Room-temperature fast conversion of waste frying oil to biodiesel enabled by a Pickering interfacial catalyst

The heterogeneous solid base catalyst integrates catalytic activity with emulsifying capacity. • 94.51% conversion was achieved for WFO to biodiesel in 36 min at 20℃. • The catalyst exhibits excellent water and free fatty acid tolerance. • The catalyst has excellent reusability and regenerability. Due to heterogeneous nature, the biodiesel synthesis via transesterification typically requires high temperatures or long reaction times even under catalytic conditions. To address this challenge, we designed a bifunctional composite solid base catalyst by loading K₂CO₃ onto activated carbon (K 2 CO₃/AC), which synergistically integrates catalytic activity and emulsifying capacity. With the formation of Pickering emulsions in the alcohol-oil system, transesterification reaction is remarkably accelerated via enhanced interfacial contact. Specifically, for waste frying oil methanolysis, a conversion of 94.51% was achieved within 36 min at 20℃. Mechanism investigations indicate that a high K 2 CO 3 loading combined with an appropriate particle size of the catalyst is crucial for achieving efficient emulsification and catalysis. The catalyst demonstrated exceptional impurity tolerance, maintaining > 90% biodiesel conversion even with 1.5 wt% free fatty acids (FFAs) and 2.4 wt% water, which demonstrates significant improvements in FFA and water tolerance over homogeneous base catalysts. Moreover, the as-synthesized biodiesel satisfied the specifications of the international standards ASTMD 6751 and EN −14214 in terms of key physicochemical properties. In addition, it exhibited superior reusability (>90% conversion after three cycles) and easy regenerability via simple K 2 CO 3 re-impregnation. Featuring facile preparation, excellent catalytic performance at room temperature, and high stability, this amphiphilic catalyst presents an industrially feasible and impurity-tolerant solution for biodiesel synthesis.