Valorization of Carica papaya seed oil into biodiesel using a stable CuO–Al2O3 nanocatalyst under optimized condition

Abstract

This study investigates the extraction of biodiesel from Carica papaya L. seed oil, an underutilized, non-edible agricultural byproduct, using a copper oxide–alumina (CuO–Al₂O₃) nanocomposite as a catalyst in the transesterification process. The synthesized catalyst combined the high surface area of mesoporous γ-Al₂O₃ with the catalytic activity of dispersed CuO nanoparticles, as confirmed by SEM, XRD, EDX, and FTIR analyses. Key transesterification parameters, including nanocatalyst concentration (NCC), methanol-to-oil molar ratio (MOR), reaction temperature (RTP), and reaction time (RTE), were optimized using response surface methodology. ANOVA results indicated that RTE had the greatest effect on biodiesel yield (55.6 %), followed by MOR (24.1 %) and NCC (16.9 %). Optimal conditions (149 ppm NCC, 9:1 MOR, 70 °C RTP, and 92 min RTE) developed a maximum yield of 96.9 %, which was validated experimentally. The catalyst retained >95 % activity over five reuse cycles before gradual decline, confirming its reusability. FTIR confirmed ester carbonyl and methoxy groups, while fatty acid methyl ester profiling identified oleic acid methyl ester as the dominant component. The physicochemical propertiesD6751complied with ASTM D6751 and were close to EN 14214 requirements, with slight shortfalls in cetane number and oxidation stability that can be addressed by antioxidants or blending. These results demonstrate that papaya seed oil, in combination with a reusable CuO–Al₂O₃ catalyst under optimized conditions, can serve as a viable source for bioenergy extraction.