The mechanism of ultrasonic and chemical synergistic demulsification
JinbiaoGao1,2,3
ShuailingWang1
HaiboZhao1,2
YushenWu3
MiZhang4✉Emailï¿¿17884835407@139.com
QingheGao5
1Earth Science CollegeNortheast Petroleum University163318DaqingChina
2Exploration and Development Research Institute of PetroChinaDaqing Oil Field Co Ltd163712DaqingChina
3State Key Laboratory of Acoustics and Marine Information, Institute of AcousticsChinese Academy of Sciences100190BeijingChina
4School of Computer Science and Engineering, School of Artificial Intelligence)Chongqing University of Science and Technology401331ChongqingChina
5Heilongjiang Provincial Key Laboratory of Oilfield Applied Chemistry and TechnologyDaqing Normal University163712DaqingChina
Jinbiao Gao1, 2, 3, Shuailing Wang1, Haibo Zhao1, 2, Yushen Wu3, Mi Zhang4, *, Qinghe Gao5, *
Corresponding author email: 17884835407@139.com
1Earth Science College, Northeast Petroleum University, Daqing, 163318, China
2 Exploration and Development Research Institute of PetroChina, Daqing Oil Field Co Ltd, Daqing, 163712, China
3State Key Laboratory of Acoustics and Marine Information, Institute of Acoustics, Chinese Academy of Sciences, Beijing, 100190, China
4School of Computer Science and Engineering(School of Artificial Intelligence), Chongqing University of Science and Technology, Chongqing, 401331, China
5Heilongjiang Provincial Key Laboratory of Oilfield Applied Chemistry and Technology, Daqing Normal University, Daqing, 163712, China
Abstract
The complex and stable emulsion formed during tertiary oil recovery can significantly reduce oil recovery efficiency, making effective oil-water separation a critical challenge. In this study, a novel demulsifier was synthesized for emulsions with high wax content. Subsequently synergistic experiments were conducted in combination with ultrasonic treatment to evaluate and compare their combined effectiveness. The mechanism of oil-water separation was ultimately elucidated through a comprehensive comparison of interfacial tension, viscosity, and microscopic morphology analyses. The results indicate that when the demulsifier is used alone, the dehydration rate of oil samples exhibits an “N”-shaped change with increasing temperature under different demulsifier concentrations, and the maximum dehydration rate is 31.33%. When ultrasound and the demulsifier are used in combination, given a constant ultrasound power, the dehydration rate increases and then decreases with the increasing concentration of the demulsifier, and the dehydration rate can reach 45.56%. The demulsifier reduces the viscosity of emulsion and disrupts the molecular structure of wax crystals. Meanwhile, ultrasonic irradiation generates high temperature, high pressure, shock wave, and micro-jet, which enhance the dispersion of demulsifier molecules and accelerate collisions between droplets. The synergistic effect of these two mechanisms can amplify the demulsification effect, outweighing the emulsification effect. This ultimately lowers the interfacial tension at the oil-water interface, thereby facilitating more effective separation of oil and water.
Keywords
Acoustic cavitation
Ultrasound
Demulsifier
Demulsification
Interfacial tension
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1. Introduction
During production, crude oil typically mixes with brine to form stable water-in-oil (W/O) emulsions. This issue is exacerbated during tertiary oil recovery, where the extentsive use of surfactants (or chemical agents) may significantly increase the stability of emulsions, rendering them extremely difficult, if not impossible to demulsify. Thus, devoping effective and efficient demulsification methods is essential for maximizing the utilization efficiency of emulsions[1–4]. Currently, commonly used demulsification methods include electric field treatment, biological treatment, and centrifugal treatment. However, each method faces specific challenges. For instance, electric field treatment requires high-quality of extracted crude oil. Biological treatment faces difficulties in cultivating and selecting the bacterial colonies. The universality is limited due to the specific requirements of microbial strains for different oil samples and the lengthy process of screening for target strains[5–8].
