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To investigate the influence of structure variables of polymeric additives on the pour-point depression and rheological behavior of waxy crude oil, maleic anhydride co-polymer and its derivatives with different polar and/or aromatic pendant chains were designed and synthesized. All prepared additives were characterized by Fourier transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC). The pour-point and rheological properties of Changqing (CQ) crude oil with a low asphaltene content before and after additive beneficiation were studied in detail. Differential scanning calorimetry (DSC) and polarizing light microscopy were employed to gain insight on the interactions between such additives and wax crystals. The results are encouraging and showed that all four polymeric additives exhibited good efficiency as flow improvers in CQ crude oil. The reduction of pour-point and rheological parameters after additive addition largely related to the polymer structure. The polymer containing aromatic units showed the best performance, which could depress the pour point by 19 °C and decrease the yield stress as well as viscosity to a large extent.

A new class of hybrid pour point depressants (PPDs) are developed on the basis of poly­(octadecyl acrylate) (POA) functionality and POA/nanosilica hybrid particles. Activity performance is demonstrated using a model waxy oil system consisting of 10 wt % macrocrystalline wax dissolved in dodecane, effectively emulating the essential characteristics of waxy petroleum fluids. Differential scanning calorimetry (DSC) evidence confirms that POA molecules enhance the solubility of wax in the continuous oil phase, reducing the wax appearance temperature. The presence of POA also serves effectively to modulate the crystal morphology to a more regular spherical-like shape, instead of the disc-like morphologies common to pristine paraffin wax crystals, affecting reduced gelation temperatures in accordance with percolation theory predictions. In addition, rheometric yield stresses decrease with increasing dosage rates of POA. A solvent-blending protocol is followed to subsequently prepare POA/nanosilica hybrid particles. Optimal PPD performance of the hybrid particle system is attained at a dosage rate of 100 ppm. At dosages higher than the optimal dose, the gel strength increases in an analogous manner to the directionality of the Einstein equation for viscosity. The POA/nanosilica hybrid particle system provides spherical templates for wax precipitation, resulting in a compact precipitate structure, which suppresses gelation and improves the flowability of the model waxy oil by several orders of magnitude. DSC data confirm that a vast majority of the POA molecules become solubilized in the continuous oil phase upon dispersion of the hybrid nanoparticle system. As such, the free POA molecules enhance wax solubility in the continuous oil phase. Hydrophobic nanoparticles retain a more robust ability to modulate waxy oil rheology at low-dosage rates, as compared to purely polymeric functionality. The primary mechanism of hybrid particle PPDs involves heterogeneous nucleation activity. The hybrid particles effectively provide solid–liquid interface sites as wax precipitation templates, which result in spherical-like spherical wax morphologies. The compact morphologies hinder and suppress the percolation process necessary to form a volume-spanning network of wax crystals. As such, the hybrid nanoparticles constitute effective and economic PPD additives and may serve as the basis for next-generation environmentally friendly wax inhibition agents, by reducing the amount of additives needed.

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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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