Ultrafiltration of triglyceride from biodiesel using the phase diagram of oil–FAME–MeOH

To continuously obtain biodiesel of high purity, a membrane separator integrated with liquid–liquid extraction for the oil–FAME–MeOH system is studied. The liquid–liquid phase equilibrium data for the oil–FAME–MeOH are determined experimentally and compared with the general prediction of the modified UNIFAC. The tie line test demonstrates that composition of the methanol-rich phase is free of TG at 20 °C. Using the continuous cross-flow ultrafiltration, the oil-rich phase can be rejected by the ceramic membranes while the methanol-rich phase permeates through the membranes. When the feed bulk composition is controlled within the two-phase zone, such as the oil:FAME:MeOH of 20:30:50 wt.%, the permeate is found to be free of oil while the obtained permeate flux is higher than 300 kg/m² h under the transmembrane pressure of 600 mmHg and the inlet flow rate of 300 ml/min at 20 °C. By contrast, it shows almost no separation when the inlet concentration of oil–FAME–MeOH locates on its boundary line or within the single-phase zone. The quantitative filtration tests show that the compositions in the two liquid phases and the operating parameters are also considered simultaneously to screen the origin oil and get the FAME product of high purity.