Catalyst derived from waste Marigold flowers ( Tagetes erecta ) via a two-pronged approach for the effective conversion of non-edible sesame oil into biodiesel

Waste Marigold (MG) flowers, also known as Tagetes erecta, were used to synthesize a heterogeneous ash-based catalyst via two distinct methods. The first method involved a one-stage calcination process performed directly after powdering waste flowers at 650 °C, 700 °C, 750 °C, and 800 °C for 2 h (Marigold Ash - MGA class). The second method consisted of a two-step process: powdered flower was burnt in open air, followed by calcination at different temperatures (450 °C, 475 °C, 500 °C, 550 °C, and 600 °C) for 1 h and 1.5 h, respectively (Marigold Calcined Ash - MGCA class). The EDX analysis of the MGA 650 reported the cumulative K and Ca content of 42.2%. In contrast, the MGCA 600 1h and MGCA 600 1.5 h samples had cumulative K and Ca contents of 60.8% and 48.4%, respectively. The two-step calcination process concentrates metals in the residual ash after volatile matter removal. The transesterification reaction was carried out using non-edible sesame oil. The highest yields (87.3%) and conversion (93.1%) of biodiesel were obtained using the MGA 650 at optimal conditions of 6 wt.% of catalyst loading, a methanol-to-oil ratio of 10:1, and a temperature of 65 °C for 6 h. The yield and conversion of biodiesel were 92.6% and 95.6%, respectively, using the MGCA 600 1h catalyst (5 wt.% catalyst loading at 65 °C for a time duration of 5 h with a methanol-to-oil ratio of 10:1).