Molecular simulation of wax molecule adsorption and aggregation behaviour on Fe surfaces

Abstract The adsorption and aggregation behaviour of wax molecules on Fe surfaces was performed by molecular dynamics (MD) simulations. A model system comprising petroleum molecules (including colloids, aromatics, saturated hydrocarbons, and asphaltenes) and wax crystal molecules was constructed and simulated using J-OCTA software. Adsorption energy calculations revealed that wax crystal molecules exhibit higher adsorption energies on the Fe surface than petroleum molecules, making them more prone to forming adsorption layers. Low temperatures (260 K) favour the ordered aggregation and crystallization of wax crystal molecules, while high temperatures (300 K) suppress aggregation. Analysis of mean square displacement (MSD) further confirmed the negative correlation between aggregation structure and temperature. Simulations at varying shear rates revealed that increasing shear rate drives wax crystal molecules from the lower wall region toward the centre of the pipe, thereby suppressing wax crystal deposition. This study reveals the deposition and evolution mechanisms of wax crystals in metallic pipelines at the molecular level. It proposes a molecular mechanism for regulating wax crystallization through factors such as flow field and temperature, providing molecular-scale insights for optimizing wax blockage issues in oil and gas transportation.