Comparative Study of Homogeneous Heteropoly Acid Catalysts for Biodiesel Production from Canola Oil: Correlation of...

Biodiesel, predominantly derived from canola oil, is recognized as an essential renewable and ecofriendly fuel, significantly reducing greenhouse gas emissions and fossil fuel dependency. Despite its advantages, optimizing catalytic reactions remains challenging. This research systematically evaluates the catalytic efficiency and selectivity of three homogeneous heteropoly acids (HPAs)phosphotungstic acid (PWA), phosphomolybdic acid (PMo), and silicotungstic acid (SiW)for biodiesel production using canola oil. Under the optimized homogeneous reaction conditions, the Brønsted acidity was quantitatively analyzed using UV-vis spectroscopy with 4-nitroaniline, while solvent-dependent dissociation characteristics were confirmed via FT-IR spectroscopy. Among the HPAs, PWA and PMo exhibited higher methanol solubility, correlating to significantly greater FAME yields (43.97% and 47.22%, respectively) compared with SiW (21.81%). Product analysis revealed that W-based catalysts (PWA, SiW) predominantly produced polyunsaturated esters such as C18:3 (65.9% and 67.5%, respectively), while PMo favored monounsaturated esters such as C18:1 (55.1%), reflecting intrinsic differences in acidity and catalyst configuration. Effective biphasic separation using dichloromethane and water facilitated catalyst recovery and product purification, with FT-IR confirming HPAs' retention in the aqueous phase. This study underscores the necessity of concurrently managing catalyst solubility and acidity to optimize biodiesel production and product selectivity using homogeneous HPAs, in which the process of efficient phase separation is an advantage for effective management.