Objective With the rapid global development of new energy, declining demand for refined oil products has left some pipelines idle, while methanol demand as a clean energy source grows. Repurposing idle refined oil pipelines for methanol transport can optimize the allocation of resources. As storage tanks serve as the primary facilities for methanol storage and transport, precise calculation of breathing capacity is crucial for minimizing evaporation losses and optimizing tank design. However, existing breathing capacity calculation methods focus on traditional oil products, with no specific method for methanol storage tanks.

Methods A model tank test platform was constructed to measure the evaporation rates of methanol and gasoline at various temperatures. The evaporation characteristics of methanol and gasoline were compared, and commonly used empirical formulas for small breathing loss calculation were screened and optimized based on the test data.

Results The test results indicated that gasoline exhibited a higher evaporation rate than methanol at the same temperature and demonstrated greater sensitivity to temperature changes. Both gasoline and methanol showed significantly increased evaporation rates at 30 °C–35 °C. From a molecular dynamics perspective, the increase in temperature was observed to raise the kinetic energy of liquid-phase molecules and the number of molecules entering the gas phase, thereby accelerating the growth trend of evaporation rate with temperature. Additionally, due to the presence of intermolecular hydrogen bonds, methanol was found to possess stronger intermolecular forces and greater resistance to phase transition, resulting in a lower evaporation rate compared to gasoline at the same temperature.

Conclusion In the temperature range of 15 °C–45 °C, gasoline exhibits higher evaporation rates and greater sensitivity to temperature changes, while methanol’s evaporation loss remains relatively low. Therefore, when repurposing refined oil storage tanks for methanol transport, increasing the breathing system’s displacement is unnecessary. Both media show rapid evaporation rate increases between 30 °C and 35 °C. To effectively minimize small breathing loss, gas temperatures should be maintained below 30 °C in gasoline tanks and below 35 °C in methanol tanks during storage. The calculation method recommended in the Design Guideline for Energy Conservation of Petroleum Depots demonstrates high accuracy in estimating small breathing loss for methanol storage tanks. Based on this, key empirical formula coefficients can be adjusted to reflect methanol’s evaporation characteristics, providing technical support for the design and management of methanol storage tanks.