Demulsification of Water-in-Crude Oil Emulsions by Microwave

Article pubs.acs.org/EF

Demulsification of Water-in-Crude Oil Emulsions by Microwave Radiation: Effect of Aging, Demulsifier Addition, and Selective Heating Bianca M. S. Ferreira,*,†,‡ Joaõ B. V. S. Ramalho,† and Elizabete F. Lucas‡ †

Petrobras Research Center, Avenida Horácio Macedo, 950, Cidade Universitária, CEP 21941-915, Rio de Janeiro, Rio de Janeiro (RJ), Brazil ‡ Laboratory of Macromolecules and Colloids for Petroleum Industry, Institute of Macromolecules, Federal University of Rio de Janeiro, Avenida Horácio Macedo, 2030, Ilha do Fundão, CEP 21941-598, Rio de Janeiro, Rio de Janeiro (RJ), Brazil ABSTRACT: Microwave radiation to promote the destabilization of water-in-crude oil petroleum emulsions is already an alternative technology for heating. Recent studies have suggested that microwave heating is more effective than conventional heating. This study assessed the following effects on the demulsification process: the aging of emulsions for the two types of heating (microwave and conventional), the time interval between microwave heating and the addition of a chemical demulsifier, and the time of microwave irradiation on the heating of petroleum and brine fluids. In addition, this study compared the efficiency of water separation by conventional heating and microwave heating regarding the (a) mean temperature of the emulsion and (b) temperature of water droplets. It was observed that water separation is less efficient for the two types of heating when the emulsion is subjected to aging. The efficiency of water separation using microwave heating is greater than with conventional heating when the mean temperature of the emulsion remains the same. However, they were equivalent when the temperatures of the water droplets are equal. This fact indicates that the advantage of selectively heating water droplets by microwave radiation is that the temperature of the treatment of emulsions can be reduced: the higher temperature that is located in region of interest (water droplets and the periphery) facilitates the drainage of the interfacial film and the stage of coalescence between the water droplets.

1. INTRODUCTION During petroleum production, there is a co-production of water, sediments, and gas. Because of the shear imposed by the flow of these fluids (water, oil, and gas) from the reservoir to the production units and the presence of surfactants in the composition of petroleum, water-in-crude oil (W/O) emulsions are formed.1−4 The stability of the emulsion and the increased viscosity significantly affect the capacity of the petroleum pumping systems. Therefore, in the production unit, the primary treatment of fluids is carried out, which consists of separating the oil, gas, and water phases. Currently, the concept of primary processing of petroleum is to separate water from oil by heating the fluid when it arrives at the production unit using heat exchangers (conventional heating) and adding a chemical demulsifying product (chemical treatment); subsequently, the actual separation takes place inside gravitational and electrostatic separator vessels. Various studies have been published about microwave radiation as an alternative heating technology with the aim of promoting the destabilization of W/O petroleum emulsions.5−22 These studies are based on the selective heating of the aqueous phase by the increased interaction of water with microwave radiation. The direct consequence of this good interaction is an increase of the thermal motion of the droplets and a reduction of viscosity in the peripheral region of the droplets because of the increase of the local temperature; this increases the rate of coalescence of the emulsified water droplets and the efficiency of demulsification. © 2012 American Chemical Society

Microwaves are non-ionizing electromagnetic waves in the frequency (f) range between 30 and 0.3 GHz and wavelength (λ) varying between 0.01 and 1 m.23 The effect of microwaves on materials is based on the reorganization of the charges of the polar molecules and free ions of dielectric materials, induced by the electric field of the radiation.24−26 This type of effect closely depends upon the frequency of the electrical field and the dielectric properties of the material to be heated, which can vary substantially (for example, the dielectric constants of water and petroleum are 76.727 and 2.1−2.6,28 respectively). The efficiency of the energy conversion of microwaves into heat is different for each material and depends upon the ratio between the loss factor (ε″), which quantifies the capacity of the material to store electromagnetic energy, and the dielectric permittivity (ε′), which determines the ability of the material to convert the energy stored into heat.23,29,30 The first studies were carried out using household equipment, and they showed that microwave heating was more efficient than conventional heating.5−7 It was found that the higher the content of emulsified water, the lower the irradiation time8 and that the rate of demulsification and the efficiency of water separation increased with the increased size of water droplets that were dispersed in the continuous oil phase and with the increasing concentration of electrolytes in the aqueous phase.9 Results from both model emulsions14 and petroleum Received: January 27, 2012 Revised: December 19, 2012 Published: December 19, 2012 615

