The presence of water in wax deposition from water-in-oil emulsion for petroleum transportation in pipelines has received much attention in recent years. This study investigated the formation of wax deposition with water droplets, considering interfacial adsorption by wax crystals. The prepared 20 vol % water-in-oil emulsion was used for the wax deposition experiment with an analysis of deposition mass/thickness and water volume fraction in deposition, determining that the water content in deposition during the whole deposition duration was constant and equaled to the water content in emulsion. Moreover, a polarizing microscope was employed to observe the microstructure of wax deposition, revealing that some water droplets were covered with wax crystals due to interfacial adsorption, while some droplets were enclosed by the network of wax crystals. Depending on these findings, two kinds of entrapment of water droplets in deposition were proposed. One contained the formation and growth of a crystal network accompanied with these wax-covered water droplets themselves; another one indicated that water droplets were surrounded by a crystal network, resulting in the movement of these droplets being limited and therefore the droplets settling in deposition. Furthermore, a comparison of the distribution of water droplets in deposition using a microscope and that in emulsion by focused-beam reflectance measurement was presented. It was observed that these small droplets were more likely to be incorporated into deposition in contrast with these large ones. The largest size measured for an entrapped water droplet was 115 μm, which was in accordance with the previous research claiming that the general diameter of water droplets incorporated into deposition was no more than ∼100 μm. Interfacial adsorption of wax crystals provides an additional insight to investigate water droplets in wax deposition.
A nanocomposite pour point depressant (NPPD), as a new type of wax additive or flow improver for waxy oil, has raised wide attention. Recent advances have been made in the modification of the crystal morphology and the rheological behavior of waxy oil by NPPD. In this work, the effect of NPPD on wax deposition behavior has been studied via a cold finger apparatus. It was found that the deposition mass is obviously eliminated with the addition of NPPD, while the composition analysis by hightemperature gas chromatography (HTGC) indicates that the wax content in the deposit increases. Further, the measured variation of the initial gel time and mass, the critical carbon number, and the carbon number distribution of the deposit is found and should be owed to the effect of NPPD.
Crystallization modification has been applied in many fields, such as materials science, petroleum engineering, and chemical engineering. The modification of organic–inorganic hybrids via paraffin hydrocarbon crystallization has been significantly important for the exploration of undersea oil and gas resources. In this work, a metal oxide organic–inorganic hybrid pour point depressant (MOIH-PPD) is provided along with an analysis of the microscopic structure of the paraffin hydrocarbon crystal employing small-angle X-ray scattering and X-ray diffraction. The MOIH-PPD modified crystal grain exhibited a decrease in the long period and in the radius of gyration of the crystal grain and an increase in the thickness of the interface layer compared with those of the unmodified paraffin crystal. In addition, the synergistic effect of heterogeneous nucleation and the magnetic response of MOIH-PPD on the paraffin hydrocarbon system was also investigated, revealing that the synergism modification yields stress superior to that of MOIH-PPD or magnetic field alone, which provides insight into the possibility of the modification of paraffin hydrocarbon crystallization.
Crude oil adhesion issues are widespread in the petroleum industry, leading to inefficient production and high maintenance costs. Developing efficient antifouling materials and investigating the microscopic adhesion mechanism are of substantial significance. In the present work, a superhydrophilic/ underwater superoleophobic PAFC coating with excellent antifouling properties was constructed by the coordination-driven self-assembly of phytic acid (PA) and FeCl 3 (FC). The atomic force microscope (AFM) droplet probe technique was employed to elucidate the underlying mechanism of the anti-oil-adhesion property of the PAFC coating. Results showed that the PAFC modification achieved the optimum effect at a molar ratio of 1:3 between PA and Fe III . Applying a (3-aminopropyl)triethoxysilane (APTES) interlayer can effectively improve the performance of the PAFC coating on silica substrates. AFM droplet probe experiments indicated that the adhesion force between submerged micrometer-sized oil droplets and PAFC-modified substrates was significantly weaker than that with the untreated substrate. Meanwhile, the adhesion forces between oil droplets and surfaces were inversely proportional to the contact angle of the oil in water and were enhanced by higher salinity, lower collision velocity, and stronger loading force. The oil injection and wall sticking tests also confirmed the effectiveness of the PAFC modification in resisting the adhesion of crude oil.
The stabilization mechanism of water-in-oil (W/O) emulsions has been studied by measuring the interactions between two water droplets in n-tetradecane using atomic force microscopy. The effects of water-soluble surfactants (SDS/CTAB/Tween 80), an oil-soluble surfactant (Span 20), and the coexistence of the water and oil-soluble surfactants on the stability of water droplets in oil were investigated separately. It is found that the addition of oil-soluble surfactants (Span 20) prevents the coalescence of water droplets in oil. To discuss the role of an oil-soluble surfactant, we analyzed the force curve by applying the theoretical model. The results demonstrate that the oil-soluble surfactant (Span 20) stabilizes dispersed droplets by adsorbing onto the interface and forming a relatively tighter layer with the increase in surfactant concentration, which hinders film rupture. This behavior of the surfactant could also be properly characterized by steric hindrance. A further step was taken by introducing another water-soluble surfactant. It is found that the addition of either SDS or CTAB into the water phase is futile in inducing droplet coalescence in the presence of Span 20. In contrast, Tween 80 was found to be effective in destabilizing water droplets, which could be due to the competitive adsorption between Tween 80 and Span 20 at the interface. By characterizing the interfacial adsorption of Tween 80 and Span 20 with a theoretical adsorption isotherm model, the result indicates that interface replacement would result in a loose adsorption layer that is insufficient to hinder droplet coalescence. Our study provides an intriguing understanding of the role of surfactants in the stabilization and destabilization of water-in-oil emulsions.
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