Abstract
Biodiesel emerges as an eco-friendly alternative to petrochemical resources. However, traditional production methods often involve costly and complex processes. Thus, this study explores a facile green heterogeneous catalyst that could produce biodiesel. Phosphotungstic acid (HPW) stands out as an environmentally friendly acid catalyst but inferior for low surface area and high solubility. This research functionalizes Keggin-type HPW on cost-effective, eggshell-derived calcium oxide (CaO) through one-pot hydrothermal treatment to produce calcium-phosphotungstate (CaPW12). BET confirms HPW encapsulation onto CaO with an increase of specific surface area (23.8809 m2/g), pore volume (0.073137 cm3/g), and pore size (12.2502 nm). CaPW12 exhibits Type II isotherm with sigmoidal curve, indicating the catalyst surface is non-porous or macroporous. FESEM image reveals orthorhombic crystal structures of HPW and well-distributed of HPW into CaO. The well-ordered and crystallized CaPW12 confirmed by XRD. FTIR spectra suggest strong interactions of CaO and HPW, including the P-Oa and the W-Oc-W of HPW. The palm oil conversion of 85.22 % and FAME yield of 75.72 % were achieved by CaPW12 under optimized conditions (5 wt% catalyst loading, 9:1 methanol/palm oil ratio, 1 h reaction duration and 65 °C). The catalyst is thermally stable that can be recycled up to four times with 70 % FAME yield.