Objective Methanol, an emerging energy source, is vital for the energy transition. The batch transportation of methanol through refined oil pipelines reduce the long-distance methanol transportation cost and alleviate the low throughput of refined oil pipelines. During the batch transportation of methanol and refined oil, mixed oil is inevitable. The miscibility of methanol and refined oil as well as methanol residue in refined oil are crucial for selecting the separation and treatment processes of the mixed oil.

Methods A liquid-liquid phase equilibrium experimental setup was independently designed and built to investigate the effects of methanol volume fraction, water content, temperature, and other factors on the miscibility of methanol and refined oil. Gas chromatography-mass spectrometry (GC-MS) was employed to determine the methanol content in the gasoline/diesel layer, revealing the variation in methanol concentration in refined oil under different conditions.

Results In the temperature range of −10 °C to 50 °C, methanol and gasoline exhibited good miscibility. However, due to polarity differences, as the methanol volume fraction increased, their miscibility first decreased and then increased. Methanol and diesel had poor miscibility and were hard to fully mix, yet trace amounts of methanol could dissolve in the diesel layer. As the temperature dropped, methanol droplets precipitated in the diesel layer, causing turbidity. Simultaneously, as the methanol volume fraction in the mixture rose, the methanol concentration in the gasoline/diesel layer first increased and then decreased. In the gasoline layer, the methanol mass concentration reached a maximum of 69.91 g/L at a 30％ methanol volume fraction; in the diesel layer, it peaked at 17.24 g/L at a 50％ volume fraction. Lowering the temperature and increasing the water content of methanol significantly reduced methanol solubility in refined oil. As the temperature continued to fall, the methanol mass concentration in the gasoline and diesel layers decreased from 137.36 g/L to 61.84 g/L and from 17.24 g/L to 5.16 g/L, respectively. When the water content of methanol increased from 0.5％ to 1.25％, the corresponding mass concentrations in the gasoline and diesel layers decreased from 82.73 g/L to 48.65 g/L and from 30.73 g/L to 12.75 g/L, respectively.

Conclusion The solubility of methanol in refined oil is influenced by various factors, including methanol volume fraction, temperature, water content, and oil type. It is advisable to employ techniques such as distillation, gravity separation, and centrifugation for separating the mixed oil during the batch transportation of methanol and refined oil.