Abstract: In order to study the diffusion behavior of hydrocarbon molecules from FCC diesel fractions in ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate ([C6mim][BF4]), a molecular simulation method was used to study the diffusion behavior of hydrocarbon molecules in the blend model system of the hydrocarbons molecules and [C6mim][BF4]. The mean square displacement of different hydrocarbon molecules in the [C6mim][BF4] system were calculated, and the interactions between hydrocarbon molecules and [C6mim][BF4] were analyzed. The results show that saturated hydrocarbon molecules diffuse more easily in the [C6mim][BF4] system than aromatic hydrocarbon molecules, and the interaction between saturated hydrocarbons and [C6mim][BF4] is dominated by van der Waals interaction. As the number of aromatic rings increases, the electrostatic interaction between aromatic molecules and [C6mim][BF4] is gradually enhanced. For tricyclic aromatic hydrocarbons, the electrostatic interaction is the main interaction between [C6mim][BF4] and aromatic hydrocarbons. The smaller the molecular volume is, the stronger the interaction with the ionic liquid is, and the smaller the free volume fraction of the blends is.

Key words: ionic liquids, hydrocarbon molecule, diffusion behavior, inter-molecular interaction, molecular sizes, free volume, molecular simulation