Compared with the aforementioned methods, ultrasonic treatment offers several advantages including low energy consumption, high economic efficiency, broad applicability, and minimal environmental pollution[9–11]. Whether used alone or in combination with other methods, ultrasound has demonstrated significant effectiveness in demulsifying oil-water emulsion. However, a unified consensus on the precise mechanism of ultrasonic demulsification has yet to be reached[4, 12–17]. Antes et al. believed that the mechanism of ultrasonic demulsification is attributed to the turbulence generated by the nonlinear effect of ultrasound. When the intensity of this turbulence reaches a certain threshold, it disrupts the oil-water interfacial film, thereby facilitating demulsification[2]. However, some researchers propose that the intense energy generated by ultrasound disrupts the barrier between the droplets without breaking the droplets themselves. This action facilitates the settling of the droplets, thereby inducing a dewatering effect in the emulsion[16]. Luo et al. concluded that low-frequency ultrasound is particularly effective in for demulsifying oil-water emulsions with low viscosity and high interfacial strength. They also found that increasing energy density to a certain level can enhance cavitation, thereby promoting the demulsification process[15]. Some other researchers have attributed the decrease in dehydration rate with increasing sound intensity to the cavitation threshold. Specifically, once the cavitation threshold is exceeded, ultrasound can begin to re-emulsify the emulsion[18, 19], thereby reducing the dehydration rate.
In addition, chemical demulsification is more widely utilized as a traditional method[20–22]. Ye et al. treated W/O emulsions by synthesizing amphiphilic and interfacially active baryon ion liquids, achieving demulsification rates of 99.89% and 99.79%, respectively[23]. Hailan et al. designed an adsorbent using recycled low-density polyethylene, which now demonstrates excellent performance in treating oil-water emulsions. This method is not only cost-effective but also environmentally friendly by reducing pollution[24]. Amiri et al. synthesized magnetic cellulose nanocrystals through a simple method, and empirically demonstrated that this chemical emulsion breaker proves highly effective in treating oil-water emulsions[25].
With the increasing integration of interdisciplinary research, the synergistic effect of ultrasound and chemical demulsifiers in demulsifying oil-water emulsions holds great promise for practical applications. Yi et al. investigated the individual and combined effects of ultrasound and chemical demulsifiers on oil-water emulsions at different temperatures. The results revealed that the synergistic effect of ultrasound and chemical demulsifiers was the best[26]. Romanova et al. showed that the combined use of ultrasound with a power of 1 kW power and aluminum nitride nanopowder (AIN) can destroy over 99% of stable W/O emulsions. This study highlights the significant potential of synergistic treatment using ultrasonic irradiation and nanoreagents for effective demulsification[4].
However, these methods face specific challenges. For instance, ultrasonic treatment lacks clear boundaries between demulsification and emulsification, and its underlying mechanism has yet to reach a unified consensus. The chemical method exhibits a high degree of specificity in selecting demulsifiers for different emulsions[20–26]. Moreover, the mechanism underlying the synergy between these two methods remains unclear. Therefore, in this study, a new demulsifier was synthesized by analyzing the impact of wax content on the strength of the oil-water interfacial film. The oil-water emulsion was then synergistically treated with ultrasonic irradiation. The mechanism of demulsification was elucidated through comprehensive comparisons.
2. Method
2.1. Materials
Crude oil sample: Provided by PetroChina Daqing Oilfield Co., Ltd. The composition of the sample is detailed in Table 1. At 50°C, its viscosity and density were 52.308 mPa⋅s and 0.8646 g/cm3, respectively. Petroleum ether (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 678–2002[27]. Toluene (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 684–1999[28]. Anhydrous ethanol (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 678–2023[29].
Type | Wax | Asphaltene | Resin | Saturated hydrocarbon | Aromatic hydrocarbon |
|---|---|---|---|---|---|
Content(%) | 29.75 | 0.3 | 5.6 | 72.3 | 21.8 |
2.2. Instruments
LC-JY92-IIN Ultrasonic Cell Breaker: Shanghai Li-Chen Technology Co., Ltd. SY-1 Constant Temperature Water Bath: Tianjin ONAO Instrument Co., Ltd. PT-3100 Vertical Disperser: Baochuang Science & Technology Co., Ltd. FRD-6C Scientific Research-grade Trinocular Inverted Fluorescence Microscope: SGI Instruments Co. Model UW4200H Electronic Analytical Balance: Shimadzu Enterprise Management (China) Co., Ltd. Model SVM3000 Kinematic Viscometer/Dynamic Viscometer: Suzhou Sainz Instrument Co., Ltd. Model TX500C Rotary Droplet Interfacial Tension Meter: Shanghai Solon Information Technology Co. LDJ2050M Centrifuge: Hunan Xiangyi Laboratory Instrument Development Co., Ltd. Zeta Potentiostat: Beijing Orinoco Instruments. SY-40 Graphite Disintegrator: Feiyue Instrument Co., Ltd. FTIR-7600 Fourier Transform Infrared Spectrometer: Tianheng Instrument Co.
