The mechanism of ultrasonic and chemical synergistic demulsification

The mechanism of ultrasonic and chemical synergistic demulsification | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The mechanism of ultrasonic and chemical synergistic demulsification Jinbiao Gao, Shuailing Wang, Haibo Zhao, Yushen Wu, Mi Zhang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7147044/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version 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. Acoustic cavitation Ultrasound Demulsifier Demulsification Interfacial tension Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 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. Methods 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/cm 3 , 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 ] . Table 1 Composition of the original crude oil sample 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 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. 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, %; V 1 denotes the volume of water removed, ml; and V 0 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. 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 ( 13 C 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 CH 3 and CH 2 , 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. 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. 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. 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. 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. 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. 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. 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. 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. 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: 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. 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. 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. Declarations 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. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any noncommercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. 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. 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. References ZHENG W L, PANG R S. Experimental study on aging oil dehydration technology optimization in Yushulin oilfield[J/OL]. Advanced Materials Research. 2011, 393-395: 746-749. DOI:10.4028/www.scientific.net/AMR.393-395.746. ANTES F G, DIEHL L O, PEREIRA J S F, et al. 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18:08:16","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":828931,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic \u0026nbsp;\u0026nbsp;morphology of oil samples under different power treatments\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7147044/v1/80a18df0c769b57a7c22d0fa.png"},{"id":92538798,"identity":"352edd2a-9946-426c-8b1f-5032193a0747","added_by":"auto","created_at":"2025-09-30 18:08:16","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":405801,"visible":true,"origin":"","legend":"\u003cp\u003eMechanism diagram of ultrasonic synergistic demulsifier\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7147044/v1/0288593cb8d53eeaf865ca11.png"},{"id":105443592,"identity":"40892e72-06ed-4a3d-8843-c788afc81003","added_by":"auto","created_at":"2026-03-26 06:42:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4005172,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7147044/v1/ae9d4d5c-ec0b-4b79-80a8-9e63cee16dc7.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The mechanism of ultrasonic and chemical synergistic demulsification","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDuring 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\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eCompared with the aforementioned methods, ultrasonic treatment offers several advantages including low energy consumption, high economic efficiency, broad applicability, and minimal environmental pollution\u003csup\u003e[\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, thereby reducing the dehydration rate.\u003c/p\u003e\u003cp\u003eIn addition, chemical demulsification is more widely utilized as a traditional method\u003csup\u003e[\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eWith 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\u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eHowever, 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\u003csup\u003e[\u003cspan additionalcitationids=\"CR21 CR22 CR23 CR24 CR25\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. 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.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Materials\u003c/h2\u003e\n \u003cp\u003eCrude oil sample: Provided by PetroChina Daqing Oilfield Co., Ltd. The composition of the sample is detailed in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. At 50\u0026deg;C, its viscosity and density were 52.308 mPa\u0026sdot;s and 0.8646 g/cm\u003csup\u003e3\u003c/sup\u003e, respectively. Petroleum ether (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 678\u0026ndash;2002\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. Toluene (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 684\u0026ndash;1999\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Anhydrous ethanol (analytical pure): Liaoning Quanrui Reagent Co., Ltd, conforms to the standard GB/T 678\u0026ndash;2023\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComposition of the original crude oil sample\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWax\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAsphaltene\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eResin\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSaturated hydrocarbon\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAromatic hydrocarbon\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eContent(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Instruments\u003c/h2\u003e\n \u003cp\u003eLC-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 \u0026amp; 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.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Experimental process\u003c/h2\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.1. Wax extraction\u003c/h2\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, 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.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.2. Demulsifier synthesis\u003c/h2\u003e\n \u003cp\u003eAiming 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. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, 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.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.3. Demulsifier interface experiments\u003c/h2\u003e\n \u003cp\u003eTo 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.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.4. Emulsion preparation\u003c/h2\u003e\n \u003cp\u003eTo 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%.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.5. Demulsifier bottle test demonstration\u003c/h2\u003e\n \u003cp\u003eTo 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:\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"130\" height=\"79\"\u003e\u003c/p\u003e\n \u003cp\u003eWhere \u003cimg src=\"data:image/png;base64,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\" width=\"19\" height=\"24\" style=\"width: 19px;\"\u003e\u0026nbsp;denotes the dehydration rate, %; V\u003csub\u003e1\u003c/sub\u003e denotes the volume of water removed, ml; and V\u003csub\u003e0\u003c/sub\u003e denotes the initial volume of water in the oil-water emulsion, ml.