Objective Against the backdrop of the “dual carbon” goals, methanol holds significant potential for large-scale pipeline transport as a clean liquid fuel and hydrogen carrier. Given the high investment and long construction cycles of dedicated pipelines, batch transportation of methanol via existing product oil pipelines offers a practical alternative. Nevertheless, since methanol differs substantially from gasoline and diesel in physical properties and miscibility, its mixing dynamics during batch transportation remain unclear, necessitating systematic research under engineering-scale conditions.

Methods With reference to mixing dynamics in conventional gasoline and diesel batch transportation, this research was conducted through miscibility tests and pilot-scale flow experiments. The miscibility characteristics between methanol and gasoline/diesel, alongside their effects on product oil quality, were analyzed. A self-built pilot-scale test loop was adopted to carry out batch transportation tests for methanol-gasoline and methanol-diesel under turbulent flow. Tests were performed across different flow velocities, transportation sequences, and pipeline lengths. Combined with visual observations through transparent pipeline segments and data from online densimeters, the mixed oil concentration distribution and axial development of mixed oil length were quantitatively characterized.

Results The test results indicated that methanol and gasoline exhibited good miscibility. During batch transportation, the mixed oil section maintained high transparency, and the concentration changed continuously along the pipeline axis, sharing marked similarities with traditional gasoline-diesel mixing dynamics. Within the investigated operating conditions, the mixed oil length of the methanol-gasoline system decreased with increasing flow velocity, whereas the transportation sequence exerted negligible influence. In contrast, methanol and diesel exhibited poor miscibility and distinct physical properties. Longer mixed oil sections and pronounced tailing characteristics were observed during their batch transportation, making the mixed oil length more sensitive to the transportation sequence. Although increasing the flow velocity restrained the mixed oil growth rate, it failed to completely eliminate the mixed oil expansion caused by poor miscibility and viscosity differences.

Conclusion The mixing dynamics of methanol-gasoline batch transportation can be inferred from the operational experience of traditional gasoline-diesel systems, rendering this mode technically feasible for engineering applications under properly controlled flow velocities. Conversely, the batch transportation of methanol and diesel involves a more complex mixing process. Consequently, process design should prioritize the selection of the transportation sequence, optimization of operating parameters, and formulation of mixed oil cutting strategies. These research findings provide a valuable reference for engineering tests and operational optimization of methanol batch transportation in existing product oil pipelines.