Valorization of Biogenic Calcium-Rich Wastes as a Composite CaO Catalyst for Optimized Palm Kernel Oil Biodiesel Synthesis

Abstract

Biodiesel is a sustainable alternative to petroleum diesel, but developing efficient, low-cost, and environmentally friendly heterogeneous catalysts remains challenging. This study investigated biodiesel production from crude palm kernel oil using a composite calcium oxide catalyst derived from waste eggshells and snail shells. The catalyst was calcined at 900 °C for 3 h and characterized by XRD and FTIR, confirming predominantly crystalline CaO with minor Ca(OH)₂ and carbonate species. Response Surface Methodology using a Central Composite Design optimized reaction time, temperature, catalyst loading, and methanol-to-oil ratio. The quadratic model was significant (F = 60.25, p < 0.0001) and demonstrated high predictive capability (R² = 0.9825, Adjusted R² = 0.9662, Predicted R² = 0.9099). Optimum conditions of 82.5 min, 60 °C, 5.5 wt% catalyst, and 6:1 methanol-to-oil ratio yielded 91.273 wt% biodiesel. The composite catalyst outperformed calcined eggshell (87.0 wt%) and snail shell (85.5 wt%) catalysts under identical conditions. Biodiesel properties complied with ASTM specifications, with acid value of 0.431 mg KOH.g⁻¹, flash point of 129 °C, and dynamic viscosity of 4.53 mPa.s. The findings demonstrate the catalyst's potential for sustainable and low-cost biodiesel production while promoting agricultural waste valorization without the need for further catalyst modification. Copyright © 2027 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).