Full Length ArticlePerformance improvement of the ethylene-vinyl acetate copolymer (EVA) pour point depressant by small dosages of the polymethylsilsesquioxane (PMSQ) microsphere: An experimental study

•Small dosages of the PMSQ microsphere (≤10 ppm) improve the performance of EVA PPD.•The best dosage of the PMSQ microsphere is found to be around 2.5 ppm.•The EVA molecules can adsorb and concentrate on the PMSQ microsphere.•The formed EVA/PMSQ composite particles can act as the nucleation template for wax precipitation.•The formed composite particles greatly modify the precipitated wax crystals' morphology.

In a previous work, the addition of the polymethylsilsesquioxane (PMSQ) microsphere (50-400 ppm) can improve the flow behavior of waxy crude oil through the spacial hindrance effect. However, the flow improving efficiency of the neat PMSQ microsphere is not as good as the traditional polymeric pour point depressants (PPDs). In this paper, the effect of the ethylene-vinyl acetate copolymer (EVA2806) PPD together with the PMSQ microsphere (with the size around 2 µm) on the flow behavior of a typical waxy crude oil was investigated. The results show that adding 50 ppm EVA PPD can greatly improve the flow behavior of the oil. The neat PMSQ microsphere cannot improve the flow behavior of the oil at small dosages (≤10 ppm), but can significantly improve the performance of the EVA PPD. The gelation point, G′, G″, transient apparent viscosity and yield stress of the oil decrease further after adding both 50 ppm EVA and a small amount of the PMSQ microsphere (≤10 ppm). The best flow improving efficiency is found at 50 ppm EVA + 2.5 ppm PMSQ. The addition of the PMSQ microsphere has little influence on the WAT and precipitated wax crystal amount of the oil doped with EVA, but outstandingly changes the morphology of the precipitated wax crystals into larger and more compact flocs. The adsorption tests show that the EVA molecules can adsorb and concentrate on the PMSQ microsphere, thus causing the formation of the EVA/PMSQ composite particles. The composite particles can act as nucleation templates for the wax precipitation, resulting in larger and more compact wax microstructures and then further improving the flow behavior of the oil. The PMSQ microsphere dosage and the amount of EVA PPD adsorbed on the microsphere obviously influence the performance of the composite particle with the best performance at 50 ppm EVA + 2.5 ppm PMSQ. The findings mentioned above provide a new way to improve the performance of polymeric PPDs efficiently.