Synthesis and Performance Evaluation of the Modified EVA Pour Point Depressants (PPDs) with Different Side Alkyl Chain Lengths.

Graft modification of commercial EVA pour point depressants (PPDs) to prepare new PPDs with high performance is a research hotspot in the crude oil pipelining industry. However, the acting law and mechanism of the grafted EVA PPDs were still unclear. In this paper, based on a commercial EVA PPD (EVA-2), the modified EVA PPDs with different side alkyl chain lengths (EVA-4, EVA-10, and EVA-18) were successfully synthesized through a novel "alcoholysis-acyl substitution" reacting route. The effect of the side alkyl chain length (2-18) on the performance of the modified EVA PPDs for the model waxy oil without (MO-1)/with (MO-2) 500 ppm asphaltene was systemically studied. The influencing mechanism was also disclosed based on the microstructure of wax crystals, the asphaltene precipitation test, and the analysis of PPDs-paraffin wax-asphaltene interactions. For MO-1, the cocrystallization effect of the modified EVA PPDs and paraffin wax determines the performance of the PPDs. With the increase of side alkyl chain length, the cocrystallization effect first decreases and then increases, and the sequence is EVA-18 > EVA-2 > EVA-10 > EVA-4. The EVA-18 has the strongest cocrystallization effect and the best performance for MO-1, but the pour point reduction is only 4 °C. For MO-2, the performance of the modified EVA PPDs is governed by both the cocrystallization effect and the synergistic effect between the PPDs and asphaltene, and the synergistic effect significantly improves the performance of the PPDs. The synergistic effect is improved by increasing the side alkyl chain length. The EVA-18 PPD has the strongest cocrystallization effect and synergistic effect, which facilitate the formation of dense and the biggest wax aggregates. Therefore, EVA-18 has the largest pour point reduction of 14 °C for MO-2. These findings provide valuable insights into the role of alkyl side chain length in optimizing EVA-based PPDs, offering a promising strategy for mitigating flow assurance challenges in the pipeline transportation of waxy crude oils.