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Green Nano-Composite of CaO/K-Sulfated TiO2 and Its Potential as a Single-Step Reaction Solid Catalyst for Biofuel Production

In the esterification-transesterification method, a catalyst increases the reaction rate to produce biofuel (biodiesel). This study investigated the use of a solid catalyst consisting of green nano-CaO as a support modified by KOH solution and sulfated TiO2 for converting waste frying oil (WFO) into biodiesel in a single-step esterification-transesterification reaction. With nano-CaO prepared from eggshell, a green nanocomposite of CaO/K-sulfated TiO2 was synthesized by physical mixing and the hydrothermal method. Crystallite size, surface basicity-acidity, functional groups, and surface morphology were used to characterize the solid catalyst, which was then tested for its ability to convert WFO into biodiesel. The results showed that green-CaO had nanoparticles (93.13 nm) and that its size decreased after being modified with KOH (46.43 nm) and sulfated TiO2 (62.10 nm), with CaO/K-sulfated TiO2 being the optimum surface acidity-basicity. The optimum conditions for conversion were found to be 5% catalyst concentration to oil, a molar ratio of methanol/oil of 9:1, and a reaction time of 60 minutes, which resulted in a biodiesel mass yield of 94.17% higher than CaO/K (67.88%). WFO was successfully converted into fatty acid methyl esters, according to the GC-MS analysis of the biodiesel. The synthesized solid catalyst has the potential to be used in single-step esterification-transesterification reactions to produce biodiesel. 
Keywords: Biofuel, CaO/K-sulfated TiO2Green Nano-composite, Eggshell, Single-step Reaction, Waste Frying Oil