2.3. Experimental process
2.3.1. Wax extraction
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As shown in Table 1, the oil samples have a relatively high wax content, which may be one of the primary factors contributing to the difficulty in oil-water separation. Therefore, this study focuses on analyzing the impact of wax. The wax extraction process is as follows: Initially, a small amount of crude oil sample was dissolved in petroleum ether. The resulting crude oil-petroleum ether solution is then passed through a chromatographic column packed with a mixture of silica gel: silica gel-white clay (8:1), and silica gel in a ratio of 1:8:1. Subsequently, the column was continuously eluted with petroleum ether. The wax-petroleum ether solution was collected once the effluent from the column became clear. Afterwards, the container holding the wax-petroleum ether solution was placed in a graphite evaporator and heated until only a small amount of liquid remained at the bottom. Then, 10 ml of ice-cold anhydrous ethanol was added, and the mixture was refrigerated 12 h. Next, the wax-anhydrous ethanol solution was filtered through a funnel lined with degreased cotton. Meanwhile, the rim of the funnel was repeatedly rinsed with hot petroleum ether to ensure complete transfer of the wax. Finally, the collected wax-petroleum ether solution was evaporated to dryness to obtain the wax.2.3.2. Demulsifier synthesis
Aiming to address the oil-water separation problem in with high-wax-content emulsion, this study synthesized a novel demulsifier. The synthetic route is shown in Fig. 1, and is described as follows: Aromatic polyether (octylphenol polyether) and acrylic acid were used as raw materials to synthesize the esterification intermediates denoted as EOP-X, through an esterification reaction. Then the esterification intermediates are subjected to the polymerization reaction to synthesize the final product denoted as PEOP-X.
Fig. 1
The synthesis route of polyether ester demulsifier
2.3.3. Demulsifier interface experiments
To determine whether the demulsifier developed in this study would impact the interfacial tension of liquids with varying wax contents, simulated oils containing different amounts of wax-toluene were prepared in this section, with wax contents of 0%, 10%, 20%, and 30%, respectively. Then, interfacial tensiometers were used to measure the interfacial tension values between the wax-toluene-containing simulated oils (with varying wax contents) and water. Next, the demulsifier-toluene solution was added to the group of wax-toluene-containing simulated oils that exhibited the lowest interfacial tension, resulting in demulsifier concentrations of 25, 50, 75, and 100 ppm in the mixed solutions, respectively. Finally, the interfacial tension values of the wax-toluene-containing simulated oils with varying concentrations of the demulsifier were measured using an interfacial tensiometer, with ultrapure water serving as the reference medium.
2.3.4. Emulsion preparation
To ensure the homogeneity of samples from different layers, the original crude oil samples were pre-treated before the experiment. Specifically, the aqueous crude oil sample was first centrifuged at 11000 r/min for 20 mins to obtain the anhydrous crude oil sample. Then the anhydrous crude oil sample and ultrapure water were preheated in a water bath for over 10 mins. Finally, the anhydrous crude oil and ultrapure water were mixed at a volume ratio of 7:3 and homogenized using a stirrer for 5 mins, resulting in an oil-water emulsion with a water content of 30%.
2.3.5. Demulsifier bottle test demonstration
To investigate the demulsifying effect of the demulsifier, the freshly prepared oil-water emulsion with a 30% water content was first placed into a thermostatic water bath. Then, four static sedimentation tubes (100 ml) were numbered separately (25, 50, 75, 100 ppm). Next, the desired demulsifier-toluene solution (with a demulsifier concentration of 2500 ppm) was added to each static sedimentation tube. After adding 30 ml of the oil-water emulsion to each tube, the resulting concentration of demulsifier in the mixed solution was 25, 50, 75, and 100 ppm, respectively. Finally, the static sedimentation tube was shaken approximately 100 times and then placed into a constant-temperature water bath for static sedimentation experiments. Data were recorded every 10 mins until no further changes occurred. The dehydration rate was calculated by the following formula:
Where 
denotes the dehydration rate, %; V1 denotes the volume of water removed, ml; and V0 denotes the initial volume of water in the oil-water emulsion, ml.
