presented an emulsion formulation that appears to be close to the balanced affinity between water and oil phases (near the transitional phase inversion region; HLD = 0). We pointed out that, maintaining all variables constant and increasing only the AA content, the W/O emulsion becomes less stable under a centrifugal field. If more AA is added, the system experiences a sudden decrease of stability (characteristic of a thermodynamic phase transition) and W/O emulsions are no longer formed. The emulsion formulation mentioned (experiment 6; 0.025 mL of AA/100 mL of emulsion; Figure 7) separated 80% of the
Figure 8. Mapping resulting from the emulsion inversion experiment. Replication 1 is compared to the conductometer measurement in the same experiment, and also replication 1 is compared to replicate 2. The horizontal axes correspond to the inversion route pathway. F
DOI: 10.1021/ef502815x Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels pronounced to the oil phase. At this point, this inversion was visually detected by the emulsion changing its color from brown to black. It is important to point out that the conductometer was not able to detect this transition. A second transition was observed from the “lipophilic unstable dispersion” to “hydrophilic unstable dispersion”. This transition represents the transitional inversion point of emulsion. The conductometer detected this transition. The wavenumber presented was of 6000 cm−1, but wavenumbers not related to the water peak signal, such as around 4500 or 8000 cm−1, presented good results. Finally, in the third transition, the “hydrophilic unstable dispersion” turned to O/W emulsion. This last transition was quite well-recognized by both instruments used: conductometer and NIR. The O/W emulsion formed was unstable but not as much as the dispersion formed in the transition region. The results in Figure 8 are shown in duplicate for NIR monitoring. Even though the reproducibility of the emulsion inversion experiment was not as good as for inversion of model systems,33 the emulsion transitions were observed successfully in accordance with conductometer monitoring. Besides providing information on the influence of AA on emulsion phase behavior, the emulsion inversion experiment demonstrated that it is possible to study the general phase behavior related to emulsion formulation by a dynamic experiment of emulsion inversion. In the present work, the dynamic experiment generated information about the physicochemical properties related to HLD, which are many times described in the literature by phase equilibrium experiments in simple model systems. Figure 9 shows the spectra collected during dynamic emulsion inversion. The use of NIR was especially important
Figure 10. Emulsion patterns observed during the inversion route in the WOR map (replication 1).
follows: (1) In certain concentrations, a substantial change occurs in formulation of the systems and the emulsions become unstable. (2) The transitions occurred within small AA concentration intervals, such as in the phase behavior of model emulsion systems. (3) In lower concentrations, the AAs slightly decreased the emulsion stability. It was still necessary long centrifugal testing to separate small amounts of water from these stable emulsions. (4) Anti-agglomeration usage at high water cuts should have the formulation carefully controlled to avoid the physicochemical state of the system turn into “hydrophilic” like and, therefore, have water as the preferred continuous phase. Thus, the concentration of AA should be maintained in a secure range to prevent emulsion transition. Ideally, other products that do not pose this risk should be designed to find the best AA formulation taking into account the results presented here. These emulsion patterns with hydrate formation will be experimented for the emulsion matrices observed here. Dynamic emulsion transitions from W/O emulsion to unstable balanced emulsion to subsequently O/W emulsion were found when a QA was added. Hence, it was possible to obtain information about the phase behavior related with emulsion formulation of a crude oil and aqueous phase system through dynamic experiments of emulsion inversion.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: tavares@eq ufrj.br. Notes
Figure 9. NIR spectra collected during the dynamic emulsion inversion.
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank CNPq, CAPES, ANP, Petrobras, and FAPERJ for scholarships and financial support. The authors thank Petrobras for the oil samples.
in the transition region, providing more information than the conductometer. Using these data, the inversion route for the transitions observed in replicate 1 is reploted in Figure 10. The different phase behaviors are clearly identified and shown in this figure.
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REFERENCES
(1) Kelland, M. A. Reviews history of the development of low dosage hydrate inhibitors. Energy Fuels 2006, 20, 825−847. (2) Frostman, L. M.; Przybylinski J. L. Successful applications of antiagglomerant hydrate inhibitors. Proceedings of the SPE International
CONCLUSION There is a meaningful interaction between AAs and waxy crude oil emulsion properties. The main conclusions are itemized as G
DOI: 10.1021/ef502815x Energy Fuels XXXX, XXX, XXX−XXX
Article
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DOI: 10.1021/ef502815x Energy Fuels XXXX, XXX, XXX−XXX
