A review of magnetic solid catalyst development for sustainable biodiesel production

Biodiesel is one of the most widely studied biofuels in the literature, which has a bright potential to serve as an alternative source for fossil fuel. Biodiesel is produced from transesterification or esterification reaction and usually requires a catalyst to enhance its product yield. The commercially available homogeneous catalyst generally faces several challenges, including difficulties in product separation, large volume of wastewater effluent discharged from the downstream purification process, and formation of undesirable soap by-product from the reaction between high FFA content feedstock and homogeneous base catalysts. As a result, the application of heterogeneous magnetic catalysts in biodiesel production has attracted many researchers attention due to its relatively simple catalyst separation and higher catalyst recovery rate at a shorter duration. Herein, this review focused on the preparation methods of heterogeneous magnetic acid and base catalysts as well as its effectiveness in biodiesel production. Besides, different synthesis methods of magnetic particles were reviewed as well. The reaction mechanism of heterogeneous catalysts in facilitating the formation of biodiesel via transesterification or esterification processes was also elucidated. For a more sustainable biodiesel industry, more research works are required to utilise waste materials as support for the synthesis of heterogeneous magnetic acid and base catalysts.