Additionally, to analyze the effect of demulsifier on the viscosity of oil-water emulsions, the viscosity of emulsions with demulsifier concentrations of 0, 25, 50, 75, and 100 ppm was measured as a function of temperature using a viscometer.
2.3.6. Synergistic experiment of demulsifier and ultrasound
To investigate the synergistic effect of ultrasound and demulsifier on the demulsification of oil-water emulsions, the demulsifier-toluene solution (with a demulsifier concentration of 2500 ppm) was added into four separate 50 ml beakers. After adding 30 ml of oil-water emulsion to each breaker, the resulting concentrations of demulsifier in the mixed solutions were 25, 50, 75 and 100 ppm, respectively. Then the ultrasonic probe was immersed approximately 2 cm below the liquid surface and applied to the oil-water emulsion under various ultrasonic power settings (with a total power of 650 W). Finally, the oil-water emulsion, after being subjected to ultrasonic treatment for 5 mins, was transferred into a static sedimentation tube for evaluation of the demulsification effect.
2.3.7. Microscopic morphology characterization
A polarized light microscope was used to examine the microscopic morphology of oil samples. Specifically, observations were made before and after treatment with various concentrations of demulsifiers, as well as before and after exposure to different ultrasonic power levels. This approach was used to elucidate the mechanisms underlying emulsion demulsification and dehydration.
3. Results and discussion
3.1. Interfacial tension analysis of waxed toluene simulating oil
Figure 2 presents the changes in interfacial tension over time for simulated oils with varying wax contents. The blue line indicates the interfacial tension variation for the toluene solution alone, which initially has the highest interfacial tension and tends to decrease over time. The gray and red lines represent the changes in interfacial tension for wax-containing toluene solutions with 10% and 30% wax content, respectively. In the initial 8 minutes, the difference in interfacial tension among the solutions are not pronounced. However, these differences gradually widen over time, with all showing a downward trend. The green line represents the interfacial tension change for the 20% waxed toluene solution, which remains relatively low and exhibits minimal variation over time. Figure 2 also shows the spinning droplets of the waxed toluene simulated oils with different wax contents during interfacial tension measurement.
The overall results show that the interfacial tension values for toluene-simulated oils with different wax contents follow this order: toluene solution alone > 10% toluene simulated oil > 30% wax-containing toluene simulated oil > 20% wax-containing toluene simulated oil. The results demonstrate that the wax content significantly influences the interfacial tension of the waxed toluene simulated oil. Specifically, the interfacial tension is the highest when the wax content is 20%, indicating that the emulsion is the most stable under these conditions. Therefore, this study selects the 20% wax-containing toluene simulated oil as the experimental sample.
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A Figure 2. Variation of interfacial tension with time for simulated oils with different wax contents |
3.2. Demulsifier characterization
Figure 3(b) represents the Fourier Transform Infrared Spectroscopy (FT-IR) spectra of different esterification intermediates, with the blue, orange, and gray curves indicating the spectra of OP2, EOP2, and PEOP2, respectively. As shown in the figure, the characteristic absorption bands are as follows: the stretching vibration regions of the C-H bond appear at 2963 cm− 1 and 2865 cm− 1, the band near 3481 cm− 1 is attributed to the stretching vibration of the O-H bond, and the band near 1600 cm− 1 corresponds to the stretching vibration of the C = C bond. These spectral features confirm that the synthesized compounds are aromatic hydrocarbons.
Figure 3(c) represents the NMR spectra (13C NMR) of different esterification intermediates. The gray, blue, and red curves correspond to the esterification intermediates OPO2, EOP2, and PEOP2, respectively. The peaks of OP2, EOP2, and PEOP2 at 70 ppm correspond to C-O-C bonds, while the peak at 125 ppm corresponds to C = C double bonds. The peaks at 30.22 ppm and 36 ppm correspond to CH3 and CH2, respectively. Notably, the peak at 170.12 ppm corresponds to the -COOR group, indicating the successful synthesis of the aromatic-structured chemical demulsifier through the esterification reaction.
