Synergistic effect of asphaltenes and octadecyl acrylate-maleic anhydride copolymers modified by aromatic pendants on the flow behavior of model waxy oils

Abstract

Asphaltenes in waxy crude oils greatly influence the performance of polymeric pour point depressants (PPDs), and the relevant mechanism needs to be further discovered. In this article, polyoctadecylacrylate (POA), polyoctadecyl-acrylate-maleic anhydride (POA-MA) and its aromatic pendants-modified derivatives, polyoctadecyl-acrylate-maleic anhydride-aniline (POA-MA-AN) and polyoctadecyl-acrylate-maleic anhydride-naphthylamine (POA-MA-NA) were synthesized and characterized. Subsequently, the performance of the four PPDs on the pure model waxy oil (MO-1) and the model waxy oil containing 0.3 wt% asphaltenes (MO-2) were investigated through the rheological test, DSC analysis and micro-observation. The results showed that the four PPDs could improve the flowability of MO-1 to some extent, and adding 500 ppm POA exhibited the best performance: the pour point decreased from the initial 29 °C to 22 °C and the yield stress at 10 °C reduced from the initial 627.20 Pa to 69.58 Pa. Adding comb-like PPDs could observably improve the flowability of MO-2, meaning that a synergistic effect exits between the asphaltenes and comb-like PPDs. Adding 500 ppm POA-MA-AN in MO-2 showed the best performance: the pour point decreased to 3 °C, the yield stress at 10 °C reduced to 1.27 Pa. The quantitative asphaltenes precipitation test and molecular dynamics simulations revealed that adding POA-MA-AN could significantly reduce the percentage of precipitated asphaltenes in the mixed solution and the interaction energy between POA-MA-AN and asphaltenes was the lowest. This indicates that introducing aromatic pendants in comb-like PPDs strengthens the interactions between asphaltenes and PPDs, facilitating the adsorption of PPDs on asphaltenes to form the composite particles and thus greatly improving the flowability of waxy oils.