dx.doi.org/10.1021/ef301110m | Energy Fuels 2013, 27, 615−621

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Table 1. Final Temperature of the Samples after Microwave Irradiation final temperature of the sample (°C) reading point (mL)

heating time (s)

1

2

3

average

1

2

3

average

without Teflon Insulation 67.0 63.0 56.5

without Homogenization 69.5 67.5 64.5 63.0 57.0 57.0

80 50 15

70.0 64.0 57.,0


80 50 15

60.5 55.0 50.0


80 50 15

58.0 54.0 48.0


80 50 15

52.0 49.5 44.5


80 50 15

51.5 48.0 44.0


80 50 15

42.5 41.0 39.5


80 50 15

43.0 41.5 40.5


80 50 15

31.0 30.5 30.0

without Homogenization 315 32.0 31.0 31.5 30.0 30.0

31.0 30.0 29.0


80 50 15 50

40

30

20

10 80 50 15

emulsions17 show that the heating time necessary to promote the phase separation is significantly lower when using microwaves. The discovery that the efficiency of demulsification via microwaves is related to the power of the radiation, to the irradiation time, and to the initial temperature of the emulsion has been observed both in batch experiments18 and under conditions of continuous flow,19 and the heating rate is the key factor in the process. It is thought that any compositional or

68.0 68.0 63.5 67.0 56.8 67.0 with Teflon Insulation 68.7 67.5 62.1 67.0 55.5 67.0 without Teflon Insulation 60.0 59.0 55.7 58.0 49.7 59.5 with Teflon Insulation 58.8 59.5 54.8 61.0 49.1 57.0 without Teflon Insulation 49.8 51.0 47.5 50.5 43.5 50.5 with Teflon Insulation 51.2 54.5 47.8 54.5 44.7 54.5 without Teflon Insulation 42.3 42.0 41.0 42.5 39.5 42.5 with Teflon Insulation 44.0 44.5 41.7 44.5 40.7 44.0 without Teflon Insulation 31.5 31.0 31.0 31.0 30.0 31.0 with Teflon Insulation 31.5 30.8 29.8

30.5 30.5 30.5

with Homogenization 65.0 65.0 65.0 64.5 65.0 64.5

66.0 65.5 65.5


69.5 68.0 68.0


60.0 59.0 60.0


59.8 60.0 58.1


50.5 51.0 50.5


53.8 53.8 54.1


42.3 42.5 42.7


43.8 43.8 43.7


31.3 31.3 31.0


30.7 30.7 30.5

operational condition that accentuates the absorption of microwave energy by the sample encourages demulsification, except when such a condition also contributes to the stability of the emulsion.20−22 This study aims to extend the current knowledge by specifically focusing on the influence of aging, the addition time of the demulsifier, and the selective heating on the 616


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Table 2. Final Temperatures of the Oil Phase (Oil) and the Aqueous Phase (Brine) final temperature of the sample (°C) without Teflon insulation reading point (mL)

initial temperature of the sample (°C)

40 15 40 15 40 15 40 15

irradiation time (s)

18 24 40

18 24 40

1

2

3

average

24.0 23.5 24.0 24.0

23.5 23.5 24.5 24.5

24.0 23.5 24.5 25.0

38.5 40.0 58.5 60.0

39.5 39.0 59.0 59.5

40.0 38.5 59.5 59.0

with Teflon insulation 1

Petroleum 23.6 24.0 23.4 24.0 24.3 24.0 24.5 24.0 Brine 39.3 39.0 39.2 38.5 59.0 59.0 59.5 60.0

