Growing interest in renewable fuels has increased the need for efficient, recoverable and environmentally preferable catalysts for biodiesel production. This study evaluated an alumina–chitosan nanocomposite as a heterogeneous catalyst for transesterification of seed oils obtained from Carica papaya (pawpaw) and Citrullus lanatus (watermelon), with potassium hydroxide (KOH) used as the homogeneous-catalyst comparator. Chitosan was prepared from the hard tissues of Rhynchophorus phoenicis and incorporated with alumina to form the nanocomposite. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). FTIR showed characteristic chitosan functional groups with shifts after alumina incorporation; SEM showed that the nanocomposite had smaller particles and a more porous surface than chitosan; and XRD confirmed distinct crystalline features. The seed oils were converted to biodiesel by transesterification, and the effects of alcohol-to-oil molar ratio, catalyst dose, reaction temperature and reaction time were evaluated. The optimum conditions identified in the thesis were a 12:1 alcohol-to-oil molar ratio, 4 g catalyst dose, 80 °C reaction temperature and 120 min reaction time. Under the molar-ratio experiment, Carica papaya with the nanocomposite reached 97.10 ± 0.95% yield, compared with 92.04 ± 0.55% with KOH; Citrullus lanatus reached 83.40 ± 1.45% with the nanocomposite and 81.20 ± 0.55% with KOH. The nanocomposite generally produced higher biodiesel yields than KOH, while Carica papaya gave the strongest overall performance. These findings support alumina–chitosan nanocomposite as a promising heterogeneous catalyst for biodiesel production from underutilized seed-oil feedstocks.

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