Ethylene-Vinyl Acetate Copolymer (EVA) and Resin-Stabilized Asphaltenes Synergistically Improve the Flow Behavior of Model Waxy Oils. 3. Effect of Vinyl Acetate Content

Abstract

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.

Experimental Investigation on the Interactions between Asphaltenes and Comb-like Octadecyl Acrylate (OA) Polymeric Flow Improvers at the Model Oil/Water Interface

“…One can obtained from the table that the values of interactive energy are all negative values, meaning that the interactions between asphaltenes and OA polymers happen spontaneously. The interactive mechanism could lie on the attraction between the polar groups in the OA polymers and the heteroatoms in the asphaltenes. ,, The molecules of OA polymers could adhere to the asphaltene molecule/aggregates by the attractive force between the polar moieties of OA polymers and asphaltenes, thus constituting the OA/asphaltene composite particles. Meanwhile, the nonpolar moieties in the OA polymers (mostly composed of alkyl chains) could not be bonded with asphaltenes.…”

“…On the other hand, the interfacial properties of OA polymers with inherent interfacial affinities have been seldom studied, let alone the binary system containing both OA polymers and asphaltenes. A series of research studies showed that polymeric flow improvers can interact with asphaltenes by influencing the dispersion state of asphaltenes in the bulk phase. ,, These interactions may also cause variations in the structural properties of the interfacial layer that contains both OA polymers and asphaltenes.…”

“…A series of research studies showed that polymeric flow improvers can interact with asphaltenes by influencing the dispersion state of asphaltenes in the bulk phase. 12,29,30 These interactions may also cause variations in the structural properties of the interfacial layer that contains both OA polymers and asphaltenes.…”

Asphaltene Inhibition and Flow Improvement of Crude Oil with a High Content of Asphaltene and Wax by Polymers Bearing Ultra-Long Side Chain

“…In another work, Zhang et al [20] pointed out that the comb-like PPDs could not only affect the crystallization behavior of wax, but also synergistically improve the rheology of oil samples with asphaltenes. Yao et al [21][22][23] also found that PPDs molecules can adsorb on asphaltenes, and then enhance the dispersion stability of asphaltene and improve the flowability of waxy oils. Based on the above work, a hypothesis was proposed that the comb-like PPDs could be adsorbed onto the surface of aggregated asphaltene particles to form composite PPDs, thus resulting in a significant improvement in the rheology of waxy oils.…”

Influence of Asphaltene Aggregation State on the Wax Crystallization Process and the Efficiency of EVA as a Wax Crystal Modifier: A Study Using Model Systems

“…Therefore, the wax concentration gradient between the sample and the deposition interface declined, leading to lower deposition rates . More recently, Yao et al − have studied the synergistic effect of EVA and asphaltenes on the flow behavior of model waxy oils in a series of publications covering the effect of wax and asphaltene contents and the EVA composition. The authors observed that both ethylene–vinyl acetate (EVA) and asphaltenes reduce, moderately, the pour point of the system.…”