Molecular dynamics simulation of asphaltene aggregation and wax crystallization in waxy crude oil under different thermal treatment temperatures

Thermal treatment is an important modification method for waxy crude oil, but the mechanism of thermal treatment is not clear at present. In this paper, continental and island asphaltene were selected, and the aggregation of asphaltene and its effect on wax crystallization characteristics at different thermal treatment temperatures were studied based on molecular dynamics simulation. It was found that as the thermal treatment temperature gradually increased from 50 °C to 90 °C, the aggregation state of asphaltene was first dispersed and then aggregated. The change in the aggregation state of asphaltene affected the interaction between asphaltene and wax molecules during the subsequent cooling process. The behavior of asphaltene in wax crystallization is related to factors such as thermal treatment temperature, asphaltene type, asphaltene concentration, and resin concentration. The simulation results show that: (1) When the alkyl side chain structure of asphaltene is similar to that of wax molecules, the alkyl side chains in asphaltene aggregates are easy to co-crystallize with wax molecules through nucleation and eutectic effect. (2) On the surface of wax crystals that have been nucleated, some asphaltene aggregates also tend to adsorb on the surface of wax crystals through adsorption, thereby limiting the further growth of wax crystals. (3) For asphaltene aggregates with larger aggregation scales, they will also hinder the aggregation of wax molecules and the growth of wax crystals through steric hindrance.