Effect of asphaltenes on the stratification phenomenon of wax-oil gel deposits formed in a new cylindrical Couette device

Li, Chuanxian; Cai, Jinyang; Yang, Fei; Zhang, Ying; Bai, Fan; Ma, Yangyang; Yao, Bo

doi:10.1016/j.petrol.2016.01.004

Cited by 39 publications

(50 citation statements)

References 36 publications

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“…And the relationship between the thickness of deposition layer and time was explored. Chuanxian et al , studied the influence mechanism of asphaltene on the gelation and deposition behavior using the Couette deposition experimental device. It was found that the associated particles of asphaltene could accumulate in the inner wax deposition layer through Brownian motion and participate in the process of wax crystallization and precipitation, which would improve the waxy crystals’ structure and result in the higher structural strength of the inner deposition layer than that of the outer layer.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

et al. 2021

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For ensuring the safe and stable operation of waxy crude oil pipeline transportation, in this research, the molecular dynamics model was established to characterize the deposition and wall sticking behavior of waxy crude oil multiphase system pipeline transportation. The equal density interpolation fitting method was proposed to determine the wall contact angle of simulation results. Through verification, the error between the simulation results and the experimental results measured by Dos Santos et al. (2006) was less than 5%, which showed that the established model was accurate and reliable. Using the established model, the deposition and wall sticking behavior of waxy crude oil nucleated clusters was simulated. It was found that the nucleated clusters would first adhere to the wall surface to form the solidified oil layer. Then, the wax and asphaltene molecules would diffuse to the deposit layer, and the oil molecules in the solidified oil layer reverse diffused to the direction of the oil flow. With the adhering and spreading degree of clusters on the wall surface increasing, the deposit layer gradually aged, and the gelled deposit layer with a higher density and hardness would form. On this basis, the micro influence mechanism of the surface free energy was studied. It was found that the higher the surface free energy, the more hydrophilic the pipeline wall was, and the higher the adhesion degree would be. Moreover, based on the ABF sampling and the potential of mean force calculations, the selective deposition process of waxy crude oil deposited on the sedimentary layer was studied. The micro information on the deposition sites, the binding conformation, and the binding energy of different molecules in clusters deposited on different molecules in sedimentary layer were analyzed. The investigations in this study could provide theoretical support for paraffin removal and control, which could ensure the safe and stable operation of the waxy crude oil production system.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

et al. 2021

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“…Metals such as vanadium and nickel are also present in this fraction as part of porphyrinic or nonporphyrinic groups. , Asphaltene molecules often exist in the crude oil as asphaltene aggregates due to the strong self-association propensity of the molecules, and the aggregate size could range from nano- to micrometer. , During the last 2 decades, the effects of asphaltenes on the flow behavior of a model waxy oil have been widely studied. The asphaltenes were first extracted from real crude oil by n -pentane/ n -heptane precipitation, and then the extracted asphaltenes were redispersed in waxy oil with the aid of heating and agitation. − The results showed that − (a) the asphaltenes disperse in oil phase as asphaltene aggregates; (b) a small dosage of asphaltenes (around 0.1 wt %) can greatly modify the morphology of precipitated wax crystals, thus improving the flow behavior of waxy oil; (c) the effect of asphaltenes on the WAT of waxy oil is controversial, as some works show that the WAT decreases after adding asphaltenes, but some other works get the opposite result; (d) redispersion of asphaltenes in waxy oil is difficult due to the lack of resins, and the dispersion state of asphaltenes in waxy oil is quite different from that in real crude oil. Therefore, a more reasonable method should be proposed to ensure the similar dispersion state of asphaltenes in model waxy oil and real crude oil.…”

Section: Introductionmentioning

confidence: 99%

Ethylene–Vinyl Acetate Copolymer and Resin-Stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils. 1. Effect of Wax Content and the Synergistic Mechanism

