Molecular dynamics simulation of wax molecules aggregational crystallization behavior during cooling of crude oil mixture

Abstract

The crystallization behavior of wax molecules is the root cause of wax deposition. In this study, molecular dynamics simulations were used to investigate the aggregational crystallization behavior of wax molecules in a crude oil system. The results show that wax molecules produce ordered wax crystal structures from the disordered liquid phase crude oil system under van der Waals forces at low temperatures. The crystallization of wax molecules consists of three main processes: carbon chain extension, nucleation of wax molecules and wax crystal growth. The lower the temperature of the crude oil system and the lower the cooling rate, the higher the degree of aggregation of wax molecules, the smaller the number of wax crystals and the larger the crystal size. In addition, asphaltene molecules are found to aggregate by face-to-face stacking and T-shaped stacking at low temperatures. Based on the spatial steric hindrance effect, the asphaltene aggregates prevent further aggregation between wax crystal clusters. Asphaltenes lead to an increase in the liquid content of the wax deposit layer, causing the yield stress of the deposit to decrease and the structural strength to weaken.

Keywords

• Waxy crude oil
• Molecular dynamics simulation
• Wax crystal
• Aggregation
• Asphaltene