2

3

average

24.0 24.0 24.0 24.5

24.0 24.0 24.0 24.0

24.0 23.9 24.0 24.2

39.5 38.5 59.0 59.0

39.0 40.0 58.5 59.5

39.2 39.0 58.8 59.5

samples was taken at two different points of the graduated tube (40 and 15 mL). The mean of three tests was used as the final result. 2.2.5. Gravitational Separation via Microwave and Conventional Heating. Testing of gravitational separation of petroleum emulsions was carried out in graduated tubes.3 The microwave heating was evaluated at temperatures of 40 and 60 °C with exposure times of 18 and 40 s, respectively. With conventional heating (in a New Ethics thermostatic bath), temperatures of 40, 51, 60, and 85 °C were evaluated with a mean heating time of 30 min. Demulsifier dosages of 20, 30, 40, and 60 ppm were used. Immediately after the emulsion reached the desired temperature, the demulsifier product was added and the system was homogenized for 1 min. The percentage of water separation was visually quantified as a function of time. 2.2.6. Influence of Emulsion Aging on the Efficiency of Water Separation Using Conventional Heating. Gravitational separation tests were conducted with emulsion that was preheated to a temperature of 51 °C (temperature of water droplets at an irradiation time of 18 s), followed by the addition of the demulsifier at a concentration of 30 ppm. The separation of water was measured over time. 2.2.7. Influence of Emulsion Aging on the Efficiency of Water Separation via Microwave Heating. Gravitational separation tests were conducted with samples that were heated in a microwave and kept in a thermostatic bath at a test temperature (40 and 60 °C) for 30 min. Then, the demulsifier was added, and the percentage of water separation was visually quantified over time. The concentrations of demulsifier that were assessed were 20, 30, 40, and 60 ppm. 2.2.8. Influence of the Addition Time of the Additive on the Efficiency of Water−Oil Separation with Microwave Heating. In this study, the following variables were assessed: the temperature of heating of emulsions via microwave (40 and 60 °C), the dosage of the demulsifier (20, 30, 40, and 60 ppm), and the time of addition of the demulsifier after the emulsion reached the desired temperature (immediate, 1, 5, 10, and 15 min). When the addition of the additive was not immediate, the samples were transferred to a thermostatic bath and kept at the test temperature. Finally, the separation of water as a function of time was quantified.

demulsification process of W/O emulsions using microwave radiation.

2. EXPERIMENTAL SECTION 2.1. Materials. The Brazilian petroleum, supplied by Petrobras, had an American Petroleum Institute (API) gravity of 28.7° and saturates, aromatics, resins, and asphaltenes (SARA) composition of 54, 24, 22, and 0.5 wt %, respectively. The temperature required to achieve viscosity of 16 cSt was 42 °C. The demulsifying surfactant, supplied by Clariant S.A. and based on a co-polymer of poly(ethylene oxide-b-propylene oxide), had a number average molecular weight of 2330 g/mol, dispersity of 4.9, and ethylene oxide (EO)/propylene oxide (PO) ratio of 0.43. Sodium chloride (NaCl) was purchased from Vetec Quimica Fina, Brazil. 2.2. Methods. 2.2.1. Preparation of Petroleum Emulsions. Synthetic emulsions were prepared from petroleum containing 40.0% (v/v) aqueous solution at 50 g/L NaCl, at room temperature, using a Polytron PT 3100 homogenizer, at 8000 rpm for 3 min. The aqueous phase content was chosen in function of the best results obtained for water separation using microwave heating.20 The NaCl concentration is related to the salt concentration in several Brazilian oil fields. 2.2.2. Microwave Operational Conditions. A domestic Brastemp (model Frost Inox) microwave oven was used at maximum power (800 W), to ensure a constant irradiation over time, at 2450 MHz. The rotating tray of the oven was used during the tests. The sample bottle was placed in the middle of the tray, the region indicated as being subject to the greatest microwave radiation. The glass bottles, especially made for performing gravitational bottle tests, are conical, transparent, and volume-graduated, with a screw cap. 2.2.3. Determination of the Microwave Heating Period. The main objective of this test was to verify the exposure time of emulsions to microwave radiation that is required to reach temperatures of 40 and 60 °C. Aliquots of 100 mL of emulsion were transferred to graduated tubes and evaluated at exposure times of 50, 40, 30, 20, and 10 s. The tests were carried out with and without Teflon insulation and with and without homogenization of the emulsion after heating. The final temperatures of the samples were recorded at three different points of the graduated tube (80, 50, and 15 mL). All tests were triplicated, and the mean of the readings was used as the final result. The experimental error was ±2 mL. 2.2.4. Determination of the Temperatures of the Oil and Aqueous Phases under Microwave Heating. The purpose of this test was to quantify the heating of the oil and aqueous phases, individually, when subjected to the same time of exposure to microwave radiation as the synthetic emulsion. The tests with petroleum were carried out with 51.46 g of material, and the tests with the aqueous phase were carried out with 40.13 g of brine. These tests, evaluated at exposure times of 18 and 40 s, were also carried out with and without Teflon insulation. The final temperature of the