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Figure 3. (a) Esterification rate with different reagents; (b) FT-IR spectrum; (c) 13C NMR spectrum |
3.3. Interfacial tension analysis of demulsifier
Figure 4 demonstrates the variation of interfacial tension with time for simulated oils containing waxed toluene under different demulsifier concentrations. The black, red, green, blue, and gray curves correspond to demulsifier concentrations of 0, 25, 50, 75, and 100 ppm, respectively. The lowest interfacial tension values are found at 0 and 75 ppm, while the intermediate values are found at 25 and 50 ppm. The highest interfacial tension is observed at 100 ppm. Overall, the interfacial tension varies in the order of 100 ppm > 50 ppm > 25 ppm > 75 ppm. The significant increase in interfacial tension at 100 ppm may be attributed to demulsifier clustering due to the high demulsifier concentration.
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Figure 4. Interfacial tension analysis of waxy toluene-containing simulated oils with different demulsifier concentrations |
3.4. Evaluation of demulsifier properties
Figure 5 shows the variation in dehydration rate of oil samples with time at different temperatures and demulsifier concentrations. The dewatering rate increases gradually and eventually stabilizes over time. When the dewatering rate is low, the time required to reach a stable state is relatively short, whereas when the dewatering rate is higher, it takes longer to reach a stable state. For example, at 40°C, the dewatering rate at each demulsifier concentration is very low, and the system reaches a stable dewatering rate in approximately 60 minutes. The dehydration rates described in the following paragraphs refer to the values when the oil samples reach a stable state, where the dehydration rate no longer changes with time.
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Figure 5. Dehydration rate of oil samples with time at different temperatures and demulsifier concentrations | |
Figure 6 demonstrates the variation trend of the dehydration rate of oil samples with temperature at different demulsifier concentrations. The red, green, blue, and gray curves indicate the conditions when the demulsifier concentration is 25, 50, 75, and 100 ppm, respectively. Overall, the dehydration rate of different oil samples shows an “N-shaped” trend with increasing temperature, first increasing, then decreasing, and then increasing again. The rate of dewatering in general shows an upward trend with increasing temperature, mainly because increasing temperature reduces the strength of the oil-water interfacial film and enhances the thermal movement of demulsifier molecules, thereby accelerating their migration to the oil-water interface. In addition, the dewatering rate of oil samples at 40–60°C first increases and then decreases with increasing demulsifier concentration. The highest dehydration rate among the tested temperatures is observed at 50°C. However, at a demulsifier concentration of 100 ppm, the dewatering rate decreases, possibly due to demulsifier aggregation at high concentrations. The highest dehydration rate is observed at 70°C and a demulsifier concentration of 100 ppm. This may be attributed to the combined effects of increased temperature and higher demulsifier concentration, which enhance the demulsification efficiency.
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A Figure 6. Variation of dewatering rate with temperature for oil samples with different demulsifier concentrations |
Figure 7 shows the variation of the viscosity of oil samples with temperature under different concentrations of demulsifier. The black, red, green, blue, and gray curves correspond to demulsifier concentrations of 0, 25, 50, 75, and 100 ppm, respectively. The viscosity of the oil samples at different demulsifier concentrations gradually decreases as the temperature increases. The viscosity of the oil samples containing demulsifier is significantly reduced compared with the original oil samples.
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Figure 7. Viscosity-temperature curves of oil-water emulsions at different demulsifier concentrations |
Figure 8 illustrates the microscopic morphology of the oil-water emulsion at different demulsifier concentrations, with a scale bar of 5 µm. As shown in the figure (the white box is a representative droplet), the oil samples without demulsifier are complex in composition, with droplets arranged compactly and irregularly. The oil-water interfacial film is thicker and stronger in this state. Moreover, the presence of mechanical impurity particles in the oil samples further strengthens the stability of oil-water emulsion and increases the difficulty of demulsification. In contrast, the microscopic morphology of the oil-water emulsion after the addition of demulsifier exhibits simpler oil sample composition, looser and more regular droplet arrangement, and a tendency of the thinning of the oil-water interfacial film. The most significant changes are observed at a demulsifier concentration of 75 ppm, which is consistent with the trend observed in the dehydration rate.
