Simultaneously carbonized and sulfonated mango seed husk as a solid acid catalyst for the esterification of oleic acid with methanol

Abstract The Philippines has mandated an increase in biodiesel blending from B2 (2%) to B5 (5%) under the Biofuels Act of 2006, increasing the demand for efficient and sustainable catalysts for biodiesel production. Although homogeneous catalysts are widely used, they are economically impractical since it is difficult to recover, expensive, and not reusable. This study investigated mango seed husk (MSH) as a carbon-based precursor for a solid acid catalyst (MSH-SAC) for biodiesel production through heterogeneous esterification. Nine MSH-SAC samples were synthesized using a full factorial design with varying synthesis temperatures (100, 150, and 200°C) and times (4, 5, and 6 h) through simultaneous sulfonation and carbonization. Catalytic performance was evaluated in the esterification of oleic acid with methanol at 65°C for 6 h, using a 10:1 methanol-to-oil molar ratio and 8 wt% catalyst loading. Esterification conversions ranged from approximately 61% to 84%. Catalysts synthesized at 150°C for 4 and 5 h achieved the highest conversion of 84%. The 150°C, 4 h catalyst retained approximately 78% of its initial activity after four reuse cycles, demonstrating promising stability and reusability.