3. RESULTS AND DISCUSSION The temperature of 40 °C was selected because it is standard procedure of Petrobras to carry out gravitational separation tests under ∼16 cSt kinematic viscosity conditions. 3.1. Effect of the Time of Microwave Irradiation on the Final Temperature of the Synthetic Emulsion. The final temperature of the synthetic petroleum emulsion was measured after a certain time of exposure to microwave radiation. The study tested the influence of the use of a Teflon chamber (which was used to prevent the loss of heat to the external environment), the effects of homogenization, and the position of measuring the temperature inside the tube that 617


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with TSF = 51 °C. Case II, irradiation time of 40 s

contained the emulsion. The values considered for analysis were taken from the mean of three measurements. The results in Table 1 show that (i) in all cases, there is a temperature gradient along the tube when the test is carried out without homogenization, which highlights that the sample needs to have a homogenization stage, (ii) the difference in the temperature between the heated samples with and without the Teflon compartment is not very significant; i.e., the heat loss from the heated sample to the environment is not significant, (iii) as expected, the final temperatures of the samples increase with an increasing irradiation time, and (iv) when the values of the mean temperature were plotted, with homogenization and without the Teflon compartment, as a function of the irradiation time, it was found that it takes 40 s of irradiation to reach the final temperature of the sample of 60 °C and 18 s of irradiation to reach the final temperature of the sample of 40 °C. 3.2. Effect of Microwave Heating on Petroleum and Brine. The aim of this stage of the study was to determine the values of the final temperature separately for the oil and aqueous phases, when subjected to previously determined times of microwave irradiation (18 and 40 s). Under these conditions, the synthetic oil emulsion reached temperatures of 40 and 60 °C, respectively. The results in Table 2 confirm that there was no observable influence of the use of a Teflon compartment on the final temperatures of the systems that were evaluated. Another important observation is that only the aqueous phase underwent a temperature rise when subjected to microwave radiation, and this increase was a function of the irradiation time, as observed for the synthetic emulsion. Moreover, there is clearly a loss of heat to the environment because of the heating of the brine: calculations of energy balance show that, after 18 s of heating, the water droplets should reach a temperature of 51 °C and, after 40 s of heating, the water droplets should reach a temperature of 85 °C. These values of 51 and 85 °C will be used later for gravitational separation testing with conventional heating and will be compared to tests with microwave heating at temperatures of 40 and 60 °C, respectively. The energy balance calculations were based on the heattransfer mechanism, because when an oil-in-water petroleum emulsion is heated by microwaves, the brine is heated and heat is transferred from the brine to the oil phase; i.e., the mean final temperature of an emulsion is the result of this heat transfer between the fluids. The temperature that was reached by the water drops in the emulsion was calculated for irradiation times of 18 and 40 s, using eq 1