\u003c/p\u003e\n \u003cp\u003eAdditionally, 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.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.6. Synergistic experiment of demulsifier and ultrasound\u003c/h2\u003e\n \u003cp\u003eTo 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.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.7. Microscopic morphology characterization\u003c/h2\u003e\n \u003cp\u003eA 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.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Interfacial tension analysis of waxed toluene simulating oil\u003c/h2\u003e\n \u003cp\u003eFigure 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\u0026nbsp;2 also shows the spinning droplets of the waxed toluene simulated oils with different wax contents during interfacial tension measurement.\u003c/p\u003e\n \u003cp\u003eThe overall results show that the interfacial tension values for toluene-simulated oils with different wax contents follow this order: toluene solution alone\u0026thinsp;\u0026gt;\u0026thinsp;10% toluene simulated oil\u0026thinsp;\u0026gt;\u0026thinsp;30% wax-containing toluene simulated oil\u0026thinsp;\u0026gt;\u0026thinsp;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.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Demulsifier characterization\u003c/h2\u003e\n \u003cp\u003eFigure 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\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2865 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the band near 3481 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the stretching vibration of the O-H bond, and the band near 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the stretching vibration of the C\u0026thinsp;=\u0026thinsp;C bond. These spectral features confirm that the synthesized compounds are aromatic hydrocarbons.\u003c/p\u003e\n \u003cp\u003eFigure 3(c) represents the NMR spectra (\u003csup\u003e13\u003c/sup\u003eC 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\u0026thinsp;=\u0026thinsp;C double bonds. The peaks at 30.22 ppm and 36 ppm correspond to CH\u003csub\u003e3\u003c/sub\u003e and CH\u003csub\u003e2\u003c/sub\u003e, 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.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Interfacial tension analysis of demulsifier\u003c/h2\u003e\n \u003cp\u003eFigure 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\u0026thinsp;\u0026gt;\u0026thinsp;50 ppm\u0026thinsp;\u0026gt;\u0026thinsp;25 ppm\u0026thinsp;\u0026gt;\u0026thinsp;75 ppm. The significant increase in interfacial tension at 100 ppm may be attributed to demulsifier clustering due to the high demulsifier concentration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Evaluation of demulsifier properties\u003c/h2\u003e\n \u003cp\u003eFigure 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\u0026deg;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.\u003c/p\u003e\n \u003cp\u003eFigure 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 \u0026ldquo;N-shaped\u0026rdquo; 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\u0026ndash;60\u0026deg;C first increases and then decreases with increasing demulsifier concentration. The highest dehydration rate among the tested temperatures is observed at 50\u0026deg;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\u0026deg;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.\u003c/p\u003e\n \u003cp\u003eFigure 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.\u003c/p\u003e\n \u003cp\u003eFigure 8 illustrates the microscopic morphology of the oil-water emulsion at different demulsifier concentrations, with a scale bar of 5 \u0026micro;m. 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.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5. Synergistic effect of ultrasound and demulsifier\u003c/h2\u003e\n \u003cp\u003eSince Fig.\u0026nbsp;6 shows that the dehydration rate peaks at a temperature of 50\u0026deg;C, to ensure comparability, the synergistic experiments of ultrasound and demulsifier will be carried out at the same temperature in this section. Figure\u0026nbsp;9 illustrates the relationship between the dehydration rate (static sedimentation result at 50\u0026deg;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.\u003c/p\u003e\n \u003cp\u003eCompared 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.\u003c/p\u003e\n \u003cp\u003eFigure 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.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6. Mechanism analysis\u003c/h2\u003e\n \u003cp\u003eThe 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\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. 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.\u003c/p\u003e\n \u003cp\u003eThe demulsifier evaluation experiment revealed that, at a constant demulsifier concentration, the dehydration rate of oil samples roughly exhibits an \u0026ldquo;N-shaped\u0026rdquo; 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\u0026deg;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 \u0026pi;-\u0026pi; 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\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eSimilar 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\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. 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\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e, 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.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eTo 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:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe 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\u0026deg;C.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eAt 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\u0026deg;C.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe 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.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe 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.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOpen Access\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any noncommercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article\u0026rsquo;s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article\u0026rsquo;s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis 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.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThis 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.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZHENG W L, PANG R S. 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DOI:10.1016/j.ultsonch.2017.08.037.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Acoustic cavitation, Ultrasound, Demulsifier, Demulsification, Interfacial tension","lastPublishedDoi":"10.21203/rs.3.rs-7147044/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7147044/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe 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 \u0026ldquo;N\u0026rdquo;-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.\u003c/p\u003e","manuscriptTitle":"The mechanism of ultrasonic and chemical synergistic demulsification","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-30 18:08:10","doi":"10.21203/rs.3.rs-7147044/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4820cbff-b8e5-44d6-8e4d-a3b06efbb430","owner":[],"postedDate":"September 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-26T06:42:02+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-30 18:08:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7147044","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7147044","identity":"rs-7147044","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}