Effect of temperature on the aggregation kinetic and interaction mode of asphaltene in Toluene-Heptane system at molecular level using molecular dynamics (MD) simulation

Abstract

For many years, the asphaltene aggregation has been the research focus in the petroleum industry. However, few widely held beliefs have achieved on the microscopic process of asphaltene aggregation. To this end, molecular dynamics (MD) simulation was adapted to study the asphaltene aggregation in asphaltene-heptane-toluene system, and the interaction between asphaltene molecules during this process was also revealed from the density distribution, mean square displacement (MSD), diffusion coefficient, interaction energy and cohesive energy density (CED). Three main findings were made: (1) The increase in temperature can increase the diffusion rate of asphaltene molecules. However, it has a greater effect on the diffusion rate of asphaltenes in the heptane-rich system, while it has little effect in the toluene-rich system. (2) In system with more heptane, the increase of temperature will reduce the aggregation of asphaltene molecules, while the increase of temperature will promote the aggregation of asphaltene molecules in system with more toluene. (3) Interaction energy and cohesive energy density show that the interaction between asphaltenes and toluene in the toluene-rich system restricts the movement of asphaltene molecules, and the toluene molecules tend to surround asphaltene molecules to form a “Cage”, creating the illusion of increased density and aggregation of asphaltenes. The findings can help for understanding of the interaction between asphaltene molecules, and provide theoretical support for the flow assurance in asphaltene oil production systems.