Design of a sodium peroxide/sulfonic acid functionalized SBA-16 bi-functional catalyst for improving the conversion of waste cooking oil to biodiesel

Abstract

A sodium peroxide/sulfonic acid-functionalized SBA-16 (Na2O2/SBA-16-SO3H) bifunctional catalyst was successfully developed to improve the conversion of waste cooking oil (WCO) to biodiesel. High-resolution X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Fourier transform infrared spectroscopy analysis results showed that 3D cubic mesoporous SBA-16 and SBA-16-SO3H were successfully synthesized through a hydrothermal reaction and that the 3D cubic mesoporous structure of SBA-16 was not damaged after modifying the Na2O2 particles and -SO3H functional groups. The results of the activity tests showed that modifying SBA-16 with Na2O2 as the alkali catalyst and the -SO3H group as the acidic catalyst could remarkably accelerate transesterification and esterification reactions simultaneously, resulting in an increased conversion efficiency of WCO to biodiesel. The biodiesel conversion efficiency of Na2O2/SBA-16-SO3H reached 81% after a 6 h reaction, which is approximately 3.5 times higher than that of SBA-16. Moreover, the results show that increasing the methanol/WCO molar ratio from 6:1 to 18:1 inhibited saponification and accelerated the transesterification and esterification reactions, shortening the reaction time for fatty acid methyl ester conversion from 8 h to 4 h, providing possibilities for practical application in the future. The Na2O2/SBA-16-SO3H catalyst showed optimal activity when the free fatty acid content was controlled at 3%, the methanol/WCO ratio was controlled at 18:1, and the biodiesel yield reached 93% after 4 h of reaction.