Enhancing transesterification of used soybean frying oil using CaO.ZnO (10%) NiO (8%) catalyst: Response surface optimization and characterization

Biodiesel production from used oils could be considered as a sustainable replacement for fossil fuels. But efficiency often comes down to the type of catalyst used. This study evaluates a novel heterogeneous catalyst, CaO/ ZnO (10 %)/NiO (8 %), developed using the solid-state method which uniquely combines ZnO and NiO to enhance catalytic activity by minimizing the amount of catalyst and alcohol required. The research seeks to optimize biodiesel production conditions using this catalyst and evaluate its effectiveness compared to conventional methods. Box-Behnken Design (BBD) was utilized to optimize the process of the catalytic transesterification, while the catalyst was characterized using XRD, SEM, FTIR, and BET techniques to assess its structure, morphology, and surface properties. A model was designed to investigate the influence of transesterification reaction variables including: oil molar ratio (3:1 to 12:1), reaction temperature (50-70 degrees C), catalyst weight (1-3 % by weight) and Reaction time (3 h-5 h) on the model response (biodiesel yield). The results obtained indicated an optimal biodiesel yield under the conditions of an oil molar ratio of 8.18:1, catalyst weight of 1.95 wt%, reaction temperature of 62.5 degrees C, and reaction time of 4.18 h. Gas chromatography-mass spectrometry (GC-MS) analysis identified the main types of fatty acids in used soybean frying oil methyl ester SFOME, namely hexadecanoic acid methyl ester (C16:0), 9,12-Octadecadienoic acid (Z,Z)-, methyl ester (C18:2); 9-Octadecenoic acid, methyl ester, (E)- (C18:1) with retention times 38.787, 44.286 and 44.588 min, respectively.