Research on Effect of Wax Precipitation on Waxy Oil Thermal Conductivity

Abstract In the process of crude oil transportation, the waxy crude oil pipeline inevitably needs to be shut down for maintenance or due to accidents, and then restarted. The waxy crude oil thermal conductivity is an important parameter for calculating the temperature drop during shutdown. In this study, the PPD was added to regulate the wax precipitation of waxy oil, and the influence of wax crystal morphology on the thermal conductivity of waxy oil was explored. The results indicate that as the dosage of PPD increases, the wax crystal size enlarges, the aspect ratio decreases, and the thermal conductivity of waxy oil significantly decreases. The mechanism by which PPD reduces the thermal conductivity of waxy oil was investigated through micro-photograph analysis of wax crystals and molecular dynamics simulations. From the perspective of wax crystal scale, changes in morphology help reduce the overlap of wax crystals, which not only lowers the pour point of waxy oil but also inhibits the thermal conduction pathways between wax crystals. From the molecular scale, the co-crystallization of PPD and wax molecules reduces the crystallinity of paraffin wax, leading to lattice defects that cause phonon scattering and thus decrease the thermal conductivity of the system. The results are of significant importance for ensuring the safety of shutdown and restart of waxy crude oil pipelines.