40.13 × 0.95 (TAF − 22) + 51.46 × 0.51 (24 − 22) = 40.13 × 0.95 (60 − 22) + 51.46 × 0.51 (60 − 22)

with TSF = 85 °C. 3.3. Comparison between the Performances of the Gravitational Separation of the Emulsion Using Conventional and Microwave Heating on the Mean Temperature of the Emulsion. The comparative results of separation efficiency, using varying dosages of demulsifier, with conventional and microwave heating, are shown in Figures 1 and 2 at temperatures of 40 and 60 °C, respectively. It is important to highlight that the emulsions without demulsifier do not exhibit any phase separation at the essay time.

Figure 1. Comparison of the performances of conventional (bath) and microwave (MW) heating in synthetic petroleum emulsions at a temperature of 40 °C (51 °C) and demulsifier doses of (a) 20 ppm, (b) 30 ppm, (c) 40 ppm, and (d) 60 ppm.

The results in Figure 1, for the test temperature of 40 °C, show that the maximum efficiency of gravitational separation is achieved in much shorter times with microwave heating than with conventional heating for all of the demulsifier dosages tested. Increasing the dosage of additive increases the process

MSCp (TSF − TSI) + mOCp (TOF − TOI) S

O

= mSCp (TE − TSI) + mOCp (TE − TOI) S

O

(1)

where MS is the mass of brine, CpS is the specific heat of brine, TSF is the final temperature of brine, TSI is the initial temperature of brine, mO is the mass of oil, CpO is the specific heat of oil, TOF is the final temperature of the oil, TOI is the initial temperature of the oil, and TE is the mean temperature of the emulsion. Case I, irradiation time of 18 s Figure 2. Comparison of the performances of conventional (bath) and microwave (MW) heating in synthetic petroleum emulsions at a temperature of 60 °C (85 °C) and demulsifier doses of (a) 20 ppm, (b) 30 ppm, (c) 40 ppm, and (d) 60 ppm.

40.13 × 0.95 (TAF − 22) + 51.46 × 0.51 (24 − 22) = 40.13 × 0.95 (40 − 22) + 51.46 × 0.51 (40 − 22) 618


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aqueous phase reached 51 °C. Thus, the results obtained with microwave heating at 40 °C and conventional heating at 51 °C were compared. This was also carried out for the time of heating in the microwave for 40 s. Figure 1 shows that the separation efficiency percentage with conventional heating at 51 °C is greater than that observed at 40 °C and lower than that observed at 60 °C (Figure 2). This result is consistent with the behavior of better performance with an increasing temperature. The curves obtained with conventional heating at 51 °C (Figure 1) are closer to the curves obtained with microwave heating than those obtained with the same temperature, and this proximity is accentuated for higher doses of demulsifier; at 60 ppm of additive, the two curves are very similar (Figure 1d). Similar behavior can be seen in Figure 2; in this case, at the higher temperature, the performance with conventional heating (85 °C) is equal to the performance with microwave heating (60 °C), at a dosage of 60 ppm of added demulsifier. The expected outcome in all trials was that the water separation performance via conventional heating at the water droplets temperature would be equivalent to that of microwave heating on the emulsion temperature, because in a W/O emulsion, water is the substance that heats under irradiation and that transfers heat to the oil. Thus, when the temperatures that the water droplets reach are equalized, by either microwave or conventional heating, the performance should be equivalent. One possible explanation for this unexpected result could be the aging effect of the emulsion during the performance test via conventional heating, because the sample has to remain in a thermostatic bath for 30 min until the test temperature is reached and the demulsifier is added. The aging strongly affects the emulsion phase separation process by changing the characteristics of the interfacial film of the emulsion.31−38 3.5. Effect of Aging on the Water Separation of Emulsions in Conventional Heating. To investigate the assumption of the effect of aging on the performance results of conventional heating, further tests were carried out in which the fluids (petroleum and brine) were preheated to the test temperature, followed by the preparation of synthetic emulsion. After preparation, the sample was transferred to a thermostatic bath and the demulsifier was added. This test was conducted with microwave heating at 40 °C (mean temperature reached by the emulsion with an irradiation time of 18 s) and conventional heating at 51 °C (temperature that the water droplets reach after 18 s of microwave heating) and 30 ppm dosage of demulsifier. Figure 3 shows the gravitational separation efficiency of the emulsions for the two types of heating without the effect of aging. Comparing this result to the result in Figure 1b shows