Yao

Zhang

et al. 2018

Energy Fuels

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Both polymeric pour point depressants (PPDs) and asphaltenes can improve the flowability of waxy oils. However, the effect of polymeric PPDs together with asphaltenes on the flowability of waxy oils is not clear. In this paper, the synergistic effect of ethylene–vinyl acetate (EVA) PPD (100 ppm) and resin-stabilized asphaltenes (0.75 wt %) on the flow behavior of model waxy oils (10–20 wt % wax content) was investigated through rheological tests, DSC analysis, microscopic observation, and asphaltenes precipitation tests. The results showed that the asphaltenes disperse well in the xylene/mineral oil solvent as small aggregates (around 550 nm) with the aid of resins. The EVA or asphaltenes alone moderately improve the flow behavior of waxy oils by changing the wax crystals’ morphology from long and needlelike to a large, radial pattern or fine particles, respectively. The wax precipitation temperatures (WPTs) of waxy oils are also slightly decreased by adding EVA or asphaltenes, meaning that the cocrystallization effect between the additives and waxes is dominant. The addition of EVA together with asphaltenes cannot further decrease the WPT, but it can dramatically decrease the pour point, gelation point, G′, G″, and apparent viscosity of waxy oils, indicating that a synergistic effect exists between EVA and asphaltenes. The synergistic effect deteriorates upon increasing the wax content of waxy oils. The EVA molecules can adsorb on the surface of asphaltene aggregates, thus inhibiting the asphaltenes precipitation and forming the EVA/asphaltenes composite particles. The formed composite particles can act as wax-crystallizing templates and then greatly change the wax crystals’ morphology into large, compact, and spherelike wax crystal flocs, thus dramatically improving the waxy oil flow behavior. This work enriches the theory of micro/nano composite PPDs, which is helpful for developing new PPDs with high efficiency.

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“…The interactions of asphaltenes and wax have been the subject of many studies on waxy crude oils in the last 2 decades. − The effect of asphaltenes on the thermodynamic behavior of waxy oils is usually elucidated by examining the WAT, the onset temperature at which wax crystallization is microscopically observed. The literature, however, contains conflicting views about the effect.…”

Section: Introductionmentioning

confidence: 99%

“…For instance, Lei et al found that asphaltenes in a more dispersed state tend to interact with wax on a molecular level and hinder wax crystal growth, whereas asphaltenes in a more aggregated state can act as additional junction points bridging different wax crystals . In addition to the effect of asphaltene on crystallization and gelation of waxy oils, two recent studies report that adding asphaltenes can reduce the wax deposition rate and result in the formation of a two-layer deposit morphology, with each layer showing considerably different strength, microstructure, and wax content. , …”

Section: Introductionmentioning

confidence: 99%

Influence of Asphaltene Polarity on Crystallization and Gelation of Waxy Oils

Han

et al. 2018

Energy Fuels

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We report for the first time the results from a systematic investigation of how asphaltenes of different polarity affect crystallization and gelation of waxy oils. The more polar asphaltenes were found to be more aromatic in nature and more highly self-aggregated in the solvent. The presence of less polar asphaltenes in the waxy oil reduced the wax appearance temperature and wax precipitation to a greater degree compared to more polar asphaltenes, which was mainly attributed to the difference in the aggregation state of asphaltenes of different polarity. Reducing the polarity of asphaltenes present in the oil also resulted in a lower gelation temperature, lower storage modulus, and lower yield stress, which was probably because the less polar asphaltenes were more similar to wax on the molecular level and, thus, more readily interacting with wax. Notably, a 99% reduction in the yield stress was observed upon the addition of the least polar asphaltenes examined in the present work, in contrast to the 62% yield stress reduction upon the addition of the most polar asphaltenes. This observation may be of industrial significance because it suggests that the crude oil containing less polar asphaltenes may form a softer gel or deposit that is more easily broken or removed. Microscopic analysis showed that the wax crystals precipitated in the presence of less polar asphaltenes have a smaller aspect ratio.

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Effect of asphaltenes on the stratification phenomenon of wax-oil gel deposits formed in a new cylindrical Couette device

Cited by 39 publications

References 36 publications

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

Ethylene–Vinyl Acetate Copolymer and Resin-Stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils. 1. Effect of Wax Content and the Synergistic Mechanism

Influence of Asphaltene Polarity on Crystallization and Gelation of Waxy Oils

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