Sustainable biodiesel production via thermally induced transesterification using meso-macroporous silica derived from marine diatom following fucoxanthin extraction.

Climate change is a global environmental challenge, and is accelerating the transition from fossil fuels to renewable (bio)fuels. Among these, biodiesel (BD) is a promising alternative to petroleum diesel, exhibiting seamless compatibility with existing internal combustion engines. This transition requires the development of greener BD production routes, particularly through the use of low-toxic dimethyl carbonate (DMC) as a substitute for methanol, the conventional acyl acceptor in transesterification. However, the conventional DMC-based transesterification processes using homogeneous catalysts suffer from slow reaction kinetics, which limits their practical applicability. This study proposes a DMC-based thermally induced (non-catalytic) transesterification process. The reaction is based on the hypothesis that BD conversion occurs through a heterogeneous reaction between liquid-phase triglycerides and gas-phase DMC, and that the reaction kinetics are enhanced by confinement effects within the pore structures of porous materials, which may facilitate heterogeneous interactions. To improve process sustainability, the marine diatom (Melosira nummuloides) was utilized for dual valorization: fucoxanthin extraction and biosilica production. Fucoxanthin was first recovered as a value-added product, and the remaining biosilica-rich residue was subsequently converted into a porous biosilica material. This biosilica was then employed as a porous medium for DMC-based thermally induced transesterification of soybean oil. The process yielded 93.0 wt% BD at 355 ˚C, comparable to that obtained using commercial silica under identical conditions. Moreover, the biosilica exhibited stable BD recovery (93.0-96.8 wt%) over ten consecutive reuse cycles. These results indicate that the proposed approach enables efficient BD production with stable performance over ten reuse cycles.