efficiency, and maximum efficiency is achieved with 40 ppm of additive for microwave heating, whereas with conventional heating, there was no ideal maximum dose, at the concentrations used. It is possible that a further increase in dosage of the demulsifier with conventional heating would lead to a performance comparable to that observed with microwave heating at low dosages of additive. With microwave heating, at a dosage of 40 ppm of demulsifier, 100% efficiency of separation was achieved in about 9 min. These results show that the greater performance of microwave heating on the gravitational separation results in a lower consumption of chemical demulsifier. This may be explained by the fact that, because of the pronounced dielectric properties of water (it interacts well with microwave radiation), there is a superior and selective heating of water droplets that are dispersed in emulsions. This increased heating of water droplets and peripheral region reduces the viscosity of the interfacial film that surrounds the droplets; this facilitates the action of the demulsifier on the destabilization of emulsions and, consequently, accelerates the water coalescence and separation phase. Moreover, because microwave heating is much faster than conventional heating, there will be greater diffusivity of the demulsifier in samples heated by microwave; thus, the interface region will be reached more quickly, resulting in a synergy with the effect of higher localized temperature at the water droplets. The results in Figure 2 for the test temperature of 60 °C clearly show the performance with microwave heating improves as the dosage of additive increases; however, the variations of efficiency with the conventional heating are more significant. The performance at 60 °C is better than at 40 °C (Figures 1 and 2). At 40 ppm of demulsifier and 60 °C, 100% efficiency of separation is achieved in about 3 min compared to 9 min at 40 °C. This is because, at higher temperatures, the viscosity of the continuous phase is lower; thus, the system has greater mobility, and there are more collisions between the water droplets. In addition, at higher temperatures, the demulsifier diffusivity is faster; it therefore acts on the interfacial film for a shorter period of time during which the value of the elastic component of this film (which greatly affects the stability of an emulsion) is not significant. This was an expected result, as already discussed in the literature.18 3.4. Comparison between the Performances of Gravitational Separation of the Emulsion with Conventional Heating on the Temperature of Water Droplets and with Microwave Heating on the Mean Temperature of the Emulsion. Figure 1 also shows the comparative results between the performances of conventional heating at 51 °C (temperature that the water droplets reach with 18 s of microwave irradiation) and microwave heating at 40 °C (mean temperature reached by emulsion with 18 s of microwave heating) at varying doses of demulsifier. Figure 2 also shows the same comparative study with conventional heating at 85 °C (the temperature that the water droplets reach with 40 s of microwave heating) and microwave heating at 60 °C (mean temperature reached by the emulsion with 40 s of microwave heating). The objective of this stage of the study was to compare the behavior of the gravitational separation of the systems heated by the two techniques under study, causing the aqueous phase, in both cases, to reach the same temperature. That is, it was observed that, by heating the emulsion with microwaves for 18 s, the temperature of the emulsion reached 40 °C and the

Figure 3. Efficiency of gravitational separation of synthetic petroleum emulsions without the effect of aging, at temperatures of 40 and 51 °C and at a dosage of 30 ppm of demulsifier, using conventional (bath) and microwave (MW) heating. 619


