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.

In the last two published papers, the influences of wax and asphaltene content on the synergistic performance of ethylene-vinyl acetate (EVA) copolymer together with resin-stabilized asphaltenes on the flow behavior improving of model waxy oil were systematically investigated, and a relevant mechanism has been proposed. Here, the effects of vinyl acetate (VA) content (12–40 wt %) on the synergistic performance between EVA and asphaltenes is continuously studied to develop and complete the synergistic theories. Results show that different VA contents slightly influence the rheological properties of model waxy oils doped with neat EVA but play a significant role in the flow behavior improvement of the oil doped with EVA and asphaltenes. EVA with moderate VA content (28 wt %) possesses the best flow-improving efficiency among the neat EVA PPDs, but associated with asphaltenes, EVA with a higher VA content (33 wt %) does the best. According to the DSC tests, when the VA content is low or moderate (12–33 wt %), the wax precipitation temperature (WPT) of the waxy oil is found to be decreased after adding neat EVA, while the phenomenon for the EVA with too high VA content (40 wt %) is the opposite. The WPT of oil would not be further suppressed by EVA/asphaltenes, but EVA/asphaltenes can facilitate the crystallization of paraffin waxes and accelerate the precipitation process of wax crystals below WPT. Increasing the polarity of EVA (12–33 wt %) can strengthen the polar interaction between EVA and asphaltenes in the oil phase, promoting EVA molecules to adsorb onto the asphaltene aggregates to form the EVA/asphaltenes composite particles. The composite particles favor the formation of large, compact, and spherical wax flocs to release more of the liquid oil phase, reduce the solid–liquid interfacial areas, and weaken the interactions between wax crystals, therefore facilitating the outstanding rheological improvement of waxy oils. As VA content increases to a much higher level (40 wt %), however, the rigidity of EVA molecules is high, which is adverse for the good oil-dispersing ability of EVA and the corresponding interactions with wax molecules. Meanwhile, the high polar EVA disperses the wax crystals into smaller sizes. Both of these two sides enlarge the solid–liquid interfacial area and strengthen the interactions between wax crystals, making them more able to build up a continuous wax crystal’s network structure and leading to the performance deterioration of the EVA together with asphaltenes. This conclusion that the modest increase of PPD’s polarity facilitates the improving efficiency between PPDs and asphaltenes gives another powerful proof to the correctness of the EVA/asphaltenes composite particles mechanism.

In part 1 (10.1021/acs.energyfuels.7b03657), the synergistic effect of ethylene–vinyl acetate copolymer (EVA) pour point depressant (PPD) and rensin-stabilized asphaltenes on improving the flowability of synthetic waxy oil has been verified. This paper is a continuous work studying the effect of the asphaltene content (0.01–3 wt %) on the synergistic effect between EVA PPD and resin-stabilized asphaltenes. The results showed that, in the absence of EVA and with the increase of the asphaltene content, the precipitated wax crystals of the waxy oil tend to grow gradually from initial big needle-like to smaller and more regular (spherical-like) particles with a larger amount; therefore, adding aphaltenes can only decrease the apparent viscosity of waxy oil at the temperature range slightly lower than the wax precipitation temperature (WPT) (the precipitated wax crystal amount is low), and the temperature range is broadened by increasing the asphaltene content. When the temperature is decreased far below the WPT of the oil, however, the apparent viscosity of oil rises up with increasing the aphaltene content as a result of the large amount of wax crystals and asphaltenes. In addition, only a part of the asphaltenes participates in the wax precipitation process, and the rest of the asphaltenes disperses in the oil phase as asphaltene aggregates, which could adhere or adsorb on the existing wax crystal flocs, strengthening the interactions between wax flocs. After asphaltenes are added together with EVA, EVA molecules can adsorb onto the asphaltene aggregates to generate the formation of the EVA/asphaltene composite particles, and the synergistic effect of the EVA/asphaltene composite particles on the flowability of waxy oil improves first with the increase of the asphaltene content and then somewhat deteriorates at a higher asphaltene content (3 wt %). When the asphaltene content is low, the wax crystal modification by the composite particles is insufficient and the formed large wax flocs have a very loose structure, which favor the wax crystal structure building. When the asphaltene content is too high (3 wt %), EVA/asphaltene composite particles disperse the precipitated wax flocs into relatively small spherical-like wax flocs with a larger amount. Although the structure of the wax flocs is compact, the large amounts of wax flocs and asphaltene aggregates in the oil phase lead to somewhat deterioration of the synergistic performance of EVA and asphaltenes. At the middle contents of asphaltenes (0.75–1.5 wt %), EVA/asphaltene composite particles cause the formation of relatively large spherical-like wax flocs with a compact structure and the asphaltene content is moderate, both of which greatly promote the flow behavior improvement of the oil.

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For a variety of applications, the brass alloy has been utilized to replace titanium tubes in heat exchangers. Copper alloys’ high corrosion rate during the acid cleaning procedure remains a significant concern. To inhibit the corrosion of brass alloys, we prepared two novel gemini surfactants (GSs), N 1 , N 3 -dibenzyl- N 1 , N 1 , N 3 , N 3 -tetramethylpropane-1,3-diaminium tetrafluoroborate (I H) and N 1 , N 1 , N 3 , N 3 -tetramethyl- N 1 , N 3 -bis (4-methyl benzyl) propane-1,3-diaminium tetrafluoroborate (I Me), and they were characterized using Fourier transform infrared spectroscopy and 1 H nuclear magnetic resonance spectroscopy. Their inhibition performance against corrosion of brass alloys in 1 M HCl was studied using electrochemical techniques including potentiodynamic polarization (PP), electrochemical impedance spectroscopy, and electrochemical frequency modulation. The inhibition effect of the synthesized compounds was high, and it increased as the inhibitor’s concentration was increased. The maximum level of inhibition efficiency was achieved at an inhibitor concentration of 100 ppm, reaching 96.42% according to PP measurements. From Langmuir data, the mechanisms of adsorption of the two GSs on the surface of copper was found to be physisorption and chemisorption adsorption. X-ray photoelectron spectroscopy and scanning electron microscopy show that the addition of the two compounds lowers the dissolution of brass ions in the corrosive solution and forms a protective layer on the surface of the brass.

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The research on the flowability of waxy oil has spanned more than a century and is still attracting much attention. How to improve the flowability of waxy oil to ensure safe and efficient pipeline transportation and storage is of great practical importance for the industry. In this work, we have systematically reviewed the research advances in improving the flowability of waxy oil. First, the crystallization properties and phase behavior of waxes are described based on their chemical structure, thermodynamic properties, and solution phase properties, with emphasis on the solventized layer properties of wax crystals. Then, the mechanisms, process, and research progress in flow improvement of waxy oil are discussed from three major aspects: process improvement, equipment improvement, and chemical treatment, with emphasis on the summary of waxy oil pour point depressants in recent years. The remaining challenges and perspectives for future research on flow improvement of waxy oil are presented.