Efficient photocatalytic esterification of waste cooking oil over empty fruit bunches ash-supported TiO2

Abstract

Biodiesel production from waste cooking oil (WCO) holds promise as a renewable and sustainable energy source. However, high levels of free fatty acids (FFAs) in WCO require efficient pretreatment before transesterification. Utilizing solar energy for heterogeneous catalytic reactions offers an alternative to thermal-driven processes. TiO2EFBA, synthesized via the wet impregnation method, exhibits distinctive physicochemical properties confirming the successful incorporation of titanium dioxide (TiO2) onto the metal oxides of empty fruit bunches ash (EFBA), thereby enhancing the catalystâs performance and stability. Results showed that TiO2EFBA exhibits superior FFA conversion compared to TiO2 alone. Under optimized reaction conditions, employing 4 wt% TiO2EFBA catalyst, 20:1 methanol to oil molar ratio, and 2 h reaction time at room temperature under Ultra Violet (UV) light, achieves a remarkable 78% conversion rate of FFAs in WCO. Mechanistic investigation reveals the crucial role of electron/hole (eâ/h+) species in reducing FFAs by suppressing the eâ/h+ mechanism. Notably, TiO2EFBA facilitates easy separation and can be reused for 10 cycles, demonstrating its stability as a heterogeneous photocatalyst. Research Hightlights

• Successful reduction of high free fatty acid (FFAs) content of waste cooking oil (WCO) from 12.4 wt% to 2.7 wt% using semiconductor photocatalyst (TiO₂EFBA) achieved up to 78% conversion.
• TiO₂EFBA is highly active heterogeneous semiconductor photocatalyst in esterification of WCO under 365 nm UV light.
• TiO₂ doped EFBA reduce the bandgap energy of TiO₂ and increase the performance of photocatalyst.
• EFBA can serve as trapping agent by capture the electron-holes pair from recombination and enhanced the charge carrier separation.
• TiO₂EFBA can reused up to 10 times without reduction of catalytic performance.