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Figure 8. Microscopic morphology of oil samples under the influence of different concentrations of demulsifiers | |
3.5. Synergistic effect of ultrasound and demulsifier
Since Fig. 6 shows that the dehydration rate peaks at a temperature of 50°C, to ensure comparability, the synergistic experiments of ultrasound and demulsifier will be carried out at the same temperature in this section. Figure 9 illustrates the relationship between the dehydration rate (static sedimentation result at 50°C) and the demulsifier concentration of the oil samples under different ultrasonic power conditions. The blue and red bars correspond to ultrasonic power of 50%P and 100%P, respectively. With increasing demulsifier concentration, the dehydration rate first increases and then decreases, reaching the maximum value at 75 ppm, which is similar to the results obtained with the demulsifier alone. When the demulsifier concentration is constant, the dewatering rate of the oil samples with 50%P ultrasonic power is significantly higher than with 100%P ultrasonic power, indicating that higher ultrasonic power does not necessarily enhance the dewatering rate.
Compared with the results obtained with the demulsifier alone, the dehydration rate in both cases reaches the maximum at 75 ppm. However, when the ultrasonic power is 50%P, the dehydration rate is significantly higher than that of the demulsifier alone, reaching up to 45.56% under these conditions. This indicates that the synergism between ultrasound and demulsifier can improve the dehydration effect of the oil samples. In contrast, when the ultrasonic power is 100%P, the dehydration rate is slightly lower than that of the results of the demulsifier alone, which indicates that excessive ultrasonic power may inhibit the dehydration effect of oil samples.
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A Figure 9. Viscosity-temperature curves of oil-water emulsions at different demulsifier concentrations |
Figure 10 shows the microscopic morphology of the oil samples obtained by polarized light microscopy under different ultrasonic powers and demulsifier concentrations. The oil samples treated with 50%P ultrasonic power have fewer droplets with larger diameters, which means that the aggregation of droplets is more pronounced, leading to a stronger demulsification effect. In contrast, the oil samples with 100%P ultrasonic power have a greater number of droplets with smaller diameters, suggesting that the droplets are more stable, resulting in a weaker demulsification effect. In addition, the microscopic morphology of the oil samples at a demulsifier concentration of 75 ppm appears smoother and flatter, and these samples contain significantly fewer solid impurity particles compared to those at other concentrations under the same ultrasonic power. This is one of the factors contributing to the highest dewatering rate observed at this concentration.
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Figure 10. Microscopic morphology of oil samples under different power treatments | |
3.6. Mechanism analysis
The stability of the oil-water interfacial film is the primary cause of the difficulty in separating oil and water in the emulsion, and this stability depends on the combined effects of colloid, asphaltene, wax, and mechanical impurities[30–32]. The oil samples used in this study have relatively low contents of asphaltenes and colloids but a high content of wax. The interfacial tensions of toluene-simulated oils with different wax contents have been confirmed to be significantly different through the preliminary experiments, indicating that wax is a key factor contributing to the demulsification difficulties of the oil samples used in this study. Accordingly, a new type of demulsifier is synthesized in this paper, which can effectively change the interfacial tension of wax-containing toluene-simulated oil, as demonstrated by interfacial tension analysis. This demulsifier is expected to facilitate the demulsification and dehydration of oil-water emulsions.
The demulsifier evaluation experiment revealed that, at a constant demulsifier concentration, the dehydration rate of oil samples roughly exhibits an “N-shaped” trend with the increase of temperature, indicating that low temperature is not conducive to the diffusion of the demulsifier molecules and may lead to clustering. Although increasing temperature can enhance demulsifier diffusion and reduce oil sample viscosity, the demulsifier concentration also restricts the change in dehydration rate. The highest dewatering rate (31.33%) and the lowest interfacial tension of the wax-containing toluene-simulated oil are observed at 50°C and a demulsifier concentration of 75 ppm. Microscopic morphology indicates that the composition of the oil samples becomes simpler, and the thickness of the oil-water interfacial film is reduced. This suggests that demulsifier molecules can form hydrogen bonds with the emulsion more effectively at this temperature, thereby displacing resin molecules from the original emulsion. In addition, the electronegativity of the oxygen atom is altered during demulsifier synthesis, facilitating the reorganization of hydrogen bonding at the interfacial film, thus reducing π-π interactions. Meanwhile, the long alkyl chains of the demulsifier molecules can disrupt wax crystal structures, thereby effectively reducing the stability of the oil-water interfacial film to achieve demulsification and dehydration of the oil samples[7, 32, 33].
