Self-crystallization behavior of paraffin and the mechanism study of SiO2 nanoparticles affecting paraffin crystallization

The crystallization behavior of paraffin severely inhibits the extraction and transportation of waxy crude oil. Therefore, in this study, the self-crystallization behavior of paraffin and the mechanism of SiO2 nanoparticles (NPs) affecting paraffin crystallization were investigated microscopically through molecular dynamics (MD) simulations. By analyzing the crystallization morphology and crystallization process of paraffin at different simulated temperatures, we observed the difference in the crystallization of long-chain paraffin molecules and short-chain paraffin molecules from a molecular point of view. Three processes of nucleation, aggregation and crystallization of paraffin crystals were clearly observed. Meanwhile, compared with the light oil system, in waxy heavy oil, a small amount of asphaltene can slightly inhibit the molecular crystallization of paraffin. However, the existence of a large amount of asphaltene changes the structure of paraffin crystals, which makes the paraffin crystals with asphaltene as heterogeneous core intertwined, showing a more complex network aggregation structure. Most importantly, the addition of NPs can significantly improve the diffusion coefficient of paraffin. From the microscopic point of view, the co-crystallization behavior of the grafted carbon chains on the surface of the grafted nanoparticles and the paraffin was observed, which further enhanced the nucleation of the nanoparticles and reduced the crystal size.