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that there is an effect of aging of the emulsion and that it reduces the separation performance of water via conventional heating. When the effect of aging is eliminated, the performances of the two types of heating using the same temperature condition of the water droplets were equivalent, which confirms the hypothesis. 3.6. Effect of Aging on the Water Separation of Emulsions with Microwave Heating. Once it had been observed that the effect of aging affected the performance of the water separation in tests with conventional heating, studies were conducted to verify this impact in tests with microwave heating. For this purpose, the sample was heated in a microwave oven and then transferred to the thermostatic bath for 30 min before adding the demulsifier. The performances were then compared (microwave and conventional). This test was carried out at all doses of demulsifier. Figure 4 shows the results of efficiency of gravitational separation of emulsions with 40 ppm of demulsifier heated to

Figure 5. Efficiency of gravitational separation of synthetic petroleum emulsions, with microwave heating, as a function of the addition time of demulsifier, for different temperatures and different dosages of additive: (a) 40 °C and 20 ppm, (b) 40 °C and 60 ppm, (c) 60 °C and 20 ppm, and (d) 60 °C and 60 ppm.

only under more favorable demulsification conditions (high additive dose and temperature) is the effect of addition time of the additive less significant. This behavior can also be related to the effect of emulsion aging.

4. CONCLUSION The efficiency of water separation is reduced for both microwave and conventional heating when the emulsion is subjected to the aging process: the performance with microwave radiation is similar to that of conventional heating. However, because the rate of microwave heating is much higher than that of the conventional heating, the aging effect is minimized. Another factor that reduces the water separation performance is an increase in the time interval between the microwave radiation heating of the sample and the addition of the demulsifier product. This is not true when high concentrations of demulsifier were added to the sample. The petroleum heating is not significant when subjected to microwave radiation at 800 W and 2450 MHz. The water separation efficiency with microwave heating is higher than that with conventional heating when comparing systems at the same mean temperature of the emulsion. However, the performances are equivalent when the temperature of the water droplets are equal, which indicates that the advantage of selective heating of water droplets by microwave radiation is that it reduces the temperature of the treatment of emulsions, because the higher temperature of the region of interest (water droplets and periphery) facilitates the drainage of the interfacial film and the step of coalescence between the water droplets.

Figure 4. Efficiency of gravitational separation of synthetic petroleum emulsions under the influence of aging at a temperature of 60 °C and at a dosage of 60 ppm of demulsifier, using conventional (bath) and microwave (MW) heating.

60 °C. Curves obtained with microwave heating and aging are compared to the conventional heating curve. The results show that the aging of the emulsion also reduces the water separation performance with microwave heating, making it behave almost the same as with conventional heating. This behavior is also observed at a temperature of 40 °C and for all other demulsifier dosages (20, 30, and 60 ppm). It is important to highlight that one advantage of microwave heating is that it has a high rate of heating; thus, during the separation process, the effect of the aging time on the sample is minimized. 3.7. Effect of the Addition Time of Demulsifier on the Water Separation Efficiency via Microwave. The study of the effect of the addition time of demulsifier on the efficiency of emulsion phase separation was carried out at dosages of 20, 30, 40, and 60 ppm of additive and at temperatures of 40 and 60 °C. The times that were evaluated were immediate addition and 1, 5, 10, and 15 min; i.e., after reaching the desired temperature with microwave heating, the emulsions were left in a thermostatic bath during the pre-established period before the addition of the demulsifier. Figure 5 shows only the results for heating of 40 and 60 °C, at lower (20 ppm) and higher (60 ppm) doses of the demulsifier. It can be seen (Figure 5a) that gravitational separation efficiency decreases with the increase of time of addition of the additive; however, this effect tends to disappear for higher concentrations of additive (Figure 5b). The same behavior is observed for the temperature of 60 °C (panels c and d of Figure 5). When one compares the same dosage of additive (20 ppm) at different temperatures (panels a and c of Figure 5), the effect of addition time is less pronounced at higher temperatures. It can be concluded that

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Petrobras and the Brazilian Council for Scientific and Technological Development (CNPq) for their support of this study. 620


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