Similar to the demulsifier alone, when the ultrasonic power is constant, the rate of dehydration of the oil samples first increases and then decreases as the concentration of the demulsifier increases, with the maximum rate of dehydration (45.56%) at 50%P and 75 ppm demulsifier concentration. When the ultrasonic power is 50%P, the dewatering rate of the oil samples is significantly higher than that without ultrasonic irradiation, mainly because the high temperature, high pressure, shock wave, and microjet generated by ultrasonic waves can promote the diffusion of demulsifier molecules and reduce the clustering effect[34–37]. Simultaneously, the high-intensity ultrasonic cavitation effect can destroy wax crystal structures and alter the components of oil samples. The thermal effect can reduce the viscosity of oil samples and increase the mobility of demulsifier molecules. The mechanical effect can increase the mutual collision rate of droplets in the emulsion, and enhance the probability of collisions between the demulsifier molecules and the droplets. This indicates that the synergistic effect of ultrasound and the demulsifier is considerably greater than that of the demulsifier alone. However, when the ultrasonic power is 100%P, the dewatering rate of the oil samples is significantly reduced, indicating that higher power does not necessarily enhance demulsification. Different from the findings of previous studies[7, 18, 19, 38], we believe that the ultrasonic cavitation effect can separate the oil from the water and that the demulsification and emulsification coexist simultaneously during ultrasonic irradiation, whereas an increase in power may enhance emulsification, thereby reducing the dewatering rate.
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Fig. 11
Mechanism diagram of ultrasonic synergistic demulsifier
4. Conclusion
To address the challenge of oil-water separation in emulsions, this study synthesized a new type of polyether ester demulsifier, and processed oil samples using a synergistic ultrasonic method. Comprehensive analysis methods, including interfacial tension, viscosity, and microscopic morphology analyses, reveal the mechanism of oil-water separation. The main conclusions are:
(1)
The dewatering rate of the oil samples exhibits an N-shaped trend with increasing temperature, first increasing, then decreasing and then increasing again, and reaching a maximum of 31.33% at 75 ppm demulsifier concentration and 50°C.
(2)
At constant ultrasonic power, the dewatering rate increases and then decreases with increasing demulsifier concentration, reaching a maximum of 45.56% at 50%P ultrasonic power and 50°C.
(3)
The long-chain alkanes in the demulsifier can destroy the wax crystal structures in the oil-water emulsion, reducing emulsion viscosity and weakening the oil-water interfacial film, thereby facilitating oil-water separation. The high temperatures, high pressures, shock waves, and micro-jet generated by ultrasonic irradiation can increase the dispersion of the molecules of the demulsifier and the probability of collision with the droplets, thereby disrupting wax crystal structures and changing the components of the oil samples. The synergistic effect of the two enhances demulsification over emulsification, thereby increasing the dewatering rate of oil samples.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Acknowledgments
This work is supported by the Chongqing Natural Science Foundation (No. CSTB2023NSCQ-MSX0968), the open research project of State Key Laboratory of Acoustics and Marine Information, Chinese Academy of Sciences (No. SKLA202412). We acknowledge the contributions of Mrs. Haifeng Wang (Daqing Normal University) for her assistance with experimental characterizations. Thanks to the workers (Department of Foreign Languages, University of Chinese Academy of Sciences) for help with the English writing and corrections.
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Author Contribution
J.G. Conceived the research idea and designed the overall experimental protocol; J.G. and S.W. Conducted the main experimental operations and data - collection; Z.H.and Y.W. Performed detailed statistical analysis and processing of the collected data; M.Z and S.W. Wrote the main parts of the paper, including the Introduction, Methods, and Results sections;All authors participated in the final review and approval of the manuscript.
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