Supercritical Biodiesel Production from Beef Tallow Using Methanol and Carbon Dioxide: A Response Surface Methodology Study

This study investigates the supercritical transesterification of waste beef tallow using methanol, with carbon dioxide employed as a cosolvent to reduce the operating pressure. The experimental design, guided by response surface methodology, evaluated the effects of reaction temperature (250–360 °C), carbon dioxide/methanol molar ratio (0.000–0.421), and methanol/beef tallow molar ratio (40–50) on conversion and quality during 60 min in a batch reactor. Bulk properties and spectroscopic analyses confirmed that the fatty acid methyl esters (FAMEs) met reference standard values. The results showed that temperature was the most significant factor affecting conversion, while carbon dioxide addition proved beneficial at high methanol-to-fat ratios. The process proved to be a feasible method for producing high-quality biodiesel while lowering required pressure compared with non-cosolvent supercritical systems.