Production of biodiesel from waste culinary oil catalyzed by S2O82−/TiO2–SiO2 solid super-acid catalyst prepared with recovered TiO2 from spent SCR

Recovery and valorization of natural resources from waste materials are crucial for promoting sustainable development. In light of this, the present study explores the transesterification of waste culinary oil into biodiesel production using a silica-supported solid super-acid catalyst (S2O82−/TiO2–SiO2) prepared with recovered TiO2 from spent SCR. The synthesized materials were characterized through XRD, SEM-DES, XPS, FT-IR, NH3-TPD, and N2-BET analysis. Notably, the crystal structure of recovered TiO2 was not destroyed during the whole process. N2-BET analysis showed that the silica-supported catalyst significantly increased the specific surface area from 47.89 to 101.16 g/m2. The presence of superacid sites (Brønsted and Lewis acid sites) on the surface of the catalyst was confirmed by NH3-TPD and FT-IR analysis. The silica-supported catalyst (S2O82−/TiO2–SiO2) exhibited high catalytic activity for free fatty acid (FFA) about a conversion rate of 90.7 % under optimal reaction conditions: a reaction time of 4 h, at 180 °C with a 5 wt% catalyst loading, and a methanol-to-oil molar ratio of 12:1. The biodiesel production was confirmed by using FT-IR and 1HNMR techniques. Furthermore, the catalytic performance of the prepared catalyst was compared with other catalysts prepared from pure TiO2 reported in the literature. This approach showed a potential for sustainable biodiesel production by using low-cost solid acid catalyst synthesized from recovered materials.