Continuous Biodiesel Production from Waste Soybean Oil Using a Nano-Fe3O4 Microwave Catalysis

In this study, we conducted an efficient microwave-assisted transesterification process combining homogeneous and heterogeneous catalytic phases to produce biodiesel from waste soybean oil. A cylindrical quartz reactor packed with nanoparticles of Fe3O4 as a co-catalyst was applied to improve the reaction. The process was carried out with a methanol-to-oil molar ratio of 6:1, power of 560 W, and residence time of 30 s. The specifications of the biodiesel produced in this study were compared with two standards, i.e., ASTM D6751 and EN 14214. We found that the continuous conversion of waste soybean oil to methyl ester was approximately 95%. The biodiesel showed a higher flash point and a higher carbon residue content than that of both standards, and the viscosity (5.356 mm(2)/s) and density (898.1 kg/m(3)) were both at a high level. Compared to a conventional heating plate, the energy consumption was significantly reduced by nearly 93%. It is expected that these findings will provide useful information for green and sustainable processes for the regeneration and reuse of oil.